Transfer RNA bindings to antitumor estradiol-platinum(II) hybrid and cisplatin.

The anticancer platinum (Pt) drugs exert their antitumor activity by direct or indirect Pt-DNA binding. It has been shown that Pt drugs can induce major DNA damage and minor RNA damage during cancer treatment. A recent report showed that a new anticancer estradiol-Pt(II) hybrid molecule (CD-37) binds DNA bases indirectly, while being more effective than cis-diaminedichloroplatinum(II) (cisplatin) against several types of cancer. In this report, we examine the bindings of CD-37 and cisplatin drugs with transfer RNA (tRNA) in vitro and compare the results to those of the corresponding Pt-DNA complexes. Solutions containing various CD-37 or cisplatin concentrations were reacted with tRNA at physiological pH. Using Fourier transform infrared (FTIR), UV-visible, and circular dichroism spectroscopic methods, the drug binding mode, the binding constant, and RNA structural variations are determined for Pt-tRNA complexes in aqueous solution. Structural analysis showed direct binding of cisplatin drug to guanine and adenine N7 sites, while both direct and indirect interactions of CD-37 with tRNA bases and the backbone phosphate group were observed. The overall binding constants estimated were K(CD-37) = 2.77 (+/-0.90) x 10(4) M(1) and K(cisplatin) = 1.72 (+/-0.50) x 10(4) M(1). Major aggregation of tRNA occurs at high CD-37 concentrations, while RNA remains in the A-family structure.