Use of traditional chemotherapeutic drugs is restricted by severe side effects and lack of tumor specificity of these cytotoxic agents. Less toxic prodrug that can be selectively activated in tumor tissue have been explored in attempts to improve the therapeutic index. Some approaches to the development of tumor activating prodrugs take advantage of inherent properties of the tumor, for example, selective enzyme expression, hypoxia, or low extracellular pH in the vicinity of the tumor. CoBioRes makes use of capped, tetrapeptidic prodrug of existing chemotherapeutics. Doxorubicin (Dox) was the first chemotherapeutic that was linked to the tetrapeptide sequence and tested experimentally (PhAc-ALGP-Dox). This approach makes the prodrug impermeable to cell membranes of both normal and tumor cells. Furthermore, it remains stable in blood by the use of the capping group on the amino-terminal group of the peptide that prevents aspecific activation by circulating esopeptidases. The prodrug as such is thus not active. The peptide sequences have been developed to be sensitive to the hydrolytic action of a selected group of peptidases that are released within the tumor microenvironment. These peptidases, which accumulate in the tumors, also play an important role in cancer cell invasion and metastasis. What makes this approach unique is that it is not targeting a single enzyme, but requires, for its selectivity, a two-step activation based on enzymes with an increasing selectivity. In vivo activation starts when the tetrapeptide prodrug is exposed to endonucleases (CD10 and THOP1) leading to the formation of intermediates that are still inactive and poorly permeable through cell membranes. This leads to a tissue distribution that is determined by the expression of the endonucleases. Since these are known to be overexpressed in several tumors, and only present at lower level in some normal tissues, the prodrug will be preferentially located and activated in the vicinity of tumors. The second step of the activation is the cleavage at the prolyl by dipeptidases FAP and DPPIV, releasing the free doxorubicin. The simultaneous expression of all the enzymes involved in the prodrug activation was confirmed both in human triple negative breast cancer biopsies and in experimental triple negative breast cancer models. In vitro analysis of PhAc-ALGP-Dox reveals higher tumor cells tropism and higher cytotoxicity in cancer cells than in normal cells. In vivo PhAc-ALGP-Dox gives promising preliminary results in terms of systemic tolerance even at high concentration, and in vivo efficacy in xenograft mouse models compared to free doxorubicin. Taken together, these results provide a strong rationale for further investigation aimed at unleashing the potential clinical value of this compound.
Citation Format: Andrea Casazza, Massimiliano Mazzone, Peter Pokreisz. PhAc-ALGP-Dox is a new tumor selective peptide prodrug of doxorubicin that shows improved efficacy and systemic tolerance in triple negative breast cancer models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 180. doi:10.1158/1538-7445.AM2017-180