Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.1 (phosphodiesterase)
 18,767 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Tiazofurin exhibits antitumor activity in murine and human tumor cells. In a recent phase I/II trial in patients with end-stage leukemia, tiazofurin showed good response; however, repeated treatment resulted in clinical resistance to the drug. To elucidate the mechanisms of resistance in human leukemic cells, two variants of human myelogenous leukemia K652 cells resistant to tiazofurin were developed by drug-selection pressure. Compared to a concentration producing 50% cell proliferation reduction that was 9.1 microM in sensitive cells, the resistant variants displayed concentrations producing 50% cell proliferation reductions of 12 and 16 mM. The activity of the target enzyme, IMP dehydrogenase, was not altered in the resistant cells. Studies on tiazofurin metabolism revealed that resistant variants formed < 10% of the active metabolite, thiazole-4-carboxamide adenine dinucleotide. This correlated with the activity of NAD pyrophosphorylase, the enzyme that synthesizes thiazole-4-carboxamide adenine dinucleotide, which was reduced to 10% in the resistant lines. Concurrently, the activity of thiazole-4-carboxamide adenine dinucleotide phosphodiesterase was elevated in the refractory cells. Compared to the sensitive counterpart, the levels of GMP and NAD were lower in the resistant lines. Guanine salvage activity was decreased in the resistant cells. Basal dGTP and dATP concentrations were elevated in the resistant line; nevertheless, tiazofurin incubation decreased dGTP levels in only the sensitive cells. Although there was no difference in the Km of tiazofurin transport or efflux, the Vmax of uptake of the drug was reduced in the resistant lines. Sensitive and resistant cells exhibit similar cytotoxicity to agents which do not share the mechanism of action of tiazofurin, suggesting that refractory cells are still sensitive to other standard antileukemic drugs.
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PMID:Biochemical consequences of resistance to tiazofurin in human myelogenous leukemic K562 cells. 809 64

8-Chloroadenosine 3',5'-monophosphate (8-Cl-cAMP) is a potential new anticancer agent, but its mechanism of action is not clearly defined. In this work we have studied the effect of various heat inactivated and heat untreated human sera in the absence or in the presence of a nonspecific phosphodiesterase (PDE) inhibitor, IBMX, or of nucleoside transport inhibitor and cGMP-specific PDE inhibitor dipiridamole (DP), or of inosine-monophosphatedehydrogenase (IMPDH) inhibitor, tiazofurin, (T), on the antiproliferative 8-Cl-cAMP action towards two human malignant cell lines, K562 and HeLa cells, in vitro. Cell survival was determined 72 hrs after the agents action, using MTT assay. The results obtained, indicated the similar inhibitory effect of 8-Cl-cAMP on HeLa cell survival in the presence of four different heat untreated human sera (IC50 = 4-4.8 microM). Serum heat inactivation caused decrease in 8-Cl-cAMP antiproliferative action depending on the blood donor (IC50 = 23 microM, 15 microM, 19 microM, and 9 microM) and suggesting that some thermolabile ingredient(s) present in sera is involved, at least partially, in the induction or permittance of antiproliferative 8-Cl-cAMP action. K562 Cells were not as much resistant to 8-Cl-cAMP as HeLa cells, or mouse melanoma B16 cells; in the presence of heat untreated FBS, IC50 = 16 microM, while for B16 cells IC50 was 8 microM. Different human sera show different effect on 8-Cl-cAMP action on K562 cells: IC50 = 7.5 microM and 16.5 microM. In the presence of heat inactivated human sera 8-Cl-cAMP IC50 concentrations were higher, with relevant mutual differences. The effect of different sera on 8-Cl-cAMP action was only partly abrogated in the presence of a nonspecific PDE inhibitor, IBMX, suggesting that the serum PDE action is one of the various factors contributing to the induction of 8-Cl-cAMP antiproliferative action. Nucleoside transport inhibitor and cGMP-specific PDE inhibitor dipiridamole inhibited the antiproliferative 8-Cl-cAMP action to HeLa and K562 cells. Tiazofurin and 8-Cl-cAMP acted as antagonists on HeLa, but not on K562 cells.
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PMID:The mechanism of 8-Cl-cAMP action. 989 61