A Phase I/II Dose-Escalation Study Evaluating the Safety of 21 Gy, 23 Gy, and 25 Gy for High Dose Rate (HDR) Prostate Brachytherapy: An Interim Toxicity Report

PURPOSE/OBJECTIVE(S)

Single-fraction high dose rate (HDR) prostate brachytherapy has shown improved actuarial biochemical control rates from 66% to 82% with dose escalation from 19 to 20.5 Gy, respectively, but is still inferior to the reported low dose rate brachytherapy control rates of over 90%. We aimed to identify whether dose escalation to 21, 23, and 25 Gy can be safely accomplished.

MATERIALS/METHODS

Patients with previously untreated, pathologically confirmed, low-risk (cT1-T2a, Gleason ≤6, PSA <10 ng/mL) or favorable intermediate risk (Gleason 3+4, percentage of positive biopsy cores <50%, ≤1 NCCN intermediate risk factor) prostate adenocarcinoma were enrolled from a single institution. PSA and toxicity assessment were performed at baseline and at routine 6-month follow-ups.

RESULTS

From May 9, 2018 to May 12, 2022, 18 patients were enrolled. None had received prior androgen deprivation therapy, 44% had low risk disease, and 61% were ECOG 0 at baseline. Median age was 68 years (total range: 43-79), and 83% were Caucasian. Eight patients received 21 Gy, nine patients received 23 Gy, and one patient received 25 Gy, with the 25 Gy cohort still accruing. The mean prostate size and range, determined by pre-operative prostate volume study on trans-rectal ultrasound, were as follows: 21Gy cohort (mean: 41.2cc; range: 21.9-63.1cc), 23Gy Cohort (mean: 41.2cc, range 28.3-71.7cc), 25Gy cohort (65.3cc). A median of 17 catheters (range: 16-20) were implanted. At a median follow-up of 35.7 months (range: IQR 4.4 - 50.2), only one grade 3 toxicity was reported, which was an ulcerative colitis (UC) flare noted in a patient whose UC was poorly controlled, requiring multiple courses of prednisone in the 6 months prior to his brachytherapy. Regarding toxicities attributable to therapy, fourteen and four patients experienced a grade 1 and 2 genitourinary toxicity respectively; four and four patients experienced a grade 1 and 2 reproductive system toxicity respectively; one patient experienced a grade 1 GI toxicity. Two patients needed foley catheters upon discharge, with neither requiring the foley long term. There were two treatment failures in the 21Gy cohort at 1.39 and 1.67 years from date of HDR brachytherapy; date of failure was defined by the first PSA 2.0ng/mL over nadir. Of these patients, one underwent focal salvage HDR, whilst the other underwent radical prostatectomy with only 1% of the volume involved by prostate cancer. Of note, there was seminal vesicle involvement on restaging prostate biopsy for the patient that underwent radical prostatectomy, however, this was not appreciated on the final prostatectomy specimen. Both patients have no evidence of disease currently.

CONCLUSION

HDR brachytherapy appears well tolerated in patients with low to favorable intermediate risk prostate cancer at 21 and 23 Gy, with more accrual needed at 25Gy. Long-term follow-up needed to assess efficacy.

Association of Managed Medicaid Plans and Cancer Stage at Diagnosis

PURPOSE/OBJECTIVE(S)

Managed care organizations provide insurance to many Medicare (Advantage) and Medicaid beneficiaries and seek to maintain quality while controlling provider networks, utilization, and costs. In prior research, patients with Medicare Advantage plans had restricted access to care, including at cancer centers, and had higher mortality after cancer surgery than patients with traditional Medicare. Over 80% of Medicaid patients nationally are enrolled in managed care plans; despite their prevalence, there is a paucity of evidence regarding the quality of cancer care provided by these plans. We examined associations of state-level managed Medicaid rates and cancer stage at diagnosis.

MATERIALS/METHODS

Adults ages 18-64 years with Medicaid coverage diagnosed with cancer from 2007-2016 were identified from Surveillance, Epidemiology, and End Results program data covering 12 states. Note that 2016 was the last year with unsuppressed insurance status data. Year-varying state-level rates of types of managed Medicaid plans (comprehensive risk-based managed care, limited benefit plans, and primary care case management) were obtained from the Medicaid and CHIP Payment and Access Commission and categorized in quartiles. The association of state levels of each type of managed Medicaid plan with localized stage diagnoses was evaluated using multivariable linear probability models with cluster-robust standard errors (state clusters) accounting for state fixed effects, year fixed effects, age, sex, race, metropolitan residence, marital status, county-level income and education, state Medicaid expansion status, and cancer type.

RESULTS

A total of 229,227 Medicaid patients were identified. The average state-level rates of comprehensive managed care, limited benefit, and primary care case management plans were 47%, 47%, and 5.6%, respectively. In adjusted analyses, relative to states with <20% of Medicaid recipients enrolled in comprehensive managed care plans, states with 40-80% (-2.07 percentage points, 95% CI = -3.31 to -0.83, P = .001) and >80% (-1.49, 95% CI = -2.49 to -0.50, P = .003) had fewer localized stage diagnoses. States with >2% relative to 0-1% of recipients enrolled in primary care case management plans had more localized stage diagnoses (1.02, 95% CI = 0.27 to 1.77, P = .008). States with higher levels of limited benefit plans had more localized stage diagnoses (P = .011), though associations were attenuated with increasing levels (20-40%: 1.22; 40-80%: 0.53; >80%: 0.40). Patterns were similar across most cancer types.

CONCLUSION

The prevalence and type of Medicaid managed care plans are associated with early-stage cancer diagnoses. Higher levels of comprehensive managed care plans were associated with fewer early diagnoses, raising concerns about barriers to symptom evaluation and diagnostic workup. In contrast, higher levels of primary care case management plans were associated with more early diagnoses, potentially through streamlined care coordination.

Disparities in Inpatient Care Including Receipt of Radiotherapy and Mortality in Unhoused Adults with Cancer in the United States

PURPOSE/OBJECTIVE(S)

Cancer is the second leading cause of death among unhoused individuals in the United States. This study aims to assess inpatient care and outcomes of unhoused vs. housed adults with cancer. We hypothesize that unhoused patients receive less intensive care than housed patients during hospitalization.

MATERIALS/METHODS

All hospitalized adults age ≥18 with a principal cancer diagnosis were identified in the 2016-2020 National Inpatient Sample (NIS). Logistic regression models tested for associations between housing status and primary outcomes: care management (i.e., receipt of invasive procedures, systemic therapy, or radiation therapy [RT]) and inpatient death. Adjusted analyses accounted for patient demographics, socioeconomic status, comorbidities, and potential interactions between housing status and length of stay (LOS).

RESULTS

A total of 9,030 unhoused and 2,758,693 housed hospitalized adults with cancer were included in this study. At baseline, there were significant (p<0.05) differences in age <65 years (77% unhoused vs. 41% housed), male sex (75% vs. 53%), race (Black, 25% vs. 13%; White, 58% vs. 71%), and insurance type (Private, 6% vs. 27%; Medicaid, 53% vs. 11%) between groups. There were also differences in the prevalence of certain cancer histologies, including lung (17% vs. 14%) and liver (8% vs. 3%) cancer. Additionally, while comorbidities such as congestive heart failure (18% vs. 15%) and HIV (10% vs. 1%) were more common among unhoused patients, other conditions such as autoimmune disease (21% vs. 26%) and diabetes mellitus (38% vs. 43%) were more common among housed patients. Compared to housed patients, unhoused patients had longer LOS (median 6 vs. 4 days), with 62% hospitalized for ≥5 days (vs. 46%). On adjusted analysis, unhoused patients were less likely to undergo invasive procedures (48% vs. 58%; aOR [95% CI], 0.34 [0.27-0.42]) or receive systemic therapy (6% vs. 8%; 0.41 [0.20-0.85]) while inpatient. There were no significant differences in odds of receipt of RT (2% vs. 1%; 0.85 [0.21-3.41]) or odds of inpatient death (4% vs. 6%; 0.78 [0.52-1.15]) between groups.

CONCLUSION

In this first nationally representative analysis of housing status among hospitalized adults with cancer, unhoused adults were significantly less likely to receive invasive procedures or systemic therapy while inpatient, despite a higher prevalence of certain aggressive cancers and serious comorbidities compared to housed adults. Although there were no significant differences in the receipt of RT or death, disparities in inpatient management among unhoused patients highlight missed opportunities to promote equitable cancer care in this vulnerable population.

State Mandatory Paid Family Leave and Survival among Children with Cancer

PURPOSE/OBJECTIVE(S)

Childhood cancer treatment is often costly and time intensive and may require parents/caregivers to stop working. Since 2012, several states have introduced mandatory paid family leave policies. We hypothesized that such policies, whether by reducing financial toxicity or by providing parents greater flexibility to care for their sick children, would improve outcomes among children with cancer.

MATERIALS/METHODS

Children ages 0-18 years diagnosed with cancer between 2010 and 2019 were identified from the Surveillance, Epidemiology, and End Results program (SEER) database. The primary outcome was overall survival (OS). The exposure of interest was state mandatory paid family leave. Difference-in-differences (DID) analyses with additive hazards regression models were utilized to compare changes in OS from pre- to post- mandatory paid sick leave policy implementation in states with vs. without paid sick leave policies. The models were adjusted for year fixed effects, state fixed effects, state Medicaid expansion status, age, race, sex, metropolitan residence status, county-level income and education, cancer site, cancer stage, and insurance status. Clustered standard errors by state were achieved via the cluster bootstrap. The plausibility of the common trends assumption was tested using event study analyses and was satisfied for all analyses.

RESULTS

A total of 38,053 children with cancer were identified. In adjusted difference-in-differences analyses, there was no significant change in OS in states with vs. without state mandatory paid family leave policies after policy enactment (hazard difference: 0.0001, 95% CI = -0.0002 to 0.0016, P = .47). However, among non-metropolitan residents, 1-year OS improved from 93.0% to 95.5% (2-year OS: 88.6% to 93.4%) in states with mandatory paid family leave policies compared to 92.7% to 92.5% (2-year OS: 88.0% to 87.7%) in states without such policies after policy enactment. This translates to a 2.7% improvement in 1-year OS (5.2%, 2-year OS) (hazard difference: -0.0021, 95% CI = -0.0034 to -0.0005, P = .037). There was no corresponding change for metropolitan residents (hazard DID = 0.0001, P = .47). By cancer site, the largest policy-associated improvements in survival were observed for rhabdomyosarcoma (hazard DID = -0.0037, P = .11), osteosarcoma (hazard DID = -0.0036, P<.001), and Intracranial and intraspinal embryonal tumors (hazard DID = -0.0026, P = .061).

CONCLUSION

State mandatory paid family leave policies were associated with improved survival for some children with cancer, most notably for those residing in non-metropolitan areas. The improvements for non-metropolitan residents may be related to alleviating otherwise increased travel burdens for cancer treatment if treatment occurs out-of-town, where working while taking care of a child is less feasible. These data also suggest a slight narrowing in rural-urban-metropolitan childhood cancer disparities associated with paid family leave policies.

Tumour-associated macrophages drive stromal cell-dependent collagen crosslinking and stiffening to promote breast cancer aggression

Stromal stiffening accompanies malignancy, compromises treatment and promotes tumour aggression. Clarifying the molecular nature and the factors that regulate stromal stiffening in tumours should identify biomarkers to stratify patients for therapy and interventions to improve outcome. We profiled lysyl hydroxylase-mediated and lysyl oxidase-mediated collagen crosslinks and quantified the greatest abundance of total and complex collagen crosslinks in aggressive human breast cancer subtypes with the stiffest stroma. These tissues harbour the highest number of tumour-associated macrophages, whose therapeutic ablation in experimental models reduced metastasis, and decreased collagen crosslinks and stromal stiffening. Epithelial-targeted expression of the crosslinking enzyme, lysyl oxidase, had no impact on collagen crosslinking in PyMT mammary tumours, whereas stromal cell targeting did. Stromal cells in microdissected human tumours expressed the highest level of collagen crosslinking enzymes. Immunohistochemical analysis of biopsies from a cohort of patients with breast cancer revealed that stromal expression of lysyl hydroxylase 2, an enzyme that induces hydroxylysine aldehyde-derived collagen crosslinks and stromal stiffening, correlated significantly with disease specific mortality. The findings link tissue inflammation, stromal cell-mediated collagen crosslinking and stiffening to tumour aggression and identify lysyl hydroxylase 2 as a stromal biomarker.

A bulky glycocalyx fosters metastasis formation by promoting G1 cell cycle progression

Metastasis depends upon cancer cell growth and survival within the metastatic niche. Tumors which remodel their glycocalyces, by overexpressing bulky glycoproteins like mucins, exhibit a higher predisposition to metastasize, but the role of mucins in oncogenesis remains poorly understood. Here we report that a bulky glycocalyx promotes the expansion of disseminated tumor cells in vivo by fostering integrin adhesion assembly to permit G1 cell cycle progression. We engineered tumor cells to display glycocalyces of various thicknesses by coating them with synthetic mucin-mimetic glycopolymers. Cells adorned with longer glycopolymers showed increased metastatic potential, enhanced cell cycle progression, and greater levels of integrin-FAK mechanosignaling and Akt signaling in a syngeneic mouse model of metastasis. These effects were mirrored by expression of the ectodomain of cancer-associated mucin MUC1. These findings functionally link mucinous proteins with tumor aggression, and offer a new view of the cancer glycocalyx as a major driver of disease progression.

Tissue mechanics regulate brain development, homeostasis and disease

All cells sense and integrate mechanical and biochemical cues from their environment to orchestrate organismal development and maintain tissue homeostasis. Mechanotransduction is the evolutionarily conserved process whereby mechanical force is translated into biochemical signals that can influence cell differentiation, survival, proliferation and migration to change tissue behavior. Not surprisingly, disease develops if these mechanical cues are abnormal or are misinterpreted by the cells - for example, when interstitial pressure or compression force aberrantly increases, or the extracellular matrix (ECM) abnormally stiffens. Disease might also develop if the ability of cells to regulate their contractility becomes corrupted. Consistently, disease states, such as cardiovascular disease, fibrosis and cancer, are characterized by dramatic changes in cell and tissue mechanics, and dysregulation of forces at the cell and tissue level can activate mechanosignaling to compromise tissue integrity and function, and promote disease progression. In this Commentary, we discuss the impact of cell and tissue mechanics on tissue homeostasis and disease, focusing on their role in brain development, homeostasis and neural degeneration, as well as in brain cancer.

Integrin-mediated traction force enhances paxillin molecular associations and adhesion dynamics that increase the invasiveness of tumor cells into a three-dimensional extracellular matrix

Mammary tumor cells adopt a basal-like phenotype when invading through a dense, stiffened, 3D matrix. These cells exert higher integrin-mediated traction forces, consistent with a physical motor-clutch model, display an altered molecular organization at the nanoscale, and recruit a suite of paxillin-associated proteins implicated in metastasis.

Metastasis requires tumor cells to navigate through a stiff stroma and squeeze through confined microenvironments. Whether tumors exploit unique biophysical properties to metastasize remains unclear. Data show that invading mammary tumor cells, when cultured in a stiffened three-dimensional extracellular matrix that recapitulates the primary tumor stroma, adopt a basal-like phenotype. Metastatic tumor cells and basal-like tumor cells exert higher integrin-mediated traction forces at the bulk and molecular levels, consistent with a motor-clutch model in which motors and clutches are both increased. Basal-like nonmalignant mammary epithelial cells also display an altered integrin adhesion molecular organization at the nanoscale and recruit a suite of paxillin-associated proteins implicated in invasion and metastasis. Phosphorylation of paxillin by Src family kinases, which regulates adhesion turnover, is similarly enhanced in the metastatic and basal-like tumor cells, fostered by a stiff matrix, and critical for tumor cell invasion in our assays. Bioinformatics reveals an unappreciated relationship between Src kinases, paxillin, and survival of breast cancer patients. Thus adoption of the basal-like adhesion phenotype may favor the recruitment of molecules that facilitate tumor metastasis to integrin-based adhesions. Analysis of the physical properties of tumor cells and integrin adhesion composition in biopsies may be predictive of patient outcome.

Abstract PR05: Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression

Glioblastoma multiforme (GBM) is a malignant glioma whose progression is associated with rampant extracellular matrix (ECM) remodeling. We recently found that GBM ECM stiffness predicts reduced survival in human patients. Instead of collagen fibrosis, which is common in many solid tumors, we showed that GBM stiffening involves increased production of extracellular glycoproteins, glycosaminoglycans, and sugar-binding proteins. Using bioinformatics, we revealed that genes of the glycocalyx (transmembrane glycoproteins and their interacting partners) are disproportionately upregulated in GBM relative to lower grade gliomas. Further, these genes are overexpressed within GBM in the mesenchymal (MES) relative to the proneural (PRO) subtype, the former of which is associated with treatment resistance and relapse. Using mouse models of human GBM, we showed that MES tumors are more lethal than PRO, and present with elevated ECM stiffness and mechanical signaling. To test our hypothesis that mechanical signaling can drive the MES phenotype, we engineered PRO GBM cells with constitutively-elevated integrin signaling. Compared to control PRO cells, these undergo a robust MES-like transition, upregulate bulky glycoprotein expression, and result in stiffer and more lethal tumors. This phenotype was reversed by the inhibition of focal adhesion kinase in MES cells. To test whether an enhanced glycocalyx can directly elevate mechanical signaling, we decorated GBM cells with synthetic glycoprotein polymers. Indeed, this resulted in enhanced integrin-focal adhesion signaling and more aggressive tumor progression. The invasive properties and therapy resistance observed in mesenchymal tumor cells are often associated with elevated stem cell-like features. To investigate a link between the glycocalyx, tissue mechanics, and the mesenchymal-stem cell phenotype, we interfered with components of the gylcocalyx or mechanical signaling machinery and found a reduction in stem cell genes and surface proteins, as well as increased sensitivity to chemotherapy. These data support a model in which glycoprotein-mediated tissue stiffening drives GBM aggression through promotion of a mesenchymal phenotype.

This abstract is also being presented as Poster A39.

Citation Format: J. Matthew Barnes, Elliot C. Woods, Russell O. Bainer, Yekaterina A. Miroshnikova, Kan Lu, Gabriele Bergers, Carolyn Bertozzi, Valerie M. Weaver. Glycoprotein-mediated tissue mechanics regulate glioblastoma aggression. [abstract]. In: Proceedings of the AACR Special Conference on Engineering and Physical Sciences in Oncology; 2016 Jun 25-28; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2017;77(2 Suppl):Abstract nr PR05.

Abstract PR10: A glycoprotein-mediated mechanical switch promotes glioma aggression

Glioblastoma multiforme (GBM) is a malignant brain tumor whose progression is associated with rampant extracellular matrix (ECM) remodeling. We recently found that ECM stiffness correlates with poor survival in human GBM specimens. Glycoproteins are the major constituent of normal brain ECM and many are overexpressed in brain tumors, yet the interplay between glycoproteins and mechanical signaling in GBM pathogenesis remains poorly understood. Here, we show that bulky glycoproteins and sugar-binding proteins are broadly upregulated in GBM relative to lower grade gliomas. Further, these genes are overexpressed in the mesenchymal (Mes) relative to the proneural (Pro) GBM subclass, the former of which is associated with treatment resistance and relapse. We took a specific interest in the hyaluronic acid (HA)-producing enzyme, HAS2, and the galactoside-binding lectin galectin-1 (Gal1) due to their ability to modulate tissue structure and rheology. Using mouse models of human GBM we showed that Mes tumors are enriched in HA and fibronectin, coincident with elevated ECM stiffness and mechanical signaling. These data suggest the possibility that aberrant glycoprotein expression drives GBM aggression through enhanced mechanical signaling resulting from tissue stiffening. Consistent with this hypothesis, by elevating mechanical signaling in Pro GBMs we induce a robust Mes-like transition and we see the opposite when reducing Gal1 expression or HA content in Mes tumors. Our data provides evidence of a feed-forward mechanism whereby mechanical signaling drives Gal1 and HA production which reinforce ECM stiffness, thus sustaining pro-tumorigenic mechanical signaling.

This abstract is also presented as Poster A21.

Citation Format: J Matthew Barnes, Yekaterina A. Miroshnikova, Jason C. Tung, Russel O. Bainer, Valerie M. Weaver. A glycoprotein-mediated mechanical switch promotes glioma aggression. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr PR10.

Fighting the force: Potential of homeobox genes for tumor microenvironment regulation

Tumor cells exist in a constantly evolving stromal microenvironment composed of vasculature, immune cells and cancer-associated fibroblasts, all residing within a dynamic extracellular matrix. In this review, we examine the biochemical and biophysical interactions between these various stromal cells and their matrix microenvironment. While the stroma can alter tumor progression via multiple mechanisms, we emphasize the role of homeobox genes in detecting and modulating the mechanical changes in the microenvironment during tumor progression.

Tumor mechanics and metabolic dysfunction

Desmosplasia is a characteristic of most solid tumors and leads to fibrosis through abnormal extracellular matrix (ECM) deposition, remodeling, and posttranslational modifications. The resulting stiff tumor stroma not only compromises vascular integrity to induce hypoxia and impede drug delivery, but also promotes aggressiveness by potentiating the activity of key growth, invasion, and survival pathways. Intriguingly, many of the protumorigenic signaling pathways that are mechanically activated by ECM stiffness also promote glucose uptake and aerobic glycolysis, and an altered metabolism is a recognized hallmark of cancer. Indeed, emerging evidence suggests that metabolic alterations and an abnormal ECM may cooperatively drive cancer cell aggression and treatment resistance. Accordingly, improved methods to monitor tissue mechanics and metabolism promise to improve diagnostics and treatments to ameliorate ECM stiffening and elevated mechanosignaling may improve patient outcome. Here we discuss the interplay between ECM mechanics and metabolism in tumor biology and suggest that monitoring these processes and targeting their regulatory pathways may improve diagnostics, therapy, and the prevention of malignant transformation.

Abstract B04: The role of mechanical force and integrin-ECM signaling in glioblastoma aggression

Glioblastoma multiforme (GBM) is characterized by extensive angiogenesis, inflammation, and edema. These changes are associated with increased extracellular matrix (ECM) deposition and stiffness as well as increased intracranial pressure and tissue compression. Our lab has shown that stiffened ECM leads to enhanced integrin signaling and cell contractility, which promotes tumor cell invasion and progression of breast cancer. We therefore hypothesized that the unique force environment of brain tumors promotes aggressive behavior of GBM cells through similar mechanisms.

We began by testing whether a correlation exists between malignancy and the ECM makeup and tensional state of GBM tumors. GBMs have recently been grouped into molecular subclasses, including proneural and mesenchymal, which are predictive of better and worse response to therapy and patient survival, respectively. Using mouse orthotopic xenografts we showed that, compared to proneural, mesenchymal tumors exhibit increased ECM content, integrin clustering, focal adhesions and myosin activity; predictive of a stiffer tumor with greater tumor cell contractility. This data suggests a negative correlation between patient survival and the tension state of the tumor. Whether an increased force environment is a result or a driver of GBM progression is unclear. To test the idea that an increased force environment can drive a proneural-mesenchymal transition we cultured cells on ECM gels of increasing stiffness (ranging from 0.4-40.0kPa, where normal brain is on average less than 1.0kPa and mesenchymal xenografts are ~2.5kPa). While the morphology of mesenchymal cells was similar on all gels, proneural cells plated on gels greater than 2.7kPa adopted a morphology and transcriptional state reminiscent of mesenchymal cells. Quantitative PCR and immunofluorescence staining revealed significant increases in the mesenchymal markers N-cadherin, fibronectin, vimentin, TGFβ, ZEB1, and nuclear (active) YAP. Antibody blocking of beta1 integrin and small molecule inhibition of focal adhesion kinase or ROCK led to partial rescue of proneural morphology and gene expression. Thus integrin-ECM engagement and myosin activity are necessary for this apparent proneural-mesenchymal transition. The results of increased substrate rigidity were mimicked by enhancing beta1 integrin clustering (through expression of the ITGB1V737N mutant developed in our lab).

Collectively these findings suggest that mechanical forces, arising through enhanced cell-ECM interactions and transduced via integrin-focal adhesion signaling, act to drive a mesenchymal, malignant state in GBM cells. In vivo experiments interrogating the effect of forced integrin clustering and cell contractility on GBM aggressiveness and progression are ongoing.

Citation Format: J. Matthew Barnes, Valerie M. Weaver. The role of mechanical force and integrin-ECM signaling in glioblastoma aggression. [abstract]. In: Proceedings of the Third AACR International Conference on Frontiers in Basic Cancer Research; Sep 18-22, 2013; National Harbor, MD. Philadelphia (PA): AACR; Cancer Res 2013;73(19 Suppl):Abstract nr B04.

Resistance to fluid shear stress is a conserved biophysical property of malignant cells

During metastasis, cancer cells enter the circulation in order to gain access to distant tissues, but how this fluid microenvironment influences cancer cell biology is poorly understood. A longstanding view is that circulating cancer cells derived from solid tissues may be susceptible to damage from hemodynamic shear forces, contributing to metastatic inefficiency. Here we report that compared to non-transformed epithelial cells, transformed cells are remarkably resistant to fluid shear stress (FSS) in a microfluidic protocol, exhibiting a biphasic decrease in viability when subjected to a series of millisecond pulses of high FSS. We show that magnitude of FSS resistance is influenced by several oncogenes, is an adaptive and transient response triggered by plasma membrane damage and requires extracellular calcium and actin cytoskeletal dynamics. This novel property of malignant cancer cells may facilitate hematogenous metastasis and indicates, contrary to expectations, that cancer cells are quite resistant to destruction by hemodynamic shear forces.

Abstract 436: Resistance to fluid shear stress is a conserved novel biophysical property of malignant cells

During metastasis, cancer cells access distant tissues via the circulation but how this fluid microenvironment influences cancer cell biology is poorly understood. It has been suggested that physical destruction of carcinoma cells due to exposure to hemodynamic forces during circulation is a barrier to metastasis. Here we report that transformed cells are remarkably resistant to fluid shear stress (FSS) in a novel microfluidic protocol. When subjected to a series of millisecond pulses of high FSS, transformed cells exhibit a biphasic decrease in viability. Significantly, human red and white blood cells survived the forces in this protocol. In stark contrast, non-transformed epithelial cells are markedly more susceptible to death under FSS. Accordingly, we show that FSS resistance is a property conferred by oncogenes. We reveal FSS resistance to be a transient and adaptive response triggered by plasma membrane damage and mediated by both extracellular calcium influx and dynamic reorganization of the actin cytoskeleton. This property of malignant cancer cells may facilitate hematogenous metastasis and indicates, contrary to expectations, that cancer cells are quite resistant to FSS. Thus, destruction of circulating cancer cells by hemodynamic shear is not likely to limit metastasis. Our data suggest that FSS resistance is a biophysical biomarker which may be used to rapidly discriminate between malignant and benign cells and, by virtue of representing phenotypic integration of oncogenic transformation, may be more tractable than conventional molecular biomarkers.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 436. doi:1538-7445.AM2012-436

Capture-recapture to estimate completeness of tuberculosis surveillance in two communities in South Africa

BACKGROUND

Reliable surveillance is essential for any tuberculosis (TB) control programme; however, under-registration of TB cases due to under-notification of patients on treatment or failure to initiate treatment has been well-documented internationally.

OBJECTIVE

To determine the contribution of capture-recapture methods in estimating the completeness of bacteriologically confirmed pulmonary TB registration in two high-incident communities in South Africa.

METHODS

Record linkage between the TB treatment register and two laboratory sputum TB result registers and three-source log-linear capture-recapture analysis.

RESULTS

The number of bacteriologically confirmed pulmonary TB cases in the TB treatment register was 243, with an additional 63 cases identified in the two laboratory databases, resulting in 306 TB cases. The observed completeness of the TB treatment register was 79%. The log-linear model estimated 326 (95%CI 314-355) TB cases, resulting in an estimated completeness of registration of 75% (95%CI 68-77).

CONCLUSION

Capture-recapture can be useful in evaluating the completeness of TB control surveillance and registration, including in resource-limited settings; however, methodology and results should be carefully assessed. Interventions are needed to increase the completeness of registration and to reduce the number of initial defaulters.

The ARF tumor suppressor inhibits tumor cell colonization independent of p53 in a novel mouse model of pancreatic ductal adenocarcinoma metastasis

Pancreatic ductal adenocarcinoma (PDAC) is an incurable, highly metastatic disease that is largely resistant to existing treatments. A better understanding of the genetic basis of PDAC metastasis should facilitate development of improved therapies. To that end, we developed a novel mouse xenograft model of PDAC metastasis to expedite testing of candidate genes associated with the disease. Human PDAC cell lines BxPC-3, MiaPaCa-2, and Panc-1 stably expressing luciferase were generated and introduced by intracardiac injections into immunodeficient mice to model hematogenous dissemination of cancer cells. Tumor development was monitored by bioluminescence imaging. Bioluminescent MiaPaCa-2 cells most effectively recapitulated PDAC tumor development and metastatic distribution in vivo. Tumors formed in nearly 90% of mice and in multiple tissues, including normal sites of PDAC metastasis. Effects of p14ARF, a known suppressor of PDAC, were tested to validate the model. In vitro, p14ARF acted through a CtBP2-dependent, p53-independent pathway to inhibit MiaPaCa-2-invasive phenotypes, which correlated with reduced tumor cell colonization in vivo. These findings establish a new bioluminescent mouse tumor model for rapidly assessing the biological significance of suspected PDAC metastasis genes. This system may also provide a valuable platform for testing innovative therapies.

Accuracy and completeness of recording of confirmed tuberculosis in two South African communities

BACKGROUND

Although tuberculosis (TB) treatment registers and laboratory records are essential tools for recording and reporting in TB control programmes, the accuracy and completeness of routinely collected data are seldom monitored.

OBJECTIVE

To assess the accuracy and completeness of TB treatment register data in two South African urban communities using record linkage.

METHODS

All cases of bacteriologically confirmed TB, defined as two smear-positive results and/or at least one culture-positive result, were included. Record linkage was performed between three data sources: 1) TB treatment registers, 2) the nearest central laboratory, and 3) the referral hospital laboratory.

RESULTS

The TB treatment registers had 435 TB cases recorded, of which 204 (47%) were bacteriologically confirmed. An additional 39 cases recorded as non-bacteriological cases in the TB treatment registers were reclassified as bacteriologically confirmed, and 63 bacteriologically confirmed cases were identified from the laboratory databases that were not recorded in the TB treatment registers. The final number of bacteriologically confirmed TB cases was 306, giving an increase of 50%.

CONCLUSIONS

The accuracy and completeness of the TB treatment register and central laboratory data were inadequate. A high percentage of bacteriologically confirmed cases from both laboratories were not recorded in the TB treatment registers. We are developing an electronic result management system to improve the management of laboratory results.

ZEB1 coordinately regulates laminin-332 and {beta}4 integrin expression altering the invasive phenotype of prostate cancer cells

Metastasis involves the invasion of cancer cells across both the extracellular matrix and cellular barriers, and an evolving theme is that epithelial-to-mesenchymal transition (EMT) may mediate invasive cellular behavior. Previously, we isolated and analyzed a subpopulation of PC-3 prostate cancer cells, TEM4-18, and found that these cells both invaded an endothelial barrier more efficiently and exhibited enhanced metastatic colonization in vivo. Transendothelial migration of these cells depended on expression of ZEB1, a known regulator of EMT. Surprisingly, these cells were much less invasive than parental PC-3 cells in assays that involve matrix barriers. Here, we report that TEM4-18 cells express significantly reduced levels of two subunits of laminin-332 (β3 and γ2) and that exogenous laminin-332, or co-culture with laminin-332-expressing cells, rescues the in vitro invasion phenotype in these cells. Stable knockdown of ZEB1 in prostate cancer cells up-regulated LAMC2 and ITGB4 mRNA and protein and resulted in a concomitant increase in Transwell migration. Using chromatin immunoprecipitation (ChIP), we show that ZEB1 directly interacts with the promoters of LAMC2 and ITGB4. These results provide a novel molecular basis for reduced laminin-332 observed in clinical prostate cancer specimens and demonstrate a context-dependent role for EMT in invasive cellular behavior.

Endothelin-1 inhibits prostate cancer growth in vivo through vasoconstriction of tumor-feeding arterioles

The vasoactive peptide endothelin-1 (ET-1) has been implicated in promoting the progression of prostate and other cancers though its precise mechanism(s)-of-action remain unclear. To better define the role of ET-1 in prostate cancer progression, we generated prostate cancer cell lines (PC-3 and 22Rv1) that express elevated levels of ET-1. As anticipated, increased ET-1 lead to modest autocrine growth stimulation of PC-3 cells in monolayer culture and increased colony formation in soft agar by both cell lines. Unexpectedly, however, metastatic colonization of 22Rv1 cells expressing elevated levels of ET-1 was reduced, as was the size of subcutaneous tumors produced by both 22Rv1- and PC-3 cells. Based on these data, we hypothesized that high levels of ET-1 may negatively impact the tumor microenvironment. We found that increased ET-1 expression did not consistently inhibit angiogenesis, indicating that this was not the cause of poor tumor growth. As an alternative explanation, we examined whether elevated ET-1 results in local vasoconstriction and thus reduces the blood supply available to the tumor. Consistent with this hypothesis, treatment of mice bearing PC-3 xenografts with a vasodilator increased tumor perfusion and partially restored tumor growth. Moreover, analysis of tumor vascular casts indicated vasoconstriction of tumor-feeding arterioles. Taken together, our data suggest that the local concentration of the ET-1 peptide is critical for determining a balance between its previously unrecognized tumor growth-suppressing activity (vasoconstriction) and known growth-promoting (mitogenesis, survival and angiogenesis) activities. These findings may have implications for the modification of current prostate cancer therapies involving ET-1.

Application of stereolithographic custom models for studying the impact of biofilms and mineral precipitation on fluid flow

Here we introduce the use of transparent experimental models fabricated by stereolithography for studying the impacts of biomass accumulation, minerals precipitation, and physical configuration of flow paths on liquid flow in fracture apertures. The internal configuration of the models ranged in complexity from simple geometric shapes to those that incorporate replicated surfaces of natural fractures and computationally derived fracture surfaces. High-resolution digital time-lapse imaging was employed to qualitatively observe the migration of colloidal and soluble dyes through the flow models. In this study, a Sphingomonas sp. and Sporosarcina (Bacillus) pasteurii influenced the fluid dynamics by physically altering flow paths. Microbial colonization and calcite deposition enhanced the stagnant regions adjacent to solid boundaries. Microbial growth and calcite precipitation occurred to a greater extent in areas behind the fabricated obstacles and less in high-velocity orifices.

Constraints facing the female medical practitioner in private family practice in the Western Cape

OBJECTIVES

To assess the existence and extent of employment-related problems facing female family practitioners in the context of a rapidly growing number of female doctors in South Africa.

SUBJECTS AND METHODS

A descriptive survey was conducted using bilingual questionnaires. These were posted to all 280 female family practitioners in private practice in the Western Cape.

RESULTS

Of the 280 questionnaires posted 169 were returned, but 45 of these were missampled. A response rate of 53% was obtained. The largest age category was 30-39 years. Of those not in solo practice, 68 (75%) were able to negotiate the terms of their working hours, 13 (19%) negotiated sick leave on commencing work, and only half had paid leave. Vacation leave was negotiated by 34 (50%), while only 6 (9%) discussed maternity leave with employers or colleagues. Of the 124 practices included in the survey, 6 (5%) had formal arrangements to cope with maternity leave. One hundred and seven respondents (86%) felt there was a need for maternity leave guidelines in the private sector in South Africa. Regarding practice-related problems, 33 female family practitioners (27%) reported some incidents of sexual harassment by patients. Despite these constraints, 88 respondents (71%) planned to continue working in this field.

CONCLUSION

Definite obstacles exist in private family practice with regard to working conditions, in particular the lack of national regulations regarding maternity leave and the absence of legislation on pregnancy discrimination. This has important implications for the inclusion of female doctors in group practices and managed health care organisations--private primary health care of the present and future!

Selenium reduction by a denitrifying consortium

A denitrifying bacterial consortium obtained from the Pullman, Washington wastewater treatment facility was enriched under denitrifying conditions and its ability to reduce selenite and selenate was studied. Replicate experiments at two different experimental conditions were performed. All experiments were performed under electron-acceptor limiting conditions, with acetate as the carbon source and nitrate the electron acceptor. In the first set of experiments, selenite was present, whereas, in the second set, selenate was added. A significant lag period of approximately 150 h was necessary before selenite or selenate reduction was observed. During this lag period, nitrate and nitrite use was observed. Once selenite or selenate reduction had started, nitrate and nitrite reduction was concomitant with selenium species reduction. Trace amounts of selenite were detected during the selenate reduction study. Analysis of the data indicates that, once selenium species reduction was induced, the rate of reduction was proportional to the selenium species concentration and to the biomass concentration. Furthermore, at similar biomass and contaminant concentrations, selenite reduction is approximately four times faster than selenate reduction. Copyright 1999 John Wiley & Sons, Inc.

Distribution of S(-)-zacopride-insensitive [125I]R(+)-zacopride binding sites in the rat brain and peripheral tissues

Increasing evidence indicates that the 5-HT3 receptor antagonist R(+)-zacopride labels an additional site in brain tissue that is not sensitive to 5-HT (non-5-HT R(+)-zacopride site, R(+)-site). Since the levels of R(+)-sites in the brain are relatively low, the present studies explored the use of [125I]R(+)-zacopride to label the R(+)-site; the incorporation of an [125I] atom considerably increasing the specific activity of the radioligand relative to [3H]R(+)-zacopride that has been utilised previously. Competition experiments with [125I]R(+)-zacopride (1.0 nM) binding to rat whole brain homogenates, in the presence of the 5-HT3 receptor antagonist granisetron (1.0 microM), identified that R(+)-zacopride and prazosin bound to two sites (pIC50: 7.59 and 5.28, respectively, for R(+)-zacopride; 6.75 and 4.42, respectively, for prazosin) whereas S(-)-zacopride and mianserin possessed relatively low affinity (pIC50: 4.37 and 3.80, respectively) while (-)sulpiride and 5-HT failed to compete for [125I]R(+)-zacopride binding at concentrations up to 10 microM. Autoradiographic radioligand binding studies using [125I]R(+)-zacopride (0.5 nM) identified a heterogeneous distribution of specific binding sites (defined by unlabelled R(+)-zacopride, 1.0 microM) throughout the rat brain. In the presence of a saturating concentration of granisetron (1.0 microM), highest levels of specific [125I]R(+)-zacopride, binding sites (defined by R(+)-zacopride, 1.0 microM; R(+)-site), were detected in the olfactory tubercle, thalamus, corpus callosum, colliculus, dorsal and median raphe nucleus, spinal cord and the pons (8.0-13.0 fmol/mg). Moderate densities of R(+)-sites were located in the striatum, nucleus accumbens, substantia nigra, ventral tegmental area, globus pallidus, septal nuclei, frontal cortex and cerebellum (2.0-7.9 fmol/mg). In the hippocampus, amygdala and cortical areas. R(+)-site levels were low but detectable (0.1-1.9 fmol/mg). [125I]R(+)-zacopride labelled R(+)-sites were also detected in some rat peripheral tissues, for instance kidney cortex, adrenal gland and liver (2.4-6.8 fmol/mg). The present results indicate that specific non-5-HT [125I]R(+)-zacopride sites are heterogeneously distributed throughout the rat brain and are expressed in various peripheral tissues.

Autoradiographic distribution of [3H]-(S)-zacopride-labelled 5-HT3 receptors in human brain

Autoradiographic binding studies using the 5-HT3 (5-hydroxytryptamine3) receptor radioligand, [3H]-(S)-zacopride (0.5 nM), identified a heterogeneous distribution of specific binding sites (defined by granisetron, 1 microM) throughout the human brain. Highest radiolabelled 5-HT3 receptor densities were detected in discrete nuclei within the brainstem (nucleus tractus solitarius, area postrema, spinal trigeminal nerve nucleus; 50-200 fmol/mg tissue equivalent) with more modest levels of expression in the forebrain (e.g. hippocampus, nucleus accumbens, putamen, caudate; 4-17 fmol/mg tissue equivalent). Within the hippocampal formation, radiolabelled 5-HT3 receptors were differentially distributed with highest levels in the granule cell layer of the dentate gyrus. Saturation studies with [3H]-(S)-zacopride (0.05-16 nM; non-specific binding defined by granisetron, 10 microM) binding to homogenates of human putamen indicated that [3H]-(S)-zacopride (0.05-16 nM; non-specific binding defined by granisetron, 10 microM) binding to homogenates of human putamen indicated that [3H]-(S)-zacopride labelled an apparently homogenous population of binding sites (Bmax = 72 + 7 fmol mg-1 protein, pKd = 8.69 +/- 0.09, Hill coefficient = 0.99 +/- 0.06, mean +/- SEM, n = 4). The pharmacological profile of [3H]-(S)-zacopride binding to homogenates of putamen indicated the selective labelling of the human variant of the 5-HT3 receptor. The marked differences, however, in the pharmacology (e.g. low affinity for D-tubocurarine) and relative distribution (e.g. presence of 5-HT3 receptors in the human extrapyramidal system) of 5-HT3 receptors in the human forebrain when compared with other species further necessitates caution in predicting clinical responses based on data generated in animal models of disease.

Barriers to compliance with OBRA'90 regulations in community pharmacies

OBJECTIVE

To identify which barriers have been most significant to community pharmacists in their ability to comply with the Omnibus Budget Reconciliation Act of 1990 (OBRA'90) regulations during its first year of implementation.

METHODS

Mailing of a two-page survey in April 1994.

SETTING

Four hundred randomly selected community pharmacies in the Commonwealth of Massachusetts.

PARTICIPANTS

Of 400 pharmacies surveyed, 156 surveys were completed and returned for analysis.

RESULTS

Barriers that were considered most significant to pharmacies surveyed in their ability to implement OBRA'90 regulations were excessive workload, lack of financial compensation, and patients' attitudes. Of least significance were inadequate knowledge about drugs, inadequate references, and store layout. Almost half the responding pharmacists indicated that OBRA'90 regulations had not affected or changed their practice, one-quarter of the pharmacists believed their practice was less rewarding after OBRA'90, and about one-fifth believed it was more rewarding.

CONCLUSIONS

Community pharmacists in Massachusetts are making an attempt to comply with OBRA'90, but there are specific barriers that are affecting their ability to do so. The OBRA'90 regulations appear to have had little impact on the practice of most community pharmacies. Community pharmacy management needs to examine (1) expanded roles of supportive personnel to give pharmacists more time to spend counseling patients, (2) reimbursement mechanisms for cognitive service, and (3) approaches to educating patients about these changes in the pharmacy profession.

Regulation of glutamate release by presynaptic kainate receptors in the hippocampus

Most reported actions of kainate are mediated by AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate) receptors. Here we report that, unlike AMPA which stimulates, kainate elicits a dose-dependent decrease in L-glutamate release from rat hippocampal synaptosomes and also depresses glutamatergic synaptic transmission. Brief exposure to kainate inhibited Ca(2+)-dependent [3H]L-glutamate release by up to 80%. Inhibition was reversed by kainate antagonists but not by the AMPA-selective non-competitive antagonist 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466). A corresponding reversible kainate-evoked depression of NMDA (N-methyl-D-aspartate) receptor-mediated excitatory postsynaptic currents (e.p.s.cs) was observed when AMPA receptors were blocked by GYKI 52466. The synaptic depression was preceded by a brief period of enhanced release and a small inward current was also observed. The effects of kainate were unaffected by metabotropic glutamate (mGlu), GABAA, GABAB, glycine and adenosine receptor antagonists. These results indicate that glutamate release can be modulated directly by kainate autoreceptors.

Cyclothiazide unmasks AMPA-evoked stimulation of [3H]-L-glutamate release from rat hippocampal synaptosomes

The effect of alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA) on Ca(2+)-sensitive, tetrodotoxin (TTX)-insensitive K(+)-stimulated [3H]-L-glutamate release from rat hippocampal synaptosomes was determined. AMPA in the presence, but not in the absence of cyclothiazide, a drug which blocks AMPA receptor desensitization, elicited a dose-dependent increase in K(+)-stimulated [3H]-L-glutamate release but had no effect on basal release. The AMPA/cyclothiazide stimulation was blocked by CNQX and by GYKI 52466, an antagonist at the cyclothiazide site. These results indicate that AMPA receptors are present on presynaptic terminals and suggest that they may play a role in the regulation of neurotransmitter release.

Quantitative analysis of the distributions of glutamatergic ligand binding sites in goldfish brain

Goldfish brain is a widely used model system for the study of the mechanisms involved in neuronal regeneration and synaptic plasticity. Because of the proposed role of glutamate receptors in these processes we have investigated the anatomical localisations of [3H]AMPA (alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate), [3H]kainate, [3H]CNQX (6-cyano-7-nitroquinoxaline-2,3-dione) and [3H]L-glutamate binding sites in horizontal and sagittal sections. Binding sites for [3H]L-glutamate were the most widespread and both NMDA (N-methyl-D-aspartate) and non-NMDA sensitive components were detected. The density of [3H]kainate binding was very high in the cerebellum compared to other regions and in comparison with the other radioligands used. Conversely, relatively low amounts of [3H]AMPA binding were present with the telencephalon being the most densely labelled structure. [3H]CNQX binding was most densely localised in the tectum with the cerebellum also possessing high binding. In addition, there was a small population of [3H]CNQX binding sites located in the telencephalon and lobus vagi that appeared insensitive to AMPA and kainate.

Interaction of guanine nucleotides with [3H]kainate and 6-[3H]cyano-7-nitroquinoxaline-2,3-dione binding in goldfish brain

Recent reports have suggested that a major proportion of [3H]kainate binding in goldfish brain is to a novel form of G-protein-linked glutamate receptor. Here we confirm that guanine nucleotides decrease [3H]kainate binding in goldfish brain membranes, but that binding is also reduced to a similar extent under conditions where G-protein modulation should be minimised. Inclusion of GTP gamma S resulted in an approximately twofold decrease in the affinity of [3H]kainate binding and a 50% reduction in the apparent Bmax values in both Mg2+/Na+ and Mg2+/Na(+)-free buffer when assayed at 0 degrees C. The pharmacology of [3H]kainate binding is similar to that of well-characterised ionotropic kainate receptors but unlike that of known metabotropic glutamate receptors, with neither 1S,3R-amino-1,3-cyclopentanedicarboxylic acid (1S,3R-ACPD) nor ibotenic acid being effective competitors. The molecular mass of the [3H]kainate binding protein, as determined by radiation inactivation, was 40 kDa, similar to the subunit sizes of other lower vertebrate kainate binding proteins that are believed to comprise ligand-gated ion channels. Furthermore, GTP gamma S also inhibited the binding of the non-NMDA receptor-selective antagonist 6-[3H]cyano-7-nitroquinoxaline-2,3-dione. These data strongly suggest that the regulatory interaction between guanine nucleotides and [3H]kainate and 6-[3H]cyano-7-nitroquinoxaline-2,3-dione binding is complex and involves competition at the agonist/antagonist binding site in addition to any G-protein-mediated modulation.

Autoradiographic distribution of glutamatergic ligand binding sites in Xenopus brain: evidence for intracellular [3H]AMPA binding sites

The binding of a series of [3H]glutamatergic ligands was determined by receptor autoradiography of membrane homogenate pellets and horizontal sections of Xenopus brain. Consistent with previous reports that a 'unitary' glutamate receptor is present in Xenopus CNS, the radioligands showed similar densities of binding sites in the membrane homogenate pellets. Furthermore, [3H]kainate binding was completely displaced by AMPA or CNQX, [3H]AMPA binding was completely displaced by kainate or CNQX and [3H]CNQX binding was completely displaced by AMPA or kainate. However, in whole brain sections there were apparently 2- to 5-fold more [3H]AMPA and [3H]CNQX than [3H]kainate sites. The absence of these extra sites in broken-washed membrane preparations suggests that the additional [3H]AMPA and [3H]CNQX binding may be due to cytosolic sites. The observation that all [3H]AMPA and [3H]CNQX binding in the brain sections is displaced by kainate indicates that the putative cytosolic sites are sensitive to relatively high concentrations of kainate but that they differ from the previously characterised Xenopus CNS unitary receptors.

Molecular size of the kainate binding protein in goldfish brain determined by radiation inactivation

Radiation inactivation analysis was used to estimate the target size of a putative glutamate receptor subtype in goldfish brain. A simple, linear inactivation curve was obtained. The calculated molecular size of the [3H]kainate binding site was 33.8 kDa. The results presented here are comparable to the molecular masses determined for putative glutamate receptors in other lower vertebrates but are markedly different from the sizes of the corresponding glutamate receptor subtypes in mammalian central nervous system.

Differential binding characteristics of agonists at 5-HT3 receptor recognition sites in NG108-15 neuroblastoma-glioma cells labelled by [3H]-(S)-zacopride and [3H]granisetron

The pharmacological characteristics of 5-HT3 receptor (5-hydroxytryptamine3 receptor) recognition sites labelled with [3H]-(S)-zacopride and [3H]granisetron in membranes prepared from NG108-15 neuroblastoma-glioma cells were directly compared to investigate further differences in the binding characteristics of these two radioligands. Competition curves generated with increasing concentrations of 5-HT3 receptor ligands emphasized the pharmacological similarity of the two recognition sites labelled by [3H]-(S)-zacopride and [3H]granisetron. However, analysis of the nature of the competition curves indicated that 5-HT3 receptor agonists (5-hydroxytryptamine, 2-methyl-5-hydroxytryptamine, phenylbiguanide) and quipazine generated Hill coefficients greater than unity when the 5-HT3 receptor recognition sites were labelled with [3H]granisetron whilst these competing compounds displayed Hill coefficients of around unity when the sites were labelled with [3H]-(S)-zacopride. Competition for either [3H]-(S)-zacopride or [3H]granisetron binding by the 5-HT3 receptor antagonists granisetron and ondansetron generated Hill coefficients around unity. Furthermore, addition of unlabelled (S)-zacopride (1.0 nM) failed to alter the nature by which quipazine competed for the [3H]granisetron-labelled 5-HT3 receptor recognition site. Consistent with 5-HT3 receptors radiolabelled in rat cortical membranes, the present studies indicate that [3H]-(S)-zacopride may label a different site on the 5-HT3-receptor complex compared to [3H]granisetron.

Identification and characterisation of angiotensin II receptor subtypes in human brain

Autoradiographic and homogenate binding studies using the radioligand, [125I]angiotensin II, identified a heterogeneous distribution of specific binding sites (defined by angiotensin II, 1.0 microM) throughout the human forebrain. Highest AT receptor densities were detected in the paraventricular nucleus, median eminence, substantia nigra, putamen and caudate nucleus (2.4, 1.2, 1.0, 0.30 and 0.24 fmol/mg tissue equivalent, respectively). The AT1 receptor antagonist, losartan (1.0 microM) competed for the majority of the specific binding. [125I]Angiotensin II-specific binding (although not consistently above non-specific binding levels) was also detected in various other brain regions (e.g. amygdala, entorhinal cortex, frontal cortex, hippocampus, inferior colliculus, nucleus accumbens, parietal cortex, periaquaductal grey, superior colliculus, striate cortex, temporal cortex, thalamus). In the presence of losartan (1.0 microM), angiotensin II, saralasin, losartan and PD123177 competed for [125I]angiotensin II binding to membranes prepared from the cerebellum or substantia nigra with a rank order of affinity; angiotensin II = saralasin > PD123177 > losartan. In the presence of PD123177 (1.0 microM), the rank order of affinity of losartan and PD123177 was reversed. These studies indicate the presence of both AT1 and AT2 receptor subtypes within various regions of the human forebrain.