MOLECULAR AND CELLULAR INTERACTIONS BETWEEN INTOPLICINE, DNA, AND TOPOISOMERASE-II STUDIED BY SURFACE-ENHANCED RAMAN-SCATTERING SPECTROSCOPY

The surface-enhanced Raman scattering spectra of the new antitumoral a gent, intoplicine (RP 60475, NSC 645008), and those of its complexes w ith DNA and topoisomerase II in vitro and in K562 cancer cells were ob tained. Intoplicine was found to unwind DNA and to inhibit purified ca lf thymus topoisomerase II via a stabilization of the ternary cleavabl e complex. The intensity of the surface-enhanced Raman scattering spec trum of intoplicine was not modified by the addition of plasmid pBR322 or calf thymus DNA. In the complex of this antitumor agent with topoi somerase II, the signal of intoplicine was completely abolished, indic ating that at least some portion of intoplicine binds to an internal p art of the enzyme. During the formation of the ternary complex, intopl icine was released from the interior of the protein and formed hydroge n bonds via its hydroxyl and/or amino groups. Similar modifications of the intoplicine spectra were found by microsurface-enhanced Raman sca ttering spectroscopy of the compound in the nucleus of treated K562 ce lls. In contrast, intoplicine was found to be in a free form in the cy toplasm.