Abstract 1237: Antitumor studies of an E2f1 promoter sequence binding peptide - penetratin conjugate as a molecule targeting E2f in prostate cancer

BACKGROUND: Mutation or inactivation of the retinoblastoma protein is frequently involved in prostate cancer tumorigenesis resulting in overexpression/deregulation of E2F activity. E2F1-3a overexpression induces genes involved in DNA synthesis and leads to abnormal cellular proliferation, tumor growth, and invasion. Therefore, inhibiting the overexpression of one or more activating E2Fs is a recognized target in cancer therapeutics. In our previous studies we showed that a novel penetratin conjugated 7-mer peptide (PEP) bound tightly to an immobilized consensus E2F1 promoter sequence, was cytotoxic at low micro molar concentrations to many malignant cell lines and as the PEP was unstable in serum, the PEP was encapsulated in PEGylated liposomes and treatment of tumor xenografts of small cell lung cancer H-69 and DU145 tumors propagated in mice caused tumor regression. OBJECTIVE: To determine the antitumor activity and stability of two different modified penetratin peptides: D-Arg PEP (substituting L-Arginine with D-Arginine in the peptide sequence) and N-acetylated as well as C-methylated PEP analog. METHODS: DU145 (prostate cancer) and H196 (small cell lung cancer) cells were used. To compare the efficacy of the peptides, we tested the IC50s of peptides at different time points using the MTS assay. Drug combination experiment results were analyzed using the combination index (CI) method. Peptide conformational studies were carried out using the Amber 12 suite of biomolecular simulation programs. RESULTS: Molecular simulation studies showed that the D-Arg PEP secondary structure is more stable than the L-Arg peptide structure in water. D-Arg PEP was more potent compared to L-Arg PEP, and it was also found to be more resistant to degradation by serum proteases than the L-form. The other modified form, N-acetylated, C-methylated PEP was marginally more effective than the unmodified PEP. Drug combination studies showed that the D-Arg PEP in combination with docetaxel, caused synergistic cytotoxicity against DU 145 cells. Our findings validate D-Arg peptide, an inhibitor of E2F1and 3a transcription, as a drug candidate for targeted molecular therapy of prostate cancers with elevated levels of activated E2F’s. Studies in progress are evaluating the combination of the PEGylated liposome encapsulated D-Arg PEP in combination with docetaxel against DU145 xenografts and against primary prostate cancer cells. Supported in part by a grant from the Lung Cancer Research Foundation. Citation Format: Tazeem Shaik, Nitu Bansal, Nadine Johnson Farley, John Kerrigan, Olga Garbuzenko, Tamara Minko, Emine Abali, Zoltan Szekely, Kathleen Scotto, Debabrata Banerjee, Joseph Bertino. Antitumor studies of an E2f1 promoter sequence binding peptide - penetratin conjugate as a molecule targeting E2f in prostate cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1237. doi:10.1158/1538-7445.AM2015-1237