Abstract C217: Genz-644282, a novel non-camptothecin topoisomerase I inhibitor for cancer treatment

Abstract

Abstract Topoisomerase I (Top1), a well-established anticancer target, is a nuclear enzyme producing a single-strand DNA break to allow transcription. Camptothecin Top1 inhibitors are important drugs for the treatment of a variety of cancers including colon cancer, leukemias and ovarian cancer. Potent non-camptothecin Top1 inhibitors were identified. One of these, Genz-644282, binds tightly and selectively to the DNA:Top1 complex. The effects of Genz-644282, topotecan and irinotecan/SN38 in cell-based assays were compared. The colony formation assay is the gold-standard for determination of the cytotoxicity of compounds toward bone marrow and malignant cells as it measures the survival/killing of cells capable of self-renewal. Mouse and human bone marrow were subjected to colony forming unit -granulocyte/macrophage (CFU-GM) assays over a 5-log concentration range with continuous exposure to the compounds for 13–15 days. The IC90s for topotecan and SN38 for mouse CFU-GM were 519 nM and 331 nM, respectively. For human CFU-GM, the IC90s for topotecan and SN38 were 19 nM and 26 nM, resulting in mouse to human differentials of 28- and 13-fold. Genz-644282 was more potent, with IC90s of 8.4nM for mouse CFU-GM and 1.2 nM for human CFU-GM; thus only a 7-fold differential between species. The cytotoxicities of topotecan, SN38 and Genz-644282 were compared in the ability of seven human tumor cell lines of varied histologies to form colonies after a week of exposure to a 5-log concentration range of each compound. Human bone marrow CFU-GM was much more sensitive to topotecan than were RPMI-8226 multiple myeloma, KBV-1 cervical carcinoma or NCI-H460 non-small cell lung carcinoma cells. The IC90s for topotecan ranged between 11 and 257 nM. SN38 cytotoxicity to human bone marrow CFU-GM and to several human tumor cell lines was very similar with IC90s in the cancer lines ranging between 2 and 55 nM. HT29 human colon cancer cells, however, were markedly sensitive to SN38 (IC90 = 2 nM). Genz-644282 was a more potent cytotoxic agent than topotecan or SN38 with IC90 values ranging between 0.7 and 9.1 nM across the seven cell lines. MDA-MB-231 human breast carcinoma, HT29 colon carcinoma and RPMI-8226 cells were most sensitive to Genz-644282 with IC90s ranging between 0.7 and 7.0 nM. The growth inhibition produced by 72-hr exposure to Genz-644282 was examined in 26 established human tumor cell lines representing pancreatic carcinoma, melanoma, non-small cell lung cancer, breast carcinoma, ovarian carcinoma and renal cell carcinoma using a Cell TiterGlo ATP content endpoint. The IC90s for Genz-644282 ranged between 0.054 micromolar and 5 micromolar in this assay. The most sensitive tumor lines were 4 of 6 pancreatic cancer lines and the least sensitive lines included 3 of 4 melanoma lines. Colony formation data were analyzed by non-linear regression using SAS version 8.2. Based upon these findings and other data, Genz-644282 was selected as a development candidate. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C217.