Receptor tyrosine kinase-dependent PI3K activation is an escape mechanism to vertical suppression of the EGFR/RAS/MAPK pathway in KRAS-mutated human colorectal cancer cell lines

• Published in: Journal of experimental & clinical cancer research Vol. 38; no. 1; p. 41
• Main Authors: Vitiello, Pietro Paolo, Cardone, Claudia, Martini, Giulia, Ciardiello, Davide, Belli, Valentina, Matrone, Nunzia, Barra, Giusi, Napolitano, Stefania, Della Corte, Carmina, Turano, Mimmo, Furia, Maria, Troiani, Teresa, Morgillo, Floriana, De Vita, Ferdinando, Ciardiello, Fortunato, Martinelli, Erika
• Format: Journal Article
• Language: English
• Published: England BioMed Central Ltd 28.01.2019; BioMed Central; BMC
• Subjects: Analysis; Antibodies; Cells (Biology); Cetuximab; Colorectal cancer; DNA microarrays; Epidermal growth factor receptor (EGFR); Epidermal growth factors; Fluorescent antibody technique; MAPK pathway; Monoclonal antibodies; Panitumumab; Parenting; Phenols (Class of compounds); PI3K pathway; RAS mutation; Tumor cell biology; Tumors; Tyrosine; MAPK pathway; AKT inhibitor; Epidermal growth factor receptor (EGFR); Colorectal cancer; PI3K inhibitor; PI3K pathway; MEK inhibitor; RAS mutation; Vertical suppression; Tumor cell biology
• ISSN: 1756-9966; 0392-9078; 1756-9966
• DOI: 10.1186/s13046-019-1035-0

Previous studies showed that the combination of an anti-Epidermal growth factor (EGFR) and a MEK-inhibitor is able to prevent the onset of resistance to anti-EGFR monoclonal antibodies in KRAS-wild type colorectal cancer (CRC), while the same combination reverts anti-EGFR primary resistance in KRAS mutated CRC cell lines. However, rapid onset of resistance is a limit to combination therapies in KRAS mutated CRC. We generated four different KRAS mutated CRC cell lines resistant to a combination of cetuximab (an anti-EGFR antibody) and refametinib (a selective MEK-inhibitor) after continuous exposure to increasing concentration of the drugs. We characterized these resistant cell lines by evaluating the expression and activation status of a panel of receptor tyrosine kinases (RTKs) and intracellular transducers by immunoblot and qRT-PCR. Oncomine comprehensive assay and microarray analysis were carried out to investigate new acquired mutations or transcriptomic adaptation, respectively, in the resistant cell lines. Immunofluorescence assay was used to show the localization of RTKs in resistant and parental clones. We found that PI3K-AKT pathway activation acts as an escape mechanism in cell lines with acquired resistance to combined inhibition of EGFR and MEK. AKT pathway activation is coupled to the activation of multiple RTKs such as HER2, HER3 and IGF1R, though its pharmacological inhibition is not sufficient to revert the resistant phenotype. PI3K pathway activation is mediated by autocrine loops and by heterodimerization of multiple receptors. PI3K activation plays a central role in the acquired resistance to the combination of anti-EGFR and MEK-inhibitor in KRAS mutated colorectal cancer cell lines. PI3K activation is cooperatively achieved through the activation of multiple RTKs such as HER2, HER3 and IGF1R.