The novel agent VP79s synergistically enhances venetoclax activity in multiple myeloma cells.

Despite advances in new therapies, multiple myeloma (MM) remains incurable with most patients relapsing or becoming refractory to treatment demonstrating the need for novel therapeutic strategies. We previously identified VP79s, a novel guanidinium-based compound, with potent anti-myeloma activity which targets the dysregulated IL-6/JAK/STAT signalling pathway. Here, we aim to further evaluate the translational potential of VP79s by examining whether it synergises with the BH3 mimetic venetoclax and exploring the mechanisms underlying this effect. The pro-apoptotic effect of VP79s and venetoclax alone or in combination was assessed by annexin V/propidium iodide staining followed by flow cytometry analysis. Western blotting was performed to evaluate the expression level of key pro- and anti-apoptotic members of the Bcl-2 family. BH3 profiling assessed apoptotic priming of cells to a Bim-domain peptide. Co-treatment of NCI-H929 and MM1.S cells with VP79s/venetoclax resulted in a synergistic enhancement of apoptosis which correlated with a decrease in anti-apoptotic Mcl-1 and concurrent increase in pro-apoptotic Bim S. Synergy was not observed in U266B1 cells possibly because these cells demonstrated relative resistance to venetoclax and exhibited a lower level of apoptotic priming in response to a Bim peptide. Importantly, co-treatment of NCI-H929 cells with VP79s and venetoclax was shown to overcome bone marrow stromal cell induced drug resistance. Preliminary findings also indicate that the combination treatment induced an enhanced reduction in viability of ex vivo myeloma patient samples with minimal cytotoxicity toward healthy donor lymphocytes observed. These findings support further preclinical investigation of VP79s in combination with venetoclax as a potential therapeutic strategy in MM.