Rongxin Ren, Shiming Fan, Linfang Wang,Min Cheng, Dongxia Shi, Wei Zhang,Renxiang Tang, Ying Yu, Longxian Jiao, Jun Ni, Haibin Yang, Huaqing Cai,Feng Zhou, Weihan Zhang, Weiguo Qing, Weiguo Su
Purpose: Esophageal cancer (EC) is a high prevalence cancer type in China, which lacking effective targeted therapy. Accordingly to past studies, over 50% EC patients are with over-expression of EGFR, and this is usually associated with poor prognosis. Unlike colorectal cancer, K-Ras mutations are quite rare in EC, so EGFR may become one of the targets for esophageal cancer treatments. However, clinical trials with anti-EGFR antibodies or small molecule EGFR inhibitors (gefitinib, erlotinib, icotinib) have showed disappointing anti-tumor effects. The possible causes might be: 1. Clinical trial enrollments lacking EGFR screening or EGFR enrollment criteria need further optimization. For example, gefitinib ph3 III Trans-COG retrospective analysis suggested that, for patients with EGFR gene amplification or increased copy numbers, overall survival of the gefitinib treatment group is significantly longer than the placebo group; 2. Relevant EGFR small molecule inhibitors need to be improved in terms of affinities and inhibition activities to the wild-type EGFR. Theliatinib is a novel small molecule EGFR inhibitor, with high affinity and potent inhibitory activity to the wild-type EGFR. This study use pre-clinical molecular, cell and animal models to explore the inhibition to the wild-type EGFR, and relevance between esophageal cancer treatment efficacy and EGFR expression level.
Methods: Use z-lyteTM method to determination theliatinib, erlotinib and gefitinib’s inhibition constants to the wild-type EGFR kinase, “Ki”, compare their targeted inhibition activities on EGFR-dependence cell lines and cytotoxicity effectiveness on the tumor cells. On several nude mice transplanted PDX (patient derived xenograft) models, which are derived from esophageal cancer patient tissue, study the expression levels of EGFR genes, proteins and theliatinib’s anti-tumor efficacy. Also investigated other relevant genes or protein abnormalities that might affect the activities of EGFR pathway.
Results: Theliatinib’s Ki to the wild-type EGFR inhibition is 0.05 nM, is 7 ~ 10 times of gefitinib and erlotinib; on multiple EGFR-dependent cell lines, theliatinib’s EGFR phosphorylation and cytotoxicity activity is 3 ~ 6 times stronger than similar compounds. On two EGFR gene amplification and EGFR protein over-expression PDX models, theliatinib at oral clinically relevant dose, can make tumor volume decreasing by > 30%; In several models with high EGFR protein expression (immunohistochemical H score > 250) but no EGFR gene amplification, theliatinib shows tumor growth inhibition rate up to 67% ~ 100%. While for models with low EGFR protein expression (immunehistochemical H score < 200), the inhibition effect of tumor growth is not significance. In multiple models above, at clinically relevant doses, theliatinib shows significantly stronger anti-tumor efficacy than gefitinib (P < 0.05). In addition, if esophageal cancer patients with EGFR over expression, who also have over expression of FGFR1, PIK3CA mutation or PTEN deletion, will reduce theliatinib’s antitumor efficacy.
Conclusion: EGFR may be a feasible target for esophageal cancer treatment, which is worthy further clinical researches. Explorations with EGFR screening criteria and other biomarkers influencing EGFR inhibition efficacy that can bring benefit to patients, is critical to successful of clinical trials. Theliatinib clinical trial in advanced esophageal cancer (NCT02601274) is ongoing.
Keywords: esophageal cancer, EGFR, targeted therapy, theliatinib, PDX model