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Ligand-induced down-regulation controls the signaling potency of the epidermal growth factor receptor (EGFR/ErbB1). Overexpression studies have identifiedCbl-mediated ubiquitinylation of EGFR as a mechanism of ligand-induced EGFR down-regulation. However, the role of endogenous Cbl in EGFR down-regulation and the precise step in the endocytic pathway regulated by Cbl remain unclear. Using Cbl ؊/؊ mouse embryonic fibroblast cell lines, we demonstrate that endogenous Cbl is essential for ligand-induced ubiquitinylation and efficient degradation of EGFR. Further analyses using Chinese hamster ovary cells with a temperature-sensitive defect in ubiquitinylation confirm a crucial role of the ubiquitin machinery in Cbl-mediated EGFR degradation. However, internalization into early endosomes did not require Cbl function or an intact ubiquitin pathway. Confocal immunolocalization studies indicated that Cbl-dependent ubiquitinylation plays a critical role at the early endosome to late endosome/lysosome sorting step of EGFR down-regulation. These findings establish Cbl as the major endogenous ubiquitin ligase responsible for EGFR degradation, and show that the critical role of Cbl-mediated ubiquitinylation is at the level of endosomal sorting, rather than at the level of internalization. Growth factor receptor tyrosine kinases (RTKs)1 play crucial roles in cellular proliferation, survival, migration, and differentiation. Epidermal growth factor receptor (EGFR/ErbB1) is a member of the ErbB family (ErbB1-4) of RTKs, which play crucial homeostatic roles and are implicated in oncogenesis. Ligand-induced activation of RTKs leads to the assembly of signaling protein complexes and subsequent activation of downstream signaling pathways. The ligand-activated RTKs also undergo rapid endocytosis (1). The endocytosed receptors then undergo a sorting process, which determines receptor fate and signal intensity. The receptors can be targeted to the lysosome for degradation, which terminates receptor signals. Alternatively, the internalized receptors can be recycled back to the cell surface for continued ligand binding and signaling (2-5). The relative efficiency of lysosomal sorting versus recycling is a key determinant of the signaling potency of RTKs (6). For example, EGFR is predominantly delivered to lysosomes when activated by EGF. In contrast, heregulin-activated ErbB2 is primarily recycled. The greater efficiency of the recycling process is thought to be a major determinant of the signaling superiority of ErbB2 over EGFR (7-9).Despite a critical role of endocytic sorting as a determinant of ErbB receptor down-regulation, the biochemical mechanisms that regulate this process have only recently begun to be elucidated. We, and others, have identified Cbl as one such regulator (10 -12). Cbl is recruited to the activated EGFR through both direct and indirect binding. Direct Cbl-EGFR interaction is mediated through the N-terminal tyrosine kinase-binding domain of Cbl, which binds to phosphorylated Tyr-1045 on EGFR (13). Indirect Cbl-E...

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Inhibition of the signal transducer and activator of transcription 3 (STAT3) signaling pathway has been considered a novel therapeutic strategy to treat human cancers with constitutively active STAT3. In this study, we report the identification of niclosamide, an FDA-approved anthelmintic drug, as a new small-molecule inhibitor of the STAT3 signaling pathway. This compound potently inhibited the activation and transcriptional function of STAT3 and consequently induced cell growth inhibition, apoptosis, and cell cycle arrest of cancer cells with constitutively active STAT3. Our study provides a new promising lead compound with a salicylic amide scaffold for the development of STAT3 pathway inhibitors as novel molecularly targeted anticancer drugs.

Discoidin domain receptor 1 (DDR1) is an emerging potential molecular target for new anticancer drug discovery. We have discovered a series of 3-(2-(pyrazolo[1,5-a]pyrimidin-6-yl) ethynyl)benzamides that are selective and orally bioavailable DDR1 inhibitors. The two most promising compounds (7rh and 7rj) inhibited the enzymatic activity of DDR1, with IC50 values of 6.8 and 7.0 nM, respectively, but were significantly less potent in suppressing the kinase activities of DDR2, Bcr-Abl, and c-Kit. Further study revealed that 7rh bound with DDR1 with a Kd value of 0.6 nM, while it was significantly less potent to the other 455 kinases tested. The S(35) and S(10) selectivity scores of 7rh were 0.035 and 0.008, respectively. The compounds also potently inhibited the proliferation of cancer cells expressing high levels of DDR1 and strongly suppressed cancer cell invasion, adhesion, and tumorigenicity. Preliminary pharmacokinetic studies suggested that they possessed good PK profiles, with oral bioavailabilities of 67.4% and 56.2%, respectively.

Drug delivery for tumor theranostics involves the extensive use of the enhanced permeability and retention (EPR) effect. Previously, various types of nanomedicines have been demonstrated to accumulate in solid tumors via the EPR effect. However, EPR is a highly variable phenomenon because of tumor heterogeneity, resulting in low drug delivery efficacy in clinical trials. Because ultrasonication using micro/nanobubbles as contrast agents can disrupt blood vessels and enhance the specific delivery of drugs, it is an effective approach to improve the EPR effect for the passive targeting of tumors. In this review, the basic thermal effect, acoustic streaming, and cavitation mechanisms of ultrasound, which are characteristics that can be utilized to enhance the EPR effect, are briefly introduced. Second, micro/nanobubble-enhanced ultrasound imaging is discussed to understand the validity and variability of the EPR effect. Third, because the tumor microenvironment is complicated owing to elevated interstitial fluid pressure and the deregulated extracellular matrix components, which may be unfavorable for the EPR effect, few new trends in smart bubble drug delivery systems, which may improve the accuracy of EPR-mediated passive drug targeting, are summarized. Finally, the challenging and major concerns that should be considered in the next generation of micro/nanobubble-contrast-enhanced ultrasound theranostics for EPR-mediated passive drug targeting are also discussed.

Objective. To evaluate disparities in substance abuse treatment completion between and within racial and ethnic groups in publicly funded treatment in Los Angeles County, California. Data Source. The Los Angeles County Participant Reporting System with multicross-sectional annual data (2006)(2007)(2008)(2009) for adult participants (n = 16,637) who received treatment from publicly funded programs (n = 276) for the first time. Study Design. Retrospective analyses of county discharge and admission data. Hierarchical linear regressions models were used to test the hypotheses. Data Collection. Client data were collected during personal interviews at admission and discharge for most participants. Principal Findings. African Americans and Latinos reported lower odds of completing treatment compared with Whites. Within-group analysis revealed significant heterogeneity within racial and ethnic groups, highlighting primary drug problem, days of drug use before admission, and homelessness as significant factors affecting treatment completion. Service factors, such as referral by the criminal justice system, enabled completion among Latinos and Whites only. Conclusions. These findings have implications for reducing health disparities among members of racial and ethnic minorities by identifying individual and service factors associated with treatment adherence, particularly for first-time clients.