Masih‐Khan, Esther

Abstract In this study, we investigated tumor intrinsic mechanisms of resistance to cevostamab, a bispecific T-cell engager targeting Fc receptor-like protein 5 (FCRL5) and CD3 that has shown promising clinical activity and durable responses in advanced MM. Longitudinal bone marrow aspirates from nine MM patients treated with cevostamab were analyzed. All patients had previously been treated with both immunomodulatory drugs (IMiDs) and proteasome inhibitors (PI) and eight patients had received daratumumab prior to cevostamab, which was, on average, the 6th line of treatment (mean treatment duration 220±273 days). Five of nine patients responded with ≥PR. Whole genome and transcriptome sequencing was performed on sorted CD138+ MM cells at baseline, and whole exome and transcriptome sequencing was performed on five and three samples, respectively, following cevostamab discontinuation. Baseline FCRL5 expression levels did not correlate with clinical response. However, in one non-responder patient, FCRL5 expression increased four-fold after 28 days of treatment. Given the location of the FCRL5 gene on chromosome 1q—commonly amplified in advanced MM—we evaluated the presence of Gain(1q) in our study cohort. All patients whose best response was ≤PR (n=6) harbored a Gain(1q), whereas it was absent in those who achieved VGPR and sCR (n=3). Crucially, one of the patients that achieved sCR was initially treated with 60 mg of cevostamab for one year and then escalated to a higher dose cohort (90 mg) in the second year. At progression, a clonal FCRL5E115A missense mutation (allelic frequency = 56%) and a subclonal FCRL5G455Efs*19(allelic frequency = 5%) frameshift deletion mutation were detected, both absent at baseline. The missense mutation was located on the extracellular domain of FCRL5 targeted by cevostamab. To validate the functional impact of FCRL5E115Aand FCRL5G455Efs*19 on the sensitivity to cevostamab in vitro, we generated a FCRL5 knockout (KO) model utilizing CRISPR-Cas9 technology in OPM2 MM cells. In vitro cevostamab cytotoxicity assay with PBMCs and pan T cells from healthy donors at various effector to target (E:T) ratios confirmed a complete loss of cevostamab sensitivity in our FCRL5KO models. cDNA encoding patient-derived FCRL5 alterations (FCRL5E115Aand FCRL5G455Efs*19) as well as FCRL5wtwere cloned into mammalian expression vector and reintroduced into FCRL5KO cells. Cevostamab sensitivity was reinstated by FCRL5wt expression in KO cells. In contrast, FCRL5E115A conferred complete resistance to cevostamab (p<0,001) and FCRL5G455Efs*19 depicted a significant decline in cevostamab sensitivity relative to FCRL5wt expressing models. Additional experiment utilizing direct stochastic optical reconstruction microscopy (dSTORM) are ongoing to monitor the membrane localization of FCRL5 mutants. By integrating genomic, transcriptomic and functional data with clinical outcomes, this work is the first to report on acquired FCRL5 mutations causing resistance to cevostamab. We hypothesize that the prolonged treatment duration may have contributed to the acquisition of the target mutations and note a subsequent durable sCR response to BCMA-targeted immunotherapy in the same patient, suggesting immune-related factors such as T cell exhaustion, were not drivers of cevostamab resistance. Due to the limited sample size, these findings require validation in larger cohorts. Nonetheless, our findings begin to elucidate tumor intrinsic mechanisms associated with cevostamab resistance.

Abstract The identification of the t(4;14) translocation in Multiple Myeloma (MM) provided the first indication that fibroblast growth factor 3 (FGFR3) could act as an oncogene. Several studies have assessed the potential of FGFR3 as a drug target and have shown that inhibition of FGFRs using tyrosine kinase inhibitors induces cell death of FGFR3 expressing MM cells. To clarify the signaling pathways implicated in FGFR3 dependent myeloma, we assessed gene expression changes associated with treatment of MM cell lines with three known small molecule FGFR inhibitors, PD173074, SU5402 and a third novel compound using Human U133_Plus2 arrays. In addition to describing the unique pharmacogenomic signals of each drug in myeloma, 845 differentially expressed genes, common to all three FGFR3 inhibitors, were identified. Cell cycle, DNA replication and ATP binding proteins were the most common (47%) functional classes of genes effected. Further validation and refinement of this gene list was conducted using FGFR3 siRNA inhibition and FGF ligand induction. 120 genes were altered between FGFR3 RNAi and scrambled control and 892 were induced by FGF ligand. Ten genes were commonly identified as significantly regulated by all 4 FGFR3 inhibitors and induced in the opposing direction by ligand. Of these macrophage inflammatory protein (MIP)-1alpha, and dual specific phosphatase 6 (DUSP6) were positively regulative while ANXA9, CR2, AL531683, ZNF589, AW274468, FRMD3, LTB and WDR42A were negatively regulated by FGFR3 signaling. Validating our findings, a feedback loop between FGFR/ERK/MAP kinase activation and DUSP6 has previously been described in the literature. MIP-1alpha however was the most significantly altered (12 fold) on array, and MIP-1alpha regulation in response to FGFR3 pathway stimulation was confirmed by flow cytometry and Western blot. Mining of publicly available array datasets on 174 MM patients significantly associated MIP1-alpha with FGFR3 expression (p=0.01). Of note down-regulation of MIP-1alpha was not observed following FGFR3 inhibition in MM cells with RAS mutations. Based on these, and previous findings, we hypothesized that MIP-1alpha was regulated by the FGFR3/ERK/MAP kinase pathway. Indeed, inhibition of ERK in FGFR inhibitor resistant cells with RAS mutations also led to down regulation of MIP-1alpha. Because of the recognized role of MIP1-alpha (CCL3) in survival and proliferation of MM cells and in MM bone disease, our observations raise the possibility that pharmacological inhibition of MIP-1 alpha may hold therapeutic promise in t(4;14) MM and may serve as a biomarker for successful FGFR3 or RAS signaling inhibition.

Abstract Oral cyclophosphamide and prednisone is a convenient regimen in relapsed and refractory multiple myeloma (MM), with a partial response (PR) rate of 40% and median progression-free survival of 19 months in our retrospective analysis of patients in first or second relapse after autologous stem cell transplantation (ASCT) (Trieu Y, et al, Mayo Clin Proc2005; 80: 1582). We sought to enhance the efficacy of this regimen by adding oral lenalidomide (Revlimid®), a potent anti-myeloma agent, in a phase I-II trial. The CPR regimen consisted of cyclophosphamide on days 1, 8 and 15, lenalidomide on days 1–21, and prednisone 100 mg every other day in a 28-day cycle. ASA 81 mg/day was given to all patients (pts) as prophylaxis for DVT. Three dose levels were evaluated using a 3 by 3 dose escalation design. Between 11/2007–07/2008, 15 pts with relapsed/refractory MM were entered onto study. Median age was 60 (45–78) years and 60% were male. Immunoglobulin subtype was IgGκ:λ in 10:1; IgA κ:λ in 2:1 and κ light chain in 1. Median number of prior regimens was 2 (1–3) and 14 had undergone previous ASCT, including double transplants in 2 pts. Prior therapy also included thalidomide in 3 (20%) and bortezomib in 6 (40%). FISH cytogenetics were available in 9, but none had 13q deletion, t(4;14) or p53 deletion. At the time of protocol entry, median β2-microglobulin level was 222 (92–325) nm/L, albumin 38 (35–46) g/L, creatinine 78 (50–100) μmol/L, platelet count 230 (93–318) x 109/L and ANC 2.5 (1.9–9.0) x 109/L. Protocol treatment is summarized in Table 1. Dose level N Cyclophosphamide dose (mg/m2) Lenalidomide dose (mg) Prednisone dose (mg) Median # cycles given 1 3 150 15 100 9 2 3 150 25 100 6 3 6 300 25 100 4 3 (expanded) 3 300 25 100 1 Dose limiting toxicity was not observed during cycle 1 at any of the dose levels and the maximum tolerated dose of this regimen has not yet been reached at the highest dose level planned; all pts remain on active therapy. Grade 3/4 thrombocytopenia was seen in 1 pt (cohort 2) and neutropenia in 4 pts (1 in cohort 1, 1 in cohort 2 and 2 in cohort 3) and were managed with dose reduction and/or growth factor support. No episodes of febrile neutropenia occurred in any pt. Only 1 pt experienced varicella zoster; routine antiviral prophylaxis was not used. Other grade 3/4 non-hematologic toxicities were uncommon and included abdominal pain/bacteremia in 1 pt in cohort 1, hypokalemia in 1 pt in cohort 2, and DVT in 1 pt in cohort 3. Mild grade 1/2 constipation (47%), muscle cramps (33%) and fatigue (33%) were also noted. To date, best response includes the following: dose level 1 (1 near complete remission [nCR], 2 PR); dose level 2 (3 PR); dose level 3 (4 PR, 2 minimal response [MR]); expanded cohort 3 (1 MR, 2 too early). We conclude: 1) the combination of full doses of the agents in CPR can be given in a 28-day cycle with minimal toxicity; 2) the overall response rate (nCR + PR + MR) in 13 evaluable pts to date is 87%; 3) no pts have progressed in this preliminary analysis; 4) longer follow-up is required to assess the long-term efficacy of this regimen.

Abstract Abstract 3055 Lenalidomide (Revlimid®) and dexamethasone is an effective regimen for relapsed/refractory (rel/ref) multiple myeloma (MM) patients (pts) with an overall response rate of 60% and median time to progression of 13.4 months (Dimopoulos ME, et al. Leukemia 2009; 23: 2147-52). We combined lenalidomide with the alkylating agent combination of cyclophosphamide and prednisone—an older regimen with minimal cumulative myelosuppression and good activity as second or third line therapy (Trieu Y, et al, Mayo Clin Proc 2005; 80: 1582). The CPR regimen consisted of cyclophosphamide (CY) on days 1, 8, and 15, lenalidomide on days 1–21 and prednisone 100 mg q 2 days in a 28-day cycle. ASA 81 mg/day was given as DVT prophylaxis. Three dose levels were evaluated using a 3 × 3 dose escalation design. Thirty-two pts were entered between 11/2007-06/2009; median age was 64 (42-80) yrs, 60% were male, and immunoglobulin isotype was IgG in 19 (62%), IgA in 8 (25%) and light chain in 4 (13%) pts. Median β2-microglobulin level was 257 (92-767) nm/L, albumin 39 (34-48) g/L, creatinine 83 (50-126) μmol/L, platelet count 355 (75-479) × 109/L and ANC 2.5 (1.1-6.1) × 109/L. The median number of prior regimens was 2 (1-5). Prior therapy included: ASCT (single in 91%; double in 19%), thalidomide (28%) and bortezomib (50%). FISH cytogenetics were available in 13 pts; 1 had del 13q but none had t(4;14) or del p53. Table 1 summarizes protocol treatment delivered. Table 1. Dose level N Cyclophosphamide dose (mg/m2) Lenalidomide dose (mg) Prednisone dose (mg) Median # cycles given 1 3 150 15 100 12 (12–34+) 2 3 150 25 100 10 (9–23) 3 26 300 25 100 17 (5–28+) 1–3 (All) 32 150–300 15–25 100 19 (5–34+) Dose limiting toxicity was not observed during cycle 1 at any dose level. Grade 3–4 toxicities during the trial included: thrombocytopenia in 7 (22%) and neutropenia in 9 (29%), managed with dose reduction and/or growth factors; five episodes of febrile neutropenia occurred, all at dose level 3. In cohort 3, other grade 3–4 non-hematologic toxicities included 1 episode each of abdominal pain/bacteremia, hypokalemia, fatigue, sick sinus syndrome, cardiac amyloidosis, perforated diverticulum and 2 episodes of DVT. Two heavily pretreated pts developed 2° MDS, including 1 previously treated for lymphoma, 43 and 190 mos after the diagnosis of MM. The best response using modified EBMT criteria was documented at a median of 7 (1-26) cycles and included the following: dose level 1 (1 CR, 2 PR); dose level 2 (1 VGPR, 2 PR); dose level 3 (4 CR, 14 VGPR, 11 PR, 1 MR and 1 stable disease). At a median F/U of 16 (5-34) months, 13 pts remain on study and 18 have progressed at a median of 10 (2-23) mos; 1 was lost to F/U and 9 have died of progressive MM. The 1-year actuarial OS and PFS rates are 93% (95% CI 76–98%) and 78% (95% CI 60–89%), respectively. We conclude: 1) the combination of full doses of the agents in CPR can be given in a 28 day cycle with an acceptable safety profile; 2) the objective response rate (CR + PR + MR) in all 32 pts to date is 94%; 3) the 1-year OS of 93% and PFS of 78% compare favorably with other 3-drug combinations in rel/ref MM pts; 4) further evaluation of this regimen in newly diagnosed pts would be of interest. Disclosures: Reece: Celgene: Honoraria, Research Funding. Off Label Use: Combination of lenalidomide and cyclophosphamide and prednisone in relapsed and refractory myeloma patients. Chen:Celgene Corporation: Consultancy, Honoraria, Research Funding. Kukreti:Celgene: Honoraria.

Abstract Abstract 1874 Poster Board I-899 Lenalidomide (Revlimid®) and dexamethasone is an effective regimen in relapsed/refractory multiple myeloma (MM) patients (pts), with an overall response rate of 60.6% and median time to progression (TTP) of 13.4 months (Dimopoulos MA, et al, Leukemia 2009 Jul 23 [Epub ahead of print]). Oral cyclophosphamide and prednisone is an older regimen with excellent patient tolerance, and we sought to enhance the efficacy of lenalidomide by adding oral cyclophosphamide and prednisone in this phase I-II trial. The CPR regimen consisted of cyclophosphamide on days 1, 8 and 15; lenalidomide on days 1–21; and prednisone 100 mg every other day in a 28 day cycle. ASA 81 mg/day was given to all pts as DVT prophylaxis. Three dose levels were evaluated using a 3 by 3 dose escalation design. Between 11/2007–07/2009, 31 pts with relapsed/refractory MM who had not previously received lenalidomide were entered onto study. Median age was 61 (40–78) years and 61% were male. Immunoglobulin subtype was IgG in 19 pts (61%), IgA in 8 pts (26%) and light chain only in 4 pts (13%). Median number of prior regimens was 2 (1–5) and 28 pts had undergone previous ASCT, including double transplants in 6 pts. Prior therapy included thalidomide in 9 (29%) and bortezomib in 15 (48%). FISH cytogenetics were available in 13 pts; one had 13q deletion but none had t(4;14) or p53 deletion. At the time of protocol entry, median β 2-microglobulin level was 246 (92–767) nm/L, albumin 39 (34–48) g/L, creatinine 83 (50–126) μmol/L, platelet count 230 (75–337) × 109/L and ANC 2.5 (1.1–6.1) x 109/L. Protocol treatment is summarized in Table 1. Dose limiting toxicity was not observed during cycle 1 at any dose level. Grade 3–4 toxicities included thrombocytopenia in 5 pts (16%) and neutropenia in 9 pts (29%). These were managed with dose reduction and/or growth factor support. Four episodes of febrile neutropenia occurred. Other grade 3–4 non-hematologic toxicities included abdominal pain/bacteremia in 1 pt in cohort 1; hypokalemia in 1 pt in cohort 2; and DVT in 2 pts, dizziness in 2 pts and fatigue in 1 pt in cohort 3. Using the International uniform response criteria (Durie BG, et al, Leukemia 2006; 20:1467–1473), the best response was documented at a median of 6 (1–5) cycles and included the following: dose level 1 (1 CR, 2 PR); dose level 2 (1 VGPR, 2 PR); dose level 3 (5 CR, 9 VGPR, 9 PR, 1 MR and 1 stable disease). At a median follow-up (F/U) of 12 (8–21) months, 20 pts remain on study, 2 have withdrawn and 9 pts have progressed at a median of 9 (4–13) months; only 1 one has died (due to MM). We conclude: 1) the combination of full doses of the agents in CPR can be given in a 28 day cycle with minimal toxicity; 2) the overall response rate (CR + VGPR + PR) in 31 pts to date is 93%; 3) at a median F/U of 1 year, only 9 pts (29%) have progressed; 4) longer follow-up is required to assess the TTP and survival of the CPR regimen. Disclosures: Reece: Celgene: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Off Label Use: Lenalidomide in combination with drugs other than dexamethasone. Anglin:Celgene: Honoraria. Chen:Celgene: Honoraria, Research Funding. Kukreti:Celgene: Honoraria. Mikhael:Celgene: Honoraria. Trudel:Celgene: Honoraria.

Abstract Abstract 2876 Poster Board II-852 Multiple myeloma (MM) patients (pts) are immunosuppressed given the underlying disease, previous treatments and myelosuppression seen on lenalidomide (Revlimid, Rev). We evaluated the infectious complications seen on Celgene's Expanded Access Rev program at Princess Margaret Hospital. We have treated 75 pts who had progressed after at least one prior therapy as part of a national study in Canada. At entry, pts were required to have a neutrophil count of ≥1.0 ×109/L. The median age was 61 yrs (range 35-79); 52% were males. Prior therapy included stem cell transplant in 65, thalidomide in 54 and bortezomib in 24. Number of lines of prior therapy were as follows: 24 (one), 29 (two), 16 (three), 8 (four) and one (five). Neupogen was used liberally (63%) after a patient had a dose delay on trial due to neutropenia. Patients were treated with full dose lenalidomide at entry onto clinical trial and were maintained on full dosing unless platelet counts were <30×109/L or ANC was <1.0×109/L. No other dose adjustments were made for renal dysfunction. Results: There were 32 pts (43%) who had a clinically evident infection; the majority (91%) was on prophylactic antibiotics (septra/ciprofloxacin) at the time. There were two deaths due to infection and 23 pts (72%) required hospitalization (range 2-27 days). The majority of infections occurred within the first 4 cycles of treatment (26 pts) and seemed to occur more in pts with several lines of prior therapy – 7/24 (29%) with 1 prior therapy, 14/29 (48%) with 2, 9/16 (56%) with 3 and 2/8 (25%) with 4 prior therapies. Sixteen were neutropenic of which 7 had febrile neutropenia (9%). The types of infections were: respiratory in 14 (1 with pneumocystis pneumonia), cellulitis in 4, herpes simplex and herpes zoster in 2 pts each. These included streptococcus pneumoniae (1), staphylococcus aureus (3), respiratory syncitial virus (1) and mycobacterium chelonae (1). Rev was held during the infection in 23 pts (72%). Conclusions: 1) Infections are frequent in this patient population (43%) and often lead to hospitalization (72%); respiratory infections accounted for a large majority (43%). 2) Early aggressive growth factor support and broader antibiotic prophylaxis may be of benefit especially in heavily pretreated patients. 3) Dose reduction of Rev in the context of serious infections should be further evaluated. Disclosures: Kukreti: Celgene: Honoraria. Trudel:Celgene: Honoraria, Speakers Bureau; Ortho Biotech: Honoraria. Chen:Celgene: Honoraria.

SummaryThis single institution, open label Phase I‐II dose escalation trial evaluated the safety and efficacy of the combination of lenalidomide (Revlimid®), cyclophosphamide and prednisone (CPR) in patients with relapsed/refractory multiple myeloma. The maximal administered dose of CPR consisted of cyclophosphamide 300 mg/m2 on day 1, 8, and 15, lenalidomide 25 mg on d 1–21 and prednisone 100 mg every other day in a 28‐d cycle. Between November 2007 and June 2009, 32 patients were entered in cohorts of three at three dose levels. The median age was 64 years, 59% were male, with a median two prior regimens. Responding patients could stay on treatment until progression. The full‐dose CPR regimen produced no dose‐limiting toxicity and was delivered for a median of 16 months (3·5–65 months) with acceptable safety and tolerance. The overall response rate (≥ partial response) was 94% at a median follow up of 28 months. The median progression‐free survival was 16·1 months [95% confidence interval (CI); 10·9–22·5 months], while the median overall survival was 27·6 months (95% CI; 16·8–36·6 months). Only the beta‐2 microglobulin level at protocol entry correlated with a better survival (P = 0·047). These observations compare favourably with other 2‐ and 3‐ drug combinations for relapsed/refractory myeloma, and suggest that CPR should be evaluated further in the setting of relapsed/refractory disease, or in newly diagnosed patients.

Abstract Overexpression of fibroblast growth factor receptor 3 (FGFR3) is a hallmark of t(4;14) multiple myeloma (MM). To dissect the mechanism of FGFR3 oncogenesis in MM, we used 3 FGFR selective kinase inhibitors—CHIR258, PD173074, and SU5402—and FGFR3-specific siRNA to modulate FGFR3 activity. Conversely, the ligand FGF was used to stimulate FGFR3 function in human MM cells. The transcriptional response to FGFR3 modification was recorded, and gene expression changes common to all 5 modifiers were documented. Ten genes were commonly regulated. Macrophage inflammatory protein-1 alpha (MIP-1α) was the single most differentially altered gene. MIP-1 α promoter function, gene expression, and protein secretion were each down-regulated following inhibition of FGFR3 signaling. Down-regulation of MIP-1 α was not, however, observed following FGFR3 inhibition in MM cells with RAS mutations implicating RAS-MAPK in MIP-1 α regulation. As confirmation, inhibition of ERK1 also down-regulated MIP-1 α in FGFR3 inhibitor-resistant cells harboring RAS mutations. MIP-1 α is implicated in the survival and proliferation of MM cells and the pathogenesis of MM bone disease. Our observation is the first to directly link an initiating IgH translocation not only to MM-cell growth and survival but also to the disease-associated bone disease.