Identification, characterization and potent antitumor activity of ECO-4601, a novel peripheral benzodiazepine receptor ligand.
OBJECTIVE
ECO-4601 is a structurally novel farnesylated dibenzodiazepinone discovered through DECIPHER technology, Thallion's proprietary drug discovery platform. 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 antitumor evaluation were performed.


METHODS
Since ECO-4601 has a benzodiazepinone moiety, 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 inhibit 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 pharmacokinetic analysis of ECO-4601 was evaluated following intravenous (i.v.), subcutaneous (s.c.), and intraperitoneal (i.p.) 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 s.c. and i.p. administration 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) xenograft 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, i.v. 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.
Gourdeau
Henriette
H
Thallion Pharmaceuticals Inc., 7150 Alexander-Fleming, St Laurent, QC, Canada H4S 2C8. hgourdeau@thallion.com
McAlpine
James B
JB
Ranger
Maxime
M
Simard
Bryan
B
Berger
Francois
F
Beaudry
Francis
F
Farnet
Chris M
CM
Falardeau
Pierre
P
D000818:Animals; D000970:Antineoplastic Agents; D019540:Area Under Curve; D001569:Benzodiazepines / Q000008:administration & dosage / Q000493:pharmacokinetics / Q000494:pharmacology*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003975:Diazepam / Q000494:pharmacology; D003984:Dibenzazepines; D004305:Dose-Response Relationship, Drug; D005260:Female; D018757:GABA Modulators / Q000494:pharmacology; D005910:Glioma / Q000188:drug therapy / Q000378:metabolism; D006801:Humans; D008024:Ligands; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000096:biosynthesis / Q000187:drug effects* / Q000235:genetics; D014183:Transplantation, Heterologous
D000970:Antineoplastic Agents; D003984:Dibenzazepines; D018757:GABA Modulators; D008024:Ligands; D011963:Receptors, GABA-A; D001569:Benzodiazepines; D003975:Diazepam; C492422:diazepinomicin