P46: Histotripsy ablation abrogates tumor hypoxia and induces immunogenic cancer cell death

Friday, March 24, 2023

3:21 PM – 3:26 PM

Location: SSO HUB: Melanoma & Sarcoma Zone

Poster Presenter(s)

Anutosh Ganguly, Ph.D

Research Scientist
University of Michigan Medical School, United States

Disclosure information not submitted.

Author(s)

Anutosh Ganguly, Ph.D

Research Scientist
University of Michigan Medical School, United States

Disclosure information not submitted.
BS

Brian Song, n/a

Research Assistant
University of Michigan, United States

Disclosure information not submitted.
RM

Reliza McGinnis, BS

Graduate Student
University of Michigan, United States

Disclosure information not submitted.
ZX

Zhen Xu, PhD

Professor
University of Michigan, United States

Disclosure information not submitted.
MO

Michal Olszewski, PhD

Professor
University of Michigan Medical School, United States

Disclosure information not submitted.
CC

Clifford S. Cho, MD FACS

C. Gardner Child Professor, Vice Chair
University of Michigan Medical School
Ann Arbor, Michigan, United States

Disclosure information not submitted.

Introduction: Histotripsy (HT) is a novel, non-invasive focused ultrasound ablation technology that is currently in multicenter phase 1 clinical evaluation. By creating millimeter-precision cavitation to liquefy tumors into acellular debris, HT mediates a non-thermal and purely mechanical cytotoxicity that triggers powerful immune-mediated regression of both treated and distant, untreated tumors (abscopal effect). The pervasive hypoxia that characterizes the tumor microenvironment exerts profoundly immunosuppressive effects. We sought to evaluate the possibility that restoration of intratumoral normoxia contributes to the potent immunostimulatory effects of HT tumor ablation.

Methods: Subtotal sham or HT tumor ablation was performed 10 days after implantation of syngeneic flank B16F10 melanoma tumors in immunocompetent C57BL/6 mice. Tumor growth was measured, and RNA sequencing (RNASeq) and immunofluorescence (IF) characterization of protein expression and immune cell infiltration were performed at various time points.

Results: Subtotal HT ablation arrested tumor growth. IF and RNASeq analyses of hypoxia-inducible factor 1a (HIF-1a) and hypoxia-driven beta-III tubulin expression demonstrated that the pervasive tumor hypoxia seen before and after sham ablation was abrogated 2 days after HT. The geographic distribution of HIF-1a suppression in the tumor microenvironment was heterogeneous, and regions of HIF-1a downregulation were infiltrated with CXCL10+ monocytes 2 days after HT and with CD8+ T cells 3-7 days after HT. Accumulation of the ferroptosis byproduct HNEJ2 and release of the damage-associated molecular pattern HMGB1 among melanoma cells in close proximity to infiltrating CD8+ T cells suggested the onset of ferroptosis – a mechanism of cell death induced by immunotherapy-primed CD8+ T cells. Gradual expression of HIF1a and other hypoxia response elements was observed beginning 7 days after HT, and this restoration of hypoxia was temporally and spatially correlated with a decline of CD8+ T cells and melanoma cell ferroptosis, and a progressive infiltration of CXCR4+ regulatory T cells.

Conclusions: HT causes a transient interruption of tumor hypoxia that is temporally and spatially associated with innate and adaptive immune response that lead to systemic anti-tumor effects. The eventual reversion to hypoxia and immune suppression suggests that adjunctive interventions to block tumor hypoxia may further enhance the potent immunotherapeutic effects of HT tumor ablation.

Learning Objectives:

describe focused ultrasound tumor ablation.
explain the impact of hypoxia on anti-tumor immune responses.
understand the significance of ferroptotic cancer cell death.