Abstract 2653: Thermally targeted delivery of an acid-labile derivative of doxorubicin by elastin-like polypeptide

Abstract

Abstract Doxorubicin (Dox) is an anthracycline used in the treatment of many types of cancer. It intercalates into the strands of DNA to inhibit the progression of topoisomerase II, stopping the cell from replicating. The side effects, however, are severe and include neutropenia, alopecia, nausea, myelosuppression, and cardiotoxicity. The drug is nonspecific; as a result, high doses are needed to treat cancer cells. These high doses are inadvertently harmful to normal cells. Therefore, there is a need for an efficient drug delivery system in order to deliver doxorubicin to the tumor site. Our lab has developed a macromolecular carrier that can provide this targeted delivery. This elastin-like polypeptide (ELP) is thermally responsive as it remains in solution at physiological temperature and aggregates upon heating at 42 °C. The N-terminus of ELP was modified with three different cell penetrating peptides (CPPs) - Bac, Tat, and SynB1. These peptides are derived from the bactenecin family of antimicrobial peptides, truncated version of the HIV-1 Tat protein, and porcine leukocytes, respectively. This study compared the efficiency of these three CPP-ELP carriers to deliver doxorubicin to the cells. ELP was attached to a hydrazone derivative of doxorubicin (DOXO) by conjugation of a 6-maleimidocaproyl moiety on the drug with a terminal cysteine residue on ELP. This linker allows the drug to be cleaved at acidic pH in the cell. The three CPP-ELP-DOXO conjugates had transition temperatures within the range of 38-42°C. All three carriers of DOXO inhibited MCF-7 breast cancer cell proliferation 2-fold more at 42 °C than at 37 °C, indicating that the hyperthermia induced phase transition of ELP does increase the local concentration of the drug. Inhibition of cell proliferation may be due to apoptosis, since apoptosis was enhanced 2.3-fold in MCF-7 cells when SynB1-ELP-DOXO aggregation was induced with hyperthermia. CPP-ELP-DOXO accumulated in cells to the same level as free Dox. Confocal imaging showed that when cells were treated with any of the three CPP-ELP-DOXO derivatives, Dox localized in the nucleus, similar to the free Dox. The results suggest that CPP-ELP-DOXO conjugates may provide a means to thermally target solid tumors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2653.