Chanan‐Khan, Asher

Background The ubiquitin proteasome system (UPS) maintains homeostasis in eukaryotic cells by degrading and recycling proteins associated with DNA transcription and cell cycle regulation. In tumor cells with a high protein turnover rate, particularly in immunoglobulin secreting cancers such as Waldenströms Macroglobulinemia (WM), proteasomes are critical for sustained cell proliferation. Proteasome inhibitors (PI) such as bortezomib and carfilzomib target the B5 subunit of the proteasome catalytic core and disrupt its activity leading to accumulation of polyubiquitinated proteins. Although highly effective in WM, persistent use of bortezomib eventually leads to emergence of a bortezomib resistant (BR) subclone. Point mutation in the PSMB5 gene (encoding the B5 subunit) leading to altered binding kinetics is identified as a potential underlying mechanism of PI resistance. Despite these adaptive modifications that support resistance to PI resistance, the UPS as a whole remains a relevant target with vulnerable sites that can be therapeutically exploited. The 19S cap of the proteasome contains deubiquitinating enzymes (DUBS) that function to deubiquitinate proteins prior to their entry into the proteasomal core. Using a novel DUB-inhibitor b-AP15, which blocks the UCHL5 and USP14 DUBS, D’Arcy et al demonstrated that disruption of these DUBS does not alter proteasomal activity yet induces robust tumor cell death in various cancers. Aim Investigation of b-AP15 in preclinical models of BR WM and characterization of associated downstream signaling interactions. Methods For these studies, we developed and used BR variants of the most commonly used WM cell lines (variants termed BCWM.1/BR, RPCI-WM1/BR and MWCL-1/BR). Proteasomal activity was measured in these cells using synthetic fluorogenic peptide substrates and apoptosis was measured by annexin-v/PI staining. For gene expression profiling (GEP), the Nanostring nCounter mRNA quantification assay was utilized. Results We treated all BR WM clones with either single agent bortezomib (10nM), carfilzomib (10nM), b-AP15 (100nM) or all three agents in combination and assessed their effect on chymotrypsin-like, caspase-like and trypsin-like proteasomal activity. b-AP15, either alone or in combination with the other PI, did not alter proteasomal activity, nor did it abrogate the inhibition of chymotrypsin-like activity of other PI. Although proteasomal activity was not disrupted, we observed an increase in high molecular weight ubiquitinated proteins on immunoblot analysis. We hypothesized that despite the BR cells resistance to B5-targeting PI, they would remain sensitive to UPS inhibition if targeted through DUB inhibition. We treated BR cells with b-AP15 at concentrations ranging from 50nM - 1.25uM and observed that b-AP15 induced robust WM cell death in a dose and time dependent manner. Apoptosis was more pronounced in MWCL-1/BR cells and optimal cell death (55%) was observed at 500nM; however a commitment towards cellular demise was evident by PARP-1 and caspase cleavage as early as 3 hrs. Use of a pan-caspase inhibitor resulted in rescuing of the BR WM cells from b-AP15 mediated death and demonstrated a caspase-dependent death process. In order to gain further mechanistic insight into the processes that regulates response to b-AP15, we performed GEP and immunoblot of BR WM cells treated with 50nM of b-AP15. We observed an increase in phospho-p38 protein, which belongs to the MAPK family and regulates IL8 secretion. When BR WM cells were treated with a p38 inhibitor in combination with b-AP15, a significant decrease in cell viability was noted relative to b-AP15 (100nM) alone. Furthermore, GEP and network analysis identified key regulator genes associated with p53, cell cycle and MAPK signaling. Summary We provide first evidence that inhibition of the DUBS, UCHL5 and USP14 with b-AP15 results in caspase-dependent apoptosis of BR WM cells. Our investigation uncovers important molecular interactions that may dictate the BR cells responsiveness to DUB-inhibition by b-AP15. These observations validate the pervasive role of the UPS and confirm alternate therapeutics targets using our unique BR WM models. We are grateful to the Waterfall Waldenström Macroglobulinemia Research Fund, the Leukemia and Lymphoma Society and the International Waldenström Macroglobulinemia Foundation for their continued support. Disclosures: Martin: Teva: Consultancy, Research Funding; Celgene: Consultancy, Research Funding; Genentech: Speakers Bureau; Millennium: Research Funding; Seattle Genetics: Consultancy, Speakers Bureau.

Abstract Background: CLL is the most common leukemia diagnosis in adults and its treatment has undergone significant change from chemotherapy, to immunotherapy and now targeted kinase inhibitors, leading to improved overall survival (OS). With improving survivorship, SPMs can occur but an in-depth analysis of risks and trends of SPMs in CLL survivors is lacking. We performed a population-based analysis to evaluate this. Methods: Patients in the Surveillance, Epidemiology and End Results (SEER) database diagnosed with CLL between 1973-2015 were included. Due to variation in management techniques over time, the cohort was divided in four time periods: 1973-1982, 1983-1992, 1993-2002 and 2003-2015. We evaluated differences in risk for SPMs among CLL survivors compared to risk of individual malignancies expected in the general population during these time periods and studied the effect of demographics and time since CLL diagnosis. Results: Over a nearly 270,000 person-year follow up, 6,467 new SPMs were diagnosed with a standardized incidence ratio (SIR) of 1.2 (95% CI 1.17-1.23), which resulted in a 39 excess cancers per 10,000 population. The CLL survivors had a 20% overall increased risk of developing SPMs (excluding non-squamous skin cancer) compared to the general population. The risks for both solid (SIR 1.15 CI 95% 1.12-1.18) and hematological malignancies (SIR 1.61 95% CI 1.5-1.73) was higher than the expected in the general population. However, the risk for individual cancers was heterogeneous. The tumors associated with the highest risk were Hodgkin lymphoma (almost 8 times higher), Kaposi Sarcoma (4 times), non-epithelial skin cancers (4 times), salivary gland cancer (3 times) and acute lymphocytic leukemia (3 times). In contrast, tumors in the hepatobiliary system, female breast and female genital system were associated with a lower risk than the general population. The highest SIR across the study periods was observed in the younger population (ages 15-49). Although the risk increased in all ethnicities, it was statistically significant only in Caucasians. There was no gender-wise difference in SIR during any of the four time periods. A statistically significant increase in SIR was observed for both men and women from 1973-1982 to 2003-2015. This was mostly due to an increase in risk of hematological malignancies from 1.08 early in the study to 2.56 in the most recent study period. The SIR in solid tumors did not change significantly over time; in absolute terms, however, lung carcinoma contributed the most to the excess risk, followed by non-epithelial skin cancers and non-Hodgkin's lymphoma. The risk of developing a SPM was higher for the CLL survivors during most of the latency periods, but it was statistically significant during the 2-5 months and 12-59 months after diagnosis. A multivariate analysis was conducted to evaluate the impact of period of diagnosis on the development of SPMs among these patients. After adjusting for gender, ethnicity, radiation therapy, chemotherapy, and age at diagnosis of CLL, patients diagnosed with CLL in the most recent time period were at 45% higher risk of developing SPMs as compared to the patient diagnosed during 1973-1982 (Hazard ratio(HR) =1.45 95%CI:1.34-1.6, p<0.001). Moreover increased HRs were also observed for 1983-1992 and 1993-2002 time periods (Fig. 1) Conclusions: With improving therapeutics for cancer treatment, survivorship is improving as well and the risk of SPMs needs to be better understood and addressed. This is truer for CLL, where majority of patients have a favorable survival. The risk of SPMs was 20% higher in CLL survivors than in the general population and was most prominent in the survivors aged 15-49 years at the time of CLL diagnosis. The risk of individual malignancies may be heterogenous but there has been an increase in risk of SPMs over time, mainly due to an increase of secondary hematological malignancies in recent years. Active survivorship plans and long-term surveillance for SPMs is crucial for improved outcomes of patients with a history of CLL. Disclosures Ailawadhi: Janssen: Consultancy; Celgene: Consultancy; Amgen: Consultancy; Takeda: Consultancy; Pharmacyclics: Research Funding.

Abstract Background Waldenstršms macroglobulinemia (WM) is a rare and incurable indolent Non-Hodgkin's lymphoplasmacytic lymphoma. Rarity and limited availability of authentic preclinical models has been a major constraint in drug development for WM. We recently reported the establishment and characterization of a novel human WM cell line, RPCI-WM1. Thereafter we evaluated the tumorigenic potential of this unique WM cell line in a xenograft mouse model along with its ability to produce human IgM in vivo. Moreover, we assessed its potential as a possible model for enhanced understanding of WM cell biology in vivo and a mechanism to conduct functional studies and preclinical anti-WM drug evaluation. Aim The primary goal of this experiment was to develop and validate an in vivo WM model that can be used to investigate WM cell biology as well as drug evaluation. Methods The RPCI-WM1 cell line (1x106 cells) was injected both subcutaneously and via tail vein into female SCID mice. Engraftment was validated via detection of human IgM (ELISA) and tumor growth (as well as response to therapy) was monitored by weekly assessment of IgM levels and external tumor formation measurements. Results After subcutaneous injection (flank) into mice, the RPCI-WM1 cells developed localized tumors that secreted human IgM detectable in serum as early as 14 days. Progressive increase in IgM was measured in the serum and this corresponded with tumor growth in a time-dependent fashion. On average, tumor tissues grew to a median of 3 cm and IgM levels reached a median of 823 ng/mL by Day 30 post-implantation. We also assessed the practical utility of this xenograft mouse model for evaluation of therapeutics, using a compound X (propriety drug with demonstrable in vitro anti-WM effects). Eleven days post-implantation, the mice were randomized into 3 groups receiving either DMSO (n=6), 100 mg of compound X (n=7) or 200 mg/kg of compound X (n=7) every alternate day via intraperitoneal injection for 26 days. On Day 37, mice were sacrificed and tumor volume was measured. We observed a 48% reduction in tumor volume in the 100mg/kg cohort, with no additional anti-WM benefit noted in the 200mg/kg cohort. Human IgM secreted by the xenografted tumors was measured by ELISA and was significantly lower in mice treated with compound X versus the control group (Figure 1). We also conducted immunohistochemistry (IHC) analysis on tumor tissues obtained from 9 mice treated with compound X (both dose cohorts) or DMSO alone. IHC staining demonstrated changes in the known target proteins of compound X (such as BCL2, p53, Ki-67) between the treated and untreated mice. Summary Thus we demonstrate that the RPCI-WM1 cell line can be dependably used to induce tumor growth through xenotransplantation in SCID mice and this mimics the IgM secreting clinical disease model. This can then be used to serve as a platform for preclinical testing of novel anti-WM therapeutics and allow for subsequent correlative studies for pharmacodynamics purpose. Comprehensive data regarding this model its utility in evaluation of various biological questions such as those relevant to the tumor microenvironment as well therapeutic modeling will be presented. We are grateful to the Leukemia and Lymphoma Society and the International Waldenstršm Macroglobulinemia Foundation for their continued support. Disclosures: No relevant conflicts of interest to declare.

Abstract Background: Clinical trials are fundamental to advance therapeutics systematically and improve patient outcomes. Despite this, enrollment on clinical trials remains dismal in the United States (US) and is a constant focus of healthcare policy. We studied distribution of clinical trials for B-cell malignancies over time across the US and unique clinical trial opportunities i.e. individual clinical trials for the given diagnosis at a site that patients may have access to participate. Methods: We abstracted data from clinicaltrials.gov for all trials that had non-Hodgkin lymphoma (NHL) or multiple myeloma (MM) as an inclusion indication between 1999-2018. Clinical trial characteristics and distribution over US geographical divisions (West, Midwest, Northeast, and South) were studied, and differences were assessed by Chi-square test. Results: A total of 1930 trials were identified (NHL: 982, MM: 948), of which 483 were recruiting at the time of data abstraction (NHL: 250, MM: 233). Over the past 2 decades, 182691 patients were enrolled on the various trials (NHL: 81592, MM: 101099). Trials by phase of study included phase 1: 629, phase 1/2: 316, phase 2: 813, phase 2/3: 11 and phase 3: 161. Number of trials by phase separated by NHL and MM are shown in Figure 1. Of these, 197 trials were randomized (NHL: 67, MM: 130). Geographical distribution of trials by diagnosis type is shown in Figure 2. A total of 31806 unique trial opportunities were noted for MM and NHL, of which 9,513 were international and 22,293 were in the US, with a geographical distribution of 5080 in West, 8198 in Midwest, 3944 in Northeast, and 5071 in South. 4,883 of the unique trial opportunities were available at NCI/NCCN accredited sites and 17,410 were at non-NCI/NCCN sites in the US. Treatment characteristics of the trials included monoclonal antibodies in 1218, other targeted agents in 2641, stem cell transplant in 526, and other agents in 517 trials with several trials utilizing more than one of these therapeutic options. There was no statistically significant difference in the distribution of clinical trials by phase of study across various US geographical regions for MM (p=0.71), NHL (p=0.98) or combined MM+NHL (p=0.16). On the other hand, unique trial opportunities were significantly different by study phase and geographical distribution for MM, NHL or MM+NHL (all p<0.001) (Figure 3). Conclusions: Widespread access to clinical trials within a cancer diagnosis is imperative for generalizability of trial results. In a comprehensive, national analysis we noted that while it may appear that clinical trials are available across the US, sites where they are open are distributed unevenly, giving rise to a disparity in access to evidence-based therapeutic advancements for patients. Disclosures Ailawadhi: Janssen: Consultancy; Amgen: Consultancy; Pharmacyclics: Research Funding; Takeda: Consultancy; Celgene: Consultancy. Sher:Affimed: Research Funding.

Abstract INTRODUCTION: Patients undergoing HSCT are reported to have a high prevalence of depression and anxiety. These comorbid mood disorders have been known to be associated with alteration in pain perception in patients without hematological malignancies. Pharmacological compounds such as opioid and benzodiazepines are frequently used to manage patient symptomology including pain and anxiety. Patients undergoing HSCT are a unique population where the impact of depression and anxiety on opioid and benzodiazepine use has not been well studied. METHODS: The study population consisted of patients who underwent HSCT at a single center for a variety of hematological malignancies from 2015-2018. Opioid and benzodiazepine exposure and dosage was defined in a) Patients who were exposed to opioid including those who were previously exposed and those who were exposed during hospitalization for HSCT b) Patients who were neither exposed to opioid previously, nor during the hospitalization for HSCT. Depression and Anxiety was defined as per PHQ-9 and GAD-7 scales prior to hospital admission. Multivariable analysis was performed to identify differences in opioid status, previous benzodiazepine use, transplant type, Karnofsky score, gender, age, race, and marital status with associated Diazepam Equivalent Daily Dosage (DEDD) (Negative Binomial Regression), and Morphine Milligram Equivalent Daily Dosages (MMEDD) (Logistic and Zero Truncated Negative Binomial Regression). RESULTS: A total of 275 patients underwent HSCT including autologous and allogeneic from 2015-2018. Anxious or depressed HSCT recipients had an increased incidence of higher DEDD with an IRR of 1.69 (95% CI: 1.15, 2.49) compared to those who were neither depressed nor anxious (Figure 1). However, patients who reported anxiety and depression did not have a different DEDD than those not anxious nor depressed. In addition, patients who were not naïve to benzodiazepine use prior to admission had an increased incidence of a higher DEDD [IRR of 2.23 (95% CI: 1.61, 3.05)]. Patients undergoing autologous stem cell transplant had a decreased incidence of receiving a higher DEDD [IRR of 0.65 (95% CI: 0.47-0.90)]. African American and other populations had a decreased incidence of receiving a higher DEDD [IRR of 0.40 (95% CI: 0.27, 0.59)]. Patients receiving higher MMEDD had a higher DEDD incidence [IRR of 1.01 (95% CI: 1.01, 1.02)]. Patients who were both anxious and depressed had increased odds of receiving an opioid [OR of 3.35 (95% CI: 1.62, 6.94)] compared to patients who were neither depressed nor anxious. However, patients who were either depressed or anxious did not have different odds of receiving an opioid compared to those who were neither depressed nor anxious. Patients undergoing autologous stem cell transplant had reduced odds of receiving an opioid [OR of 0.17 (95% CI: 0.07, 0.40)]. Patients with less than normal Karnofsky performance status (<90 on scale of 1-100) had an increased incidence of receiving a higher MMEDD [IRR of 2.34 (95% CI: 1.07, 5.12)] when modeled by Zero Truncated Negative Binomial Regression. Finally, HSCT recipients who were both anxious and depressed had reduced odds of being naïve to opioids [OR0.31 (95% CI: 0.15, 0.67)] compared to recipients who were neither depressed nor anxious. New opioid users had reduced odds of receiving a greater MMEDD [OR of 0.98 (95% CI: 0.96, 0.99)] when compared to previous users. In addition, autologous stem cell transplant recipients had reduced odds of receiving greater MMEDD compared to allogeneic transplant recipients (OR 0.33, 95% CI: 0.16, 0.66). CONCLUSION: Comorbid depression and /or anxiety impact opioid and benzodiazepine use in patients undergoing HSCT. The presence of these comorbid conditions and their association with increased use of opioids and benzodiazepines can also affect various health related outcomes. Larger studies are needed to fully understand the potential impact of this association on health related outcomes. Figure 1. Figure 1. Disclosures Kharfan-Dabaja: Incyte Corp: Speakers Bureau; Alexion Pharmaceuticals: Speakers Bureau; Seattle Genetics: Speakers Bureau. Ailawadhi:Amgen: Consultancy; Pharmacyclics: Research Funding; Celgene: Consultancy; Janssen: Consultancy; Takeda: Consultancy.

Abstract Abstract 2859 Introduction: Patients with chronic lymphocytic leukemia who relapse following purine-analog or bendamustine-based treatments have a poor prognosis. These patients have limited therapeutic options and novel agents with alternative mechanisms of action are needed. In phase 1 and 2 trials, escalating dose regimens of the immunomodulatory agent lenalidomide demonstrated promising activity with relapsed/refractory CLL. Of interest, the data indicate that superior efficacy might be achieved by a starting dose above 2.5 mg daily lenalidomide. A phase 2 trial (CLL-009 study) was developed to investigate the safety of different starting doses of lenalidomide followed by a step-wise dose escalation as tolerated in relapsed/refractory CLL. Methods: In this ongoing trial, eligible subjects with relapsed/refractory CLL who have received at least 1 prior treatment regimen are being enrolled. Subjects are randomized 1 :1 :1 to receive a double-blinded starting dose of 5 mg, 10 mg, or 15 mg oral lenalidomide on days 1–28 of each 28-day cycle. The primary objectives are to determine the safety and efficacy of the different lenalidomide starting doses of 5 mg, 10 mg or 15 mg daily, followed by an intra-patient escalation up to a maximum of 25 mg daily using a Bayesian approach. Based on individual patient tolerability, the daily lenalidomide dose can be escalated every 28 days by 5 mg increments. Dose reductions also occur in 5 mg increments; however, dose levels below 5 mg sequentially include 2.5 mg and 1.25 mg daily. Tumor lysis syndrome (TLS) prophylaxis, comprised of oral hydration and allopurinol 300 mg/day is initiated at least 3 days prior to starting study drug and for a minimum of the first 3 treatment cycles. This adaptive design trial is considering joint efficacy and toxicity outcomes to stop randomization of less promising arms. Accrual to a starting dose arm will be stopped if unacceptable toxicities and/or high progression rate are observed in that arm. A total of 90 subjects will be enrolled in the study. Results: To date, 51 subjects with a median age of 63 years (range 39–78) have been enrolled. Subjects to date are primarily male (65%) and Caucasian (84%), and slightly more than half (53%) are ≥ 65 years old. Cytogenetic data is available for 42 subjects; 10 have del(11q), 8 have del(17p), and 24 have del(13q). Overall, 31 subjects had at least one cytogenetic deletion. Based on the Binet and Rai staging systems: 3 (6%), 10 (20%) and 15 (29%) of subjects are stage A, B and C, respectively; and, 6 (12%), 7 (14%) and 7 (14%) subjects are low, intermediate or high-risk disease, respectively. For 3 (6%) subjects the Binet/Rai staging is currently unknown. The most common hematological grade 3/4 adverse events (AEs) thus far include neutropenia (41% of patients) and thrombocytopenia (24%). The most common non-hematological grade 3/4 AEs include fatigue (12%) and tumor flare (12%). Only 1 subject (2%) experienced tumor lysis syndrome of grade 1. Over half of the subjects (53%) remain on therapy; 24 (47%) subjects have discontinued treatment. The longest subject has completed 17 cycles, and remains on study medication. The most common reasons for study discontinuation include disease progression (n = 8) and AEs (n = 10). To date, 20 subjects (54% of eligible patients) have successfully dose escalated above their respective starting double blinded dose level, including 3, 3, 2 and 12 subjects undergoing 4, 3, 2, and 1 dose escalations, respectively. As 14 patients are still in the first cycle of the study, a total of 20 subjects have had no dose level reduction or escalations. The average duration of treatment is 4.34 cycles, and the median number of cycles is 3. Efficacy evaluations are completed monthly after 3 months of study drug treatment. By investigator assessment, 34 subjects have been evaluated to date, including 1 (3%) complete response, 12 (35%) partial response, 7 (21%) stable disease, 10 (29%) progressive disease and 4 (12%) not evaluable. Conclusion: The independent Data Monitoring Committee, as of March 24, 2011 (N=41), recommended that accrual into all three treatment arms should continue as planned, suggesting all three starting doses were tolerated. To date, the ORR is 38% (13/34 evaluable subjects), and 54% of subjects (20/37) have dose escalated at least once. In this relapsed/refractory CLL population lenalidomide appears active, and completion of accrual will hopefully demonstrate the appropriate starting dose. Disclosures: Wendtner: Celgene: Consultancy, Honoraria, Research Funding. Off Label Use: lenalidomide in cll. Goldberg:Celgene: Honoraria, Research Funding, Speakers Bureau. Bloor:Celgene: Honoraria, Research Funding. Stilgenbauer:Celgene: Consultancy, Honoraria, Research Funding. Cymbalista:Roche: Research Funding; Mundipharma: Honoraria; Genzyme: Honoraria. Kipps:Celgene: Consultancy, Research Funding; Abbott Industries: Research Funding; Genentech: Research Funding; Gilead Sciences: Consultancy, Research Funding; Igenica: Membership on an entity's Board of Directors or advisory committees. Purse:Celgene: Employment, Equity Ownership. Zhang:Celgene: Employment, Equity Ownership. Mei:Celgene: Employment.

Abstract Abstract 678 Background: Second primary malignancies (SPM) among multiple myeloma (MM) patients have been reported with an estimated incidence varying from 1%–15%. We have previously reported that significant disparity exists in MM survival across patients of different ethnicities. We undertook a Surveillance Epidemiology and End Results (SEER) based analysis to describe the incidence of SPM among MM patients of different ethnicities, in order to explore the variable impact that SPM might have on MM outcomes of patients across racial subgroups. Methods: SEER database was used to examine the standardized incidence rates (SIR) of SPM among MM patients diagnosed between 1973–2008. Observed to expected ratio (O/E) of SPM was calculated using incidence rates of cancers for the general population. The 95% confidence limits (CI) were constructed using Fisher's exact test. The analysis was restricted to patients with MM as first primary, microscopic confirmation of diagnosis, reporting sources not coded as autopsy- or death-certificate-only, and SPM reported more than 2 month after MM diagnosis. Mutually exclusive race/ethnicity categories were: African-Americans (AA), Asians/Pacific Islanders (API), Hispanic whites (HW), Non-Hispanic whites (NHW), and others. The risk of SPM among MM patients was explored by ethnicity, type of SPM, and latency period. Results: A total of 3090 cases of MM with SPM were diagnosed between 1973–2008, of which, 2021 patients met our inclusion criteria. Stratification of SPM by ethnicity revealed: 387 AA (19%), 72 API (4%), 51 HW (3%), 1500 NHW (74%) and 11 other (<1%) cases. There was an average 4.7-year latency period between diagnosis of MM and SPM (mean age 68.2 and 72.9 years, respectively). The latency period was not significantly different by type of SPM (solid organ vs. hematological) or ethnicity. AA had the youngest age at diagnosis for both, MM and SPM (65.6 and 70.1 year, respectively). (Figure 1) For all SPM sites analyzed together, there was no significant difference between the observed and expected incidence (O/E 0.98; 95% CI 0.94–1.02). However, O/E risk was significantly decreased for solid organ SPM (N=1695; O/E 0.92; 95% CI 0.88–0.96) and increased for hematological malignancies (N=263; O/E 1.63; 95% CI 1.44–1.84). Highest excess risk among all SPM was noted for acute non-lymphocytic leukemia (ANLL) (O/E 6.51; 95% CI 5.37–7.83). The overall risk of observed SPM was not different from expected rates by ethnicity, with the exception of HW who had a significantly decreased overall SPM risk. Table 1 summarizes significant results of O/E risk of SPM by race and site. HW and NHW were less likely to develop overall solid organ SPM. Within solid organ sites, HW had a significantly decreased O/E risk of developing lung/bronchus and prostate SPM. NHW were the only ethnic subgroup with an increased O/E risk of developing melanoma of skin, while the O/E risk of developing SPM of kidney/renal pelvis was increased only among AA. The risk of ANLL as SPM was significantly increased among AA, API, and NHW, while risk of NHL as SPM was only increased among NHW. Conclusion: Exploring potential causes of outcome disparities is important for evaluating disease characteristics and optimal triaging of healthcare resources for specific patient populations. We have performed the largest population-based analysis for the risk of SPM in MM patients stratified by race/ethnicity. We found that the risk of developing SPM among MM patients is variable depending on the patient's ethnic background. This warrants further exploration of the impact of SPM on outcomes of MM patients across different racial subgroups. Disclosures: No relevant conflicts of interest to declare.

Abstract Abstract 845 Background: Waldenstrom's macroglobulinemia (WM) is a relatively uncommon plasma cell disorder and most of previous literature is limited to small patient series. We have noted ethnic disparities in multiple myeloma, another plasma cell disorder. We undertook a large Surveillance Epidemiology and End Results (SEER) based analysis to describe outcome disparities in different subgroups of WM patients, with a focus on various ethnicities, so that therapeutic resources can be targeted more effectively. Methods: The SEER 17 Registry data (1973–2008) was utilized for patients with confirmed diagnosis of WM. To avoid bias of under representation of different ethnicities, analysis was restricted to patients with a diagnosis date of 1992 or later. Cases that received a diagnosis at death certificate or autopsy, no follow-up records, as well as lacking documentation on age at diagnosis, sex, or race/ethnicity were excluded. Cox proportional hazards models, adjusted for gender, age, race, year of diagnosis, marital status and stratified by SEER registries were used to evaluate associatio n between patient characteristics and survival. All statistical tests were two-sided and utilized the SAS software (v9.2) with a significance level of 0.05. Results: The final analysis included 2,840 WM patients (1,759 males; 62%, 1,081 females; 38%). The studied age-group cohorts included: 18–64 yrs (845; 30%), 65–74 yrs (795; 28%) and >75 yrs (1,200; 42%). Patients were stratified by race/ethnicity: White (2,471; 87%), African-American (AA) (102; 4%), Hispanic (133; 5%), Asian (129; 5%), and Native American (5; 0.1%). Patients were also stratified based on year of diagnosis (before or after 2002) to study the impact of certain novel agents (proteasome inhibitors, IMiDs) on WM treatment. There was a significant difference in the age at diagnosis of WM patients across different ethnicities, with AA the youngest (median 61.5 years) and Whites the oldest (median 73 years) subgroup (p<0.001). (Figure 1) Cause-specific mortality could not be evaluated due to variable documentation of reported causes of death for WM patients in the database. Survival analysis revealed that for all patients, females had better median overall survival (OS) than males (7.3 years vs. 6.2 years, HR 0.834; 95% CI 0.740, 0.939; p=0.003). Among the different age cohorts, patients with age ≥75 years had a significantly worse median OS (4.1 years) than those 65–74 year-old (7.3 years) or 18–64 year-old (10+ years) (p<0.001). Patients diagnosed after 2002 had a significantly better median OS (7.3 years) as compared to patients diagnosed previously (6.1 years) (p=0.002). Hispanics had the worst median OS (5 years) and Whites had the best median OS (6.8 years) across various ethnicities. In a multivariate model using gender, age, marital status, year of diagnosis and race, a significant interaction was noted between race, age and survival, with Hispanics having a significantly worse OS than Whites (HR 1.86; 95% CI 1.269, 2.726; p=0.003) (Figure 2). Conclusions: Studies of outcome disparities are important for evaluating disease characteristics and management needs of specific patient populations as well as optimal triaging of healthcare resources. We have performed the largest population-based analysis for WM including various ethnicities in the novel therapeutic agent era. We observed that AA patients had a significantly younger age at WM diagnosis. Older patients had worse OS across all ethnic subgroups and patients diagnosed after 2002 had a better OS suggesting an impact of novel therapeutic agents (e.g., proteasome inhibitors, IMiDs). Hispanic WM patients had the worst OS among all ethnicities. This survival difference was more significant and pronounced in patients >75 years. This suggests that the impact of race on survival is influenced by patient's age. These results will help in better understanding of various influences on disease biology and clinical behavior. Disclosures: No relevant conflicts of interest to declare.

Abstract Massively parallel sequencing analyses have revealed a common mutation within the MYD88 gene (MYD88L265P) occurring at high frequencies in many non-Hodgkin lymphomas (NHL) including the rare lymphoplasmacytic lymphoma, Waldenström’s macroglobulinemia (WM). Using whole exome sequencing, Sanger sequencing and allele-specific PCR, we validate the initial studies and detect the MYD88L265P mutation in the tumor genome of 97% of WM patients analyzed (n=39). MYD88L265P was detected at lower frequencies in other indolent lymphomas including LPL (0%), MALT (4%), nodal MZL (5%) and splenic MZL (8%); all but one MYD88L265P was heterozygous. Due to the high frequency of MYD88 mutation in WM and other NHL, and its known effects on malignant B cell survival, therapeutic targeting of MYD88 signaling pathways may be useful clinically. However, while the effects of MYD88L265P on the activity of IRAK1/4 and NF-κB are have been studied previously, we are lacking a thorough characterization of the role of intermediary signaling proteins such as TRAF6 and TAK1 on the biology of MYD88L265P-expressing B cells. A better understanding of the proteins involved in MYD88L265P signaling may lead to the development of more targeted and effective therapeutic approaches. In an attempt to identify MYD88L265P –specific therapeutic targets we first wanted to characterize the role of intermediary signaling proteins that facilitate the downstream activation of NF-κB. Upon activation of TLRs or IL-1b receptors, MYD88 forms a homodimer and recruits IRAK1/4 and TRAF6 into a complex resulting in association and phosphorylation of TAK1 followed by activation of NF-κB. We monitored the formation of a complex comprised of MYD88, IRAK1, IRAK4 and TRAF6 and immunoprecipitation of either endogenous IRAK4 or IRAK1 revealed constitutive association of IRAK with TRAF6 and MYD88L265P. To assess if the formation of a MYD88L265P/IRAK/TRAF6 complex results in downstream activation of TAK1, constitutive TAK1 phosphorylation was measured and detected in all three cell lines that express MYD88L265P. An association between TAK1 and TRAF6, another measure of TAK1 activation, was also detectable. When a similar analysis of TAK1 was performed in DLBCL cells expressing wild-type MYD88, no phosphorylation of TAK1 was detected, nor was TAK1 associated with TRAF6. IRAK1, IRAK4, TAK1, TRAF6, and MYD88 were expressed at similar levels in all cell lines studied and therefore did not contribute the differences in MYD88 complex formation observed between cell lines. These studies were further confirmed using HEK 293T cells that were transduced with either a vector control plasmid or HA-tagged MYD88WT or MYD88L265P expression plasmids. Together, these studies suggest that MYD88L265P forms a complex with IRAK and TRAF6 resulting in constitutive activation of TAK1 and NF-κB. To confirm the significance of TAK1-mediated MYD88L265P signaling on lymphoma cell growth, the effect of the selective TAK1 inhibitor, (5Z)-7-Oxozeaenol, on cell proliferation was tested. All MYD88L265P-expressing cell lines were sensitive to TAK1 inhibition in a dose-dependent manner (0-10 μM). In contrast, NHL cells expressing MYD88WT were found to be insensitive to TAK1 inhibition. We next tested the impact of the TAK1 inhibitor on a MYD88L265P positive WM patient sample. Similar to what was seen in the WM cell lines, the TAK1 inhibitor inhibited WM cell growth and survival in a dose dependent manner. Additionally, the TAK1 inhibitor significantly reduced the level of IL-10 secreted by each of the cell lines. Together, these data suggest that MYD88L265P drives cell proliferation and cytokine secretion through a TAK1-dependent mechanism. In conclusion, we are the first to validate by NGS in a large patient cohort the high prevalence and specificity of MYD88L265P in WM. Cells harboring the L265P mutation but not wild-type MYD88 exhibit constitutive signaling leading to the hyperactivation of NF-κB. We have established the role of TAK1 as an integral component of MYD88L265P signaling in both WM and DLBCL cell. Our data suggest that targeting TAK1 clinically may be an effective strategy for the treatment of WM and other lymphomas driven by MYD88L265P signaling. Disclosures: Fonseca: millennium: Consultancy; amgen: Consultancy; Binding site: Consultancy; onyx: Consultancy; medtronic: Consultancy; Genzyme: Consultancy; Otsuka: Consultancy; Celgene: Consultancy; lilly: Consultancy; Onyx: Research Funding; cylene: Research Funding.

Abstract Background Multiple myeloma (MM) is the second most common hematologic malignancy in the U.S. and is characterized by increased immunoglobulin production and infiltration of the bone marrow by malignant plasma cells. Myeloma cell growth is supported by both the elements present in the bone marrow microenvironment as well as deregulation of internal cellular systems associated with proliferation and apoptosis. Defective programmed cell death by BCL2 or MCL1 upregulation is observed in >80% of myeloma cases and is associated with an aggressive clinical course. Remarkably, there is no approved drug with the ability to target BCL2 or MCL1. Various strategies to mitigate the effects of increased BCL2 functionality, via small molecule inhibitors or BCL2-specific antisense oligonucleotides have been previously examined in MM. These studies revealed that 1) apart from BCL2, additional anti-apoptotic members belonging to the BCL2 family (i.e. MCL1, BCL-xL) play integral roles in maintenance of the myeloma cell phenotype, 2) drugs, which target only BCL2 offer limited therapeutic advantage and 3) given that survival factors engaged in MM are multifactorial, perhaps isolated targeting of the BCL2 pathways may not be sufficient. We therefore hypothesized that the clinical development of drugs that target various antiapoptotic BCL2 family members will require a partnership with established anti-MM regimens whose activity can potentially be further enhanced with correction of the apoptotic response system. Aim Since lenalidomide and dexamethasone (LD) is an established therapy for plasma cell cancers, we investigated if the pan-BCL2 inhibitor AT-101 (BH3 mimetic), which has high binding specificity for BCL2, MCL1 and BCL-xL, can be an effective therapeutic partner to enhance anti-MM effects of LD. Methods Human MM (KMS11, U266, OPM2) and WM (BCWM.1) cell lines along with their corresponding bortezomib resistant (BR) clones, (KMS11/BR, U266/BR, OPM2/BR and BCWM.1/BR) which were developed in our laboratory were used in this study. For gene expression profiling, the Illumina HumanHT-12 v3 whole-genome gene expression array and Nanostring nCounter mRNA quantification assays (NanoString, Seattle, WA) were utilized. Statistical analysis was conducted using R-based packages and the MeV software (TIGR). Apoptosis was measured by annexin-v/PI staining, and mitochondrial membrane permeability (MOMP) was assessed using TMRM followed by flow cytometry. Protein profiles were ascertained by western blot. Results Gene expression and immunoblot analysis of six plasma cell cancer models showed upregulation of various BCL2 family members, notably MCL1 and BCL-xL. In a dose-dependent manner, AT-101 was able to downregulate BCL2 and MCL1 and induced apoptotic cell death in MM and WM cells in a dose dependent manner. Tumor cell death was associated with caspase and PARP-1 cleavage accompanied by an increase in MOMP. This cytotoxic effect and BCL2 downregulation were further potentiated when AT-101 was combined with lenalidomide/dexamethasone (LDA). Nanostring nCounter mRNA quantification and IPA analysis revealed differential changes in the CCNA, FRZB, FYN, IRF1, PTPN11 genes in LDA treated cells. IPA canonical pathway analysis demonstrated the p53 signaling and the cyclins and cell cycle regulation pathways to be the most significantly activated by LDA therapy. Summary In summary, we describe for the first time the cellular and molecular events associated with the use of AT-101 in combination with lenalidomide/dexamethasone in preclinical models of plasma cell malignancy. This study lays the rationale for engaging and handicapping the intrinsic apoptotic system through the pan-BCL2 targeting capabilities of AT-101; thus enhancing the anti-MM effects of lenalidomide/dexamethasone. Disclosures: Foran: Celgene: Research Funding.