Furthemore, in erlotinib- or gefitinib-resistant cell lines of eleven18, PLACE-SSCP analysis demonstrated obvious decrease of greater than 50% with the mutant EGFR gene copy, along with reasonably decreased levels of the mutant EGFR protein, as compared with their parental cell line. Transfection of activating mutant EGFR cDNA into erlotinib-resistant subline of 1118 also restored sensitivity to erlotinib, suggesting again the shut connection of your partial reduction of mutant EGFR gene with acquisition of drug resistance in 1118. One particular could argue why the reduction of activating mutant EGFR gene allele confer drug-resistant phenotype and PI3K/Akt activation. Acquired drug resistance to kinase inhibitors in general can lead to reactivation of the target protein, activation of up-stream or downstream effectors, and/or activation of bypass pathway .
Of those pleiotropic proteins involving acquired resistance to EGFRtargeted selleck PD98059 medication, we examined whether other EGFR household proteins could play a function in constitutive activation of PI3K/Akt during acquirement of erlotinib resistance. Of three EGFR family members proteins, phosphorylation EGFR and HER3 was susceptible to the inhibitory effect of erlotinib in PC9, but phosphorylation of HER3 was not inhibited to erlotinib in its drug-resistant counterpart . Inside the parental PC9 cells, knockdown of either EGFR or HER3 resulted in decreased expression of pAkt , consistent together with the notion that activated EGFR mutation in association with HER3 or HER2 remarkably sensitize the Akt phosphorylation to EGFR-targeted drugs . HER2 knockdown itself on the other hand didn’t affect phosphorylation of Akt in PC9 cells.
In PC9/ER1 cells, knockdown of HER2 suppressed expression of pHER3 and pAkt whereas knockdown of EGFR, mostly wild-type EGFR, suppressed expression of pHER2 and pAkt, and only somewhat that of pHER3 . Furthemore, knockdown of HER3 suppressed phosphorylation of Akt in PC9/ER1 cells . For the other hand, Screening Libraries therapy with lapatinib, a dual kinase inhibitor, or BIBW2992, a pan-kinase inhibitor, suppressed phosphorylation of HER2, HER3 and Akt in PC9/ER1 cells . Kinase 6B shows that phosphorylation of Akt is highly susceptible to erlotinib when HER2 or HER3 was silenced in PC9/ER1 cells. By contrast, phosphorylation of Akt was partially suppressed by erlotinib in EGFR-knockdowned PC9/ER1cells .
In the course of choice of drug resistant cell lines from PC9, HER3 and HER2 consequently seem to activate PI3K/Akt pathway in erlotinibresistant cells, and this HER2/HER3-driven Akt activation pathway may perhaps perform a pivotal position in acquired resistance to erlotinib in PC9/ER1 cells. HER3 and HER2 in its shut connection with wild-type EGFR might possibly also in component involve acquirement of drug resistance . A pertinent examine has previously demonstrated that HER2/HER3-driven signaling pathway limits sensitivity to EGFR targeted medicines in cancer cells .