Pevonedistat and azacitidine upregulate NOXA (PMAIP1) to increase sensitivity to venetoclax in preclinical models of acute myeloid leukemia.

Dysregulation of apoptotic machinery is one mechanism by which acute myeloid leukemia (AML) acquires a clonal survival advantage. B-cell lymphoma protein-2 (BCL2) overexpression is a common feature in hematologic malignancies. The selective BCL2 inhibitor, venetoclax (VEN) is used in combination with azacitidine (AZA), a DNAmethyltransferase inhibitor (DNMTi), to treat patients with AML. Despite promising response rates to VEN/AZA, resistance to the agent is common. One identified mechanism of resistance is the upregulation of myeloid cell leukemia-1 protein (MCL1). Pevonedistat (PEV), a novel agent that inhibits NEDD8-activating enzyme, and AZA both upregulate NOXA (PMAIP1), a BCL2 family protein that competes with effector molecules at the BH3 binding site of MCL1. We demonstrate that PEV/AZA combination induces NOXA to a greater degree than either PEV or AZA alone, which enhances VEN-mediated apoptosis. Herein, using AML cell lines and primary AML patient samples ex vivo, including in cells with genetic alterations linked to treatment resistance, we demonstrate robust activity of the PEV/VEN/AZA triplet. These findings were corroborated in preclinical systemic engrafted models of AML. Collectively, these results provide rational for combining PEV/VEN/AZA as a novel therapeutic approach in overcoming AML resistance in current therapies.

A Novel MCL1 Inhibitor Combined with Venetoclax Rescues Venetoclax-Resistant Acute Myelogenous Leukemia.

Suppression of apoptosis by expression of antiapoptotic BCL2 family members is a hallmark of acute myeloblastic leukemia (AML). Induced myeloid leukemia cell differentiation protein (MCL1), an antiapoptotic BCL2 family member, is commonly upregulated in AML cells and is often a primary mode of resistance to treatment with the BCL2 inhibitor venetoclax. Here, we describe VU661013, a novel, potent, selective MCL1 inhibitor that destabilizes BIM/MCL1 association, leads to apoptosis in AML, and is active in venetoclax-resistant cells and patient-derived xenografts. In addition, VU661013 was safely combined with venetoclax for synergy in murine models of AML. Importantly, BH3 profiling of patient samples and drug-sensitivity testing ex vivo accurately predicted cellular responses to selective inhibitors of MCL1 or BCL2 and showed benefit of the combination. Taken together, these data suggest a strategy of rationally using BCL2 and MCL1 inhibitors in sequence or in combination in AML clinical trials. SIGNIFICANCE: Targeting antiapoptotic proteins in AML is a key therapeutic strategy, and MCL1 is a critical antiapoptotic oncoprotein. Armed with novel MCL1 inhibitors and the potent BCL2 inhibitor venetoclax, it may be possible to selectively induce apoptosis by combining or thoughtfully sequencing these inhibitors based on a rational evaluation of AML.See related commentary by Leber et al., p. 1511.This article is highlighted in the In This Issue feature, p. 1494.

Blastic Plasmacytoid Dendritic Cell Neoplasm Is Dependent on BCL2 and Sensitive to Venetoclax.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is an aggressive hematologic malignancy with dismal outcomes for which no standard therapy exists. We found that primary BPDCN cells were dependent on the antiapoptotic protein BCL2 and were uniformly sensitive to the BCL2 inhibitor venetoclax, as measured by direct cytotoxicity, apoptosis assays, and dynamic BH3 profiling. Animals bearing BPDCN patient-derived xenografts had disease responses and improved survival after venetoclax treatment in vivo Finally, we report on 2 patients with relapsed/refractory BPDCN who received venetoclax off-label and experienced significant disease responses. We propose that venetoclax or other BCL2 inhibitors undergo expedited clinical evaluation in BPDCN, alone or in combination with other therapies. In addition, these data illustrate an example of precision medicine to predict treatment response using ex vivo functional assessment of primary tumor tissue, without requiring a genetic biomarker. SIGNIFICANCE: Therapy for BPDCN is inadequate, and survival in patients with the disease is poor. We used primary tumor cell functional profiling to predict BCL2 antagonist sensitivity as a common feature of BPDCN, and demonstrated in vivo clinical activity of venetoclax in patient-derived xenografts and in 2 patients with relapsed chemotherapy-refractory disease. Cancer Discov; 7(2); 156-64. ©2016 AACR.This article is highlighted in the In This Issue feature, p. 115.

Discovery and biological characterization of potent myeloid cell leukemia-1 inhibitors.

Myeloid cell leukemia 1 (Mcl-1) is an antiapoptotic member of the Bcl-2 family of proteins that when overexpressed is associated with high tumor grade, poor survival, and resistance to chemotherapy. Mcl-1 is amplified in many human cancers, and knockdown of Mcl-1 using RNAi can lead to apoptosis. Thus, Mcl-1 is a promising cancer target. Here, we describe the discovery of picomolar Mcl-1 inhibitors that cause caspase activation, mitochondrial depolarization, and selective growth inhibition. These compounds represent valuable tools to study the role of Mcl-1 in cancer and serve as useful starting points for the discovery of clinically useful Mcl-1 inhibitors. PDB ID CODES: Comp. 2: 5IEZ; Comp. 5: 5IF4.

Functionally identifiable apoptosis-insensitive subpopulations determine chemoresistance in acute myeloid leukemia.

Upfront resistance to chemotherapy and relapse following remission are critical problems in leukemia that are generally attributed to subpopulations of chemoresistant tumor cells. There are, however, limited means for prospectively identifying these subpopulations, which hinders an understanding of therapeutic resistance. BH3 profiling is a functional single-cell analysis using synthetic BCL-2 BH3 domain-like peptides that measures mitochondrial apoptotic sensitivity or "priming." Here, we observed that the extent of apoptotic priming is heterogeneous within multiple cancer cell lines and is not the result of experimental noise. Apoptotic priming was also heterogeneous in treatment-naive primary human acute myeloid leukemia (AML) myeloblasts, and this heterogeneity decreased in chemotherapy-treated AML patients. The priming of the most apoptosis-resistant tumor cells, rather than the median priming of the population, best predicted patient response to induction chemotherapy. For several patients, these poorly primed subpopulations of AML tumor cells were enriched for antiapoptotic proteins. Developing techniques to identify and understand these apoptosis-insensitive subpopulations of tumor cells may yield insights into clinical chemoresistance and potentially improve therapeutic outcomes in AML.

Selective BCL-2 inhibition by ABT-199 causes on-target cell death in acute myeloid leukemia.

B-cell leukemia/lymphoma 2 (BCL-2) prevents commitment to programmed cell death at the mitochondrion. It remains a challenge to identify those tumors that are best treated by inhibition of BCL-2. Here, we demonstrate that acute myeloid leukemia (AML) cell lines, primary patient samples, and murine primary xenografts are very sensitive to treatment with the selective BCL-2 antagonist ABT-199. In primary patient cells, the median IC50 was approximately 10 nmol/L, and cell death occurred within 2 hours. Our ex vivo sensitivity results compare favorably with those observed for chronic lymphocytic leukemia, a disease for which ABT-199 has demonstrated consistent activity in clinical trials. Moreover, mitochondrial studies using BH3 profiling demonstrate activity at the mitochondrion that correlates well with cytotoxicity, supporting an on-target mitochondrial mechanism of action. Our protein and BH3 profiling studies provide promising tools that can be tested as predictive biomarkers in any clinical trial of ABT-199 in AML.

BCL-2 inhibition: stemming the tide of myeloid malignancies.

Leukemia stem cells (LSCs) are likely to be the source for both therapeutic resistance and relapse in myeloid malignancies. As reported in this issue of Cell Stem Cell, Lagadinou et al. (2013) and Goff et al. (2013) support selective targeting of LSCs by small molecule antagonists of anti-apoptotic BCL-2 family proteins.

Early changes in natural killer cell function indicate virologic response to interferon therapy for hepatitis C.

BACKGROUND & AIMS: Mathematical modeling of hepatitis C virus (HCV) kinetics indicated that cellular immune responses contribute to interferon (IFN)-induced clearance of HCV. We investigated a potential role of natural killer (NK) cells in this process. METHODS: Phenotype and function of blood and liver NK cells were studied during the first 12 weeks of treatment with pegylated IFN-alfa and ribavirin, the time period used to define the early virological response. RESULTS: Within hours of treatment initiation, NK cells of patients that had an early virological response increased expression of activating receptors NKG2D, NKp30, and CD16 and decreased expression of NKG2C and 2B4, along with inhibitory receptors SIGLEC7 and NKG2A, resulting in NK cell activation. NK cell cytotoxicity, measured by degranulation and tumor necrosis factor-related apoptosis-inducing ligand production, peaked after 24 hours (P<.01), concomitant with an increase in alanine aminotransferase levels (P<.05), whereas IFN-γ production decreased within 6 hours and did not recover for more than 4 weeks (P<.05). NK cells from liver biopsies taken 6 hours after treatment initiation had increased numbers of cytotoxic CD16+NK cells (P<.05) and a trend toward increased production of tumor necrosis factor-related apoptosis-inducing ligand. Degranulation of peripheral blood NK cells correlated with treatment-induced, first-phase decreases in viral load (P<.05) and remained higher in early virological responders than in nonresponders for weeks. CONCLUSIONS: IFN activates NK cells early after treatment is initiated. Their cytotoxic function, in particular, is strongly induced, which correlates to virologic response. Therefore, NK cell activation indicates responsiveness to IFN-α-based treatment and suggests the involvement of the innate immune cells in viral clearance.

Dendritic cells transfected with Her2 antigen-encoding RNA replicons cross-prime CD8 T cells and protect mice against tumor challenge.

Antigen-specific T cells can be induced by direct priming and cross-priming. To investigate cross-priming as a vaccination approach dendritic cells were transfected with cytopathogenic viral RNA-replicons that expressed domains of the tumor-associated Her2-antigen and injected into MHC-discordant mice that did not allow direct priming. Upon tumor challenge 75% of the vaccinated, but none of the mock-vaccinated mice remained tumor-free. The anti-tumor effect required T cells and correlated with the vigor of the cross-primed CD8 T cell response. Her2-specific antibodies were not detected. This study highlights the potential of T cell cross-priming in cancer immunotherapy.