Two oligodeoxyribonucleotides, d-CTTCTTTTTTATTTT, I(A), and d-ATTATTTTTTATTTT, II(A), where C is 5-methylcytosine and A is 8-oxoadenine, were prepared and their interactions with the duplex d-GAAGAAAAAAYAAAA/d-TTTTZTTTTTTCTTC, III.IV(Y.Z), were studied. Oligomers I(A) and II(A) each form triplexes with III.IV(G.C) at temperatures below 20 degrees C as shown by continuous variation experiments, melting experiments, and circular dichroism (CD) spectroscopy. The CD spectra of these triplexes are almost identical to those formed by I(C) and II(C), oligomers which contain cytosine in place of 8-oxoadenine. This suggests that the 8-oxoadenine-containing triplexes have conformations which are very similar to those of the cytosine-containing triplexes. The melting temperature (Tm) for dissociation of the third strand of triplex II.III.IV(A.G.C) is 22 degrees C at pH 7.0 and 8.0, whereas the Tm of the corresponding transition in triplex II.III.IV(C.G.C) decreases from 28 degrees C at pH 7.0 to 17 degrees C at pH 8.0. The pH dependence of the Tm in the latter triplex reflects the necessity of protonating the N-3 of cytosine in order for it to form two hydrogen bonds with G of the G.C base pair. It appears that the keto form of 8-oxoadenine can potentially form two hydrogen bonds with the N-7 and O-6 atoms of G of the G.C base pair, when the 8-oxoadenine is in the syn conformation and in contrast to cytosine does not require protonation of the base. Oligomer I(A) does not form triplexes with III.IV(Y.Z) when Y.Z is A.T or T.A.(ABSTRACT TRUNCATED AT 250 WORDS)

Free radical derivatives of peroxides, hydroperoxides, and anthrones are thought to mediate tumor promotion by these compounds. Further, the promoting activity of phorbol esters is attributed, in part, to their ability'to stimulate the cellular generation of oxygen radicals. A hydroperoxide metabolite of butylated hydroxytoluene, 2,6-di-tert-butyl4-hydroperoxyl4-methyl-2,5-cyclohexadienone (BHTOOH), has previously been shown to be a tumor promoter in mouse skin.BHTOOH is extensively metabolized by murine keratinocytes to several radical species. The primary radical generated from BHTOOH is a phenoxyl radical that can disproportionate to form butylated hydroxytoluene quinone methide, a reactive electrophile. Since electrophilic species have not been previously postulated to mediate tumor promotion, the present study was undertaken to examine the role of this electrophile in the promoting activity of BHTOOH. The biological activities of two chemicalanalogs of BHTOOH, 4-trideuteromethyl-BHTOOH and 4-terl-butyl-BHTOOH, were compared with that of the parent compound. 4-Trideuteromethyl-BHTOOH and 4-tertbutyl-BHTOOH have a reduced ability or inability, respectively, to form a quinone methide; however, like the parent compound, they both generate a phenoxyl radical when incubated with keratinocyte cytosol. The potency of BHTOOH, 4-trideuteromethyl-BHTOOH, and 4-tert-butyl-BHTOOH as inducers of ornithine decarboxyiase, a marker of tumor promotion, was commensurate with their capacity for generating butylated hydroxytoluene quinone metbide. These initial results were confirmed in a two-stage tumor promotion protocol in female SENCAR mice. Together, these data indicate that a quinone methide is mediating tumor promotion by BHTOOH, providing direct evidence that an electrophilic intermediate can elicit this stage of carcinogenesis.Butylated hydroxytoluene (BHT; 2,6-di-tert-butyl4methyl-phenol) has found wide commercial application because of its excellent antioxidant properties. Although BHT has attained generally regarded as safe (GRAS) status as afood additive, this phenolic antioxidant has toxic as well as carcinogenic properties (1,2). For example, BHT is toxic in both liver and lung and has been reported to increase tumorformation in the progeny ofrats that had high lifetime feeding of BHT (3). BHT is also a weak hepatocarcinogen in male mice (4). The most notable carcinogenic property of BHT, however, lies in its ability to act as a tumor promoter in a variety oftissues, including the liver, lung, colon, bladder, and thyroid (5). BHT is known to be extensively metabolized in its target tissues, and the toxic as well as tumor-promoting activities of BHT are thought to be mediated by metabolites of the parent compound. The role of the metabolism of BHT in its actions as a promoter and toxin is highlighted by the ability of several inhibitors of cytochrome P450 to suppress BHT toxicity (6, 7) and the observation that a hydroxylated metabolite is more effective than BHT as either a tumor promoter or toxin in mous...

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The preparation of oligodeoxyribonucleoside methylphosphonates derivatized with 3-[(2-aminoethyl)carbamoyl]psoralen [(ae)CP] is described. These derivatized oligomers are capable of cross-linking with single-stranded DNA via formation of a photoadduct between the furan side of the psoralen ring and a thymidine of the target DNA when the oligomer-target duplex is irradiated with 365-nm light. The photoreactions of (ae)CP-derivatized methylphosphonate oligomers with single-stranded DNA targets in which the position of the psoralen-linking site is varied are characterized and compared to results obtained with oligomers derivatized with 4'-[[N-(aminoethyl)amino]methyl]-4,5',8-trimethylpsoralen [(ae)AMT]. It appears that the psoralen ring can stack on the terminal base pair formed between the oligomer and its target DNA or can intercalate between the last two base pairs of the oligomer-target duplex. Oligomers derivatized with (ae)CP cross-link efficiently to a thymidine located in the last base pair (n position) or 3' to the last base pair (n + 1 position) of the target, whereas the (ae)AMT-derivatized oligomers cross-link most efficiently to a thymidine located in the n + 1 position. The results show that both the extent and kinetics of cross-linking are influenced by the location of the psoralen-linking site in the oligomer-target duplex.

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