Rewiring of oncogenic pathways confers carfilzomib resistance in multiple myeloma and is reversed by Rap1 inhibition

Resistance to carfilzomib, a second-generation proteasome inhibitor, represents a major barrier to effective treatment in multiple myeloma (MM). To uncover actionable vulnerabilities in drug-resistant cells, we establish two carfilzomib-resistant MM models and perform an in-depth molecular characterization of resistance-associated transcriptomic reprogramming. Comparative pathway analyses reveal consistent activation of survival-promoting signaling networks, including the Rap1, MAPK, and PI3K–Akt pathways. Guided by these findings, we systematically evaluate targeted inhibitors and identify GGTI-298, an agent that disrupts Rap1 signaling, as the most effective compound. In vivo, GGTI-298 significantly curtails tumor growth in xenograft models derived from both parental and resistant MM cells without causing detectable systemic toxicity, underscoring its therapeutic potential and safety. Mechanistically, treatment with GGTI-298 leads to downregulation of the anti-apoptotic protein BCL2 along with a concomitant reduction in the proliferation marker Ki-67. Moreover, GGTI-298 reprograms oncogenic signaling and transcriptional circuits, markedly suppressing MYC- and E2F-dependent gene expression while activating pro-apoptotic pathways such as the p53 axis. These effects are particularly evident in resistant cells, suggesting a selective vulnerability conferred by resistance-driven pathway rewiring. Collectively, our findings highlight the Rap1 signaling axis as a critical mediator of carfilzomib resistance and position GGTI-298 as a promising candidate for overcoming therapeutic failure in MM, providing a strong rationale for further clinical development of Rap1-targeted strategies in relapsed or refractory disease settings.