ABSTRACT
PURPOSE: The factors preventing the translation of preclinical findings supporting the clinical development mTOR-targeted therapy in pancreatic cancer therapy remain undetermined. Stromal cell.derived factor 1α (SDF-1α)-CXCR4 signaling was examined as a representative microenvironmental factor able to promote mTOR-targeted therapy resistance in pancreatic cancer. EXPERIMENTAL DESIGN: Primary pancreas explant xenografts and in vitro experiments were used to perform pharmacodynamic analyses of SDF-1α-CXCR4 regulation of the mTOR pathway. Combinatorial effects of CXCR4, EGFR, and mTOR pharmacologic inhibition were evaluated in temsirolimus-resistant and -sensitive xenografts. Intratumoral gene and protein expressions of mTOR pathway effectors cyclin D1, c-Myc, and VEGF were evaluated. RESULTS: Baseline intratumoral SDF-1α gene expression correlated with temsirolimus resistance in explant models. SDF-1α stimulation of pancreatic cells resulted in CXCR4-mediated PI3-kinase-dependent S6-RP phosphorylation (pS6-RP) on exposure to temsirolimus. Combinatorial therapy with AMD3465 (CXCR4 small-molecule inhibitor) and temsirolimus resulted in effective tumor growth inhibition to overcome temsirolimus resistance. In contrast, SDF-1α exposure induced a temsirolimus-resistant phenotype in temsirolimus-sensitive explants. AMD3465 inhibited CXCR4-mediated intratumoral S6-RP phosphorylation and cyclin D and c-myc gene expression. Next, CXCR4 promoted intratumoral EGFR expression in association with temsirolimus resistance. Treatment with AMD3465, temsirolimus- and erlotinib-mediated tumor growth inhibition to overcome temsirolimus resistance in the explant model. Lastly, SDF-1α-CXCR4 signaling increased intratumoral VEGF gene and protein expression. CONCLUSIONS: SDF-1α-CXCR4 signaling represents a microenvironmental factor that can maintain mTOR pathway fidelity to promote resistance to mTOR-targeted therapy in pancreatic cancer by a variety of mechanisms such as recruitment of EGFR signaling and angiogenesis.
Subject(s)
Chemokine CXCL12/metabolism , Pancreatic Neoplasms/metabolism , Receptors, CXCR4/metabolism , Sirolimus/analogs & derivatives , TOR Serine-Threonine Kinases/metabolism , Animals , Cell Line, Tumor , Cyclin D1/biosynthesis , Drug Resistance, Neoplasm , ErbB Receptors/antagonists & inhibitors , ErbB Receptors/metabolism , Erlotinib Hydrochloride , Female , Humans , Mice , Mice, Nude , Neoplasm Transplantation , Pancreatic Neoplasms/drug therapy , Phosphatidylinositol 3-Kinases/metabolism , Phosphorylation , Protein Kinase Inhibitors/pharmacology , Proto-Oncogene Proteins c-myc/biosynthesis , Pyridines/pharmacology , Quinazolines/pharmacology , RNA Interference , RNA, Small Interfering , Receptors, CXCR/genetics , Receptors, CXCR4/antagonists & inhibitors , Receptors, CXCR4/genetics , Signal Transduction , Sirolimus/pharmacology , TOR Serine-Threonine Kinases/antagonists & inhibitors , Transplantation, Heterologous , Tumor Microenvironment , Vascular Endothelial Growth Factor A/biosynthesisABSTRACT
Wnt7a is known to be a tumor suppressor that is lost in NSCLC, but no mechanism of loss has been established. Methylation of promoter regions has been established as a common mechanism of loss of tumor suppressor expression in NSCLC. We previously demonstrated that loss of Wnt7a in non-transformed lung epithelial cell lines led to increased cell growth, altered 3-D culture growth, and increased migration. The Wnt7a promoter has a higher percentage of methylation in NSCLC tumor tissue compared to matched normal lung tissue and methylation of the promoter region leads to decreased activity. We treated H157 and H1299 NSCLC cell lines with 5-Aza-2'-deoxycytidine and detected loss of Wnt7a promoter methylation, increased Wnt7a expression, and increased activity of the Wnt7a lung signaling pathway. When DNMT1 expression was knocked down by shRNA, expression of Wnt7a increased and methylation decreased. Together these data suggest that in NSCLC, Wnt7a is lost by methylation in a subset of tumors and that this methylation is maintained by DNMT1. Restoration of Wnt7a expression through demethylation could be an important therapeutic approach in the treatment of NSCLC.
