Antigen Peptide Transporter 1 (TAP1) Promotes Resistance to MEK Inhibitors in Pancreatic Cancers

Mitogen-activated protein kinase (MAPK) kinase (MEK) inhibitors show limited benefit in Kirsten rat sarcoma (KRAS) mutant pancreatic cancer due to drug resistance. To identify mechanisms of resistance to MEK inhibitor (MEKi), we employed a differential expression analysis of MEKi-sensitive versus MEKi-resistant KRAS-mutant pancreatic cancer cell lines. Here, we report that the antigen peptide transporter 1 (TAP1) expression levels of MEKi-resistant cell lines were notably higher than those of MEKi-sensitive cell lines. Suppression of TAP1 significantly sensitized the MEKi-resistant pancreatic ductal adenocarcinoma (PDAC) cells to MEKi and induced higher apoptotic rate in vitro. Moreover, knockdown of TAP1 in MEKi-resistant tumor significantly decreased tumor growth in vivo. Consistently, overexpression of TAP1 in sensitive PDAC cells resulted in increased resistance to MEKi, both in vitro and in vivo. Mechanistic studies demonstrated that TAP1 promoted chemoresistance by enhancing the transport of MEKi out of PDAC cells, leading to reduced intracellular MEKi concentration and attenuated inhibition of KRAS signaling pathways. Moreover, TAP1 expression increased spheroid formation abilities of PDAC cells. These findings suggest that TAP1 could serve as a potential marker for predicting the response of patients to MEKi. Combination of TAP1 suppression and MEKi may provide a novel therapeutic strategy for PDAC treatment.