Exploring Bakuchiol as an HSP90-Targeting Lead Against Triple-Negative Breast Cancer: Evidence from In Silico, In Vitro, and Synergy Studies.

Psoralea corylifolia holds a prominent position in traditional herbal medicine. Bakuchiol, the principal phytoconstituent present in the seeds of P. corylifolia, significantly contributes to the medicinal properties of the plant. Because of its diverse biological activities, ranging from anti-oxidative to anti-inflammatory, this natural meroterpenoid is attracting considerable attention. The present study aims to investigate the potential of bakuchiol in mitigating triple-negative breast cancer (TNBC) by targeting heat shock protein 90 (HSP90), a pivotal molecular chaperone implicated in cancer cell growth and progression. The study has employed a multi-approach strategy, by combining in-silico (Network pharmacology, molecular docking, molecular dynamics simulation), cell-free assay (N-terminal HSP90 binding activity assay), and in-vitro methodologies, to explore its anticancer activities against TNBC and to elucidate HSP90 as a target of bakuchiol, using a HSP90-inhibitor radicicol as a reference. The Chou-Talalay combination index method along with other methods (Loewe, HSA, Bliss, and Zip) was employed for determining its synergistic potential. Bakuchiol showed preferential cytotoxicity on MDA-MB-231 cells, with minimal impact on non-cancerous cells HEK-293, demonstrating a favourable selectivity index. In-silico studies identified HSP90 as a prime target via which bakuchiol exhibits its anticancer activity, and the competitive binding assay established it as a N-terminal HSP90 inhibitor. Bakuchiol downregulated the expression of HSP90 client protein EGFR, while inducing the expression of HSP70, further supporting its inhibitory effect on the N-terminal HSP90 domain. Detailed in-vitro studies further highlighted the anti-proliferative, pro-apoptotic, and anti-metastatic role of bakuchiol, with radicicol serving as a control to verify HSP90-mediated activity. Moreover, bakuchiol was also found to exhibit a synergistic effect against TNBC cells in association with the standard chemotherapeutic drug doxorubicin, thereby enhancing its therapeutic efficacy. These findings highlight bakuchiol as a promising HSP90-targeting natural compound with potential therapeutic benefit against TNBC, therefore making it a crucial lead for further research.