PF-04691503 is a dual inhibitor of both PI3K and mTOR, inhibits PI3K signaling in cancer cell lines, and exhibits in vitro and in vivo anti-proliferative activity in PI3K-pathway driven cell lines. It is a nanomolar inhibitor of all 4 isoforms of the catalytic subunit of PI3K and of both TORC1 and TORC2. Anti-cancer activity of the inhibitor is hypothesized to be through inhibition of survival, proliferative, and anti-apoptotic processes. Phosphorylation of the protein kinase, Akt, is associated with activation of the phosphatidyl 3-kinase (PI-3K)/mammalian target of rapamycin (mTOR) signaling pathway, which plays a role in cell proliferation (Witzig and Kaufmann 2006). Recent studies by Gulmann et al (2005) showed increased pAKT in human lymphoma samples, and those of Rassidakis et al (2005) suggested that inhibition of Akt phosphorylation (pAKT) may be of value in the treatment of lymphoma. Using flow cytometry we report that cells obtained from 10 of 11 lymph node biopsies of dogs with lymphoma exhibit detectable pAKT using a phospho-Akt (Ser473) antibody, compared to an IgG isotype control or a competative phospho-Akt (Ser473) blocking peptide. Cells from normal canine lymph nodes do not exhibit detectable pAKT. The majority of the pAKT signal was generated from lymphoblasts present in the malignant, but not in the normal, lymph nodes.

In separate studies, lymph node cells obtained from healthy dogs and dogs with lymphoma were stimulated in vitro with the mitogen, Con A. The novel PI3K/mTOR dual inhibitor, PF-04691503, produced dose dependent inhibition of proliferation as exemplified in a dog with T-cell lymphoma (EC50 = 18 nM)) and in a normal dog (EC50 = 53 nM)). No pAKT signal could be detected in peripheral blood mononuclear cells, from normal or lymphoma patients stimulated with hu-IGF-1 (the endogenous ligand for PI3), Con-A or LPS.

These data suggest that PI-3 kinase and pAKT (1) are activated in canine lymphoma, (2) play a role in the lymphoproliferation associated with this disease, (3) represent legitimate targets for therapeutic intervention in lymphoma, and (4) can be studied ‘translationally’ in dogs as a model for humans.

Gulmann C, Espina V, Petricoin E, et al. Proteomic analysis of apoptotic pathways reveals prognostic factors in follicular lymphoma. Clin Cancer Res 11:5847-5855, 2005.

Rassidakis GZ, Feretzaki M, Atwell C, et al. Inhibition of Akt increases p27 Kip1 levels and induces cell cycle arrest in anaplastic large cell lymphoma. Blood 105:827-829, 2005.

Witzig TE and Kaufmann SH. Inhibition of phosphatidyl 3-kinase (PI-3K)/mammalian target of rapamycin (mTOR) pathway in hematologic malignancies. Current Treatment Options in Oncology 7:285-294, 2006.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5043.