<Emphasis Type="Italic">In vitro</Emphasis> inhibitory effect of polyoxometalates on human tumor cells

H₇NiV₁₃O₃₈] was synthesized from K₇NiV₁₃O₃₈] using an ion exchange method. Then Pr₂HNiV₁₃O₃₈] was obtained by double decomposition of H₇NiV₁₃O₃₈] with Pr₂(CO₃)₃. The actual amount of praseodymium measured by elemental analysis coincides with the designed amount of praseodymium in Pr₂HNiV₁₃O₃₈]. The i.r. spectra suggested that the NiV₁₃O₃₈]^7– anion did not collapse after the ion exchange and double decomposition. The ⁵¹V n.m.r. spectrum of Pr₂HNiV₁₃O₃₈] showed four peaks and their ratio of the relative intensity was 4:4:4:1. This result agrees with the chemical environment of V atoms in the NiV₁₃O₃₈]^7– anion. In vitro antitumor activities of polyoxometalates on several human tumor cells have been investigated using the MTT method. Pr₂HNiV₁₃O₃₈] is the most effective polyoxometalate tested in this study for inhibiting KB cell. Pr₂HNiV₁₃O₃₈] also showed remarkable inhibitory effect on some other tumor cells: HCT, Bel, B₁₆, BCAP and ESCL cells. These results indicate that Pr₂HNiV₁₃O₃₈] is a potent broad spectrum antitumor agent. The structure type of polyoxometalates greatly influences their antitumor activity: the order of structure type for inhibiting KB cell is: NiV₁₃O₃₈]^7–>Mo₇O₂₄]^6–>Anderson structure Keggin structure Dawson structure. Moreover, the nature of the polyatom in the polyoxometalates also greatly influences their antitumor activity: the polyatom order for inhibiting KB cell is: V>Mo W. On the other hand, the nature of the counter cation and the heteroatom in the polyoxometalates exerted a relatively small influence on the inhibitory effect against the KB cell, although the praseodymium salt of NiV₁₃O₃₈]^7– showed a higher antitumor activity than its potassium salt.