Uniform Potent Activity of the Antiproliferative Metal Chelate Trans-Bis(resorcylaldoximato)copper(II) against a Large Panel of Human Tumor Cell Lines in vitro

Abstract

Background: The copper chelate trans-bis(salicylaldoximato)copper(II), CuSAO₂, is a powerful antitumor agent in vivo, being capable of drastically increasing the life span of mice bearing Ehrlich ascites carcinoma, and has in many cases even a curative effect. This compound as well as some congeners, most notably the 4-hydroxylated analogue trans-bis(resorcylaldoximato)copper(II), CuRES₂, also have potent antiproliferative activity against tumor cells in vitro. Methods: CuRES₂ was tested in vitro against a panel of 37 different types of human tumor cells (leukemias, small cell and non-small cell lung tumors, melanomas, as well as colon, breast, central nervous system, ovarian and renal tumors). The cells were incubated on microculture plates for 6 days, and the amount of viable cells was determined with the agent XTT, whose metabolic reduction gives a colored formazan compound. Results: CuRES₂ inhibited the proliferation of all the 37 cell lines studied. The IC₅₀ values ranged between 0.575 and 8.57 µg/ml and the IC₉₀ values between 1.74 and 20.6 µg/ml. Thus, it had distinct and very potent activity against all the cell lines studied, and the differences between the susceptibilities of different tumor types and cell lines were not very large. Discussion: Clearly, CuRES₂ is active against all the tumor cell lines studied. None of the cell lines (tumor types) demonstrates a significantly higher or lower susceptibility, but some trends appear to exist. Thus, most (but not all) of the leukemia and melanoma cell lines, the two ovarian cancer lines and one small cell lung cancer and one CNS cancer cell line were somewhat more susceptible than the cell lines on average. The results obtained for the melanomas are of special interest, since CuRES₂ (and even more so CuSAO₂) have very low aqueous solubilities. In cutaneous melanomas, their administration might, however, be very easy, since both compounds are soluble in dimethyl sulfoxide and could thus easily be administered topically in this solvent whose ability to be absorbed through the skin is well known. Conclusion: The present results on human tumor cell lines are in line with previous observations that CuSAO₂ and CuRES₂ essentially totally inhibit the proliferation of leukemia L1210 and Ehrlich ascites carcinoma cells in vitro in a concentration as low as ∼5 µg/ml.