The hormonal regulation of purine biosynthesis: basal levels of different hormones in primary gout

Glutamine Antagonist GA-607 Causes a Dramatic Accumulation of FGAR which can be used to Monitor Target Engagement

BACKGROUND

Metabolomic analyses from our group and others have shown that tumors treated with glutamine antagonists (GA) exhibit robust accumulation of formylglycinamide ribonucleotide (FGAR), an intermediate in the de novo purine synthesis pathway. The increase in FGAR is attributed to the inhibition of the enzyme FGAR amidotransferase (FGAR-AT) that catalyzes the ATP-dependent amidation of FGAR to formylglycinamidine ribonucleotide (FGAM). While perturbation of this pathway resulting from GA therapy has long been recognized, no study has reported systematic quantitation and analyses of FGAR in plasma and tumors.

OBJECTIVE

Herein, we aimed to evaluate the efficacy of our recently discovered tumor-targeted GA prodrug, GA-607 (isopropyl 2-(6-acetamido-2-(adamantane-1-carboxamido)hexanamido)-6-diazo-5-oxohexanoate), and demonstrate its target engagement by quantification of FGAR in plasma and tumors.

METHODS

Efficacy and pharmacokinetics of GA-607 were evaluated in a murine EL4 lymphoma model followed by global tumor metabolomic analysis. Liquid chromatography-mass spectrometry (LC-MS) based methods employing the ion-pair chromatography approach were developed and utilized for quantitative FGAR analyses in plasma and tumors.

RESULTS

GA-607 showed preferential tumor distribution and robust single-agent efficacy in a murine EL4 lymphoma model. While several metabolic pathways were perturbed by GA-607 treatment, FGAR showed the highest increase qualitatively. Using our newly developed sensitive and selective LC-MS method, we showed a robust >80- and >10- fold increase in tumor and plasma FGAR levels, respectively, with GA-607 treatment.

CONCLUSION

These studies describe the importance of FGAR quantification following GA therapy in cancer and underscore its importance as a valuable pharmacodynamic marker in the preclinical and clinical development of GA therapies.

Serum 17-beta-estradiol and testosterone levels in asymptomatic hyperuricaemic men

Low levels of oestrogen, FSH and LH in serum have been reported in patients with gout. The mechanism by which sex hormones affect the development of gout is unknown, but some investigators believe that it is related to the influence of oestrogens on serum uric acid levels. We studied the relationship between serum uric acid and 17 beta oestradiol (ES) levels in asymptomatic hyperuricaemic (ASH) men in order to test the hypothesis that low ES levels are associated with hyperuricaemia. Thirty-eight men with asymptomatic hyperuricaemia (ASH) were selected from a population of healthy individuals undergoing periodical multiphasic health examinations. After adjusting for the differences in albumin levels between the two groups, no significant difference in serum ES level was found. The serum testosterone levels were similar in both groups. These findings suggest that there is no difference in the sex hormone profiles between asymptomatic hyperuricaemic and normouricaemic men.

Hormonal aspects of human gout--excretion of adrenal hormone derivatives in gouty patients

Forty-seven patients with gout, 28 of whom had not previously been treated with allopurinol, and 25 normal subjects, were examined for 24-h urinary excretion of the most important adrenal steroid derivatives. Results were submitted to statistical analysis and several variables have been taken in consideration. The untreated patients showed significantly higher values of uricemia, urinary uric acid, triglycerides, slightly higher values of androsterone, 11-oxo-androsterone + 11-oxo-etiocholanolone, dehydroepiandrosterone, and slightly lower values of 11-hydroxyandrosterone and pregnanetriol, in comparison to normal subjects. The different hormonal pattern seems to discriminate between patients with gout and normal subjects.