Yusuf J. Abul-Hajj

Aromatization of androgens by human breast cancer

The metabolism of dehydroepiandrosterone and testosterone by human mammary tumor was investigated. Estrogen synthesis from dehydroepiandrosterone was observed in 9 of 10 estrogen-receptor-negative tumors and only in 2 of 8 receptor-positive tumors (p less than 0.025). Conversion of testosterone to estrogens was observed in 7 of 8 receptor-negative and 2 of 7 receptor-positive tumors. Tumors which are capable of transforming dehydroepiandrosterone to estrogens were also able to aromatize testosterone suggesting that the presence of the aromatase enzyme is inherent to certain tumor cells. No estrogen formation was detected by the mitochondrial-microsomal fraction of normal breast cells while fractions from both fat cell and tumor cell showed estrogen synthesis. Estrogen formation by tumor cell fraction ranged from 5 to 190 times that observed for fat cells. The physiological significance of these results in the neoplastic tissue and its relationship to hormone dependence are discussed.

Metabolism of dehydroepiandrosterone by hormone dependent and hormone independent human breast carcinoma

The metabolism of 7alpha-3H-dehydroepiandrosterone was studied in six human breast carcinomas in vitro. All mammary tumors transformed DHA to testosterone, dihydrotestosterone, 5alpha-androstane-3alpha, 17beta-diol and 5alpha-androstane-3,17-dione. Of the tumors investigated, three estrogen receptor-negative tumors converted DHA to estradiol and only one estrogen receptor-positive tumor produced estradiol from DHA. Observations on the relationship of androgen metabolism and hormone dependency are discussed.

Formation of estradiol-17β fatty acyl 17-esters in mammary tumors

Abstract Incubations of estradiol with human and MT/W9a-B rat mammary tumors showed the formation of a non-polar metabolite of estradiol linked with a fatty acid at the 17-position. Studies involving incubations of3H-estradiol and 14C-stearic acid and 14C-oleic acid showed that these tumors formed both the oleoyl and stearyl esters of estradiol and that the percent of oleoyl ester present in the nonpolar metabolite fraction ranged between 19% to 25% while that of stearyl ranged from 10% to 16%. The physiological significance of these results are discussed.

Metabolism of estradiol by human breast cancer

The activities of estrogen-2,4- and 16 alpha-hydroxylase as well as 17 beta-hydroxysteroid dehydrogenase (17 beta-OHSDHase) were determined in normal, benign and mammary tumor breast tissues. All three hydroxylases were absent in both normal and benign tumor breast tissues. 17 beta-OHSDHase was absent from normal breast tissues but present in all benign tumor tissues. Estrogen-2-hydroxylase was present in most breast carcinomas, was significantly higher in estrogen receptor (ER)-positive than ER-negative tumors, did not correlate with progesterone receptor (PR) and was significantly lower in the ER+PR- subgroup of breast cancers. 4-Hydroxylase activity did not correlate with either ER or PR content but was significantly lower in the ER+PR- subgroup of breast cancers. The activity of 16 alpha-hydroxylase was present in only 18% of all tumors investigated (9/50), did not correlate with the ER or PR content and was completely absent in the ER+PR- and ER-PR+ subgroups. The activity of 17 beta-OHSDHase was significantly higher than the estrogen hydroxylase but did not correlate with either the ER or PR content, and was not different among the ERPR tumor subgroups. The physiological role of these enzymes in the metabolism of estradiol in relation to breast cancer is discussed.

Relationship between estrogen receptors, 17β-hydroxysteroid dehydrogenase and estrogen content in human breast cancer

Estrone and estradiol levels in tumor tissue cytosols were determined in 11 premenopausal and 20 postmenopausal women at the same time that 17 beta-hydroxysteroid dehydrogenase and estrogen receptors (ER) were carried out on their breast cancers. Estrogen receptor positive tumors showed significantly higher levels of estrone and estradiol. However, all ER negative tumors contained measurable amounts of both estradiol and estrone. Higher levels of estrone were observed in ER negative tumors which correlates well with high 17 beta-hydroxysteroid dehydrogenase activity. These results suggest that false negative receptor assays in the premenopausal women is not likely to be due to occupancy of receptors by endogenous estrogens. Furthermore, the higher estrone content in the ER negative group is probably due to high 17 beta-hydroxysteroid dehydrogenase activity inherent to these tumor cells.

Estradiol 17β-dehydrogenase and estradiol binding in human mammary tumors

The metabolism of estradiol was studied in 31 human breast carcinoma in vitro. All 16 estrogen-receptor-poor tumors transformed estradiol to estrone with percent conversions ranging from 11.4 to 95 except for one poorly differentiated tumor where 0.5% conversion to estrone was observed. On the contrary, only 3 out of 15 estrogen-receptor-rich tumors showed higher than 10% conversion of estradiol to estrone (p = 0.001). There is indication that the enzymatic activity in receptor-poor tumors steadily decreases in premenopausal patients as they approach menopausal age, whereas, the activity steadily increases in post-menopausal patients as the duration of menopause lengthens.

Stereospecificity of hydrogen transfer from NADPH by steroid Δ4-5α- and Δ4-5β-reductase

Abstract The saturation of the C-4,5 double bond of Δ 4 -3-ketosteroids catalyzed by Δ 4 -3-ketosteroid-5β-reductase has been shown to involve a hydride ion transfer from the A-position of NADPH to the 5β-position of the steroid while the reaction catalyzed by Δ 4 -3-ketosteroid-5α-reductase involves a hydride transfer from the B-position of NADPH to the 5α-position of the steroid. Thus, this study shows that Δ 4 -5β-reductase has A-stereospecificity while Δ 4 -5α-reductase has B-stereospecificity.

Synthesis of 3,4-estrogen-O-quinone

Activated manganese dioxide was found to be an effective reagent for synthesis of estrogen-o-quinones from the corresponding catechols. The isolation and characterization of 1,5(10)-estradiene-3,4,17-trione is described.

Regioselective reaction of thiols with catechol estrogens and estrogen-O-quinones

Incubations of [3H]estradiol and [3H]2-hydroxyestradiol (2-OHE2) with rat liver microsomes and mushroom tyrosinase were carried out in the presence of glutathione and 2-mercaptoethanol. A ratio of about 3.5:1 for the C-4 and C-1 thioether conjugates of 2-OHE2 was observed. Chemical reaction of estradiol-2, 3-O-quinone with various thiols showed that alkyl and phenyl thiols gave about a 1:1 ratio of C-4 to C-1 thioethers. However, reaction of the O-quinone with 4-nitrothiophenol gave a C-4/C-1 ratio of 0.25 while 4-bromothiophenol gave a C-4/C-1 ratio of 4.0. These studies suggest that the regioselectivity of the reaction of thiols with estrogen catechols and O-quinones may be dependent on the nature of the thiol compounds and less on steric hindrance.

Metabolism of pregnenolone by human breast cancer. Evidence for 17α-hydroxylase and 17,20-lyase

Abstract The metabolism of 7- 3H-pregnenolone was studied in vitro using 16 human breast carcinomas. All mammary tumors transformed pregnenolone to progesterone. All estrogen receptor poor tumors and 4 out of 8 estrogen receptor rich tumors converted pregnenolone to 17-hydroxypregnenolone. Five estrogen receptor poor tumors showed the presence of 17,20-lyase as evidenced by formation of dehydroepiandro-sterone and androstenedione. In two estrogen receptor poor tumors, conversions of pregnenolone to progesterone, 17-hydroxy pregnenolone, dehydroepiandrosterone androstenedione and finally to estradiol was documented, providing a hypothetical pathway for steroid metabolism in human breast cancer. The conversion of pregnenolone to 17-hydroxy-pregnenolone was significantly less in receptor rich tumors and was totally absent in 4 receptor rich tumors with estrogen receptors of over 45 fmol/mg protein.