Development of a Dual-drug-loaded Silk Fibroin Hydrogel and Study on Its Drugs Release Behaviors

Injectable hydrogels, as an effective vehicle for localized drug delivery, have attracted increasing attention in recent years. With improved tumor-specific drug accumulation and lowered risk of infection, the application of in situ-forming injectable hydrogels provides an alternative to surgical implantation. In this study, based on a unique feature of regenerated silk fibroin (RSF) that it can easily form beta-sheet structures, which function as physical cross-links, under various conditions, we designed an injectable silk fibroin hydrogel which encapsulated SBA-15 for the co-delivery of a vascular disrupting agent, combretastatin A4 disodium phosphate (CA4P), and doxorubicin hydrochloride (DOX). Such a CA4P and DOX co-encapsulated hydrogel ((RSF/CA4P)-(SBA-15/DOX)), simply prepared through a designed ultrasonication procedure, showed two different types of drug release behavior. CA4P was rapidly released, and it not only targeted the abnormal vasculature of tumors, causing vascular collapse, but also inhibited tumor cell proliferation by binding to tubulin and arresting mitosis. On the other hand, the sustained release of DOX can inhibit the proliferation of tumor cells for a prolonged period of time. Because of the rapid disruption of tumor vasculature and sustained inhibition of tumor cells proliferation, the (RSF/CA4P)-(SBA-15/DOX) hydrogel showed significantly enhanced cytotoxicity against human breast carcinoma cells (MDA-MB-231). By using this co-delivery system, the required dose of DOX can be lowered, and at the same time, the superior antitumor efficacy of the drugs is maintained. Our results suggest that the application of silk fibroin hydrogels to the co-delivery of a vascular disrupting agent and a chemotherapeutic agent with different drug release behaviors is a promising strategy in tumor treatment. Moreover, after sonication, the hydrogel precursor of (RSF/CA4P)-(SBA-15/DOX), can reach target irregular-shaped tumor sites via intratumor injection, and the hydrogels then form in situ, simply induced by body heat. Such silk fibroin-based hydrogels are injectable and malleable and fluorescent in dark field, which greatly facilitates their biomedical applications.