We have previously reported that the αvβ3 inhibitor P-bi-TAT, a bifunctional version of the thyroid hormone metabolite tetraiodothyroacetic acid (tetrac) conjugated to polyethylene glycol (PEG) MW 4000, has excellent efficacy in a glioblastoma multiforme (GBM) mouse model. However, bioanalysis problems due to PEG polydispersity and large-scale synthesis issues led to a search for new molecules, culminating in the discovery of fb-PMT, a conjugate of tetrac and monodisperse PEG36, with a lipophilic 4-fluorobenzyl group at the opposite end of the PEG chain. fb-PMT reduces GBM tumor growth and viability by up to 98%, is suitable for large-scale synthesis, and is amenable to bioanalysis using mass spectrometry-based detection. We also showed that changes in lipophilicity at the opposite end of the PEG chain from the active tetrac component affected the proton NMR chemical shift of the tetrac moiety in D20 and brain levels of the compound after subcutaneous dosing.

We have recently reported on the development of fb-PMT (NP751), a conjugate of the thyroid hormone metabolite tetraiodothyroacetic acid (tetrac) and monodisperse polyethylene glycol 36. It exhibited high affinity for thyrointegrin αvβ3 receptor and potent anti-angiogenic and anticancer activity in vivo. The objective of the current study is to determine the pharmacokinetics (PK) of fb-PMT in experimental animals, such as mice, rats, and monkeys. NP751 was quantified using a propylene diamine-modified tetraiodothyroacetic acid (DAT) as an internal standard. The limit of quantification (LOQ) for fb-PMT was 1.5 ng/μL and the recovery efficiency was 93.9% with the developed method. The peak plasma concentration (Cmax) and the area under the curve (AUC) results at different doses in mice, rats and monkeys suggest that pharmacokinetics of NP751 is dose-dependent within the dose ranges administered. Results indicate that NP751 has comparable PK parameters that provides enough exposure as a molecularly tumor targeted molecule in multiple species and is a promising anticancer therapeutic.

Background Thyrointegrin αvβ3 receptors are unique molecular cancer therapeutic target because of its overexpression on cancer and rapidly dividing blood vessel cells compared and quiescent on normal cells. A macromolecule, TriAzole Tetraiodothyroacetic acid (TAT) conjugated to Polyethylene glycol with a lipophilic 4-fluorobenyl group (fb-PMT, NP751), interacts with high affinity (0.21 nM) and specificity with the thyrointegrin αvβ3 receptors on the cell surface without nuclear translocation in contrast to the non-polymer conjugated TAT. Methods The following in vitro assays were carried out to evaluate NP751 including binding affinity to different integrins, transthyretin (TTR)-binding affinity, GBM cell adhesion, proliferation assays, nuclear translocations, CAM model of angiogenesis, and microarray for molecular mechanisms. Additionally, in vivo studies were carried to evaluate anti-cancer efficacy of NP751, its biodistribution and brain GBM tumor versus plasma levels kinetics. Results NP751 demonstrated a broad spectrum anti-angiogenesis and anticancer efficacy in experimental models of angiogenesis and xenografts of human GBM cells. Tumor growth and cancer cells’ viability were markedly decreased (by > 90%; P <0.001) in fb-PMT-treated U87-Luc or three different primary human GBM xenograft-bearing mice based on tumor IVIS imaging and histopathological examination, without relapse upon treatment discontinuation. Additionally, it effectively transports across the blood brain barrier via its high affinity binding to plasma TTR with high retention in brain tumor. NP751-induced effects on gene expression support the model of molecular interference at multiple key pathways essential for GBM tumor progression and vascularization. Conclusions fb-PMT is a potent thyrointegrin αvβ3 antagonist with potential impact on GBM tumor progression.