A number of CD11b+Gr-1+ MDSCs and CD11b+CD206+ macrophages infiltrated into tumors in our model (data not shown). encouraging efficacy in the B901L xenograft model of Mut+ NSCLC. Re-induction of VEGF and subsequent direct or indirect Udenafil VEGF-dependent tumor growth was suggested as a major mechanism of erlotinib resistance, and erlotinib plus bevacizumab achieved amazingly prolonged antitumor activity in this model. mutation, VEGF, bevacizumab, erlotinib Introduction Erlotinib belongs to the class of molecular targeted drugs designed as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs). It blocks trans-phosphorylation of EGFR and subsequent downstream signaling in pathways such as the mitogen-activated protein kinase (MAPK) pathway, phosphatidylinositol 3-kinase (PI3K)-AKT pathway, and transmission transducer and activator of transcription 3 (STAT3) pathway. Erlotinib treatment results in Udenafil prolonged progression-free survival (PFS) with a Rabbit Polyclonal to SGK median of 10C14 months in patients with non-small cell lung malignancy (NSCLC) harboring exon 19 deletion or L858R mutations (EGFR Mut+ NSCLC) (1C3). However, despite these clinical benefits, almost all tumors eventually progress due to acquired resistance (4). Recently, several mechanisms of EGFR-TKI resistance have been recognized, including T790M gatekeeper mutation, activation of bypass signals (gene amplification and gene amplification), and other mechanisms (transformation to small cell lung malignancy, epithelial to mesenchymal transition, and tumor microenvironment-mediated resistance) (5). Bevacizumab, a humanized monoclonal antibody targeting vascular endothelial growth factor (VEGF), regresses preexisting tumor blood vessels and blocks the formation of new ones (6,7). Furthermore, it normalizes vascular permeability and thereby decreases interstitial fluid pressure so that it enhances delivery of co-administered drugs and therapeutic outcomes (8C10). Consequently, bevacizumab prolongs PFS and overall survival in advanced NSCLC when administered in combination with standard first-line platinum-based chemo-therapies (11). Since erlotinib and bevacizumab take action on two different pathways crucial to tumor growth, administering these drugs concomitantly may confer encouraging clinical benefits to malignancy patients with advanced disease (12,13). The Phase II JO25567 study reported that erlotinib plus bevacizumab produced a statistically significant and clinically meaningful prolongation of PFS compared with erlotinib alone in the treatment of Mut+ NSCLC (14). Several preclinical studies in various xenograft models have reported around the mechanisms of erlotinib in addition to bevacizumab (15). In those studies, erlotinib was shown to decrease VEGF expression (16,17) and block synthesis of angiogenic proteins such as basic Udenafil fibroblast growth factor (bFGF) and transforming growth factor- (TGF-) (12,18). Moreover, PTK787, an inhibitor of VEGF receptor (VEGFR) tyrosine kinases, c-Kit, and angiogenesis, was shown to improve delivery of erlotinib into the tumor in a PC-9 xenograft model (19). However, those data show the mechanisms in the erlotinib-sensitive phase, and the mechanism by which the combination of erlotinib and bevacizumab confers prolonged efficacy even into the erlotinib-refractory phase remains to be elucidated. In the present study, we established a human Mut+ NSCLC xenograft model that became Udenafil refractory in which tumor regrowth was observed by long-term erlotinib administration, and we analyzed the mechanisms of both the erlotinib-sensitive and erlotinib-refractory phases. Materials and methods Test brokers Erlotinib was provided by F. Hoffmann-La Roche Ltd. (Basel, Switzerland) and was dissolved in 6% Captisol answer (ChemScene, Monmouth Junction, NJ, USA). Bevacizumab was obtained from F. Hoffmann-La Roche Ltd. Human immunoglobulin G (HuIgG) was purchased Udenafil from MP Biomedicals (Santa Ana, CA, USA). Both bevacizumab and HuIgG were diluted with saline. Cell lines and culture conditions B901L (harboring exon 19 deletion) was purchased from your institute of Physical and Chemical Research (RIKEN, Saitama, Japan). This cell collection was managed in RPMI-1640 (Sigma-Aldrich, St. Louis, MO, USA) supplemented with 10% (v/v) fetal bovine serum (Bovogen Biologicals, Melbourne, Australia), 0.45% D-glucose (Sigma-Aldrich), 10 mM HEPES buffer (Sigma-Aldrich), and 1 mM Na-pyruvate (Thermo Fisher Scientific, Waltham, MA, USA) at 37C under 5% CO2. NCI-H1975 (harboring T790M mutation) was purchased from ATCC and maintained in RPMI-1640 supplemented with 10% (v/v) fetal bovine serum at 37C under 5% CO2. Animals Male, 5-week-old BALB/c-nu/nu mice (CAnN. Cg-Foxn1 nu /CrlCrlj nu/nu) were obtained from Charles River Laboratories Inc. (Kanagawa, Japan). All animals were allowed to acclimatize and recover from shipping-related stress for at least 1 week prior to the study. The health of the mice was monitored by daily observation. The animals were kept under a controlled light-dark cycle (12C12 h), and chlorinated water and irradiated food were provided was first amplified by PCR from DNA by using the appropriate primers and the.
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