RT Journal Article
SR Electronic
T1 Identifying the ErbB/MAPK Signaling Cascade as a Therapeutic Target in Canine Bladder Cancer
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP mol.119.115808
DO 10.1124/mol.119.115808
A1 Kathryn E Cronise
A1 Belen G Hernandez
A1 Daniel L Gustafson
A1 Dawn L Duval
YR 2019
UL http://molpharm.aspetjournals.org/content/early/2019/05/02/mol.119.115808.abstract
AB Transitional cell carcinoma (TCC) of the bladder comprises 2% of diagnosed canine cancers. TCC tumors are generally inoperable and unresponsive to traditional chemotherapy, indicating a need for more effective therapies. BRAF, a kinase in the mitogen-activated protein kinase (MAPK) pathway, is mutated in 70% of canine TCCs. In this study, we use BRAF mutant and wild-type TCC cell lines to characterize the role of BRAF mutations in TCC pathogenesis and assess the efficacy of inhibition of the MAPK pathway alone and in combination with other gene targets as a treatment for canine TCC. Analysis of MAPK target gene expression and assessment of ERK1/2 phosphorylation following serum starvation indicated constitutive MAPK activity in all TCC cell lines. BRAF mutant TCC cell lines were insensitive to the BRAF inhibitor vemurafenib, with IC50 values greater than 5 μM, but exhibited greater sensitivity to a "paradox-breaking" BRAF inhibitor (IC50: 0.2-1 μM). All TCC cell lines had IC50 values less than 7 nM to the MEK1/2 inhibitor trametinib independent of their BRAF mutation status. ERK1/2 phosphorylation decreased after 6-hour treatments with MAPK inhibitors, but rebounded by 24 hours, suggesting the presence of resistance mechanisms. Microarray analysis identified elevated expression of the ErbB family of receptors and ligands in TCC cell lines. The pan-ErbB inhibitor sapitinib synergized with BRAF inhibition in BRAF mutant Bliley TCC cells and synergized with MEK1/2 inhibition in Bliley and BRAF wild-type Kinsey cells. These findings suggest the potential for combined MAPK and ErbB receptor inhibition as a therapy for canine TCC.SIGNIFICANCE STATEMENT The results of this study (1) identify a novel combination strategy for canine bladder cancer treatment: targeting the ErbB/MAPK signaling cascade and (2) establish the utility of canine bladder cancer as a naturally-occurring model for human MAPK-driven cancers.