HSP27 functional switch drives castration-resistant prostate cancer via mTOR pathway activation, highlighting promising combination therapies

Castration-resistant prostate cancer (CRPC) is an advanced and ultimately incurable stage of the disease that arises despite androgen deprivation and remains challenging to treat due to the limited and short-lived efficacy of current therapies. Heat shock protein 27 (HSP27), a molecular chaperone, has been implicated in prostate cancer (PC) progression and therapy resistance; however, its mechanistic roles remain incompletely understood. This study aimed to delineate the HSP27 interactome in PC cells during PC progression and to explore its functional significance, particularly in relation to the mTOR signaling pathway, which is activated in most cases, primarily due to PTEN loss. We performed affinity purification-mass spectrometry (AP-MS) to identify HSP27-interacting proteins in a panel of prostate cell lines with increasing aggressiveness: PNT1A (non-malignant), LNCaP (androgen-sensitive), DU-145, and PC-3 (both androgen-independent CRPC models). Functional enrichment and network analyses were conducted to uncover pathways associated with HSP27 interactors. Validation experiments included Western blotting, co-immunoprecipitation, and pharmacological inhibition using OGX-427 and mTOR inhibitors (Everolimus, Sapanisertib) in prostate cancer cell lines, patient-derived organoids (PDOs), and xenograft models. HSP27 exhibited a progressively expanded interactome in CRPC models, with enrichment of proteins involved in stress adaptation, proteostasis, and mTOR signaling. These insights highlight HSP27 not only as a molecular chaperone but also as a dynamic network hub that may promotes survival in stress-adapted tumor states. In PC-3 cells, HSP27 stabilized key mTORC1 components, including RAPTOR, S6K1, and 4E-BP1 via its chaperone function, thereby enhancing mTORC1 activation. Combined inhibition of HSP27 using the antisense oligonucleotide OGX-427 (Apatorsen) and mTOR blockade via Sapanisertib induced a robust synergistic anti-tumor effect across diverse preclinical models, including advanced PC Patient-derived organoid (PDOs) and CRPC xenografts. Our findings reveal novel insights into HSP27’s role in PC progression and its modulation of the mTOR signaling pathway in CRPC, highlighting dual HSP27/mTOR inhibition as a promising therapeutic approach for advanced, treatment-resistant disease.