Cu²⁺-Pyropheophorbide a-Cystine Conjugate: Synergistic Photodynamic/Chemodynamic Therapy and Glutathione Depletion Improves the Antitumor Efficacy and Downregulates the Hypoxia-Inducing Factor

Abstract

Cancer immune escape, metastasis, recurrence, and multidrug resistance are all associated with hypoxia in the tumor microenvironment (TME). We synthesized a CuPPaCC conjugate for reactive oxygen species (ROS)-mediated cancer therapy. CuPPaCC continuously produced cytotoxic ROS and oxygen through a photo-chemocycloreaction, alleviated hypoxia, and inhibited the expression of a hypoxia-inducing factor (HIF-1α). CuPPaCC was synthesized from pyromania phyllophyllic acid a (PPa), cystine (CC), and copper ions, and its structure was characterized by nuclear magnetic resonance (NMR) and mass spectrometry (MS). The ability of CuPPaCC to produce ROS and oxygen after photodynamic therapy (PDT) in vitro and in vivo was investigated. The ability of CuPPaCC to consume glutathione was investigated. CuPPaCC toxicity (light and dark) in CT26 cells was analyzed by MTT and live/dead cell staining. The anticancer effect of CuPPaCC in vivo was investigated in CT26 Balb/c mice. When stimulated by the TME, CuPPaCC released Cu2+ and PPaCC, and the singlet oxygen yield increased from 34 to 56.5%. The dual ROS-generating mechanism via a Fenton-like reaction/photoreaction and dual glutathione depletion via Cu2+/CC multiplied the antitumor efficacy of CuPPaCC. The photo-chemocycloreaction continued to produce oxygen and maintained high ROS levels even after PDT, significantly alleviating hypoxia in the TME and downregulating the expression of HIF-1α. CuPPaCC thus showed excellent antitumor activity in vitro and in vivo. These results showed that the strategy could be effective in improving the antitumor efficacy of CuPPaCC and could be used as a synergistic regimen for cancer therapy.