Where do we go from here? - Opportunities and barriers to the career development of trial managers: a survey of UK-based trial management professionals.

BACKGROUND: Clinical trials commonly have a dedicated trial manager and effective trial management is essential to the successful delivery of high-quality trials. Trial managers have diverse experience and currently there is no standardised structured career pathway. The UK Trial Managers' Network (UKTMN) surveyed its members to understand what is important to them with respect to career development since this would be important in the development of any initiative intended to develop a skilled workforce. METHODS: We conducted an online survey of UKTMN members, who are trial management professionals, working on academic-led trials in the UK. Members were asked what they perceive as opportunities and barriers to career development. Two reminders were sent to facilitate completion of the survey, and responders were offered the opportunity to enter a prize draw for waived fees at the UKTMN annual meeting. Data were analysed descriptively by using Stata (version 15.1), and free-text responses were reviewed for themes. RESULTS: The survey was sent to 819 UKTMN members; 433 responses were received, although 13 were from non-UKTMN members; thus 420 respondents' data were included in analyses. Respondents were representative of UKTMN membership; however, more responses were received by trial managers based in registered clinical trials units (CTUs). The top three opportunities for career development were (i) training, (ii) helping design trials and (iii) undertaking relevant qualifications. The top three barriers were (i) funding, (ii) few opportunities to get involved in development activities aside from managing a trial and (iii) unclear organisational career pathway. Almost all respondents (401/420, 95.4%) considered career development either very or quite important. Although all respondents had a day-to-day role in managing trials, there was huge disparity between job titles. CONCLUSION: Career development is important to trial managers yet there is a lack of a structured pathway. The enablers and disablers to career development for trial managers should be clearly considered by the clinical trial community and, in particular, employers, sponsors and funders in order to develop a highly skilled workforce of trial managers, who are key to the delivery of trials.

Pooled Analysis of external-beam RADiotherapy parameters in phase II and phase III trials in radiochemotherapy in Anal Cancer (PARADAC).

PURPOSE: Concomitant external-beam radiochemotherapy (5-fluorouracil-mitomycin C) has become the standard of care in anal cancer since the '90s. A pooled analysis of individual patient data from 7 major trials was performed quantifying the effect of radiation therapy (RT)-related parameters on the outcome of patients with anal cancer. MATERIALS AND METHODS: Pooling databases from combined modality trials, the impact of RT parameters (total dose, gap duration, OTT: overall treatment time) on outcome including locoregional failure (LRF), 5-year progression free survival (PFS) and toxicities were investigated. Individual patient data were received for 10/13 identified published studies conducted from 1987 to 2008 (n = 3031). A Cox regression model was used (landmark = 3 months after RT for first follow-up). RESULTS: After data inspection indicating severe heterogeneity between trials, only 1343 patients from 7/10 studies received were analysed (the most recent ones, since 1994; median follow-up = 4.1 years). A higher overall 5-year LRF rate [22.8% (95% confidence interval [CI] 22.3-27.3%)] significantly correlated with longer OTT (p = 0.03), larger tumour size (p < 0.001) and male gender (p = 0.045). Although significant differences were not observed, subset analyses for LRF (dose range: 50.4-59 Gy) seemed to favour lower doses (p = 0.412), and when comparing a 2-week gap versus 3 (dose: 59.4 Gy), results suggested 3 weeks might be detrimental (p = 0.245). For a 2-week gap versus none (dose range: 55-59.4 Gy), no difference was observed (p = 0.89). Five-year PFS was 65.7% (95% CI: 62.8-68.5%). Higher PFS rates were observed in women (p < 0.001), smaller tumour sizes (p < 0.001) and shorter OTT (p = 0.025). Five-year overall survival [76.7% (95% CI: 73.9%-79.3%)] correlated positively with female gender (p < 0.001), small tumour size (p = 0.027) and short OTT (p = 0.026). Descriptive toxicity data are presented. CONCLUSION: For patients receiving concurrent external-beam doublet chemoradiation, a longer OTT seems detrimental to outcome. Further trials involving modern techniques may better define optimal OTT and total dose.

Clinical endpoints in trials of chemoradiation for patients with anal cancer.

This Review examines the reporting of endpoints in randomised controlled trials (RCTs) of radical chemoradiation for treatment of squamous cell carcinoma of the anus. The types, frequency, and definitions of clinical primary and secondary endpoints, and patient-reported outcome measures, reported in the methods and results sections of papers (and protocols, if available) were examined. Only six published RCTs comprising 2877 patients were identified. Primary outcome measures varied across the trials analysed: two used disease-free survival, one used progression-free survival, two used local failure, and one used colostomy-free survival. Secondary endpoints included overall survival, complete clinical response, quality of life, toxicity, and compliance. The definitions for primary and secondary endpoints were not consistent across trials, particularly for treatment failure (local, regional, and distant). We conclude that the quality of outcome reporting in RCTs of squamous cell carcinoma of the anus is inconsistent. A core set of outcomes, including clinical and patient-reported outcome measures with standardised definitions, is needed to improve the reporting of RCTs examining chemoradiation for treatment of patients with squamous cell carcinoma of the anus.

Best time to assess complete clinical response after chemoradiotherapy in squamous cell carcinoma of the anus (ACT II): a post-hoc analysis of randomised controlled phase 3 trial.

BACKGROUND: Guidelines for anal cancer recommend assessment of response at 6-12 weeks after starting treatment. Using data from the ACT II trial, we determined the optimum timepoint to assess clinical tumour response after chemoradiotherapy. METHODS: The previously reported ACT II trial was a phase 3 randomised trial of patients of any age with newly diagnosed, histologically confirmed, squamous cell carcinoma of the anus without metastatic disease from 59 centres in the UK. We randomly assigned patients (by minimisation) to receive either intravenous mitomycin (one dose of 12 mg/m2 on day 1) or intravenous cisplatin (one dose of 60 mg/m2 on days 1 and 29), with intravenous fluorouracil (one dose of 1000 mg/m2 per day on days 1-4 and 29-32) and radiotherapy (50·4 Gy in 28 daily fractions); and also did a second randomisation after initial therapy to maintenance chemotherapy (fluorouracil and cisplatin) or no maintenance chemotherapy. The primary outcome was complete clinical response (the absence of primary and nodal tumour by clinical examination), in addition to overall survival and progression-free survival from time of randomisation. In this post-hoc analysis, we analysed complete clinical response at three timepoints: 11 weeks from the start of chemoradiotherapy (assessment 1), 18 weeks from the start of chemoradiotherapy (assessment 2), and 26 weeks from the start of chemoradiotherapy (assessment 3) as well as the overall and progression-free survival estimates of patients with complete clinical response or without complete clinical response at each assessment. We analysed both the overall trial population and a subgroup of patients who had attended each of the three assessments by modified intention-to-treat. This study is registered at controlled-trials.com, ISRCTN 26715889. FINDINGS: We enrolled 940 patients from June 4, 2001, until Dec 16, 2008. Complete clinical response was achieved in 492 (52%) of 940 patients at assessment 1 (11 weeks), 665 (71%) of patients at assessment 2 (18 weeks), and 730 (78%) of patients at assessment 3 (26 weeks). 691 patients attended all three assessments and in this subgroup, complete clinical response was reported in 441 (64%) patients at assessment 1, 556 (80%) at assessment 2, and 590 (85%) at assessments 3. 151 (72%) of the 209 patients who had not had a complete clinical response at assessment 1 had a complete clinical response by assessment 3. In the overall trial population of 940 patients, 5 year overall survival in patients who had a clinical response at assessments 1, 2, 3 was 83% (95% CI 79-86), 84% (81-87), and 87% (84-89), respectively and was 72% (66-78), 59% (49-67), and 46% (37-55) for patients who did not have a complete clinical response at assessments 1, 2, 3, respectively. In the subgroup of 691 patients, 5 year overall survival in patients who had a clinical response at assessment 1, 2, 3 was 85% (81-88), 86% (82-88), and 87% (84-90), respectively, and was 75% (68-80), 61% (50-70), and 48% (36-58) for patients who did not have a complete clinical response at assessment 1, 2, 3, respectively. Similarly, progression-free survival in both the overall trial population and the subgroup was longer in patients who had a complete clinical response, compared with patients who did not have a complete clinical response, at all three assessments. INTERPRETATION: Many patients who do not have a complete clinical response when assessed at 11 weeks after commencing chemoradiotherapy do in fact respond by 26 weeks, and the earlier assessment could lead to some patients having unnecessary surgery. Our data suggests that the optimum time for assessment of complete clinical response after chemoradiotherapy for patients with squamous cell carcinoma of the anus is 26 weeks from starting chemoradiotherapy. We suggest that guidelines should be revised to indicate that later assessment is acceptable. FUNDING: Cancer Research UK.

Mitomycin or cisplatin chemoradiation with or without maintenance chemotherapy for treatment of squamous-cell carcinoma of the anus (ACT II): a randomised, phase 3, open-label, 2 × 2 factorial trial.

BACKGROUND: Chemoradiation became the standard of care for anal cancer after the ACT I trial. However, only two-thirds of patients achieved local control, with 5-year survival of 50%; therefore, better treatments are needed. We investigated whether replacing mitomycin with cisplatin in chemoradiation improves response, and whether maintenance chemotherapy after chemoradiation improves survival. METHODS: In this 2 × 2 factorial trial, we enrolled patients with histologically confirmed squamous-cell carcinoma of the anus without metastatic disease from 59 centres in the UK. Patients were randomly assigned to one of four groups, to receive either mitomycin (12 mg/m(2) on day 1) or cisplatin (60 mg/m(2) on days 1 and 29), with fluorouracil (1000 mg/m(2) per day on days 1-4 and 29-32) and radiotherapy (50.4 Gy in 28 daily fractions); with or without two courses of maintenance chemotherapy (fluorouracil and cisplatin at weeks 11 and 14). The random allocation was generated by computer and patients assigned by telephone. Randomisation was done by minimisation and stratified by tumour site, T and N stage, sex, age, and renal function. Neither patients nor investigators were masked to assignment. Primary endpoints were complete response at 26 weeks and acute toxic effects (for chemoradiation), and progression-free survival (for maintenance). The primary analyses were done by intention to treat. This study is registered at controlled-trials.com, number 26715889. FINDINGS: We enrolled 940 patients: 472 were assigned to mitomycin, of whom 246 were assigned to no maintenance, 226 to maintenance; 468 were assigned to cisplatin, of whom 246 were assigned to no maintenance, 222 to maintenance. Median follow-up was 5.1 years (IQR 3.9-6.9). 391 of 432 (90.5%) patients in the mitomycin group versus 386 of 431 (89.6%) in the cisplatin group had a complete response at 26 weeks (difference -0.9%, 95% CI -4.9 to 3.1; p=0.64). Overall, toxic effects were similar in each group (334/472 [71%] for mitomycin vs 337/468 [72%] for cisplatin). The most common grade 3-4 toxic effects were skin (228/472 [48%] vs 222/468 [47%]), pain (122/472 [26%] vs 135/468 [29%]), haematological (124/472 [26%] vs 73/468 [16%]), and gastrointestinal (75/472 [16%] vs 85/468 [18%]). 3-year progression-free survival was 74% (95% CI 69-77; maintenance) versus 73% (95% CI 68-77; no maintenance; hazard ratio 0.95, 95% CI 0.75-1.21; p=0.70). INTERPRETATION: The results of our trial--the largest in anal cancer to date--show that fluorouracil and mitomycin with 50.4 Gy radiotherapy in 28 daily fractions should remain standard practice in the UK. FUNDING: Cancer Research UK.

Prognostic factors for recurrence and survival in anal cancer: generating hypotheses from the mature outcomes of the first United Kingdom Coordinating Committee on Cancer Research Anal Cancer Trial (ACT I).

BACKGROUND: Only 2 prospective studies have previously reported prognostic factors for anal cancer, European Organization for Research and Treatment of Cancer trial 22861 (EORTC 22861) and Radiation Therapy Oncology Group trial 98-11 (RTOG 98-11). Both of those trials reported that clinically positive lymph nodes and male sex predicted poorer overall survival (OS). The EORTC 22861 trial indicated that the same factors were prognostic for locoregional control. In the current report, the authors investigated potential prognostic factors from the first United Kingdom Coordinating Committee on Cancer Research Anal Cancer Trial (ACT I), in which patients were randomized to receive either radiotherapy alone or chemoradiation (CRT) with concurrent 5-fluorouracil/mitomycin C. METHODS: In the ACT I trial, associations between several baseline characteristics and 3 endpoints were investigated: locoregional failure (LRF), anal cancer death (ACD), and OS. The analyses were restricted to 292 patients who received CRT, which subsequently became standard treatment. A score was derived using multivariable Cox regression to identify the set of factors that, together, had the best prognostic performance. This score was then validated with a large, independent prospective trial (the ACT II trial). RESULTS: Palpable, clinically positive lymph nodes were associated with LRF (P = .012), a greater risk of ACD (P = .031), and decreased OS (P = .006) in multivariable analyses. Men had worse outcomes than women for LRF (P = .036), ACD (P = .039), and OS (P = .008). On average, a lower hemoglobin level had an adverse effect on ACD (P = .008), and a higher white blood cell count had an adverse effect on OS (P = .001). However, external validation of the score was poor for LRF (area under the curve [AUC] = 54%) but was better for ACD (AUC = 67%) and OS (AUC = 63%). CONCLUSIONS: The results from this analysis of the ACT I trial supported evidence for palpable lymph nodes and male sex as prognostic factors for LRF and OS, and lower hemoglobin levels and a higher white blood cell count were identified as prognostic factors for ACD and OS, respectively.

Safety and long term efficacy of porfimer sodium photodynamic therapy in locally advanced biliary tract carcinoma.

BACKGROUND: In patients with unresectable cholangiocarcinoma, photodynamic therapy (PDT) with porfimer sodium promotes biliary drainage and may improve survival and quality of life. AIM: To prospectively evaluate the safety and efficacy of PDT in patients with locally advanced biliary tract carcinoma. METHODS: Eligible patients had unresectable, histologically confirmed disease, a Karnofsky performance status of ≥30% and life expectancy >12 weeks. Patients received 2mg/kg i.v. of porfimer sodium, followed by endobiliary laser activation and stent replacement 48 h later. Patients were assessed clinically and radiologically before treatment and on day 28, and followed up thereafter at three-monthly intervals until death. RESULTS: 36 patients were entered over an 18 months period: 14 males, 22 females, with a median age of 65 (30-79)yr and performance status of 80 (50-100). PDT was technically successful in all cases and was generally well tolerated; there was no grade 4 toxicity and no treatment-associated mortality. The median survival was 12 (1-84) months. CONCLUSIONS: Porfimer sodium PDT can be delivered safely to patients with biliary tract cancer and is suitable for testing in phase III studies (UKCRN ID 1218).

Three cytotoxic drugs combined with pelvic radiation and as maintenance chemotherapy for patients with squamous cell carcinoma of the anus (SCCA): long-term follow-up of a phase II pilot study using 5-fluorouracil, mitomycin C and cisplatin.

PURPOSE: Phase III trials in the 1990s for squamous cell carcinoma of the anus (SCCA) demonstrated 5-fluorouracil (5FU) and mitomycinC (MMC) chemoradiation (CRT) improved outcome compared to radiation (RT) alone, but local recurrence remained significant. This prospective pilot study intensified treatment by integrating 3 cytotoxic drugs into CRT and maintenance chemotherapy. METHODS: CRT comprised 5-FU 1000 mg/m(2) days 1-4,29-32, MMC 10 mg/m(2) day 1 and Cisplatin (CDDP) 60 mg/m(2) days1 and 29, with 45 Gy in 25 daily fractions, followed by a 15 Gy boost. Maintenance chemotherapy started 4-8 weeks later, three courses repeated every 21 days, using 5-FU/CDDP doses above, with MMC reduced to 7 mg/m(2) and administered with the first and third cycles. RESULTS: In CRT only 14/19 (74%) patients received protocol-defined chemotherapy doses in week 5. Compliance to maintenance chemotherapy was poor. 15/19 started cycle 1, 13 started cycle 2 and 11 cycle 3. 17/19 experienced G3-G5 toxicity (16 Grade 3/4 and one Grade 5). 16/19 patients (84%) remain alive and disease-free - median follow-up 79 months (34-115). CONCLUSIONS: Despite favourable results, the significant toxicity and low compliance of the three-drug CRT regimen used, deemed it unsuitable for testing in a phase III trial. A two-drug maintenance regimen was explored in the ACT II trial.

"Mind the gap"--the impact of variations in the duration of the treatment gap and overall treatment time in the first UK Anal Cancer Trial (ACT I).

PURPOSE: The United Kingdom Coordinating Committee on Cancer Research anal cancer trial demonstrated the benefit of combined modality treatment (CMT) using radiotherapy (RT), infusional 5-fluorouracil, and mitomycin C over RT alone. The present study retrospectively examines the impact of the recommended 6-week treatment gap and local RT boost on long-term outcome. METHODS AND MATERIALS: A total of 577 patients were randomly assigned RT alone or CMT. After a 6-week gap responders received a boost using either additional external beam radiotherapy (EBRT) (15 Gy) or iridium-192 implant (25 Gy). The effect of boost, the gap between initial treatment (RT alone or CMT) and boost (Tgap), and overall treatment time (OTT) were examined for their impact on outcome. RESULTS: Among the 490 good responders, 436 (89%) patients received a boost after initial treatment. For boosted patients, the risk of anal cancer death decreased by 38% (hazard ratio [HR]: 0.62, 99% CI 0.35-1.12; p=0.04), but there was no evidence this was mediated via a reduction in locoregional failure (LRF) (HR: 0.90, 99% CI 0.48-1.68; p=0.66). The difference in Tgap was only 1.4 days longer for EBRT boost, compared with implant (p=0.51). OTT was longer by 6.1 days for EBRT (p=0.006). Tgap and OTT were not associated with LRF. Radionecrosis was reported in 8% of boosted, compared with 0% in unboosted patients (p=0.03). CONCLUSIONS: These results question the benefit of a radiotherapy boost after a 6-week gap. The higher doses of a boost may contribute more to an increased risk of late morbidity, rather than local control.

Population patch-clamp electrophysiology analysis of recombinant GABAA alpha1beta3gamma2 channels expressed in HEK-293 cells.

Gamma-amino butyric acid (GABA)-activated Cl- channels are critical mediators of inhibitory postsynaptic potentials in the CNS. To date, rational design efforts to identify potent and selective GABA(A) subtype ligands have been hampered by the absence of suitable high-throughput screening approaches. The authors describe 384-well population patch-clamp (PPC) planar array electrophysiology methods for the study of GABA(A) receptor pharmacology. In HEK293 cells stably expressing human alpha1beta3gamma2 GABA(A) channels, GABA evoked outward currents at 0 mV of 1.05 +/- 0.08 nA, measured 8 s post GABA addition. The I(GABA) was linear and reversed close to the theoretical E(Cl) (-56 mV). Concentration-response curve analysis yielded a mean pEC(50) value of 5.4 and Hill slope of 1.5, and for a series of agonists, the rank order of potency was muscimol > GABA > isoguvacine. A range of known positive modulators, including diazepam and pentobarbital, produced concentration-dependent augmentation of the GABA EC( 20) response (1 microM). The competitive antagonists bicuculline and gabazine produced concentration-dependent, parallel, rightward displacement of GABA curves with pA(2) and slope values of 5.7 and 1.0 and 6.7 and 1.0, respectively. In contrast, picrotoxin (0.2-150 microM) depressed the maximal GABA response, implying a non-competitive antagonism. Overall, the pharmacology of human alpha1beta3gamma2 GABA(A) determined by PPC was highly similar to that obtained by conventional patch-clamp methods. In small-scale single-shot screens, Z' values of >0.5 were obtained in agonist, modulator, and antagonist formats with hit rates of 0% to 3%. The authors conclude that despite the inability of the method to resolve the peak agonist responses, PPC can rapidly and usefully quantify pharmacology for the alpha1beta3gamma2 GABA(A) isoform. These data suggest that PPC may be a valuable approach for a focused set and secondary screening of GABA(A) receptors and other slow ligand-gated ion channels.

EXTRA--a multicenter phase II study of chemoradiation using a 5 day per week oral regimen of capecitabine and intravenous mitomycin C in anal cancer.

PURPOSE: 5-Fluorouracil (5-FU) + mitomycin C (MMC)-based chemoradiotherapy is standard treatment for patients with epidermoid anal carcinoma. Clinical trials in other cancers have confirmed 5-FU can successfully be replaced by the oral fluoropyrimidine capecitabine. This phase II trial aimed to determine the feasibility, toxicity, and efficacy of capecitabine, MMC and radiotherapy (RT) in anal cancer patients. METHODS AND MATERIALS: Radiotherapy comprised the schedule of the UK Anal Cancer Trial (ACT) II trial (50.4 Gy in 28 fractions of 1.8 Gy). With MMC (12 mg/m2) on Day 1 and capecitabine on each RT treatment day in two divided doses (825 mg/m2 b.i.d). The endpoints were complete response at 4 weeks, local control at 6 months and toxicity. RESULTS: Thirty-one patients entered the trial. The median age was 61 years (range 45-86) with 14 males and 17 females. Compliance with chemotherapy with no dose interruptions or delays was 68%, and with RT was 81%. Eighteen (58%) patients completed both modalities of treatment as planned. Dose-limiting Grade 3 or 4 diarrhea was seen in 1 of 31 patients. Three patients experienced Grade 3 neutropenia. There were no treatment-related deaths. Four weeks following completion of chemoradiation, 24 patients (77%) had a complete clinical response, and 4 (16%) a partial response. With a median follow-up of 14 months, three locoregional relapses occurred. CONCLUSIONS: Capecitabine with MMC and RT in with patients anal carcinoma is well tolerated, with minimal toxicity and acceptable compliance. We recommend testing this schedule in future national Phase III studies in anal cancer.

mGlu4 potentiation of K(2P)2.1 is dependant on C-terminal dephosphorylation.

Two-pore domain potassium (K(2P)) channels are proposed to underlie the background or leak current found in many excitable cells. Extensive studies have been performed investigating the inhibition of K(2P)2.1 by Galpha(q)- and Galpha(s)-coupled G-protein-coupled receptors (GPCRs), whereas in the present study we investigate the mechanisms underlying Galpha(i)/Galpha(o)-coupled GPCR increases in K(2P)2.1 activity. Activation of mGlu4 increases K(2P)2.1 activity, with pharmacological inhibition of protein kinases and phosphatases revealing the involvement of PKA whereas PKC, PKG or protein phosphatases play no role. Mutational analysis of potential C-terminal phosphorylation sites indicates S333 to control approximately 70%, with S300 controlling approximately 30% of the increase in K(2P)2.1 activity following mGlu4 activation. These data reveal that activation of mGlu4 leads to an increase in K(2P)2.1 activity through a reduction in C-terminal phosphorylation, which represents a novel mechanism by which group III mGlu receptors may regulate cell excitability and synaptic activity.

Improved functional expression of recombinant human ether-a-go-go (hERG) K+ channels by cultivation at reduced temperature.

BACKGROUND: HERG potassium channel blockade is the major cause for drug-induced long QT syndrome, which sometimes cause cardiac disrhythmias and sudden death. There is a strong interest in the pharmaceutical industry to develop high quality medium to high-throughput assays for detecting compounds with potential cardiac liability at the earliest stages of drug development. Cultivation of cells at lower temperature has been used to improve the folding and membrane localization of trafficking defective hERG mutant proteins. The objective of this study was to investigate the effect of lower temperature maintenance on wild type hERG expression and assay performance. RESULTS: Wild type hERG was stably expressed in CHO-K1 cells, with the majority of channel protein being located in the cytoplasm, but relatively little on the cell surface. Expression at both locations was increased several-fold by cultivation at lower growth temperatures. Intracellular hERG protein levels were highest at 27 degrees C and this correlated with maximal 3H-dofetilide binding activity. In contrast, the expression of functionally active cell surface-associated hERG measured by patch clamp electrophysiology was optimal at 30 degrees C. The majority of the cytoplasmic hERG protein was associated with the membranes of cytoplasmic vesicles, which markedly increased in quantity and size at lower temperatures or in the presence of the Ca2+-ATPase inhibitor, thapsigargin. Incubation with the endocytic trafficking blocker, nocodazole, led to an increase in hERG activity at 37 degrees C, but not at 30 degrees C. CONCLUSION: Our results are consistent with the concept that maintenance of cells at reduced temperature can be used to boost the functional expression of difficult-to-express membrane proteins and improve the quality of assays for medium to high-throughput compound screening. In addition, these results shed some light on the trafficking of hERG protein under these growth conditions.

Novel 384-well population patch clamp electrophysiology assays for Ca2+-activated K+ channels.

Planar array electrophysiology techniques were applied to assays for modulators of recombinant hIK and hSK3 Ca2+-activated K+ channels. In CHO-hIK-expressing cells, under asymmetric K+ gradients, small-molecule channel activators evoked time- and voltage-independent currents characteristic of those previously described by classical patch clamp electrophysiology methods. In single-hole (cell) experiments, the large cell-to-cell heterogeneity in channel expression rendered it difficult to generate activator concentration-response curves. However, in population patch clamp mode, in which signals are averaged from up to 64 cells, well-to-well variation was substantially reduced such that concentration-response curves could be easily constructed. The absolute EC50 values and rank order of potency for a range of activators, including 1-EBIO and DC-EBIO, corresponded well with conventional patch clamp data. Activator responses of hIK and hSK3 channels could be fully and specifically blocked by the selective inhibitors TRAM-34 and apamin, with IC50 values of 0.31 microM and 3 nM, respectively. To demonstrate assay precision and robustness, a test set of 704 compounds was screened in a 384-well format of the hIK assay. All plates had Z' values greater than 0.6, and the statistical cutoff for activity was 8%. Eleven hits (1.6%) were identified from this set, in addition to the randomly spiked wells with known activators. Overall, our findings demonstrate that population patch clamp is a powerful and enabling method for screening Ca2+-activated K+ channels and provides significant advantages over single-cell electrophysiology (IonWorks(HT)) and other previously published approaches. Moreover, this work demonstrates for the 1st time the utility of population patch clamp for ion channel activator assays and for non-voltage-gated ion channels.

Selective block of the human 2-P domain potassium channel, TASK-3, and the native leak potassium current, IKSO, by zinc.

Background potassium channels control the resting membrane potential of neurones and regulate their excitability. Two-pore-domain potassium (2-PK) channels have been shown to underlie a number of such neuronal background currents. Currents through human TASK-1, TASK-2 and TASK-3 channels expressed in Xenopus oocytes were inhibited by extracellular acidification. For TASK-3, mutation of histidine 98 to aspartate or alanine considerably reduced this effect of pH. Zinc was found to be a selective blocker of TASK-3 with virtually no effect on TASK-1 or TASK-2. Zinc had an IC(50) of 19.8 microM for TASK-3, at +80 mV, with little voltage dependence associated with this inhibition. TASK-3 H98A had a much reduced sensitivity to zinc suggesting this site is important for zinc block. Surprisingly, TASK-1 also has histidine in position 98 but is insensitive to zinc block. TASK-3 and TASK-1 differ at position 70 with glutamate for TASK-3 and lysine for TASK-1. TASK-3 E70K also had a much reduced sensitivity to zinc while the corresponding reverse mutation in TASK-1, K70E, induced zinc sensitivity. A TASK-3-TASK-1 concatamer channel was comparatively zinc insensitive. For TASK-3, it is concluded that positions E70 and H98 are both critical for zinc block. The native cerebellar granule neurone (CGN) leak current, IK(SO), is sensitive to block by zinc, with current reduced to 0.58 of control values in the presence of 100 microM zinc. This suggests that TASK-3 channels underlie a major component of IK(SO). It has recently been suggested that zinc is released from inhibitory synapses onto CGNs. Therefore it is possible that inhibition of IK(SO) in cerebellar granule cells by synaptically released zinc may have important physiological consequences.

Cloning and functional expression of a human orthologue of rat vanilloid receptor-1.

Capsaicin, resiniferatoxin, protons or heat have been shown to activate an ion channel, termed the rat vanilloid receptor-1 (rVR1), originally isolated by expression cloning for a capsaicin sensitive phenotype. Here we describe the cloning of a human vanilloid receptor-1 (hVR1) cDNA containing a 2517 bp open reading frame that encodes a protein with 92% homology to the rat vanilloid receptor-1. Oocytes or mammalian cells expressing this cDNA respond to capsaicin, pH and temperature by generating inward membrane currents. Mammalian cells transfected with human VR1 respond to capsaicin with an increase in intracellular calcium. The human VR1 has a chromosomal location of 17p13 and is expressed in human dorsal root ganglia and also at low levels throughout a wide range of CNS and peripheral tissues. Together the sequence homology, similar expression profile and functional properties confirm that the cloned cDNA represents the human orthologue of rat VR1.