Labeled EGFr-TK irreversible inhibitor (ML03): in vitro and in vivo properties, potential as PET biomarker for cancer and feasibility as anticancer drug.

Radiosynthesis of ML03 (N-[4-[(4,5-dichloro-2-fluorophenyl)amino]quinazolin-6-yl]acrylamide), an irreversible EGFr-TK inhibitor, was developed. Its in vitro and in vivo properties, its potential as PET biomarker in cancer and the feasibility of this type of compounds to be used as anticancer drug agents were evaluated. The compound was labeled with carbon-11 at the acryloyl amide group, via automated method with high yield, chemical and radiochemical purities. ELISA carried out with A431 lysate showed high potency of ML03 with an apparent IC(50) of 0.037 nM. The irreversible binding nature of ML03 was studied and 97.5% EGFr-TK autophosphorylation inhibition was observed in intact A431 cells 8 hr post incubation with the inhibitor. Specific binding (67%) of [(11)C]ML03 was obtained in cells. An A431 tumor-bearing rat model was developed and the validity of the model was tested. In biodistribution studies carried out with tumor-bearing rats, moderate uptake was observed in tumor and high uptake in liver, kidney and intestine. In metabolic studies, fast degradation of [(11)C]ML03 was observed in liver and blood indicating a short half-life of the compound in the body. PET scan with tumor-bearing rats confirmed the results obtained in the ex vivo biodistribution studies. Although in vitro experiments may indicate efficacy of ML03, non-specific binding, ligand delivery and degradation in vivo make ML03 ineffective as PET bioprobe. Derivatives of ML03 with lower metabolic clearance rate and higher bioavailability should be synthesized and their potential as anticancer drugs and PET bioprobes evaluated. Copyright 2002 Wiley-Liss, Inc.