Derivation and characterization of a monoclonal antibody against human glycinamide ribonucleotide formyltransferase

Features of potentially predictive biomarkers of chemotherapeutic efficacy in small cell lung cancer

INTRODUCTION

One-size-fits-all chemotherapy does not improve survival in patients with small cell lung cancer (SCLC). Excision repair cross-complementing group 1 (ERCC1), ribonucleotide reductase 1 (RRM1), thymidylate synthase (TS), and topoisomerase 2alpha (Topo2alpha) expression levels are predictive of chemotherapeutic efficacy in some malignancies. Our aim was to determine the expression levels of these proteins to assess their potential clinical utility in SCLC.

METHODS

We used an immunofluorescence-based automated quantitative technique to score RRM1, ERCC1, TS, and Topo2alpha levels in tumor specimens from 100 patients with SCLC and immunohistochemistry to semiquantitatively score levels of TS, 5-phosphoribosyl-glycinamide formyl-transferase, and folyl-polyglutamate synthase expression. Confocal microscopy was used for subcellular localization in SCLC cells.

RESULTS

RRM1, ERCC1, and Topo2alpha staining was predominantly nuclear and TS mainly cytoplasmic. Using immunohistochemistry, we found that TS (antibody 106) and TS (antibody 4H4) scores were strongly correlated (r = 0.82, p < 0.0001). By automated quantitative technique, RRM1 and Topo2alpha levels were highly correlated (r = 0.56, p < 0.0001). ERCC1 and TS levels had a narrow and low range of expression. There was no correlation between any of these biomarkers and patients' age or sex.

CONCLUSION

Considering this clinical evidence, expression levels of RRM1 and Topo2alpha may have utility for chemotherapy customization. Clinical validation of their predictive power is desirable in a prospective clinical trial.

Derivation and characterization of monoclonal antibodies against human folypolyglutamate synthetase

Folypolyglutamate synthetase (FPGS) plays a critical role in the cellular retention of both folates and antifolates. Resistance to antifolates is in part related to changes in FPGS enzyme activity and levels of messenger RNA, or in some instances, protein as evaluated by Western blots using polyclonal antisera. The present study was designed to derive a series of monoclonal antibodies (MAb) against the native protein, to characterize them in terms of specificity and epitope mapping, and to determine kinetic constants by Biacore. We report on 3 IgG(1) kappa MAbs-namely, 4-2, 4-3, and 4-18-with epitopes localized to the carboxyl domain of the protein. These antibodies recognize a single band on Western blots of HeLa cell lysates, which is significantly reduced following RNAi knockdown. The recognition of both the native and denatured conformations of FPGS by these MAbs should provide useful reagents for FPGS quantitation in either tumor cell lysates or in tumor biopsies.