Further studies on cytostatic activity of alkoxymethyl purine and pyrimidine acyclonucleosides

The influence of 14 acyclonucleosides(1), derivatives of adenine, guanine, uracil and thymine on the phosphorylation of dAdo, dGuo, dCyd and dThd occu rring in the cytosol of growing amelanotic melanoma transplanted to Syrian hamsters, as well as on inhibition of tumor growth were studied. From among the studied ACNs eight were tested earlier (Modrzejewska et nl., 1996, The influence of alkoxymethyl purine and pyrimidine acyclonucleosides on growt h inhibition of Kirkman-Robbins hepatoma and possible mechanism of their cy tostatic activity, Z. Naturforch, 51c, 75-80); from among the newly synthes ized ACNs, 1,3-N,N-diallyloxymethylthymine (AMT2), 1-N-allyloxymelhyl-5,6-t etramethyleneuracil (AMUTM), and tested previously 1-N-allyloxymethylthymin e (AMT1), administered i.p, in a dose of 0.2 mmol /kg body weight reduce th e tumor mass from 0.98 g to 0.64 g +/- : 0.11 g (i.e. 35% +/- 12%). 48 hour s after i.p. administration of the mentioned ACNs in the same dose a reduct ion of tumor mass is accompanied by the inhibition of dAMP, dGMP and dTMP s ynthesis, AMT1 inhibits dThd phosphorylation from 6.2 to 4.22; AMT2 suppres ses dAdo, dGuo and dThd phosphorylation by correspondingly, from 2.8 to 1.7 , from 10.8 to 7.5 and from 6.2 to 4.2; AMUTM depresses dAMP synthesis from 2.8 to 1.6 (all data: mu mol of 2'dNMP formed per mg of protein per min. x 10(-4)). None of the 14 studied acyclonucleosides influences dCMP synthesi s. In vivo, after hydration of allyloxymethyl group to hydroxypropoxymethyl residue (having -CH2OH group), AMT1, AMT2 and AMUTM undergo phosphorylatio n to corresponding triphosphates. Phosphorylated ACNs are not incorporated into tumor DNA, however they inhibit dAdo, dGuo and dThd incorporation into DNA. It is concluded that ACN triphosphates are not substrates for DNA pol ymerase but, competing with dATP dGTP and dTTP, inhibit incorporation of th ese 2'dNTP into DNA and, in consequence, reduce tumor growth, which is pres umed to be the main mechanism of cytostatic activity of the studied ACNs.