Abstract #1766: Study of transforming potential and drug sensitivity of ErbB2 variants identifies lapatinib-resistant kinase domain mutations
Authors: Ramakrishna Kancha, Nikolas Bubnoff, Christian Peschel, Justus Duyster
Journal: Cancer Research (2009)

Overexpression of ErbB2 kinase is a frequent event in breast carcinogenesis. The dual ErbB1/ErbB2 tyrosine kinase inhibitor lapatinib recently was approved for the treatment of advanced ErbB2-positive breast cancer. Recently variants of ErbB2 were reported in breast, gastric, colorectal and lung cancer. Importantly polymorphism at aa I654 to V654 was reported to be associated with higher risk of breast cancer. However, the effect of this polymorphism on kinase activity and drug sensitivity was not known. In this study, both V654 and I654 showed similar kinase activity and transformed BaF3 cells to IL-3 independence. Moreover, sensitivity of both variants were similar towards gefitinib, erlotinib, AEE788 and lapatinib. However, ErbB2 variants were more sensitive to dual inhibitors AEE788 and lapatinib. Conversely, the ErbB1 L858R, which is frequently found in ErbB1 mutated NSCLC was very sensitive to gefitinib, erlotinib and AEE788, but displayed higher IC50 values to lapatinib. Development of secondary drug resistance due to kinase domain mutations in BCR-ABL (CML) and ErbB1 (NSCLC) was previously reported. We hypothesized that mutations in ErbB2 kinase domain might confer lapatinib resistance. To test this, we used an in vitro screen to identify mutations that cause lapatinib resistance. BaF3 cell line transformed by wt ErbB2 was used for this purpose. Analysis of resistant clones revealed two lapatinib resistant mutations L755S and T862A. Interestingly, the L755S exchange was reported in breast cancer patients. Thus, lapatinib treatment in patients harboring L755S, in contrast to ErbB2 wt or the polymorphism I654V may not be effective. However, L755S is relatively sensitive to alternative ErbB2 inhibitors such as AEE788, with an IC50 of 1\#956;M. Thus, alternative ErbB2 inhibitors may be superior to lapatinib in breast cancer patients with the L755S mutation. We then tested a panel of ErbB2 kinase domain mutations that were reported in breast, colorectal and lung cancer. All mutants transformed BaF3 cells and displayed differential sensitivity to specific drugs. ErbB1 T790M causes gefitinib resistance in NSCLC. We therefore cloned the analogous mutation in ErbB2 (T798M) and tested for drug sensitivity. T798M was fully resistant to all drugs tested with IC50 values above 1 \#956;M. Thus, ErbB2 T798M probably will emerge in the future as more breast cancer patients are treated with ErbB2 inhibitors, similar to the Bcr-Abl T315I mutation in CML. We believe that specific activity and resistance profiles will be helpful in selecting patients with specific ErbB2 variants for treatment with a particular drug not only in the setting of ErbB2-positive breast cancer, but also in selected cases of gastric, colorectal and lung cancer. Identification of drug resistant mutations also is a prerequisite for the development of new inhibitors that may overcome secondary resistance.  Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 1766.