Wen, Z.; Janz, S.; Wang, Y.; Katzenellenbogen, B. S.; Katzenellenbogen, J. A.; Kim, S. H.; Onitilo, A. A.

Despite significant improvements in the prognosis of Multiple Myeloma (MM), relapsed/refractory MM remains a major challenge. BCL2 inhibitor Venetoclax induced complete or very good partial responses in 6% of non-t(11;14) MM cases, compared to 27% in t(11;14) cases, when used as monotherapy in relapsed/refractory MM. Though Venetoclax was proposed to treat t(11;14) cases, the resistance became a concern. Furthermore, non-t(11;14) cases account for 80-85% of MM cases, which underscores the value of Venetoclax in non-t(11;14) MM. Here, we report a recently-invented small molecule inhibitor of FOXM1 NB73 synergizing with Venetoclax in killing MM cells. FOXM1, a critical forkhead box transcription factor in high-risk and relapsed/refractory MM, represents a promising therapeutic target of MM. We examined the mechanisms underlying the synergies of Venetoclax and NB73 using multi-omics and molecular and cellular biology tools in non-t(11;14) myeloma cell lines with high FOXM1 expression. NB73 induces immediate loss of FOXM1, decreases BCL2 expression, and increases Puma expression in myeloma cells. Venetoclax enhances NB73-induced FOXM1 ubiquitination and degradation. The NB73-Venetoclax combination abrogates the binding of FOXM1 to the promoters of genes in the MYC pathway, such as PLK1, MYC, CDC20, and CCNA2, leading to the repression of the transcription of these MYC pathway genes. The PLK1-specific inhibitor GSK461364 synergies with NB73 in suppressing myeloma cell growth. Therefore, NB73 synergizes with Venetoclax in killing myeloma cells. Conclusively, the NB73-Venetoclax combination abolishes FOXM1-mediated transcriptional activation of the MYC pathway, resulting in intensive apoptosis of myeloma cells without t(11;14) but with high FOXM1 expression.