Sequential release of MTH1 inhibitor and chemotherapeutic drug using a pH-sensitive polymeric delivery system induces apoptosis in human tongue squamous cell carcinoma CAL-27 cells in vitro

To avoid apoptosis induced by reactive oxygen species (ROS), the tumor cells often activate the repair mechanism to repair the damaged DNA and by which maintain the stability and survival of cancer cells. Human MutT homolog 1 (MTH1) is an important oxidative DNA repair enzyme. TH287 is a highly effective inhibitor of MTH1 enzyme, which can induce cell apoptosis. Doxorubicin (DOX) primarily exerts its anticancer effects by inducing DNA damage via topoisomerase II inhibition and free radical generation in redox reactions. Therefore, the combination of DOX and TH287 may have a surprising anti-tumor effect. The optimal integration of nanomicelles with combination therapy promises to deliver an effective drug system with synergistic effects. In this investigation, we engineered pH-responsive nanomicelles utilizing HPAH to simultaneously deliver the chemotherapeutic drug DOX and the MTH1 inhibitor TH287 for the management of oral squamous cell carcinoma (OSCC). Conjugating hydrophobic DOX with hydrophilic, pH-responsive HPAH creates HPAH-DOX, which can self-assemble into nanomicelles in aqueous solution and encapsulate the MTH1 inhibitor TH287. The release of these agents exhibits pH-dependent kinetics, with TH287 exhibiting significantly faster release than DOX at mildly acidic pH levels. In vitro assessments revealed pH-responsive drug delivery dynamics, where the TH287-loaded HPAH-DOX micelles achieved rapid cellular internalization followed by endolysosomal pH-triggered liberation of therapeutic payloads. TH287-loaded HPAH-DOX micelles demonstrated stronger inhibition of tumor cell proliferation compared to HPAH-DOX micelles alone and the physical mixture of HPAH-DOX and TH287. The preferentially released TH287 demonstrated a synergistic effect by significantly inhibiting tumor cell proliferation. This inhibition was attributed to the suppression of autophagy in tumor cells, leading to increased sensitivity to the subsequent release of DOX. The TH287-loaded HPAH-DOX micelles demonstrate superior therapeutic outcomes compared to the HPAH-DOX micelles or the physical mixture of HPAH-DOX and TH287. This investigation validates the translational promise of stimuli-responsive nanovehicles as coordinated drug delivery platforms integrating chemotherapeutic agents with MTH1-targeting therapeutics, establishing a synergistic therapeutic strategy for treatment-refractory oral squamous cell carcinoma.