Human Melanoma Xenograft Model Research Articles

Assay for the quinocarmycin analog DX-52-1 in human plasma using high-performance liquid chromatography with automated column switching and low wavelength ultraviolet detection

The hydrocyanated derivative of the antitumor antibiotic quinocarmycin, DX-52-1 (I), exhibits impressive activity against human melanoma xenograft models in vivo. Phase I clinical trials to evaluate this compound as an antineoplastic agent have been initiated by the US National Cancer Institute. We have developed an HPLC assay for the determination of I in human plasma involving automated column switching and UV detection at 210 nm. The preparation of samples for chromatographic analysis entails the preliminary removal of plasma proteins by precipitation with acetonitrile, acidifying the clear supernatant to pH 4.5, then extracting twice with tert.-butyl methyl ether to recover the drug. A heart-cutting procedure employing two HPLC columns with contrasting retention characteristics under isocratic reversed-phase conditions was used to achieve the selectivity required for low wavelength UV detection of the analyte. The sample extract was initially loaded onto a column packed with a cyanopropyl stationary phase. During the predetermined time interval that I eluted from this column, a fully automated six-position switching valve was used to direct the effluent onto an octadecylsilane analytical column. The assay has been thoroughly validated with regard to linearity, inter- and intra-day accuracy and precision, recovery, selectivity and specificity. Using a sample volume of 1.0 ml, the lowest concentration of I quantified with acceptable day-to-day reproducibility was found to be 2.56 ng/ml (R.S.D. 18.9%, n=21, 4 months). This proved to be sufficiently sensitive for pharmacokinetic drug level monitoring in cancer patients treated with a 6-h continuous intravenous infusion of I, even at the starting dose of 3 mg/m 2. The successful performance and reliability of the assay has been demonstrated through extensive application to the routine analysis of plasma specimens acquired during a phase I clinical trial of the drug.

Effect of single and multiple administration of an O6-benzylguanine/temozolomide combination: an evaluation in a human melanoma xenograft model.

The purpose of the present study was to examine the effect of O6-benzylguanine (O6-BG) on the antitumour activity and toxicity of 8-carbamoyl-3-methylimidazo [5, 1-d]-1,2,3,5-tetrazine-4(3H)-one (temozolomide) in a human malignant melanoma xenograft model following single and multiple administration of the combination. O6-BG irreversibly inactivates the DNA-repair protein O6-alkylguanine-DNA alkyltransferase (AGT), which confers resistance to temozolomide. Preadministration of O6-BG (35 mg/kg, i.p.) 1 h prior to temozolomide (i.p.) was examined using single and daily x5 dosing regimens in athymic mice bearing subcutaneous A375P xenografts. The AGT activity of A375P tumors was 95 +/- 8 fmol/mg protein (mean +/- SE, n = 4). O6-BG alone completely suppressed xenograft AGT activity within 1 h of administration but had no effect upon tumor growth. O6-BG did not significantly increase the tumor growth delay induced by a single 200-mg/ kg dose of temozolomide (P > 0.05, two-tailed Mann-Whitney test) but did increase the associated mean body weight loss (P < 0.025). In contrast, when the same dose of temozolomide was divided into five equal fractions (40 mg/kg) and given with O6-BG on 5 consecutive days, a comparable increase in toxicity was accompanied by a very significant increase in tumor growth delay (P < 0.0025), equivalent to that produced by a 3-fold greater dose of temozolomide alone. O6-BG with temozolomide also produced a greater antitumour effect than an equitoxic dose of temozolomide alone on this schedule (P < 0.005). These data indicate that the enhancement of temozolomide antitumour activity by O6-BG preadministration is dependent upon the schedule of drug administration, with multiple dosing of O6-BG + temozolomide producing the greatest effect. The results also suggest that prolonged administration of the combination can lead to an increase in the therapeutic index of temozolomide.