Development of a chiral HPLC method to evaluate in vivo enantiomeric inversion of an unstable, polar radiosensitizer in plasma

A chiral HPLC method to quantify in vivo enantiomeric inversion of prodrug CI-1010 (IR) or its drug IIR (PD 146923), a radiosensitizer, upon X-irradia tion of dosed rats was developed. These polar enantiomers were separated on ly by using normal-phase chiral HPLC. A Chiralpak AS column provided the be st separation. Isolation of analytes from plasma employed solid-phase extra ction (SPE), and required conditions that were compatible with normal-phase HPLC. Options for SPE were restricted by the chemically reactive nature of both prodrug and drug, which produced analyte losses as high as 100%. Acce ptable recoveries using SPE required evaluation of conditions for analyte c hemical stability. The validated method gave a lower-limit of quantitation (LLOQ) of 200 ng/ml for each enantiomer extracted from 0.15 mi of plasma. T he LLOQ of the inverted enantiomer could be detected in the presence of 10 000 ng/ml of the dosed enantiomer. Precision (RSD) ranged from 14.2 to 4.4% , and from 24.2 to 5.1% for IIS and IIR, respectively. Accuracy (RE) was +/ - 13.1 and +/- 13.2%, respectively. Recoveries ranged from 44.3 to 71.4%, a nd from 40.7 to 67.9%, for IIS and IIR, respectively. (C) 1999 Elsevier Sci ence B.V. All rights reserved.