In vitro effects of the PI3K/mTOR dual-inhibitor, VDC597, in canine lymphoma and leukemia

Background Hematopoietic tumors are among the most common tumors in dogs and advancements in treatment are necessary to improve outcomes. The phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K), AKT serine/threonine kinase (AKT), mechanistic target of rapamycin (mTOR) signaling pathway is frequently dysregulated in canine hematopoietic tumors and contributes to poorer outcomes. Targeted signal transduction inhibition offers a potentially beneficial avenue for improving treatment of these tumors. Methods This study aimed to investigate the efficacy of a PI3K/mTOR dual-inhibitor, VDC597, against canine lymphoma and leukemia cells in vitro andto immunohistochemically evaluate this signaling pathway in spontaneous canine B-cell lymphoma. In vitro efficacy of VDC597, alone and incombination with standard of care chemotherapy drugs, was assessed via cell viability and growth inhibition assays, live cell imaging and cell deathassays, VEGF ELISA, and western and immunohistochemistry to evaluate activation of signal transduction. 118 samples of lymph nodes from 84 dogs diagnosed with spontaneous B-cell lymphoma were examined and scored immunohistochemically for pathway activation. Tests for statistical significance and comparisons between groups were made via ANOVA, Kruskal-Wallis, Mann-Whitney, two tailed t-test, or Mantel-Cox methodologies as appropriate. Results VDC597 inhibited PI3K/AKT/mTOR signal transduction, reduced cell viability and proliferation, promoted cell death, and inhibited angiogenic factor production in a dose dependent manner in canine lymphoma/leukemia cells in vitro. Expression of phosphorylated proteins indicating pathway activation was variable in samples of spontaneous canine B-cell lymphoma. In these samples, phosphorylated protein expression correlated in the hypothesized manner to two prognostic indicators, but not to outcome data. Major histocompatibility complex class II expression and post-treatment relapse status were correlated to phosphorylated AKT and phosphorylated eukaryotic translation initiation factor 4E-binding protein 1 expression, respectively. Conclusions These results suggest that PI3K/mTOR inhibition may be a useful anti-cancer strategy for the treatment of canine lymphoma and leukemia. However, immunohistochemical results suggest that signaling pathway activation is variable in canine B-cell lymphoma and that more research is needed to elucidate the prognostic role of pathway activation in this tumor type.