Evaluation of Physicochemical Properties, Pharmacokinetics, Biodistribution, Toxicity, and Contrast-Enhanced Cancer MRI of a Cancer-Targeting Contrast Agent, MT218

Abstract

Objectives Preclinical assessments were performed according to the US Food and Drug Administration guidelines to determine the physicochemical properties, pharmacokinetics, clearance, safety, and tumor-specific magnetic resonance (MR) imaging of MT218, a peptidic gadolinium-based MR imaging agent targeting to extradomain B fibronectin for MR molecular imaging of aggressive tumors. Materials and Methods Relaxivity, chelation stability, binding affinity, safety-related target profiling, and effects on CYP450 enzymes and transporters were evaluated in vitro. Magnetic resonance imaging was performed with rats bearing prostate cancer xenografts, immunocompetent mice bearing murine pancreatic cancer allografts, and mice bearing lung cancer xenografts at different doses of MT218. Pharmacological effects on cardiovascular, respiratory, and central nervous systems were determined in rats and conscious beagle dogs. Pharmacokinetics were tested in rats and dogs. Biodistribution and excretion were studied in rats. Single and repeated dosing toxicity was evaluated in rats and dogs. In vitro and in vivo genotoxicity, in vitro hemolysis, and anaphylactic reactivity were also performed. Results At 1.4 T, the r 1 and r 2 relaxivities of MT218 were 5.43 and 7.40 mM −1 s −1 in pure water, 6.58 and 8.87 mM −1 s −1 in phosphate-buffered saline, and 6.54 and 8.70 mM −1 s −1 in aqueous solution of human serum albumin, respectively. The binding affinity of MT218 to extradomain B fragment is 3.45 μM. MT218 exhibited no dissociation of the Gd(III) chelates under physiological conditions. The peptide degradation half-life ( t 1/2 ) of MT218 was 1.63, 5.85, and 2.63 hours in rat, dog, and human plasma, respectively. It had little effect on CYP450 enzymes and transporters. MT218 produced up to 7-fold increase of contrast-to-noise ratios in the extradomain B fibronectin–rich tumors with a dose of 0.04 mmol/kg for at least 30 minutes. MT218 had little pharmacological effect on central nervous, cardiovascular, or respiratory systems. MT218 had a mean plasma elimination half-life ( t 1/2 ) of 0.31 and 0.89 hours in rats and dogs at 0.1 mmol/kg, respectively. No detectable Gd deposition was observed in the brain at 6 hours postinjection of MT218 at 0.1 mmol/kg in rats. MT218 was not mutagenic and had no mortality or morbidity in the rats or dogs up to 1.39 and 0.70 mmol/kg/d, respectively. The no observed adverse effect level of MT218 in Sprague-Dawley rats was 1.39 mmol/kg for single dosing and 0.46 mmol/kg/d for repeated dosing. The no observed adverse effect level in dogs was 0.07 mmol/kg/d. MT218 exhibited no genotoxicity, hemolysis, and anaphylacti...

Targeted Contrast Agents for Magnetic Resonance Molecular Imaging of Cancer

“…In contrast, MRMI of fibrin-FN clots with a CREKA targeted agent is not able to differentiate PC3 and LNCaP tumors, possibly because the clots are formed by accumulations of the plasma proteins in the tumor periphery rich of angiogenic blood vessels. 1 The optimized targeted agent MT218 was able to produce robust signal enhancement in rats bearing PC3 tumors at substantially reduced doses of 0.02 and 0.04 mmol/kg, producing a 3-and 6-fold CNR, respectively, 4 The preclinical studies have demonstrated that small peptide targeted GBCAs specific to abundant targets in the tumor ECM are able to generate detectable MRI signal enhancement for delineation of primary tumors and micrometastases in rodent models. The lead targeted GBCA, MT218, shows promise for detecting several types of EDB-FN positive aggressive cancers, differentiating the tumor heterogeneity based on the EDB-FN expression levels, and to noninvasively assess the tumor response to therapies, including development of drug resistance in correlation with the biology of EDB-FN in cancer.…”

“…Overall, MT218 has similar pharmacokinetics and clearance as other clinical macrocyclic GBCAs and no detectable brain retention and minimal retention in other organs and tissues. 4 MT218 has an excellent safety profile as demonstrated in the mandated physicochemical characterization and preclinical efficacy, pharmacokinetics, pharmacology, and safety assessments for an investigational new drug (IND) application to the FDA. IND approval is the first step in a lengthy FDA approval process for in-human use of CAs and represents a major milestone on the way to clinical development and application.…”

“…R. Li, Y. Gao, S. Jiang, H. Ayat, N. Laney, V. Nicolescu, C. Sun, W. Tweedle, M. F. Lu, Z. R. 202257639 …”

“…The binding affinities of the ZD2 targeted Gd­(HP-DO3A) conjugates were determined by surface plasmon resonance. Both ZD2-Gd­(HP-DO3A) ( K d = 1.7 μM) and ZD2-N3-Gd­(HP-DO3A) ( K d = 3.45 μM) have a modest binding affinity, slightly higher than that of the cyclic ZD2 peptide (K d = 11 μM) to the EDB protein fragment. Up to 40 μM ZD2-Gd­(HP-DO3A) has been shown to bind to aggressive tumors .…”

“…4 Compresive characterization shows that MT218 has excellent chelation stability and safety prof ile for clinical translation and has the potential diagnostic and prognostic MRI of multiple cancers.…”