E2F1-3a overexpression due to amplification or to mutation or loss of the retinoblastoma gene, induces genes involved in
DNA synthesis and leads to abnormal cellular proliferation,
tumor growth, and invasion. Therefore, inhibiting the overexpression of one or more of these activating E2Fs is a recognized target in
cancer therapeutics. In previous studies we identified by phage display, a novel 7-mer
peptide (PEP) that bound tightly to an immobilized consensus E2F1 promoter sequence, and when conjugated to
penetratin to increase its uptake into cells, was cytotoxic to several malignant cell lines and human prostate and
small cell lung cancer xenografts. Based on molecular simulation studies that showed that the D-Arg
penetratin peptide (D-Arg PEP) secondary structure is more stable than the L-Arg PEP, the L-Arg in the
peptide was substituted with D-Arg. In vitro studies confirmed that it was more stable than the L- form and was more cytotoxic as compared to the L-Arg PEP when tested against the human castrate resistant cell line, DU145 and the human
lung cancer H196 cell line. When encapsulated in PEGylated
liposomes, the D-Arg-PEP potently inhibited growth of the DU145 xenograft in mice. Our findings validate D- Arg PEP, an inhibitor of E2F1and 3a transcription, as an improved second generation drug candidate for
targeted molecular therapy of
cancers with elevated levels of activated E2F(s).