Proinflammatory macrophage-derived medium enhances temozolomide sensitivity in glioblastoma via pSTAT3-mediated downregulation of DNA repair enzymes

Chemoresistance to temozolomide (TMZ), the main agent in glioblastoma (GBM) treatment, negatively impacts prognosis due to efficient repair of TMZ-induced DNA lesions. Reduced expression of the DNA repair enzyme O6-methylguanine DNA-methyltransferase (MGMT) has been associated with improved chemotherapy response, though not consistently across patients. Our previous findings suggested that N-methylpurine-DNA-glycosylase (MPG), which repairs the most common TMZ-induced DNA adducts, would be implicated in glioblastoma resistance to TMZ, but its role in chemoresistance remains unclear. Tumor-associated macrophages (TAMs), a key component of the GBM microenvironment, impair chemotherapy efficacy, though mechanisms by which they contribute to drug resistance are not well defined. This study shows that reducing MPG expression with specific siRNAs sensitizes tumor cells to TMZ, and this effect is potentiated by simultaneously downregulating both MPG and MGMT. We also provide the first evidence that conditioned medium from proinflammatory macrophages (CM-M1), by suppressing STAT3 phosphorylation, reduces repair enzyme expression in glioblastoma cells, enhancing TMZ cytotoxicity. Molecular analysis of tumor samples from glioblastoma patients confirmed an association between high repair enzyme expression and STAT3 activation. Our findings uncover a novel mechanism by which TAMs contribute to chemoresistance, supporting strategies to reprogram TAMs towards an M1-phenotype to improve TMZ efficacy in GBM treatment.