Potent inhibition of human telomerase by U-73122

Abstract

SummaryTelomerase activity is repressed in normal human somatic cells, but is activated in most cancers, suggesting that telomerase may be an important target for cancer therapy. In this study, we report that U-73122, an amphiphilic alkylating agent that is commonly used as an inhibitor for phospholipase C, is also a potent and selective inhibitor of human telomerase. The inhibition of telomerase by U-73122 was attributed primarily to the pyrrole-2,5-dione group, since its structural analog U-73343 did not inhibit telomerase. In confirmation, we observed that telomerase was inhibited by N-ethylmaleimide, but not N-ethylsuccinimide. The IC 50 value of U-73122 for the in vitro inhibition of telomerase activity is 0.2 lM, which is comparable to or slightly more sensitive than that for phospholipase C. The inhibitory action of U-73122 on telomerase appears to be rather selective since the presence of externally added proteins did not protect the inhibition and the IC 50 values for the other enzymes tested in this study were at least an order of magnitude higher than that for telomerase. Furthermore, we demonstrate that U-73122 can inhibit telomerase in hematopoietic cancer cells. The potent and selective inhibition of telomerase by U-73122 raises the potential exploitation of this drug and other alkylating agents as telomerase inhibitor.

Exploring the mechanism of inhibition of human telomerase by cysteine‐reactive compounds

“…Finally, even if none of our compounds was really selective, we noticed that some of them could decrease telomerase activity in cancer cells cultured in vitro . As in previous studies , this was associated with a rapid cellular toxicity that is most probably not related to telomerase inhibition, as a comparable toxicity was observed on telomerase‐negative cell lines. In conclusion, our analysis supports the view that cysteine‐reactive molecules are a promising class of drug to efficiently inhibit telomerase, but highly specific inhibitors need to be developed to be able to target this enzyme by these class of reagents in humans.…”

“…Therefore, in comparative experiments between several polymerases, the selectivity of the inhibitor may only be apparent, reflecting high differences in sensitivity between different enzymes. Indeed, telomerase has been pointed to be among the most N ‐ethylmaleimide‐sensitive enzymes reported in the literature . Therefore, previous studies may have just observed the particular sensitivity of telomerase to non‐specific sulfhydryl reagents rather than having discovered a truly selective inhibitor, resulting from a specific molecular recognition.…”

“…However, this hypothesis has never been confirmed by the direct detection of the adduct on the protein, and the putative position of the targeted residue(s) remains elusive. More interestingly, it has been noticed that telomerase is particularly sensitive to sulfhydryl reagents compared to other enzymes , but the molecular basis of this property is also unknown. Indeed, telomerase does not use cysteines in its catalytic site, and reducing agents are not required for in vitro enzymatic activity .…”

The vignette for V13N5 Issue

“…Interestingly, it is inactive in most adult tissues but active in many caner cells and cultured cells. In this study, the authors have shown the effectiveness of an amphiphilic alkylating agent U-73122 in telomerase inhibition both in cultured cells and cell-free systems [17]. Search for inhibitors of telomerase is thus important to further our under-standing of telomerase as well as improving cancer intervention.…”

Progensa™ PCA3 test for prostate cancer detection

“…Of course, another use of these markers is as targets for therapy. For example, both epigenetic modifiers and small molecule inhibitors of telomerase activity have been evaluated with conventional and novel cytotoxic drugs in various cancers [29][30][31] including prostate cancer [32,33].…”