Monitoring strategies for clinical intervention studies.

BACKGROUND: Trial monitoring is an important component of good clinical practice to ensure the safety and rights of study participants, confidentiality of personal information, and quality of data. However, the effectiveness of various existing monitoring approaches is unclear. Information to guide the choice of monitoring methods in clinical intervention studies may help trialists, support units, and monitors to effectively adjust their approaches to current knowledge and evidence. OBJECTIVES: To evaluate the advantages and disadvantages of different monitoring strategies (including risk-based strategies and others) for clinical intervention studies examined in prospective comparative studies of monitoring interventions. SEARCH METHODS: We systematically searched CENTRAL, PubMed, and Embase via Ovid for relevant published literature up to March 2021. We searched the online 'Studies within A Trial' (SWAT) repository, grey literature, and trial registries for ongoing or unpublished studies. SELECTION CRITERIA: We included randomized or non-randomized prospective, empirical evaluation studies of different monitoring strategies in one or more clinical intervention studies. We applied no restrictions for language or date of publication. DATA COLLECTION AND ANALYSIS: We extracted data on the evaluated monitoring methods, countries involved, study population, study setting, randomization method, and numbers and proportions in each intervention group. Our primary outcome was critical and major monitoring findings in prospective intervention studies. Monitoring findings were classified according to different error domains (e.g. major eligibility violations) and the primary outcome measure was a composite of these domains. Secondary outcomes were individual error domains, participant recruitment and follow-up, and resource use. If we identified more than one study for a comparison and outcome definitions were similar across identified studies, we quantitatively summarized effects in a meta-analysis using a random-effects model. Otherwise, we qualitatively summarized the results of eligible studies stratified by different comparisons of monitoring strategies. We used the GRADE approach to assess the certainty of the evidence for different groups of comparisons. MAIN RESULTS: We identified eight eligible studies, which we grouped into five comparisons. 1. Risk-based versus extensive on-site monitoring: based on two large studies, we found moderate certainty of evidence for the combined primary outcome of major or critical findings that risk-based monitoring is not inferior to extensive on-site monitoring. Although the risk ratio was close to 'no difference' (1.03 with a 95% confidence interval [CI] of 0.81 to 1.33, below 1.0 in favor of the risk-based strategy), the high imprecision in one study and the small number of eligible studies resulted in a wide CI of the summary estimate. Low certainty of evidence suggested that monitoring strategies with extensive on-site monitoring were associated with considerably higher resource use and costs (up to a factor of 3.4). Data on recruitment or retention of trial participants were not available. 2. Central monitoring with triggered on-site visits versus regular on-site visits: combining the results of two eligible studies yielded low certainty of evidence with a risk ratio of 1.83 (95% CI 0.51 to 6.55) in favor of triggered monitoring intervention. Data on recruitment, retention, and resource use were not available. 3. Central statistical monitoring and local monitoring performed by site staff with annual on-site visits versus central statistical monitoring and local monitoring only: based on one study, there was moderate certainty of evidence that a small number of major and critical findings were missed with the central monitoring approach without on-site visits: 3.8% of participants in the group without on-site visits and 6.4% in the group with on-site visits had a major or critical monitoring finding (odds ratio 1.7, 95% CI 1.1 to 2.7; P = 0.03). The absolute number of monitoring findings was very low, probably because defined major and critical findings were very study specific and central monitoring was present in both intervention groups. Very low certainty of evidence did not suggest a relevant effect on participant retention, and very low certainty evidence indicated an extra cost for on-site visits of USD 2,035,392. There were no data on recruitment. 4. Traditional 100% source data verification (SDV) versus targeted or remote SDV: the two studies assessing targeted and remote SDV reported findings only related to source documents. Compared to the final database obtained using the full SDV monitoring process, only a small proportion of remaining errors on overall data were identified using the targeted SDV process in the MONITORING study (absolute difference 1.47%, 95% CI 1.41% to 1.53%). Targeted SDV was effective in the verification of source documents, but increased the workload on data management. The other included study was a pilot study, which compared traditional on-site SDV versus remote SDV and found little difference in monitoring findings and the ability to locate data values despite marked differences in remote access in two clinical trial networks. There were no data on recruitment or retention. 5. Systematic on-site initiation visit versus on-site initiation visit upon request: very low certainty of evidence suggested no difference in retention and recruitment between the two approaches. There were no data on critical and major findings or on resource use. AUTHORS' CONCLUSIONS: The evidence base is limited in terms of quantity and quality. Ideally, for each of the five identified comparisons, more prospective, comparative monitoring studies nested in clinical trials and measuring effects on all outcomes specified in this review are necessary to draw more reliable conclusions. However, the results suggesting risk-based, targeted, and mainly central monitoring as an efficient strategy are promising. The development of reliable triggers for on-site visits is ongoing; different triggers might be used in different settings. More evidence on risk indicators that identify sites with problems or the prognostic value of triggers is needed to further optimize central monitoring strategies. In particular, approaches with an initial assessment of trial-specific risks that need to be closely monitored centrally during trial conduct with triggered on-site visits should be evaluated in future research.

Quantification of pre-mRNA escape rate and synergy in splicing.

Splicing reactions generally combine high speed with accuracy. However, some of the pre-mRNAs escape the nucleus with a retained intron. Intron retention can control gene expression and increase proteome diversity. We calculated the escape rate for the yeast PTC7 intron and pre-mRNA. This prediction was facilitated by the observation that splicing is a linear process and by deriving simple algebraic expressions from a model of co- and post-transcriptional splicing and RNA surveillance that determines the rate of the nonsense-mediated decay (NMD) of the pre-mRNAs with the retained intron. The escape rate was consistent with the observed threshold of splicing rate below which the mature mRNA level declined. When an mRNA contains multiple introns, the outcome of splicing becomes more difficult to predict since not only the escape rate of the pre-mRNA has to be considered, but also the possibility that the splicing of each intron is influenced by the others. We showed that the two adjacent introns in the SUS1 mRNA are spliced cooperatively, but this does not counteract the escape of the partially spliced mRNA. These findings will help to infer promoter activity and to predict the behavior of and to control splicing regulatory networks.

The angiotensin II type 1 receptor antagonist Losartan binds and activates bradykinin B2 receptor signaling.

The angiotensin II type 1 receptor (AT1R) blocker (ARB) Losartan has cardioprotective effects during ischemia-reperfusion injury and inhibits reperfusion arrhythmias -effects that go beyond the benefits of lowering blood pressure. The renin-angiotensin and kallikrein-kinin systems are intricately connected and some of the cardioprotective effects of Losartan are abolished by blocking the bradykinin B2 receptor (B2R) signaling. In this study, we investigated the ability of six clinically available ARBs to specifically bind and activate the B2R. First, we investigated their ability to activate phosphoinositide (PI) hydrolysis in COS-7 cells transiently expressing the B2R. We found that only Losartan activated the B2R, working as a partial agonist compared to the endogenous ligand bradykinin. This effect was blocked by the B2R antagonist HOE 140. A competitive binding analysis revealed that Losartan does not significantly compete with bradykinin and does not change the binding affinity of bradykinin on the B2R. Furthermore, Losartan but not Candesartan mimicked the ability of bradykinin to increase the recovery of contractile force after metabolic stress in rat atrial tissue strips. In conclusion, Losartan is a partial agonist of the B2R through direct binding and activation, suggesting that B2R agonism could partly explain the beneficial effects of Losartan.

Biased signaling of the angiotensin II type 1 receptor can be mediated through distinct mechanisms.

BACKGROUND: Seven transmembrane receptors (7TMRs) can adopt different active conformations facilitating a selective activation of either G protein or ß-arrestin-dependent signaling pathways. This represents an opportunity for development of novel therapeutics targeting selective biological effects of a given receptor. Several studies on pathway separation have been performed, many of these on the Angiotensin II type 1 receptor (AT1R). It has been shown that certain ligands or mutations facilitate internalization and/or recruitment of ß-arrestins without activation of G proteins. However, the underlying molecular mechanisms remain largely unresolved. For instance, it is unclear whether such selective G protein-uncoupling is caused by a lack of ability to interact with G proteins or rather by an increased ability of the receptor to recruit ß-arrestins. Since uncoupling of G proteins by increased ability to recruit ß-arrestins could lead to different cellular or in vivo outcomes than lack of ability to interact with G proteins, it is essential to distinguish between these two mechanisms. METHODOLOGY/PRINCIPAL FINDINGS: We studied five AT1R mutants previously published to display pathway separation: D74N, DRY/AAY, Y292F, N298A, and Y302F (Ballesteros-Weinstein numbering: 2.50, 3.49-3.51, 7.43, 7.49, and 7.53). We find that D74N, DRY/AAY, and N298A mutants are more prone to ß-arrestin recruitment than WT. In contrast, receptor mutants Y292F and Y302F showed impaired ability to recruit ß-arrestin in response to Sar1-Ile4-Ile8 (SII) Ang II, a ligand solely activating the ß-arrestin pathway. CONCLUSIONS/SIGNIFICANCE: Our analysis reveals that the underlying conformations induced by these AT1R mutants most likely represent principally different mechanisms of uncoupling the G protein, which for some mutants may be due to their increased ability to recruit ß-arrestin2. Hereby, these findings have important implications for drug discovery and 7TMR biology and illustrate the necessity of uncovering the exact molecular determinants for G protein-coupling and ß-arrestin recruitment, respectively.

An angiotensin II type 1 receptor activation switch patch revealed through evolutionary trace analysis.

Seven transmembrane (7TM) or G protein-coupled receptors constitute a large superfamily of cell surface receptors sharing a structural motif of seven transmembrane spanning alpha helices. Their activation mechanism most likely involves concerted movements of the transmembrane helices, but remains to be completely resolved. Evolutionary Trace (ET) analysis is a computational method, which identifies clusters of functionally important residues by integrating information on evolutionary important residue variations with receptor structure. Combined with known mutational data, ET predicted a patch of residues in the cytoplasmic parts of TM2, TM3, and TM6 to form an activation switch that is common to all family A 7TM receptors. We tested this hypothesis in the rat Angiotensin II (Ang II) type 1a (AT1a) receptor. The receptor has important roles in the cardiovascular system, but has also frequently been applied as a model for 7TM receptor activation and signaling. Six mutations: F66A, L67R, L70R, L119R, D125A, and I245F were targeted to the putative switch and assayed for changes in activation state by their ligand binding, signaling, and trafficking properties. All but one receptor mutant (that was not expressed well) displayed phenotypes associated with changed activation state, such as increased agonist affinity or basal activity, promiscuous activation, or constitutive internalization highlighting the importance of testing different signaling pathways. We conclude that this evolutionary important patch mediates interactions important for maintaining the inactive state. More broadly, these observations in the AT1 receptor are consistent with computational predictions of a generic role for this patch in 7TM receptor activation.

Molecular determinants of angiotensin II type 1 receptor functional selectivity.

The angiotensin AT(1) receptor is an important pharmacological target in the treatment of cardiovascular disorders, such as hypertension, diabetic nephropathy, cardiac hypertrophy, arrhythmia and failure. Simultaneously, the AT(1) receptor has emerged to be a prominent model for the emerging concept that receptors may attain multiple active states with differentiated functional outcomes. Two major signalling pathways are employed by the AT(1) receptor, namely 1) the canonical G(q) protein-dependent activation of inositol phosphate turnover and intracellular calcium release, and 2) G protein-independent recruitment of beta-arrestin-scaffolded signalling complexes that activate protein kinase pathways. Different states of receptor activation with preference for individual downstream pathways (functional selectivity) have been demonstrated in mutational studies of the AT(1) receptor and by pharmacological probing with analogues of angiotensin II. These studies also provide clues about the conformational changes that underlie different functional outcomes. In this review, we evaluate current knowledge of the molecular determinants of AT(1) receptor activation, which may distinguish G protein-dependent and -independent behaviour. While G protein activation is known to be detrimental, G protein-independent signalling by the AT(1) receptor has been associated with phenotypes such as cell survival and renewal, regulation of cardiac contraction and cell migration. It is therefore currently hypothesized that selective blockade of G protein actions and simultaneous activation of G protein-independent signalling will prove to be a feasible strategy for improved cardiovascular therapy. The pharmacological perspectives of functional selectivity by receptors, such as the AT(1) receptor, urge the elucidation of molecular mechanisms that govern disparate signalling events.

The human angiotensin AT(1) receptor supports G protein-independent extracellular signal-regulated kinase 1/2 activation and cellular proliferation.

The angiotensin AT(1) receptor is a key regulator of blood pressure and body fluid homeostasis, and it plays a key role in the pathophysiology of several cardiovascular diseases such as hypertension, cardiac hypertrophy, congestive heart failure, and arrhythmia. The importance of human angiotensin AT(1) receptor signalling is illustrated by the common use of angiotensin AT(1) receptor-inverse agonists in clinical practice. It is well established that rodent orthologues of the angiotensin AT(1) receptor can selectively signal through G protein-dependent and -independent mechanisms in recombinant expression systems, primary cells and in vivo. The in vivo work clearly demonstrates profoundly different cellular consequences of angiotensin AT(1) receptor signalling in the cardiovascular system, suggesting pharmacological potential for drugs which specifically affect a subset of angiotensin AT(1) receptor actions. However, it is currently unknown whether the human angiotensin AT(1) receptor can signal through G protein-independent mechanisms - and if so, what the physiological impact of such signalling is. We have performed a detailed pharmacological analysis of the human angiotensin AT(1) receptor using a battery of angiotensin analogues and registered drugs targeting this receptor. We show that the human angiotensin AT(1) receptor signals directly through G protein-independent pathways and supports NIH3T3 cellular proliferation. The realization of G protein-independent signalling by the human angiotensin AT(1) receptor has clear pharmacological implications for development of drugs with pathway-specific actions and defined biological outcomes.

Family C 7TM receptor dimerization and activation.

The family C seven transmembrane (7TM) receptors constitutes a small and especially well characterized subfamily of the large 7TM receptor superfamily. Approximately 50% of current prescription drugs target 7TM receptors, this biologically important family represents the largest class of drug-targets today. It is well established that family C 7TM receptors form homo- or hetero-dimers on the cell surface of living cells. The large extra-cellular domains (ECD) have been crystallized as a dimer in the presence and absence of agonist. Upon agonist binding, the dimeric ECD undergoes large conformational changes that lead to receptor activation. Despite extensive studies of the receptor transmembrane domain, several key features, including the exact organization of the complete receptor dimer, the sequence of events leading to receptor activation, and the functional significance of dimerization, have yet to be fully defined. This review presents the biochemical support for family C 7TM receptor dimerization and discusses its importance for receptor biosynthesis, surface expression, ligand binding and activation, since lessons learnt here may well be applicable to the whole superfamily of 7TM receptors.