De novo resistance and rapid recurrence often characterize responses of B-cell malignancies to ibrutinib (IBR), indicating a need to develop drug combinations that block compensatory survival signaling and give deeper, more durable responses. To identify such combinations, we previously performed a combinatorial drug screen and identified the Bcl-2 inhibitor venetoclax (VEN) as a promising partner for combination with IBR in Mantle Cell Lymphoma (MCL). We have opened a multi-institutional clinical trial to test this combination. However, analysis of primary samples from patients with MCL as well as chronic lymphocytic leukemia (CLL) revealed unexpected heterogeneous de novo resistance even to the IBR+VEN combination. In the current study, we demonstrate that resistance to the combination can be generated by microenvironmental agonists: IL-10, CD40L and, most potently, CpG-oligodeoxynucleotides (CpG-ODN), which is a surrogate for unmethylated DNA and a specific agonist for TLR9 signaling. Incubation with these agonists caused robust activation of NF-κB signaling, especially alternative NF-κB, which led to enhanced expression of the anti-apoptotic proteins Mcl-1, Bcl-xL, and survivin, thus decreasing dependence on Bcl-2. Inhibitors of NF-κB signaling blocked overexpression of these anti-apoptotic proteins and overcame resistance. Inhibitors of Mcl-1, Bcl-xL, or survivin also overcame this resistance, and showed synergistic benefit with the IBR+VEN combination. We conclude that microenvironmental factors, particularly the TLR9 agonist, can generate de novo resistance to the IBR+VEN combination in CLL and MCL cells. This signaling pathway presents targets for overcoming drug resistance induced by extrinsic microenvironmental factors in diverse B-cell malignancies.

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Mantle Cell Lymphoma, characterized by the t(11;14)(q13; q32) chromosomal translocation and cyclin D1 expression, remains one of the most challenging lymphoma subtypes to treat. Therapy can be divided into treatment modalities for younger, stem cell transplant (SCT)-eligible patients vs older, SCT-ineligible patients. For clinically fit patients younger than 60-65 years of age we recommend cytarabine-containing induction and conditioning regimens such as Rituximab (R)-CHOP alternating with R-DHAP followed by autologous SCT consolidation. Elderly patients benefit from R-bendamustine or R-CHOP with maintenance rituximab following induction therapy, especially after R-CHOP. While standard chemoimmunotherapy provides high overall response rates, the responses are not durable and sequential therapies are thus necessary. MCL is proving to be sensitive to novel therapies that may in the near future become useful adjuncts to standard regimens. For example, bortezomib, lenalidomide, and temsirolimus each have single-agent efficacy in relapsed and refractory disease. Several targeted agents are emerging that likewise may transform management of MCL. The B-cell receptor pathway appears to be critical in the pathogenesis of MCL, and novel agents such as ibrutinib and idelalisib that target this signaling pathway are highly active in relapsed and refractory MCL. Similarly, cell cycle inhibitors targeting cyclin dependent kinases as well as HDAC inhibitors have shown promise in early studies.

Bruton tyrosine kinase (BTK) is critical to both normal B-cell development and the pathogenesis of B-cell malignancies. Ibrutinib is a recently FDA-approved small molecule irreversible inhibitor of BTK. In Phase II studies of single-agent ibrutinib in MCL (Wang ML et al, NEJM 2013) and CLL (Byrd JC, et al, NEJM 2013) the overall response rate was 68% and 89% (CR, PR, and PR with lymphocytosis), respectively, with PR as the best response in the majority of patients. Thus, not all patients respond and complete responses are infrequent with single agent ibrutinib. We previously reported that the BCL2 inhibitor, ABT-199, and the proteasome inhibitor, carfilzomib, were highly synergistic with ibrutinib in MCL cell lines using a focused drug panel (Axelrod M et al, Leukemia 2014). We sought to confirm these findings in MCL and CLL patient samples and to determine the mechanisms of synergy. Peripheral blood buffy coat samples from patients with circulating tumor cells were exposed to ibrutinib, ABT-199, carfilzomib and the combinations of ibrutinib and ABT-199 and ibrutinib and carfilzomib at pharmacologically-achievable doses for 72 hours. Apoptosis was assessed using PARP cleavage by FACS analysis of CD3-, CD5+, CD19+ cells representing the neoplastic clones. The combination of Ibrutinib and ABT-199 substantially induced apoptosis compared to each single agent alone (combo: 23%, ibrutinib: 3.8%, ABT-199: 3.0%). Ibrutinib plus carfilzomib also substantially induced apoptosis compared to each single agent alone (combo: 5.5%, Ibrutinib 3.8%, carfilzomib 1.7%) though to a less degree than the ABT-199 combination. The normal B-cell population (CD3-, CD5-, CD19+) in these samples was too small for analysis, thus normal T-cells (CD3+, CD5+, CD19-) from the same patients were used to identify the effects on normal lymphocytes. Minimal apoptosis was seen in normal T-cells with the single agents or the combinations. In a cohort of CLL and normal donor samples, heterogeneity in response to the combination of ibrutinib and ABT-199 was seen. When evaluated by Bliss modeling, 5 of 9 CLL samples had a synergistic improvement in apoptosis with the combination with the other 4 having no change. No increased apoptosis was seen in two tested peripheral blood lymphocyte (CD3-, CD5-, CD19+) populations from healthy donors. Gene expression profiling with Illumina Bead Chip array was used to evaluate the mechanisms of synergy with ABT-199 plus ibrutinib after 6 hours of drug exposure. The MCL cell line JVM2 was exposed to pharmacologically-achievable doses of ibrutinib, ABT-199 and combinations of each dose. Ibrutinib alone induced transcriptional change whereas ABT-199 did little to change gene expression. The combination induced both potentiative transcriptional changes (changes present in isolation and enhanced by the combination) and emergent transcriptional changes (changes only seen with the combination, unchanged by each single agent). Protein-protein interaction networks generated using the drug targets (BTK and BCL2) and emergent genes as input to STRING revealed activation of apoptosis via p53 and BIM as mechanisms of synergy. In conclusion, Ibrutinib and ABT-199 induce synergistic apoptosis in MCL cell lines and leukemic patient samples. The combination also induced apoptosis in some, but not all, CLL patient samples. No apoptosis was seen with either drug or the combination in normal T-cells from patients, suggesting little off-target effect. Emergent changes were seen when combining ABT-199 with ibrutinib in MCL cell lines. These changes suggest activation of p53 and BIM as potential mechanisms of synergy. A clinical trial with ABT-199 and ibrutinib is planned. Disclosures Off Label Use: Pre-clinical data with ABT-199 for MCL and CLL, not FDA approved. Williams:Pharmacyclics, Janssen: Consultancy, Research Funding.

Large granular lymphocyte (LGL) leukemia is an indolent lymphoproliferative malignancy which dysregulates humoral immunity and underlies the myriad autoimmune phenomena. We describe a 62-year-old woman with Felty's syndrome who developed a severe bleeding diathesis. Laboratory evaluation demonstrated acquired inhibitors to both factor VIII (FVIII) and fibrinogen, likely secondary to T-cell LGL leukemia. After a complicated course, the patient's inhibitors were extinguished with rituximab and high-dose corticosteroids. Bleeding was controlled with alternating FEIBA (factor eight inhibitor bypassing activity) and recombinant activated FVII. This report reviews the literature comparing the efficacy of various treatment modalities for both disorders. To our knowledge, this is the first reported case of a patient with LGL leukemia acquiring an inhibitor to FVIII or fibrinogen.