Hyaluronic Acid-Based Nanogel–Drug Conjugates with Enhanced Anticancer Activity Designed for the Targeting of CD44-Positive and Drug-Resistant Tumors

Many drug-resistant tumors and cancer stem cells (CSC) express elevated levels of CD44 receptor, a cellular glycoprotein binding hyaluronic acid (HA). Here, we report the synthesis of nanogel–drug conjugates based on membranotropic cholesteryl-HA (CHA) for efficient targeting and suppression of drug-resistant tumors. These conjugates significantly increased the bioavailability of poorly soluble drugs with previously reported activity against CSC, such as etoposide, salinomycin, and curcumin. The small nanogel particles (diameter 20–40 nm) with a hydrophobic core and high drug loads (up to 20%) formed after ultrasonication and demonstrated a sustained drug release following the hydrolysis of biodegradable ester linkage. Importantly, CHA–drug nanogels demonstrated 2–7 times higher cytotoxicity in CD44-expressing drug-resistant human breast and pancreatic adenocarcinoma cells compared to that of free drugs and nonmodified HA–drug conjugates. These nanogels were efficiently internalized via CD44 receptor-mediated endocytosis and simultaneous interaction with the cancer cell membrane. Anchoring by cholesterol moieties in the cellular membrane after nanogel unfolding evidently caused more efficient drug accumulation in cancer cells compared to that in nonmodified HA–drug conjugates. CHA–drug nanogels were able to penetrate multicellular cancer spheroids and displayed a higher cytotoxic effect in the system modeling tumor environment than both free drugs and HA–drug conjugates. In conclusion, the proposed design of nanogel–drug conjugates allowed us to significantly enhance drug bioavailability, cancer cell targeting, and the treatment efficacy against drug-resistant cancer cells and multicellular spheroids.