Abstract 2168: Optimizing doxorubicin derivatives delivery using temperature sensitive biopolymers in multidrug resistant breast cancer cells
Authors: Dragojevic Sonja , Ryu Jung Su , Kratz Felix , Raucher Drazen 
Published: July 2016

Abstract
The anticancer agent doxorubicin is an anthracycline compound that shows high potency in treating cancer, and it is one of the most widely used chemotherapeutics. However, efficiency of doxorubicin treatment is limited by low blood plasma solubility, poor blood pharmacokinetics, and non-selective cell killing that results in serious toxicity to healthy tissues. Additionally, cancer cells often develop drug resistance, which is a significant limiting factor to the drug's effectiveness. Motivated by these problems, we have designed a drug delivery system that can specifically deliver drug to the tumor site while overcoming doxorubicin resistance in breast cancer cell lines. This drug delivery system consists of: ELP - Elastin like polypeptide, CPP - Cell penetrating peptide, a cleavable linker – to enable doxorubicin release in the targeted low pH environment, and a derivative of the anticancer agent Doxorubicin (modified by a 6-maleimidocaproyl moiety for conjugation to a terminal cysteine residue on ELP). ELP is thermally responsive and improves the complex's pharmacokinetics by prolonging its clearance rate while the CPP mediates cellular uptake of large macromolecules. The linker is an acid sensitive amino acid sequence (Gly-Phe-Leu-Gly) that serves as a substrate for lysosomal enzymes. In this study, we compared cytotoxicity of a cleavable (cDox) and non-cleavable (ncDox) doxorubicin derivative delivered by ELP biopolymer in the breast cancer cell lines MCF-7 and MCF7/ADR (doxorubicin resistant cell line). We showed that cDox had two fold higher cytotoxicity than ncDox in both cell lines. When ncDox, however, was conjugated to the ELP biopolymer containing a lysosomally degradable GFLG spacer, the drug delivery construct was equally cytotoxic to both sensitive and resistant cell lines, indicating that the construct delivers doxorubicin into cells by a mechanism that bypasses doxorubicin resistance. Confocal fluorescence microscopy showed that after two hours of exposure to the doxorubicin derivatives, cDox was predominantly localized in the nucleus in both cell lines. However, ncDox was localized in the plasma membrane and cytosol. Intracellular doxorubicin accumulation examined by flow cytometry indicated 3 fold higher uptake of ELP-cDox in sensitive MCF 7 cells compared to resistant MCF7 ADR cells. Cellular uptake of ELP-cDox was further enhanced two fold when conjugated with CPP. In conclusion, our current results indicate that ELP-doxorubicin conjugates may successfully overcome drug resistance in breast cancer cells, providing a promising approach for the use of chemotherapeutic agents such as doxorubicin in patients with drug resistant breast cancers.
Citation Format: Sonja Dragojevic, Jung Su Ryu, Felix Kratz, Drazen Raucher. Optimizing doxorubicin derivatives delivery using temperature sensitive biopolymers in multidrug resistant breast cancer cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2168.