Effect of hyperthermia on the in vitro metabolism of doxorubicin.

The effect of hyperthermia on the uptake and metabolism of doxorubicin (ADM) was studied in in vitro systems. ADM uptake in rat liver slices was not affected by increasing the temperature from 37 degrees C to 43 degrees C. In rat liver homogenates, the aerobic transformation of ADM was low and was not affected by hyperthermia. Approximately 90% of the parent drug remained unchanged after 60 minutes of incubation, and two metabolites, adriamycinol and a polar metabolite, were formed in small amounts. Under anaerobic conditions, ADM was quickly and extensively converted to two metabolites identified as 7-deoxyadriamycinol aglycone and 7-deoxyadriamycin aglycone. Whereas the disappearance of ADM and the formation of 7-deoxyadriamycin aglycone were not modified by the hyperthermic conditions, there was a slight but significant increase of the formation of 7-deoxyadriamycinol alycone (area under the concentration versus time curve in microM X minute: 216 +/- 24 at 37 degrees C; 235 +/- 24 at 39.5 degrees C; and 271 +/- 8 at 42 degrees C; P less than or equal to 0.05). However, the percentage of dA3 was not significantly different at the end of the incubation.

Interactions between cyclophosphamide and doxorubicin metabolism in rats. II. Effect of cyclophosphamide on the aldoketoreductase system.

Under anaerobic conditions, in comparison to liver microsomes obtained from normal controls, liver microsomes obtained from rats pretreated with cyclophosphamide formed significantly less 7-deoxydoxorubicinol aglycone (P less than or equal to .05), whereas the disappearance of doxorubicin and the formation of 7-deoxydoxorubicin aglycone were unaffected. When directly investigated, the reduction of 7-deoxydoxorubicin aglycone to 7-deoxydoxorubicinol aglycone by microsomes was inhibited by cyclophosphamide pretreatment. Liver cytosols from controls and cyclophosphamide-treated rats reduced daunorubicin to daunorubicinol and 7-deoxydoxorubicin aglycone to 7-deoxydoxorubicinol aglycone at the same rate, which indicates the lack of effect of cyclophosphamide pretreatment on the cytosolic aldoketoreductase. The results suggest the existence of a microsomal carbonyl reduction system for anthracycline antibiotics and indicate that cyclophosphamide does affect the metabolism of doxorubicin; in rats, this interaction results only in an alteration of the relative concentrations of presumably inactive metabolites, the 7-deoxyaglycones. The importance of these findings for the pharmacological interaction between doxorubicin and cyclophosphamide in humans remains to be investigated.

Plasma pharmacokinetics and tissue distribution of thiotepa in mice.

We defined the plasma and tissue concentrations and pharmacokinetics of thiotepa in 22.8-29.3-g male Swiss-Webster mice injected iv with thiotepa at a dose of 5 mg/kg. Concentrations of thiotepa in ethyl acetate extracts of tissue and plasma were determined by gas chromatography. Plasma concentrations of thiotepa declined in a biexponential fashion that was well-described by the equation: Ct = 52.03e-3.36t + 3.10e-0.072t, indicating an alpha-half-life of 0.21 mins and a beta-half-life of 9.62 mins. Thiotepa was rapidly and extensively distributed through the tissues studied and was not concentrated in any particular tissue, although the liver consistently contained concentrations of thiotepa much lower than any other tissue studied. By 1 hr after injection, there was little thiotepa in plasma or any tissue.

Interactions between cyclophosphamide and adriamycin metabolism in rats.

Rat liver microsomes under anaerobic conditions metabolize adriamycin (ADM) to 7-deoxyadriamycinol aglycone and 7-deoxyadriamycin aglycone. The metabolism of ADM and the concentration of cytochrome P-450 were not affected by preincubation with 2.76 mM cyclophosphamide. After preincubation of microsomes with 0.2 mM 4-hydroperoxycyclophosphamide, a prodrug of 4-hydroxycyclophosphamide, there was complete denaturation of the cytochrome P-450, and 22.8% inhibition of NADPH-cytochrome P-450 reductase. Under these conditions, the degradation of ADM was delayed (area under the concentration vs. time curve in micromolar X minutes: 15.6 +/- 2.4 for the controls, and 59.8 +/- 7.3 in the presence of 4-hydroperoxycyclophosphamide, P less than or equal to .005), 7-deoxyadriamycin aglycone increased progressively to reach a plateau at 20 min instead of showing a peak at 2 min and the formation of 7-deoxyadriamycinol aglycone was reduced. Microsomes from animals pretreated with cyclophosphamide (180 mg/kg i.p. once 4 days before sacrifice) showed a 24.0% reduction of NADPH-cytochrome P-450 reductase activity (P less than or equal to .02). This was accompanied by a decreased formation of 7-deoxyadriamycinol aglycone during the first 20 min of incubation (area under the concentration vs. time curve in micromolar X minutes: 68.0 +/- 15.7 in the controls, and 25.6 +/- 3.1 in the treated animals, P less than or equal to .005), whereas the formation of 7-deoxyadriamycin animals, P less than or equal to .005), whereas the formation of 7-deoxyadriamycin aglycone was not affected. These data indicate an interaction between the metabolism of cyclophosphamide and ADM in rats.