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Cyclic Induction of Senescence with Intermittent AZT Treatment Accelerates both Apoptosis and Telomere Loss

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Abstract

Background. 3′-azido-2′,3′-dideoxythymidine (AZT) is phosphorylated intracellularly to 3′-azido-3′-deoxythymidine-5′-triphosphate (AZT-TP), which is incorporated into telomeric DNA, thereby blocking chain elongation. AZT is also known to inhibit reverse transcriptase, as well as other cellular enzymes including DNA polymerase γ, thymidine kinase, and telomerase.

Methods. We induced cancer cell senescence by treating MCF-7 cells with AZT in dosages of IC10 and IC20 for an extended period (about 120 population doublings (PD)). We then investigated the sequential changes in cellular growth, expression of telomerase subunits and transcription factors (c-Myc, Mad1), telomerase activity and telomere length.

Results. Senescence, apoptosis, growth delay, inhibition of telomerase activity and shortening of telomere length were all observed in a dose- and time-dependent manner. After the onset of senescence, the apoptosis rate increased slowly during early PDs. In contrast to senescence, the apoptotic rate showed little change after AZT removal, while it increased suddenly and significantly in a dose-dependent manner upon the second introduction of AZT. Continuous shortening of the telomeric length was observed with AZT, and, upon re-exposure to AZT, shortening of the telomere occurred more rapidly than with first exposure. Of the telomerase subunits, telomerase reverse transcriptase (hTERT) and c-Myc were the first to show a reduction in activity after AZT treatment, followed by changes in hTER , Mad1 and hTEP-1.

Conclusion. Cyclic treatment with AZT initially suppressed hTERT and c-Myc, followed by suppression of hTER, Mad1 and hTEP-1. Furthermore, the treatment accelerated both telomere loss and apoptosis, even when administered at a senescence-inducing dosage level.

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Abbreviations

AZT:

3′-azido-2′,3′-dideoxythymidine

AZT-TP:

3′-azido-3′-deoxythymidine-5′-triphosphate

CHAPS:

3-[(3-cholamidopropyl)dimethylammonio]-1-propane-sulfonate

EGTA:

ethylene glycol-bis(β-aminoethyl Ether)

hTER:

telomerase RNA

hTERT:

telomerase reverse transcriptase

TEP:

telomerase-associated protein

TRAP:

telomeric repeat amplification protocol

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Authors and Affiliations

  1. Cancer Metastasis Research Center, Young Cancer Center, Yonsei University College of Medicine, Seoul, Seodaemun-Ku, Korea

    Hyun Jung Ji, Sun Young Rha, Hei Cheul Jeung, Sang Hwa Yang, Sung Whan An & Hyun Cheol Chung

  2. Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine, Seoul, Seodaemun-Ku, Korea

    Hyun Jung Ji, Sun Young Rha, Hei Cheul Jeung & Hyun Cheol Chung

  3. Department of Internal Medicine, Seoul, Seodaemun-Ku, Korea

    Hyun Cheol Chung

  4. Yonsei University College of Medicine, Yonsei Cancer Center, Seoul, Seodaemun-Ku, Korea

    Hyun Jung Ji, Sun Young Rha, Hei Cheul Jeung, Sang Hwa Yang & Hyun Cheol Chung

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  1. Hyun Jung Ji
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Ji, H.J., Rha, S.Y., Jeung, H. et al. Cyclic Induction of Senescence with Intermittent AZT Treatment Accelerates both Apoptosis and Telomere Loss. Breast Cancer Res Treat 93, 227–236 (2005). https://doi.org/10.1007/s10549-005-5156-0

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