Abstract 5073: mPGES-1 deficiency impairs self-renewal properties of colon cancer stem cells

Dysregulation of prostaglandin E2 (PGE2) signaling is a hallmark of many cancers, including colorectal cancer (CRC). Direct suppression of inducible PGE2 synthesis by genetic deletion of Ptges1 (mPGES-1) affords dramatic cancer protection to the colon. However, the precise mechanisms by which this effect occurs remain incompletely understood. Recent evidence points to a fundamental role of PGE2 signaling in the expansion of cancer stem cells. In the present study, using an organoid system established from Apc mutant mice, we have evaluated the influence of PGE2 and related prostanoids on the viability of cancer stem cells in the colon. To establish cancer organoids, colon tumors were harvested from 16 week-old ApcΔ14/+ mice with or without mPGES-1 (D14:WT and D14:KO). Colon tumor multiplicity in D14:KO mice is approximately half the number of tumors in D14:WT mice. Tumor tissues were digested with collagenase and dispase, and cultured in Matrigel with complete organoid media. Organoid growth was scored daily over a one-week time period, and passaged. Tumor organoids generated from D14:WT and D14:KO mice showed no obvious differences in their growth characteristics nor morphological features during the first week of ex-vivo growth. After the first passage, however, the growth rate of D14:KO organoids was significantly reduced (175% vs. 80%, WT and KO, respectively), and by the second passage, D14:KO organoids failed to maintain cell viability. Immunohistochemical analysis of the organoids showed strong nuclear localization of s-catenin and loss of Apc expression regardless of mPGES-1 genotype, indicating intact Wnt-driven cancer growth mechanisms that were independent of inducible PGE2 signaling. These observations indicate that alternative mechanisms are contributing to the compromised stem cell expansion observed in the D14:KO organoids. Since mPGES-1 is expressed within the tumor stroma, we postulated that the inactivation of mPGES-1 would cause a marked microenvironmental change. To test this possibility, we used GC-MS/MS to measure a panel of prostanoids within the tumor tissue. Targeted lipidomic analysis showed significant metabolite redirection of tissue prostanoids, with a significant increase (2-fold) in PGD2in the D14:KO mice. Interestingly, administration of PGD2 was recently shown to reduce the growth and regeneration potential of stem cells within a hair follicle organ culture system. Given new evidence that PGD2 may have a direct influence on ‘stem cell-ness9 in other organ systems, we propose that the colon tumor microenvironment, deficient in inducible PGE2, may undergo permanent molecular changes that directly influence the growth characteristics and viability of cancer stem cells as reflected in our organoid culture system. New data is presented to define the long-lasting influence of eicosanoid metabolic changes on cancer-derived stem cell viability and proliferative capacity. Citation Format: Masako Nakanishi, Daniel W. Rosenberg. mPGES-1 deficiency impairs self-renewal properties of colon cancer stem cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5073.