Stroma-Mediated Resistance to S63845 and Venetoclax through MCL-1 and BCL-2 Expression Changes Induced by miR-193b-3p and miR-21-5p Dysregulation in Multiple Myeloma.

BH3-mimetics targeting anti-apoptotic proteins such as MCL-1 (S63845) or BCL-2 (venetoclax) are currently being evaluated as effective therapies for the treatment of multiple myeloma (MM). Interleukin 6, produced by mesenchymal stromal cells (MSCs), has been shown to modify the expression of anti-apoptotic proteins and their interaction with the pro-apoptotic BIM protein in MM cells. In this study, we assess the efficacy of S63845 and venetoclax in MM cells in direct co-culture with MSCs derived from MM patients (pMSCs) to identify additional mechanisms involved in the stroma-induced resistance to these agents. MicroRNAs miR-193b-3p and miR-21-5p emerged among the top deregulated miRNAs in myeloma cells when directly co-cultured with pMSCs, and we show their contribution to changes in MCL-1 and BCL-2 protein expression and in the activity of S63845 and venetoclax. Additionally, direct contact with pMSCs under S63845 and/or venetoclax treatment modifies myeloma cell dependence on different BCL-2 family anti-apoptotic proteins in relation to BIM, making myeloma cells more dependent on the non-targeted anti-apoptotic protein or BCL-XL. Finally, we show a potent effect of the combination of S63845 and venetoclax even in the presence of pMSCs, which supports this combinatorial approach for the treatment of MM.

Protein Translation Inhibition is Involved in the Activity of the Pan-PIM Kinase Inhibitor PIM447 in Combination with Pomalidomide-Dexamethasone in Multiple Myeloma.

BACKGROUND: Proviral Insertion site for Moloney murine leukemia virus (PIM) kinases are overexpressed in hematologic malignancies, including multiple myeloma. Previous preclinical data from our group demonstrated the anti-myeloma effect of the pan-PIM kinase inhibitor PIM447. METHODS: Based on those data, we evaluate here, by in vitro and in vivo studies, the activity of the triple combination of PIM447 + pomalidomide + dexamethasone (PIM-Pd) in multiple myeloma. RESULTS: Our results show that the PIM-Pd combination exerts a potent anti-myeloma effect in vitro and in vivo, where it markedly delays tumor growth and prolongs survival of treated mice. Mechanism of action studies performed in vitro and on mice tumor samples suggest that the combination PIM-Pd inhibits protein translation processes through the convergent inhibition of c-Myc and mTORC1, which subsequently disrupts the function of eIF4E. Interestingly the MM pro-survival factor IRF4 is also downregulated after PIM-Pd treatment. As a whole, all these molecular changes would promote cell cycle arrest and deregulation of metabolic pathways, including glycolysis and lipid biosynthesis, leading to inhibition of myeloma cell proliferation. CONCLUSIONS: Altogether, our data support the clinical evaluation of the triple combination PIM-Pd for the treatment of patients with multiple myeloma.

Biological Background of Resistance to Current Standards of Care in Multiple Myeloma.

A high priority problem in multiple myeloma (MM) management is the development of resistance to administered therapies, with most myeloma patients facing successively shorter periods of response and relapse. Herewith, we review the current knowledge on the mechanisms of resistance to the standard backbones in MM treatment: proteasome inhibitors (PIs), immunomodulatory agents (IMiDs), and monoclonal antibodies (mAbs). In some cases, strategies to overcome resistance have been discerned, and an effort should be made to evaluate whether resensitization to these agents is feasible in the clinical setting. Additionally, at a time in which we are moving towards precision medicine in MM, it is equally important to identify reliable and accurate biomarkers of sensitivity/refractoriness to these main therapeutic agents with the goal of having more efficacious treatments and, if possible, prevent the development of relapse.

The Novel Pan-PIM Kinase Inhibitor, PIM447, Displays Dual Antimyeloma and Bone-Protective Effects, and Potently Synergizes with Current Standards of Care.

PURPOSE: PIM kinases are a family of serine/threonine kinases recently proposed as therapeutic targets in oncology. In the present work, we have investigated the effects of the novel pan-PIM kinase inhibitor, PIM447, on myeloma cells and myeloma-associated bone disease using different preclinical models. EXPERIMENTAL DESIGN: In vitro/ex vivo cytotoxicity of PIM447 was evaluated on myeloma cell lines and patient samples. Synergistic combinations with standard treatments were analyzed with Calcusyn Software. PIM447 effects on bone cells were assessed on osteogenic and osteoclastogenic cultures. The mechanisms of PIM447 were explored by immunoblotting, qPCR, and immunofluorescence. A murine model of disseminated multiple myeloma was employed for in vivo studies. RESULTS: PIM447 is cytotoxic for myeloma cells due to cell-cycle disruption and induction of apoptosis mediated by a decrease in phospho-Bad (Ser112) and c-Myc levels and the inhibition of mTORC1 pathway. Importantly, PIM447 demonstrates a very strong synergy with different standard treatments such as bortezomib + dexamethasone (combination index, CI = 0.002), lenalidomide + dexamethasone (CI = 0.065), and pomalidomide + dexamethasone (CI = 0.077). PIM447 also inhibits in vitro osteoclast formation and resorption, downregulates key molecules involved in these processes, and partially disrupts the F-actin ring, while increasing osteoblast activity and mineralization. Finally, PIM447 significantly reduced the tumor burden and prevented tumor-associated bone loss in a disseminated murine model of human myeloma. CONCLUSIONS: Our results demonstrate dual antitumoral and bone-protective effects of PIM447. This fact, together with the very strong synergy exhibited with standard-of-care treatments, supports the future clinical development of this drug in multiple myeloma. Clin Cancer Res; 23(1); 225-38. ©2016 AACR.