D. H.W. Ho

Treatment of cultured human colon carcinoma cells with fluorinated pyrimidines

The shape of the initial part of the dose‐dependent response curve of LoVo cells, an established human colon carcinoma cell line, exposed for 1 hr to graded concentrations of 5‐FU depended on the medium supplement, i.e., fetal calf serum (FCS), in which the cells were treated and subsequently incubated for colony‐formation. At concentrations of 50–100 μg/ml (equivalent to peak plasma levels following an in vivo bolus dose of 15 mg/kg) cell kill was completely prevented by FCS. The serum did not contain thymidine (TdR) but had significant amounts of uridine (UR). When 5‐FU was delivered in dialyzed FCS, concentrations of 50–100 μg/ml achieved only a modest 15% cell kill after 1 hour treatment. Regardless of medium supplement, the killing effect of 5‐FU did not increase beyond concentrations greater than 2,000 μg/ml. Increasing the exposure interval dramatically increased the killing of LoVo cells by 5‐FU, although the effects of medium supplement on the degree of cell survival persisted for about 12 hours. Virtually all of the incorporated 5‐FU was transformed into 5‐FUR, and a very small proportion eventually was incorporated into nucleic acids, suggesting that the killing effect of 5‐FU on LoVo cells is mediated mostly by ribosidation and not by conversion into the deoxyribonucleoside. This conclusion is supported by the failure of 5‐FUdR to kill LoVo cells after a treatment interval of one hour, even at concentrations of 5000 μg/ml; yet after the same exposure interval, 5‐FUR effectively killed cells at concentrations of 50–100 μg/ml. TdR afforded no protection from cell kill by 5‐FU. In contrast, UR was capable of protecting LoVo cells from the lethal effects of both 5‐FU and 5‐FUR even at concentrations as low as 10 μg/ml. Ftorafur exposed to LoVo cells for 1 hour had a slight killing effect (about 20–25%) at concentrations ranging up to 2000 μg/ml. Although the lethal effect of ftorafur was slightly increased after longer periods of incubation, it failed to reach 90% even after intervals of 48 hours. The results on cellular sensitivity that we obtained for LoVo cells treated with various fluorinated pyrimidines differ substantially from those of other investigators who used different methods to assess cell killing on nonhuman and noncolonic cell systems. The predictive relevance of these data as compared to those obtained in other systems is justified by the suboptimal results with these agents in clinical practice.

Radioimmunoassay for the detection and quantitation of bruceantin

Abstract A radioimmunoassay for a new anticancer drug, bruceantin, has been developed using [ 3 H]acetylbruceantin and antibody induced by immunizing rabbits with succinylbruceantin-bovine serum albumin conjugates. [ 3 H]Acetylbruceantin was synthesized by reacting bruceantin with [ 3 H]acetyl anhydride. The assay is simple and reproducible. The standard curve was linear on a logit-log plot, and the lower limit of sensitivity of the assay was 1 ng/ml. Using this assay, drug levels were easily determined in tissues of experimental animals following bruceantin administration. The assay procedure does not require sample extraction for plasma, urine, and bile. Bruceantin in other tissues can be extracted quantitatively with ethanol before being measured by the radioimmunoassay.

Clinical pharmacology of bruceantin by radioimmunoassay.

SummaryDuring the phase I clinical trial of a new antitumor agent, bruceantin, the pharmacology was studied in 18 cancer patients. The drug was infused intravenously (IV) for 3 h at doses ranging from 1 to 3.6 mg/m2 per day for 5 days. The plasma drug disappearance curves were biphasic, with a fast initial half-life of less than 15 min. The second half-life (t1/2β) varied from 0.7 to 38 h among different patients and was not dose-related. The difference between the t1/2β on day 1 and that on day 5 was not significant. In patients with normal liver function, the mean plasma concentration at the end of infusion was 22 ng/ml, and the value of the area under the concentration x time curve (AUC) was 111 (ng/ml)h. In contrast, in patients with abnormal liver function the corresponding values were 115 ng/ml and 830 (ng/ml)h, respectively. In addition, these patients had a slower elimination half-life of 10.9 h and a decreased total clearance of 157. ml/min/m2, as compared with 2.6 h and 671 ml/min/m2, respectively, for the normal group. All these differences were statistically significant.Patients with abnormal liver function developed more severe toxicity, including fever, severe nausea, vomiting, and hypotension. Two patients with severe hepatic dysfunction received a reduced dose and developed no toxicity. These results demonstrated the importance of the effects of liver dysfunction on drug disposition and showed that the dosage should be reduced in patients with hepatic dysfunction.