Cytotoxicity evaluation of natural coptisine and synthesis of coptisine from berberine.

The crude extract (80% MeOH in water) of Chelidonii herba exhibited very interesting cytotoxicity against brine shrimp (Artemia salina Leach) nauplii and cultured human tumour cell in vitro, the colon carcinoma HT 29 (144 h treatment). Fractionation of the crude extract and bioassay-guided procedures showed that the cytotoxic and the antitumour activities were concentrated in the basic extract. On the basis of IR, MS and 1H NMR the compound responsible of the cytotoxic activity was determined to be coptisine. Cytotoxicity evaluation of coptisine was next extended to a panel of human and murine cell lines in comparison with the established antitumour drugs mitoxantrone, doxorubicin (Dx) and cisplatin (CDDP). Coptisine was cytotoxic on LoVo and HT 29 and less potent on L-1210, and it was partially crossresistant on the human tumour colon cell line resistant to Dx, LoVo/Dx, whereas it was not significantly crossresistant on the murine leukaemia cell line resistant to CDDP, L-1210/CDDP. Coptisine alkaloid was then synthesised in gram amount from commercial berberine. A four-step synthetic route was elaborated. The overall yield was about 8-10%. The structural identity of synthetic coptisine was verified by IR and NMR methods. A comparison of the cytotoxic effects on the human tumour colon cell line LoVo and on the murine leukaemia L1210 showed, for both natural and synthetic coptisines, a comparable cytotoxic activity more evident against HT 29 cell line and LoVo cell line, while the activity was lower against the L1210 cell line.

Sulfation of alpha-hydroxytamoxifen catalyzed by human hydroxysteroid sulfotransferase results in tamoxifen-DNA adducts.

The formation of tamoxifen (TAM)-derived DNA adducts was investigated by incubation of DNA with (E)-alpha-hydroxytamoxifen [(E)-alpha-OHTAM], 3'-phosphoadenosine 5'-phosphosulfate (PAPS), and human recombinant sulfotransferase. Using 32P-post-labeling and HPLC analysis, two TAM-DNA adducts were detected in incubations that included the human hydroxysteroid sulfotransferase SULT2A1 (hHST). When compared with standards of stereoisomers of alpha-(N2-deoxyguanosinyl)tamoxifen 3'-monophosphate (dG3'P-N2-TAM), the major adduct was identified chromatographically as an epimer of the transform of dG-N2-TAM, and the minor adduct was identified as an epimer of the cis-form. The amount of TAM adducts formed by hHST was approximately three times less than that formed by an equivalent amount of rat hydroxysteroid (alcohol) sulfotransferase a. These results indicate that sulfation of alpha-OHTAM catalyzed by hHST results in the formation of dG-N2-TAMs, highly miscoding lesions, in human tissues.

Translesional synthesis on DNA templates containing an estrogen quinone-derived adduct: N2-(2-hydroxyestron-6-yl)-2'-deoxyguanosine and N6-(2-hydroxyestron-6-yl)-2'-deoxyadenosine.

Miscoding properties induced by estrogen quinone-derived DNA adducts were analyzed using an in vitro experimental system to quantify base substitutions and deletions. Site-specifically modified oligodeoxynucleotides containing a single N2-(2-hydroxyestron-6-yl)-2'-deoxyguanosine (2-OHE1-N2-dG) or N6-(2-hydroxyestron-6-yl)-2'-deoxyadenosine (2-OHE1-N6-dA) were prepared postsynthetically and used as templates in primer extension reactions catalyzed by mammalian DNA polymerases (pol) alpha, beta, and delta. The 2-OHE1-N2-dG adduct blocked primer extension reactions more strongly than 2-OHE1-N6-dA. Using pol alpha and delta, 2-OHE1-N2-dG promoted incorporation of dCMP (6.3 and 3.1%, respectively), the correct base, opposite the lesion: when pol delta was used, misincorporation of dTMP (0.52%) was detected. 2-OHE1-N6-dA also promoted incorporation of dTMP, the correct base, opposite the lesion, accompanied by misincorporation of dCTP (0.54% for pol alpha and 3.2% for pol delta) and one-base deletion (0.3-0.5%). Using pol beta, no miscoding was detected. The miscoding occurred only when replicative DNA polymerases were used. Kinetic data were consistent with those obtained from the analysis of fully extended products formed by pol alpha or pol beta. These results indicate that endogenous estrogen quinone-derived DNA adducts have miscoding potential: G --> A and A --> G transitions and deletions are predicted in mammalian cells.

Alpha-hydroxytamoxifen is a substrate of hydroxysteroid (alcohol) sulfotransferase, resulting in tamoxifen DNA adducts.

When alpha-hydroxytamoxifen (alpha-OHTAM) was incubated with rat liver hydroxysteroid (alcohol) sulfotransferase a (STa) and 3'-phosphoadenosine 5'-phosphosulfate, (E)-alpha-OHTAM was found to be a better substrate for STa than (Z)-alpha-OHTAM. To explore the formation of tamoxifen (TAM)-derived DNA adducts, DNA was incubated with STa and either (E)-alpha-OHTAM or (Z)-alpha-OHTAM in the presence of 3'-phosphoadenosine 5'-phosphosulfate. Using 32P-postlabeling analysis, the amount of TAM-DNA adducts resulting from (E)-alpha-OHTAM was 29 times higher than that observed with (E)-alpha-OHTAM alone. Using (Z)-alpha-OHTAM and STa, some TAM-DNA adducts were also detected but at levels 6.5 times lower than that observed with (E)-alpha-OHTAM and STa. When compared with standards of stereoisomers of 2'-deoxyguanosine 3'-monophosphate-N2-tamoxifen, the major tamoxifen adduct was identified chromatographically as an epimer of the trans form of alpha-(N2-deoxyguanosinyl)tamoxifen, and the minor adduct was identified as an epimer of the cis form. In the reaction mixture, a conversion from (E)-alpha-OHTAM to (Z)-alpha-OHTAM through the carbocation intermediate was also detected. These results show that sulfation of alpha-OHTAM catalyzed by STa results in the formation of TAM-DNA adducts.

Miscoding potential of tamoxifen-derived DNA adducts: alpha-(N2-deoxyguanosinyl)tamoxifen.

The treatment of tamoxifen, widely used as adjuvant chemotherapy for breast cancer, increases significantly the risk of developing endometrial cancer. The miscoding properties of tamoxifen-derived DNA adducts, alpha-(N2-deoxyguanosinyl)tamoxifens (dG-N2-tamoxifen), have been explored, using an in vitro experimental system to quantify base substitutions and deletions. Site-specifically modified oligodeoxynucleotides containing an epimer of trans- and cis-forms of dG-N2-tamoxifens were prepared postsynthetically and used as templates in primer extension reactions catalyzed by mammalian DNA polymerases alpha, beta, and delta. Pol alpha catalyzed incorporation of dCMP and dAMP opposite all four stereoisomers of dG-N2-tamoxifen, accompanied by lesser amounts of dGMP. In contrast, pol delta catalyzed preferential incorporation of dCMP, a correct base, opposite the lesions; one of the trans-forms of dG-N2-tamoxifens only promoted incorporation of dTMP. Using pol beta, preferential incorporation of dCMP, along with small amounts of incorporation of dAMP and dGMP, was detected. One- and two base deletions were also observed with pol alpha and pol beta. The miscoding specificities and frequencies of dG-N2-tamoxifens varied depending on the DNA polymerase used. In addition, with pol alpha and pol beta, large amounts of 5-base deletions were preferentially formed at the cis-forms of dG-N2-tamoxifen, but not at the trans-forms of dG-N2-tamoxifen. We conclude that dG-N2-tamoxifen adducts have high miscoding potentials.

Identification of tamoxifen-DNA adducts formed by alpha-sulfate tamoxifen and alpha-acetoxytamoxifen.

alpha-Sulfate trans-tamoxifen and alpha-sulfate cis-tamoxifen were synthesized as proposed active metabolites of tamoxifen that react with DNA. alpha-Acetoxytamoxifen was prepared as a model-activated form to produce a reactive carbocation. Calf thymus DNA was reacted with alpha-hydroxytamoxifen or the activated forms of tamoxifen, and tamoxifen-DNA adducts were analyzed by a 32P-postlabeling method. The reactivity of alpha-sulfate trans-tamoxifen to DNA was much higher than that of alpha-hydroxytamoxifen. The formation of tamoxifen-DNA adducts induced by alpha-acetoxytamoxifen and alpha-sulfate cis-tamoxifen was 1100- and 1600-fold, respectively, higher than that of alpha-hydroxytamoxifen. Both alpha-sulfate tamoxifens and alpha-acetoxytamoxifen were highly reactive to 2'-deoxyguanosine. Four reaction products of dG-tamoxifen were isolated by HPLC and characterized by mass- and proton magnetic resonance spectroscopy. Fractions 1 and 2 that eluted first were identified as the epimers of trans form of dG-N2-tamoxifen. Fractions 3 and 4 were identified as the epimers of cis form of dG-N2-tamoxifen. When DNA was reacted with alpha-acetoxytamoxifen in vitro, three isomers of dG-N2-tamoxifen were detected: fraction 2 was the major adduct while fractions 1 and 3 were minor adducts.