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In this study we employed self-designed PDLLA-PEG-PDLLA (PLEL) thermosensitive hydrogel to blend with norcantharidin (NCTD), a hydrophilic chemotherapeutic drug possessing curative effect on primary hepatocellular carcinoma (HCC) and adverse effects, then utilized the composite in HCC interstitial chemotherapy. PLEL copolymer was synthesized by ring-opening polymerization, NCTD-loaded PLEL hydrogel was prepared in a simple and reasonable way. The addition of NCTD had no significant effect on the temperature-dependent rheological properties of PLEL hydrogel. The pH values of NCTD-loaded gel solutions (13 wt%) and free NCTD solutions with three drug concentrations of 0.4 mg/mL, 0.8 mg/mL and 1.2 mg/mL under different storage conditions met the pH requirement of small-volume injection. There was no significant difference among the drug release behaviors of NCTD-loaded gels with drug concentrations of 0.4 mg/mL, 0.8 mg/mL and 1.2 mg/mL, they fitted first-order dynamics, exhibited significantly slower drug release than free drug solutions and the release was mainly based on drug diffusion. Drug-loaded gel solution (13 wt%) could evenly distribute throughout tumor tissue before converting into gel after being intratumorally injected and was able to significantly prolong retention time of the drug in tumor compared to free drug solution. The sustained-release performance of NCTD-loaded gel (13 wt%) was confirmed from the perspective of pharmacodynamics in vitro. The in vivo evaluation demonstrated that intratumoral injection of NCTD-loaded PLEL gel (13 wt%) was capable of improving curative effect of the drug and reducing its toxicity.

Systemic administration of anticancer therapeutic agents remains a crucial strategy for clinical cancer therapy. However, poor drug accumulation at tumor sites and severe side effects to normal tissues induced by off-target effects lower their therapeutic efficiency and limit their deep application in clinical settings. How to overcome these issues has continuously raised concerns. Reportedly, injectable thermosensitive hydrogels are good carriers for local drug delivery systems, demonstrating a flowable and injectable sol state at room temperature, easily loading therapeutic agents with large loading contents. Under normal body temperature, these hydrogels are stimulated to undergo a phase transition to an immobile gel state, which serves as a drug reservoir at local injection sites. After intratumoral or peritumoral injection, the localized hydrogel reservoir shows a slow and sustained drug release behavior, and can also targeted deliver therapeutic agents to cancer cells instead of normal cells, improving the therapeutic efficiency and reducing systemic side effects. This review summarizes the development of injectable thermosensitive hydrogel systems, reviews the research application advances of these systems in different therapy strategies for cancer, discusses the present issues and awaits their future in clinical applications.

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