Ambazone (1,4-
benzoquinone guanylhydrazone
thiosemicarbazone) was found to be active against various transplantable
tumors in mice as well as rats. When administered orally for 4-9 days, the effective therapeutic dose ranged between 60 and 125 mg/kg. The
antineoplastic effect of
ambazone appeared to be mediated, at least in part, by the immune system. In order to characterize the
drug, biophysical and biophysicochemical studies were carried out using thin-layer chromatography, absorption spectroscopy and polarographic measurements. The distribution of
ambazone in an
n-octanol/water system indicated low hydrophobicity, thereby excluding the possibility of a preferential contribution from hydrophobic forces to the mode of action of
ambazone.
Ambazone undergoes three protonation reactions with pK values at 10.69 (equilibrium between the negatively charged and neutral forms), 7.39 (equilibrium between the neutral and singly positively charged form) and 6.22 (equilibrium between the singly and doubly positively charge form). Interaction of the
drug with model membrane system was monitored by spectrophotometric and fluorescence measurements. Using the fluorescence label 1-anilino-8-naphthalenesulfonic
acid (ANS) as a probe pointed to the interaction of
ambazone with the inner area of the
phospholipid bilayer matrix of
liposomes as being nonspecific.
Ambazone induces an overall increase in the cellular cAMP content of
leukemia cells and macrophages. So far, membrane interaction has provided a molecular basis for both immunological and
antineoplastic activities of the
drug. By performing DNA melting experiments, it was shown that neutral or singly positively charged
ambazone species stabilize the secondary structure of
DNA, while the doubly positively charged form binds more strongly and destabilizes the
DNA. After
oral administration to rats and mice,
ambazone was found to be incompletely absorbed from the gastrointestinal tract, to an extent of about 35-50%. Absorbed
ambazone binds only weakly to
plasma proteins, whereas its binding to red blood cells is relatively strong. The mutagenic potential of
ambazone shown in bacterial systems and human lymphocytes corresponds to its relatively weak interaction with
DNA. The
toxic action of
ambazone on the intestine is believed to be due to inhibition by the
drug of
bacterial DNA,
RNA and
protein syntheses. It is assumed that the reported affinity of
ambazone for different cellular targets, i.e., membranes,
nucleic acids and
proteins, contributes to the overall antibacterial effect. The weak
antiviral activity of
ambazone in the Sendai virus/chicken embryo fibroblast system is probably the result of the interaction with Sendai virus NH
glycoprotein.