NA1-115-7, from Zygogynum pancheri, is a new selective MCL-1 inhibitor inducing the apoptosis of hematological cancer cells but non-toxic to normal blood cells or cardiomyocytes

Overview of BH3 mimetics in ovarian cancer

Ovarian carcinoma is the leading cause of gynecological cancer-related death, still with a dismal five-year prognosis, mainly due to late diagnosis and the emergence of resistance to cytotoxic and targeted agents. Bcl-2 family proteins have a key role in apoptosis and are associated with tumor development/progression and response to therapy in different cancer types, including ovarian carcinoma. In tumors, evasion of apoptosis is a possible mechanism of resistance to therapy. BH3 mimetics are small molecules that occupy the hydrophobic pocket on pro-survival proteins, allowing the induction of apoptosis, and are currently under study as single agents and/or in combination with cytotoxic and targeted agents in solid tumors. Here, we discuss recent advances in targeting anti-apoptotic proteins of the Bcl-2 family for the treatment of ovarian cancer, focusing on BH3 mimetics, and how these approaches could potentially offer an alternative/complementary way to treat patients and overcome or delay resistance to current treatments.

PBRM1 loss is associated with increased sensitivity to MCL1 and CDK9 inhibition in clear cell renal cancer

MCL1 is a member of the BCL2 family of apoptosis regulators, which play a critical role in promoting cancer survival and drug resistance. We previously described PRT1419, a potent, MCL1 inhibitor with anti-tumor efficacy in various solid and hematologic malignancies. To identify novel biomarkers that predict sensitivity to MCL1 inhibition, we conducted a gene essentiality analysis using gene dependency data generated from CRISPR/Cas9 cell viability screens. We observed that clear cell renal cancer (ccRCC) cell lines with damaging PBRM1 mutations displayed a strong dependency on MCL1. PBRM1 (BAF180), is a chromatin-targeting subunit of mammalian pBAF complexes. PBRM1 is frequently altered in various cancers particularly ccRCC with ~40% of tumors harboring damaging PBRM1 alterations. We observed potent inhibition of tumor growth and induction of apoptosis by PRT1419 in various preclinical models of PBRM1-mutant ccRCC but not PBRM1-WT. Depletion of PBRM1 in PBRM1-WT ccRCC cell lines induced sensitivity to PRT1419. Mechanistically, PBRM1 depletion coincided with increased expression of pro-apoptotic factors, priming cells for caspase-mediated apoptosis following MCL1 inhibition. Increased MCL1 activity has been described as a resistance mechanism to Sunitinib and Everolimus, two approved agents for ccRCC. PRT1419 synergized with both agents to potently inhibit tumor growth in PBRM1-loss ccRCC. PRT2527, a potent CDK9 inhibitor which depletes MCL1, was similarly efficacious in monotherapy and in combination with Sunitinib in PBRM1-loss cells. Taken together, these findings suggest PBRM1 loss is associated with MCL1i sensitivity in ccRCC and provide rationale for the evaluation of PRT1419 and PRT2527 for the treatment for PBRM1-deficient ccRCC.

Targeting MCL-1 protein to treat cancer: opportunities and challenges

Evading apoptosis has been linked to tumor development and chemoresistance. One mechanism for this evasion is the overexpression of prosurvival B-cell lymphoma-2 (BCL-2) family proteins, which gives cancer cells a survival advantage. Mcl-1, a member of the BCL-2 family, is among the most frequently amplified genes in cancer. Targeting myeloid cell leukemia-1 (MCL-1) protein is a successful strategy to induce apoptosis and overcome tumor resistance to chemotherapy and targeted therapy. Various strategies to inhibit the antiapoptotic activity of MCL-1 protein, including transcription, translation, and the degradation of MCL-1 protein, have been tested. Neutralizing MCL-1's function by targeting its interactions with other proteins via BCL-2 interacting mediator (BIM)S2A has been shown to be an equally effective approach. Encouraged by the design of venetoclax and its efficacy in chronic lymphocytic leukemia, scientists have developed other BCL-2 homology (BH3) mimetics-particularly MCL-1 inhibitors (MCL-1i)-that are currently in clinical trials for various cancers. While extensive reviews of MCL-1i are available, critical analyses focusing on the challenges of MCL-1i and their optimization are lacking. In this review, we discuss the current knowledge regarding clinically relevant MCL-1i and focus on predictive biomarkers of response, mechanisms of resistance, major issues associated with use of MCL-1i, and the future use of and maximization of the benefits from these agents.

Final step of B-cell differentiation into plasmablasts; the right time to activate plasma cell PIM2 kinase

The differentiation of B cells into antibody-secreting plasma cells is a complex process that involves extensive changes in morphology, lifespan, and cellular metabolism to support the high rates of antibody production. During the final stage of differentiation, B cells undergo significant expansion of their endoplasmic reticulum and mitochondria, which induces cellular stress and may lead to cell death in absence of effective inhibition of the apoptotic pathway. These changes are tightly regulated at transcriptional and epigenetic levels, as well as at post-translational level, with protein modifications playing a critical role in the process of cellular modification and adaptation. Our recent research has highlighted the pivotal role of the serine/threonine kinase PIM2 in B cell differentiation, from commitment stage to plasmablast and maintenance of expression in mature plasma cells. PIM2 has been shown to promote cell cycle progression during the final stage of differentiation and to inhibit Caspase 3 activation, raising the threshold for apoptosis. In this review, we examine the key molecular mechanisms controlled by PIM2 that contribute to plasma cell development and maintenance.

Targeting Mcl-1 Degradation by Bergenin Inhibits Tumorigenesis of Colorectal Cancer Cells

Myeloid leukemia 1 (Mcl-1) is frequently overexpressed in human malignancies and emerged as a promising drug target. In this study, we verified the inhibitory effect of bergenin on colorectal cancer cells both in vivo and in vitro. In an in vitro setting, bergenin significantly reduced the viability and colony formation and promoted apoptosis of CRC cells dose-dependently. Bergenin decreased the activity of Akt/GSK3β signaling and enhanced the interaction between FBW7 and Mcl-1, which eventually induced Mcl-1 ubiquitination and degradation. Using the HA-Ub K48R mutant, we demonstrated that bergenin promotes Mcl-1 K48-linked polyubiquitination and degradation. In vivo studies showed that bergenin significantly reduced tumor size and weight without toxicity to vital organs in mice. Overall, our results support the role of bergenin in inhibiting CRC cells via inducing Mcl-1 destruction, suggesting that targeting Mcl-1 ubiquitination could be an alternative strategy for antitumor therapy.

In vitro evaluation of NA1-115-7-loaded nanoemulsions, an MCL-1-specific inhibitor of natural origin, intended to treat B-cell lymphoproliferative disorders after oral administration

MCL-1, an anti-apoptotic member of the BCL-2 protein family, is overexpressed in many types of cancer and contributes to chemotherapy resistance. The drimane derivative NA1-115-7 is a natural compound isolated from Zygogynum pancheri that can be considered as a very promising lead for treating MCL-1-dependent hematological malignancies. As this drug suffers from low stability in acidic conditions and poor aqueous solubility, we evaluated the potential oral use of NA1-115-7 by encapsulating it in lipid nanoemulsions (NA-NEs) prepared by spontaneous emulsification. NA-NEs showed a particle size of 41.9 ± 2.2 nm, PDI of 0.131 ± 0.016, zeta potential of -5.8 ± 3.4 mV, encapsulation efficiency of approximately 100 % at a concentration of 24 mM. The stability of NA-1-115-7 was sixfold higher than that of the unencapsulated drug in simulated gastric fluid. NA-NEs significantly restored apoptosis and halved the effective doses of NA1-115-7 on BL2, a Burkitt lymphoma cell line, without toxicity in normal cells. Such a drug-delivery system appears to be particularly interesting for the oral administration of NA1-115-7, as it improves its solubility and stability, as well as efficacy, by reducing the therapeutic dose, making it possible to further consider in-vivo studies of this promising drug in BL2 xenografted mice.