Targeting Multidrug Resistance- Assiciated Protein 4 (MRP4/ ABCC4) in Pancreatic Cancer

MAY, MARIA; DIEZ, FEDERICO; CAROZZO, ALEJANDRO; COPSEL, SABRINA; MOHR, NORA RAQUEL; GOMEZ, NATALIA; FERNANDEZ, NATALIA; DAVIO, CARLOS; ITURBE, JULIAN; SHAYO, KARINA

Barcelona

Congreso; WC ESMO; 2016

ESMO

BackgroundPancreatic ductal adenocarcinoma (PDAC) is one of the most brutal types of cancer, and because of its earlydevelopment of resistance to standard therapeutic agents, and its late diagnosis, it seems imperative to identifyand validate new and key biomarkers and therapeutic targets.A lot of evidence relates disturbances in cAMP cascade and PDAC, making this second messenger signalingpathway potentially oncogenic in this setting. To the already known classical mechanisms of regulation ofcAMP, it is recently added its extrusion to the extracellular compartment mediated principally by MRP4. In thisway, we described the key role of MRP4 in the regulation of cAMP levels in acute myeloid leukemia cellssuggesting that this transporter may represent a new potential target for leukemia differentiation therapy. Sincethen, numerous works arose describing the antiproliferative effects of MRP4-inhibtion, its potential as a markerof poor prognosis and its up-regulation in several tumors.Regarding PDAC, we have newly described a deregulation in the expression of MRP4 that correlates directlywith cell dedifferentiation. The regulatory effect produced by silencing this transporter alters cAMP efflux, andsignificantly correlates with proliferative and migratory processes (unpublished data).The aim of this work was, on the one hand, to study in vivo effects of MRP4 inhibition in PDAC humanxenografts and, on the other hand, to explore the expression of MRP4 in human PDAC samples in order tovalidate MRP4 as a new potential therapeutic target and biomarker for PDAC.Mat & MetHuman tumor xenografts were established by injecting subcutaneously immunodeficient mice (NUDE andNSG) with PANC-1 cells expressing two different selected clones for shRNA against MRP4; scrambled wasused as control. Tumor size was measured three times per week during 35 days.Human PDAC samples, including primary and metastatic setting, were included in the analysis. IHC for MRP4,Pan-CK, apoptotic (tunnel) and proliferation (ki-67) markers, were performed in both mice and human samples.Scoring of MRP4 label and its sub- cellular localization was assessed.ResultsSilencing MRP4 strongly reduced tumor growth in both animal models. Moreover, the incidence of palpabletumors was greatly decreased in silenced xenografts, indicating a loss of tumorigenicity of these cells.When comparing both silenced clones, effects on both tumor growth and incidence strictly correlated with theexpression level of MRP4.Routine H&E evaluation revealed significant differences regarding the amount of epithelial neoplastic cells,apoptotic bodies and mitosis between silenced and control tumors. These findings were confirmed by IHC forPan-CK, tunnel and ki67 respectively.Although the apoptotic index was similar in the three clones, the cell exchange ratio (n° mitosis/n° apoptosis),was significantly lower in the MRP4-silenced clones indicating that cells with lower MRP4 expression,proliferate less and die more.Regarding human PDAC samples, MRP4 was expressed in 100% (8/8) of the individuals with disregard of theclinical stage of the disease. We found a clear association between the staining intensity of membranousMRP4 and ki67, suggesting that there is a subset of cells within the tumor that display more MRP4 and whichare actively proliferating.ConclusionOur results allows for validating MRP4 as a new therapeutic target, and as a possible biomarker for PDAC.Retrospective studies with human samples are being carried out with a bigger number of patients.