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Theophylline- and caffeine-treated B16-F10 cells exhibited low adhesion to laminin/collagen type IV and reduced invasion through Matrigel in an in vitro assay. In contrast, theobromine appeared ineffective. When young adult C57BL/6 mice were injected intravenously with theophylline-treated B16-F10 cells, the number of surface lung tumours was markedly reduced. Densitometric analyses performed on digitalized microscopic images of histological sections of lung were used to estimate the frequency (number of lung foci; NLF) and the size (average area of metastatic foci; AMF) of the resulting tumour foci. These parameters were correlated to the proliferation (AMF) and invasion (NLF) of melanoma cells in vivo. The data showed a similar theophylline-induced decrease in the AMF and NLF values (71%, P < 0.01). Caffeine treatment produced a more pronounced decrease in the AMF (61%, P < 0.01) than in the NLF (25%, P < 0.01). To our knowledge, this is the first demonstration that theophylline and caffeine possess the capacity to inhibit not only cell proliferation, but also the metastatic behaviour of melanoma cancer cells.

Hepatocyte growth factor (HGF)/scatter factor (SF) is a pleiotropic cytokine that acts as a mitogen, motogen, and morphogen for a variety of cell types. HGF/NK1 and HGF/NK2 are two naturally occurring truncated variants of HGF/SF, which extend from the NH2 terminus through the first and second kringle domain, respectively. Although these variants have been reported to have agonistic or antagonistic activity relative to HGF/SF in assays of cell proliferation and motility, their potential morphogenic activity has not been investigated. To address this issue, we assessed the ability of HGF/NK1 and HGF/NK2 to induce tube formation by (a) MCF-10A mammary epithelial cells grown within collagen gels and (b) human umbilical vein endothelial (HUVE) cells grown on Matrigel. We found that HGF/NK1 stimulated tubulogenesis by both MCF-10A and HUVE cells, whereas HGF/NK2 did not stimulate tubulogenesis, but efficiently antagonized the morphogenic effect of full-length HGF/SF. HGF/NK1 and HGF/NK2 also had agonistic and antagonistic effects, respectively, on MCF-10A cell proliferation and HUVE cell migration. These results demonstrate that HGF/NK1, which only consists of the NH2-terminal hairpin and first kringle domain, is sufficient to activate the intracellular signaling pathways required to induce morphogenic responses in epithelial and endothelial cells. In contrast, HGF/NK2, which differs from HGF/ NK1 by the presence of the second kringle domain, is devoid of intrinsic activity but opposes the effects of HGF/SF. The differential properties of the two HGF/SF isoforms provide a basis for the design of more potent HGF/SF agonists and antagonists.