Abstract 3475: PI3K inhibition by the βGBP cytokine in colon cancer cells. Combined activation of intrinsic and extrinsic apoptosis

Abstract

Abstract βGBP (monomeric β-galactoside binding protein) is a newly discovered antiproliferative cytokine produced by CD4+ and CD8+-activated T cells and endogenously released by somatic cells. In normal cells βGBP negatively regulates the cell cycle; in cancer cells βGBP induces apoptosis through pathways which involve inhibition of mitogenic signaling and inhibition of survival signaling. Mechanisms of action initiate with downregulation of class 1A and class 1B phosphatidylinositol 3-OH kinase (PI3K) via functional inhibition of their p110 catalytic subunit. The study has the purpose of defining signaling routes to apoptosis downstream of PI3K in cells from colorectal carcinomas, which epitomise cancers made aggressive and refractory to therapies by accumulated genetic changes. We examined cancer cells of primary (SW480) and metastatic derivation (SW620, LoVo). Pathways investigated consequent to PI3K downregulation are those relating to Ras-ERK signaling and cell cycle parameters, to Akt signaling and to Rac mediated signaling. Apoptosis was assessed by changes in mitochondrial membrane potential, redistribution of phosphatidylserine, caspase 3 activation and DNA fragmentation. We found colon cancer cells to be sensitive to minimal doses of βGBP which, while unable to inhibit Ras-ERK activity and Akt expression consequent to inhibition of PI3K activity, led to apoptosis through unprecedented outstanding events: a dramatic rearrangemant of the cytoskeletal network and the concurrent activation of both intrinsic and extrinsic apoptosis. Mechanisms involved related to two set of events. One event was characterised by overexpression and stabilisation of cyclin E, inhibition of DNA synthesis, Chk2 activation and overexpression of deregulated E2F1, a condition for the activation of intrinsic apoptosis; the other related to changes in macromolecular mobility in the plane of the membrane and CD95/Fas clustering, a condition for the activation of extrinsic apoptosis. In vivo experiments in immunodeficient mice show that βGBP inhibits/prevents tumor development with no harm to the mouse. The ability of βGBP to induce death in cancer cells notoriously resistant to apoptosis, and to induce death by combined routes is a unique property with important therapeutic implications. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3475.