Harnessing the therapeutic potential of histotripsy focused ultrasound-induced immunogenic cancer cell death

PROJECT SUMMARY/ABSTRACT Immunotherapy can be highly effective against cancers that elicit some recognition from the immune system (e.g., melanoma), but it remains ineffectual against cancers that are largely invisible to immune detection (e.g., pancreatic cancer). Advances in cancer immunotherapy will require interventions that can make cancers more apparent to the immune system. A growing body of evidence suggests that focused ultrasound (FUS) tumor ablation could be that intervention. By non-invasively disrupting cancer cells, thermal and mechanical modes of FUS have been shown to trigger surprisingly potent immune responses against tumors. We have found that histotripsy, a non-thermal mode of mechanical FUS, stimulates a powerful and systemic anti-tumor immune response strong enough to cause abscopal regression of distant, non-ablated tumor sites – effects not generally seen with traditional therapies like radiation or thermal ablation. Histotripsy is a technology that is presently being introduced into clinical use; therefore, it will be imperative to understand the mechanistic underpinnings of histotripsy immunostimulation. Our preliminary studies point to a stepwise series of events that may explain this phenomenon. First, histotripsy causes the release of subcellular cancer cell antigens in a manner that preserves their immunogenic integrity. Second, histotripsy induces cancer cells to undergo a specific pathway of cellular suicide called necroptosis – a death pathway that attracts inflammation and immune attention, effectively priming the immune system to recognize cancer antigens. What follows is a progressive infiltration of CD8+ T cells into distant tumors that is accompanied by another pathway of cancer cell death called ferroptosis – a death pathway recently discovered to be the critical mechanism by which immunotherapy-primed CD8+ T cells kill cancer cells. In this proposal, we will retrace these steps to understand how histotripsy exerts its unusually potent immune effects. First, we will quantitatively fine-tune the parameters of histotripsy tissue cavitation that cause maximally immunogenic tumor antigen release. Next, we will focus on the early induction of necroptosis to determine if this is a necessary local precursor event on which later manifestations of histotripsy immunostimulation depend. Then, we will examine the later process of CD8+ T cell-driven ferroptosis to determine if this is the mechanism by which the distant, abscopal effects of histotripsy are mediated. Finally, we will leverage mechanistic insights gained from these investigations to develop and test potential preclinical strategies with which the effects of histotripsy on tumor antigen release, necroptosis, and ferroptosis could be maximized for cancer immunotherapy. We have assembled a multidisciplinary team with expertise in FUS, immunology and cancer immunotherapy to pursue this work, which promises to reveal insights and strategies to bring the impact of cancer immunotherapy to a wider range of patients in need of cure.