Investigators Seek Markers for Sensitivity to EGFR Inhibitors

NEW YORK-The drive to findmarkers that will predict which patientswill benefit from erlotinib(Tarceva) and gefitinib (Iressa) inchedforward with studies reported fromtwo groups at the 40th annual meetingof the American Society of ClinicalOncology. Both studies used humannon-small-cell lung cancer(NSCLC) cell lines to identify panelsof markers that not only provide thebasis for development of clinically usefulscreening tests for erlotinib andgefitinib sensitivity, but also open newpossibilities for overcoming resistanceto these agents.Roman Perez-Soler, MD, ofMontefiore Medical Center, NewYork, and colleagues reported that ina panel of nine human NSCLC celllines, two were highly sensitive toerlotinib (Tarceva) and both expressedepidermal growth factor receptor(EGFR). The other seven celllines were resistant, but five of themexpressed EGFR (abstract 7026).Erlotinib induced G1-S phase arrestin sensitive cells and to some extentin resistant cells. Sensitivity toerlotinib did not correlate with expressionof ErbB family genes, norwas there any correlation betweendrug sensitivity and baseline p-HER1or EGFR expression.There were no differences inbaseline expression of P-EGFR betweensensitive and resistant cell lines.Baseline expression of P-ERK1/2,P-AKT, and P-STAT-3 was undetectableor low in sensitive cell lines buthigh in most resistant cell lines.Erlotinib resistance correlatedwith higher baseline expression ofp-MAPK, p-Akt, and p-STAT. Inductionof p-HER1/EGFR and p-AKT byEGF was seen in both sensitive andresistant cells and was blocked byerlotinib in both groups."These data support the hypothesisthat HER1/EGFR-independentbaseline activation of downstream signalingmolecules may define the patientsubpopulation less likely to deriveclinical benefit from erlotinibtherapy," Dr. Perez-Soler said.The investigators analyzed effects of erlotinib on the cell cycle by flowcytometry. They measured expressionof the activated upstream and downstreamelements of the EGFR pathway(EGFR, ERK1/2, AKT, and STAT-3) at baseline and after stimulationwith EGF, determined by western blotanalysis.Second StudyIn the second study, investigatorFred R. Hirsch, MD, of the Universityof Colorado Health Sciences Centerin Denver reported gene array datashowing that E-cadherin signalingplays a central role in determininggefitinib sensitivity (abstract 7015).High expression of E-cadherin correlatedwith high sensitivity to gefitiniband that high expression of SIP-1 andZEB-1 correlated with high resistanceto gefitinib.Dr. Hirsch and colleagues determinedgefitinib sensitivity in 18NSCLC cell lines. Ten cells lines werestudied using oligonucleotidemicroarray analysis. The researchersused three distinct filtration and normalizationalgorithms to process theexpression data and generate a list of144 candidate genes. This approachwas combined with five machinelearningalgorithms to build a test setfor predictor genes. The 16 geneswhose expression was more thanthreefold different in sensitive vs resistant cells were verified by quantitativereal-time reverse transcriptasepolymerase chain reaction (RT-PCR).The final analysis identified a panelof 13 different genes that were ableto predict gefitinib in 9 of 10 cell linesused for validation. "This biomarkerpanel may be of significant value forselecting NSCLC patients for gefitinibtreatment," Dr. Hirsch said.Future StudyDirectionsAccording to Dr. Hirsch, futuredirections for this research will includeconfirming the predictive value of Ecadherin,HER3, SIP-1, and ZEB-1expression in a test set of cell lines andidentifying genes in the microarraygene set that are controlled by SIP-1and ZEB-1.Early work has already shown thatfive markers from this set predictedgefitinib sensitivity in 9 of 10 cell linestested. "We will also continue attemptsto overcome resistance, by blockingZEB-1 and SIP-1," he said.The researchers have attempted todo this by using histone deacetylaseinhibitors but they were unsuccessful.They will be trying sRNA constructsnext. A prospective trial evaluatingthe relationship of expression ofSIP-1, ZEB-1, E-cadherin, and HER3to EGFR mutations is being plannedinvestigators noted.