Mari Lowe Center for Comparative Oncology Research

3800 Spruce Street, Philadelphia, PA 19104

Characterization of NF-kappa(k)B activity and the effects of its inhibition by NEMO binding domain peptide in spontaneously occurring canine cancer

NF-kappa(k)B is a highly evolutionary conserved family of transcription factors that play important roles in the regulation of genes involved in immune responses, inflammation, stress responses, cellular proliferation, differentiation and apoptosis. However, the role of NF-kappa(k)B in oncogenesis has only been recognized recently. NF-kappa(k)B activation is highly regulated and in the inactive state, NF-kappa(k)B proteins are sequestered in the cytoplasm through their association with the inhibitory IkB and p100 proteins. Impaired regulation of NF-kappa(k)B activation can lead to loss of its highly controlled inducibility and constitutive activity. This results in aberrant expression of anti-apoptotic and pro-survival genes and genes that are involved in cell cycle control and migration, processes that occur in the initiation and progression of cancer. Indeed, NF-kappa(k)B is constitutively active in many solid tumors, where it contributes to malignant cell proliferation, growth and survival. NF-kappa(k)B also regulates the expression of a number of genes that are important in the process of tumor metastases and constitutive activation of NF-kappa(k)B has been reported in highly metastatic tumor cell lines. Finally, recent studies have indicated that constitutive NF-kappa(k)B activation in malignant cells is responsible for their observed chemoresistance.

As such, attention has focused on the use of NF-kappa(k)B inhibitors as potential therapeutic agents to prevent cancer progression and metastasis and increase sensitivity to currently used chemotherapeutics. Recent studies have shown that inhibitors of NF-kappa(k)B activation suppress the development of carcinogen-induced tumors, inhibit cancer cell growth, induce apoptosis in malignant cell populations and may sensitize malignant cells to the apoptotic effects of more conventional chemotherapeutic agents. The Nemo Binding Domain (NBD) peptide is an established selective inhibitor of IKK and inhibits NF-kappa(k)B activation. This leads to inhibition of cell proliferation and induction of apoptosis. Importantly, it has been shown in vivo that the appropriate dosage of NBD peptide does not affect basal NF-kappa(k)B activity while NF-kappa(k)B activity that is inducible by proinflammatory stimuli is effectively blocked. This indicates that the normal cellular functions of NF-kappa(k)B are unaffected by NBD peptide and suggests that activation via TNF and EGF which contribute to oncogenesis may be selectively blocked by NBD peptide.

Basic and translational researchers Dr. Michael May and Dr. Nicola Mason at PennVet are working together to evaluate the role of NF-kappa(k)B in canine oncogenesis and the potential therapeutic use of NBD peptide to inhibit NF-kappa(k)B in the treatment of canine cancer. Using low passage primary tumor cell lines, generated from spontaneously occurring canine tumors obtained from the PennVet Tumor Tissue Bank, Drs. Mason and May are characterizing the role of NF-kappa(k)B family members and the effects of the NBD peptide on NF-kappa(k)B activation, anti-apoptotic, tumor suppressor and cell cycle gene expression and in vitro viability, growth and proliferation in a variety of canine cancers. The overall hypothesis is that NBD peptide will inhibit constitutive NF-kappa(k)B activation resulting in decreased cell growth, proliferation and survival. It is anticipated that this work will lead to a pilot clinical trial to evaluate the safety and efficacy of the NBD peptide as an adjunct therapy in the treatment of a wide range of canine cancers that include transitional cell carcinoma, mesothelioma and lymphoma. This work is supported by the NIH/Merck Summer Research Program 2008.