This Article Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Boucher, P. D. Articles by Shewach, D. S. Search for Related Content PubMed PubMed Citation Articles by Boucher, P. D. Articles by Shewach, D. S.

Synergistic Enhancement of Herpes Simplex Virus Thymidine Kinase/Ganciclovir-mediated Cytotoxicity by Hydroxyurea¹

Department of Pharmacology, University of Michigan Medical Center, Ann Arbor, Michigan 48109

We have previously demonstrated (L. Z. Rubsam et al., Cancer Res., 59: 669–675, 1999) that low ganciclovir (GCV) triphosphate (TP) levels similar to cellular deoxynucleotide concentrations can induce multilog killing in cells stably expressing herpes simplex virus thymidine kinase (HSV-TK). In this study, we evaluated whether reducing the endogenous competitor of GCV-TP, dGTP, enhanced GCV-mediated cytotoxicity. In SW620 human colon carcinoma cells stably expressing HSV-TK, the addition of the ribonucleotide reductase inhibitor, hydroxyurea (HU), decreased cellular dGTP pools and simultaneously increased the accumulation of GCV-TP levels. The amount of GCV nucleotide transfer from HSV-TK-expressing to nonexpressing (bystander) cells was quantitated in physically separated pHook-expressing bystander cells. Elevation of the GCV-TP:dGTP ratio by HU resulted in increased levels of GCV nucleotides transferred from HSV-TK-expressing to bystander cells during a 24 h drug incubation and enhanced GCV monophosphate incorporation into DNA after drug removal. Isobologram analysis demonstrated that the combination of GCV and HU was additive in 100% HSV-TK cultures and synergistic in HSV-TK/bystander mixtures. IC₅₀ values for GCV in 1:1 cocultures of HSV-TK-expressing and nonexpressing SW620 cells were reduced from 1.5 µM to 0.07 µM with 2 mM HU. A similar reduction was also observed with HT-29 cells and U251 cells. With 2 mM HU, IC₅₀ values for GCV in 10:90, 5:95, and 1:99 SW620 HSV-TK-expressing and nonexpressing cocultures were reduced from 55 µM to 0.3 µM, 71 µM to 0.8 µM, and 118 µM to 7 µM, respectively. These results demonstrate the ability to pharmacologically enhance HSV-TK/GCV-mediated bystander killing and may have an important therapeutic impact.

This article has been cited by other articles:

				B. G. Gentry, P. D. Boucher, and D. S. Shewach Hydroxyurea Induces Bystander Cytotoxicity in Cocultures of Herpes Simplex Virus Thymidine Kinase-Expressing and Nonexpressing HeLa Cells Incubated with Ganciclovir. Cancer Res., April 1, 2006; 66(7): 3845 - 3851. [Abstract] [Full Text] [PDF]

				P. D. Boucher, M. M. Im, S. O. Freytag, and D. S. Shewach A novel mechanism of synergistic cytotoxicity with 5-fluorocytosine and ganciclovir in double suicide gene therapy. Cancer Res., March 15, 2006; 66(6): 3230 - 3237. [Abstract] [Full Text] [PDF]

				X. Zheng, M. Johansson, and A. Karlsson Bystander Effects of Cancer Cell Lines Transduced with the Multisubstrate Deoxyribonucleoside Kinase of Drosophila melanogaster and Synergistic Enhancement by Hydroxyurea Mol. Pharmacol., August 1, 2001; 60(2): 262 - 266. [Abstract] [Full Text] [PDF]

				X. Zheng, M. Johansson, and A. Karlsson Retroviral Transduction of Cancer Cell Lines with the Gene Encoding Drosophila melanogaster Multisubstrate Deoxyribonucleoside Kinase J. Biol. Chem., December 8, 2000; 275(50): 39125 - 39129. [Abstract] [Full Text] [PDF]