There is a strong rationale to therapeutically target the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in breast cancer since it is highly deregulated in this disease and it also mediates resistance to anti-HER2 therapies. However, initial studies with rapalogs, allosteric inhibitors of mTORC1, have resulted in limited clinical efficacy probably due to the release of a negative regulatory feedback loop that triggers AKT and ERK signaling. Since activation of AKT occurs via PI3K, we decided to explore whether PI3K inhibitors prevent the activation of these compensatory pathways. Using HER2-overexpressing breast cancer cells as a model, we observed that PI3K inhibitors abolished AKT activation. However, PI3K inhibition resulted in a compensatory activation of the ERK signaling pathway. This enhanced ERK signaling occurred as a result of activation of HER family receptors as evidenced by induction of HER receptors dimerization and phosphorylation, increased expression of HER3 and binding of adaptor molecules to HER2 and HER3. The activation of ERK was prevented with either MEK inhibitors or anti-HER2 monoclonal antibodies and tyrosine kinase inhibitors. Combined administration of PI3K inhibitors with either HER2 or MEK inhibitors resulted in decreased proliferation, enhanced cell death and superior anti-tumor activity compared with single agent PI3K inhibitors. Our findings indicate that PI3K inhibition in HER2-overexpressing breast cancer activates a new compensatory pathway that results in ERK dependency. Combined anti-MEK or anti-HER2 therapy with PI3K inhibitors may be required in order to achieve optimal efficacy in HER2-overexpressing breast cancer. This approach warrants clinical evaluation.

Effective development of targeted anticancer agents includes the definition of the optimal biological dose and biomarkers of drug activity. Currently available preclinical models are not optimal to this end. We aimed at generating a model for translational drug development using pancreatic cancer as a prototype. Resected pancreatic cancers from 14 patients were xenografted and expanded in successive groups of nude mice to develop cohorts of tumor-bearing mice suitable for drug therapy in simulated early clinical trials.The xenografted tumors maintain their fundamental genotypic features despite serial passages and recapitulate the genetic heterogeneity of pancreatic cancer. The in vivo platform is useful for integrating drug screening with biomarker discovery. Passages of tumors in successive cohorts of mice do not change their susceptibility to anticancer agents and represent a perpetual live bank, facilitating the application of new technologies that will result in the creation of an integrated stable database of tumor-drug response data and biomarkers.

ATI may be transient and do not always lead to a worse clinical outcome. Sustained high levels of ATI, however, lead to permanent LOR. Patients with low IFX trough levels at week 14 are at risk for ATI formation and IFX discontinuation. Therefore, we recommend to measure IFX trough levels at week 14 and at time of LOR. When undetectable or low, ATI should be determined and if positive followed up on consecutive time points to rule out sustained ATI.

A method for monitoring formation of latex particle pairs by chemilumnescence is described. Molecular oxygen is excited by a photosensitizer and an antenna dye that are dissolved in one ofthe particles. 1A02dlffse to the second particle and initiates a hi quantum yield chemilu ent reaction of an olefin that is dissolved in it. An alternative homogeneous method utilizes immunochemical aggregation of ligand-or receptor-labeled particles (latex agglutination) (3). Detection of agglutination by conventional light scattering requires formation of large aggregates and has limited sensitivity. Low-angle light scattering measurements provide higher sensitivity but require rigorously exclusion of adventitious particles (4,5).In the present study, nonenzymatic channeling of 1.02 is used to provide exquisitely sensitive real-time monitoring of particle-particle interactions. The prepared by adding concentrated ammonia to 500-kDadextran (Pharmacia) that had been activated by reaction with epichlorohydrin and Zn(BF4)2. The product was purified by precipitation with methanol. Fluorescein-biotin (Fl-biotin) was prepared by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) coupling of Fl-5'-COOH to 1,12-diamino-4,9-dioxadodecane followed by reaction with biotinyl-6-aminohexanoic acid N-hydroxysuccinimide ester (biotin-LC-NHS, Pierce). Bis-(6-hydroxyhexyl) disulfide and 6-amino-

ObjectiveAlthough low infliximab trough concentrations and antibodies to infliximab (ATI) are associated with poor outcomes in patients with Crohn's disease (CD), the clinical relevance of ATI in patients with adequate infliximab concentrations is uncertain. We evaluated this question using an assay sensitive for identification of ATI in the presence of infliximab.DesignIn an observational study, 1487 trough serum samples from 483 patients with CD who participated in four clinical studies of maintenance infliximab therapy were analysed using a fluid phase mobility shift assay. Infliximab and ATI concentrations most discriminant for remission, defined as a C-reactive protein concentration of ≤5 mg/L, were determined by receiver operating characteristic curves. A multivariable regression model evaluated these factors as independent predictors of remission.ResultsBased upon analysis of 1487 samples, 77.1% of patients had detectable and 22.9% had undetectable infliximab concentrations, of which 9.5% and 71.8%, respectively, were positive for ATI. An infliximab concentration of >2.79 μg/mL (area under the curve (AUC)=0.681; 95% CI 0.632 to 0.731) and ATI concentration of <3.15 U/mL (AUC=0.632; 95% CI 0.589 to 0.676) were associated with remission. Multivariable analysis showed that concentrations of both infliximab trough (OR 1.8; 95% CI 1.3 to 2.5; p<0.001) and ATI (OR 0.57; 95% CI 0.39 to 0.81; p=0.002) were independent predictors of remission.ConclusionsThe development of ATI increases the probability of active disease even at low concentrations and in the presence of a therapeutic concentration of drug during infliximab maintenance therapy. Evaluation of strategies to prevent ATI formation, including therapeutic drug monitoring with selective infliximab dose intensification, is needed.