Vijay Yajnik

Hedgehog is an early and late mediator of pancreatic cancer tumorigenesis

Hedgehog signalling—an essential pathway during embryonic pancreatic development, the misregulation of which has been implicated in several forms of cancer—may also be an important mediator in human pancreatic carcinoma. Here we report that sonic hedgehog, a secreted hedgehog ligand, is abnormally expressed in pancreatic adenocarcinoma and its precursor lesions: pancreatic intraepithelial neoplasia (PanIN). Pancreata of Pdx–Shh mice (in which Shh is misexpressed in the pancreatic endoderm) develop abnormal tubular structures, a phenocopy of human PanIN-1 and -2. Moreover, these PanIN-like lesions also contain mutations in K-ras and overexpress HER-2/neu, which are genetic mutations found early in the progression of human pancreatic cancer. Furthermore, hedgehog signalling remains active in cell lines established from primary and metastatic pancreatic adenocarcinomas. Notably, inhibition of hedgehog signalling by cyclopamine induced apoptosis and blocked proliferation in a subset of the pancreatic cancer cell lines both in vitro and in vivo. These data suggest that this pathway may have an early and critical role in the genesis of this cancer, and that maintenance of hedgehog signalling is important for aberrant proliferation and tumorigenesis.

DOCK4, a GTPase activator, is disrupted during tumorigenesis

We used representational difference analysis to identify homozygous genomic deletions selected during tumor progression in the mouse NF2 and TP53 tumor model. We describe a deletion targeting DOCK4, a member of the CDM gene family encoding regulators of small GTPases. DOCK4 specifically activates Rap GTPase, enhancing the formation of adherens junctions. DOCK4 mutations are present in a subset of human cancer cell lines; a recurrent missense mutant identified in human prostate and ovarian cancers encodes a protein that is defective in Rap1 activation. The engulfment defect of C. elegans mutants lacking the CDM gene ced-5 is rescued by wild-type DOCK4, but not by the mutant allele. Expression of wild-type, but not mutant, DOCK4 in mouse osteosarcoma cells with a deletion of the endogenous gene suppresses growth in soft agar and tumor invasion in vivo. DOCK4 therefore encodes a CDM family member that regulates intercellular junctions and is disrupted during tumorigenesis.

Treg cells expressing the coinhibitory molecule TIGIT selectively inhibit proinflammatory Th1 and Th17 cell responses.

Foxp3(+) T regulatory (Treg) cells regulate immune responses and maintain self-tolerance. Recent work shows that Treg cells are comprised of many subpopulations with specialized regulatory functions. Here we identified Foxp3(+) T cells expressing the coinhibitory molecule TIGIT as a distinct Treg cell subset that specifically suppresses proinflammatory T helper 1 (Th1) and Th17 cell, but not Th2 cell responses. Transcriptional profiling characterized TIGIT(+) Treg cells as an activated Treg cell subset with high expression of Treg signature genes. Ligation of TIGIT on Treg cells induced expression of the effector molecule fibrinogen-like protein 2 (Fgl2), which promoted Treg-cell-mediated suppression of T effector cell proliferation. In addition, Fgl2 was necessary to prevent suppression of Th2 cytokine production in a model of allergic airway inflammation. TIGIT expression therefore identifies a Treg cell subset that demonstrates selectivity for suppression of Th1 and Th17 cell but not Th2 cell responses.

Efficacy of Vedolizumab as Induction Therapy in Refractory IBD Patients: A Multicenter Cohort.

Background:Vedolizumab (VDZ) demonstrated efficacy in Crohns disease (CD) and ulcerative colitis (UC) in the GEMINI trials. Our aim was to evaluate the efficacy of VDZ at week 14 in inflammatory bowel disease in a multicenter cohort of patients. Methods:Patients at Massachusetts General Hospital and Brigham and Womens Hospital were considered for inclusion. VDZ (300 mg) was administered at weeks 0, 2, 6, and 14. Efficacy was assessed using the Harvey–Bradshaw index for CD, the simple clinical colitis activity index for UC and physician assessment, along with C-reactive protein and decrease of corticosteroid therapy. Clinical response was defined as decrease in Harvey–Bradshaw index ≥3 and simple clinical colitis activity index ≥3 and remission as Harvey–Bradshaw index ⩽4, simple clinical colitis activity index ⩽2 and physician assessment of response and remission. Results:Our study included 172 patients (107 CD, 59 UC, 6 inflammatory bowel disease-unclassified, men 48.3%, mean age 40 years and disease duration 14 years). Fourteen patients had ostomy and 9 ileoanal pouch, and only 35.5% fulfilled eligibility for the GEMINI trials. Previous treatment failures with ≥ 2 anti-TNFs occurred in 70.9%, one-third were on an immunomodulator and 46% systemic steroids at baseline. In CD, 48.9% and 23.9% and in UC, 53.9% and 29.3% had clinical response and clinical remission at week 14, respectively. Adverse events occurred in 10.5%. Conclusions:VDZ is safe and well tolerated in refractory inflammatory bowel disease patients in a clinical practice with efficacy in UC and CD with responses similar to what was seen in clinical trials.

A Steric-Inhibition Model for Regulation of Nucleotide Exchange via the Dock180 Family of GEFs

CDM (CED-5, Dock180, Myoblast city) family members have been recently identified as novel, evolutionarily conserved guanine nucleotide exchange factors (GEFs) for Rho-family GTPases . They regulate multiple processes, including embryonic development, cell migration, apoptotic-cell engulfment, tumor invasion, and HIV-1 infection, in diverse model systems . However, the mechanism(s) of regulation of CDM proteins has not been well understood. Here, our studies on the prototype member Dock180 reveal a steric-inhibition model for regulating the Dock180 family of GEFs. At basal state, the N-terminal SH3 domain of Dock180 binds to the distant catalytic Docker domain and negatively regulates the function of Dock180. Further studies revealed that the SH3:Docker interaction sterically blocks Rac access to the Docker domain. Interestingly, ELMO binding to the SH3 domain of Dock180 disrupted the SH3:Docker interaction, facilitated Rac access to the Docker domain, and contributed to the GEF activity of the Dock180/ELMO complex. Additional genetic rescue studies in C. elegans suggested that the regulation of the Docker-domain-mediated GEF activity by the SH3 domain and its adjoining region is evolutionarily conserved. This steric-inhibition model may be a general mechanism for regulating multiple SH3-domain-containing Dock180 family members and may have implications for a variety of biological processes.

Older age is associated with higher rate of discontinuation of anti‐TNF therapy in patients with inflammatory bowel disease

Background:In increasingly aging populations, awareness of outcomes of older patients treated with biologics is becoming more important. However, few studies to date have investigated the safety and durability of anti-tumor necrosis factor (TNF) therapy in this subgroup. Methods:This was a retrospective single-center study with cases comprising all IBD patients who began anti-TNF treatment at age >60 years. Cases of Crohns disease (CD) and ulcerative colitis (UC) were identified from medical record review. Our controls consisted of patients younger than age 60 years on anti-TNF treatment and patients >60 years on treatment with immunomodulators. Kaplan–Meier survival estimates were used to calculate the probability of remaining on anti-TNF therapy. Results:We identified a total of 54 IBD patients who initiated anti-TNF therapy over the age of 60 years (mean 73, range 61–97 years). Among these, a total of 38 patients (70%) discontinued anti-TNF therapy after a mean of 24.1 months. At 12 months after initiation, 75% of patients older than age 60 years were still on anti-TNF agents compared to 93% among younger users and 82% among older AZA users (P < 0.05). Compared to older AZA users, older anti-TNF users remained more likely to require early therapy cessation (hazard ratio 2.21, 95% confidence interval 1.29–3.78). Conclusions:The IBD population older than age 60 at the time of initiation of anti-TNF therapy is at higher risk for discontinuation of therapy. They may also be particularly vulnerable to infectious complications requiring hospitalization, suggesting the need for careful monitoring during therapy.

Differential Effect of Genetic Burden on Disease Phenotypes in Crohn's Disease and Ulcerative Colitis: Analysis of a North American Cohort

OBJECTIVES:Crohns disease (CD) and ulcerative colitis (UC) are chronic immunologically mediated diseases with a progressive relapsing remitting course. There is considerable heterogeneity in disease course and accurate prediction of natural history has been challenging. The phenotypic implication of increasing genetic predisposition to CD or UC is unknown.METHODS:The data source for our study was a prospective cohort of CD and UC patients recruited from a tertiary referral center. All patients underwent genotyping on the Illumina Immunochip. A genetic risk score (GRS) incorporating strength of association (log odds ratio) and allele dose for each of the 163 inflammatory bowel disease (IBD) risk loci was calculated and phenotypic associations examined across GRS quartiles.RESULTS:Our study cohort included 1,105 patients (697 CD, 408 UC). Increasing genetic burden was associated with earlier age of diagnosis of CD (Ptrend=0.008). Patients in the highest GRS quartile were likely to develop disease 5 years earlier than those in the lowest quartile. Increasing genetic burden was also associated with ileal involvement in CD (Ptrend <0.0001). The effect of genetic burden was independent of the NOD2 locus and was stronger among those with no NOD2 variants, and in never smokers. UC patients with an involved first-degree relative had a higher genetic burden, but GRS was not associated with disease phenotype in UC.CONCLUSIONS:Increasing genetic burden is associated with early age of diagnosis in CD, but not UC. The expanded panel of IBD risk loci explains only a fraction of variance of disease phenotype, suggesting limited clinical utility of genetics in predicting natural history.

Cell Migration Is Regulated by Platelet-Derived Growth Factor Receptor Endocytosis

ABSTRACT Cell migration requires spatial and temporal processes that detect and transfer extracellular stimuli into intracellular signals. The platelet-derived growth factor (PDGF) receptor is a cell surface receptor on fibroblasts that regulates proliferation and chemotaxis in response to PDGF. How the PDGF signal is transmitted accurately through the receptor into cells is an unresolved question. Here, we report a new intracellular signaling pathway by which DOCK4, a Rac1 guanine exchange factor, and Dynamin regulate cell migration by PDGF receptor endocytosis. We showed by a series of biochemical and microscopy techniques that Grb2 serves as an adaptor protein in the formation of a ternary complex between the PDGF receptor, DOCK4, and Dynamin, which is formed at the leading edge of cells. We found that this ternary complex regulates PDGF-dependent cell migration by promoting PDGF receptor endocytosis and Rac1 activation at the cell membrane. This study revealed a new mechanism by which cell migration is regulated by PDGF receptor endocytosis.

Pretreatment 25-Hydroxyvitamin D Levels and Durability of Anti–Tumor Necrosis Factor–α Therapy in Inflammatory Bowel Diseases

INTRODUCTION Emerging evidence supports an immunologic role for 25-hydroxyvitamin D (25(OH)D) in inflammatory bowel disease (IBD). Here we examined if pretreatment vitamin D status influences durability of anti-tumor necrosis factor (TNF)-α therapy in patients with Crohns disease (CD) or ulcerative colitis (UC). METHODS All IBD patients who had plasma 25(OH)D level checked <3 months prior to initiating anti-TNF-α therapy were included in this retrospective single-center cohort study. Our main predictor variable was insufficient plasma 25(OH)D (<30 ng/mL). Cox proportional hazards model adjusting for potential confounders was used to identify the independent effect of pretreatment vitamin D on biologic treatment cessation. RESULTS Our study included 101 IBD patients (74 CD; median disease duration 9 years). The median index 25(OH)D level was 27 ng/mL (interquartile range, 20-33 ng/mL). One-third of the patients had prior exposure to anti-TNF-α therapy. On multivariate analysis, patients with insufficient vitamin D demonstrated earlier cessation of anti-TNF-α therapy (hazard ratio [HR], 2.13; 95% confidence interval [CI], 1.03-4.39; P = .04). This effect was significant in patients who stopped treatment for loss of response (HR, 3.49; 95% CI, 1.34-9.09) and stronger for CD (HR, 2.38; 95% CI, 0.95-5.99) than UC (P = NS). CONCLUSIONS Our findings suggest that vitamin D levels may influence durability of anti-TNF-α induction and maintenance therapy. Larger cohort studies and clinical trials of supplemental vitamin D use with disease activity as an end point may be warranted.

Inflammatory bowel disease and cancer: The role of inflammation, immunosuppression, and cancer treatment.

In patients with inflammatory bowel disease (IBD), chronic inflammation is a major risk factor for the development of gastrointestinal malignancies. The pathogenesis of colitis-associated cancer is distinct from sporadic colorectal carcinoma and the critical molecular mechanisms underlying this process have yet to be elucidated. Patients with IBD have also been shown to be at increased risk of developing extra-intestinal malignancies. Medical therapies that diminish the mucosal inflammatory response represent the foundation of treatment in IBD, and recent evidence supports their introduction earlier in the disease course. However, therapies that alter the immune system, often used for long durations, may also promote carcinogenesis. As the population of patients with IBD grows older, with longer duration of chronic inflammation and longer exposure to immunosuppression, there is an increasing risk of cancer development. Many of these patients will require cancer treatment, including chemotherapy, radiation, hormonal therapy, and surgery. Many patients will require further treatment for their IBD. This review seeks to explore the characteristics and risks of cancer in patients with IBD, and to evaluate the limited data on patients with IBD and cancer, including management of IBD after a diagnosis of cancer, the effects of cancer treatment on IBD, and the effect of IBD and medications for IBD on cancer outcomes.