Ivermectin converts cold tumors hot and synergies with immune checkpoint blockade for treatment of breast cancer

We show that treatment with the FDA-approved anti-parasitic drug ivermectin induces immunogenic cancer cell death (ICD) and robust T cell infiltration into breast tumors. As an allosteric modulator of the ATP/P2×4/P2×7 axis which operates in both cancer and immune cells, ivermectin also selectively targets immunosuppressive populations including myeloid cells and Tregs, resulting in enhanced Teff/Tregs ratio. While neither agent alone showed efficacy in vivo , combination therapy with ivermectin and checkpoint inhibitor anti-PD1 antibody achieved synergy in limiting tumor growth (p=0.03) and promoted complete responses (p<0.01), also leading to immunity against contralateral re-challenge with demonstrated anti-tumor immune responses. Going beyond primary tumors, this combination achieved significant reduction in relapse after neoadjuvant (p=0.03) and adjuvant treatment (p<0.001), and potential cures in metastatic disease (p<0.001). Statistical modeling confirmed bona fide synergistic activity in both the adjuvant (p=0.007) and metastatic settings (p<0.001). Ivermectin has dual immunomodulatory and ICD-inducing effects in breast cancer, converting ‘cold’ tumors ‘hot’, thus represents a rational mechanistic partner with checkpoint blockade.