Effects of long-term exposure to MST-312 on lung cancer cells tumorigenesis: Role of SHH/GLI-1 axis.

Replicative immortality is a key feature of cancer cells and it is maintained by the expression of telomerase, a promising target of novel therapies. Long-term telomerase inhibition can induce resistance, but the mechanisms underlying this process remain unclear. The Sonic hedgehog pathway (SHH) is an embryogenic pathway involved in tumorigenesis and modulates the transcription of telomerase. We evaluated the effects of long-term treatment of the telomerase inhibitor MST-312 in morphology, proliferation, resistance, and in the SHH pathway molecules expression levels in lung cancer cells. Cells treated for 12 weeks with MST-312 showed changes in morphology, such as spindle-shaped cells, and a shift in the distribution of F-ACTIN from cortical to diffuse. Treatment also significantly reduced cells' efficiency to form spheroids and their clonogenic potential, independently of the cell cycle and telomeric DNA content. Moreover, GLI-1 expression levels were significantly reduced after 12 weeks of MST-312 treatment, indicating a possible inhibition of this signaling axis in the SHH pathway, without hindering NANOG and OCT4 expression. Here, we described a novel implication of long-term treatment with MST-312 functionally and molecularly, shedding new light on the molecular mechanisms of this drug in vitro.

Effects of in vitro short- and long-term treatment with telomerase inhibitor in U-251 glioma cells.

BACKGROUND: The inhibition of the enzyme telomerase (TERT) has been widely investigated as a new pharmacological approach for cancer treatment, but its real potential and the biochemical consequences are not totally understood. OBJECTIVE: Here, we investigated the effects of the telomerase inhibitor MST-312 on a human glioma cell line after both short- and long-term (290 days) treatments. METHODS: Effects on cell growth, viability, cell cycle, morphology, cell death and genes expression were assessed. RESULTS: We found that short-term treatment promoted cell cycle arrest followed by apoptosis. Importantly, cells with telomerase knock-down revealed that the toxic effects of MST-312 are partially TERT dependent. In contrast, although the long-term treatment decreased cell proliferation at first, it also caused adaptations potentially related to treatment resistance and tumor aggressiveness after long time of exposition. CONCLUSIONS: Despite the short-term effects of telomerase inhibition not being due to telomere erosion, they are at least partially related to the enzyme inhibition, which may represent an important strategy to pave the way for tumor growth control, especially through modulation of the non-canonical functions of telomerase. On the other hand, long-term exposure to the inhibitor had the potential to induce cell adaptations with possible negative clinical implications.

Long-term in vitro treatment with telomerase inhibitor MST-312 induces resistance by selecting long telomeres cells.

Telomerase is a good target for new anticancer drug development because it is present in over 85% of human tumours. However, despite chronic therapy is a condition for anti-telomerase approach, the effects of long-term treatment with telomerase inhibitors remain not well understood. In this work, it was evaluated the effects of long-term treatment of human MDA-MB-231 breast cancer cells with the telomerase inhibitor MST-312. Cells were treated for 72 hours or 140 days, and it was accessed their viability, proliferation rate, morphology, telomeric DNA content, and resistance mechanism. The drug had a clear short-term effect, including chemosensitizing cells for docetaxel and irinotecan, but the chronic exposition led to selection of long telomeres clones, changing characteristics of original cell line. This effect was confirmed in a clonal culture with homogenous karyotype. MRP-1 expression and alternative lengthening of telomeres (ALT) were discarded as additional mechanisms of resistance. This data suggest that, considering the intra-tumour heterogeneity (ITH), what is already a big challenge for treatment of cancer, chronic exposition to telomerase inhibitors can promote tumour adaptations with potential clinical repercussion, drawing attention to ongoing clinical trials and pointing important considerations most times neglected on studies about use of these inhibitors on cancer therapy. SIGNIFICANCE OF THE STUDY: Antitumour action of telomerase inhibitors is well known, but it depends on a long-term exposition because cells will undergo telomere erosion only after many duplication cycles. Recently, the frustrating results of clinical trials with these inhibitors aroused the interest of the scientific community to understand the mechanisms of resistance to anti-telomerase therapy. In this study, we conducted an 18-week experiment to show that telomerase inhibition can lead to cell adaptations and selection of long-telomeres clones, leading to acquisition of resistance. However, we also showed that this inhibitor can sensitize cells to the chemotherapeutic drugs docetaxel and irinotecan.