Identification of tumor stem-like cells in a mouse myeloma cell line

We used colony formation assay in the soft agar media or the serum-free media, the methods of identifying BrdU-label-retaining cells and the SP cells as well as the tumorigenicity test in BALB/c mice, respectively, to analyze tumor stem like cells in the SP2/0 cell line. The results showed that a few SP2/0 cells were capable of forming colonies in the soft agar media, contained BrdU-label-immortal strand in the SP2/0 cell line. The SP2/0 cells in the serum-free media gained higher tumorigenicity in the BALB/c mice than the SP2/0 cells cultivated in the complete media did. Overall, only a few of the SP2/0 cells were found to possess the characteristics of tumor stem-like cells, such as high proliferative potency, more self-renewal and stronger tumorigenesis, or greater similarity to the tumor stem cells (TSCs) traits. The biology of tumor stem-like cells contributes to the identification of molecular targets important for future tumor therapy.

Interaction between sorafenib and erlotinib

2500

Background: The combination of sorafenib plus erlotinib was evaluated in patients with recurrent glioblastoma (GBM). In addition to defining the maximum tolerated dose (MTD), pharmacokinetics (PKs) for single agent and combination were determined. Methods: Adults with recurrent GBM with the usual phase I inclusion/exclusion criteria were eligible. No enzyme inducing anti-epileptic agents were allowed. Starting doses for erlotinib and sorafenib were 100mg PO QD and 200 mg PO BID, respectively, for 28 days (a cycle). For cycle 1 PKs, erlotinib was started on day 1 followed on day 2 by sorafenib. Eight plasma samples were collected over 24hrs on days 1, 15 and 28. Sorafenib and its metabolite (N-oxide) were analyzed by HPLC and erlotinib and OSI-420 by LC/MS. PK parameters were characterized by standard non-compartmental methods. Results: The MTD was sorafenib 200 mg PO BID and erlotinib 100 mg PO QD. The PKs for erlotinib (OSI) are displayed below. Conclusions: The PKs for sorafenib are in agreement with previous reports and not affected by the co-administration of erlotinib. However, there is an apparent affect of sorafenib on the PKs of erlotinib. The expected accumulation of erlotinib's Cmax and AUC at steady-state was not observed. This interaction results in at least a 2+ fold decrease in exposure to erlotinib and its active metabolite. The interaction does not appear to be the classical enzyme induction due to the rapidity of the onset/offset. This same phenomenon has been reported with the co-administration of sorafenib with gefitinib (Clin Cancer Res 13:2684,2007). Increasing the maximal velocity (Vmax) of CYP3A4, not the quantity of enzyme, is suggested as a testable hypothesis (J Pharmacol Exp Ther 290:1.1998). The clinical relevance of this interaction with regard to toxicity and efficacy warrants further evaluation.

[Table: see text]

No significant financial relationships to disclose.

Correlative tumor molecular profiling and plasma biomarker analysis in a phase II study of XL184 in patients with progressive or recurrent glioblastoma multiforme (GBM)

2049

Background: XL184 is an oral inhibitor of MET, RET, KIT, and VEGFR-2 with potent antitumor effects in preclinical models of GBM. Clinically, elevated levels of MET, KIT, VEGFR-2, and VEGF-A are found in GBM, where MET and KIT levels correlate with poor prognosis. XL184–201 is a fully enrolled GBM study (N = 46) which mandated collection of archival tumors and serial plasma samples. The encouraging clinical activity of XL184 in this study is the subject of a separate abstract. Methods: Tumor profiling focused on genomic alterations prevalent in GBM, reflecting dysregulation of key signaling pathways (Nature 2008; 455:1061), or XL184 targets. Plasma samples were analyzed with ELISA assays. Correlation of results with clinical outcomes is a secondary objective of study XL184–201. Results: Tumor genotyping assessments included EGFR and KIT copy number; PTEN, PIK3CA, PIK3R1, and NF1 sequencing, as well as MGMT and PTEN promoter methylation. Results from the first 12 cases indicate sequence variations & frequencies similar to reports in the literature. IHC analysis of MET, RET, and VEGFR-2 protein expression was also performed. In ∼ 80% of samples, tumor cells stained positive for MET with a lower fraction positive for RET and VEGFR-2 in tumor cells (42% and 58%, respectively). RET and VEGFR-2 expression was often seen in tumor-associated blood vessels, while MET signal in blood vessels was more limited (33%). Preliminary biomarker analysis established significant modulation of plasma levels of VEGF-A, sMET, sVEGFR-2, sKIT, and PlGF, consistent with multiple on target effects. Objective response was observed in the presence or absence of tumor EGFR amplification, PTEN mutation, and MGMT promoter methylation. The potential predictive value of these and other biomarkers is under investigation. Conclusions: Plasma biomarkers confirm pharmacodynamic activity of XL184 in advanced GBM where marked clinical activity has been observed. Upon completed analysis of a full set of biological samples and with mature clinical data, predictive markers for clinical activity of XL184 will be evaluated.

[Table: see text]

Phase I trial of vatalanib (PTK787) in combination with standard radiation and temozolomide in patients with newly diagnosed glioblastoma

2035

Background: Anti-vascular endothelial growth factor (VEGF) agents are hypothesized to work synergistically with chemotherapy and radiation (RT). Vatalanib (MW 347, T1/2 4.6 h) is an oral, pan-VEGFR tyrosine kinase inhibitor that has shown activity in patients with recurrent glioblastoma. Methods: This phase I study was designed to determine the maximal tolerated dose of vatalanib in combination with RT and TMZ for patients with newly diagnosed GBM who were taking enzyme-inducing anti-epileptic drugs. RT and TMZ were administered at standard doses. Vatalanib was initiated 5 days prior to the start of RT and continued daily until tumor progression, unacceptable toxicity or a maximum of up to 12 cycles of post-RT TMZ. Cohorts of 3 patients were treated during RT and TMZ at doses of 250mg daily, 250mg BID, or 500mg BID of vatalanib. Following the completion of RT, patients were treated with vatalanib 750mg BID for the remainder of the study. Results: Nineteen patients were enrolled of which 17 took 5 or more days of vatalanib (1 patient withdrew consent prior to start of vatalanib and 1 withdrew consent after only 1 dose). The median age was 58 and the median KPS was 90. Eight patients had a diagnostic biopsy only. The MTD has not been reached. Potentially related grade 3–4 toxicities included elevated transaminases (2 patients), thrombocytopenia (1 patient), leukopenia (1 patient), neutropenia (1 patient), depressed level of consciousness (1 patient), and fatigue (1 patient). Only 1 patient suffered an asymptomatic intracerebral hemorrhage and no patient experienced wound dehiscence or infection. Five patients remain on vatalanib and the median follow-up for all patients is 6.5 months. Seven patients have died. The best responses for the 13 patients who completed combination RT/TMZ/vatalanib was 2 PR, 7 SD, and 2 PD. Two patients were clinically stable with biopsy proven pseudoprogression. Median PFS is 18.4+ months and OS has not been reached. Conclusions: Vatalanib is safe and well tolerated when added to standard RT and TMZ. The MTD has not been reached and dose escalation continues in this population of patients on enzyme inducing anti-epileptic drugs.

[Table: see text]

Use of neurovascular imaging in GBM patients (pts) to quantify early physiologic changes after treatment with XL184, an inhibitor of multiple receptor tyrosine kinases: Results from a phase II study

2048

Background: Treatment of recurrent glioblastoma by targeting VEGF has gained recent attention. Bevacizumab (bev) or cediranib block VEGFR signaling which is detectable within one day by MRI; early changes on MRI may correlate with clinical outcome. XL184 is a potent orally bioavailable inhibitor of MET, RET, KIT, and VEGFR2; MET and VEGFR2 have been shown to play important roles in tumor angiogenesis. In preclinical models, simultaneous inhibition of MET and VEGFR2 with XL184 results in profound regression of tumor vasculature which is qualitatively different from that observed with other antiangiogenic agents. Methods: A multicenter phase II study of XL184 in 46 pts with relapsed or progressive GBM with primary endpoints of 6-month progression free survival and safety is fully enrolled. Vascular neuroimaging including DCE-MRI, CBV/CBF, diffusion, and magnetic resonance spectroscopy (MRS) is performed in these GBM pts treated with XL184. Lesion volumes are also calculated. Assessments are at baseline, 24 hours post first dose, at 4 weeks and 8 weeks. Results: As of January 1, 2009, 38 pts have undergone imaging. In all 9 pts with imaging available at Day 28, decreases in tumor size were seen on post-Gd T1 (mean drop 51%, SD 31%, p = 0.03 by t-test) and FLAIR (mean drop 53%, SD 20%, p = 0.001) consistent with an anti-vascular/anti-edema effect. In 11 of 14 pts T1 volume decrease was visible on Day 1 (mean drop 20%, SD 12%, p = 0.01), consistent with the rapid changes seen with VEGF inhibition. Two of 3 pts with no Day 1 decrease in enhancing lesion volume were bev-pretreated. Pts treated with other VEGF inhibitors (vandetanib, VEGF-TRAP) responded similarly to naïve pts at Day 1 and 28. Assessment of Ktrans in 5 pts showed a 79% decrease (SD 13%, p = 0.04). MRS from 3 pts showed an increase of the NAA/Choline ratio (10–100%) between the baseline and Day 28 scans, and a decrease in lipid levels (50–100%), suggesting inhibition of tumor progression. Conclusions: Treatment with XL184 results in significant decreases in lesion volume and Ktrans at Day 1 and even greater decreases at Day 28, suggestive of biological activity in GBM.

[Table: see text]

Phase I/II study of erlotinib and temsirolimus for patients with recurrent malignant gliomas (MG) (NABTC 04–02)

2004

Background: Glioblastomas (GBM) frequently have EGFR amplification/mutations and inactivation of PTEN. Although single agent EGFR and mTOR inhibitors have limited activity, combinations of these agents may be more effective. Methods: The North American Brain Tumor Consortium conducted a phase I/II study of the EGFR inhibitor erlotinib in combination with the mTOR inhibitor temsirolimus in recurrent MG. Eligibility criteria were histologically proven GBM and anaplastic gliomas (AG), radiologic progression, >18 years old, KPS >60, adequate bone marrow and organ function. There was no limit on the number of prior relapses for phase I and no more than two prior relapses for phase II. Patients must not be receiving enzyme-inducing antiepileptic drugs. The dose of erlotinib was 150 mg/d in phase I and titrated up to maximum of 200mg/d in phase II depending on tolerability. Patients initially received temsirolimus 50 mg i.v. once weekly and the dose adjusted based on toxicities. Escalation was performed in groups of three. MTD was defined as the dose with 1/6 or fewer patients with dose-limiting toxicities (DLTs). Primary endpoint for the phase II component was PFS6. Results: In phase I, 22 patients were enrolled (15 GBM; 7 AG). Median age was 54 years (26–74); median KPS 90 (70–100); median prior relapses 1 (0–3). The MTD was determined to be 150 mg of erlotinib daily combined with 15 mg of temsirolimus weekly. DLTs were rash, mucositis, and liver function abnormalities. Pharmacokinetic data were similar to that for single agent erlotinib and temsirolimus; there was no interaction between the two drugs. AUC accumulation ratios between cycle 1 and 2 for erlotinib and OSI-420 were 3.6 and 4.6, respectively. In phase II, there were 56 patients (including 12 phase I patients treated at the MTD): 40 GBM; 16 AG, median age 47 years (20–72); median KPS 90 (range 60–100), median prior relapses 1 (range 1–3). Six patients discontinued therapy as a result of toxicities. For GBM patients, there was no PR, 30% SD, and PFS6 was 12.5%. For AG patients there was 12.5% PR, 12.5% SD, and PFS6 was 6.25%. Conclusions: The combination of erlotinib and temsirolimus was associated with a higher than expected incidence of toxicities and had minimal activity in recurrent MG.

[Table: see text]

A phase II study of XL184 in patients (pts) with progressive glioblastoma multiforme (GBM) in first or second relapse

2047

Background: XL184 is a potent orally bioavailable inhibitor of MET, RET, KIT, and VEGFR2. Elevated levels of VEGFR2 and its ligand VEGF are found in GBM, and elevated levels of MET and KIT are correlated with poor prognosis in GBM pts. Treatment with XL184 results in potent inhibition of GBM in preclinical models. Methods: This is a phase II study of 46 pts with recurrent GBM who received XL184 175mg PO qd. Co-primary objectives are 6-month progression-free survival (PFS6) and safety. Secondary objectives include response rate (per MacDonald Criteria), duration of response, overall survival, pharmacodynamic and pharmacokinetic parameters, vascular imaging, and changes in steroid usage. Results: As of January 6, 2009, all 46 pts have been enrolled. At least 1 post-baseline tumor assessment at 4 weeks was available for 26 pts. Of these, 17 pts had not received prior therapy with an anti-angiogenic agent, whereas 9 pts had received prior therapy with bevacizumab (n = 6), vandetanib (n = 2), or VEGF-TRAP (n = 1). Safety: 6 pts have experienced a total of 9 possibly related grade 3/4 SAEs including increased troponin I and myocarditis (n = 1); dehydration, nausea, and fatigue (n = 1); elevated ALT (n = 1); pulmonary embolism (n = 2); and CNS hemorrhage (n = 1). 24/46 (52%) pts have required a dose interruption or reduction due to AEs or SAEs. Based on investigator assessment of bidimensional contrast-enhancing tumor measurements, 10 pts (38%) had a best radiologic response of >= 50% reduction from baseline (including 1 pt with a 100% reduction), 9 pts (35%) had tumor measurement changes ranging from +24% and -49%, and 7 pts (27%) had a >= 25% increase in tumor burden. Of the 17 anti-angiogenic-naïve pts, 9 (53%) had a best radiologic response of >= 50% reduction in tumor burden. 1 pt with prior vandetanib therapy has experienced a best radiologic response of >= 50%. Of the 4 pts with > 6 months follow-up, 3 remain on study with a sustained radiologic response. Conclusions: XL184 at a dose of 175 mg PO qd, has demonstrated substantial activity in pts with progressive or recurrent GBM. Updated safety and efficacy results including centrally reviewed PFS6 and response rate will be reported.

[Table: see text]

Phase II trials of erlotinib or gefitinib in patients with recurrent meningiomas

2062

Background: No effective treatment is available for recurrent meningiomas when surgical and radiation options are exhausted. The epidermal growth factor receptor (EGFR) is often over-expressed in meningiomas and may promote tumor growth. In open label, single arm phase II studies of the EGFR inhibitors gefitinib (NABTC 00–01) and erlotinib (NABTC 01–03) for recurrent malignant gliomas, we included exploratory subsets of recurrent meningioma patients. We have pooled the data and report the results here. Methods: Patients with recurrent histologically confirmed meningiomas and no more than two previous chemotherapy regimens were treated with gefitinib 500 mg/day or erlotinib 150 mg/day until tumor progression or unacceptable toxicity. Results: Twenty-five eligible patients were enrolled with median age 57 years (range 29–81) and median Karnofsky performance status (KPS) score 90 (range 60–100). Sixteen patients (64%) received gefitinib and nine (36%) erlotinib. Eight patients (32%) had benign tumors, 9 (36%) atypical, and eight (32%) malignant. For benign tumors, the 6-month progression-free survival (PFS6) was 29%, 12-month PFS (PFS12) 0%, 6-month overall survival (OS6) 63%, and 12-month OS (OS12) 50%. For atypical/malignant tumors, PFS6 was 25%, PFS12 19%, OS6 81%, and OS12 68%. There were no significant PFS or OS differences by histology. Of 21 evaluable patients, there were no responses; eight patients (38%) had stable disease, and 13 (62%) had progressive disease. Treatment was well-tolerated. Rash was not a significant predictor of PFS or OS. Conclusions: Neither gefitinib nor erlotinib appear to have significant activity against recurrent meningioma. The role of EGFR inhibitors in meningiomas is unclear but evaluation of EGFR inhibitors in combination with other targeted molecular agents may be warranted.

No significant financial relationships to disclose.

EEG human head modelling based on heterogeneous tissue conductivity

This paper studies the effect of heterogeneous tissue conductivity in a human head model for the EEG forward problem. Firstly, the tissue heterogeneity in conductivity was characterised from measured data in the literature. Then a method was developed to include this feature in modelling. Finally, the effect of tissue heterogeneity on EEG signals was studied. Based on these studies the paper concludes that the inclusion of tissue heterogeneity is significant in accurate head modelling for the EEG problem.

Phase I trial and pharmacokinetic study of oral gimatecan in adults with malignant glioma

1559

Background: Gimatecan (GT) is an orally available camptothecin analogue with potent preclinical antitumor activity. A phase I trial was conducted to determine the maximum tolerated dose (MTD), toxicity profile, and pharmacokinetics (PK) of GT in patients (pts) with recurrent malignant glioma. Methods: GT was given orally once daily for 5 days every 28 days. The starting dose, 1.6 mg/m2 over 5 days, was independently escalated in pts who were and were not concurrently receiving enzyme inducing antiseizure drugs (±EIASD). PK samples were obtained up to 24 after dosing on day 1 and 168 h after dosing on day 5 of cycle 1. Results: A total of 43 pts were enrolled, 18 in the +EIASD arm and 25 in the -EIASD arm, with a median age of 51 years (range, 23–70) and median KPS of 80 (range, 60–100). All pts had prior irradiation and 84% had prior chemotherapy. Dose levels evaluated were 1.6, 3.2, 5.3, 8.0, 11.2, and 15.0 mg/m2 in the +EIASD arm and 1.6, 3.2, 5.3, 6.1, and 8.0 mg/m2 in the -EIASD arm. No dose-limiting toxicities (DLTs) occurred during 49 cycles of therapy in the +EIASD arm with dose escalation terminated at 15.0 mg/m2. Grade 3–4 myelosuppression was the DLT in the -EIASD arm, occurring in 1/11 pts at the MTD of 6.1 mg/m2, and 2/3 pts at 8.0 mg/m2. Gastrointestinal disorders, the most common side effects, were grade >3 in only 7% of pts. Pts in the +EIASD arm received a median of 6 cycles of therapy and there were 2 partial responses and 6 pts with stable disease. Pts in the -EIASD arm received a median of 2 cycles of therapy and 11 pts had stable disease. GT exhibited linear PK. EIASDs significantly affected the PK, decreasing the biological half-life 2-fold from 53 ± 25 to 25 ± 12 h (mean ± SD) and increasing the apparent oral clearance (CL/F) nearly 5-fold from 1.3 ± 1.7 L/h to 6.2 ± 4.3 L/h. CL/F was independent of body surface area. Conclusions: The MTD of GT for pts not receiving EIASDs is 6.1 mg/m2 and an MTD was not established for pts receiving EIASDs due to practical limitations on dose administration. Median duration of disease stabilization or response was 6 cycles for 44% of +EIASD pts and 2 cycles for 44% of -EIASD pts.

[Table: see text]

Phase II study of POLY-ICLC in recurrent anaplastic glioma–A North American Brain Tumor Consortium study

1550

Background: The goals of this study were to determine the 6-month progression free survival (PFS) for patients with recurrent anaplastic glioma (AG) treated with the immune-modulatory agent POLY-ICLC, and to evaluate toxicity. Low dose Poly-ICLC has a direct immune enhancing action which includes an increased antibody response to antigen and activation of NK-cells, T-cells, macrophages and cytokines. Previously documented side effects include transient flu-like symptoms, which responds to acetaminophen and pain related to the intramuscular administration. Methods: Eligibility included age >18 years, recurrent AG, no more than 2 prior relapses, normal laboratory parameters and informed consent. Poly-ICLC was administered at 20mcg/kg 3x/week by intramuscular injection in 4 week cycles continuously. Dose reductions were allowed for toxicities. Patients were assessed for tumor response every 2 months. Treatment continued until tumor progression, unacceptable toxicity or patient withdrawal. The study had a 2 stage design with the initial assessment of 6 month PFS for the first 22 patients with possible expansion to a total of 46 patients, if more than 7 patients of the 22 had a 6 month PFS. Results: As of 12/05, 46 patients were treated (49% males). Median age was 42 years (range 21–70 years) and median KPS was 90. The agent was well tolerated and the toxicity profile was as previously reported. The response rate and 6 month PFS of the 22 patients in the first stage of the study was 9% and 23% respectively. Based on these findings the cohort was expanded to 46 patients. Of the 15 patients in the second cohort with at least 1 post treatment response assessment available, there is 1PR and 7 SD (47%). Conclusions: 6 month PFS for the entire cohort continues to be assessed but preliminary results suggest antitumor activity of this agent in recurrent anaplastic glioma.

No significant financial relationships to disclose.

The impact of inhomogeneous tissue anisotropy on potential distribution within head model

This paper investigates the influence of inhomogeneous head tissue conductivity on EEGs. A head model with inhomogeneity of radial and tangential conductivity is built up. Based on this model the EEG signals are calculated using the finite elements method. The results show that the inhomogeneous radial and tangential conductivity of skull tissue, which has been ignored so far, can cause about 5% difference compared with commonly used homogeneous conductivity head models.

Realistic human head model for EEG from both the geometry and conductivity aspects

This paper describes modelling and simulation of a had model which incorporates both the geometries and conductivities of the human head. It focuses on the inclusion of tissue conductivity inhomogeneity in a realistically-shaped head model, and investigates the impact of this inclusion on the potential distribution within the model. The result show that the impact, which has been neglected in realistic head models so far, is significant.

Detection of early atherosclerosis with radiolabeled monocyte chemoattractant protein-1 in prediabeteic Zucker rats

BACKGROUND

Migration of monocytes into the arterial wall is an early finding of atherosclerosis. Monocytes are attracted to sites of vascular endothelial cell injury, the initiating event in the development of atheromatous disease, by a chemokine known as monocyte chemoattractant protein-1 (MCP-1). Injured vascular endothelial and smooth muscle cells selectively secrete MCP-1.

OBJECTIVE

This study was performed to determine if radiolabeled MCP-1 would co-localize at sites of monocyte/macrophage concentration in an experimental model of transplant-induced vasculopathy in diabetic animals.

MATERIALS AND METHODS

Hearts from 3-month-old male Zucker rats, heterozygote (Lean) or homozygote (Fat) for the diabetes-associated gene fa, were transplanted into the abdomens of genetically matched recipients. Lean and Fat animals were then fed normal or high-fat diets for 90 days.

RESULTS

At 90 days significant increases (P < 0.013) of MCP-1 graft uptake were seen at imaging and confirmed on scintillation gamma well counting studies in Lean (n = 5) and Fat (n = 12) animals, regardless of diet, 400 % and 40 %, above control values, respectively. MCP-1 uptake of native and grafted hearts correlated with increased numbers of perivascular macrophages (P < 0.02), as seen by immunostaining with an antibody specific for macrophages (ED 2).

CONCLUSION

Radiolabeled MCP-1 can detect abnormally increased numbers of perivascular mononuclear cells in native and grafted hearts in prediabetic rats. MCP-1 may be useful in the screening of diabetic children for early atherosclerotic disease.

Transplant coronary artery disease: a novel model independent of cellular alloimmune response

BACKGROUND

Allograft coronary atherosclerosis (TxCAD) is the leading cause of death after the first year after transplantation. TxCAD is believed to be a form of chronic rejection of the cardiac allografts. This study was undertaken to determine whether TxCAD could develop in the absence of a cellular alloimmune response.

METHODS AND RESULTS

Inbred lean Zucker rats (>26 generations) served as donors and recipients of the cardiac grafts. Donor hearts were explanted at 60 or 90 days. Explanted hearts were processed for coronary artery histological analysis. Cytokine expression was determined by reverse transcription-polymerase chain reaction, and the presence of T cells within the explanted hearts was evaluated by immunohistochemistry. Forty-six transplantations were made, and TxCAD developed in all but one of the transplanted hearts. Overall, one third of the vessels examined were affected by TxCAD, and in roughly half of these vessels, the disease was severe. Native hearts were free of atherosclerosis. Interleukin-2 was absent from the transplanted hearts, and T cells were present in minimal amounts (<1 per low-power field).

CONCLUSIONS

TxCAD developed in the absence of a cellular alloimmune response in these genetically similar donors and recipients. The observed TxCAD was significant and comparable to what is found in rat allografting models.

Comparison study of different head model structures with homogeneous/inhomogeneous conductivity

Most of the human head models used in dipole localisation research, which have been reported in the literature to date, assume a simplified cranial structure wherein the head is modelled as a set of distinct homogenous tissue compartments. The inherent inhomogeneity of the tissues has so far been ignored in these models due to the difficulties involved in obtaining the conductivity characteristics with sufficiently high enough spatial resolution throughout the head. A technique for developing an inhomogeneous head model based on the generation of pseudo-conductivity values from the existing but sparse conductivity values is proposed in this paper. Comparative studies are conducted on different model structures and different mechanisms for generating the pseudo conductivities. An evaluation of the results of these studies as reported in this paper, shows that contrary to current simplifying assumptions, tissue inhomogeneity has a major influence on the computation of electrical potential distributions in the head.

Presenilin-1 binds cytoplasmic epithelial cadherin, inhibits cadherin/p120 association, and regulates stability and function of the cadherin/catenin adhesion complex

Here we show that presenilin-1 (PS1), a protein involved in Alzheimer's disease, binds directly to epithelial cadherin (E-cadherin). This binding is mediated by the large cytoplasmic loop of PS1 and requires the membrane-proximal cytoplasmic sequence 604-615 of mature E-cadherin. This sequence is also required for E-cadherin binding of protein p120, a known regulator of cadherin-mediated cell adhesion. Using wild-type and PS1 knockout cells, we found that increasing PS1 levels suppresses p120/E-cadherin binding, and increasing p120 levels suppresses PS1/E-cadherin binding. Thus PS1 and p120 bind to and mutually compete for cellular E-cadherin. Furthermore, PS1 stimulates E-cadherin binding to beta- and gamma-catenin, promotes cytoskeletal association of the cadherin/catenin complexes, and increases Ca(2+)-dependent cell-cell aggregation. Remarkably, PS1 familial Alzheimer disease mutant DeltaE9 increased neither the levels of cadherin/catenin complexes nor cell aggregation, suggesting that this familial Alzheimer disease mutation interferes with cadherin-based cell-cell adhesion. These data identify PS1 as an E-cadherin-binding protein and a regulator of E-cadherin function in vivo.