| Target Validation Information | |||||
|---|---|---|---|---|---|
| TTD ID | T62553 | ||||
| Target Name | Herpes simplex virus Ribonucleoside-diphosphate reductase (HSV RIR1) | ||||
| Type of Target |
Discontinued |
||||
| Action against Disease Model | Clofarabine | Drug Info | The in vitro efficacies of three new drugs--clofarabine (CLOF), nelarabine (NEL) and flavopiridol (FP) - were assessed in a panel of acute lymphoblastic leukaemia (ALL) cell lines. The 50% inhibitory concentration (IC50) for CLOF across all lines was 188-fold lower than that of NEL. B-lineage, but not T-lineage lines, were >7-fold more sensitive to CLOF than cytosine arabinoside (ARAC). NEL IC50 was 25-fold and 113-fold higher than ARAC in T- and B-lineage, respectively. T-ALL cells were eightfold more sensitive to NEL than B-lineage but there was considerable overlap. FP was more potent in vitro than glucocorticoids and thiopurines and at doses that recent phase I experience predicts will translate into clinical efficacy. Potential cross-resistance of CLOF, NEL and FP was observed with many front-line ALL therapeutics but not methotrexate or thiopurines. Methotrexate sensitivity was inversely related to that of NEL and FP. Whilst NEL was particularly effective in T-ALL, a subset of patients with B-lineage ALL might also be sensitive. CLOF appeared to be marginally more effective in B-lineage than T-ALL and has a distinct resistance profile that may prove useful in combination with other compounds. FP should be widely effective in ALL if sufficient plasma levels can be achieved clinically. | [1] | |
| Hydroxyurea | Drug Info | The inhibition of ribonucleotide reductase (RR) of intact Ehrlich ascites t uMor cells by different antit uMor agents was compared using EPR spectroscopy. The inactivation of M2subunit was measured via quenching of the functionally essential tyrosine radical. Inhibitors of different classes, for example, hydroxyurea, pyrogallol, and thiosemicarbazones, differ in their efficiency by three orders of magnitude. Most effective inhibition was found for isoquinoline-1-aldehyde-thiosemicarbazone (IQ-1) with an IC50 value of 0.18 microM. Inhibition of RR inside t uMor cells is comparable with that reported for isolated enzymes. | [2] | ||
| References | |||||
| REF 1 | In vitro cytotoxicity of nelarabine, clofarabine and flavopiridol in paediatric acute lymphoblastic leukaemia. Br J Haematol. 2007 Apr;137(2):109-16. | ||||
| REF 2 | Quenching of tyrosine radicals of M2 subunit from ribonucleotide reductase in tumor cells by different antitumor agents: an EPR study. Free Radic Biol Med. 1990;9(1):1-4. | ||||
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