Bioanalytical method for quantitative determination of mithramycin analogs in mouse plasma by HPLC-QTOF.

Mithramycin (MTM) has potent anticancer activity, but severe toxicities restrict its clinical use. Semi-synthetic approaches have yielded novel MTM analogs with potentially lower toxicity and similar efficacy. In an effort to transition these analogs into in vivo models, a bioanalytical method was developed for their quantification in mouse plasma. Here we present the validation of the method for the quantitation of mithramycin SA-tryptophan (MTMSA-Trp) as well as the applicability of the methodology for assaying additional analogs, including MTM, mithramycin SK (MTMSK) and mithramycin SA-phenylalanine (MTMSA-Phe) with run times of 6 min. Assay linearity ranged from 5 to 100 ng/mL. Accuracies of calibration standards and quality control samples were within 15% of nominal with precision variability of <20%. MTMSA-Trp was stable for 30 days at -80°C and for at least three freeze-thaw cycles. Methanol (-80°C) extraction afforded 92% of MTMSA-Trp from plasma. Calibration curves for MTM and analogs were also linear from ≤5 to 100 ng/mL. This versatile method was used to quantitate MTM analogs in plasma samples collected during preclinical pharmacokinetic studies.

Quantitative determination of mithramycin in human plasma by a novel, sensitive ultra-HPLC-MS/MS method for clinical pharmacokinetic application.

Mithramycin is a neoplastic antibiotic synthesized by various Streptomyces bacteria. It is under investigation as a chemotherapeutic treatment for a wide variety of cancers. Ongoing and forthcoming clinical trials will require pharmacokinetic analysis of mithramycin in humans, both to see if target concentrations are achieved and to optimize dosing and correlate outcomes (response/toxicity) with pharmacokinetics. Two published methods for mithramycin quantitation exist, but both are immunoassays that lack current bioanalytical standards of selectivity and sensitivity. To provide an upgraded and more widely applicable assay, a UPLC-MS/MS method for quantitation of mithramycin in human plasma was developed. Solid-phase extraction allowed for excellent recoveries (>90%) necessary for high throughput analyses on sensitive instrumentation. However, a ∼55% reduction in analyte signal was observed as a result of plasma matrix effects. Mithramycin and the internal standard chromomycin were separated on a Waters Acquity BEH C18 column (2.1×50 mm, 1.7 µm) and detected using electrospray ionization operated in the negative mode at mass transitions m/z 1083.5→268.9 and 1181.5→269.0, respectively, on an AB Sciex QTrap 5500. The assay range was 0.5-500 ng/mL and proved to be linear (r(2)>0.996), accurate (≤10% deviation), and precise (CV<15%). Mithramycin was stable in plasma at room temperature for 24 h, as well as through three freeze-thaw cycles. This method was subsequently used to quantitate mithramycin plasma concentrations from patients enrolled on two clinical trials at the NCI.

Determination of plicamycin in plasma by radioimmunoassay.

This article describes a method for the determination of plicamycin in plasma by radioimmunoassay. The anti-plicamycin antibody was produced against a plicamycin-bovine serum albumin conjugate prepared by using diazotized p-aminobenzoic acid as a cross-linker. The radiolabeled ligand, 125I-plicamycin, was prepared by the chloramine-T method. The linear plicamycin concentration range was 7-400 ng/ml. The coefficients of variation for intra- and interday variabilities were 7.5 and 15%, respectively. No interference was observed from either the structurally related chromomycin A or concomitantly used drugs hydroxyurea or allopurinol. With this method of testing, plicamycin levels in plasma could be determined in patients receiving small (0.85-1.0 mg/m2) therapeutic plicamycin doses. Preliminary pharmacokinetic data in humans indicate that the plasma drug disappearance curve was biphasic with a mean elimination half-life of 10.6 +/- 1.7 h, total clearance rate of 11.1 +/- 0.4 ml/min/m2, and area under the plasma drug concentration-time curve of 1,289-1,546 ng-h/ml. This assay method is clinically useful for pharmacokinetic studies of plicamycin and may be helpful in the design of rational therapeutic drug trials.