Antitumor and modeling studies of a penetratin-peptide that targets E2F-1 in small cell lung cancer

Abstract

E2F-1, a key transcription factor necessary for cell growth, DNA repair, and differentiation, is an attractive target for development of anticancer drugs in tumors that are E2F “oncogene addicted”. We identified a peptide isolated from phage clones that bound tightly to the E2F-1 promoter consensus sequence. The peptide was coupled to penetratin to enhance cellular uptake. Modeling of the penetratin-peptide (PEP) binding to the DNA E2F-1 promoter demonstrated favorable interactions that also involved the participation of most of the penetratin sequence. The penetratin-peptide (PEP) demonstrated potent in vitro cytotoxic effects against a range of cancer cell lines, particularly against Burkitt lymphoma cells and small cell lung cancer (SCLC) cells. Further studies in the H-69 SCLC cell line showed that the PEP inhibited transcription of E2F-1 and also several important E2F-regulated enzymes involved in DNA synthesis, namely, thymidylate synthase, thymidine kinase, and ribonucleotide reductase. As the PEP was found to be relatively unstable in serum, it was encapsulated in PEGylated liposomes for in vivo studies. Treatment of mice bearing the human small cell lung carcinoma H-69 with the PEP encapsulated in PEGylated liposomes (PL-PEP) caused tumor regression without significant toxicity. The liposome encapsulated PEP has promise as an antitumor agent, alone or in combination with inhibitors of DNA synthesis.

Keywords: :

• E2F-1
• penetratin peptide
• small cell lung cancer
• pegylated liposomes
• mouse xenografts

Disclosure of Potential Conflicts of Interest

No potential conflict of interest was disclosed.

Acknowledgments

Supported by grant NIH NCI CA 08010 and NIH NCI RO-1 CA 100098 and a grant from the Lung Cancer Research Foundation.

Authors' Contributions

XX designed and conducted experiments and helped to write the manuscript. JEK designed experiments, conducted modeling studies, and helped to write manuscript. TM designed and constructed liposomes and participated in writing of the manuscript. OG designed and conducted experiments with liposomes. KCL conducted CHiP assays and expression assays. AS isolated the peptides from phage clones. EEA designed experiments and helped in writing the manuscript. TBA performed studies with CD34⁺ cells and designed experiments. NJF conducted cell culture studies. DB designed experiments and helped write the manuscript. KWS designed experiments and helped write the manuscript. JRB had overall responsibility for the studies, designed experiments, and wrote the manuscript.