EO9: A novel bioreductive alkylating indoloquinone with preferential solid tumour activity and lack of bone marrow toxicity in preclinical models

Abstract

EO9 is a novel and fully synthetic bioreductive alkylating indoloquinone. Although structurally-related to mitomycin C, EO9 exhibits a distinct preclinical antitumour profile and there are also differences in its biochemical activation. In this study, EO9 was found to demonstrate preferential cytotoxicity against solid tumours in vitro as compared to leukaemia cell lines both in the Corbett two-tumour assay and in the disease-oriented human tumour cell line panel of the U.S. National Cancer Institute. In the latter system activity was particularly apparent in colon, melanoma and central nervous system lines, together with some renal and non-small cell lung lines. Preferential cytotoxicity towards hypoxic versus aerobic EMT6 mouse mammary tumour cells was observed. In vivo, EO9 was inactive against the P388 murine leukaemia, while exerting significant antiproliferative effects against several murine and human solid tumours, including the generally resistant MAC mouse colon tumours and gastric, ovarian and breast xenografts. These results confirmed in vitro observations of preferential solid tumour activity. In animal toxicology studies, EO9 induced vascular congestion in the gastrointestinal tract, but no significant bone marrow toxicity. The LD10 value of EO9 after a single intravenous injection into mice was 9 mg/kg (27 mg/m2). A dose of one-tenth of the mouse equivalent LD10 (2.7 mg/m2), the recommended starting dose for clinical phase I studies, was found to be safe in rats. Considering its distinct mechanism of bioactivation as compared to mitomycin C, its preferential solid tumour activity, its excellent activity against hypoxic cells, and lack of significant bone marrow toxicity in animals studies, EO9 has been selected for clinical evaluation within the framework of the EORTC.

DT-diaphorase activity in normal and neoplastic human tissues; an indicator for sensitivity to bioreductive agents?

“…This was in line with other studies, reporting levels varying around 20% of that of DTD (Schlager and Powis 1990;Walton et al, 1992;Hendriks et al, 1993;Ross et al, 1993). Relatively high levels of these enzymes contribute to the reduction of DCPIP in the DTD assay, as was noticed in normal liver.…”

“…For AZQ and E09 this reduction however leads to bioactivation of reactive groups, inducing their toxic properties such as DNA damage (Siegel et al, 1990;Walton et al, 1991;1992a). E09, a bioreductive alkylating indoloquinone, is a structural analogue of MMC and has shown selective activity against solid tumour types, in vitro and in animal models (Oostveen and Speckamp, 1987;Hendriks et al, 1993). Clinical phase I trials with E09 have just been finished (Schellens et al, 1994).…”

Professor Tom Connors and the development of novel cancer therapies by the Phase I/II Clinical Trials Committee of Cancer Research UK

“…A number of agents undergo activation by NQO1, including the clinically used agent mitomycin C, simpler quinones such as AZQ, RH1 and EO9, and also CB1954 (Riley and Workman, 1992;Fitzsimmons et al, 1996;Sharp et al, 2000, see below). EO9 was developed for clinical trials under the auspices of EORTC (Hendriks et al, 1993;Plumb and Workman, 1994). Clinical results were disappointing, probably because of the rapid clearance of the drug , but the agent may find a role in the treatment of DT-diaphorase-rich bladder cancers by intravesicular administration.…”

Evaluation of a novel in vitro assay for assessing drug penetration into avascular regions of tumours

“…With the exception of early studies using nitroimadazole-based radiosensitizers (Chapman et al, 1981Garrecht and Chapman, 1983;Franko, 1985;Rasey et al, 1985), relatively few studies have focused on the ability of bioreductive drugs to penetrate through several layers of cells. This is due largely to the fact Stirrer bioreductive indoloquinone compound 5-aziridino-3-hydroxymethyl-i -methyl-2-[ 1 H-indole-4,7-dione]prop-4-en-ox-ol (EO9), which, despite promising activity in preclinical models (Hendriks et al, 1993), has proved disappointing in the clinic . Studies demonstrating that spheroids are more resistant than monolayers to E09 suggest that drug penetration barriers may exist and this study provides experimental evidence to support the hypothesis that the failure of E09 in the clinic is due to poor penetration into tumours, in conjunction with rapid elimination kinetics in vivo.…”