Abstract 988: Synthesis and preclinical evaluation of dual-stimuli responsive doxorubicin prodrug activated by histone deacetylases and cathepsin L

Doxorubicin (DOX) an anthracycline is a leading anticancer drug with a broad spectrum of activity against numerous solid and hematologic malignancies. However, its clinical application is limited by lower efficacy, severe cardiotoxicity and occurrence of secondary malignancies. There is an urgent need for eliminating the Dox adverse effects while retaining its anticancer efficacy. One of the major goals of cancer therapy is the selective targeting of malignancies over normal tissues. One way to avoid these severe adverse reactions is to develop tumor-targeted prodrugs that are converted to active antitumor drugs at tumor sites in the presence of enzymes that are overexpressed human cancers. Among these, the histone deacetylases (HDACs) and cathepsin L (CTSL) are highly expressed in cancer cells and are considered as potential cancer-specific targets. HDACs are critical enzymes involved in the regulation of histone and non-histone proteins and elevated HDACs in tumor cells are known to be closely associated with tumor initiation, progression, and metastasis. Similarly, the lysosomal cysteine protease CTSL plays key roles at multiple stages of tumor progression and metastasis. In the present study, we developed a new prodrug by coupling an acetylated lysine group to doxorubicin (Lys(Ac)-Dox), a masked cytotoxic agent, which is consecutively activated by HDACs and a CTSL to liberate doxorubicin. We first verified whether Lys(Ac)-Dox could be specifically cleaved by HDACs and CTSL in vitro. The results showed that after incubating with HDACs and CTSL at 37 °C for 20 h, the hydrolysis of Lys(Ac)-Dox reached 99%, suggesting that Lys(Ac)-Dox could be successfully cleaved by the target enzymes. To prove that the Lys(Ac)-Dox would have a much improved growth-inhibitory effect against cancer cells, the cytotoxicity of free DOX and Lys(Ac)-Dox against lung cancer cell lines normal human lung epithelial cell line was determined. The dose-response curves obtained from the cell lines tested indicated that Dox was equally cytotoxic against both cancer and normal cells. In contrast, Lys(Ac)-Dox highly cytotoxic against cancer cells and non-toxic to the normal counterparts. To measure the in vivo anticancer efficacy of Lys(Ac)-Dox vis-vis Dox, we developed subcutaneous xenografts by injecting human lung cancer A549 and H460 cells in nude mice. Lys (Ac)-Dox and Dox were administered daily i.p. at 5 mg/kg. The prodrug showed a significantly higher (>2-fold) tumor regression than Dox. A diminished circulating reticulocyte counts from whole blood after Dox treatment is known to reflect the hematological toxicity caused by the drug. Only Dox caused significant reticulocyte ablation while the prodrug did not, validating our drug design. Biochemical tests involving topo II inhibition and ROS production by the prodrug are in progress (supported by CPRIT grant RP 170207 to KSS). Note: This abstract was not presented at the meeting. Citation Format: Surendra R. Punganuru, Hanumantha Rao Madala, Viswanath Arutla, Kalkunte S. Srivenugopal. Synthesis and preclinical evaluation of dual-stimuli responsive doxorubicin prodrug activated by histone deacetylases and cathepsin L [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 988.