The diimide drug PIPER has a cytotoxic dose-dependent effect in vitro and inhibits telomere elongation in HELA cells.
It is known that, in vitro, PIPER (N,N'-bis [2-(1-piperidino)ethyl]-3,4,9,10-tetracarboxylic diimide) induces the formation of the Hoogsteen quadruplex structure in telomere DNA, thus inhibiting the polymerisation of telomeric repeats. Since the action of PIPER in vivo has been scarcely investigated, this study was addressed to gain some insight into the effects of this drug on cultured HeLa cells. Vital staining with erythrosine, performed on cells exposed to different PIPER concentrations (from 1 to 50 microM), showed that the drug exerts a dose-dependent cytotoxic effect, clearly evident after a short-term (24 h) treatment. This early cytotoxic effect of PIPER on cultured HeLa cells was confirmed by a spectrophotometric/colorimetric method employing methylthiazoletetrazolium (Mossmann assay). Hematoxylin/eosin staining of cells treated with PIPER for 24 h showed a nuclear condensation and a cytoplasmic vacuolisation, very pronounced at higher drug concentrations. These pictures suggest that PIPER-induced cell death might be of the apoptotic type. Finally, the anti-telomerase activity of PIPER was monitored by TRAP assay, performed on HeLa cell nuclear extracts treated with increasing drug concentrations. It was found that some inhibition of telomerase is apparent even at low concentrations, while at the highest concentration the enzyme is completely inhibited. These results indicate that the cytotoxic power of PIPER is possibly related to its antitelomeric effect.