Evaluation of Expression and Function of Vegfr2, Pdgfrα, Pdgfrβ, Kit, and Ret in Canine Apocrine Gland of the Anal Sac Adenocarcinoma and Thyroid Carcinoma. Graduate Program in Comparative and Veterinary Medicine. The Ohio State University, 2012;84.
Biological responses to toceranib phosphate have been reported in both canine apocrine gland anal sac adenocarcinomas (AGASACA) and thyroid carcinomas (TC). However, little is known about the molecular biology of either of these tumor types and the mechanism of the biological activity of toceranib. In the present study, we investigated the presence and expression of known targets of toceranib and interrogated AGASACA and TC samples for the expression of VEGFR2, PDGFR, KIT and RET at both the message and protein level to begin to dissect the molecular basis for this observed activity. Samples from 24 primary AGASACA, 11 with paired metastatic lymph nodes, and 15 TC were evaluated using reverse-transcriptase polymerase chain reaction for detection of mRNA, phosphoprotein arrays to screen for evidence of protein phosphorylation, and tissue microarrays for immunohistochemical evaluation of protein expression. Messenger RNA from VEGFR2, PDGFR, KIT and RET was detected in all AGASACA samples. Messenger RNA for VEGFR2, PDGFR, and Kit was detected in all TC samples, while mRNA for Ret was amplified in 10/15 TC samples. Evidence of phosphorylation of VEGFR2, PDGFR, and KIT was not detected on phosphoprotein arrays in either tumor. Evidence of phosphorylation of RET was detected in 54% of the primary AGASACA and 20% of TC. Positive immunoreactivity for VEGFR2 was noted in 19/24 primary and 6/10 metastatic AGASACA and 6/15 TC samples. Positive immunoreactivity for KIT was noted in 8/24 primary and 3/10 metastatic AGASACA and 9/15 TC samples. PDGFR was noted in all primary and metastatic AGASACA and all of the TC samples. PDGFR expression was noted in 4/24 primary and 1/10 metastatic AGASACA and 4/15 TC tumor cells, while intense stromal staining was noted in all tumor samples. Known targets of toceranib are present in both AGASAC and TC at both the level of message and protein expression. Our findings of VEGFR2 and PDGFR protein expression and phosphorylation of RET merit further investigation as to their roles in the biology of AGSACA and TC as well as to their contribution to the observed response to toceranib.