A Favorable BCL-2 Family Expression Profile May Explain the Increased Susceptibility of the t(11;14) Multiple Myeloma Subgroup to Single Agent Venetoclax

Background: In preclinical studies, multiple myeloma (MM) cells are sensitive to selective inhibition of the pro-survival protein BCL-2 by venetoclax (VEN). Resistance to VEN in these models was mediated through BCL-XL and MCL-1, and MCL-1 mediated resistance was neutralized by co-treatment with the proteasome inhibitor bortezomib (BTZ). MM cells harboring the t(11;14) translocation have a higher ratio of BCL-2 relative to MCL-1 mRNA and increased sensitivity to VEN alone, compared to cells with other cytogenetic abnormalities, suggesting that MM subgroups with a favorable BCL-2 family profile might be particularly sensitive to VEN. Clinically, VEN has shown activity in CLL, a disease typically expressing high BCL-2 and low BCL-XL and MCL-1 expression. In MM, VEN is being evaluated as a single agent (NCT01794520) and in combination with BTZ and dexamethasone (Dex) (NCT01794507, NCT02755597) in relapsed/refractory (R/R) patients. As a single agent, improved objective response rates were observed in patients with R/R t(11;14) MM (40% in t(11;14) vs 6% in non-t(11;14)-). In the BTZ/Dex combination study, patients with high BCL-2 expression had an increased objective response rate. Thus, BCL-2 family profiling may explain increased susceptibility of certain MM subgroups to antitumor activity of VEN both as a single agent and in combination. We analyzed MM subgroups for expression of BCL-2 family members to better understand and identify the patient population that can benefit with VEN. Methods: We used publically available data (GSE4581; GSE9782) to analyze BCL-2 family mRNA expression within molecular/cytogenetic defined subgroups among newly diagnosed (NDMM n=414), and R/R (n=264) MM patients, and in comparison to other hematological malignancies (genealogic database). Results: BCL-2, BCL-XL and MCL-1 expression was assessed in MM and compared with 12 major hematologic malignancies. Based on median expression, BCL-2 in MM ranked 6th of 12 tested, with highest BCL-2 expression observed in small lymphocytic leukemia and mantle cell lymphoma. In MM, BCL-2 expression varied significantly across molecular and cytogenetic subgroups. Highest expression was among patients with t(11;14) molecular subtypes (CD1, CD2), in addition to subtypes that are not enriched with t(11;14) like the hyperdiploid and low bone disease subtypes, and lowest in the high-risk subtypes (proliferation, MMSET, MAF/MAFB) (p=0.0001), both in NDMM and R/R MM. BCL-XL and MCL-1 were highly expressed in MM relative to other hematologic malignancies. Expression of BCL-XL and MCL-1 were lowest in the t(11;14) MM population (both p Conclusions: Our analysis suggests that MM subgroups are associated with distinct BCL-2 family expression profiles, and the t(11;14) subgroup amongst MM subgroups may be particularly suited for single agent VEN activity due to a high BCL-2/MCL-1 and BCL-2/BCL-XL ratio. In the non-t(11;14) MM subgroups, VEN treatment in earlier lines of therapy, as well as combination strategies with agents that will down-modulate BCL-XL and/or MCL-1, such as BTZ, may enable maximum VEN activity, and will be further assessed in clinical studies. Disclosures Wu:Genentech: Employment. Ross:AbbVie: Employment, Equity Ownership. Peale:Genentech: Employment, Equity Ownership. Shaughnessy:Signal Genetics: Consultancy, Equity Ownership. Van Laar:Signal Genetics, Inc.: Employment. Morgan:Takeda: Consultancy, Honoraria; Janssen: Research Funding; Bristol Meyers: Consultancy, Honoraria; Univ of AR for Medical Sciences: Employment; Celgene: Consultancy, Honoraria, Research Funding. Venstrom:Genentech: Employment. Punnoose:Genetech, Inc.: Employment.