prostaglandin-a1 and Melanoma

Previous studies have shown that cyclopentenone prostaglandins are endowed with antitumour activity in various murine and human tumour models. In the present investigation four human melanoma cell lines were treated with graded concentrations (4-16microg/ml) of prostaglandin A1 (PGA1) for 24 or 48 h in vitro. At the end of the treatment, cell proliferation (measured in terms of DNA synthesis) and telomerase activity were determined. The results showed that PGA1 induced concentration-dependent inhibition of DNA synthesis at 48 h but not at 24 h in SK-MEL-28 cells. In contrast, marked inhibition of telomerase activity was detected after only 24 h of PGA1 treatment. Moreover, after 48h of treatment with the agent, inhibition of telomerase was more pronounced than inhibition of cell proliferation. Additional studies performed with three freshly generated melanoma cell lines confirmed that PGA1 produced early inhibition of cell growth accompanied by marked impairment of telomerase activity. These results suggest that PGA1 could be of potential value as antitumour agent, on the basis of two distinct mechanisms: direct cytostatic/cytotoxic effects on melanoma cells, and inhibitory activity on a tumour-associated enzymatic function (i.e. telomerase) that is responsible for cancer cell immortality.

Topics: Cell Division; DNA Replication; DNA, Neoplasm; Dose-Response Relationship, Drug; Growth Inhibitors; Humans; Melanocytes; Melanoma; Neoplasm Proteins; Neoplastic Stem Cells; Prostaglandins A; Skin Neoplasms; Telomerase

The effects of prostaglandins (PGs) on the Cloudman S91 melanoma CCL 53.1 cell line indicate that melanogenesis and proliferation are regulated by separate mechanisms that are not necessarily cyclic AMP (cAMP) dependent. These cells responded to PGE1 and PGE2 in a dose-dependent manner, by an increase of tyrosinase activity and by inhibition of proliferation. PGA1 and PGD2 inhibited cellular proliferation and tyrosinase activity, while PGF2 alpha had no effect after 24 h of treatment. PGE1, but not PGE2 or PGD2, increased cellular cAMP levels after 30 min of treatment. Treatment with 10 micrograms/ml PGE1 inhibited cellular proliferation after 4 h and enhanced tyrosinase activity after 12 h. Tyrosinase stimulation by PGE1 required de novo transcription and translation. Actinomycin D, cycloheximide, and the tyrosinase inhibitor phenylthiocarbamide blocked tyrosinase activation but did not alter the inhibitory effect of PGE1 on proliferation. Dibutyryl cAMP and 3-isobutyl-1-methylxanthine augmented tyrosinase activation by PGE1 without enhancing the inhibitory action of PGE1 on cell growth. Neither blockage nor enhancement of the PGE1 effect on tyrosinase altered the PGE1-induced retardation of proliferation. These results are in marked contrast to the traditional concept that elevation of cAMP levels in melanoma cells necessarily results in stimulation of melanogenesis and inhibition of proliferation. The data presented propose independent and possibly alternative pathways for the regulation of these two cellular events.

Topics: 1-Methyl-3-isobutylxanthine; Alprostadil; Bucladesine; Cell Division; Cycloheximide; Dactinomycin; Dinoprostone; In Vitro Techniques; Melanins; Melanoma; Monophenol Monooxygenase; Prostaglandin D2; Prostaglandins; Prostaglandins A; Prostaglandins D; Prostaglandins E

Our interest in prostaglandins (PGs) as antitumor agents stemmed from the report of Bregman and Meyskens (Cancer Res., 43: 1642-1645, 1983) that PGA1, PGA2, and PGD2 inhibited colony formation by human melanoma cells obtained from fresh biopsies of melanoma patients. We tested several PGs and found that PGA1, PGA2, and PGD2 were the most cytotoxic to L1210 cells in culture. Therefore, we studied these PGs for their effects on growth, cell survival, and cell progression of murine (B16) and human (RPMI7932,SK Mel 28) melanoma cells in culture. Although the three PGs equally inhibited the growth of B16 cells, PGD2 was more inhibitory to RPMI 7932 or SK Mel 28 than PGA1 or PGA2. Similarly the three PGs were almost equally active in inhibiting colony formation by B16 cells. However, against human melanoma cells, PGD2 was much more active than PGA1, whereas PGA2 was inactive. Towards the end of our study, we obtained PGJ2 and found that it was as cytotoxic as PGD2 for L1210 cells but was more lethal for human melanoma cells. The primary effect of all three PGs was to block cell progression from G1 to S. At 2.5 micrograms of PGD2 per ml, the blockade of cells in G1 and normal progression through the other phases resulted in accumulation of 80-90% of the cells in G1. At this dose, there was no inhibition of DNA synthesis, and cells in S progressed apparently normally through S, until all cells were blocked in G1. DNA synthesis was inhibited at 5 micrograms/ml which slowed cell progression through S and accumulated cells in G1. The partial synchronization of cells in G1 may be useful in devising new combinations of PGD2 with antitumor drugs.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Cycle; Cell Survival; Cells, Cultured; DNA, Neoplasm; Humans; Melanoma; Mice; Neoplasm Proteins; Prostaglandin D2; Prostaglandins A; Prostaglandins D; RNA, Neoplasm

The direct effect of continuous exposure to prostaglandins on the cloning efficiency and proliferative capacity of human malignant melanoma colony-forming cells in soft agar was evaluated. Prostaglandin A1 (PGA1) and prostaglandin E1 (PGE1) effected a dose-dependent inhibition of colony formation and proliferative capacity. PGA1 at a concentration of 5 microgram/ml reduced colony formation of cells from human melanoma cell strains C8054, C8130, and C822 by at least 85%. PGA1 also inhibited colony formation of cells obtained directly from biopsies of melanoma tissues from eight patients by greater than 70% at a concentration of 5 microgram/ml. A steep dose-response curve was evident by the little effect of PGA1 on colony formation at a concentration of 0.5 microgram/ml. The mean 50% inhibitory doses for PGA1 and PGE1 were 1.25 and 4.25 microgram/ml, respectively. Prostaglandin A2 was much less effective than PGA1 in inhibiting melanoma colony formation. The related prostaglandins (prostaglandin B1, prostaglandin F1 alpha, and prostaglandin E2 alpha) had little or no effect on colony formation. Overall, these results suggested that the presence of a carbonyl group at position 9 of the cyclopentane ring may be required for inhibitory activity as prostaglandins of the A and E series inhibited human melanoma cell growth. PGA1 and PGE1 did not effect a rise in cyclic adenosine 3':5'-monophosphate levels in C8054 and C8130 cells. However, while alpha-melanocyte-stimulating hormone and prostaglandin F2 alpha did generate a rise in adenosine 3':5'-monophosphate levels in C8054 cells, these hormones had no effect on colony formation. These results are consistent with the notion that the PGA1 and PGE1 inhibition of melanoma colony-forming cells occurs via a noncyclic nucleotide mechanism.

Topics: Alprostadil; Cell Division; Cells, Cultured; Dinoprost; Humans; Kinetics; Melanocyte-Stimulating Hormones; Melanoma; Prostaglandins A; Prostaglandins E; Prostaglandins F; Structure-Activity Relationship

Topics: Agar; Alprostadil; Animals; Cell Adhesion; Cell Division; Cell Line; Cyclic AMP; Cyclic GMP; Melanocyte-Stimulating Hormones; Melanoma; Mice; Prostaglandins A; Prostaglandins E