Enhancement of Trimetrexate Cytotoxicity in Vitro and in Vivo by Carboxypeptidase G2

Antonella Romanini, Alberto F. Sobrero, Ting Chao Chou, Roger F. Sherwood, Joseph R. Bertino

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)6019-6023
Number of pages5
JournalCancer Research
Issue number21
StatePublished - Nov 1 1989

All Science Journal Classification (ASJC) codes

  • Oncology
  • Cancer Research

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