Abstract 1729: Mitochondrial necrosis pathway drives tumor progression.

Abstract

Abstract Necrosis is a prominent feature of aggressive and invasive cancers. Previous clinical/epidemiological studies have suggested an association between the extent of tumor necrosis and poor prognosis and survivorship for some cancers. Evasion of apoptosis is widely accepted as a hallmark of cancer. However, whether necrotic cell death plays no role, limits, or drives carcinogenesis has not been studied in any cancer. Recent work suggests that necrosis may be an actively regulated form of cell death. In contrast to apoptosis where permeabilization of the outer mitochondrial membrane is the defining event, the central event in necrosis is the opening of a pore in the inner mitochondrial membrane termed the mitochondrial permeability transition pore (mPTP). Cyclophilin D, a peptidyl prolyl cis-trans isomerase in the mitochondrial matrix, encoded by the gene ppif, is critical for opening of the mPTP. Stable expression of ppif shRNA was used to deplete cyclophilin D in Met-1 cells, a metastatic breast cancer cell line. We first confirmed that knockdown of ppif in Met-1 cells abrogated necrosis, but not apoptosis. When these cells were transplanted into the mammary glands of wildtype FVB mice, tumors resulting from cells that express ppif shRNA were markedly smaller, with decreased volume and mass, than those derived from cells expressing control shRNA. Reconstitution of ppif knockdown cells with wild type cyclophilin D, but not an enzymatically inactive mutant, rescued tumor volume and mass. As expected, tumors arising from ppif knockdown cells exhibited less necrosis, while rates of apoptosis were unchanged. Moreover, rates of BrdU incorporation were significantly decreased in these tumors. Necrotic cell death is characterized by loss of plasma membrane integrity resulting in a marked inflammatory response. Neutrophils and macrophages recruited to tumors often secrete growth/survival/angiogenic factors that promote tumor growth and metastasis. Consistent with this model, both macrophage and neutrophil recruitment were reduced in tumors derived from ppif knockdown cells. In addition, rates of spontaneous pulmonary metastasis were markedly decreased in mice harboring tumors derived from ppif knockdown cells compared with controls. Our data suggest that, in contrast to apoptotic cell death which limits carcinogenesis, necrotic cell death actually drives disease progression by altering the tumor microenvironment. These findings may have therapeutic implications in that they suggest that inhibition - rather than promotion - of necrotic cell death may provide a novel treatment paradigm for some cancers. Citation Format: Melissa K. James, Richard N. Kitsis. Mitochondrial necrosis pathway drives tumor progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1729. doi:10.1158/1538-7445.AM2013-1729