TY - JOUR
T1 - Enhancement of Trimetrexate Cytotoxicity in Vitro and in Vivo by Carboxypeptidase G2
AU - Romanini, Antonella
AU - Sobrero, Alberto F.
AU - Chou, Ting Chao
AU - Sherwood, Roger F.
AU - Bertino, Joseph R.
PY - 1989/11/1
Y1 - 1989/11/1
N2 - Carboxypeptidase G2 (CPG2), an enzyme produced by Pseudomonas strain RS-16, hydrolyzes the glutamate residue from methotrexate and other folates. The possibility of enhancing trimetrexate cytotoxicity by CPG2 induced folate depletion was investigated in vitro in a human leukemia ceU line, CCRF-CEM, and in three sublines of these cells each with a different methotrexate resistance phenotype. The cytotoxic effect in vitro was detected using a colorimetric assay with a tetrazolium salt, 3-4,5-dimethylthiazol-2-yl)-2,5-iiphenyltetrazolium bromide. Dose-effect relationships of drugs alone and in combination were analyzed by the median effect principle and by the combination indices for quantitation of synergy or antagonism with the aid of a computer program. Trimetrexate alone was cytotoxic against the parent and all the resistant cell lines with the drug concentrations required to decrease the cell count to 50% of control in the nanomolar range (1.4, 1.6, 1.5, and 0.7 nM in CCRF-CEM, CCRF-CEM/E, CCRF-CEM/P, and CCRF-CEM/T, respectively) following 5 days of exposure. The concentration of CPG2 required to decrease the cell count to 50% control for these cell lines was 3.5, 2.6, 26.6, and 7.9 x HT5 units/ml for CCRF-CEM, CCRF-CEM/E, CCRF-CEM/P, and CCRF-CEM/T, respectively. A synergistic cytotoxic effect of trimetrexate after simultaneous continuous exposure with CPG2 was observed with CCRF-CEM ceUs and with the three resistant cell lines. This drug combination given to BALB/c x DBA/2 Fi mice bearing LI 210 cells also produced synergy over a narrow range of drug doses. The activity of this combination in both methotrexate sensitive and methotrexate resistant cell lines indicates that clinical trials of this combination should be undertaken.
AB - Carboxypeptidase G2 (CPG2), an enzyme produced by Pseudomonas strain RS-16, hydrolyzes the glutamate residue from methotrexate and other folates. The possibility of enhancing trimetrexate cytotoxicity by CPG2 induced folate depletion was investigated in vitro in a human leukemia ceU line, CCRF-CEM, and in three sublines of these cells each with a different methotrexate resistance phenotype. The cytotoxic effect in vitro was detected using a colorimetric assay with a tetrazolium salt, 3-4,5-dimethylthiazol-2-yl)-2,5-iiphenyltetrazolium bromide. Dose-effect relationships of drugs alone and in combination were analyzed by the median effect principle and by the combination indices for quantitation of synergy or antagonism with the aid of a computer program. Trimetrexate alone was cytotoxic against the parent and all the resistant cell lines with the drug concentrations required to decrease the cell count to 50% of control in the nanomolar range (1.4, 1.6, 1.5, and 0.7 nM in CCRF-CEM, CCRF-CEM/E, CCRF-CEM/P, and CCRF-CEM/T, respectively) following 5 days of exposure. The concentration of CPG2 required to decrease the cell count to 50% control for these cell lines was 3.5, 2.6, 26.6, and 7.9 x HT5 units/ml for CCRF-CEM, CCRF-CEM/E, CCRF-CEM/P, and CCRF-CEM/T, respectively. A synergistic cytotoxic effect of trimetrexate after simultaneous continuous exposure with CPG2 was observed with CCRF-CEM ceUs and with the three resistant cell lines. This drug combination given to BALB/c x DBA/2 Fi mice bearing LI 210 cells also produced synergy over a narrow range of drug doses. The activity of this combination in both methotrexate sensitive and methotrexate resistant cell lines indicates that clinical trials of this combination should be undertaken.
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M3 - Article
C2 - 2529027
SN - 0008-5472
VL - 49
SP - 6019
EP - 6023
JO - Cancer Research
JF - Cancer Research
IS - 21
ER -