Glioblastoma (GBM) remains a daunting challenge in oncology due to its resistance to existing standard-of-care therapies and inevitable progression to a lethal outcome. Our lab has previously proposed a successful novel combinatorial regimen, including the tricyclic antidepressant (TCA) imipramine, the vascular endothelial growth factor (VEGF) inhibitor bevacizumab, and the immune checkpoint inhibitor anti-PD-L1, which demonstrated significant therapeutic benefit in GBM mouse models (Chryplewicz et al.; Cancer Cell, 2022). This triple combination was effective by inducing immunostimulatory autophagy in cancer cells, reprogramming tumor-associated macrophages, and remodeling the tumor vasculature, all contributing to the recruitment and activation of T cells. These promising results have incentivized a proof-of-concept clinical trial, where GBM patients who fail the standard-of-care treatment will receive this triple combination as a second-line therapy. Motivated by these results and encouraged by the clinical support, we aim to further improve this therapeutic regimen by disrupting various capabilities of tumors required for their growth and therapeutic resistance.

To optimize this regimen for clinical translation, we screened multiple TCAs - trimipramine, clomipramine, and amitriptyline - alongside imipramine in mouse and human GBM cell lines to evaluate their impact on cell viability. In parallel, we conducted ex vivo experiments using bone marrow-derived macrophages polarized toward an M2-like phenotype to assess the reprogramming potential of TCA treatment.

Among the tested TCAs, trimipramine exhibited the strongest induction of GBM cell death across multiple viability assays. Additionally, all TCAs significantly downregulated M2-like macrophage markers, suggesting their potential to reverse the immunosuppressive tumor microenvironment. These initial findings indicate that TCAs possess anticancer and immunomodulatory properties, prompting further evaluation in preclinical models. Moreover, we are investigating mechanisms of adaptive resistance and relapse following the proposed triplet immunotherapy, with the goal of identifying pharmacological strategies to extend the survival benefit in GBM mouse models.

This study aims to delve deeper into TCA mechanisms of action, assess potential synergies with VEGF pathway inhibitors and immune checkpoint blockade, and ultimately provide critical insights to optimize the proposed triple combination regimen. By leveraging drug repurposing and simultaneously targeting multiple tumor hallmarks, this approach holds significant promise for improving GBM therapeutic outcomes.