Enhanced uptake of a thermally responsive polypeptide by tumor cells in response to its hyperthermia-mediated phase transition

Elastin-like polypeptides (ELPs) composed of a VPGXG repeat undergo a rever sible phase transition in aqueous solution. They are hydrophilic and solubl e in aqueous solution below their transition temperature (T-t), but they be come hydrophobic and aggregate when the temperature is raised above their T -t. In this study, we examine the quantitative uptake of a fluorescence-lab eled, thermally responsive ELP as a function of ELP concentration between 5 and 15 muM in solution in response to hyperthermia by three cultured cance r cell lines. Flow cytometry of fluorescein-ELP conjugates showed that hype rthermia enhanced the cellular uptake of the thermally responsive ELP in hu man ovarian carcinoma cells (SKOV-3) and in HeLa cells at a concentration o f 10 muM or higher, but not at a concentration of 5 muM, as compared with t he uptake of a thermally inactive ELP control. In FaDu cells, hyperthermia stimulated uptake of the thermally responsive ELP at all solution concentra tions of ELP between 5 and 15 muM. In particular, a >2-fold greater uptake of thermally responsive ELP compared with the thermally inactive control EL P was observed for FaDu cells at a solution concentration of 15 muM in heat ed cells. Confocal fluorescence microscopy of tumor cells incubated with a rhodamine conjugate of the thermally responsive ELP showed that the cytopla sm was uniformly stained below the T-nu. Above the T-nu, fluorescent partic les were observed in the cytoplasm, suggesting that these particles are agg regates of the thermally responsive polypeptide resulting from the ELP phas e transition. These studies demonstrate that the endocytotic uptake of a th ermally responsive ELP is significantly enhanced by the thermally triggered phase transition of the polypeptide.