PO-519 Combined inhibition of MEK and PI3KCA pathway induces synergic antitumor activity in HER2 amplified colorectal cancer models

Abstract

IntroductionCetuximab and panitumumab, antibodies directed against the epidermal growth factor receptor (EGFR), are an effective clinical therapy for patients with metastatic colorectal cancer (mCRC), particularly for those with KRAS, NRAS, BRAF and PI3KCA wild-type cancer. However, only a fraction of patients receives clinical benefit from therapy with anti-EGFR antibodies. The HER2 gene amplification has been implicated as one of the mechanisms for primary and acquired resistance to anti-EGFR therapies in mCRC. However, little is known about the role of HER2 in cancer resistance to anti-EGFR antibodies.Material and methodsWe transfected stably colon cancer cells, sensitive to anti-EGFR antibodies (LIM1215 and SW48), with HER2 plasmid. We characterised the transfected cells in terms of molecular profile and sensitivity to several drugs through cell proliferation assays and western blot analysis. Furthermore, HER2 amplified cells were engrafted into nude mice and treated to find the best therapeutic treatment.Results and discussionsWe observed a strong upregulation on the HER family receptors EGFR, HER3, and HER4 in cells with HER2 amplification, but also an over-expression of intracellular transducers such as AKT, MAPK, and MEK proteins compared to parental cells. Furthermore, we treated LIM1215-HER2 and SW48-HER2 cells with several combinations of antibodies and small molecules directed to HER receptor family, such as anti-EGFR receptor antibodies of first, second and third generation (cetuximab, SYM004 and MM151); trastuzumab, pertuzumab and lapatinib directed against HER2 receptor; and duligotuzumab as anti-HER3 receptor. We observed a strongest growth inhibition effect after treatment with trastuzumab in combination with lapatinib compared to other treatments. Moreover, we incubated the HER2 amplified cells with drugs directed to the downstream pathway, such as refametinib and pictilisib which are the MEK and PI3KCA inhibitors, respectively. Interestingly, cells with HER2 amplification are highly sensitive to refametinib and pictilisib and further, we observed higher antitumor activity when both drugs were administrated in combination compared to their single treatment and to therapy-based on anti-HER family antibodies. The antitumor activity has been confirmed by the in vivo xenografts CRC models.ConclusionThese results suggest that the treatment with refamentinib and pictilisib could be a strategy for patients with HER2 amplification that do not receive clinical benefit from standard anti-EGFR therapies.