mitoguazone and Melanoma

In order to better understand the development of skeletal metastases, we developed an appropriate animal model, as the natural progression of metastases in humans cannot be studied on the cellular level. In this study, we established a new animal model which developed bone metastasis in a bone grafted subcutaneously. C57BL/6 mice, which had received a bone (femur or tibia) transplanted in the dorsal subcutis, were injected with B16 melanoma cells into the left heart ventricle. Metastasis was found in approximately 70% of the extraskeletal bones. Using this model, the antimetastatic effect of a polyamine synthesis inhibitor was investigated. Inhibitors of the polyamine biosynthetic pathway have received considerable attention for their potential use in the treatment of cancer as they are responsible for the greatly increased production of the polyamines putrescine, spermidine, and spermine. A polyamine synthesis inhibitor, methylglyoxal-bis(cyclopentylamidinohydrazone) MGBCP, was investigated for its inhibitory effects on bone metastases. MGBCP (20 mg/kg) was administered intraperitoneally every day for 4 weeks and demonstrated strong inhibitory effects on bone metastases. MGBCP inhibited angiogenesis in the transplanted bone and the growth of B16 melanoma cells, thus suggesting a preventive mechanism in bone metastasis. No remarkable adverse effects of MGBCP were observed in any animal throughout the experimental period. Our results indicate that MGBCP has a strong potential for use as an anti-metastatic drug.

Topics: Animals; Antineoplastic Agents; Bone Neoplasms; Disease Models, Animal; DNA Fragmentation; Melanoma; Mice; Mice, Inbred C57BL; Mitoguazone; Neovascularization, Pathologic; Polyamines; Tumor Cells, Cultured

Both 2-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (EC 4.1.1.17), and methylglyoxal bis(guanylhydrazone) (MGBG), a competitive inhibitor of S-adenosylmethionine decarboxylase (EC 4.1.1.50), strikingly stimulated melanotic expression of murine Cloudman S91 melanoma cells. The stimulation of tyrosinase (EC 1.10.3.1) activity and melanin formation by DFMO was closely associated with intracellular depletion of putrescine and spermidine developed in response to the drug. However, little or no evidence was obtained indicating that enhanced melanogenesis in response to MGBG was mediated through an inhibition of polyamine biosynthesis. Indirect inhibitors of ornithine decarboxylase, such as 1,3-diaminopropane and 1,3-diaminopropan-2-ol, but not putrescine, likewise inhibited the growth of the melanoma cells and stimulated their melanin production. The stimulation of melanogenesis by polyamine antimetabolites was not mediated by cyclic adenosine 3':5'-monophosphate, in contrast to the effect elicited by alpha-melanotropin. It is also unlikely that MGBG or the diamines acted as lysosomotropic agents capable of stimulating tyrosinase activity in situ, since the enzyme activity was stimulated by the drugs irrespective of whether assayed in cultured cells or using cell-free homogenates. None of the agents stimulated tyrosinase activity in vitro. The effect of DFMO and MGBG on melanoma cell proliferation was reversible, but the restoration of normal growth and melanin formation, especially in cells exposed to DFMO, was remarkably slow. The present results represent a further experimental model, in which the inhibition of polyamine accumulation is accompanied by signs of terminal differentiation.

Topics: Animals; Cell Division; Cells, Cultured; Eflornithine; Guanidines; Melanins; Melanoma; Mice; Mitoguazone; Monophenol Monooxygenase; Ornithine; Polyamines

An exposure of cultured Cloudman S91 melanoma cells to inhibitors of polyamine biosynthesis, 2-difluoromethylornithine (DFMO) and methylglyoxal bis(guanylhydrazone) (MGBG), distinctly promoted the expression of differentiated biochemical functions of the tumor cells. Slight to moderate growth inhibition produced by the compounds was associated with a stimulation of melanogenesis, as reflected by a striking enhancement of tyrosinase (EC 1.10.3.1) activity and an increase in cellular melanin content. Both antimetabolites acted synergistically with alpha-melanotropin (MSH), as regards the stimulation of melanogenesis. Exposure of the melanoma cells to MSH resulted in most experiments in a marked decrease of the intracellular polyamine pools, usually involving all three polyamines (putrescine, spermidine and spermine). The DFMO-induced stimulation of melanogenesis was totally suppressed by the administration of putrescine, whereas the MSH-stimulated tyrosinase activity was not influenced by the diamine. Although many recent reports indicate that terminal differentiation is accompanied by a distinct stimulation of polyamine biosynthesis, our results suggest that in certain cells polyamine deprivation may lead to an enhanced expression of differentiated phenotype.

Topics: Animals; Antineoplastic Agents; Cell Differentiation; Cell Division; Cell Line; Drug Synergism; Eflornithine; Guanidines; Melanins; Melanocyte-Stimulating Hormones; Melanoma; Mice; Mitoguazone; Monophenol Monooxygenase; Ornithine; Polyamines

Topics: Animals; Cricetinae; Female; Guanidines; Male; Melanoma; Mesocricetus; Mice; Mice, Inbred Strains; Mitoguazone; Neoplasms, Experimental; Skin Neoplasms

The toxicity to cultured cells of the cancer chemotherapeutic agent methylglyoxal-bis[guanylhydrazone] (MGBG) varies considerably between different cell lines and is always more toxic in the absence of exogenous polyamine. We have looked at the relative MGBG toxicity of two different murine melanoma tumour cell lines (Harding-Passey and Cloudman) and normal murine fibroblasts, and found wide variation with no correlation in sensitivity to MGBG between tumour and normal cells. High sensitivity to MGBG may be associated with high transport across the cell membrane.

Topics: Animals; Cell Count; Cell Line; DNA; Dose-Response Relationship, Drug; Fibroblasts; Guanidines; Melanoma; Mice; Mitoguazone; Mitosis; Neoplasms, Experimental; Protein Biosynthesis; Spermine

Methyl-GAG was tested in organotypic cultures of malignant tumors of human and mice. In 3 cases, a reduction of the activity of two oxydoreductases (lactate dehydrogenase and NADH-diaphorase) after treatment with methyl-GAG was observed whereas in 19 other cultivated tumors no change of enzyme activity was induced by methyl-GAG. Electronmicroscopy revealed only minor structural alterations of tumor cells after application of methyl-GAG as compared with control cultures.

Topics: Animals; Breast Neoplasms; Cells, Cultured; Female; Guanidines; Histocytochemistry; Humans; L-Lactate Dehydrogenase; Mammary Neoplasms, Experimental; Melanoma; Mice; Mitoguazone; NADPH Dehydrogenase; Ovarian Neoplasms