Studies on the formation of phthalanilide-deoxyribonucleic acid complexes and their relationship to chemotherapeutic activity.

nucleus are thought to be critical to the function of DNA as a coding template for messenger RNA synthesis (1, 3, 13, 30). Oligoamines and diamines have been reported to interact with DNA to raise the temperature at which the helix †" 4 coil transition occurs (10, 16†" 19, 31). Diamines, such as cadaverine, also protect against the dark inactiva tion of DNA in the presence of proflavine (10). The asso ciation of aromatic amidines with DNA is suggested by the prevention of the antimicrobial action of stilbamidine by the addition of DNA to the growth medium (2). Thus, the finding that the polybasic substituted phthalanilides, which are potent chemotherapeutic agents against rodent leukemias (27), bind to DNA (28) has prompted an investi gation into the nature of this interaction to determine its possible relationship to the chemotherapeutic effect of the drugs. This report deals with the specificity of the interaction with regard to both drug structure and source of DNA. The stability of the DNA-phthalanilide complex to heat and in urea and salt solutions also was studied in order to define partially the forces involved in the binding of phthalaniides to DNA. MATERIALS AND METHODS The interaction between DNA and phthalanilides was characterized by spectral measurements, which were made at room temperature with a Zeiss spectrophotometer model PM Qil. Complex formation was measured as the absorbance of the DNA-phthalanilide solution at 325 m@s minus the absorbance of the phthalanilide solution at 325 mM;the contribution of DNA at 325 m@i was negligible (A3,@= 0.002 †" 0.005). The changes in spectra were ob served immediately on mixing of the DNA and phthalani lide solutions. Although the spectra were constant up to 24 hr at room temperature (28), measurements were generally made within 30 min of the time the solutions were prepared. It was determined previously that the hyperchromic maximum of the difference spectrum oc curred at 325 ms and that the magnitude of the absorbance at 325 m@ increased in proportion to increased DNA con 902 SUMMARY Complexes between DNA3 and substituted iso-and terephthalanilides occur in dilute aqueous solution and are measured by spectrophotometric methods. There appears to be no specificity among DNA preparations from different sources or different phthalanilides with regard to the stoichiometry of the interaction. The DNA-phthal anilide complex is less affected by heating and cooling than DNA alone. Most of the phthalanilide-DNA complexes examined …