NEW YORK-The drive to find markers that will predict which patients will benefit from erlotinib (Tarceva) and gefitinib(Drug information on gefitinib) (Iressa) inched forward with studies reported from two groups. Both studies used human non-small-cell lung cancer (NSCLC) cell lines to identify panels of markers that not only provide the basis for development of clinically useful screening tests for erlotinib and gefitinib sensitivity, but also open new possibilities for overcoming resistance. EGFR-Independent Activation Roman Perez-Soler, MD, of Montefiore Medical Center, New York, and colleagues reported that in a panel of nine human NSCLC cell lines, two were highly sensitive to erlotinib (Tarceva) and both expressed epithelial growth factor receptor (EGFR). The other seven cell lines were resistant, but five of them expressed EGFR (abstract 7026). Erlotinib induced G1-S phase arrest in sensitive cells and to some extent in resistant cells. Sensitivity to erlotinib did not correlate with expression of ErbB family genes, nor was there any correlation between drug sensitivity and baseline p-HER1 or epithelial growth factor receptor (EGFR) expression. There were no differences in baseline expression of P-EGFR between sensitive and resistant cell lines. Baseline expression of P-ERK1/2, P-AKT, and P-STAT-3 was undetectable or low in sensitive cell lines but high in most resistant cell lines. Erlotinib resistance correlated with higher baseline expression of p-MAPK, p-Akt, and p-STAT. Induction of p-HER1/EGFR and p-AKT by EGF was seen in both sensitive and resistant cells and was blocked by erlotinib in both groups. "These data support the hypothesis that HER1/EGFR-independent baseline activation of downstream signaling molecules may define the patient subpopulation that is less likely to derive a clinical benefit from erlotinib therapy," Dr. Perez-Soler said. The investigators analyzed effects of erlotinib on the cell cycle by flow cytometry. They measured expression of the activated upstream and downstream elements of the EGFR pathway (EGFR, ERK1/2, AKT, and STAT-3) at baseline and after stimulation with EGF, determined by western blot analysis. In the second study, investigator Fred R. Hirsch, MD, of the University of Colorado Health Sciences Center in Denver reported gene array data showing that E-cadherin signaling plays a central role in determining gefitinib sensitivity. High expression of E-cadherin correlated with high sensitivity to gefitinib and that high expression of SIP-1 and ZEB-1 correlated with high resistance to gefitinib. Dr. Hirsch and colleagues determined gefitinib sensitivity in 18 NSCLC cell lines. Ten cells lines were studied using oligonucleotide microarray analysis. The researchers used three distinct filtration and normalization normalization algorithms to process the expression data and generate a list of 144 candidate genes. This approach was combined with five machine-learning algorithms to build a test set for predictor genes. The 16 genes whose expression was more than threefold different in sensitive vs resistant cells were verified by quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR). The final analysis identified a panel of 13 different genes that were able to predict gefitinib in 9 of 10 cell lines used for validation. "This biomarker panel may be of significant value for selecting NSCLC patients for gefitinib treatment," Dr. Hirsch said. Future Study Direction According to Dr. Hirsch, future directions for this research will include confirming the predictive value of E-cadherin, HER3, SIP-1, and ZEB-1 expression in a test set of cell lines and identifying genes in the microarray gene set that are controlled by SIP-1 and ZEB-1. Dr. Hirsch told Oncology News International that early work has already shown that five markers from this set predicted gefitinib sensitivity in 9 of 10 cell lines tested. "We will also continue attempts to overcome resistance by blocking ZEB-1 and SIP-1," he said. The researchers have attempted unsuccessfully to do this by using histone deacetylase inhibitors and will be trying sRNA constructs next. A prospective trial evaluating the relationship of expression of SIP-1, ZEB-1, E-cadherin, and HER3 to EGFR mutations is being planned.