ORIGINAL ARTICLE Identification, characterization and potent antitumor activity of ECO-4601, a novel peripheral benzodiazepine receptor ligand Henriette Gourdeau Æ James B. McAlpine Æ Maxime Ranger Æ Bryan Simard Æ Francois Berger Æ Francis Beaudry Æ Pierre Falardeau Received: 11 January 2007 / Accepted: 5 June 2007 / Published online: 11 July 2007 Ó Springer-Verlag 2007 Abstract Purpose ECO-4601 is a structurally novel farnesylated dibenzodiazepinone discovered through DECIPHER Ò technology, Thallion’s proprietary drug discovery plat- form. The compound was shown to have a broad cytotoxic activity in the low micromolar range when tested in the NCI 60 cell line panel. In the work presented here, ECO- 4601 was further evaluated against brain tumor cell lines. Preliminary mechanistic studies as well as in vivo antitu- mor evaluation were performed. Methods Since ECO-4601 has a benzodiazepinone moi- ety, we first investigated if it binds the central and/or peripheral benzodiazepine receptors. ECO-4601 was tested in radioligand binding assays on benzodiazepine receptors obtained from rat hearts. The ability of ECO-4601 to in- hibit the growth of CNS cancers was evaluated on a panel of mouse, rat and human glioma cell lines using a standard MTT assay. Antitumor efficacy studies were performed on gliomas (rat and human), human breast and human prostate mouse tumor xenografts. Antitumor activity and pharma- cokinetic analysis of ECO-4601 was evaluated following intravenous (IV), subcutaneous (SC), and intraperitoneal (IP) bolus administrations. Results ECO-4601 was shown to bind the peripheral but not the central benzodiazepine receptor and inhibited the growth of CNS tumor cell lines. Bolus SC and IP admin- istration gave rise to low but sustained drug exposure, and resulted in moderate to significant antitumor activity at doses that were well tolerated. In a rat glioma (C6) xeno- graft model, ECO-4601 produced up to 70% tumor growth inhibition (TGI) while in a human glioma (U-87MG) xenograft, TGI was 34%. Antitumor activity was highly significant in both human hormone-independent breast (MDA-MB-231) and prostate (PC-3) xenografts, resulting in TGI of 72 and 100%, respectively. On the other hand, IV dosing was followed by rapid elimination of the drug and was ineffective. Conclusions Antitumor efficacy of ECO-4601 appears to be associated with the exposure parameter AUC and/or sustained drug levels rather than C max . These in vivo data constitute a rationale for clinical studies testing prolonged continuous administration of ECO-4601. Keywords Dibenzodiazepine Á Peripheral benzodiazepine receptor (PBR) Á Cancer Á Glioma Á Xenografts Abbreviations AAALAC International Association for Assessment and Accreditation of Laboratory Animal Care AUC Area under the curve CCAC Canadian Council on Animal Care CBR; GABA A Central benzodiazepine receptor D5W 5% dextrose H. Gourdeau (&) Á J. B. McAlpine Á M. Ranger Á P. Falardeau Thallion Pharmaceuticals Inc., 7150 Alexander-Fleming, St Laurent, QC, Canada H4S 2C8 e-mail: hgourdeau@thallion.com B. Simard Á F. Berger INSERM U318, Grenoble, France F. Beaudry Department of Veterinary Biomedicine, Faculty of Veterinary Medicine, University of Montreal, St Hyacinthe, QC, Canada J2S 2M2 123 Cancer Chemother Pharmacol (2008) 61:911–921 DOI 10.1007/s00280-007-0544-2