Marcellomycin

Desorption chemical ionization mass spectrometry with ammonia as the reagent gas was used to obtain positive ion spectra of twelve alkyl-anthraquinones, seven anthracyclinones, eleven anthracycline antibiotics and nine oligosaccharides (di- and trisaccharides). Ions corresponding to the intact molecules (M) were present in all spectra as pseudo-molecular ions [M + H]+ and/or [M + NH]+. However, the most significant results were obtained in the case of anthracyclines and oligosaccharides. With anthracyclines, in addition to the preceding ions, spectra exhibited characteristic fragment ions due to the aglycon or to the sugar moiety while ions corresponding to the sequential loss of monosaccharide units were observed with oligosaccharides. All these fragment ions can be readily explained by an initial site of protonation located at the oxygen atom of the glycosidic linkages.

Marcellomycin is a strong inhibitor of the Escherichia coli RNA polymerase-catalyzed synthesis of RNA from the strong A promoters of bacteriophage T7 DNA. Marcellomycin inhibits preferentially the last phase of transcription initiation. During this phase a stabilized ternary complex is formed consisting of RNA polymerase, DNA template, and a nascent RNA oligonucleotide about 11 nucleotides long, resulting from the extension of the RNA dinucleotide component of the corresponding early ternary complex. Marcellomycin is also responsible for minor inhibition of the formation of the open binary RNA polymerase-template complex, which serves as the precursor of the ternary complex. These findings suggest that marcellomycin may be a potentially useful tool in the study of the late stages of transcription initiation. The present findings may also contribute to a better overall understanding of the mode of drug action at the level of individual genes.

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.