While the aberrant translocation of the mixed-lineage leukemia (MLL) gene drives pathogenesis of acute myeloid leukemia (AML), it represents an independent predictor for poor prognosis of adult AML patients. Thus, small molecule inhibitors targeting menin-MLL fusion protein interaction have been emerging for the treatment of MLL-rearranged AML. As both inhibitors of histone deacetylase (HDAC) and menin-MLL interaction target the transcription-regulatory machinery involving epigenetic regulation of chromatin remodeling that governs the expression of genes involved in tumorigenesis, we hypothesized that these two classes of agents might interact to kill MLL-rearranged (MLL-r) AML cells. Here, we report that the combination treatment with subtoxic doses of the HDAC inhibitor chidamide and the menin-MLL interaction inhibitor MI-3 displayed a highly synergistic anti-tumor activity against human MLL-r AML cells in vitro and in vivo, but not those without this genetic aberration. Mechanistically, co-exposure to chidamide and MI-3 led to robust apoptosis in MLL-r AML cells, in association with loss of mitochondrial membrane potential and a sharp increase in ROS generation. Combined treatment also disrupted DNA damage checkpoint at the level of CHK1 and CHK2 kinases, rather than their upstream kinases (ATR and ATM), as well as DNA repair likely via homologous recombination (HR), but not non-homologous end joining (NHEJ). Genome-wide RNAseq revealed gene expression alterations involving several potential signaling pathways (e.g., cell cycle, DNA repair, MAPK, NF-κB) that might account for or contribute to the mechanisms of action underlying anti-leukemia activity of chidamide and MI-3 as a single agent and particularly in combination in MLL-r AML. Collectively, these findings provide a preclinical basis for further clinical investigation of this novel targeted strategy combining HDAC and Menin-MLL interaction inhibitors to improve therapeutic outcomes in a subset of patients with poor-prognostic MLL-r leukemia.

High-grade B-cell lymphoma with concurrent MYC and BCL2 rearrangements (HGBL-DHL) is a rare, aggressive mature B-cell malignancy with a high likelihood of treatment failure following front-line immunochemotherapies. Patients with HGBL-DHL who develop a relapsed or refractory disease have little effective therapeutic strategies and show very poor clinical outcomes, thus calling for development of novel therapies for this specific patient population. In this study, we investigated the preclinical anti-lymphoma efficacies and potential mechanism of action of a novel treatment approach, combining the BCL2 inhibitor venetoclax with CS2164, a new orally active multitarget inhibitor, in HGBL-DHL models. This combination therapy exhibited a robust synergistic cytotoxicity against HGBL-DHL cells, evidenced by cooperatively inducing loss of cell viability and promoting cell apoptosis. Moreover, coadministration of CS2164 and venetoclax resulted in significant superior suppression of HGBL-DHL cell growth and remarkably abrogated tumor burden in a HGBL-DHL-xenografted mouse model. The synergistic lethality of CS2164 and venetoclax in HGBL-DHL cells was associated with induction of DNA damage and impairment of DNA repair ability. Of importance, the combined treatment almost abolished the expression of both BCL2 and MYC, two hallmark proteins of HGBL-DHL, and substantially blunted the activity of PI3K/AKT/mTOR signaling cascade. In addition, MCL1 and BCL-XL, two well-characterized contributors for venetoclax resistance, were significantly lessened in the presence of CS2164 and venetoclax, thus leading to the accumulation of proapoptotic proteins BAX and PUMA and then initiating the intrinsic apoptosis pathway. Taken together, these findings suggest that the regimen of CS2164 and venetoclax is highly effective to eliminate HGBL-DHL cells in the preclinical setting, warranting further clinical investigations of this regimen for the treatment of unfavorable HGBL-DHL patients.

Bcl-2 inhibitors display an effective activity in acute myeloid leukemia (AML), but its clinical efficacy as a monotherapy was limited in part owing to failure to target other antiapoptotic Bcl-2 family proteins, such as Mcl-1. In this context, the combination strategy may be a promising approach to overcome this barrier. Here, we report the preclinical efficacy of a novel strategy combining ABT-199 with triptolide (TPL), a natural product extracted from a traditional Chinese medicine, in AML. Combination treatment exhibited markedly increased cytotoxicity in leukemic cells irrespective of p53 status while largely sparing normal cells of the hematopoietic lineage. Moreover, co-administration of ABT-199 with TPL dramatically suppressed leukemia progression as well as prolonged animal survival in a xenograft AML model. The potentiated effect of ABT-199 and TPL against AML was associated with activation of the mitochondrum-related intrinsic apoptotic pathway through a mechanism reciprocally modulating Bcl-2 family proteins. In this case, TPL not only downregulated Mcl-1 but also upregulated proapoptotic BH3-only proteins, thereby overcoming the resistance toward ABT-199. Conversely, ABT-199 abrogated Bcl-2-mediated cytoprotection against TPL. Together, these findings suggest that the regimen combining TPL and ABT-199 might be active against AML by inducing robust apoptosis through reciprocal regulation of anti- and proapoptotic Bcl-2 family proteins, therefore providing a strong rationale for the clinical investigation of this combination regimen for the treatment of AML.

High-grade B-cell lymphoma with concurrentMYCandBCL2rearrangements (HGBCL-DHL) is a rare and aggressive B-cell disorder with a high likelihood of nonresponsiveness to the front-line immunochemotherapy. Patients with HGBCL-DHL who develop a recurrent or progressive disease have limited effective therapeutics and show very poor clinical outcomes. Therefore, it calls for the development of novel targeted therapies for this specific patient populations. In this study, we showed that combination of BCL2 inhibitor venetoclax and CS2164, a novel orally active multitarget inhibitor, is a potent therapeutic strategy against HGBCL-DHL in the preclinical setting. BCL2rearrangement, a hallmark feature of HGBCL-DHL, often results in increased BCL2 protein that counteracts the proapoptotic proteins of BCL2 family, and thus blocks cell death. BCL2 blockage with venetoclax shows promising clinical responses in various human malignancies. However, resistance to venetoclax takes place following its continuous administration, suggesting that venetoclax should combine with other agents to prevent disease progression. CS2164 is originally developed by China and designed to perturb three key characteristics of neoplasms: tumor angiogenesis, cell mitosis and chronic inflammation. Our previous study demonstrated that CS2164 exerted potently antilymphoma activities in MYC-driven lymphomas, providing evidence that CS2164 could potentiate the effect of venetoclax for MYC/BCL2 driven HGBCL-DHL. In the present work, we first observed that both venetoclax and CS2164 as single agent reduced the capability of cell proliferation in HGBCL-DHL cell lines. Next, we found that CS2164 synergized with venetoclax to suppress cell proliferation and trigger cell apoptosis in HGBCL-DHLin vitro. More importantly, when compared with each single drug groups, coadministration of venetoclax and CS2164 resulted in superior suppression of HGBCL-DHL cell growth and remarkably abrogated tumor burden in a HGBCL-DHL-xenografted mouse model. The synergistic lethality of venetoclax and CS2164 towards HGBCL-DHL cells was associated with the modulation of multiple molecular mechanisms. The underlying mechanisms for the synergy of the two drugs included the blockade of Rad51 recombinase-dependent DNA repair, the perturbation of the delicate balance of BCL2 family proteins that induced mitochondrial membrane depolarization and subsequently led to the proapoptotic effect, as well as the inhibition of PI3K/AKT/mTOR pathway and MYC expression. In summary, these findings suggest that the regimen of CS2164 and venetoclax combination is highly effective to eliminate HGBCL-DHL cellsin vitroandin vivoand thus provide a rational treatment paradigm to strip HGBCL-DHL of its protection fromMYCandBCL2rearrangements. Disclosures No relevant conflicts of interest to declare. OffLabel Disclosure: CS2164 originally developed by China is a novel orally active multitarget inhibitor that is evaluating in clinical trials against multiple solid tumors.