A Bispecific, Tetravalent Antibody Targeting Inflammatory and Pruritogenic Pathways in Atopic Dermatitis.

Inhibition of IL-4/IL-13 signaling has dramatically improved the treatment of atopic dermatitis (AD). However, in many patients, clinical responses are slow to develop and remain modest. Indeed, some symptoms of AD are dependent on IL-31, which is only partially reduced by IL-4/IL-13 inhibition. Thus, there is an unmet need for AD treatments that concomitantly block IL-4/IL-13 and IL-31 pathways. We engineered NM26-2198, a bispecific tetravalent antibody designed to accomplish this task. In reporter cell lines, NM26-2198 concomitantly inhibited IL-4/IL-13 and IL-31 signaling with a potency comparable with that of the combination of an anti-IL-4Rα antibody (dupilumab) and an anti-IL-31 antibody (BMS-981164). In human PBMCs, NM26-2198 inhibited IL-4-induced upregulation of CD23, demonstrating functional binding to FcγRII (CD32). NM26-2198 also inhibited the secretion of the AD biomarker thymus and activation-regulated chemokine (TARC) in blood samples from healthy human donors. In male cynomolgus monkeys, NM26-2198 exhibited favorable pharmacokinetics and significantly inhibited IL-31-induced scratching at a dose of 30 mg/kg. In a repeat-dose, good laboratory practice toxicology study in cynomolgus monkeys, no adverse effects of NM26-2198 were observed at a weekly dose of 125 mg/kg. Together, these results justify the clinical investigation of NM26-2198 as a treatment for moderate-to-severe AD.

An engineered T-cell engager with selectivity for high mesothelin-expressing cells and activity in the presence of soluble mesothelin.

Mesothelin (MSLN) is an attractive immuno-oncology target, but the development of MSLN-targeting therapies has been impeded by tumor shedding of soluble MSLN (sMSLN), on-target off-tumor activity, and an immunosuppressive tumor microenvironment. We sought to engineer an antibody-based, MSLN-targeted T-cell engager (αMSLN/αCD3) with enhanced ability to discriminate high MSLN-expressing tumors from normal tissue, and activity in the presence of sMSLN. We also studied the in vivo antitumor efficacy of this molecule (NM28-2746) alone and in combination with the multifunctional checkpoint inhibitor/T-cell co-activator NM21-1480 (αPD-L1/α4-1BB). Cytotoxicity and T-cell activation induced by NM28-2746 were studied in co-cultures of peripheral blood mononuclear cells and cell lines exhibiting different levels of MSLN expression, including in the presence of soluble MSLN. Xenotransplant models of human pancreatic cancer were used to study the inhibition of tumor growth and stimulation of T-cell infiltration into tumors induced by NM28-2746 alone and in combination with NM21-1480. The bivalent αMSLN T-cell engager NM28-2746 potently induced T-cell activation and T-cell mediated cytotoxicity of high MSLN-expressing cells but had much lower potency against low MSLN-expressing cells. A monovalent counterpart of NM28-2746 had much lower ability to discriminate high MSLN-expressing from low MSLN-expressing cells. The bivalent molecule retained this discriminant ability in the presence of high concentrations of sMSLN. In xenograft models, NM28-2746 exhibited significant tumor suppressing activity, which was significantly enhanced by combination therapy with NM21-1480. NM28-2746, alone or in combination with NM21-1480, may overcome shortcomings of previous MSLN-targeted immuno-oncology drugs, exhibiting enhanced discrimination of high MSLN-expressing cell activity in the presence of sMSLN.

Lubiprostone for Pediatric Functional Constipation: Randomized, Controlled, Double-Blind Study With Long-term Extension.

BACKGROUND & AIMS: Pediatric functional constipation (PFC) is a common problem in children that causes distress and presents treatment challenges to health care professionals. We conducted a randomized, placebo-controlled trial (study 1) in patients with PFC (6-17 years of age) to evaluate the efficacy and safety of lubiprostone, followed by an open-label extension for those who completed the placebo-controlled phase (study 2). METHODS: Study 1 (NCT02042183) was a phase 3, multicenter, randomized, double-blind, placebo-controlled, 12-week study evaluating the efficacy and safety of lubiprostone 12 µg twice daily (BID) and 24 µg BID. Study 2 (NCT02138136) was a phase 3, long-term, open-label extension of study 1. In both studies, lubiprostone doses were based on patients' weight. Efficacy was assessed solely based on study 1, with a primary endpoint of overall spontaneous bowel movement (SBM) response (increase of ≥1 SBM/wk vs baseline and ≥3 SBMs/wk for ≥9 weeks, including 3 of the final 4 weeks). RESULTS: 606 patients were randomized to treatment (placebo: n = 202; lubiprostone: n = 404) in study 1. No statistically significant difference in overall SBM response rate was observed between the lubiprostone and placebo groups (18.5% vs 14.4%; P = .2245). Both the 12-µg BID and 24-µg BID doses of lubiprostone were well tolerated in the double-blind and extension phases, with a safety profile consistent with that seen in adult studies. CONCLUSIONS: Lubiprostone did not demonstrate statistically significant effectiveness over placebo in children and adolescents with PFC but did demonstrate a safety profile similar to that in adults. (ClinicalTrials.gov: Number: NCT02042183; Number: NCT02138136).

Capsule and Sprinkle Formulations of Lubiprostone Are Not Biologically Similar in Patients with Functional Constipation.

INTRODUCTION: Lubiprostone capsules are approved for managing three different chronic constipation conditions. A "sprinkle" formulation may facilitate use in individuals with difficulty swallowing capsules. Our objective was to evaluate the bioequivalence, pharmacokinetics (PK), and bioavailability of lubiprostone sprinkles vs lubiprostone capsules, compared with placebo. METHODS: A 1-week randomized, placebo-controlled, double-blinded, bioequivalence study (study 302) and a single-dose PK and bioavailability crossover study (study 304) were conducted. In study 302, 522 subjects with chronic constipation were randomized to lubiprostone sprinkle 24 µg twice daily (BID), lubiprostone capsule 24 µg BID, or placebo. The primary efficacy endpoint was observed spontaneous bowel movement (SBM) counts (equivalence defined as showing the 90% confidence interval [CI] of the "between-group SBM ratio" to be contained within 0.8-1.25). Study 304 included two cohorts of healthy volunteers randomized to a single 48-µg lubiprostone dose, sprinkle, or capsule (n = 35) or to a single 48-µg sprinkle dose, in fed or fasted state (n = 14). RESULTS: Both lubiprostone formulations significantly improved SBM count (sprinkle, 4.82 ± 3.66, P = 0.002; capsule, 5.74 ± 3.79, P < 0.0001) vs placebo (3.68 ± 2.16), but equivalent efficacy was not demonstrated, with a 90% CI for the SBM count ratio of 0.69-0.95. Quantifiable PK data on lubiprostone were limited; however, overall exposure to the M3 metabolite was approximately 44% higher with sprinkles vs capsules under fasted conditions (geometric mean ratio 1.441 [90% CI, 1.166, 1.782]), and exposure with the sprinkle formulation was 11% lower in the fed state vs the fasted state (geometric mean ratio 0.888 [90% CI, 0.675, 1.168]). Both formulations were generally well tolerated. CONCLUSION: Despite the significant improvement in SBM counts vs placebo, the sprinkle formulation did not demonstrate bioequivalence to the capsule formulation in either pharmacodynamic or PK key parameters. TRIAL REGISTRATION: Study 302: ClinicalTrials.gov identifier, NCT03097861; https://www.clinicaltrials.gov/ct2/show/NCT03097861 ; Study 304: ClinicalTrials.gov identifier, NCT03010631; https://www.clinicaltrials.gov/ct2/show/NCT03010631 .

Engineering of a trispecific tumor-targeted immunotherapy incorporating 4-1BB co-stimulation and PD-L1 blockade.

Co-stimulatory 4-1BB receptors on tumor-infiltrating T cells are a compelling target for overcoming resistance to immune checkpoint inhibitors, but initial clinical studies of 4-1BB agonist mAbs were accompanied by liver toxicity. We sought to engineer a tri-specific antibody-based molecule that stimulates intratumoral 4-1BB and blocks PD-L1/PD-1 signaling without systemic toxicity and with clinically favorable pharmacokinetics. Recombinant fusion proteins were constructed using scMATCH3 technology and humanized antibody single-chain variable fragments against PD-L1, 4-1BB, and human serum albumin. Paratope affinities were optimized using single amino acid substitutions, leading to design of the drug candidate NM21-1480. Multiple in vitro experiments evaluated pharmacodynamic properties of NM21-1480, and syngeneic mouse tumor models assessed antitumor efficacy and safety of murine analogues. A GLP multiple-dose toxicology study evaluated its safety in non-human primates. NM21-1480 inhibited PD-L1/PD-1 signaling with a potency similar to avelumab, and it potently stimulated 4-1BB signaling only in the presence of PD-L1, while exhibiting an EC50 that was largely independent of PD-L1 density. NM21-1480 exhibited high efficacy for co-activation of pre-stimulated T cells and dendritic cells. In xenograft models in syngeneic mice, NM21-1480 induced tumor regression and tumor infiltration of T cells without causing systemic T-cell activation. A GLP toxicology study revealed no evidence of liver toxicity at doses up to 140 mg/kg, and pharmacokinetic studies in non-human primates suggested a plasma half-life in humans of up to 2 weeks. NM21-1480 has the potential to overcome checkpoint resistance by co-activating tumor-infiltrating lymphocytes without liver toxicity.

Effects of Lubiprostone, an Intestinal Secretagogue, on Electrolyte Homeostasis in Chronic Idiopathic and Opioid-induced Constipation.

GOALS: To assess short-term and long-term effects of lubiprostone, a type-2 chloride channel activator, on electrolyte homeostasis. BACKGROUND: Conventional laxatives are associated with electrolyte imbalances. Lubiprostone is a type-2 chloride channel activator approved for treating chronic idiopathic constipation (CIC), opioid-induced constipation (OIC), and constipation-predominant irritable bowel syndrome in women. It induces intestinal fluid secretion, possibly affecting water and electrolyte homeostasis. We investigated short-term and long-term effects of lubiprostone on electrolyte, blood urea nitrogen (BUN), and creatinine levels using pooled data from CIC and OIC patients. STUDY: Data were pooled from 10 CIC and OIC studies-6 double-blind, randomized, placebo-controlled studies and 4 open-label, long-term studies. Total duration of lubiprostone exposure was from 3 weeks (short-term: CIC, 3 to 4 wk; OIC, placebo-controlled, 12 wk) to 48 weeks (long-term: CIC, 24 to 48 wk; OIC, 48 wk). Sodium, chloride, potassium, magnesium, BUN, and creatinine levels were examined at baseline and final assessment. RESULTS: Overall, 3209 patients were assessed. In the double-blind, placebo-controlled studies, there were no clinically meaningful differences in levels of electrolytes, BUN, and creatinine between lubiprostone and placebo groups, and in changes from baseline levels with long-term use of lubiprostone. Analyses of shifts in laboratory values (low/normal/high) at baseline and final assessment showed minimal effects on electrolytes, BUN, and creatinine. CONCLUSIONS: Lubiprostone did not cause clinically meaningful electrolyte imbalances or affect markers of renal function in either the short-term or long-term treatment of CIC or OIC.

Efficacy of Lubiprostone for the Treatment of Opioid-Induced Constipation, Analyzed by Opioid Class.

Objectives: To examine the efficacy and safety of lubiprostone for the treatment of opioid-induced constipation (OIC) in patients by opioid class received. Design: Data were pooled from three phase III, randomized, double-blind, placebo-controlled studies. Subjects/Setting: Adults with chronic noncancer pain receiving opioid therapy for 30 or more days and diagnosed with OIC. Methods: Overall mean change from baseline in spontaneous bowel movement (SBM) frequency, overall treatment response (≥1 SBM/week improvement over baseline SBM frequency in all treatment weeks with available data and ≥3 SBMs/week for ≥9 of the 12 weeks of treatment), and OIC-related symptoms were examined in patients taking opioids. Data were pooled and analyzed by opioid group. Results: In patients receiving phenanthrene opioids (e.g., oxycodone; N = 1,159), lubiprostone significantly increased overall mean changes in SBM frequency from baseline (P = 0.0001), increased overall response rate (P = 0.0024), and improved OIC symptoms (P ≤ 0.0229) vs placebo. Patients receiving phenylpiperidine opioids (e.g., fentanyl; N = 137) had significant improvement in SBM frequency (P = 0.0129) and favorable trends in response rates (21.4% vs 9.8%; P = 0.0723) and OIC symptoms vs placebo. Efficacy was not observed in overall analyses of patients receiving diphenylheptane opioids (e.g., methadone), although an increase in SBM frequency was observed in patients who received a morphine-equivalent daily dose of 200 or fewer mg, suggesting a dose-dependent negative interference of this opioid class on lubiprostone effects. For all groups, the lubiprostone adverse event profile was similar; the most common treatment-emergent adverse events were nausea and diarrhea. Conclusions: In patients using commonly prescribed opioids, lubiprostone is effective and generally well tolerated for the treatment of OIC.

The Cost Effectiveness of Lubiprostone in Chronic Idiopathic Constipation.

OBJECTIVE: The objective of this study was to evaluate the cost effectiveness of lubiprostone, prucalopride, placebo and immediate referral to secondary care in chronic idiopathic constipation (CIC) in an economic model that was used by the UK National Institute for Health and Care Excellence (NICE) in developing guidance. METHODS: We developed a cohort state-transition model to reflect the treatment pathway in CIC from the UK NHS and personal social services perspective. Time on treatment was determined by a treatment continuation rule using data from an indirect comparison and survival curves fitted to long-term data. Quality of life was defined by whether CIC was resolved or unresolved, using published values. Costs were determined by drug acquisition costs, invasive procedures and healthcare resource use (associated with resolved or unresolved CIC), using published UK sources. Deterministic and probabilistic sensitivity analyses were conducted. RESULTS: Over a 10-year time horizon, lubiprostone was more costly and more effective than placebo and immediate referral to secondary care, with incremental cost-effectiveness ratios (ICERs) of £58,979 and £21,152. Lubiprostone dominated prucalopride in the base case and with a time horizon of 1 year. The main sensitivity for the comparison against placebo was the assumptions around placebo cost and efficacy. The main sensitivity for the comparison against prucalopride was the endpoint used in the indirect comparison. CONCLUSION: Lubiprostone may be cost effective compared with prucalopride or immediate referral but not compared with placebo in the base case. The implementation of the guidance issued by NICE should increase quality of life for patients with CIC and provide a further treatment option.

Penetration of a topically administered anti-tumor necrosis factor alpha antibody fragment into the anterior chamber of the human eye.

OBJECTIVE: To determine whether topically applied ESBA105, a single-chain antibody fragment against tumor necrosis factor (TNF)-α, could efficiently penetrate into the anterior chamber of the human eye. DESIGN: Multicenter, interventional cohort study. PARTICIPANTS: Otherwise healthy patients undergoing cataract surgery (cohorts I-III) or combined cataract surgery and vitrectomy (cohort IV). METHODS: ESBA105 (n = 57) or placebo (n = 22) was preoperatively applied as eye drops to 1 eye in patients scheduled for cataract surgery (n = 73) or combined cataract surgery and vitrectomy (n = 6). ESBA105 was administered on the day of surgery at 1-hour intervals (last dose 1 hour preoperatively) as 1.6 mg in 4 drops for cohort I (n = 15) and as 3.2 mg in 8 drops for cohorts II (n = 15) and IV (n = 6). Cohort III (n = 43) was randomized 1:1 in double-masked fashion to receive either ESBA105 6.4 mg or placebo over 4 days using 4 drops per day at 4-hour intervals (last dose 12 hours preoperatively). Aqueous humor (all cohorts), vitreous humor (cohort IV only), and blood samples (all cohorts) were collected for measurement of ESBA105. MAIN OUTCOME MEASURES: ESBA105 intraocular concentration. RESULTS: Both 4 times daily over 4 days dosing (cohort III) and 8 times daily dosing (cohorts II and IV) resulted in reliably high ESBA105 concentrations in aqueous humor. Mean molar excess of intraocular ESBA105 over its target (intraocular TNF-α) was calculated as 96-fold (cohort III) to 359-fold (cohorts II and IV). Results from the cohorts receiving 4 and 8 hourly drops per 1 day (cohorts I, II, and IV) indicated that dose-dependent intraocular concentrations of ESBA105 were achieved within hours of dosing. After 8 times daily dosing, 5 of 6 vitreous samples (cohort IV) had undetectable ESBA105 levels. ESBA105 was detected in 17 of 55 preoperative serum samples but no longer detectable in serum 1 day after surgery (0 of 19 samples). In cohort III, treatment-emergent adverse events were identical between ESBA105 and placebo groups (2 cases each of eye irritation). CONCLUSIONS: These results demonstrate that the topically applied single-chain antibody fragment ESBA105 penetrated into the anterior chamber of the human eye at therapeutic levels.

Relative contribution of VEGF and TNF-alpha in the cynomolgus laser-induced CNV model: comparing the efficacy of bevacizumab, adalimumab, and ESBA105.

PURPOSE: To compare the relative contribution of VEGF and TNF-alpha in the development of laser-induced choroidal neovascularization (CNV) in monkeys and to exploit the feasibility of topical use of suitable antibody fragments for the prevention of experimental CNV. METHODS: To induce experimental CNV, small high-energy laser spots were used to treat several areas of the macula in the retinas of cynomolgus monkeys according to previously published protocols. To prevent abnormalities, bevacizumab (a potent VEGF inhibitor) and adalimumab or ESBA105 (potent TNF-alpha inhibitors) were given by intravitreal injection 1 week before and 1 week and 3 weeks after laser treatment. ESBA105 was also applied topically in a separate group. Control animals were treated with either intravitreal or topical saline. Eyes were monitored by ophthalmic examination, color photography, and fluorescein angiography. RESULTS: Inhibition of VEGF by bevacizumab completely blocked the formation of CNV. Both TNF-alpha inhibitors also significantly reduced laser-induced CNV abnormalities after intravitreal administration. Most important, topical use of the anti-TNF-alpha single-chain antibody fragment ESBA105 also reduced the formation of CNV. CONCLUSIONS: TNF-alpha contributes to laser-induced CNV formation, and its inhibition can be a new therapeutic target for CNV. This study suggests TNF-alpha as another therapeutic target for the prevention and treatment of CNV and adds to the emerging clinical data suggesting the therapeutic value of TNF-alpha inhibitors in age-related macular degeneration (AMD). Further, this study shows that topical therapy with suitable antibody fragments has the potential of being introduced to retinal disease treatment regimens.

Pharmacokinetics and posterior segment biodistribution of ESBA105, an anti-TNF-alpha single-chain antibody, upon topical administration to the rabbit eye.

PURPOSE: The purpose of this study was to characterize local distribution and systemic absorption of the tumor necrosis factor (TNF)-alpha inhibitory single-chain antibody fragment (scFv) ESBA105 following topical administration to the eye in vivo. METHODS: Rabbits received ESBA105 as topical eye drops in two dosing regimens. First, pharmacokinetics after the topical route of administration was compared to the intravenous (i.v.) route by means of applying the identical cumulative daily dose of ESBA105. In a second study rabbits received five eye drops daily for six consecutive days in a lower frequency topical dosing regimen. Kinetics and biodistribution of ESBA105 in ocular tissues and fluids as well as in sera were determined in all animals. RESULTS: After topical administration to the eye, ESBA105 quickly reaches therapeutic concentrations in all ocular compartments. Systemic exposure after topical administration is 25,000-fold lower than exposure after i.v. injection of the identical cumulative daily dose. ESBA105 levels in vitreous humor and neuroretina are significantly higher on topical administration than after i.v. injection. Absolute and relative intraocular biodistribution of ESBA105 is different with topical and systemic delivery routes. Compared to its terminal half-life in circulation (7 hours), the vitreal half-life of ESBA105 is significantly enhanced (16-24 hours). CONCLUSIONS: On topical administration, ESBA105 is efficiently absorbed and distributed to all compartments of the eye, whereby systemic drug exposure is very low. Based on its unique intraocular biodistribution and pharmacokinetics and the absolute intraocular levels reached, topical ESBA105 appears highly attractive for treatment of various ophthalmological disorders.

Efficient intraocular penetration of topical anti-TNF-alpha single-chain antibody (ESBA105) to anterior and posterior segment without penetration enhancer.

PURPOSE: This study was designed to characterize ocular penetration pathways of ESBA105, a topically administered single-chain antibody (scFv) against tumor necrosis factor (TNF)-alpha, to the anterior and posterior segment of the eye. METHODS: Fresh enucleated whole eyes and isolated corneas of rabbits mounted in perfusion chambers were used for ex vivo penetration studies. In vivo pharmacokinetics and ocular biodistribution of ESBA105 after intravitreal injection or topical administration as eye drops were investigated in rabbits. RESULTS: After topical administration as eye drops, without a penetration enhancer, ESBA105 reached therapeutic levels in the anterior and posterior segment of the eye. ESBA105 migrated to aqueous humor via corneal penetration and vitreous and retina via intrascleral penetration pathways. In vivo, ESBA105 had a significantly prolonged elimination half-life in the vitreous of 25 hours compared with its serum half-life of 7 hours after i.v. administration. Therefore, based on frequency of topical dosing, a buildup of ESBA105 to distinct steady state levels in the vitreous could be achieved. CONCLUSIONS: Topically administered ESBA105 quickly reaches therapeutic levels in the anterior and posterior segment without any need for a penetration enhancer. Drug penetration and ocular biodistribution patterns of ESBA105 applied as eye drops appear highly attractive for clinical use to treat TNF-alpha dependant diseases of the eye.

Antibody-based approaches in Alzheimer's research: safety, pharmacokinetics, metabolism, and analytical tools.

High morbidity, enormous socioeconomic costs, and lack of specific treatments emphasize the importance of research on protective therapies against Alzheimer's disease. The efficacy of anti-amyloid immunization strategies has been demonstrated preclinically, prompting the design of clinical studies. However, the detailed mechanisms of action of therapeutic antibodies, especially their influence on the complex amyloid beta peptide (Abeta) metabolism and various Abeta-equilibria present both within and outside the CNS, are far from being clear. Furthermore, physiological Abeta metabolism is poorly understood and the analytical tools to characterize and quantify treatment effects on Abeta metabolism are suboptimal. Thus, the design of immunization strategies with optimized benefit-to-risk ratios for patients is subjected to significant obstacles. Indeed, an active immunization trial with Abeta was discontinued because of severe adverse effects. Anti-Abeta immunization protocols designed to attain high blood levels of antibodies bear the potential to induce brain inflammation and/or hemorrhage, thus directing the biomedical research towards development of more predictable therapies for minimizing the risk of adverse effects. The focus of this review is to summarize current knowledge of Abeta metabolism under physiological and antibody-based therapeutic conditions and to introduce a promising approach, namely the passive immunization using antibody fragments, which are characterized by entirely different pharmacokinetic and pharmacodynamic properties compared with conventional monoclonal antibodies.

Loss of metal transcription factor-1 suppresses tumor growth through enhanced matrix deposition.

Metal transcription factor-1 (MTF-1) is a ubiquitous transcriptional regulator and chromatin insulator with roles in cellular stress responses and embryonic development. The studies described herein establish for the first time the involvement of MTF-1 in tumor development. Genetically manipulated ras-transformed mouse embryonic fibroblasts (MEFs), wild-type (MTF-1+/+), or nullizygous for MTF-1 (MTF-1-/-) were used to develop fibrosarcoma tumors. Loss of MTF-1 resulted in delayed tumor growth associated with increased matrix collagen deposition and reductions in vasculature density. Molecular consequences of MTF-1 loss include increased expression and activation of the transforming growth factor-beta1 (TGF-beta1) and tissue transglutaminase (tTG), two proteins with documented roles in the production and stabilization of extracellular matrix (ECM). Our findings support the hypothesis that MTF-1 enhances the ability of the developing tumor mass to evade fibrosis and scarring of the tumor, a critical step in tumor cell proliferation.

Metal-responsive transcription factor-1 (MTF-1) is essential for embryonic liver development and heavy metal detoxification in the adult liver.

Metal-responsive transcription factor-1 (MTF-1) activates the transcription of metallothionein genes and other target genes in response to heavy metal load and other stresses such as hypoxia and oxidative stress. It also has an essential function during embryogenesis: targeted disruption of Mtf1 in the mouse results in lethal liver degeneration on day 14 of gestation. Here we studied Mtf1 knockout mice at embryonic and adult stages, the latter by means of conditional knockout. Hepatocytes from Mtf1 null mutant and wild-type embryos were taken into culture on day 12.5 of gestation. Both initially appeared normal, but mutant cells were lost within a few days. Furthermore, Mtf1 null hepatocytes were poorly, if at all, rescued by cocultivation with wild-type rat embryo hepatocytes, indicating a cell-autonomous defect. When the Mtf1 gene was excised by Cre recombinase after birth in liver and bone marrow and to a lesser extent in other organs, mice were viable under non-stress conditions but highly susceptible to cadmium toxicity, in support of a role of MTF-1 in coping with heavy metal stress. An additional MTF-1 function was revealed upon analysis of the hematopoietic system in conditional knockout mice where leukocytes, especially lymphocytes, were found to be severely underrepresented. Together, these findings point to a critical role of MTF-1 in embryonic liver formation, heavy metal toxicity, and hematopoiesis.

Cell growth selection system to detect extracellular and transmembrane protein interactions.

The interplay among extracellular and cell surface proteins, such as the interactions between ligands and receptors or between antigens and antibodies, is involved in a multitude of physiological and pathological phenomena. In the oxidizing milieu of the secretory pathway in eukaryotic cells, many extracellular proteins build disulfide bonds that significantly contribute to their correct folding and structural stability. Thus, conventional yeast two-hybrid interaction assays, which occur in the reducing intracellular environment, might not be adequate to detect extracellular protein-protein interactions. We have exploited the properties of yeast Ire1p, a type I endoplasmic reticulum (ER) membrane protein involved in the unfolded protein response (UPR) as a dimerization-activated receptor, to develop a novel system for the detection and study of interactions between extracellular and/or membrane proteins. In our system, named SCINEX-P (screening for interactions between extracellular proteins), proteins of interest were fused to truncated Ire1p so as to substitute its N-terminal lumenal domain (NLD). Specific interaction between two partners caused dimerization of the Ire1p moiety, which, through the endogenous UPR signalling pathway, led to activation of transcription of genes that permit cell growth under selective conditions.