Emily Pisha

Synthesis of betulinic acid derivatives with activity against human melanoma.

Betulinic acid has been modified at C-3, C-20, and C-28 positions and the toxicity of the derivatives has been evaluated against cultured human melanoma (MEL-2) and human epidermoid carcinoma of the mouth (KB) cell lines. This preliminary investigation demonstrates that simple modifications of the parent structure of betulinic acid can produce potentially important derivatives, which may be developed as antitumor drugs.

Cell-based assay for the determination of estrogenic and anti-estrogenic activities

Methods are described for assessing the estrogenic or anti-estrogenic potential of test substances using cultured (human endometrial) Ishikawa cells. This cell line possesses an estrogen-inducible alkaline phosphatase, and estrogenic activity is indicated by assessing by the rate of p-nitrophenol generated from p-nitrophenylphosphate, subsequent to treatment with test compounds. Anti-estrogenic activity is indicated by a decrease in phosphatase activity when the cells are treated with test compounds in the presence of estrogen.

The reactivity of o-quinones which do not isomerize to quinone methides correlates with alkylcatechol-induced toxicity in human melanoma cells

Catechols are widespread in the environment, especially as constituents of edible plants. A number of these catechols may undergo oxidative metabolism to electrophilic o-quinones (3,5-cyclohexadien-1,2-dione) by oxidative enzymes such as cytochrome P450 and peroxidases. Alkylation of cellular nucleophiles by these intermediates and the formation of reactive oxygen species, especially through redox cycling of o-quinones, could contribute to the cytotoxic properties of the parent catechols. In contrast, isomerization of the o-quinones to electrophilic quinone methides (4-methylene-2,5-cyclohexadien-1-one, QM) could cause cellular damage primarily through alkylation. In this investigation, we treated human melanoma cells with two groups of catechols. These cells have high levels of tyrosinase required to oxidize catechols to quinoids. For catechols which are oxidized to o-quinones that cannot isomerize to quinone methides or form unstable quinone methides, plots of the cytotoxicity data (ED50) versus the reactivity of the o-quinones gave an excellent linear correlation; decreasing o-quinone reactivity led to a decrease in the cytotoxic potency of the catechol. In contrast, catechols which are metabolized by the o-quinone/p-quinone methide bioactivation pathway were equally cytotoxic but showed no correlation between the reactivity of the o-quinones and the cytotoxic potency of the catechols. The most likely explanation for this effect is a change in cytotoxic mechanism from o-quinone-mediated inhibition of cell growth to a bioactivation pathway based on both o-quinone and p-QM formation. These results substantiate the conclusion that the involvement of the o-quinone/ QM pathway in catechol toxicity depends on a combination between the rate of enzymatic formation of the o-quinone, the rate of isomerization to the more electrophilic QM, and the chemical reactivity of the quinoids.