Design, synthesis and biological evaluation of bisnoralcohol derivatives as novel IRF4 inhibitors for the treatment of multiple myeloma

Interferon regulatory factor 4 (IRF4) is specifically overexpressed in multiple myeloma (MM) and mediates MM progression and survival, making it an emerging target for MM treatment. However, no chemical entity with a defined structure capable of directly binding to and inhibiting IRF4 has been reported. We screened our small library of steroid analogs and identified bisnoralcohol (BA) derivative 18 as a novel hit compound capable of inhibiting IRF4, with an IC₅₀ of 13.46 μM. Based on 18, a series of BA derivatives was synthesized and evaluated for their inhibitory effects on IRF4 and antiproliferative activities against MM cell lines. Among these compounds, 41 (SH514) exhibited the highest potency, with an IC₅₀ value of 2.63 μM for inhibiting IRF4, and IC₅₀ values of 0.08 μM and 0.11 μM for inhibiting the proliferation of IRF4-high-expressing NCI–H929 and MM.1R MM cells, respectively. SH514 can bind to the IRF4-DBD domain with a KD of 1.28 μM. SH514 selectively and potently inhibits IRF4-high-expressing MM cells over IRF4-low-expressing MM cells. Mechanistic studies demonstrated that SH514 suppresses the downstream genes of IRF4, including CCNC, CANX, E2F5, CMYC, HK2, and Blimp1, and inhibited the expression of cell cycle-related proteins CDC2, Cyclin B1, Cyclin D1, Cyclin E1, and CMYC in MM cells. In vivo, SH514 effectively inhibited the proliferation of MM tumors, showing much better antitumor efficacy than the clinical drug lenalidomide, and exhibited no significant toxicity. Thus, these IRF4 inhibitors could serve as promising leads for the development of novel anti-multiple myeloma agents.