Abstract
Patients with Ulcerative Colitis (UC) have an increased risk to develop colitis-associated colorectal cancer (CAC). Here, we found that protein expression of ABCB1 (ATP Binding Cassette Subfamily B Member 1) / MDR1 (multidrug resistance 1) was diminished in the intestinal mucosa of patients with active UC with or without CAC, but not in non-UC patients with sporadic colon cancer. We investigated the consequences of ABCB1/MDR1 loss-of-function in a common murine model for CAC (AOM/DSS). Mice deficient in MDR1A (MDR1A KO) showed enhanced intratumoral inflammation and cellular damage, which were associated with reduced colonic tumor size and decreased degree of dysplasia, when compared to wild-type (WT). Increased cell injury correlated with reduced capacity for growth of MDR1A KO tumor spheroids cultured ex-vivo. Gene expression analysis by microarray demonstrated that MDR1A deficiency shaped the inflammatory response towards an anti-tumorigenic microenvironment by downregulating genes known to be important mediators of cancer progression (PTGS2 (COX2), EREG, IL-11). MDR1A KO tumors showed increased gene expression of TNFSF10 (TRAIL), a known inducer of cancer cell death, and CCL12, a strong trigger of B cell chemotaxis. Abundant B220+ B lymphocyte infiltrates with interspersed CD138+ plasma cells were recruited to the MDR1A KO tumor microenvironment, concomitant with high levels of immunoglobulin light chain genes. In contrast, MDR1A deficiency in RAG2 KO mice that lack both B and T cells aggravated colonic tumor progression. MDR1A KO CD19+ B cells, but not WT CD19+ B cells, suppressed growth of colonic tumor-derived spheroids from AOM/DSS-WT mice in an ex-vivo co-culture system, implying that B-cell regulated immune responses contributed to delayed tumor development in MDR1A deficiency. In conclusion, we provide first evidence that loss of ABCB1/MDR1 function may represent an essential tumor-suppressive host defense mechanism in CAC.
Highlights
Patients with long-term Ulcerative Colitis (UC) have an increased risk of developing colitisassociated colorectal cancer (CAC) [1]
Reduced ABCB1/MDR1 mRNA expression has been associated with active UC [46] and early colorectal cancer (CRC) [14]
We found that lack of ABCB1/MDR1-mediated signals promoted a B cell-dominated tumor immunogenic microenvironment and resulted in an increase in tumor cell damage, which correlated with inhibition of inflammation-associated tumor growth
Summary
Patients with long-term Ulcerative Colitis (UC) have an increased risk of developing colitisassociated colorectal cancer (CAC) [1]. Initial extent [2] and duration [3] of chronic inflammation are recognized to be among the key risk factors. Multi-drug resistance in colitis-associated tumorigenesis collection and analysis, decision to publish, or preparation of the manuscript
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