Second derivative techniques in differential scanning calorimetry of DNA modified with platinum compounds

Abstract

The second derivative techniques, which are used in spectroscopy to reveal poorly resolved bands, were adjusted for processing of calorimetric melting profiles of DNAs from higher organisms. The procedure strongly increased the sensitivity of the profiles to various distortions of the double helix and allowed clear resolution of the constituents arising from the melting of satellite DNA (minor narrow peaks) and the rest of genome (dominant wide peak). As an illustration of the advantages of the procedure, selective suppression of narrow satellite peaks was demonstrated as DNA was chemically modified by the antitumor drug cisplatin. As the cisplatin/nucleotide molar ratio increased from 0.001 to 0.05, the peaks decreased in height until they fully disappeared. The influence of cisplatin on the shape of the main peak, which corresponds to the rest of the genome, was much weaker. Transplatin, an ineffective analog of cisplatin, suppressed all constituents of the melting profile without selectivity.