Abstract 2536: Investigation of the effect of the sequence selective DNA minor groove cross-linking agent SG2000 (SJG-136) on canine tumor cells in vitro and in vivo

Abstract

Abstract SG2000 (SJG-136) is a novel sequence selective DNA minor groove cross-linking agent that causes minimal distortion of the helical structure of DNA, such that interstrand cross-links (ICLs) persist and are not easily repaired. It has potent antitumor activity against rodent and human tumour cells in vitro and in vivo and is currently in Phase II clinical trials in humans. The aim of this study was to evaluate whether SG2000 is effective against canine cancer cells in vitro and in vivo. Fourteen canine tumour cell lines, representing the main canine cancers, and two canine normal cell lines were screened for their IC50 values following SG2000 treatment using the SRB and MTT assays. A large differential activity was observed (0.33nM to >100nM following a 1 hour exposure) as previously reported in human tumour cells. Formation and persistence of ICLs were measured with the modified single cell gel electrophoresis (comet) assay in six canine tumour (two mast cell and four melanoma) cell lines. DNA damage response to SG2000-induced ICLs was also studied by measuring γH2AX foci formation in two melanoma cell lines. IC50 values were related to the peak levels of ICLs and γH2AX foci/cell. ICLs and γH2AX foci persisted for 48 hours following a 1 hour exposure. SG2000 anti-tumour and pharmacodynamic effects (ICL and γH2AX formation) were measured in vivo in athymic mice carrying a canine oral melanoma xenograft (LMeC). These were treated with 0.15 mg/Kg and 0.30 mg/Kg i.v. either as a single dose or as a weekly dose for 3 consecutive weeks. Dose-dependent tumour growth delay was observed following the single dose treatment. Greater activity was observed in the repeated dose schedule resulting in a 40 day median tumour growth delay in the 0.30 mg/Kg group. Dose-dependent ICLs were detected in both lymphocytes and tumour at 2 hours following SG2000 treatment and were still evident at 24 hours. The level of ICLs measured in peripheral lymphocytes was lower than that measured in the target tumour tissue, indicating a selective ICL formation in vivo. An increasing number of ICLs was observed in lymphocytes following repeated doses of SG2000. Other pharmacodynamic endpoints, including γH2AX (DNA double-strand breaks), caspase 3 (apoptosis), CD34 (blood vessels), Hoechst 33342 (perfusion) and pimonidazole (hypoxia) staining of tumours were also measured. Together these data suggests that SG2000 might be a valuable antitumor agent for the treatment of canine neoplasia and early phase clinical trials against solid tumours in dogs are planned. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2536. doi:10.1158/1538-7445.AM2011-2536