MISCODING POTENTIAL OF TAMOXIFEN-DERIVED DNA-ADDUCTS - ALPHA-(N-2-DEOXYGUANOSINYL)TAMOXIFEN

The treatment of tamoxifen, widely used as adjuvant chemotherapy for b reast cancer, increases significantly the risk of developing endometri al cancer. The miscoding properties of tamoxifen-derived DNA adducts, alpha-(N-2-deoxyguanosinyl)tamoxifens (dG-N-2-tamoxifen), have been ex plored, using an in vitro experimental system to quantify base substit utions and deletions. Site-specifically modified oligodeoxynucleotides containing an epimer of trans-and cis-forms of dG-N-2-tamoxifens were prepared postsynthetically and used as templates in primer extension reactions catalyzed by mammalian DNA polymerases alpha, beta, and delt a. Pol alpha catalyzed incorporation of dCMP and dAMP opposite all fou r stereoisomers of dG-N-2-tamoxifen, accompanied by lesser amounts of dGMP. In contrast, pol delta catalyzed preferential incorporation of d CMP, a correct base, opposite the lesions; one of the trans-forms of d C-N-2-tamoxifens only promoted incorporation of dTMP. Using pol beta, preferential incorporation of dCMP, along with small amounts of incorp oration of dAMP and dGMP, was detected. One-and two base deletions wer e also observed with pol alpha and pol beta. The miscoding specificiti es and frequencies of dG-N-2-tamoxifens varied depending on the DNA po lymerase used. In addition, with pol alpha and pol beta, large amounts of 5-base deletions were preferentially formed at the cis-forms of dG -N-2-tamoxifen, but not at the transforms of dG-N-2-tamoxifen. We conc lude that dG-N-2-tamoxifen adducts have high miscoding potentials.