Injectable thermosensitive hydrogel co-loading with ATRi and doxorubicin for the treatment of triple-negative breast cancer.

Chemotherapy has been the first-line treatment option for cancer. However, acquired chemo-resistance led by DNA damage repair (DDR) of cancer cells and serious side-effects of chemotherapeutic agents are huge hurdles to effectively suppress metastatic tumors. Herein, we developed an injectable thermosensitive hydrogel for localized co-delivery of ATRi-BAY-1895344 (BAY) and doxorubicin (DOX), serving as a localized drug depot to minimize systemic toxicity while ensuring sustained tumor-specific drug release exceeding 4 days. The cumulative drug release rate of DOX and BAY reached up to 73.9% and 63.3% under pH 6.5 conditions. This study pioneers the synergistic combination of a DNA-damaging agent and Ataxia telangiectasia and RAD3-related (ATR) kinase inhibitor ATRi to disrupt the DDR pathway. The ATRi-mediated inhibition of ATR kinase effectively disrupts the replication stress response by impairing the repair of DOX-induced DNA lesions. This dual mechanism significantly enhances tumor cell vulnerability to chemotherapy, ultimately achieving an 8-fold increase in chemosensitivity compared to monotherapy regimens. In triple-negative breast cancer models, the hydrogel-based DOX + BAY@Gel formulation achieved a tumor inhibition rate of 79.4%, significantly surpassing the 58% observed with free DOX monotherapy. This dual-action strategy overcomes chemo-resistance by disabling DDR compensatory mechanisms and prolongs tumor suppression through controlled drug release. The hydrogel platform represents a functional innovation in localized combination therapy, integrating stimuli-responsive drug delivery with DDR pathway disruption for synergistic efficacy.