ABSTRACT
Glutaminolysis inhibitors have shown early promise in cancer therapeutics. Specifically, kidney-type glutaminase (KGA) has been a long-standing anti-tumor drug target; KGA allosteric inhibitors have attracted great attention due to their superior enzyme specificity and good drug safety profiles. However, the main issue with allosteric inhibitors-including BPTES, CB-839, and the recently developed KGA allosteric and glutamate dehydrogenase (GDH) dual inhibitor, Hexylselen (CPD-3B)-is their low solubility; it leads to limited in vivo efficacy. To optimize their formulation, various delivery carriers were screened in the present study. Soluplus® (SOL), an amphiphilic graft polymer, showed an interesting structure-solubility/activity relationship with Selen molecules containing different middle chain sizes. Among these molecules, the long chain molecule CPD-3B showed 3000-fold increased solubility with SOL, forming well-dispersed and stable micelles 60-80 nm in size. Moreover, CPD-3B@SOL micelles exhibited good metabolic stability in both blood and liver microsomes. These advantages significantly enhanced the bioavailability and in vivo antitumor efficacy of CPD-3B@SOL micelles in the H22 hepatocarcinoma xenograft mouse model. Thus, the current study provided a practical delivery system for allosteric inhibitors of glutaminase, which is one of the bottlenecks of targeting tumor glutaminolysis.
ABSTRACT
Vanin-1 is a pantetheinase that catalyzes the hydrolysis of pantetheine to produce pantothenic acid (vitamin B5) and cysteamine. Reported here is a highly sensitive fluorescent assay using a novel fluorescently labeled pantothenate derivative. The assay has been used for characterization of a soluble version of human vanin-1 recombinant protein, identification and characterization of hits from high-throughput screening (HTS), and quantification of vanin pantothenase activity in cell lines and tissues. Under optimized assay conditions, we quantified vanin pantothenase activity in tissue lysate and found low activity in lung and liver but high activity in kidney. We demonstrated that the purified recombinant vanin-1 consisting of the extracellular portion without the glycosylphosphatidylinositol (GPI) linker was highly active with an apparent K(m) of 28 microM for pantothenate-7-amino-4-methylcoumarin (pantothenate-AMC), which was converted to pantothenic acid and AMC based on liquid chromatography-mass spectrometry (LC-MS) analysis. The assay also performed well in a 384-well microplate format under initial rate conditions (10% conversion) with a signal-to-background ratio (S/B) of 7 and a Z factor of 0.75. Preliminary screening of a library of 1280 pharmaceutically active compounds identified inhibitors with novel chemical scaffolds. This assay will be a powerful tool for target validation and drug lead identification and characterization.
