Telomerase Inhibition, Telomere Shortening, and Cellular Uptake of the Perylene Derivatives PM2 and PIPER in Prostate Cancer Cells.

Prostate cancer is the second most common cancer among men worldwide, and it is ranked first in the United States and Europe. Since prostate cancer is slow-growing, active surveillance for low-risk cancer has been increasingly supported by various guidelines. Most prostate cancers reactivate telomerase to circumvent the replicative senescence caused by the end replication problem; therefore, telomerase inhibition is potentially useful for the suppression of prostate cancer progression during this active surveillance or for the prevention of cancer recurrence after conventional therapies. In this study, we demonstrated that the perylene derivatives, PM2 and PIPER, could suppress human telomerase reverse transcriptase (hTERT) expression and telomerase activity in the short-term treatment of androgen-dependent prostate cancer cell line LNCaP and the androgen-independent prostate cancer cell line PC3 prostate cancer cells. Long-term treatment with subcytotoxic doses of these compounds in both prostate cancer cells showed telomere shortening and a significant increase in senescent cells. Although the acute cytotoxicity of PM2 was about 30 times higher than that of PIPER in both prostate cancer cells, the cellular uptake of both compounds was comparable as determined by flow cytometry and fluorescent microscopy.

Curcuminoid derivatives enhance telomerase activity in an in vitro TRAP assay.

The length of telomeres controls the life span of eukaryotic cells. Telomerase maintains the length of telomeres in certain eukaryotic cells, such as germline cells and stem cells, and allows these cells to evade replicative senescence. Here, we report for the first time a number of curcuminoid derivatives that enhance telomerase activity in an in vitro TRAP assay. A preliminary analysis of structure-activity relationships found that the minimal requirement for this enhanced telomerase activity is a curcuminoid core with at least one n-pentylpyridine side chain, while curcuminoids with two such side chains exhibit even greater activity. The finding here might lead to a new class of telomerase activators that act directly or indirectly on telomerase, rather than through the reactivation of the telomerase reverse transcriptase (TERT) gene associated with other telomerase activators found in the literature.

Ginger Extract Promotes Telomere Shortening and Cellular Senescence in A549 Lung Cancer Cells.

Replicative senescence, which is caused by telomere shortening from the end replication problem, is considered one of the tumor-suppressor mechanisms in eukaryotes. However, most cancers escape this replicative senescence by reactivating telomerase, an enzyme that extends the 3'-ends of the telomeres. Previously, we reported the telomerase inhibitory effect of a crude Zingiber officinale extract (ZOE), which suppressed hTERT expression, leading to a reduction in hTERT protein and telomerase activity in A549 lung cancer cells. In the present study, we found that ZOE-induced telomere shortening and cellular senescence during the period of 60 days when these A549 cells were treated with subcytotoxic doses of ZOE. Using assay-guided fractionation and gas chromatography/mass spectrometry analysis, we found that the major compounds in the active subfractions were paradols and shogaols of various chain lengths. The results from studies of pure 6-paradol and 6-shogaol confirmed that these two compounds could suppress hTERT expression as well as telomerase activity in A549 cells. These results suggest that these paradols and shogaols are likely the active compounds in ZOE that suppress hTERT expression and telomerase activity in these cells. Furthermore, ZOE was found to be nontoxic and had an anticlastogenic effect against diethylnitrosamine-induced liver micronucleus formation in rats. These findings suggest that ginger extract can potentially be useful in dietary cancer prevention.

Ginger extract inhibits human telomerase reverse transcriptase and c-Myc expression in A549 lung cancer cells.

The rhizome of ginger (Zingiber officinale Roscoe) has been reputed to have many curative properties in traditional medicine, and recent publications have also shown that many agents in ginger possess anticancer properties. Here we show that the ethyl acetate fraction of ginger extract can inhibit the expression of the two prominent molecular targets of cancer, the human telomerase reverse transcriptase (hTERT) and c-Myc, in A549 lung cancer cells in a time- and concentration-dependent manner. The treated cells exhibited diminished telomerase activity because of reduced protein production rather than direct inhibition of telomerase. The reduction of hTERT expression coincided with the reduction of c-Myc expression, which is one of the hTERT transcription factors; thus, the reduction in hTERT expression might be due in part to the decrease of c-Myc. As both telomerase inhibition and Myc inhibition are cancer-specific targets for cancer therapy, ginger extract might prove to be beneficial as a complementary agent in cancer prevention and maintenance therapy.