Inflammatory microenvironment accelerates liver tumor growth and metastasis by mobilizing circulating endothelial progenitor cells and increasing cancer stem like cell populations

Abstract

Objective: We aim to explore the mechanism of liver tumor growth and metastasis under inflammatory microenvironment by studying the direct role of hepatic I/R injury on mobilization of circulating endothelial progenitor cells (EPCs) and promotion of stemness features of liver cancer cell itself.

Methods: Small numbers of rat liver tumor cells (CRL1601, 500-1000 cells) were injected into right portal vein of male Buffalo rats with or without partial hepatic I/R injury (20/20 minutes duration on right and median lobes). The tumor growth and metastases were longitudinally monitored by Xenogen in vivo imaging system (IVIS) in live animals. Blood samples were taken at day1, 7, 14, 21 and 28 for detection of EPCs (CD133+CD34+) and cancer stem like cells-CSCs (CD133+CD90+, CD133+EpCAM+, CD90+EpCAM+). The proportions of CSCs were also compared in rat liver tumor tissues. To confirm the invasive features of the tumor developed in inflammatory microenvironment induced by hepatic I/R injury, the rat liver tumors were further orthotopically implanted into the liver of nude mice for a series of passages. The nude mice tumor growth/metastasis and their circulating EPCs/CSCs were also compared.

Results: Aggressive and early rat liver tumor development and metastasis were mainly found in I/R injury group. Significant higher levels of IP10/MIP2/VEGF induced by hepatic I/R injury subsequently mobilized EPCs (CD133+CD34+) to circulation compared to the control group (day1: 35 vs 12/10^5cells, p=0.004; day7: 64 vs 38/10^5cells, p=0.025; day21: 24 vs 9/10^5cells, p=0.028; day28: 18 vs 12/10^5cells, p=0.006). CD133+ cells were also found in lung metastatic nodules in I/R injury group. The numbers of circulation and tumor CSCs were also significantly increased in I/R injury group (Circulation: day 1:23.5 vs7/10^5cells, p=0.006; day28: 18.5 vs 5/10^5cells, p=0.006; Rat tumor: 290 vs 40/10^5cells, p=0.047). The nude mice implanted with tumor from I/R injury group also had higher circulation levels of EPCs (17 vs 4/10^5cells, p=0.004) and CSCs (43 vs 0/10^5cells, p=0.01). Their aggressive tumor growth and metastasis were also confirmed. The tumor from the rats underwent hepatic I/R injury could be serially implanted into nude mice orthotopically for more than 10 passages compared to 5-6 passages in non I/R group. Furthermore, IP10 treated EPCs promoted liver tumor growth and metastasis in an orthotpic liver cancer nude mice model compared to the non-IP10 treated EPCs.

Conclusion: Inflammatory microenvironment induced by hepatic I/R injury promoted liver tumor growth and metastasis by increasing cancer stem like cell populations and mobilizing circulating endothelial progenitor cells. The EPCs educated by IP10, a secretary inflammatory chemokine during hepatic I/R injury, have great potential to promote liver tumor growth and metastasis.