CAFs shape myeloid-derived suppressor cells to promote stemness of intrahepatic cholangiocarcinoma via 5-lipoxygenase.

Abstract

BACKGROUND AND AIMS\nWe previously demonstrated that cancer-associated fibroblasts (CAFs) promote tumor growth via recruiting of myeloid-derived suppressor cells (MDSCs). 5-lipoxygenase (5-LO) is highly expressed in myeloid cells and critical for synthesizing leukotriene B4 (LTB4), which is involved in tumor progression via acting its receptor Leukotriene B4 receptor type 2 (BLT2). In this study, we investigated whether and how CAFs regulate MDSC function to enhance cancer stemness, the driving force of the cancer aggressiveness and chemotherapy refractoriness, in highly desmoplastic intrahepatic cholangiocarcinoma (ICC).\n\n\nAPPROACH AND RESULTS\nRNA-sequencing analysis revealed enriched metabolic pathways but decreased inflammatory pathways in cancer MDSCs compared with blood MDSCs from ICC patients. Co-injection of ICC patient-derived CAFs promoted cancer stemness in an orthotopic ICC model, which was blunted by MDSC depletion. Conditioned media (CM) from CAF-educated MDSCs drastically promoted tumorsphere formation efficiency and stemness marker gene expression in ICC cells. CAF-CM stimulation increased expression and activity of 5-LO in MDSCs while 5-LO inhibitor impaired the stemness-enhancing capacity of MDSCs in vitro and in vivo. Furthermore, IL-6 and IL-33 mainly expressed by CAFs mediated hyperactivated 5-LO metabolism in MDSCs. We identify the LTB4-BLT2 axis as the critical downstream metabolite signaling of 5-LO in promoting cancer stemness, as treatment with LTB4 that were elevated in CAF-educated MDSCs or blockade of BLT2 that was preferentially expressed in stem-like ICC cells significantly reduced stemness-enhancing effects of CAF-educated MDSCs. Finally, BLT2 blockade augmented chemotherapeutic efficacy in ICC patient derived-xenograft (PDX) models.\n\n\nCONCLUSIONS\nOur study reveals a previously unrecognized role for CAFs in orchestrating the optimal cancer stemness-enhancing microenvironment by educating MDSCs and suggests 5-LO/LTB4-BLT2 axis as promising therapeutic targets for ICC chemoresistance by targeting cancer stemness.