Effective development of targeted anticancer agents includes the definition of the optimal biological dose and biomarkers of drug activity. Currently available preclinical models are not optimal to this end. We aimed at generating a model for translational drug development using pancreatic cancer as a prototype. Resected pancreatic cancers from 14 patients were xenografted and expanded in successive groups of nude mice to develop cohorts of tumor-bearing mice suitable for drug therapy in simulated early clinical trials.The xenografted tumors maintain their fundamental genotypic features despite serial passages and recapitulate the genetic heterogeneity of pancreatic cancer. The in vivo platform is useful for integrating drug screening with biomarker discovery. Passages of tumors in successive cohorts of mice do not change their susceptibility to anticancer agents and represent a perpetual live bank, facilitating the application of new technologies that will result in the creation of an integrated stable database of tumor-drug response data and biomarkers.

This study tested the hypothesis that the number of CA single sequence repeat (CA-SSR) in the intron 1 of the epidermal growth factor receptor (egfr) gene, which affects transcription efficiency of the gene, is associated with the response to EGFR inhibitors. To this end, we determined the number of CA dinucleotides in the intron 1 of the egfr gene in a panel of 12 head and neck cancer cell lines that lack egfr gene amplification and measured the expression of EGFR (mRNA and protein), as well as response to EGFR inhibition. Cells with lower number of CA dinucleotides in the CA-SSR had higher expression of the EGFR gene and protein and were more sensitive to the inhibitory effects of erlotinib, a small molecule inhibitor of the EGFR tyrosine-kinase. Phenotypic modification by silencing EGFR mRNA expression in a susceptible cell line induced resistance to the drug. The number of CA dinucleotide was equivalent in genomic and tumor DNA obtained from 30 patients with head and neck cancer. In a clinical study in colorectal cancer, subjects with lower number of CA dinucleotide frequently developed skin toxicity, a feature that is related to the antitumor activity of this class of drugs. These results suggest that polymorphic variations in the intron 1 of the egfr gene is associated with response to EGFR inhibitors and may provide an explanation as to why the development of skin toxicity is associated with a favorable outcome in patients treated with these agents.

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Analysis of gene expression of cancer cell lines exposed to erlotinib, a small molecule inhibitor of the epidermal growth factor receptor (EGFR), showed a marked increase in EGFR mRNA in resistant cell lines but not in susceptible ones. Because cetuximab induces EGFR down-regulation, we explored the hypothesis that treatment with cetuximab would interfere with erlotinib-induced EGFR up-regulation and result in antitumor effects. Exposure of the resistant biliary tract cancer cell line HuCCT1 but not the susceptible A431 epidermoid cell line to erlotinib induced EGFR mRNA and protein expression. Combined treatment with cetuximab blunted the erlotinib-induced EGFR up-regulation and resulted in inhibition of cell proliferation and apoptosis in the HuCCT1 cells. Blockage of erlotinib-induced EGFR synthesis in HuCCT1 cells by small interfering RNA resulted in identical antitumor effects as cetuximab, providing mechanistic specificity. In mice xenografted with A431, HuCCT1, and the pancreatic cancer cell line Panc430, maximal growth arrest and decrease in Ki67 proliferation index were documented with combined therapy, and EGFR down-regulation was observed in cetuximab-treated tumors. These results may indicate that resistance to EGFR kinase inhibition may be, at least in part, mediated by a highly dynamic feedback loop consisting of up-regulation of the EGFR upon exposure to EGFR kinase inhibitors. Abrogation of this response by small interfering RNA-mediated EGFR mRNA down-regulation and/or by cetuximab-mediated protein clearance induced tumor arrest across several cancer models with different EGFR expression levels, suggesting that resistance and sensitivity are dynamic events where proportional decrease in the target rather than absolute content dictates outcome.