Abstract B6: Folylpoly-glutamate synthetase and thymidylate synthase are associated with clinical outcome from pemetrexed-based therapy in non-small cell lung cancer (NSCLC)

• Published in: Clinical cancer research Vol. 18; no. 3_Supplement; p. B6
• Main Authors: Christoph, Daniel C., Loewendick, Heike, Peglow, Anja, Schuler, Martin, Eberhardt, Wilfried E., Hirsch, Fred R., Asuncion, Bernadette Reyna, Wynes, Murry W., Gauler, Thomas C., Wohlschlaeger, Jeremias, Theegarten, Dirk, Welter, Stefan, Tran, Cindy, Hassan, Biftu
• Format: Journal Article
• Language: English
• Published: 01.02.2012
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.12AACRIASLC-B6

Background: The antifolate pemetrexed targets multiple enzymes involved in pyrimidine and purine synthesis including thymidylate synthase (TS). After entry into cells, pemetrexed is converted to polyglutamated forms by folylpoly-γ-glutamate synthetase (FPGS), a critical step to achieve full target inhibition. We hypothesized that FPGS and TS protein expression may predict outcome following pemetrexed-treatment of patients with advanced NSCLC, like in malignant pleural mesotheliomas (Christoph et al., J Clin Oncol. 2011: 29 suppl.). This is the largest report on pemetrexed-treatment outcome based on TS and FPGS in Caucasian patients with advanced NSCLC. Methods: Pretreatment tumor samples from 161 patients (pts) with metastatic NSCLC, treated with pemetrexed combined with platinum (74 pts (46%)) or as single agent (82 pts (51%)) or within other combinations (5 pts (3%)), were retrospectively analyzed. FPGS and TS protein expression levels were evaluated by IHC using the H-Scoring system (0–300), which relies on the product of intensity (range 0 to 3) and the percentage of positive tumor cells (0–100%). Radiographic evaluation of response was performed according to RECIST criteria (version 1.1). Results: Median pretreatment H-scores were 180 for FPGS (range: 0–280) and 205 (range: 120–290) for TS. Using the log-rank test and the median H-score as cut-off, we found a significant association between low TS protein expression and improved progression-free survival (PFS) (median PFS of 5.5 months vs. 3.4 months; hazard ratio [HR] 0.66, 95% CI, 0.45 to 0.96; P=0.03) or prolonged overall survival (median OS of 33.9 months vs. 15.0 months; hazard ratio [HR] 0.52, 95% CI, 0.31 to 0.86; P=0.01). Moreover, high FPGS protein expression was only associated with better PFS (median PFS of 5.5 months vs. 3.4 months; hazard ratio [HR] 0.58, 95% CI, 0.37 to 0.89; P=0.03). Considering exclusively patients suffering from adenocarcinomas (110 pts (68%)), TS was associated with objective response to pemetrexed-based treatment (mean H-score 192 for responders vs. 210 for non-responders, P=0.03). Conclusions: We have investigated FPGS and TS protein expressions in tumor specimens from the largest series of pemetrexed-treated Caucasian NSCLC patients. Baseline determination of TS and FPGS expression by IHC using the H-score system is associated with clinical outcome from pemetrexed-based therapy in advanced NSCLC. Further prospective validation studies are warranted.