Application of thermally responsive polypeptides directed against c-Myc transcriptional function for cancer therapy

Abstract

Elastin-like polypeptides are biopolymers composed of the pentapeptide repeat Val-Pro-Gly-Xaa-Gly. Elastin-like polypeptides are soluble in aqueous solution below their transition temperature, but they hydrophobically collapse and aggregate when the temperature is raised above the transition temperature. Previous studies have suggested that the aggregation of these polypeptides in response to externally applied hyperthermia may be exploited in the use of elastin-like polypeptide for thermally targeted drug delivery. This work shows the application of elastin-like polypeptide as a delivery vehicle for a short peptide that can inhibit the transcriptional function of a specific oncogene. The coding sequence for elastin-like polypeptide was modified by the addition of the membrane translocating sequence penetratin and a peptide derived from helix 1 of the helix-loop-helix region of c-Myc (H1-S6A,F8A), known to inhibit c-Myc transcriptional function. The designed polypeptide (Pen-ELP-H1) was then expressed and purified from Escherichia coli. Cellular uptake of Pen-ELP-H1 is enhanced by both the penetratin sequence and by the hyperthermia-induced phase transition as shown by flow cytometry studies. Using immunofluorescence and reverse transcription-PCR, we show that Pen-ELP-H1 is able to disrupt the nuclear localization of c-Myc and inhibit transcriptional activation by c-Myc. Cell proliferation studies showed that Pen-ELP-H1 inhibits growth of MCF-7 cells. Furthermore, the use of hyperthermia increased the antiproliferative effect of a thermally responsive Pen-ELP-H1 approximately 2-fold compared with a nonthermally responsive control polypeptide. These studies show that genetically engineered elastin-like polypeptide carriers may provide a new way to thermally target specific oncogene inhibitors to solid tumors.