Mild Hyperthermia Enhanced Liposomal Doxorubicin Delivery and CD8+ T cell Infiltration in Triple Negative Breast Cancer

Mild hyperthermia (MHTh) is often used in combination with chemotherapy and radiotherapy for cancer treatment. In the current study, the effect of MHTh on the enhanced uptake of the FDA-approved chemotherapy drug, liposomal doxorubicin (dox) in syngeneic 4T1 tumors was investigated. Doxorubicin has inherent fluorescence properties having an emission signal at 590 nm upon excitation with a 480 nm laser. A group of mice administered with doxorubicin (dox) were exposed to MHTh (42 °C) for 30 minutes whereas control group given dox did not receive MHTh. Ex vivo optical imaging of harvested tumors confirmed higher uptake of dox in treated versus the control untreated tumors. Confocal microscopy of tumor sections indicates higher fluorescent intensity due to increased accumulation of dox in MHTh-treated compared to untreated tumors. We examined the effect of MHTh to enhance CD8 tumor infiltration, production of interferon-γ (IFN-γ) and expression of programmed death ligand-1 (PD-L1). mRNA in situ hybridization was performed to test for transcripts of CD8, IFN-γ and PD-L1. Results showed that higher expression of CD8 mRNA was observed in MHTh-administered tumors versus untreated cohorts. The signal for IFN-γ and PD-L1 in both groups were not significantly different. Taken together, our findings imply that MHTh can improve tumor uptake of dox. Importantly, our data suggests that MHTh can boost CD8+ T cell infiltration. ### Competing Interest Statement The authors have declared no competing interest.