Inhibition of telomerase and ALT pathways in MDS/AML cell lines

Abstract Background: The ability of human cancer cells to maintain telomere length over successive cell divisions rapidly emerged as an adaptive mechanism acquired by cancer cells to defy cell senescence and mortality. This mechanism of immortality of cancerous cells was first demonstrated in the 1990s. Telomerase activation is the most common pathway to avoid telomere length erosion and is used by 85% of all tumor cells, while alternative lengthening of telomere ALT is used by the remainder. Some tumors, albeit rare, demonstrate the co-activation of both telomere maintenance pathways. The consequence of continued cell proliferation of tumor cells despite their critically short telomeres allows for ongoing genomic instability and its propagation to the next generation of cells. We hypothesized that a consecutive inhibition of the two telomere maintenance pathways by first inhibiting telomerase followed by the ALT pathway inhibition will kill cancer cells. Methods: We performed successive inhibition of telomerase over time (0h-144h) followed by ALT pathway (72h-144h) on MDS-92, MDS-L (Myelodysplastic Syndromes), and OCI-AML3 (Acute Myeloid Leukemia) cell lines, and used Normal Human Primary Fibroblasts (GL51/92 Roe) as controls. Cell death was assayed by live cell imaging using NucGreen™ Dead 488 and trypan blue exclusion. Results: Consecutive inhibition of both telomere maintenance pathways showed a significant decrease in cell viability rate over 72h of treatment with 200 µM SB1532 that were 25% for MDS-L and 27% for MDS92 and 38% for OCI-AML3. Cell death was increased by adding 4 nM Trabectedin (ALT inhibition) for an additional 3 days, leading to the viability rate results at 144 hours that were 1% for MDS-L, 0% for MDS92, and 9% for OCI-AML3. Meanwhile, primary fibroblast cells at low and high passages did not show sensitivity to these molecules with a cell viability rate of 93% and 87% after 144 hours, respectively. Conclusion: Inhibition of both telomere maintenance pathways in MDS/AML cell lines demonstrated a decrease in cell viability and increased cell death while primary fibroblasts showed no significant effect on survival. In future, study of primary cells from patients is necessary to confirm these results and to pave the way for cancer treatment in hematological and solid tumor neoplasias with molecules and/or small molecules targeting telomerase and ALT pathways.