Inhibition of ovarian cancer cell proliferation by a cell cycle inhibitory peptide fused to a thermally responsive polypeptide carrier

Abstract

Current treatment of solid tumors is limited by normal tissue tolerance, resulting in a narrow therapeutic index. To increase drug specificity and efficacy and to reduce toxicity in normal tissues, we have developed a polypeptide carrier for a cell cycle inhibitory peptide, which has the potential to be thermally targeted to the tumor site. The design of this polypeptide is based on elastin‐like polypeptide (ELP). The coding sequence of ELP was modified by the addition of the cell penetrating peptide Bac‐7 at the N‐terminus and a 23 amino acid peptide derived from p21 at the C‐terminus (Bac‐ELP1‐p21). Bac‐ELP1‐p21 is soluble in aqueous solutions below physiological temperature (37°C) but aggregates when the temperature is raised above 39°C, making it a promising thermally responsive therapeutic carrier that may be actively targeted to solid tumors by application of focused hyperthermia. While Bac‐ELP1‐p21 at 37°C did not have any effect on SKOV‐3 cell proliferation, the use of hyperthermia increased the antiproliferative effect of Bac‐ELP1‐p21 compared with a thermally unresponsive control polypeptide. Bac‐ELP1‐p21 displayed both a cytoplasmic and nuclear distribution in the SKOV‐3 cells, with nuclear‐localized polypeptide enriched in the heated cells, as revealed by confocal microscopy. Using Western blotting, we show that Bac‐ELP1‐p21 caused a decrease in Rb phosphorylation levels in cells treated at 42°C. The polypeptide also induced caspase activation, PARP cleavage, and cell cycle arrest in S‐phase and G2/M‐phase. These studies indicate that ELP is a promising macromolecular carrier for the delivery of cell cycle inhibitory peptides to solid tumors.