ABSTRACT
Inhibition of monopolar spindle 1 (MPS1) kinase represents a novel approach to cancer treatment: instead of arresting the cell cycle in tumor cells, cells are driven into mitosis irrespective of DNA damage and unattached/misattached chromosomes, resulting in aneuploidy and cell death. Starting points for our optimization efforts with the goal to identify MPS1 inhibitors were two HTS hits from the distinct chemical series "triazolopyridines" and "imidazopyrazines". The major initial issue of the triazolopyridine series was the moderate potency of the HTS hits. The imidazopyrazine series displayed more than 10-fold higher potencies; however, in the early project phase, this series suffered from poor metabolic stability. Here, we outline the evolution of the two hit series to clinical candidates BAY 1161909 and BAY 1217389 and reveal how both clinical candidates bind to the ATP site of MPS1 kinase, while addressing different pockets utilizing different binding interactions, along with their synthesis and preclinical characterization in selected in vivo efficacy models.
Subject(s)
Antineoplastic Agents/metabolism , Cell Cycle Proteins/metabolism , Drug Delivery Systems/methods , Drug Discovery/methods , M Phase Cell Cycle Checkpoints/drug effects , Protein Serine-Threonine Kinases/metabolism , Protein-Tyrosine Kinases/metabolism , Spindle Apparatus/drug effects , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Cell Cycle Proteins/antagonists & inhibitors , Cell Line, Tumor , Dogs , Female , HT29 Cells , HeLa Cells , Humans , M Phase Cell Cycle Checkpoints/physiology , Male , Microsomes, Liver/drug effects , Microsomes, Liver/metabolism , Protein Serine-Threonine Kinases/antagonists & inhibitors , Protein Structure, Tertiary , Protein-Tyrosine Kinases/antagonists & inhibitors , Rats , Rats, Wistar , Spindle Apparatus/metabolism , Treatment OutcomeABSTRACT
PURPOSE: Prostate-specific membrane antigen (PSMA) is a transmembrane protein overexpressed in prostate cancer and is therefore being explored as a biomarker for diagnosing and staging of the disease. Here we report preclinical data on BAY 1075553 (a 9:1 mixture of (2S,4S)- and (2R,4S)-2-[(18)F]fluoro-4-phosphonomethyl-pentanedioic acid), a novel (18)F-labelled small molecule inhibitor of PSMA enzymatic activity, which can be efficiently synthesized from a direct radiolabelling precursor. METHODS: The (18)F-radiolabelled stereoisomers of 2-[(18)F]fluoro-4-(phosphonomethyl)-pentanedioic acid were synthesized from their respective isomerically pure precursors dimethyl 2-{[bis(benzyloxy)phosphoryl]methyl}-4-(tosyloxy)pentanedioate. In vivo positron emission tomography (PET) imaging and biodistribution studies were conducted in mice bearing LNCaP, 22Rv1 and PC-3 tumours. Pharmacokinetic parameters and dosimetry estimates were calculated based on biodistribution studies in rodents. For non-clinical safety assessment (safety pharmacology, toxicology) to support a single-dose human microdose study, off-target effects in vitro, effects on vital organ functions (cardiovascular in dogs, nervous system in rats), mutagenicity screens and an extended single-dose study in rats were conducted with the non-radioactive racemic analogue of BAY 1075553. RESULTS: BAY 1075553 showed high tumour accumulation specific to PSMA-positive tumour-bearing mice and was superior to other stereoisomers tested. Fast clearance of BAY 1075553 resulted overall in low background signals in other organs except for high uptake into kidney and bladder which was mainly caused by renal elimination of BAY 1075553. A modest uptake into bone was observed which decreased over time indicating organ-specific uptake as opposed to defluorination of BAY 1075553 in vivo. Biodistribution studies found highest organ doses for kidneys and the urinary bladder wall resulting in a projected effective dose (ED) in humans of 0.0219 mSv/MBq. Non-clinical safety studies did not show off-target activity, effects on vital organs function or dose-dependent adverse effects. CONCLUSION: BAY 1075553 was identified as a promising PET tracer for PSMA-positive prostate tumours in preclinical studies. BAY 1075553 can be produced using a robust, direct radiosynthesis procedure. Pharmacokinetic, toxicology and safety pharmacology studies support the application of BAY 1075553 in a first-in-man microdose study with single i.v. administration.
Subject(s)
Fluorine Radioisotopes , Glutamate Carboxypeptidase II/antagonists & inhibitors , Glutarates , Organophosphonates , Positron-Emission Tomography/methods , Prostatic Neoplasms/diagnostic imaging , Radiopharmaceuticals , Animals , Antigens, Surface , Dogs , Female , Glutarates/adverse effects , Glutarates/pharmacokinetics , Glutarates/pharmacology , Humans , Isotope Labeling , Male , Mice , Organophosphonates/adverse effects , Organophosphonates/pharmacokinetics , Organophosphonates/pharmacology , Radioactive Tracers , Radiochemistry , Radiopharmaceuticals/adverse effects , Radiopharmaceuticals/pharmacokinetics , Radiopharmaceuticals/pharmacology , Rats , Safety , StereoisomerismABSTRACT
OBJECTIVES: Gadoxetic acid [gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid (Gd-EOB-DTPA); Primovist] is a liver specific contrast agent for magnetic resonance imaging. For risk assessment of the single diagnostic use the toxicity of this compound was assessed. MATERIALS AND METHODS: Studies into acute, repeated-dose, reproductive and developmental toxicity, and local tolerance, contact sensitizing, and genotoxic potential were performed. RESULTS: Lethality was observed after a single intravenous administration at doses 2 orders of magnitude higher than the clinical dose. The no observed adverse effect levels after repeated administration markedly exceeds the single diagnostic dose in humans and no unexpected organ toxicity was observed. No indications of reproductive and developmental toxicity, potential contact allergenic, and genotoxic effects were observed. Gd-EOB-DTPA was well tolerated after intravenous administration. CONCLUSIONS: Gd-EOB-DTPA was well tolerated with high safety margins between the single diagnostic dose and the doses showing adverse effects in animal studies.
