Biphasic effect of vanadium salts on in vitro tumor colony growth

Vanadium is a trace element widely distributed in nature. It interferes with a variety of enzyme systems and is also reported to increase DNA-synthesis and in vitro clonal growth of human and mouse fibroblasts. The purpose of the present study was to determine the effect of vanadium salts on the in vitro growth of fresh human tumor specimens. Various concentrations of ammonium metavanadate (AMV), vanadyl sulfate trihydrate (VST) and ortho sodium vanadate (OSV) were tested in a human tumor cloning assay (HTCA). Thirty-four evaluable specimens were tested at concentrations of less than or equal to 10(-10) M of one or more vanadium salts. At this concentration, colony formation was increased by greater than or equal to 150% as compared to control at one or more concentrations in 16 specimens (47%). Twelve evaluable specimens were tested against various concentrations greater than 10(-10) M. Colony formation was inhibited by greater than or equal to 50% of the control at one or more concentrations in all specimens. In further experiments we performed a head-to-head comparison of OSV (10(-3)M) and our standard positive control for cell kill (chromomycin A3, 100 micrograms/ml) in 34 specimens. OSV led to a comparable or better cell kill in 28 tumors (82%). We conclude that vanadium salts at low concentrations (less than or equal to 10(-10)M) can stimulate in vitro colony formation from human tumors. At higher concentrations (greater than 10(-10)M) tumor colony formation is inhibited. OSV might be useful as a very inexpensive positive control in the HTCA. In addition, the value of vanadium salts as antitumor agents should be further investigated in vivo.