Hypoxia-sensitive supramolecular nanogels for the cytosolic delivery of ribonuclease A as a breast cancer therapeutic.

As the most common malignancy in women, breast cancer causes >40,000 deaths annually. Ribonuclease A (RNase), a new anti-cancer agent, has attracted intense interest due to its high efficacy and specificity. However, RNase suffers from instability, a short half-life in the circulation and poor membrane penetration. To overcome these challenges, we designed a supramolecular nanogel for the cytosolic delivery of RNase. The nanogels were fabricated using host-guest interactions between azobenzene (Azo) and β-cyclodextrin (βCD) conjugated to poly (L-glutamic acid)-graft-poly (ethylene glycol) methyl ether (PLG-g-mPEG). RNase could be loaded inside the nanogels in mild aqueous conditions. Following optimization, the RNase-loading content and efficiency of the nanogel were 23.5 wt% and 50.4%, respectively. In the presence of nitroreductase (NTR), the cross-linking point between Azo and βCD was destroyed due to the conformation transition of Azo, ensuring the hypoxia-sensitive release of cargo from the nanogels in tumors in which NTR is overexpressed. In vitro release profiles revealed that 75.0% of the RNase was released under hypoxic conditions in 72 h, whilst only 19.7% was released under normoxic conditions. Cytotoxicity assays showed that the RNase-loaded nanogels (nano-RNase) were more efficient in inhibiting the proliferation of 4T1 cells than free RNase. In vivo studies showed 68.7% tumor suppression rates (TSR %) in the nano-RNase treated group, whilst free RNase treatment led to a lack of tumor inhibition. To further enhance the hypoxia status of tumors, we combined nano-RNase with a nanoformulation of vascular disrupting agents PLG-g-mPEG/combretastatinA4 (nano-CA4) and obtained a TSR of 91.7%. The hypoxia-sensitive supramolecular nanogels provided a versatile platform for the delivery of RNase, highlighting its applicability for cancer therapy.