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

Abstract

Radiosynthesis of ML03 (N-{4 Key words: carbon-11; cancer; biodistribution; PET; EGFrGrowth factors mediate their pleiotropic actions by binding to and activating receptor tyrosine kinases. Epidermal growth factor receptor (EGFr, erb-B1) belongs to a family of proteins involved in the proliferation of normal and malignant cells. 1,2 The binding of activating ligands such as EGF, TGF ␣, AR, BTC or HB-EGF to the EGFr results in activation of the cytosolic kinase domain. Overexpression of EGFr is the hallmark of many human tumors such as breast cancer, glioma, laryngeal cancer, squamous cell carcinoma of the head and neck and prostate cancer. 3 Since the late 1980s continuous effort has been invested in the development of EGFr tyrosine kinase inhibitors as anti-neoplastic drugs. 4,5-11 Radioactively labeled small molecules with high affinity and selectivity for the tyrosine kinase domain of EGFr might offer a specific and sensitive tool to be used in positron emission tomography (PET) for diagnosis of tumors overexpressing EGFr. PET provides 3D and quantitative maps of the distribution of radioactive tracers within the human body and hence permits the measurement of physiological, biochemical and pharmacological function at the molecular level, both in healthy and pathological states. PET is based on the use of short half-life positron-emitting isotopes, such as 11 C (t 1/2 20.39 min.), 18 F (t 1/2 109.8 min.), 15 O (t 1/2 2.037 min.) and 13 N (t 1/2 9.965 min.). After injection of a suitable biomarker, the PET scan provides a mapping of the biomarker distribution and hence of a specific receptor, transporter or enzyme in the human body. Biomarkers with high selectivity for a specific receptor or enzyme might accumulate in those organs and tissues where the targeted protein is overexpressed. In the case of EGFr, its overexpression in human tumors could be non-invasively detected by labeling tyrosine kinase inhibitors with positron-emitting isotopes. The PET application of these potential biomarkers represents a new strategy for the diagnosis of EGFr-expressing tumors. [12][13][14] Moreover, the increasing demand to incorporate diagnostics into clinical studies of EGFr-targeted therapies suggests a potential future use of EGFrTK labeled inhibitors. These labeled inhibitors could help select patients for clinical trials. Cancer patients could undergo a non-invasive diagnostic PET study with labeled EGFrTK inhibitor, and if their tumor is found to overexpress EGFrTK, they could then be selected for a clinical trial that utilizes anti-EGFr therapy.In our previous work, 15 we synthesized, labeled and evaluated 4-(fluoroanilino)quinazoline derivatives as EGFrTK PET biomarkers. These molecules bind reversibly to the ATP binding site of the receptor and inhibit the autophosphorylation of the EGFrTK. Competition with intracellular ATP results in their fast dissociation from the EGFr kinase site, however, making these compounds ineffective as PET reporter probes. We therefore concluded that irreversible EGFr tyrosine kinase ...

Monitoring of Gefitinib Sensitivity with Radioiodinated PHY Based on EGFR Expression

“…14) Development of various EGFR-TK imaging agents based exclusively on the anilinoquinazoline structure has been attempted for more than a decade, but further optimization of the properties of imaging agents with respect to high specificity to EGFR, selectivity to mutant types of kinase and high tumor uptake is required. [15][16][17][18][19][20] Thus, novel imaging agents to accurately detect EGFR-TK activity are needed in order to predict and monitor the therapeutic effects.…”

The Progress and Promise of Molecular Imaging Probes in Oncologic Drug Development

“…Such was found to be the case with ML01, a 18 Flabeled reversible inhibitor of EGFR (23). ML03, a 11 C-labeled irreversible EGFR inhibitor, was not subject to washout by ATP due to covalent binding of the probe at the tyrosine kinase domain of the receptor; however, nonspecific chemical reactivity limited the bioavailability and tumor accumulation of the probe (24). A newer generation of irreversible EGFR inhibitor probes has greater stability and thus improved potential for imaging EGFR (25).…”

PET/CT in cancer research: from preclinical to clinical applications

“…Analogs of gefitinib were labeled with 11 C, 18 F and 124 I and used for detection of EGFR overexpressing tumors. All these radiolabeled compounds bind in a reversible or irreversible manner to the ATP binding site in the catalytic domain of EGFR but their pharmacokinetics properties need to be improved for clinical applications (39)(40)(41)(42)(43)(44). Gefitinib and erlotinib themselves were labeled with 11 C (45,46) and 18 F (47,48) for PET imaging studies and their biodistribution and metabolic stability were evaluated in mice and vervet monkeys.…”