Polyamine depletion and cell cycle manipulation in combination with HSV thymidine kinase/ganciclovir cancer gene therapy

Abstract

Abstract. We have shown earlier that polyamine biosynthesis inhibition is accompanied by cell cycle alterations that can be utilized to enhance the efficacy of herpes simplex virus thymidine kinase -ganciclovir (HSV-TK/GCV) cancer gene therapy. In the present study, we asked 1) can the activated polyamine catabolism instead of biosynthesis inhibition be utilized to enhance the efficacy of HSV-TK/GCV gene therapy, and 2) can other known cell cycle inhibitors be used to make tumor cells more sensitive to this form of gene therapy? We show, using rat (9L) and human (U251-MG) glioma cell populations with 15% of HSV-TK-positive cells that DENSPM-induced activation of polyamine catabolism caused a profound polyamine deprivation in U251-MG cells, but there were no associated cell cycle effects in these cells. Consequently, we did not see any enhancement of the HSV-TK/GCV system. Aphidicolin, hydroxyurea, mimosine and resveratrol, but not lovastatin induced an apparent cell cycle arrest, followed by an intense but transient increase of the S phase cells after removal of the drug. This effect was shown to potentiate the HSV-TK/GCV cytotoxicity to some extent, especially in 9L cells and when the GCV treatment was started 0-24 h before the drug treatment. However, the enhancement was weaker than observed earlier with DFMO-induced cell cycle arrest and a considerable degree of the effect appeared to result from the growth-inhibitory actions of the drugs. In summary, we demonstrate that polyamine deprivation via DENSPM action is not associated with cell cycle effects and is not sufficient to cause enhancement of the HSV-TK/GCV system. Also, drugs with a rapid effect to the cell cycle are weak boosters of the HSVTK/GCV gene therapy, thus being less useful than DFMO for enhancement of this gene therapy form in animal studies and clinical trials.

Antitumor activity of combined endostatin and thymidine kinase gene therapy in C6 glioma models

“…To confer cytotoxicity, cells were transfected with plasmids encoding TK (TK alone or TK‐ES), followed by GCV incubation. The efficacy of TK/GCV system depends largely on the proportion of proliferating cells, in which TK/GCV inhibits DNA replication and cell proliferation . In our study, the percentage of TK‐expressing cells at S phase was greatly increased after GCV exposure, whereas the proportion of cells at G2/M phase was significantly reduced.…”

Polyamines and DNA methylation in childhood leukaemia

“…It has been found that primary and cultured neoplastic cells have methylation patterns which differ from the patterns of normal cells. These changes are apparent from measurements of the methylcytosine content of the DNA, which is reduced in many tumours [5][6][7][8]. DNA regions are often hypomethylated in hepatomas and leukaemias, including those of the c-myc, Ha-ras, Ki-ras, fos, Erb-A1 and bcl-2 proto-oncogenes [9,10].…”