2-hexyl-4-pentylenic acid (HPTA) stimulates the radiotherapy-induced abscopal effect on distal tumor through polarization of tumor-associated macrophages

Objective: The aim of this study was to explore the effects of 2-hexyl-4-pentylenic acid (HPTA) in combination with radiotherapy (RT) on distant unirradiated breast tumors. Methods: Using a rat model of chemical carcinogen (7,12-dimethylbenz[a]anthracene,DMBA)-induced breast cancer, tumor volume was monitored and treatment response was evaluated by performing HE staining, immunohistochemistry, immunofluorescence, qRT-PCR, and western blot analyses. Results: The results demonstrated that HPTA in combination with RT significantly delayed the growth of distant, unirradiated breast tumors. The mechanism of action included tumor-associated macrophage (TAM) infiltration into distant tumor tissues, M1 polarization, and inhibition of tumor angiogenesis by IFN-γ. Conclusion: The results suggest that the combination of HPTA with RT has an abscopal effect on distant tumors via M1-polarized TAMs, and HPTA may be considered as a new therapeutic for amplifying the efficacy of local RT for non-targeted breast tumors.