Persistently activated or tyrosine-phosphorylated STAT3 (pSTAT3) is found in 50% of lung adenocarcinomas. pSTAT3 is found in primary adenocarcinomas and cell lines harboring somatic-activating mutations in the tyrosine kinase domain of EGFR. Treatment of cell lines with either an EGFR inhibitor or an src kinase inhibitor had no effect on pSTAT3 levels, whereas a pan-JAK inhibitor (P6) blocked activation of STAT3 and inhibited tumorigenesis. Cell lines expressing these persistently activated mutant EGFRs also produced high IL-6 levels, and blockade of the IL-6/gp130/JAK pathway led to a decrease in pSTAT3 levels. In addition, reduction of IL-6 levels by RNA interference led to a decrease in tumorigenesis. Introduction of persistently activated EGFR into immortalized breast epithelial cells led to tumorigenesis, IL-6 expression, and STAT3 activation, all of which could be inhibited with P6 or gp130 blockade. Furthermore, inhibition of EGFR activity in multiple cell lines partially blocked transcription of IL-6 and concurrently decreased production and release of IL-6. Finally, immunohistochemical analysis revealed a positive correlation between pSTAT3 and IL-6 positivity in primary lung adenocarcinomas. Therefore, mutant EGFR could activate the gp130/JAK/STAT3 pathway by means of IL-6 upregulation in primary human lung adenocarcinomas, making this pathway a potential target for cancer treatment.

Activating mutations in either BRAF or NRAS are seen in a significant number of malignant melanomas, but their incidence appears to be dependent to ultraviolet light exposure. Thus, BRAF mutations have the highest incidence in non‐chronic sun damaged (CSD), and are uncommon in acral, mucosal and CSD melanomas. More recently, activating KIT mutations have been described in rare cases of metastatic melanoma, without further reference to their clinical phenotypes. This finding is intriguing since KIT expression is downregulated in most melanomas progressing to more aggressive lesions. In this study, we investigated a group of anal melanomas for the presence of BRAF, NRAS, KIT and PDGFRA mutations. A heterozygous KIT exon 11 L576P substitution was identified in 3 of 20 cases tested. The 3 KIT mutation‐carrying tumors were strongly immunopositive for KIT protein. No KIT mutations were identified in tumors with less than 4+ KIT immunostaining. NRAS mutation was identified in one tumor. No BRAF or PDGFRA mutations were identified in either KIT positive or negative anal melanomas. In vitro drug testing of stable transformant Ba/F3 KIT^L576P mutant cells showed sensitivity for dasatinib (previously known as BMS‐354825), a dual SRC/ABL kinase inhibitor, and imatinib. However, compared to an imatinib‐sensitive KIT mutant, dasatinib was potent at lower doses than imatinib in the KIT^L576P mutant. These results suggest that a subset of anal melanomas show activating KIT mutations, which are susceptible for therapy with specific kinase inhibitors.

Amyloid-β (Aβ) peptides, consisting mainly of 40 and 42 aa (Aβ40 and Aβ42, respectively), are metabolites of the amyloid precursor protein and are believed to be major pathological determinants of Alzheimer's disease. The proteolytic cleavages that form the Aβ N and C termini are catalyzed by β-secretase and γ-secretase, respectively. Here we demonstrate that γ-secretase generation of Aβ in an N2a cell-free system is ATP dependent. In addition, the Abl kinase inhibitor imatinib mesylate (Gleevec, or STI571), which targets the ATP-binding site of Abl and several other tyrosine kinases, potently reduces Aβ production in the N2a cell-free system and in intact N2a cells. Both STI571 and a related compound, inhibitor 2, also reduce Aβ production in rat primary neuronal cultures and in vivo in guinea pig brain. STI571 does not inhibit the γ-secretase-catalyzed S3 cleavage of Notch-1. Furthermore, production of Aβ and its inhibition by STI571 were demonstrated to occur to similar extents in both Abl ^-/- and WT mouse fibroblasts, indicating that the effect of STI571 on Aβ production does not involve Abl kinase. The efficacy of STI571 in reducing Aβ without affecting Notch-1 cleavage may prove useful as a basis for developing novel therapies for Alzheimer's disease.

Purpose: Resistance is commonly acquired in patients with metastatic gastrointestinal stromal tumor who are treated with imatinib mesylate, often due to the development of secondary mutations in the KIT kinase domain. We sought to investigate the efficacy of second-line tyrosine kinase inhibitors, such as sorafenib, dasatinib, and nilotinib, against the commonly observed imatinib-resistant KIT mutations (KIT^V654A, KIT^T670I, KIT^D820Y, and KIT^N822K) expressed in the Ba/F3 cellular system. Experimental Design:In vitro drug screening of stable Ba/F3 KIT mutants recapitulating the genotype of imatinib-resistant patients harboring primary and secondary KIT mutations was investigated. Comparison was made to imatinib-sensitive Ba/F3 KIT mutant cells as well as Ba/F3 cells expressing only secondary KIT mutations. The efficacy of drug treatment was evaluated by proliferation and apoptosis assays, in addition to biochemical inhibition of KIT activation. Results: Sorafenib was potent against all imatinib-resistant Ba/F3 KIT double mutants tested, including the gatekeeper secondary mutation KIT^{WK557-8del/T670I}, which was resistant to other kinase inhibitors. Although all three drugs tested decreased cell proliferation and inhibited KIT activation against exon 13 (KIT^{V560del/V654A}) and exon 17 (KIT^V559D/D820Y) double mutants, nilotinib did so at lower concentrations. Conclusions: Our results emphasize the need for tailored salvage therapy in imatinib-refractory gastrointestinal stromal tumors according to individual molecular mechanisms of resistance. The Ba/F3 KIT^{WK557-8del/T670I} cells were sensitive only to sorafenib inhibition, whereas nilotinib was more potent on imatinib-resistant KIT^{V560del/V654A} and KIT^V559D/D820Y mutant cells than dasatinib and sorafenib.