Lee J. Wilkoff

Activity of retinoids against benzo(a)pyrene-induced hyperplasia in mouse prostate organ cultures

Abstract The antihyperplastic activity of several retinoids (with ring, side chain or polar group modifications) against benzo(a)pyrene (BP)-induced hyperplasia in mouse prostate cultures was examined. Prostate explants were made hyperplastic by treatment with BP for 8 days , followed by simultaneous treatment with BP and different concentrations of a retinoid. The anti-mitotic activity of retinoids was compared with β-retinoic acid (RA). Different retinoids produced various degrees of mitotic inhibition in the hyperplastic prostate epithelium. Five retinoids: 13-cis -retinoic acid, the methylketo cyclopentenyl analog of retinoic acid, the 1 -methoxyethyl cyclopentenyl analog of retinoic acid, N -retinoylglycine, and the 14 -fluoro derivative of the trimethylmethoxyphenyl analog of retinoic acid ethyl ester, showed greater activity than RA. Seven other retinoids were as active as RA. Two retinoids were less active than RA, and one retinoid produced no mitotic inhibitory effect.

Viability of cultured Lewis lung cell populations exposed to beta-retinoic acid.

Summary β-Retinoic acid inhibited the proliferation of cultured Lewis lung cells without decreasing the viability (as determined by cloning in semisolid medium) of the cell populations. We would like to thank Mrs. Carolyn M. Andrews and Dr. W. R. Laster for the Lewis lung tumors and Mrs. Carol S. Eldridge for excellent technical assistance with the cell culture experiments.

The Cell Cycle of Leukemia L1210 Cells in vivo and in vitro.

Summary The cell cycles of Leukemia L1210 cells proliferating in mice after serial transplantation, proliferating in mice following inoculation of cultured cells, and proliferating in vitro in spinner cultures have been examined by the method of waves of labeled mitoses following pulse exposure to thymidine-(methyl-3H). The cycles for the 3 groups of cells were essentially the same. The following mean values were obtained: TC, 15.7 hr; TG2, 1.5 hr; TM, 0.5 hr; Ts, 11.7 hr; TG1, 2.0 hr.

Effect of retinoids and estrogens on testosterone-induced hyperplasia of mouse prostate explants in organ culture.

Summary Testosterone produced epithelial hyperplasia in mouse prostate explants in organ culture. Simultaneous treatment of ex-plants with testosterone and 13-cis-retinoic acid inhibited the induction of hyperplasia. When explants were first made hyperplastic by treatment with testosterone for 8 days and followed by simultaneous treatment with testosterone and a retinoid for an additional 96 hr, the following retinoids reversed the hy-perplasia: 13-cis-retinoic acid, the 1-methox-yethylcyclopentenyl analog of retinoic acid, the trimethylmethoxyphenyl analog of retinoic acid, the trimethylphenyl analog of retinoic acid ethylamide, and the trimethylmethoxyphenyl analog of retinoic acid ethyl ester. The data indicate that these retinoids prevent androgen-induced hyperplasia in prostatic tissue in this system by a direct influence on the tissue. Since estrone or 17β-estradiol had no effect on testosterone-induced hyperplasia in the prostate explants, it is concluded that these estrogens may act by way of an indirect mechanism (pituitary-tesis axis) in preventing androgen-induced hyperplasia of the prostate.

Induction of hyperplasia and anaplasia by carcinogens in organ cultures of mouse prostate.

SummaryIn an effort to establish a test system to examine the carcinogenic potential of chemicals, mouse prostate explants were maintained as organ cultures and the effects of carcinogenic and noncarcinogenic compounds were examined at various intervals after treatment. The degree of hyperplasia produced by a compound was determined by the colcemid metaphase arrest technique. Extensive hyperplasia of the prostatic epithelium occurred at 8 days after treatment with 3-methylcholanthrene, the 11–12 epoxide of methylcholanthrene, benzo(a)pyrene and N-methyl-N-nitro-N-nitrosoguanidine. At 12 days most carcinogentreated explants were anaplastic. The noncarcinogenic compounds, pyrene and phenanthrene, did not produce a mitotic stimulatory effect on the epithelium of the explants. The data suggest that the organ culture system of mouse prostate may be employed as a test system to obtain preliminary information regarding the carcinogenicity of a compound.

Partial cross-resistance of cultured murine leukemia vincristine- -resistant p388 cells to 4'-demethylepipodophyllotoxin ethylidene- -beta-d-glucoside.

Summary Cultured P388 cells derived from vincristine-resistant cell populations developed in vivo (P388/VCR) retain their resistance to vincristine, although the degree of resistance of the P388/VCR cell populations appears to be a function of concentration and time of exposure. The P388/VCR cell population is sensitive to 4′-demethylepipodophyllotoxin ethylidene-β - D - glucoside (VP 16-213) but a degree of cross-resistance to VP 16-213 can be demonstrated. The degree of cross-resistance to VP 16-213 also appears to be a function of concentration and time of exposure. We thank Dr. H. E. Skipper, Dr. F. M. Schabel, Jr., and Dr. R. W. Brockman for their helpful discussions and encouragement; Mr. John A. Burdeshaw for statistical analysis of the data; Dr. W. R. Laster and Mrs. Mary Trader for providing the leukemia P388 and vincristine-resistant P388 tumors; and Mrs. Carol S. Eldridge for excellent technical assistance.

Kinetics of the effect of vincristine sulfate on the reproductive integrity of proliferating cultured leukemia L1210 cells.

Summary When proliferating cultured L1210 cell populations were exposed to effective concentrations of VCR or colchicine, the kinetics of the reduction in the number of viable cells did not occur at a first-order rate (the fraction of cells killed per unit of time was not constant). The minimum effective concentration of VCR required to produce an effect on the reproductive integrity of L1210 populations was < 0.01 but > 0.001 μg/ml. If the duration of drug exposure was 24 hours, extensive cell killing could be produced by VCR concentrations which were relatively low when compared to the theoretical maximum concentration attainable in the body fluids of a mouse. The kinetics of the lethal action of VCR on proliferating cultured L1210 populations indicate that this agent has cell cycle specificity.

Etoposide-resistant human colon and lung adenocarcinoma cell lines exhibit sensitivity to homoharringtonine

Human colon (HCT 116/VP48) and lung (A549B/VP29) adenocarcinoma cell lines selected for resistance to etoposide exhibited modified patterns of multidrug resistance (MDR) that included a differential sensitivity to other DNA topoisomerase II inhibitors and to the plant alkaloids homoharringtonine, vinblastine, and vincristine. The resistance and cross-resistance drug phenotype of the A549B/VP29 cell line was different from that of the HCT116/VP48 cell line. The HCT116/VP48 cell line was 50-fold resistant to etoposide and 30-fold resistant to teniposide. The degree of resistance to other DNA topoisomerase II inhibitors was of a lower magnitude: Adriamycin, 9-fold; daunomycin, 3-fold; 4′-[(9-acridinyl)-amino]-methanesulfone-m-anisidide (m-AMSA), 3-fold;, and actinomycin D, 6-fold. The HCT 116/VP48 cell line exhibited a 7-fold resistance to vincristine and a 2-fold resistance to vinblastine but was sensitive to homoharringtohine. The A549B/VP29 cell line was 5-fold resistant to etoposide and 2-fold resistant to teniposide. The A549B/VP29 cell line exhibited a 2-fold resistance to Adriamycin but was sensitive to daunomycin and showed a 3-fold resistance to m-AMSA. This cell line was sensitive to actinomycin D. The A549B/VP29 cell line was 2-fold resistant to vinblastine and sensitive to homoharringtonine. Both cell lines (HCT116/VP48 and A549/VP29) exhibited no amplification of the humanmdrl DNA sequence, the 4.3-kb P-glycoprotein transcript, or the membrane P-glycoprotein. The sensitivity of cells exhibiting an MDR phenotype not mediated by P-glycoprotein suggests a potential use for homoharringtonine in treating tumors with this type of drug resistance.

Collateral sensitivity to methotrexate and dichloromethotrexate of cultured lymphocytic leukemia l1210 cells resistant to 6-mercaptopurine.

Abstract Cultured cell populations, derived from lymphocytic leukemia L1210 resistant to 6-mercaptopurine (6-MP; L1210/6-MP) and sensitive lymphocytic leukemia (L1210/0), were propagated in Dulbeccos modified Eagles minimum essential medium supplemented with 10% horse serum and 5 μm 2-mercaptoethanol. The population doubling times (mean ± SD) were 16.6 ± 1.9 hr (L1210/0) and 16.1 ± 1.8 hr (L1210/6-MP) between cell densities of 7 × 104 − 1.0 × 105 and 2.0 × 106 cells/ml. Cultured L1210/6-MP cell populations were significantly resistant to 6-MP (1.7 to 170 μg/ml for exposure periods of 24 or 48 hr). Cultured L1210/6-MP cell populations were also collaterally sensitive to methotrexate (0.055 to 5.5 μg/ml for an exposure period of 24 hr) or to dichloromethotrexate (1.0-100 μg/ml for an exposure period of 24 hr). The results indicate that resistance to 6-MP and collateral sensitivity to the folate analogs are properties of the L1210/6-MP cells and are independent of any host factors.

Kinetics of Reduction in Viability of Cultured Leukemia L1210 Cells Exposed to Purine Analogs

Rates of reduction in viability and degree of cell killing were relatively independent of concentrations when replicating cultured L1210 cells were exposed to increasing concentrations of 6-thioguanine, 6-methylthiopurine ribonucleoside, 9-beta-D-arabinofuranosyl-9H-purine-6-thiol, or 9-ethyl-6-thiopurine. The relative lack of dependence of cell killing rate on cytotoxic concentrations suggest (a) that these agents may be only effective aganinst proliferating cells, and (b) that only limited therapeutic advantage can be gainged by increasing their concentration beyond a minimum effective level. In contrast, the rate and degree of cell killing were dependent upon concentrations when cells were exposed to increasing amounts of 4-aminopyrrolo(2,3-d)pyrimidine-beta-D-ribofuranoside or to 2-fluoroadenosine, indicating that these analogs are not cell-cycle-stage-specific and that nonreplicating cell populations may be sensitive to them.