PTEN restoration and CXCR2 depletion synergistically enhance the effect of enzalutamide and inhibit bone metastatic CRPC

Rationale: Enzalutamide (Enz) is the first-line therapy for castration-resistant prostate cancer (CRPC). However, drug resistance has hindered its further application. Moreover, CRPC is frequently prone to metastasis, particularly to bone (BmCRPC). Methods: To investigate the involvement of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) deletion and C-X-C motif chemokine receptor 2 (CXCR2) overexpression in Enz-resistant CRPC and BmCRPC, we constructed a bisphosphonate (BP) lipid-like material with high bone affinity (GB4-BPL) for the codelivery of a PTEN plasmid (pPTEN) and CXCR2 siRNA (siCXCR2) to BmCRPC. Results: GB4-BPL demonstrated twice the bone metastasis-targeting ability of GB4-lipo (which lacks bisphosphonate modification) while maintaining a gene transfection efficiency comparable to that of Lipo8000 and exhibiting significantly lower cytotoxicity. Moreover, siCXCR2 and pPTEN loaded in GB4-BPL (GB4-BPL@siCXCR2/pPTEN) synergistically inhibited tumor growth and metastasis, highly enhancing the effect of Enz by 69.45% in the Enz-resistant model. Furthermore, GB4-BPL@siCXCR2/pPTEN significantly reduced the numbers of MDSCs, Tregs, and M2-like TAMs by 55.01%, 64.75%, and 52.53%, respectively, while increasing the proportions of M1 macrophages, NK cells, and CD8+ T cells by 1.65-, 1.40-, and 4.60-fold, respectively. In addition, this nanosystem reduced skeletal-related events. Conclusions: Our studies demonstrated the potential of GB4-BPL for delivering siCXCR2/pPTEN to tumor and bone metastatic sites. GB4-BPL@siCXCR2/pPTEN alone or in combination with Enz could provide a new strategy for the treatment of drug-resistant BmCRPC.