Targeting BCL‐2 with venetoclax and dexamethasone in patients with relapsed/refractory t(11;14) multiple myeloma

Abstract Venetoclax (Ven) is a selective small‐molecule inhibitor of BCL‐2 that exhibits antitumoral activity against MM cells with t(11;14) translocation. We evaluated the safety and efficacy of Ven and dexamethasone (VenDex) combination in patients with t(11;14) positive relapsed/refractory (R/R) multiple myeloma (MM). This open‐label, multicenter study had two distinct phases (phase one [P1], phase two [P2]). Patients in both phases received VenDex (oral Ven 800 mg/day + oral Dex 40 mg [20 mg for patients ≥75 years] on days 1, 8, and 15, per 21–day cycle). The primary objective of the P1 VenDex cohort was to assess safety and pharmacokinetics. Phase two further evaluated efficacy with objective response rate (ORR) and very good partial response or better. Correlative studies explored baseline BCL2 (BCL‐2) and BCL2L1 (BCL‐XL) gene expression, cytogenetics, and recurrent somatic mutations in MM. Twenty and 31 patients in P1 and P2 with t(11;14) positive translocation received VenDex. P1/P2 patients had received a median of 3/5 lines of prior therapy, and 20%/87% were refractory to daratumumab. Predominant grade 3/4 hematological adverse events (AEs) with ≥10% occurrence included lymphopenia (20%/19%), neutropenia (15%/7%), thrombocytopenia (10%/10%), and anemia (5%/16%). At a median follow‐up of 12.3/9.2 months, ORR was 60%/48%. The duration of response estimate at 12 months was 50%/61%, and the median time to progression was 12.4/10.8 months. In biomarker evaluable patients, response to VenDex was independent of concurrent del(17p) or gain(1q) and mutations in key oncogenic signaling pathways, including MAPK and NF‐kB. VenDex demonstrated efficacy and manageable safety in heavily‐pre‐treated patients with t(11;14) R/R MM.

event-free survival periods; however, patients eventually relapse and become increasingly refractory to currently available therapies resulting in successively shorter remissions. [2][3][4][5][6] The BCL-2 family of proteins is essential in the regulation of apoptosis and cell survival. BCL-2, MCL-1, and BCL-X L are anti-apoptotic proteins of the BCL-2 family that promote MM cell survival. MM is heterogeneous with respect to BCL-2 family dependency, with some cases being more dependent on MCL-1 over BCL-2 and vice versa. 7 Thus, t (11;14) is the most common chromosome translocation in MM with an occurrence rate of 15% -20%. 8,9 Studies in human myeloma cell lines have demonstrated that the presence of t (11;14) is predictive of BCL-2 dependency. 10,11 Venetoclax (Ven) is a potent, selective, orally bioavailable inhibitor of BCL-2. Selective targeting of BCL-2 with Ven has shown promising antitumor activity in several hematologic malignancies, including chronic lymphocytic leukemia, acute myeloid leukemia, and non-Hodgkin lymphomas. in vitro data showed a high sensitivity to Ven in human myeloma cell lines and primary MM samples that were positive for the t (11;14) translocation. 12 Additionally, the sensitivity to BCL-2 inhibition in the t (11;14) subset was associated with higher expression of BCL-2 than MCL-1 or BCL-X L. 7,11 We have previously shown that Ven demonstrated promising single-agent activity in patients with t (11;14) positive relapsed/refractory (R/R) MM, with 40% objective response rate (ORR) and 27% achieving at least a very good partial response or better (≥VGPR). 13 Response to Ven monotherapy also correlated with a higher BCL2: BCL2L1 gene expression ratio, indicating BCL2L1 (BCL-X L ) may be a key resistance factor to broader Ven activity within the t(11;14) subgroup. 13 Preclinical studies in MM cell lines and primary patient samples have demonstrated that dexamethasone (Dex) used in combination with Ven can significantly increase cell death compared to Ven alone. 14 Treatment of MM cells with Dex increases expression of BCL-2 as well as pro-apoptotic proteins BIM and PUMA while decreasing the expression of BCL-X L . [14][15][16][17][18][19] Thus, Dex is hypothesized to induce "BCL-2 priming", a state where BCL-2 maintains cell survival by sequestering high levels of BIM, providing a rationale for use as a combination agent with Ven in MM. 14 Here, we report the efficacy and safety of the VenDex combination from a phase 1/2 study as a therapeutic approach to improve clinical outcomes in patients with t(11;14) R/R MM. Outcomes by baseline BCL2 and BCL2L1 gene expression, cytogenetic abnormalities concurrent with t (11;14), and somatic mutations recurrent in MM were also explored.

| Study design
This open-label phase 1/2 study (NCT01794520) had two distinct phases; phase one and phase two ( Figure S1). Phase one included dose-escalation, safety expansion, and a VenDex combination. The primary objectives of phase one were to assess the safety profile, characterize pharmacokinetics (PK), determine the dosing schedule, the maximum tolerated dose, and the recommended phase two dose of venetoclax monotherapy when administered in patients with R/R MM. In addition, the safety and PK profiles of t(11;14) positive patients treated with VenDex was also evaluated. The secondary objectives were to evaluate the preliminary efficacy of Ven monotherapy or VenDex on ORR, time to response (TTR), time to disease progression (TTP), and duration of response (DoR). Patients discontinued the study treatment if they had disease progression, toxicity or intolerability, and were followed for safety through the treatmentemergent period (ie, 30 days after the discontinuation of study drug).
Here, we present data from patients with t (11;14) positive R/R MM from the safety-expansion cohort who received VenDex.
Phase two was an expansion cohort of the VenDex combination that further evaluated the efficacy of the combination in R/R patients with t(11;14) positive MM. The primary objectives evaluated were ORR and a very good partial response or better (≥VGPR). Secondary objectives included safety, progression-free survival (PFS), TTR, TTP, DoR, and overall survival (OS). Patients discontinued treatment upon disease progression and were then followed for OS. Patients who discontinued study treatment for reasons other than disease progression were monitored for disease progression and followed for OS.
The data cut-off for this publication was September 2, 2019. The trial was conducted under the International Conference on Harmonization Good Clinical Practice guidelines and according to the Declaration of Helsinki. A local institutional review board or ethics committee approved the study at each site. All patients provided written informed consent before participation.

| Patient enrollment and treatment
Detailed eligibility criteria were previously published. 13 In brief, eligible patients were adults with R/R MM ≥18 years of age. In addition, patients included in the phase one VenDex combination cohort were t (11;14) positive as determined by the fluorescence in-situ hybridization (FISH) assay per central laboratory and had received at least one prior treatment with a PI and an IMiD, and had an Eastern Cooperative Oncology Group (ECOG) score ≤ 1.
Patients enrolled in the phase two VenDex cohort had t (11;14) positive MM as determined by the FISH assay per central laboratory testing or were enrolled at the discretion of the investigator if the  13 The optimal dose of 800 mg of Ven was selected based on an exploratory exposure-response analyses based on PK, best IMWG responses in t(11;14) positive patients, and safety (≥ grade three anemia, thrombocytopenia, and neutropenia). This analysis also found that increasing the Ven dose to 1200 mg may increase the response rates marginally; however, the reduced dose intensities at 1200 mg resulted in more inter-patient Ven exposure variability and indicated reduced compliance at the highest doses.
This suggested that a higher dose of Ven was sub-optimal for longterm therapy.

| Safety
Assessments were conducted throughout the study. Adverse events (AEs) were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (version 4.0). 20

| Efficacy
In phase one, the efficacy of VenDex was assessed as the ORR, TTP, and DoR based on the 2011 International Uniform Response Criteria for MM. 21 Efficacy in phase two further evaluated ORR and ≥ VGPR using the 2016 IMWG response criteria. 22 The OS was also assessed.

| Exploratory biomarkers
Bone marrow aspirate specimens were collected at baseline for interphase FISH analysis on cluster of differentiation (CD) 138-enriched bone marrow mononuclear cells (BMMCs) using probes for t (11;14), del(17p), gain(1q), and chromosomes (Ch) 5, 9,  Due to the small sample size of biomarker populations, the results of the two cohorts were combined.

| Statistical analysis
All t(11;14) positive patients who received at least one dose of Ven were included in the safety and efficacy analyses. Descriptive statistics, including medians, standard deviations, and ranges, were calculated. Kaplan-Meier methodology was used for time-to-event analyses. In one patient, last prior therapy outcome was not reported at the time of data cut-off; however, study enrollment and dosing occurred ≤ 60 days from last therapy stop date.

| Patient demographics and clinical characteristics
At data cut-off, 20 and 31 patients with t(11;14) positive disease were enrolled in phase one and phase two VenDex cohorts, respectively.
The median age of patients in phase one VenDex was 63 years (range: 46-77), and in phase two VenDex was 65 years (range: 48-80). The median number of prior lines of therapy received was three (range: 1-8) and five (range: 2-12) in phase one VenDex and phase two VenDex, respectively. In phase one/phase two VenDex, 25%/100% were exposed to prior daratumumab therapy of which 20%/87% were refractory to the daratumumab therapy. Key demographic and clinical characteristics are summarized in Table 1.

| Patient disposition
In phase one VenDex, 19 (95%) patients discontinued treatment of which 18 had progressive disease, and one underwent a transplant. reported, of which eight were due to progressive disease, one unknown and two due to treatment-emergent adverse events (one due to sepsis in the first month of study without confirmed progression, one due to bacterial abscess).

| Safety
Most patients (96%) treated with VenDex experienced at least one treatment-emergent adverse event (TEAE) ( (Continues) C. difficile was considered to be of grade three or four severity ( Figure S2).

| Exploratory biomarkers
The treatment with VenDex was generally safe and well-tolerated. All hematological toxicities were manageable. Commonly reported non-hematological AEs were diarrhea and nausea that were managed by the standard of care. Only two deaths were reported due to treatment-emergent adverse events in this unique population of t (11;14) positive patients who were treated with the VenDex combination. The phase three BELLINI study reported higher mortality rates in patients regardless of genetic mutation status, and the patients were treated with a combination of VenDex and the PI bortezomib. However, the mortality rates were lower among patients harboring t (11;14) translocations in BELLINI. 24 This is suggestive that t (11;14) positive patients may derive the most benefit with VenDex treatment. 25  Cross-study comparisons are challenging due to differences in patient characteristics and sample size of the studies, however, we believe that the VenDex combination shows promising efficacy in this cohort of patients with t(11;14) positive R/R MM. This study also supports the utility of a biomarker-based approach to therapy in R/R MM.
In contrast to prior observations with Ven monotherapy treatment, 13 no significant association between response and baseline BCL2L1 or BCL2:BCL2L1 expression was observed in VenDex treated patients, however higher BCL2 levels were found in patients who achieved a response which is consistent with the mechanism of action in t(11;14) positive MM. These findings are consistent with the biological rationale of dexamethasone-induced "BCL-2 priming" and the combination activity with Ven as demonstrated in preclinical studies. [14][15][16]18,19 The MM patients with the high-risk abnormality del(17p) and gain (1q) have reduced OS in MM. 27,28 In addition, bi-allelic inactivation of the tumor suppressor gene TP53, has been linked to dismal outcomes in MM. 29 We observed response to VenDex treatment in five of the Venetoclax is being developed in collaboration between AbbVie and Genentech. AbbVie and Genentech funded this study (NCT01794520) and participated in the study design, research, analysis, data collection, interpretation of data, reviewing, and approval of the publication. All authors had access to relevant data and participated in the drafting, review, and approval of this manuscript. No honoraria or payments were made for authorship.
Provision, collection and assembly of data: All authors contributed to data collection.
Data analysis and interpretation: All authors had access to the data and participated in data collection and interpretation.
Manuscript writing, editing, and approval: All authors.

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