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.