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

Abstract

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.

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

“…Then, it is interesting to investigate candidate drugs for combination therapy in lung cancer to avoid treatment failure. Since a long‐term treatment with MST‐312 on breast cancer cells increased chemosensitivity to docetaxel and irinotecan (classical drugs for breast cancer treatment), (Morais et al, 2019) we investigated chemosensitivity to cisplatin and observed no difference between treated and nontreated H460 cells. However, the combination of long‐term treatment with MST‐312 and short‐term exposure to cisplatin did not alter the viability of H460 cells when compared with cells treated with DMSO.…”

“…In colorectal and lung cancer cell lines, it was demonstrated that clonogenic potential is positively modulated by hTERT independently of its canonical activity (Khattar et al, 2016). Morais et al (2019) demonstrated that chronic exposure to MST-312 led to the selection of breast cancer cells with longer telomeres and that intratumoral heterogeneity played an important role in the survival of cells throughout the treatment. They demonstrated that MST-312 had an increased cytotoxic effect in clonal MDA-MB-231 cells in comparison with the parental cell line (Morais et al, 2019).…”

“…Chronic exposure to MST-312 could potentially inhibit the replicative immortality process, rendering the H460 cells susceptible to senescence. Since human primary cell lines can endure between 20 and 80 populational doubling events until becoming senescent, we multiplied the obtained PDT to the maximum value in this interval to determine the duration of the long-term treatment (Morais et al, 2017(Morais et al, , 2019. The calculated PDT for H460 was 26 ± 0.78 h and the established duration of the long-term treatment was 87 days (Figure 1c).…”

“…Inhibition of telomerase activity is a novel target strategy in cancer, but a continuous replication of the cells is required to significantly reduce cell viability (Morais et al, 2019). Therefore, it is important to study the in vitro long‐term effects of telomerase inhibitors.…”

Telomere-related Markers for Cancer

“…It was shown to inhibit TERT activity and reduce telomere length in cultured cancer cells without causing acute cytotoxicity, however, its efficacy is highly telomere length-dependent, so that it may not be an ideal single therapy agent for most cancers [ 5 , 180 ]. In addition, MST-312, the synthesized tea catechin EGCG analogue, was observed to potently inhibit telomerase activity in different types of malignant cells [ 182 , 183 ]. An epigenetic mechanism may be involved in the down-regulation of TERT expression mediated by EGCG and MST-312 [ 184 ].…”