In Situ Gelling of TPZ-Loaded Nanogel for Sustained Intratumoral Delivery and Enhanced Cancer Immunotherapy

TPZ is a hypoxia-activated anticancer agent that exerts selective cytotoxicity within hypoxic tumor microenvironments. Although intratumoral injection of TPZ can achieve localized antitumor activity, the drug is prone to rapid diffusion and clearance from the injection site, limiting its long-term retention and thereby reducing therapeutic durability and overall efficacy. To achieve sustained release and prolonged retention of TPZ in subcutaneous tumors, a thermosensitive nanogel loaded with TPZ (TPZ@PNA-TNG) was developed. By thoroughly mixing 3 mg/mL TPZ with 6 wt% PNA-TNG, the resulting formulation enabled continuous slow release of TPZ following intratumoral injection, resulting in favorable therapeutic outcomes. The sol-gel phase transition behavior of TPZ@PNA-TNG was investigated using the inverted vial method and rheological measurements. In vivo antitumor studies demonstrated that a single administration of TPZ@PNA-TNG effectively suppressed tumor progression, with tumor volume decreasing to 0.72 ± 0.04 times its initial size over a 14-day period. Mechanistically, TPZ@PNA-TNG markedly enhanced antitumor immune responses, inhibited tumor cell proliferation, promoted apoptosis and anti-angiogenesis, and ultimately induced extensive ischemic necrosis within subcutaneous tumors. In addition, owing to the prolonged intratumoral retention capability of PNA-TNG, TPZ@PNA-TNG enabled sustained local delivery of TPZ, thereby significantly reducing systemic toxicity and adverse effects associated with TPZ while maintaining favorable biocompatibility. These findings highlight the therapeutic potential of TPZ@PNA-TNG for cancer therapy applications.