Comparative anthracycline metabolism in rats: loss of marcellomycin fluorescence.

The in vitro metabolism of marcellomycin by rat tissue fractions showed conversion of marcellomycin to 7-deoxypyrromycinone, bisanhydropyrromycinone, and an as yet unidentified compound by rat liver homogenate, microsomes, cytosol, and mitochondria, and purified hepatic reduced nicotinamide adenine dinucleotide phosphate-cytochrome P-450 reductase, under anaerobic conditions and in the presence of reduced nicotinamide adenine dinucleotide phosphate. All these fractions except the purified reductase subsequently induced a progressive loss of fluorescence. Mitochondria, however, were much less active than microsomes, cytosol, and homogenate in inducing this latter phenomenon. Marcellomycin was converted to 7-deoxyaglycones only partially by nuclei. No loss of fluorescence was observed with this subcellular fraction. No loss of fluorescence was observed when doxorubicin or daunorubicin were incubated under similar conditions. The appearance of a compound with distinct spectrophotometric properties was demonstrated by absorbance spectrometry. The formation of a compound with different fluorescent characteristics was excluded, as was the binding of the aglycones to subcellular components. The activity inducing the loss of fluorescence was studied in greater detail with cytosol. It predominated in the liver and required both an electron donor and anaerobic conditions. The optimal pH for the reaction was between 7.5 and 8.0. Our results suggest the existence of an enzymatic pathway capable of converting the fluorescent nucleus of marcellomycin to a nonfluorescent metabolite.

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.

Human pharmacokinetics of marcellomycin.

In conjunction with two phase I clinical trials, we have investigated the pharmacokinetics of marcellomycin (MCM), a new class II anthracycline antibiotic, in nine patients with normal renal and hepatic functions and no third-space fluid accumulation. MCM was infused IV over 15 min at a dosage of 27.5, 40, or 50 mg/m2. Plasma and urine samples were collected up to 72 h. MCM and metabolites were assayed by thin-layer chromatography and quantified by specific fluorescence. The disappearance of total MCM-derived fluorescence from plasma followed first-order kinetics and lacked the rebound in total fluorescence that has been described for the structurally similar agent, aclacinomycin A. After 40-50 mg/m2, the peak MCM concentration in plasma was 1.67 +/- 0.61 microM; MCM disappeared from plasma in a triexponential fashion and was undetectable by 48 h after infusion. The area under the plasma concentration-time plot (AUC), including the infusion time, was 1.11 +/- 0.39 microM X h; plasma clearance of MCM was 1.50 +/- 0.88 l/min/m2. Five other fluorescent compounds were consistently observed in plasma. M2 was a contaminant present in the parent drug. P1 and P2 were conjugates of MCM and M2, respectively. G1 and G2 were aglycones. The peak concentrations of the metabolites were 25% or less or the peak concentration for MCM, but their persistence resulted in higher AUCs than that for MCM. For the dosage of 27.5 mg/m2, fewer data were available; but the pharmacokinetics of MCM and metabolites appeared to be similar to that at higher dosage. Urinary excretion of total fluorescence amounted to 8.0% +/- 1.6% of the total dose at 40-50 mg/m2, and to 7.0% +/- 2.3% at 27.5 mg/m2. No correlation was detected among the various pharmacokinetic parameters and toxicities encountered in these patients.

Comparative murine metabolism and disposition of class II anthracycline antibiotics.

The metabolism and tissue distribution of aclacinomycin A (ACL), marcellomycin (MCM), and musettamycin (MST), three new anthracycline antibiotics, were compared after IV administration to mice. In plasma, total MCM- and ACL-derived fluorescence declined according to first-order kinetics, whereas an initial decline followed by a rebound was observed for MST. In plasma, MCM remained the predominant compound. ACL was eliminated more quickly, and was replaced by two metabolites, the reduced glycoside M1, and an aglycone. In the case of MST, two unidentified metabolites were observed in concentrations equivalent to that of the parent drug. The three drugs were distributed widely to organs, but only ACL achieved measurable concentrations in the brain. Initially, high concentrations of all three drugs were present in the lungs, but these decreased quickly to values similar to those present in the liver and kidneys. Intermediate concentrations of the three drugs were measured in heart and skeletal muscle. Splenic concentrations of all three drugs rose progressively, reaching a maximum at 8 h after injection in the case of ACL and MST, and at 24 h after injection in the case of MCM. Concentrations of the metabolites of MCM and MST were low in all organs except liver and kidney, where the aglycones 7-deoxypyrromycinone and bisanhydropyrromycinone were seen. The metabolism of ACL was extensive. Aglycones were dominant in the liver and kidneys, whereas reduced glycosides predominated in the spleen. These observations indicate that the murine pharmacology of these three structurally similar drugs differs markedly.

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.

The murine metabolism and disposition of marcellomycin.

The metabolism and disposition of marcellomycin (MCM), a new anthracycline antitumor antibiotic, were studied after iv administration to mice. In plasma, total drug fluroescence decreased according to first order kinetics and was mainly comprised of parent drug. In addition to MCM, five compounds (M2, P1, P2, G1, G2) were seen. M2 reflected the presence of a contaminant in the parent drug. P1 and P2 represented polar conjugates of MCM and M2, respectively; and G1 and G2 proved to be aglycones. P1 and G1 were observed during the first hours after injection, and G2 was more persistent and represented 35-50% of total drug fluorescence by 8 hr after injection. MCM was distributed widely to organs, except the brain. High MCM concentrations were measured in the lungs initially but they decreased quickly and, by 60 min, reached values similar to those present in the liver and kidneys. Low MCM concentrations were observed in heart and muscles. The splenic concentration of fluorescence rose progressively and, by 16 hr, was higher than that in all other organs. The concentrations of MCM metabolites were small in all tissues except in the liver, where an aglycone identified as 7-deoxypyrromycinone, was seen during the first 4 hr after injection. Our results indicate that the metabolism of MCM in the mouse is qualitatively similar to that in man, but that important quantitative differences exist. The significance of this observation as a possible explanation of the differences in observed toxicities between the two species remains to be established.