Telomerase Inhibition and Cell Growth Arrest After Telomestatin Treatment in Multiple Myeloma

Abstract

Purpose: The aim of this study was to test the efficacy of telomestatin, an intramolecular G-quadruplex intercalating drug with specificity for telomeric sequences, as a potential therapeutic agent for multiple myeloma.Experimental Design: We treated ARD, ARP, and MM1S myeloma cells with various concentrations of telomestatin for 7 days and evaluated for telomerase activity. Myeloma cells were treated with the minimal effective telomestatin concentration for 3-5 weeks. Every 7 th day the fraction of live cells was determined by trypan blue exclusion, aliquots of cells were removed for various molecular assays, and the remaining cells were replated at the same cell number and at the same concentration of telomestatin. Telomere length, apoptosis, and gene expression changes were monitored as described in detail in "Materials and Methods."Results: Telomestatin treatment led to inhibition of telomerase activity, reduction in telomere length, and apoptotic cell death in ARD, MM1S, and ARP myeloma cells. Gene expression profile after 1 and 7 days of telomestatin treatment revealed >2-fold change in only 6 (0.027%) and 51 (0.23%) of 33,000 genes surveyed, respectively. No changes were seen in expression of genes involved in cell cycle, apoptosis, DNA repair, or recombination.Conclusions: These results demonstrate that telomestatin exerts its antiproliferative and proapoptotic effects in myeloma cells via inhibition of telomerase and subsequent reduction in telomere length. We conclude that telomerase is an important potential therapeutic target for multiple myeloma therapy, and G-quadruplex interacting agents with specificity for binding to telomeric sequences can be important agents for additional evaluation.

Telomerase inhibitor GRN163L inhibits myeloma cell growth in vitro and in vivo

“…16 Since telomerase activity is present in most cancers but absent or low in majority of normal cells, 10,12 telomerase is an attractive therapeutic target. Moreover, the median telomere length in cancer cells is shorter than normal cells, 17,18 making them susceptible to crisis and apoptosis earlier than normal cells following telomerase inhibition. A number of telomerase inhibitors have been evaluated in a variety of cancer types.…”

Targeting G-Quadruplex DNA with Small Molecules

“…[33] The second, more extensively studied mechanism, is the inhibition of telomerase, a ribonucleoprotein complex that catalyzes the 3' extension of telomeric DNA (Sections 4 and 5). [20,35,41,42,46,47] …”

“…[57] Since then a number of other ligands that exhibit a wide range of G-quadruplex affinity and specificity have been shown to bind promoterderived G-quadruplex in vitro and suppress the transcription of various genes in cell cultures. [47,[58][59][60] Some, but not all, of the genes suppressed by TMPyP4 contain a putative G-quadruplex forming sequence in or near the promoter. [60] Approximately 30-40% of human promoters contain a putative G-quadruplex motif.…”

“…[84] Since telomerase is over expressed in the majority of malignant tumor cells and in relatively few somatic cells, [84] it is widely recognized as a potential cancer-specific target. [20,35,41,42,46,47] With the knowledge that folded G-quadruplex structures are inactive substrates for telomerase, [85] many researchers have developed small-molecule inhibitors of telomerase that stabilize G-quadruplexfolded structures in the 3' overhangs of telomeric DNA. Indeed, small moleculemediated stabilization of the G-quadruplex structure(s) can effectively inhibit telomerase activity, and when applied to cells, G-quadruplex ligands can initiate apoptosis or replicative senescence.…”

“…[74] While it is unknown if this type of activity might be cancer-selective, telomestatin induces senescence and apoptosis in a number of different tumor cell types and exhibits less toxicity towards normal progenitor cells. [108][109][110][111] The administration of telomestatin to mice containing U937 xenografts reduced tumor volumes without causing signs of toxicity. [112] A total synthesis of telomestatin has recently been reported, [113] but little is known about the physicochemical and structural features important for its DNA binding and pharmacological activities.…”