Background: Nonspecific tumor targeting, potential relapse and metastasis of tumor after treatment are the main barriers in clinical photodynamic therapy (PDT) for cancer, hence, inhibiting relapse and metastasis of tumor is significant issues in clinic. Purpose: In this work, chidamide as a histone deacetylases inhibitor (HADCi) was bound onto a pH-responsive block polymer folate polyethylene glycol- b -poly(aspartic acid) (PEG- b -PAsp) grafted folate (FA-PEG- b -PAsp) to obtain the block polymer folate polyethylene glycol- b -poly(asparaginyl-chidamide) (FA-PEG- b -PAsp-chidamide, FPPC) as multimodal tumor-targeting drug-delivery carrier to inhibiting tumor cell proliferation and tumor metastasis in mice. Methods: Model photosensitizer pyropheophorbide- a (Pha) was encapsulated by FPPC in PBS to form the polymer micelles Pha@FPPC [folate polyethylene glycol- b -poly(asparaginyl-chidamide) micelles encapsulating Pha]. Pha@FPPC was characterized by transmission electron microscope and dynamic light scattering; also, antitumor activity in vivo and in vitro were investigated by determination of cellular ROS level, detection of cell apoptosis and cell cycle arrest, PDT antitumor activity in vivo and histological analysis. Results: With favorable and stable sphere morphology under transmission electron microscope (TEM) (~93.0 nm), Pha@FPPC greatly enhanced the cellular uptake due to its folate-mediated effective endocytosis by mouse melanoma B16-F10 cells and the yield of ROS in tumor cells induced by PDT, and mainly caused necrocytosis and blocked cell growth cycle not only in G2 phase but also in G1/G0 phase after PDT. Pha@FPPC exhibited lower dark cytotoxicity in vitro and a better therapeutic index because of its higher dark cytotoxicity/photocytotoxicity ratio. Moreover, Pha@FPPC not only significantly inhibited the growth of implanted tumor and prolonged the survival time of melanoma-bearing mice due to both its folate-mediated tumor-targeting and selectively accumulation at tumor site by EPR (enhanced permeability and retention)effect as micelle nanoparticles but also remarkably prevented pulmonary metastasis of mice melanoma after PDT compared to free Pha, demonstrating its dual antitumor characteristics of PDT and HDACi. Conclusion: As a folate-mediated and acid-activated chidamide-grafted drug-delivery carrier, FPPC may have great potential to inhibit tumor metastasis in clinical photodynamic treatment for cancer because of its effective and multimodal tumor-targeting performance as photosensitizer vehicle.

PD-1/PD-L1 blocking therapy has become one of the most promising methods in the field of tumor treatment. However, it encounters the challenge of immune escape due to the exhaustion of T cells. Studies have shown that the epigenetic regulation drug histone deacetylase inhibitor (HDACi) may be able to reverse exhausted T cells by changing the epigenetic transcription program. Therefore, the combination of epigenetic therapy and PD-1/PD-L1 blockade therapy is expected to reverse the immune escape, whereas the overriding goal should aim at the spontaneous release and synergy of PD-1/PD-L1 blocking siRNA and HDACi. In this study, we develop PDDS{polyethylene glycol-b-asparaginate(diethylenetriamine-vorinostat), (PEG-b-P[Asp(DET-SAHA) n ] PPDS)}encapsulating siRNA-PD-L1to provide micelles siRNA-PD-L1-loaded micelles (siRNA@PPDS). Transmission electron microscope (TEM) images demonstrate that siRNA@PPDS micelles presented spherical morphology with a size of about 120 nm; hydrodynamic data analysis indicates pH sensitivity of siRNA@PPDS micelles. The experiments reveal that siRNA@PPDS micelles could be well uptaken by the tumor cells to silence the expression of PD-L1 protein in a dose-dependent manner; compared with the free SAHA, the SAHA-loaded micelles PPDS show higher cytotoxicity to induce tumor cell apoptosis and block cell cycle in G1 phase on melanoma-bearing mice, siRNA@PPDS has shown outstanding inhibition of tumor growth and pulmonary metastasis. By comprehensively activating the immune system, lysosome activable polymeric vorinostat encapsulating PD-L1KD for the combination therapy of PD-L1-KD and HDACIs can be an effective strategy to reverse the unresponsiveness of immune checkpoint inhibitors and a promising treatment to inhibit tumor growth, recurrence, and metastasis in clinic.

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