Doreen Ma

In vitro chemosensitivity of freshly explanted tumor cells to pemetrexed is correlated with target gene expression

SummaryAim of the studymRNA expression of genes involved in the mechanism of action of pemetrexed was correlated with in vitro chemosensitivity of freshly explanted human tumor specimens.Experimental designChemosensitivity to pemetrexed was studied in soft-agar. Multiplex rtPCR experiments for reduced folate carrier (RFC), folate receptor-α (FR-α), folylpolyglutamate synthetase (FPGS), thymidylate synthase (TS), dihydrofolate reductase (DHFR), glycinamide ribonucleotide formyl transferase (GARFT), mrp4, and mrp5 were performed in parallel. Correlations, threshold optimization, sensitivity, specificity, and efficiency were analyzed using the appropriate statistical methodologies.ResultsIn 61 samples, low levels of TS, GARFT, DHFR, and mrp4 gene expression significantly correlated with chemosensitivity to pemetrexed. Optimization analyses demonstrated threshold values of 144 copies for TS and six copies for mrp4 relative to 104 copies of β-actin.ConclusionsThese results form a rational basis for the design of clinical trials to evaluate the expression of these enzymes as predictors for treatment outcome.

Molecular determinants of efficacy for 5‐FU‐based treatments in advanced colorectal cancer: mRNA expression for 18 chemotherapy‐related genes

5‐Fluorouracil (5‐FU)‐based regimens remain a cornerstone in the treatment of colorectal cancer (CRC). However, the attendant toxicity prevents these regimens from reaching maximum therapeutic potential. In this retrospective analysis, we examined the pretreatment expression of 18 genes in archival tumor bank samples from patients with advanced CRC to determine if one or more of the selected genes showed promise as either a prognostic or predictive marker of 5‐FU‐based treatment outcomes. One hundred and forty‐four CRC patient samples (collected from 1983 to 2004) were analyzed via real‐time PCR for gene expression. Univariate analyses were used to correlate gene expression with efficacy and time‐to‐event variables. Low thymidine phosphorylase (TP), dihydrofolate reductase, dihydropyrimidine dehydrogenase (DPD), excision repair cross‐complementing 1 (ERCC1) and thymidylate synthase gene expression were associated with better time‐to‐progression in the entire population. Low TP, DPD and ERCC1 expression were independently associated with improved overall survival. Low TP gene expression was also predictive of response. This study suggests that TP gene expression in particular is a predictive as well as a prognostic biomarker for advanced CRC patients. Gene panels assessing pretreatment TP, DPD, ERCC1, dihydrofolate reductase and thymidylate synthase gene expression may help improve the therapeutic potential of 5‐FU‐ or other novel antifolate‐based regimens. Further analysis of the prognostic or predictive value of these genes in prospective trials in CRC patients seems warranted.

A randomized, double-blind, phase II study of two doses of pemetrexed as first-line chemotherapy for advanced breast cancer

Purpose: Pemetrexed has shown varied response rates in advanced breast cancer. This randomized, double-blind, phase II study was conducted to assess the efficacy and safety of two doses of pemetrexed in a homogeneous population. A secondary objective was to identify molecular biomarkers correlating with response and toxicity. Experimental Design: Patients with newly diagnosed metastatic breast cancer or locally recurrent breast cancer received 600 mg/m2 (P600 arm) or 900 mg/m2 (P900 arm) of pemetrexed on day 1 of a 21-day cycle. All patients received folic acid and vitamin B12 supplementation. Results: The P600 (47 patients) and P900 (45 patients) arms had response rates of 17.0% (95% confidence interval, 7.7-30.8%) and 15.6% (95% confidence interval, 6.5-29.5%) with ∼50% stable disease per arm, median progression-free survival of 4.2 and 4.1 months, and median times to tumor progression of 4.2 and 4.6 months, respectively. Both arms exhibited minimal toxicity (grade 3/4 neutropenia <20%, leukopenia <9%, and other toxicities <5%). Tumor samples from 49 patients were assessed for the expression levels of 12 pemetrexed-related genes. Folylpolyglutamate synthetase and thymidine phosphorylase correlated with efficacy. Best response rates and median time to tumor progression for high versus low thymidine phosphorylase expression were 27.6% versus 6.3% (P = 0.023) and 5.4 versus 1.9 months (P = 0.076), and for folylpolyglutamate synthetase were 37.5% versus 10.0% (P = 0.115) and 8.6 versus 3.0 months (P = 0.019), respectively. γ-Glutamyl hydrolase expression correlated with grade 3/4 toxicities: 78.6% for high versus 27.3% for low γ-glutamyl hydrolase (P = 0.024). Conclusion: The two pemetrexed doses yielded similar efficacy and safety profiles. Exploratory biomarker analysis identified efficacy and toxicity correlations and warrants further evaluation.

Applications of yeast in drug discovery

The yeast Saccharomyces cerevisiae is perhaps the best-studied eukaryotic organism. Its experimental tractability, combined with the remarkable conservation of gene function throughout evolution, makes yeast the ideal model genetic organism. Yeast is a non-pathogenic model of fungal pathogens used to identify antifungal targets suitable for drug development and to elucidate mechanisms of action of antifungal agents. As a model of fundamental cellular processes and metabolic pathways of the human, yeast has improved our understanding and facilitated the molecular analysis of many disease genes. The completion of the Saccharomyces genome sequence helped launch the post-genomic era, focusing on functional analyses of whole genomes. Yeast paved the way for the systematic analysis of large and complex genomes by serving as a test bed for novel experimental approaches and technologies, tools that are fast becoming the standard in drug discovery research

A Randomized Phase II Trial of Pemetrexed plus Irinotecan (ALIRI) versus Leucovorin-Modulated 5-FU plus Irinotecan (FOLFIRI) in First-Line Treatment of Locally Advanced or Metastatic Colorectal Cancer

Background: This multicenter, randomized trial compared overall response rate between pemetrexed plus irinotecan (ALIRI) and leucovorin-modulated 5-fluorouracil plus irinotecan (FOLFIRI) in patients with advanced colorectal cancer. Secondary objectives included overall and progression-free survival, duration of response, toxicities, and biomarkers. Patients and Methods: ALIRI patients received pemetrexed 500 mg/m2 and irinotecan 350 mg/m2 with vitamin supplementation on day 1 of each 21-day cycle. FOLFIRI patients received irinotecan 180 mg/m2 on days 1, 15, 29; on days 1, 2, 15, 16, 29, 30, patients received leucovorin 200 mg/m2, bolus 5-fluorouracil 400 mg/m2, and 5-fluorouracil 600 mg/m2 as 22-hour infusion. Results: Of 132 patients randomly assigned, 130 patients (64 = ALIRI, 66 = FOLFIRI) received ≧1 dose of treatment. Response rates (ALIRI = 20.0%, FOLFIRI = 33.3%) were not significantly different between arms (p = 0.095). Progression-free survival was 5.7 months for ALIRI and 7.7 months for FOLFIRI (p < 0.001). Neutropenia, fatigue, diarrhea, nausea, and vomiting were the major toxicities. There were 5 drug-related deaths (ALIRI = 4, FOLFIRI = 1). Biomarker analysis failed to reveal that any of the 18 preselected genes were clearly associated with tumor response. Conclusions: Neither efficacy nor safety improved on the ALIRI arm compared to the FOLFIRI arm. Progression-free survival on FOLFIRI was significantly longer compared to ALIRI. Potential biomarkers capable of predicting response to either regimen in advanced or metastatic colorectal carcinoma need further characterization.

Correlations of mRNA expression and in vitro chemosensitivity to enzastaurin in freshly explanted human tumor cells

SummaryPurpose: Enzastaurin (LY317615) is a novel serine/threonine kinase inhibitor, targeting Protein Kinase C-beta (PKC-β), and PI3K/AKT pathways to inhibit angiogenesis and tumor cell proliferation. The aims of this study were to determine whether Enzastaurin has direct antitumor activity against freshly explanted tumor cells and to correlate mRNA expression of genes related to the proposed mechanism of action of enzastaurin with in vitro chemosensitivity. Experimental Design: Freshly biopsied tumor cells were studied using soft-agar cell cloning experiments (SACCE) to determine the in vitro chemosensitivity to enzastaurin. An aliquot of the same tumor specimens was shock-frozen and total RNA was isolated for standardized multiplex rt-PCR experiments for gene expression of PKC-β1, PKC-β2, IL-8, IL-8RA, IL-8RB, Glycogen Synthase Kinase 3 beta (GSK-3β) and TGF-β1. Correlations, threshold optimization, sensitivity, specificity, and efficiency were analyzed using the appropriate statistical methodologies. Results: Seventy-two tumor samples were collected and 63 were fully evaluable. Low levels of mRNA expression of GSK-3β and high levels of mRNA expression of IL-8 were highly significantly correlated with chemosensitivity to enzastaurin. Optimization analyses demonstrated threshold values of 4,000 copies for IL-8 and three copies for GSK-3β relative to 104 copies of β-actin. However, no correlation between mRNA expression of PKC-β1, PKC-β2, IL-8RA, IL-8RB and chemosensitivity to enzastaurin was observed. Expression of TGF-β1 mRNA was not detectable in the specimens investigated. Conclusions: mRNA expression levels of IL-8 and GSK-3β correlate with antitumor activity of enzastaurin. These results form a rational basis for clinical trials to evaluate the expression of these genes as potential predictors for treatment outcome after enzastaurin chemotherapy.