MUC4 is the principal mediator of TNFα-induced trastuzumab resistance and fosters an immunosuppressive tumor microenvironment in HER2+ breast cancer

BRUNI, SOFÍA; MERCOGLIANO, MARÍA F.; MAURO, FLORENCIA L.; SCHILLACI, ROXANA; DE MARTINO, MARA; ELIZALDE, PATRICIA V.

Congreso; Sociedad Argentina de Investigación Clínica; 2019

About 13-20% of breast cancer (BC) patients are HER2positive (HER2+) and receive trastuzumab (T), an anti-HER2 monoclonal antibody,but 30-50% of them relapse. We have demonstrated that tumor necrosis factoralpha (TNF) induces the expression of the transmembrane glycoprotein mucin 4(MUC4) that shields T epitope in HER2, impairing its antitumor effects, and thatthe soluble and transmembrane TNFα (sTNFα, tmTNFα) inhibitor Etanercept (E)downregulated MUC4 expression and sensitized de novo T-resistant BC xenografts to T. Here, we studied the invivo participation of MUC4 on T resistance and on antitumor innate immuneresponse.T-resistant JIMT-1 cell line was transduced with adoxycycline (Dox)-inducible MUC4 shRNA construct (JIMT-shMUC4). To block TNFα,we used E or the dominant negative-TNF protein INB03 (DN), able to neutralizesTNF. Nude mice bearing JIMT-1-shMUC4 tumors were assigned to the experimental(+Dox 2mg/ml in water) or control group (−Dox) and treated with IgG, T, E (5mg/kg), DN (10 mg/kg), T+E or T+DN i.p. twice a week. Tumor volume wasmonitored routinely. Tumor-infiltrating immune cells were evaluated byimmunofluorescence and flow cytometry.   In control groups, only T+E and T+DN inhibited tumorgrowth (72% and 75%, respectively, P<0.0001 vs. IgG).  MUC4 knockdown sensitized tumors to T at comparablelevels to T+E and T+DN (62%, 78% and 76% respectively, P<0.0001 vs. IgG). Thiswas accompanied by an increase in NK cells activation and degranulation and anincrease in M1/M2 macrophages ratio in the tumor microenvironment (TME). UponMUC4 downregulation, myeloid-derivedsuppressor cells infiltration was reduced and macrophage recruitment wasenhanced in the tumor bead of IgG+Dox vs. IgG-Dox groups. We conclude that MUC4is the major player in TNF-induced T resistance in vivo. In addition, MUC4 favors an immunosuppressive TME. Wepropose that patients with HER2+ and MUC4+ tumors should be treated with T and TNF-blockingagents to avoid resistance.