High sensitivity ELISA determination of taxol in various human biological fluids

Taxol (paclitaxel)-the natural product isolated from Pacific yew (Taxus bre vifolia) is a novel agent with high activity in the treatment of patients w ith several malignant turners including those resistant to other cytotoxic drugs. The therapeutic index of this promising anticancer drug could be fur ther increased by the exploration of its pharmacokinetic-pharmacodynamic re lationship in cancer patients. Since taxol is highly protein bound, a very specific and highly sensitive analytical method is required in order to det ermine free, protein unbound and biologically active taxol species in human physiological fluids: plasma; plasma ultrafiltrate; and salivary fluids. I n order to accomplish this, a new indirect competitive enzyme-linked immuno sorbent assay (ELISA), for quantitating such a low bioactive taxol concentr ation level, has been developed in our laboratories. This method uses taxol competitive inhibition of mouse anti-taxol antibodies binding to the solid phase coated antigen 7-succinyltaxol-bovine serum albumin. This indicates recognition of the active taxol in the solution phase, where a diluted hors eradish peroxidase labeled goat anti-mouse enzyme conjugate is used. While employing this technique, after systematic optimization of the experimental conditions, we are able to detect the anticipated taxol in plasma ultrafil trate and salivary fluids at the concentration level of subpicogram per mil liliter. The working range of the assay is approximately five orders in mag nitude, i.e. from pg ml(-1) to 100 ng ml(-1). The clinical part of this stu dy verified the working range of the ELISA method using samples of physiolo gical fluids from a cancer patient treated with 3 h intravenous (IV) infusi on of this drug. Our results of taxol determination in plasma, plasma ultra filtrate and saliva demonstrate the applicability of the newly developed EL ISA method for further pharmacokinetic studies of free, biologically active taxol species in cancer patients. (C) 1999 Elsevier Science B.V. All right s reserved.