Background Acquired epidermal growth factor receptor (EGFR) T790M mutation is the primary resistance mechanism to first-generation EGFR tyrosine kinase inhibitors (TKIs) used in advanced, EGFR mutation-positive non-small-cell lung cancer (NSCLC). Available data, predominantly in Asian patients, suggest that this mutation is also the major cause of resistance to the irreversible ErbB family blocker, afatinib. For EGFR T790M-positive patients who progress on EGFR TKI therapy, osimertinib is an effective treatment option. However, data on osimertinib use after afatinib are, to date, scarce. Objective To identify the prevalence of EGFR T790M mutations in predominantly Caucasian patients with stage IV EGFR mutation-positive NSCLC who progressed on afatinib, and to investigate the subsequent response to osimertinib. Patients and Methods In this single-center, retrospective analysis, EGFR T790M mutation status after afatinib failure was assessed using liquid biopsy and tissue rebiopsy. EGFR T790M-positive patients subsequently received osimertinib. Results Sixty-seven patients received afatinib in the first-, second-, or third-line (80.6%, 14.9%, and 4.5%, respectively). After afatinib failure, the T790M mutation was identified in 49 patients (73.1%). Liquid biopsy and tissue rebiopsy were concordant in 79.4% of cases. All patients with T790M-positive tumors received osimertinib (73.5% after first-line afatinib); 37 (75.5%) of these had an objective response (complete response: 22.4%; partial response: 53.1%). Response rate was independent of T790M copy number. Conclusion EGFR T790M mutation is a major mechanism of acquired resistance to afatinib. Osimertinib confers high response rates after afatinib failure in EGFR T790M-positive patients and its use in sequence potentially allows extended chemotherapy-free treatment.

Recent data suggest that the signal transducer and activator of transcription (STAT)5 contributes to differentiation and growth of mast cells. It has also been described that constitutively phosphorylated STAT5 (pSTAT5) plays a pro-oncogenic role in various myeloid neoplasms. We examined the expression of pSTAT5 in neoplastic mast cells in systemic mastocytosis and asked whether the disease-related oncoprotein KIT D816V is involved in STAT5 activation. As assessed by immunohistochemistry using the anti-pSTAT5 antibody AX1, neoplastic mast cells were found to display pSTAT5 in all SM patients examined (n = 40). Expression of pSTAT5 was also demonstrable in the KIT D816V-positive mast cell leukemia cell line HMC-1. Using various staining-protocols, pSTAT5 was found to be located in both the cytoplasmic and nuclear compartment of mast cells. To define the functional role of KIT D816V in STAT5-activation, Ba/F3 cells with doxycycline-inducible expression of KIT D816V were used. In these cells, induction of KIT D816V resulted in an increased expression of pSTAT5 without substantial increase in total STAT5. Moreover, the KIT D816V-targeting kinase-inhibitor PKC412 was found to counteract expression of pSTAT5 in HMC-1 cells as well as doxycycline-induced expression of pSTAT5 in Ba/F3 cells. Finally, a dominant negative STAT5-construct was found to inhibit growth of HMC-1 cells. Together, our data show that neoplastic mast cells express cytoplasmic and nuclear pSTAT5, that KIT D816V promotes STAT5-activation, and that STAT5-activation contributes to growth of neoplastic mast cells.

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The neurotoxm I-methyl-4-phenyl-1,2,3,6-tetrahydropyrldlne (MPTP)

Previous studies have shown that fatty acid ethyl ester synthase (FAEES) which catalyzes the formation of ethyl or 2-chloroethyl esters of long-chain fatty acids is localized in the microsomal fraction of rat liver. A recent study suggests that rat adipose tissue FAEES is similar to rat liver microsomal carboxylesterase (CE) [Tsujita and Okuda (1992) J. Biol. Chem. 267, 23489-23494]. Since the interrelationships among FAEES, 2-chloroethyl ester synthase (FACEES), and cholesterol esterase (ChE) are also not clear at present, we purified and characterized FAEES and FACEES from rat hepatic microsomes and studied their functional and structural relationships with CE and ChE. The results of these studies showed that CE, FAEES, and FACEES activities copurified during each step of purification. Although gel-filtration column chromatography of DEAE-Sephacel purified microsomal protein resolved into two peaks with an estimated molecular weight of 180 (major) and 60 kDa (minor, this paper describes characterization of only the 180 kDa protein. CE, FAEES, and FACEES activities associated with homogeneous 180 kDa protein could be inhibited by a beta-esterase inhibitor (diisopropyl fluorophosphate) in an identical manner. This protein, however, showed only the hydrolytic activity, but not the synthetic activity for cholesterol oleate, indicating that it is distinct from ChE. The purified protein could be immunoprecipitated with the antibodies raised against rat adipose tissue FAEES, but not with antibodies against rat pancreatic ChE, demonstrating again that the purified protein is distinct from ChE. A single band corresponding to 60 kDa upon SDS-PAGE, under reduced denaturing conditions, indicates that the purified protein is a trimer. N-terminal amino acid sequence of the first 27 residues were identical to that of rat hepatic microsomal CE [Robbi et al. (1990) Biochem. J., 451-458] which suggests structural similarity of the purified protein with rat hepatic microsomal CE. Therefore, the functional and structural properties of the purified protein demonstrate that FAEES, FACEES, as well as CE activities are expressed by the same protein, purified in this study, which exists as a trimer (180 kDa) and is involved in biosynthesis of long-chain fatty acid esters of xenobiotic alcohols. Further studies on purification and characterization of the enzymes responsible for the esterification of xenobiotic alcohols with endogenous fatty acids from various target organs need to be conducted to determine their functional and structural interrelationships. Inhibition and induction studies of these enzyme(s) and the extent of observed toxicity could be important in understanding their role in etiology of chronic diseases induced by alcohol abuse.

A monoclonal antibody was used to prepare immunoaffinity columns that efficiently bind monoamine oxidase B activity but not monoamine oxidase A activity from detergent extracts of human liver mitochondria. The only discrete polypeptide component that eluted from affinity columns with potassium thiocyanate migrated in sodium dodecyl sulfate-polyacrylamide gels with an apparent molecular weight of 59,000, as expected for human monoamine oxidase B. These results support the hypothesis that there is an intrinsic structural difference between monoamine oxidase A and B and demonstrate that immunoaffinity chromatography can physically resolve the two enzyme species in liver extracts.

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