Anticancer activity of Rhodiola crenulata extract in a 3D bone-metastatic prostate cancer model: Overcoming treatment resistance through intrinsic apoptosis.

Prostate cancer is the second most common cancer diagnosed and the fifth leading cause of death from cancer among men worldwide. In advanced stages, metastasis primarily occurs in the bones, affecting almost 90% of patients. Treatment resistance, influenced by protective signals and the mechanical properties of the bone metastatic microenvironment, contributes to this elevated mortality rate. Nonetheless, the absence of reliable models and effective therapies worsens the situation. To address these challenges, we employed previously established 3D in vitro models that mimic bone-metastatic prostate cancer to assess the anticancer effects of a phenolic-rich plant extract from Rhodiola crenulata (R. crenulata). Our 3D testbed was created by integrating human mesenchymal stem cells (hMSCs) and prostate cancer cell lines (PCa and PC-3) into a nanoclay-based bone-mimetic scaffold for preclinical treatment testing. Prostate cancer cells grown in these 3D bone-mimetic scaffolds showed significantly higher IC50 values, elevated Bcl-2 expression, and slowed apoptosis progression compared to 2D cultures, suggesting increased microenvironment-driven treatment resistance. R. crenulata extract triggered increased ROS production and activation of the caspase-9 cascade in the intrinsic apoptotic pathway. We observed distinct regulation of intrinsic apoptosis via p53-associated signaling in PCa cells and p53-independent apoptosis in PC-3 cells. Notably, more than 99% of hMSC-derived bone stromal cells remained viable even at higher extract levels, showing minimal toxicity to non-cancerous cells. Overall, these findings demonstrate that R. crenulata extract has therapeutic potential against advanced prostate cancer when evaluated in physiologically relevant 3D models of prostate cancer bone metastasis.