Citations

Abstract Introduction Lenalidomide is an immunomodulatory drug (IMID) used to treat Multiple Myeloma (MM). Although a role for cereblon (CRBN)-mediated degradation of Ikaros proteins (IKZF1 and IKZF3) has been shown, the complete molecular and biochemical mechanisms responsible for lenalidomide-mediated anti-MM activity and/or resistance are undiscovered. Therefore, we aimed to analyze whether IMIDs (thalidomide, lenalidomide, and pomalidomide) are inducing oxidative stress in MM and what determines these drugs varying sensitivity and/or resistance. Methodology Amplex Red Assay has been performed to analyze IMIDs-mediated inhibition of H2O2 decomposition in both, in-vitro and in-vivo assays. Lentiviruses were prepared in 293T cells for CRBN, IgL-λ & IgL-k, and Bim knockdown experiment. Quantification of MM cellular anti-oxidative capacity for determining IMID sensitivity was standardized with H2O2-mediated oxidation of FADH2 and NAD(P)H. To measure apoptosis and gene expression analysis 106 cells were incubated with lenalidomide for 24 to 96 hours before they were examined by annexin-PI and FACS analysis. Gene and protein expression were measured by RT-PCR, western blot, and immunohistochemistry. Results We discovered that IMIDs inhibit peroxidase-mediated decomposition of H2O2 in both, in vitro horseradish peroxidase (HRP) assays and in human MM cell lines (HMCLs). Of the IMIDs analyzed, pomalidomide was the more potent inhibitor. H2O2 treatment effectively degraded IKZF1 and IKZF3 in HMCLs. To confirm the central role of CRBN in IKZF1 and IKZF3 degradation by H2O2-induced oxidative stress, we used CRBN knockdown OPM2 isogeneic cells and the CRBN-overexpressing OCIMY-5 cell line. We treated both sets of isogenic cell lines with lenalidomide and H2O2 for 3 hours, and we showed that H2O2 similarly mediates IKZF1 and IKZF3 degradation in a CRBN-dependent fashion. Next, we tested viability of CRBN present and absent cell lines with increasing concentrations of lenalidomide and H2O2 for 3 days. Lenalidomide-induced cytotoxicity was CRBN dependent, but H2O2 was not after 3 days, as shown by MTT assays. The capacity of MM cells to decompose H2O2 was measured via a biochemical test that quantitatively measured cellular anti-oxidative capacity. IMID sensitivity was well correlated with cellular anti-oxidative capacity, likely, cells more efficiently decompose H2O2was resistant and cells were not sensitive to IMID. This result shows that antioxidant capacity determines lenalidomide sensitivity among HMCLs with similar CRBN protein expression. We discovered that lenalidomide-mediated cytotoxicity in MM was attributable to oxidative damage of intracellular immunoglobulin proteins. By using several sets of isogenic cells lines with and without CRBN expression, we confirmed that lenalidomide treatment caused accumulation of IgL dimers only in CRBN-positive cells. Lenalidomide-induced IgL dimerization lead to decreased secretion and consequent intracellular accumulation of IgL, as evidenced by unchanged IgL mRNA expression, increased total intracellular IgL protein, and decreased secretion of IgL. After 72 hours of lenalidomide treatment we found decreased XBP-1u, increased XBP-1s, and over-expressed GRP78/BiP endoplasmic reticulum stress (ERS) marker proteins in CRBN positive cells but not in CRBN knock-down cells. We observed Bim requirement, especially BimEL, after lenalidomide treatment in CRBN-positive lenalidomide-sensitive cells. Our data reveals that lenalidomide-mediated; progressive ERS can positively enhance bortezomib-induced apoptosis in an in-vitro MM model. We pretreated MM cells with lenalidomide and then treated them with bortezomib. OPM2 cells pretreated with lenalidomide for 2 days clearly showed increased sensitivity to bortezomib-induced apoptosis compared with cells that were not pretreated. Conclusion IMIDs inhibit H2O2 decomposition. Ikaros protein degradation is a consequence of H2O2 mediated oxidative stress. Therefore, cells producing high H2O2 and with less antioxidative capacity are more sensitive to IMIDs. On the basis of this discovery, we would be able to predict which patients will benefit from IMIDs-mediated therapy and develop new drugs other than IMIDs that can inhibit intracellular H2O2 decomposition in MM. At present, CRBN may be required for IMIDs to effectively inhibit H2O2decomposition. Disclosures Chirackal: Mayo Clinic: Patents & Royalties: Filed a professional US patent for quantifying cellular anti-oxidative capacity. Fonseca:Mayo Clinic: Patents & Royalties: Filed a professional US patent for quantifying cellular anti-oxidative capacity.

Abstract Abstract 3803 Background: The MMRC is a non-profit, disease-focused consortium founded in 2004 comprised of 13 North American centers with expertise in multiple myeloma (MM). The MMRC Inc. (Norwalk, CT), MMRC's member institutions, and several pharmaceutical partners work closely to speed early development of new treatment options for MM patients. In December 2007, MMRC headquarters staff implemented multiple project management (PM) business solutions to address trial barriers that delay activation of our phase I-II clinical trials and established trial metric benchmarks considered attainable at our member institutions. In November 2009, we reported initial data1 on trial activation: MMRC trials initiated between Sep08-Jul09 (n=5) demonstrated a 38% decrease in mean time to first patient dosed (FPFD), compared with the Early Group trials (EG) initiated before PM solutions (Jun06-Sept08; n=7 trials). These results also confirmed improvement over published metrics from Dilts et al 2,3. We present additional data on time to FPFD and now enrollment, to assess impact of the MMRC PM resources and processes on trial efficiency. Methods: Twenty-one (21) trials conducted within the MMRC from May 2006 to June 2010 had sufficient trial data for review. Data were collected by MMRC-funded project managers at the clinical centers using a web-based clinical trial management system (CTMS). FPFD was defined as the time from the member institutions' receipt of the final protocol (FP) from the trial sponsor, to the time the first patient was dosed on the trial at any participating MMRC member institution. With respect to enrollment, pre-study enrollment commitment (EC) established between MMRC and the study sponsor was defined as the total number of subjects committed to receive at least one dose of study drug across all participating MMRC centers on a trial; baseline enrollment timeline (BET) was prospectively defined as the target time period to attain EC. Results: Mean time to FPFD was 181 calendar days for the early group trials (EG, n=7) and 122 days for the recent group (RG) trials (n=14, Sep08 – Jun10), representing a 32% reduction of time to FPFD in the RG. Additionally, time from final protocol to first patient dosed at all MMRC centers on a trial decreased 18% from a mean of 7.7 months (EG) to 6.3 months (RG). With respect to MMRC trial enrollment, data was available for 16/21 trials (5 EG and 11 RG). 2 EG trials were missing data and 3 RG trials were still enrolling as of June 2010. The mean MMRC pre-study EC was 39 subjects per trial (n=16 trials; 626 enrollment target); the mean actual MMRC enrollment was 49 subjects per trial (n=16; 783 enrolled through Jun 29, 2010) representing a 25% increase in actual versus committed enrollment. Two trials did not meet MMRC EC: MMRC investigators discontinued their involvement in these trials at approximately 30% target EC due to trial complexity or low patient enrollment. 14/16 evaluable trials (88%) met their EC; 11/16 trials met EC within BET (69%) of which 8/16 trials (50%) reached EC 34% faster than their BET (representing a mean reduction of 4.5 months). The overall pre-study mean BET for 16 trials was 13.1 months. MMRC's actual mean enrollment timeline was 11.3 months for the group of 14 evaluable trials representing improvement over the original BET by a mean of 1.9 months (14%). We believe FP to FPFD is a more meaningful metric beyond that of first patient consented. Moreover, we believe that if all participating trial centers focus their efforts on dosing the first patient and within a targeted timeframe, it may improve our research efforts overall. Conclusion: Development of drugs in the clinical setting has become time and resource intensive. Activating and enrolling trials promptly is a priority for drug development. The MMRC's standardization of processes and support for site-based PM resources results in improved trial metrics. MMRC member centers met or exceeded pre-specified enrollment targets in 88% of the trials analyzed to date. Ongoing monitoring of trial conduct continues to reveal areas where increased focus is needed to realize further trial efficiencies. These trial metrics and measures to improve efficiency may be applied with similar expected benefit in all oncology disciplines. Disclosures: Wear: Multiple Myeloma Research Consortium (MMRC): Employment. Richardson:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC; Millennium: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees. Revta:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Vij:Multiple Myeloma Research Consortium (MMRC): Research Funding; Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Fiala:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Lonial:Bristo-Myers Squibb: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Millenium Pharmaceuticals Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis Pharmaceuticals: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Onyx: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Francis:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Siegel:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC; Celgene: Speakers Bureau; Millennium: Speakers Bureau. Schramm:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Jakubowiak:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC, Research Funding; Millennium: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Centocor Ortho-Biotech: Honoraria, Speakers Bureau; Exelixis: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Harvey:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Reece:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC; Celgene: Honoraria, Research Funding; Ortho Biotech: Honoraria, Research Funding; Merck: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Facet: Research Funding; Otsuka: Honoraria, Research Funding. Gul:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Jagannath:Celgene: Honoraria; Millenium: Honoraria; Orthobiotec: Honoraria; Onyx Pharma: Honoraria; Merck: Honoraria; Proteolix: Honoraria; Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. La:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Hofmeister:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Jansak:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Stewart:Millennium: Consultancy; Celgene: Honoraria; Multiple Myeloma Research Consortium: Member Institution of the MMRC. Hagerty:Mayo Clinic: Employment; Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Wolf:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC; Celgene: Speakers Bureau; Millennium: Speakers Bureau; Novartis: Speakers Bureau; Orthobiotech: Speakers Bureau. Davis:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Krishnan:Celgene: Speakers Bureau; Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Duarte:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Zimmerman:Millennium, Celgene: Speakers Bureau. Cisneros:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Kumar:Celgene: Consultancy, Research Funding; Millennium: Research Funding; Merck: Consultancy, Research Funding; Novartis: Research Funding; Genzyme: Consultancy, Research Funding; Cephalon: Research Funding; Bayer: Research Funding; Multiple Myeloma Research Consortium: Member Institution of the MMRC. Birgin:Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC. Ott:Multiple Myeloma Research Consortium (MMRC): Employment. Tasca:Multiple Myeloma Research Consortium (MMRC): Employment. Kelley:Multiple Myeloma Research Consortium (MMRC): Employment. Anderson:Millennium: Consultancy; Multiple Myeloma Research Consortium (MMRC): Member Institution of the MMRC; Celgene: Consultancy; Novartis: Consultancy; Onyx: Consultancy; Merck: Consultancy; Bristol-Myers Squibb: Consultancy; Acetylon: Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Giusti:Multiple Myeloma Research Consortium (MMRC): Employment.

Abstract Abstract 621 Background: Two- and three-drug regimens incorporating bortezomib (Velcade®, V), lenalidomide (Revlimid®, R), dexamethasone (D), or cyclophosphamide (C) have been shown to be effective and well tolerated in previously untreated multiple myeloma (MM). Combining all four drugs in a single regimen (VDCR) may further enhance efficacy. Published results from the phase 1 dose-escalation portion of the non-comparative, multi-center EVOLUTION study showed that the VDCR regimen was highly active and generally well tolerated (Kumar et al Leukemia 2010). Here we present updated results from the phase 2 portion of the trial, focusing on efficacy and safety of the VDCR, VDR, and VDC regimens. Methods: Previously untreated patients with measurable disease were randomized to one of four treatment groups receiving up to eight 21-d cycles of VDCR (V 1.3 mg/m2 d 1, 4, 8, 11; D 40 mg d 1, 8, 15; R 15 mg d 1–14; C 500 mg/m2 d 1, 8), VDR (VD as in VDCR but with R 25 mg d 1–14), VDC (VDC as in VDCR), or VDC-mod (as for VDC but with an additional dose of C on d 15) as induction therapy, followed by four 42-d maintenance cycles of V 1.3 mg/m2 (d 1, 8, 15, 22) (all treatment arms). Patients eligible for autologous stem cell transplant (SCT) could undergo stem cell mobilization any time after cycle 2 and SCT any time after cycle 4. The primary endpoint was the combined complete response (CR) + very good partial response (VGPR) rate; secondary endpoints included safety/tolerability, time to response, duration of response, progression-free survival, and rate of minimal residual disease (MRD) negativity. Responses were assessed according to International Myeloma Working Group (IMWG) uniform criteria using an automated computer algorithm. Adverse events (AEs) were graded using the CTCAE v3.0. Results: Patient characteristics were similar among the groups with respect to age, performance status, ISS stage, and proportion of patients with high-risk cytogenetic features. Patients received a median of 5, 6, 6, and 6 treatment cycles in the VDCR, VDR, VDC, and VDC-mod arms, respectively; 65%, 60%, 52%, and 47% of patients had dose reductions of any drug. In the VDCR, VDR, VDC, and VDC-mod arms, respectively, 52%, 62%, 58%, and 65% of patients completed treatment; 31%, 43%, 24%, and 41%, respectively, underwent SCT. In the phase 2 response-evaluable patients (n=132), all treatment regimens showed substantial efficacy, with CR+VGPR rates of 59% (VDCR), 50% (VDR), 41% (VDC), and 59% (VDC-mod) (Table) (includes pre-transplant responses only in SCT patients). Of MRD-assessed patients, 46% (21/46) of those who achieved CR (including sCR) or nCR were MRD-negative; 48% (10/21), 75% (9/12), 0% (0/7) and 33% (2/6) in the VDCR, VDR, VDC and VDC-mod arms, respectively. Median time to first response was similar across arms (range 1.6–1.8 months); median time to best response of CR+VGPR was 4.0 months (VDCR), 3.4 months (VDR), 5.1 months (VDC), and 3.1 months (VDC-mod). Median duration of response has not been reached in any arm to date. All treatment regimens were generally well tolerated. In the VDCR, VDR, VDC, and VDC-mod arms, at least one grade ≥3 AE was observed in 81%, 76%, 79%, and 88% of enrolled patients, respectively; serious AEs were experienced by 42%, 40%, 21%, and 41% of patients, and AEs resulting in study discontinuation were reported for 19%, 17%, 12%, and 6% of patients. The five most common all-grade AEs across all treatment groups were fatigue (range 47–67%), nausea (36–67%), constipation (40–62%), diarrhea NOS (42–65%), and neutropenia (19–52%). The incidence of grade ≥3 (grade ≥2) peripheral neuropathy (PN) was 13% (40%) in the VDCR arm, 14% (45%) VDR, 9% (48%) VDC, and 18% (41%) VDC-mod; there was no grade 4 PN. Rates of grade ≥3 neutropenia/thrombocytopenia were 42%/10% for VDCR, 7%/7% VDR, 36%/12% VDC, and 65%/18% VDC-mod. Conclusions: All regimens appear highly active and generally well tolerated in previously untreated MM patients. The four-drug combination did not result in a substantial increase in response rate and was associated with a modest increase in the incidence of hematologic toxicities. Continuous weekly C in the VDC regimen was associated with high response rates and rapid responses, comparable to the VDR and VDCR arms. Outcome data will be presented following longer follow-up. Disclosures: Kumar: Celgene: Consultancy, Research Funding; Millennium: Consultancy, Research Funding; Merck: Consultancy, Research Funding; Novartis: Research Funding; Genzyme: Consultancy, Research Funding; Cephalon: Research Funding; Bayer: Research Funding. Off Label Use: Lenalidomide for treatment of newly diagnosed myeloma. Flinn:Millennium Pharmaceuticals, Inc.: Research Funding. Richardson:Celgene, Millennium, Novartis, Johnson & Johnson: Membership on an entity's Board of Directors or advisory committees. Hari:Celgene: Research Funding. Callander:Millennium Pharmaceuticals, Inc.: Research Funding. Noga:Amgen: Honoraria, Research Funding, Speakers Bureau; Millennium: Consultancy, Honoraria, Research Funding, Speakers Bureau; Ortho-Centicor: Honoraria, Speakers Bureau; Cephalon: Honoraria, Research Funding, Speakers Bureau; Celgene: Honoraria, Research Funding, Speakers Bureau. Stewart:Millennium Pharmaceuticals, Inc.: Honoraria, Research Funding; Celgene: Honoraria. Rifkin:Millennium Pharmaceuticals, Inc.: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Speakers Bureau; Amgen: Speakers Bureau; Cephalon: Speakers Bureau; Dendreon: Speakers Bureau. Wolf:Millennium Pharmaceuticals: Consultancy, Honoraria, Speakers Bureau; Genentech and Multiple Myeloma Research: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Speakers Bureau; OrthoBiotech: Honoraria, Speakers Bureau; Celgene: Honoraria, Speakers Bureau. Estevam:Millennium Pharmaceuticals: Employment. Mulligan:Millennium Pharmaceuticals, Inc.: Employment. Shi:Millennium Pharmaceuticals: Employment. Webb:Millennium Pharmaceuticals: Employment.

Abstract Introduction: We employed a customized Multiple Myeloma (MM) specific Mutation-Panel (M3 P) to screen a homogenous cohort of refractory MM (rMM) patients in a timely and cost-effective manner. rMM was defined as progressive disease (PD) during therapy or within 60 days after discontinuation of therapy. The M3 P provides a practical alternative to whole genome/exome sequencing approaches and includes 88 genes selected for being either actionable targets, potentially related to drug response or part of known key pathways in MM biology. Patients and Methods: Tumor and germline samples of 50 rMM patients were screened using M3 P. Patients received a median of five lines of treatment at the time of tumor sampling (range 2-15 lines). All patients received at least one immunomodulatory agent (IMiD) and proteasome inhibitor (PI), and 88%, 76% and 66% were refractory to either an IMiD, PI or both. All patients had received lenalidomide and bortezomib, 48% and 34% were additionally exposed to pomalidomide and thalidomide and 18% to carfilzomib at any time prior to sampling. The majority of patients had a progressive and refractory disease immediately prior to sampling (82% and 78%), with 43% of them being IMiD-refractory and 46% being PI-refractory in the most recent line of therapy. Cytogenetic data at time of sampling were available from 78% of patients. Adverse cytogenetics were detectable in 82% of patients with gain 1q21 > 2 copies (62%), deletion 17p (33%), t(4;14) (13%) and t(14;16) (8%) being the most common. Results: An average sequencing depth of 750x was obtained across the samples. Our screening revealed an increased prevalence of mutations in the MAPK pathway (72%), including 34% of KRAS, 26% of NRAS, 18% of BRAF (with one patient carrying two BRAF mutations and 8% in actionable p.V600E). Additionally, two mutations (4%) were found in RASA2, a RAS inhibitor. Other potentially actionable mutations were seen in p.R132H IDH1 and p.R248C FGFR3 (2% each). Most prominently, the CRBN pathway was found mutated in 22% of cases, including CRBN (12%, one case with concomitant CUL4B mutations), CUL4B (4%), IRF4 (4%) and IKZF1 (2%). In CRBN we found four cases with mutations leading to a truncated protein (frameshift, nonsense and splicing) and two cases with missense mutations located within the thalidomide-binding domain, suggesting a causal effect on IMiD resistance. All CRBN mutated patients and 91% of the CRBN pathway mutated patients were at least once unresponsive to IMiD based treatment. In one patient with IRF4 mutation sensitivity to IMiDs remained unknown. A majority of patients were also resistant to PI treatment (76%), however mutations in proteasome subunits (PSMD1 and PSMB8) and XBP1 wererare (4%), but only a limited number of this gene family were represented in our panel. Other recurrently mutated genes were TP53 (26%), FAM46C (12%), ATM (10%) and TRAF3 (8%). Notably, DIS3 mutations were identified in only 6% of cases. As previously reported, TP53 mutations were associated with deletion 17p (8/13 cases, 62%). A correlation between the absolute number of mutations and previous lines of treatment was not observed (r=0.05, p=0.73). Conclusion: Targeted sequencing on a homogenous cohort of heavy pretreated rMM patients gives key insights in the landscape of the rMM genome, uncovering an increasing frequency of MAPK, TP53 and CRBN mutations. Importantly, this is the first study showing recurrent mutations in CRBN in patients unresponsive to IMiD treatment, supporting a potential association with resistance to IMiD based therapies. Disclosures Mai: Onyx: Other: Travel Grant; Janssen-Cilag: Other: Travel Grant; Celgene: Other: Travel Grant; Mundipharma: Other: Travel Grant. Merz:Janssen: Other: Travel grants; Celgene: Other: Travel grants. Hillengass:Takeda: Honoraria, Other: Travel support; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding; Sanofi: Research Funding; Janssen-Cilag: Honoraria, Other: Travel support; Celgene: Honoraria, Other: Travel support. Goldschmidt:Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Janssen-Cilag: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Millennium: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Onyx: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Chugai: Research Funding, Speakers Bureau. Stewart:Oncospire Genomics: Research Funding.

Abstract Background: Ixazomib is an experimental, orally bioavailable, proteasome inhibitor that has demonstrated anti-tumor activity in relapsed multiple myeloma (MM). In the dose escalation studies, ixazomib was tolerated up to a dose of 5.5 mg given every week as a single agent, while a dose of 4 mg was utilized in the combination studies with lenalidomide. We undertook this study to examine the efficacy and tolerability of the two doses of ixazomib in combination with dexamethasone in patients with relapsed MM. Patients and methods: This was a randomized phase 2 study of two doses of ixazomib (4mg; Arm A or 5.5 mg; Arm B) given weekly for three weeks with a week off along with weekly dexamethasone (40 mg) in patients with relapsed MM, who are proteasome inhibitor na•ve (including bortezomib) or have received less than 6 cycles of therapy with bortezomib and had a PR or better with no progression at the time of discontinuation. The primary objective was to determine the confirmed overall response rate (>=PR); secondary objectives included progression free and overall survival. A total of 71 patients were accrued from February 2013 to April 2015; one patient was ineligible. Results: Baseline characteristics were similar in the two arms; median age across the study was 70 years (46-84); 53% were male. Median number of prior therapies was 4 (range 2-6); 90% of the patients had prior IMiDs, 70% had prior transplant and 29% had prior bortezomib. At a median follow up of 10 months, 17 (49%) and 19 (54%) of patients had disease progression in arms A and B respectively with 12 (34%) patients in each arm still continuing on treatment. All patients in each arm were evaluable for response; the overall response rates were 31% in arm A (95%CI: 17-49) and 51% (95%CI: 34-69) in Arm B. The depth of response, event free survival and overall survival are outlined in Table 1. Among the patients with no prior bortezomib exposure the response rates were 38% for Arm A and 52% for Arm B. The treatment was well tolerated with 2 patients in each arm discontinuing treatment for adverse events; there were no on study deaths. A grade 3 or higher AE that was at least possibly related to treatment was seen in 21% and 54% in Arms A and B respectively; with 15% and 37% hematologic and 6% and 29% non-hematologic AEs. The most common attributable toxicities encountered included fatigue, thrombocytopenia, diarrhea and nausea with more grade 3 toxicities among Arm B. Peripheral neuropathy, possibly related to ixazomib, was seen in 55% (only grade 1 or 2) in arm A and 43% (2 patients with grade 3) in Arm B. Toxicities led to dose reduction of ixazomib in 17% and 43% of patients in Arm A and B respectively; the median number of cycles administered were 5 (1-24) and 5 (1-22) respectively. Conclusions: Ixazomib in combination with dexamethasone was well tolerated with significant anti-myeloma activity in this group of patients with relapsed MM. Deep responses including stringent CR were observed. The higher dose of ixazomib appears to be associated with a higher response rate but with higher rate of adverse events requiring dose reductions. Table 1. Treatment outcome in all patients Arm B (4 mg) (N=35) Arm C (5.5 mg) (N=35) Response Rate 31% (95%CI: 17-49) 51% (95%CI: 34-69) No. of Responders 11 18 sCR 0 1 CR 1 0 VGPR 7 8 PR 3 9 MR 5 1 Median Overall Survival1 NA NA 6 Months 100% 100% Median Event Free Survival1,2 8.4 mos (95%CI: 4.3-13.2) 8.2 mos (95%CI: 3.8-16.3) %Event Free at 6 Months 60% (95%CI: 45-81) 60% (95%CI: 45-81) Median Duration of Response1 16.7 mos (95%CI: 9.3-22.0) 16.3 mos (95%CI: 7.0-20.1) Median Time to Response 1.1 mos (range: 0.8-3.6) 1.0 mos (range: 0.8-7.5) CI: confidence interval; mo: month; NA: not attained 1Kaplan Meier 2Event-free survival time is defined as the time from registration to the first of disease progression, death due to any cause, or subsequent treatment for multiple myeloma. Disclosures Kumar: Celgene: Consultancy, Research Funding; Sanofi: Consultancy, Research Funding; Skyline: Consultancy, Honoraria; Onyx: Consultancy, Research Funding; Novartis: Research Funding; Janssen: Consultancy, Research Funding; Takeda: Consultancy, Research Funding; BMS: Consultancy.

Abstract Abstract 3031 Background: Treatment-induced peripheral neuropathy (TIPN) can be a debilitating side-effect as well as a therapy-limiting complication in multiple myeloma (MM). Thalidomide (THAL) and bortezomib (BTZ) are two therapies frequently associated with TIPN in MM. Carfilzomib (CFZ) is a novel and highly selective epoxyketone proteasome inhibitor that differs from BTZ both structurally and mechanistically. CFZ overcomes BTZ-resistance in vitro, lacks the off-target activities of BTZ in preclinical studies, and does not cause neurotoxicity in long-term (6–9 month) chronic animal toxicology studies (Kirk et al. Blood, 2008). Single-agent CFZ produces durable responses in relapsed or refractory (R/R) MM without dose-limiting PN. Here we report on the clinical experience with single-agent CFZ in the Ph 2b PX-171-003-A1 trial in patients (pts) with R/R MM and Grade (G) 1/2 PN at study entry. Methods: Pts received CFZ at 20 mg/m2 IV, on Days 1, 2, 8, 9, 15, and 16 in a 28-day cycle (C) for the first C followed by 27 mg/m2 thereafter for up to 12 C. Pts completing 12 C were eligible to enter an extension study. Responses and progression were determined according to the International Myeloma Working Group (IMWG) criteria and were assessed by an Independent Review Committee (IRC). PN data were collected for all pts on study and included neuropathy history, neurological physical exam and PN-related quality of life data (FACT-GOG/NTx v 4.0 scores) collected at screening. Prospective neurological exams and subjective reporting of PN occurred every 2 cycles until study discontinuation to proactively assess for PN. Adverse event (AE) data were also collected, with AEs reported as ‘neuropathy peripheral', ‘neuropathic pain', ‘neuropathy', and ‘peripheral sensory neuropathy' included as PN. AE reports of ‘paraesthesias' and ‘dysesthesias' were counted separately. Results: Of the 266 pts with R/R MM in PX-171-003-A1, 237 (89%) had a history of PN which was attributable to prior anti-myeloma therapy, including THAL (108 pts/41%), BTZ (134 pts/50%), or both BTZ and THAL (17 pts/6.4%). 206 of the 266 (77%) had G1/2 PN at baseline and a median disease duration of 5.9 years. This subset with active PN at baseline had received a median of 5 prior lines of therapy (range 1–20), with a median 13 anti-myeloma agents, and a median of 2 prior BTZ- and 1 prior THAL- containing regimens. Prior therapies included 100% BTZ, and 100% either THAL (77%) or prior lenalidomide (95%). Responses in the subset of pts with baseline PN were nearly identical to those seen in the full study population with an overall response rate (ORR; ≥ partial response [PR]) of 24% and a clinical benefit response rate (CBR; ≥ minimal response [MR]) of 36%. The median duration of response (≥PR) was 7.4 mo (95% CI 5.6–not reached) and median duration of MR was 6.3 months in both the overall and PN-baseline cohorts. OS and TTP data will also be reported. The most common treatment-emergent ≥G3 adverse events regardless of relationship to study drug were primarily hematologic and were as follows: thrombocytopenia (24%), anemia (21%), lymphopenia (11%), pneumonia (9%), neutropenia (9%), fatigue (7%), hypercalcemia (7%), and hyponatremia (6%). Although 77% of pts had G1/2 PN at baseline, new onset PN was infrequent with PN AEs of any grade reported in 31 (15%) pts and G3 PN reported in only 1 (0.4%) pt. New onset or worsening of paraesthesias (6.8%) and dysesthesias (0%) was also infrequent. Conclusions: Analysis of the subset of pts (77%) with active PN (G1/2) in this single-agent Ph 2 trial of CFZ in pts with R/R MM demonstrated that PN has no impact on depth or durability of responses, or on the tolerability of CFZ, in heavily pretreated pts with multiply relapsed and refractory MM. Reports of new or worsening PN were very uncommon, and paraesthesias and dysesthesia were generally infrequent and mild. CFZ can be given to pts with baseline PN with little risk of exacerbation; prolonged therapy is possible in this population. Disclosures: Martin: Celgene: Honoraria; Onyx: Consultancy. Singhal:Celgene: Speakers Bureau; Takeda/Millenium: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Onyx: Research Funding. Vij:Onyx: Honoraria. Wang:Celgene: Research Funding; Onyx: Research Funding; Millenium: Research Funding; Novartis: Research Funding. Stewart:Millennium: Consultancy; Celgene: Honoraria. Jagannath:Millenium, OrthoBiotec, Celgene, Merck, Onyx: Honoraria; Imedex, Medicom World Wide, Optum Health Education, PER Group: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Lonial:Millennium: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Novartis: Consultancy, Research Funding; BMS: Consultancy, Research Funding; Onyx: Consultancy, Research Funding. Jakubowiak:Millennium Pharmaceuticals, Inc.: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene: Consultancy, Honoraria; Centocor Ortho Biotech: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Exelixis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees. Kukreti:Celgene: Honoraria; Roche: Honoraria; Ortho Biotech: Honoraria. Alsina:Millenium: Consultancy, Research Funding; Celgene: Research Funding; Novartis: Consultancy. Zonder:Millenium: Consultancy, Honoraria, Research Funding; Cephalon: Research Funding; Celgene: Honoraria. Wong:Onyx Pharmaceuticals: Employment. Vallone:Onyx Pharmaceuticals: Employment. Chang:Onyx Pharmaceuticals: Employment. Kauffman:Onyx Pharmaceuticals: Employment. Siegel:Millenium: Consultancy, Honoraria; Celgene: Consultancy, Honoraria.

Abstract Introduction Multiple myeloma (MM) is characterized by a highly variable disease course, which can be traced to initiating and acquired genomic events. Whole exome analysis of matched tumor and germline DNA from 287 MM patients identified recurrently somatically mutated genes (RSMGs) (Lohr et al. - Cancer Cell 2014, Bolli et al. - Nat Commun 2014). Despite the fact that these RSMGs affect pathways that are biologically important in MM, the clinical relevance of many of these genes in the context of conventional prognostic markers remains to be elucidated. Aims The aims of this pilot study were: (1) To validate the prevalence of RSMGs in our newly diagnosed MM patient cohort; (2) To assess the correlation between RSMGs, clinical parameters and outcome; (3) To thereby identify the potential clinical usefulness of introducing RSMG mutational profiling in larger MM trial cohorts. Material and Methods CD138+ enriched MM cells and peripheral blood were obtained with informed consent from chemotherapy-naive patients, participating in 3 clinical trials: HOVON-65/GMMG-HD4, HOVON-87/NMSG-18 and Carthadex (EudraCT number 2004-000944-26, 2007-004007-34 and 2009-014922-40, respectively). Matched tumor and germline DNA were sequenced on an Ion Torrent sequencing platform (PGM, Life Technologies), using the M3 P Mutational Panel v3.0, comprising 1327 customized oligos (Life Technologies), targeted at the coding sequences of 88 MM-relevant genes, including the RSMGs. Somatic mutations were considered positive when present in >=10% of tumor reads and <=10% germline reads, with a minimal coverage of 10x and being non-synonymous, or splice donor variants. All statistical analyses were performed in SPSS version 23, using the log-rank and Mann-Whitney U-test, with the Bonferroni test to correct for multiple comparisons. Results A total of 206 DNA samples were sequenced from 103 patients (HOVON-65/GMMG-HD4 (n=16), HOVON-87/NMSG-18 (n=67), Carthadex (n=20)) with an average coverage of 574x in tumor DNA, 451x in germline DNA and an overall coverage of 98%. We collected follow-up data from 102/103 patients, with a median follow-up time of 30 months. 168 somatic mutations were detected in 44/88 genes. 82% of patients had at least 1 somatic mutation. Genes most frequently mutated were: (1) NRAS (26%), (2) KRAS (22%), (3) DIS3 (14%), (4) FAM46C (9%), (5) TP53 (7%) and (6) BRAF (6%) (Figure 1). Of note, NRAS and KRAS mutations were mutually exclusive in our cohort. Moreover, all TP53 mutations were located in its DNA binding domain. Three out of 6 BRAF mutations were predicted to cause a V600E amino acid change. We focused on these 6 RSMGs in all further analyses. Correlating mutational status with Progression Free Survival (PFS) and Overall Survival (OS) showed that TP53 mutated patients had a significantly shorter PFS compared to those with wildtype TP53 (adj. p-value=0,018; n=7 versus n=95). Comparing the mutational status of the 6 RSMGs, transplant versus non-transplant protocol, number of mutated genes in the M3 P panel, del17p and t(4;14) status, EMC92 score and ISS stage between patients with a PFS <=1 year and >1 year (n=23 versus n=79), only showed a significant correlation with TP53 mutational status (adj. p-value=0,012). TP53 mutational status remained the only significant prognostic factor when comparing patients with an OS <=1 year and >1 year (adj. p-value=0,003; n=13 versus n=89). When comparing the number of mutated genes, del17p and t(4;14) status, EMC92 score, transplant versus non-transplant protocol and ISS stage between TP53 mutated and wildtype MM, TP53 mutated patients had a significantly higher number of mutated genes in the M3 P panel (adj. p-value=0,001). Conclusions (1) With the M3 P Mutational Panel, we confirm the published prevalence of RSMGs in MM in our cohort of chemotherapy-naive patients. NRAS, KRAS, DIS3, FAM46C, TP53 and BRAF are the most frequently mutated genes. (2) TP53 mutational status is the strongest unfavorable prognostic factor in our cohort and it seems to be associated with greater mutational burden. Validation in a more extensive population is planned. (3) This warrants further investigation of the mutational status of these genes in larger clinical trial cohorts, enabling a more robust comparison with conventional prognostic markers in a multivariate analysis. Disclosures Broijl: Celgene: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees. Zweegman:Takeda: Research Funding; Janssen: Research Funding; Celgene: Research Funding. Sonneveld:Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Amgen: Honoraria, Research Funding; Karyopharm: Research Funding; SkylineDx: Membership on an entity's Board of Directors or advisory committees.

Abstract Abstract 39 Three randomized trials have previously reported a progression-free survival (PFS) advantage for patients receiving thalidomide (T) maintenance post ASCT in MM. Two trials reported an overall survival (OS) advantage but the largest trial reported shows no OS advantage and in very high risk MM the use of T was deleterious. Recent trial reports demonstrate a PFS but not yet an OS advantage for patients receiving maintenance lenalidomide. We report results of NCIC CTG MY.10 which compared treatment with T (200 mg daily) and prednisone (50 mg alternate days) (T/P) until progression versus observation alone when used as maintenance therapy following ASCT. Importantly, OS was the 1ry endpoint of this study, 2ry endpoints were PFS, quality of life (QoL), toxicity, and the incidence of venous thromboembolism events (VTE). Eligibility: Patients with MM who had ASCT within 1 year of beginning initial treatment for their disease. Patients were randomized 60–100 days post ASCT and had no other medical condition precluding long term use of T/P. Results: 332 patients were enrolled. Median age was 58 years and the arms were balanced. Patients were stratified by age (<60 or >60), and CR status post transplant. Median follow up is 4 years. Only 14% of patients were in CR post transplant. 111 patients died (50 versus 61 in T/P vs. observation). The median OS was 5 years for observation, and has not yet been reached for T/P, however T/P maintenance therapy did not significantly prolong OS: p = 0.18, HR of maintenance vs. observation 0.77 (95% CI 0.53–1.13). The 4 year survival rate was 68% for T/P and 60% for observation. Age and response to transplant had no significant association with OS (p=0.21), while higher disease stage was associated with shorter OS (p=0.03). The median PFS was 28 months for T/P versus 17 months for observation: p<0.0001, HR of T/P vs. observation 0.56 (95% CI 0.43 – 0.73). The 4 year PFS rate was 32% for T/P treated patients versus 14% for patients on observation. At relapse, treatment by arm (T/P vs observation) included lenalidomide (39 vs 34%), T (13 vs 22%) or bortezomib (50 versus 46%). Non hematologic toxicities were seen in more patients with treatment (Grade 3: 92% T/P vs 49% observation, grade 4: 16% vs 7%). Common toxicities of all grades that were significantly higher in T/P treated patients included hyperglycemia, edema, hypertension, fatigue, Cushingoid appearance, constipation, mouth dryness, dyspepsia, anxiety, memory loss, sensory neuropathy, tremor, blurred vision, depressed consciousness, cataracts, dyspnea and bruising. 7% of patients on maintenance T/P developed a VTE in the absence of prophylaxis versus 0% on observation. NCIC CTG standardized response analysis was use to compare QoL data between the 2 treatment arms. Overall, patients on T/P had worse QoL specifically in physical (p=0.07), role (p=0.08), cognitive (p = 0.01) and global (p=0.06) domains, and worse symptoms with dyspnea (p = 0.0007), constipation (p<0.0001), thirst (p=0.003), swelling in leg (p=0.03), numbness (p=0.02), dry mouth (p<0.0001), and balance problems (p<0.0001). However, patients on T/P reported improvement in appetite (p 0.02), and sleep (p=0.04). Conclusions: T/P maintenance did not improve overall survival, the primary objective of this trial, although a trend in favor of T/P was seen. In contrast, PFS was significantly improved in the T/P arm while toxicity was demonstrably increased and quality of life diminished. Disclosures: Stewart: Millennium: Consultancy; Celgene: Honoraria. Trudel:Celgene: Honoraria. Bahlis:Celgene: Honoraria, Research Funding, Speakers Bureau. White:Celgene: Honoraria, Research Funding. Meyer:Celgene: Honoraria.

Abstract Abstract 1923 Our understanding of the genetic abnormalities associated with the development of multiple myeloma has increased significantly in the last decade. However, very little is known about how, or if, myeloma tumor genomes change with time and if therapeutic interventions influence these events. To address these issues we studied a cohort of 29 patients for whom at least two serial samples (1-65 months, median 19 months) were available for analysis. Each serial pair was analyzed by both array-based comparative genomic hybridization (aCGH) and microarray gene expression profiling (GEP) to identify DNA copy number abnormalities (CNA) at a 25kb resolution and gene expression differences present in the bulk of the tumor mass. Though this does not address the intra-clonal heterogeneity that may exist at a given time point, it does answer if the bulk of the tumor mass is changing with time. This study has unearthed several surprising and clinically relevant findings. First, myeloma tumor genomes are not as unstable as previous cytogenetic analyses suggest. In 40% of patients we observed no detectable CNA changes (1-37 months, median 12 months). In 24% of patients we observed the exclusive acquisition of new CNA (1-12, median 3.5) (3-22 months, median 18 months). In 36% of patients we observed both the loss (1-20, median 3) and gain (1-33, median 21) of CNA (5-43 months, median 20 months). Because time was not a significant influence on the detection of stable or unstable genomes we compared CNA changes with TC class and found patients with the high-risk 4p16 and maf IgH translocations were over-represented in the latter subset of patients. These observations raise the question of what happens between multiple rounds of therapy and if different regimens influence these phenotypes differently. For two patients with no CNA changes between the first two time points there was an additional sample that extended the follow-up by 52 and 12 months. Again no CNA changes were seen between diagnosis and these final samples taken 63 and 50 months later. For one patient with CNA changes (5 shared, 29 lost, and 32 gained) we have a detailed time course of 5 samples from diagnosis through to end-stage plasma cell leukemia. This patient received continuous lenalidomide-dexamethasone (Rd) for 20 months and progessed with a clone containing a BIRC2/3 deletion, which activates the NFKB pathway. The patient received single agent PR-171 and a bortezomib containing regimen and unexpectedly, the tumor genome observed in the third sample was almost identical (32 shared, 2 lost, and 4 gained CNA) to the first time point, including two copies of BIRC2/3. Subsequently, the patient received melphalan-prednisone-bortezomib (MPV) and the tumor genome observed in the fourth and fifth samples, which were identical, were similar to that seen in the second sample (24 shared, 13 lost, and 39 gained CNA). To understand these observations better we performed FISH to ascertain if the observed clones were detectable earlier, albeit at a low frequency. These experiments proved that the two dominant subclones observed at time points 1 and 3 versus 2, 4, 5 were mutually exclusive at the single cell level. Moreover, both of these clones were detectable at diagnosis with 12% of the tumor mass being the second subclone that eventually evolved into plasma cell leukemia. Interestingly, we assayed 5 of the 39 unique CNA observed in the final two samples and only one, the 17p13 deletion, was detectable earlier. This suggests the MPV regimen effectively eliminated a clone that was previously sensitive to Rd and selected for a dramatically evolved subclone that was previously sensitive to two different proteasome inhibitors. Although it is clear that the high-risk patients are enriched in the subset with the most changes, it is not clear if the specific drugs used (Melphalan vs IMID vs proteasome inhibitor) or intervention strategy (Cycled vs continuous/maintenance) and perhaps the response achieved (PR vs CR) influences these events. These observations do highlight two important clinical concepts that need to be considered in the future. First, the meaning of a partial response needs further investigation as this may reflect effective elimination of one subclone but not another. Second, because some patients are not changing or can revert back to a previous subclone we need to consider re-chanllenging patients with previously effective regimens when patients progress. Disclosures: Fonseca: Genzyme: Consultancy; Medtronic: Consultancy; BMS: Consultancy; AMGEN: Consultancy; Otsuka: Consultancy; Celgene: Consultancy, Research Funding; Intellikine: Consultancy; Cylene: Research Funding; Onyx: Research Funding; FISH probes prognostication in myeloma: Patents & Royalties. Stewart:Millennium: Consultancy; Celgene: Honoraria. Bergsagel:Amgen: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Genentech: Membership on an entity's Board of Directors or advisory committees; Millennium: Speakers Bureau; Novartis: Speakers Bureau.

Abstract Background: Malignant cells alter metabolism in order to enable their highly anabolic state. In addition to a massive increase in glycolysis, malignant cells frequently become dependent on glutamine to feed the TCA cycle and provide key building blocks for cell growth and proliferation. CB-839 is a first-in-class potent and selective inhibitor of glutaminase (GLS), the first step in glutamine metabolism, that has broad in vitro and in vivo anti-tumor activity in solid and heme malignancies, including multiple myeloma. GLS inhibition with CB-839 induces apoptosis and/or growth arrest in multiple myeloma and lymphoma cell lines and is synergistic with pomalidomide and lenalidomide in vitro and as well as in multiple myeloma xenograft models in vivo. Methods: CX-839-002 is an ongoing Ph1 evaluation of escalating doses of CB-839 in patients with relapsed/refractory multiple myeloma (MM) or non-Hodgkins lymphoma (NHL) with the primary objective of assessing the safety profile and selecting a recommended Phase 2 dose (RP2D). Pharmacokinetics (PK) was monitored on Days 1 and 15. Initially, CB-839 was given three times daily (TID) without food, but based on PK and safety data generated across three Ph1 studies in patients with solid and heme malignancies, the drug is now being given twice daily (BID) with meals. Results: Safety data are available for a total of 14 patients (9 MM, 4 follicular lymphoma, 1 diffuse large B cell lymphoma) that have enrolled to date during the dose escalation (100-400 mg TID and 600 mg BID). The patients have received a median of 7 prior lines of systemic therapy. CB-839 has been well tolerated with only three subjects experiencing a Gr3/4 AEs considered possibly related to study drug and there have been no discontinuations due to AEs. A similar tolerability profile has been observed across three Ph1 studies for CB-839. With a total of 119 pts treated with CB-839 across the three studies, Gr3/4 drug-related AEs have occurred in 16 subjects (13%) and 4.3% of discontinuations were due to AEs. Reversible, asymptomatic elevations in transaminases have been the primary Gr3 AEs, occurring primarily on the TID schedule in 6/59 (10.2%) pts; only one occurred among 60 pts (1.7%) receiving the BID regimen. BID dosing with 600 mg was determined to be the RP2D and combination studies with pomalidomide and dexamethasone have been initiated. The half-life of CB-839 is ~4 hr, exposure increases with dose, and trough concentrations generally remain above the target threshold of 200 ng/mL for patients receiving the RP2D. Six of 8 MM pts that received ≥ 400 mg TID achieved steady state (D15) trough concentrations above the PK target threshold while 0 of 5 pts that received ≤ 250 mg TID achieved the PK threshold. Pharmacodynamic assessment of GLS activity in MM patients was consistent with a broader PK/PD assessment (across all 3 Ph1 studies), which established clear exposure-dependent inhibition of the target in peripheral blood platelets 4 hr after the first dose of CB-839, with >90% inhibition being maintained for most patients at the RP2D. Preliminary efficacy data include confirmed stable disease in 4 of 9 evaluable MM patients. Updated efficacy data and correlative studies on clinical samples will also be presented. The first pt treated with the combination of CB-839 and pomalidomide/dexamethasone (Pd) during dose escalation received 400 mg CB-839 BID, pomalidomide at 4 mg/day (D1-21) and dexamethasone at 40 mg on Days 1, 8, 15 and 22 of each 28-day cycle. This pt had a 71% decreased in urine M-protein and an 83% reduction in serum free light chain after the first 2 cycles of treatment. This pt had 11 prior lines of therapy but not pomalidomide and had two stem cell transplants and was progressing rapidly prior to study entry. The pt has tolerated the combination well and is continuing on study. Conclusions: CB-839 has been well tolerated at and above doses that produced robust inhibition of GLS in blood platelets and in tumors. Dosing BID with food has improved the PK profile and mitigated the frequency and severity of LFT elevations, which was the primary safety signal using TID dosing. Strong preclinical combination data, an excellent clinical safety profile, and initial data with CB-839 combined with Pd provide a strong rationale for continued development of CB-839 this combination in pts with relapsed/refractory multiple myeloma. Disclosures Vogl: Constellation Pharmaceuticals: Research Funding; Calithera Biosciences: Research Funding; Celgene Corporation: Consultancy; Acetylon Pharmaceuticals, Inc.: Research Funding; Millennium Pharmaceuticals: Research Funding; GSK: Research Funding. Younes:Celgene: Honoraria; Curis: Research Funding; Sanofi-Aventis: Honoraria; Seattle Genetics: Honoraria, Research Funding; Novartis: Research Funding; Janssen: Honoraria; Takeda Millenium: Honoraria; Bristol Meyer Squibb: Honoraria; Bayer: Honoraria; Incyte: Honoraria; Johnson and Johnson: Research Funding. Orford:Calithera Biosciences: Employment, Equity Ownership. Bennett:Calithera Biosciences: Employment, Equity Ownership. Siegel:Celgene Corporation: Consultancy, Speakers Bureau; Amgen: Speakers Bureau; Takeda: Speakers Bureau; Novartis: Speakers Bureau; Merck: Speakers Bureau. Berdeja:Curis: Research Funding; Acetylon: Research Funding; Novartis: Research Funding; Janssen: Research Funding; Takeda: Research Funding; BMS: Research Funding; Array: Research Funding; MEI: Research Funding; Abbvie: Research Funding; Celgene: Research Funding; Onyx: Research Funding.