Two-Drug Regimens Dolutegravir/Lamivudine and Dolutegravir/Rilpivirine Are Effective with Few Discontinuations in US Real-World Settings: Results from the TANDEM Study.

INTRODUCTION: Dolutegravir/lamivudine (DTG/3TC) and dolutegravir/rilpivirine (DTG/RPV) are fixed-dose, complete, single-tablet, two-drug regimens (2DRs) indicated for HIV-1. DTG/3TC is approved for antiretroviral therapy (ART)-naive people with HIV-1 and virologically suppressed individuals to replace current ART; DTG/RPV is indicated for virologically suppressed individuals as a switch option. Virologic efficacy and effectiveness of these DTG-based 2DRs have been demonstrated in phase 3 clinical trials and real-world cohorts, primarily from Europe. This study characterized real-world use of DTG-based 2DRs for HIV-1 treatment in the USA. METHODS: TANDEM was a retrospective medical chart review across 24 US sites. Individuals aged ≥ 18 years who initiated DTG/3TC or DTG/RPV before September 30, 2020, with ≥ 6 months of follow-up were included. One cohort included ART-naive people who initiated DTG/3TC (n = 126), and two other cohorts included virologically suppressed (HIV-1 RNA < 50 copies/mL) people on stable ART regimens for ≥ 3 months before switch to either DTG/3TC (n = 192) or DTG/RPV (n = 151). Clinical characteristics, treatment history, and outcomes are described. RESULTS: Virologically suppressed individuals were older than those who were ART-naive, and the ART-naive cohort had higher proportions of individuals assigned male at birth and of Hispanic ethnicity. The most common healthcare provider-reported reason for choosing a DTG-based 2DR was avoidance of long-term toxicities (25-33% across cohorts), followed by simplification/streamlining of treatment. Among ART-naive people on DTG/3TC, 94% achieved virologic suppression after initiation, and 83% maintained suppression at last follow-up; discontinuation rate was < 1%. Among cohorts who switched to DTG-based 2DRs, 96% maintained virologic suppression on DTG/3TC and 93% on DTG/RPV; 2% on DTG/3TC and 3% on DTG/RPV discontinued. CONCLUSION: Motivation for selecting DTG-based 2DRs was primarily driven by a desire to avoid or manage toxicities and simplify treatment. Results demonstrate that DTG/3TC and DTG/RPV are effective in real-world settings, with few discontinuations, reflecting data from clinical trials.

Real-World Effectiveness of Dolutegravir/Lamivudine in People With HIV-1 in Test-and-Treat Settings or With High Baseline Viral Loads: TANDEM Study Subgroup Analyses.

INTRODUCTION: Dolutegravir/lamivudine (DTG/3TC) was first approved by the US Food and Drug Administration in 2019 for the treatment of antiretroviral therapy (ART)-naive people with HIV-1 based on results from the pivotal GEMINI-1/GEMINI-2 trials. Around that time, immediate initiation of treatment upon diagnosis was recommended in the US Department of Health and Human Services guidelines. Here we report results from 126 treatment-naive people with HIV-1 who initiated DTG/3TC as part of a test-and-treat strategy (n = 61) or with high baseline viral loads (HIV-1 RNA ≥ 100,000 copies/ml; n = 16) from the TANDEM study. METHODS: TANDEM was a US-based, retrospective chart review study that included a cohort of 126 individuals aged ≥ 18 years with no prior history of ART who initiated DTG/3TC before September 30, 2020, and had ≥ 6 months of follow-up. Test-and-treat was defined as ART initiation shortly after diagnosis without available viral load, CD4 + cell count, or HIV-1 resistance data. Outcomes included virologic suppression (HIV-1 RNA < 50 copies/ml; overall and by baseline viral load) and discontinuations. Analyses were descriptive. RESULTS: Among 61 individuals who initiated DTG/3TC in a test-and-treat setting (median [interquartile range (IQR)] treatment duration, 1.3 [0.9-1.7] years), 57 (93%) achieved virologic suppression, and 51 (84%) remained suppressed; 1 (< 1%) individual discontinued DTG/3TC due to persistent low-level viremia. The most common healthcare provider (HCP)-reported reason for initiating DTG/3TC was avoidance of long-term toxicities among individuals in the test-and-treat subgroup. Of 16 treatment-naive individuals with high baseline viral loads (median [IQR] treatment duration, 100,000-250,000 copies/ml: 1.2 [0.8-1.8] years; > 250,000 copies/ml: 1.0 [0.7-1.1] years), 14 (88%) achieved virologic suppression, 13 (81%) remained suppressed, and none discontinued DTG/3TC. Patient preference was the most common HCP-reported reason for initiating DTG/3TC in this subgroup. CONCLUSIONS: Results demonstrate real-world effectiveness of DTG/3TC, with few discontinuations, in people with HIV-1 in test-and-treat settings or with high baseline viral loads.

Understanding Payer Perspectives on Value in the Use of Pharmaceuticals in the United States.

BACKGROUND: In recent years, value assessment frameworks have been introduced to inform discussions about how to define and assess value in the U.S. health care system. However, there is uncertainty as to how value assessment frameworks and other approaches to achieve value such as outcomes-based contracting are perceived and used in coverage decisions. OBJECTIVE: To understand how U.S. payers determine value in the use of pharmaceuticals and how it differs from payers outside the United States. METHODS: Qualitative in-depth phone interviews with 13 executive-level public and private U.S. managed care representatives and 6 health technology assessment advisors outside the United States were conducted from September to November 2017. RESULTS: Despite various mechanisms used by U.S. payers to assess value, no consistent definitions of value were provided, and U.S. payers felt limited in what they can do to achieve value in pharmaceutical decision making. Value assessment frameworks are not formally considered in formulary and reimbursement decisions but are used as a reference as they become available by most or all U.S. health plans. U.S. payers expressed concerns, including limited control over pharmaceutical pricing and budget caps, and limited ability to use incremental cost per quality-adjusted life-year thresholds. Outcomes-based contracting could have some utility in specific cases where the treatment has a particularly high cost and a clear outcomes measure, but payers indicated that outcomes-based contracts can be difficult to operationalize, and determination of savings was uncertain. Payers outside the United States-who are enabled by government health care bodies, policy tools, and analytical frameworks that have no counterpart in the United States-have a wider array of instruments at their disposal. U.S. payers were largely open to learning from other health care systems outside the United States, particularly the German health care system, where patient-relevant benefit compared with a predetermined treatment comparator is the primary determinant for price negotiations. CONCLUSIONS: Although there is interest in including value assessment frameworks during the decision-making process in the United States, there are significant challenges to operationalizing them. The current environment in the United States restricts payers' ability to make favorable contracts with manufacturers, and changes to the U.S. health system design are needed to facilitate this effort. Adoption of a value assessment framework in Medicare or Medicaid would accelerate adoption of these tools by private payers in the United States. DISCLOSURES: This study was conducted by RTI Health Solutions under the direction of The Pew Charitable Trusts and was funded by The Pew Charitable Trusts. Vekaria is employed by RTI Health Solutions. Reynolds and Coukell are employed by The Pew Charitable Trusts. Brogan and Hogue have nothing to disclose.

Payer Perspectives on Patient-Reported Outcomes in Health Care Decision Making: Oncology Examples.

BACKGROUND: Health authorities and payers increasingly recognize the importance of patient perspectives and patient-reported outcomes (PROs) in health care decision making. However, given the broad variety of PRO endpoints included in clinical programs and variations in the timing of PRO data collection and country-specific needs, the role of PRO data in reimbursement decisions requires characterization. OBJECTIVES: To (a) determine the effect of PRO data on market access and reimbursement decisions for oncology products in multiple markets and (b) assess the effect of PRO data collected after clinical progression on payer decision making. METHODS: A 3-part assessment (targeted literature review, qualitative one-on-one interviews, and online survey) was undertaken. Published literature was identified through searches in PubMed/MEDLINE and Embase. In addition, a targeted search was conducted of health technology assessment (HTA) agency websites in the United States, the United Kingdom, France, and Germany. Qualitative one-on-one interviews were conducted with 16 payers from the RTI Health Solutions global advisory panel in 14 markets (Australia, Brazil, France, Germany, Italy, South Korea, Netherlands, Poland, Spain, Sweden, Taiwan, Turkey, the United Kingdom, and the United States [n = 3]). Of the 200 payers and payer advisors from the global advisory panel invited to participate in the online survey, 20 respondents (China, France, Germany, Spain [n = 2], Taiwan, the United Kingdom, and the United States [n = 13]) completed the survey, and 6 respondents (Australia, South Korea, and the United States [n = 4]) partially completed the survey. RESULTS: Reviews of the literature and publicly available HTAs and reimbursement decisions suggested that HTA bodies and payers have varying experience with and confidence in PRO data. Payers participating in the survey indicated that PRO data may be especially influential in oncology compared with other therapeutic areas. Payers surveyed offered little differentiation by cancer type in the importance of PRO data but felt that it was most important to collect PRO data in phase 3 and postmarketing studies. Payers surveyed also anticipated an increasing significance for PRO data over the next 5-10 years. Characteristics of PRO data that maximize influence on payer decision making were reported to be (a) quality, well-controlled, and transparent PRO evidence; (b) psychometric validation of the PRO measure in targeted populations; and (c) publication in peer-reviewed journals. In markets with decentralized health care decision making, PRO data currently have more influence at the local level. Inclusion of PRO data in cancer treatment guidelines is key for centralized markets. Payers surveyed generally considered collecting PRO data postprogression to be useful. Of the 16 interviewees, 11 indicated that it is worthwhile to collect PRO data postprogression and that positive PRO data may support continued therapy at the physician's discretion upon regulatory approval, even in progressive disease. CONCLUSIONS: PRO data may help to differentiate treatments, particularly after clinical progression in oncology. Payers worldwide recognize high-quality PRO data as a key component of their decision-making process and anticipate the growing importance of PRO data in the future. DISCLOSURES: This study and preparation of this article were funded by Novartis Pharmaceuticals. This research was performed under a research contract between RTI Health Solutions and Novartis Pharmaceuticals. Brogan, Hogue, Demuro, and Barrett are employees of RTI Health Solutions. D'Alessio and Bal are employees of Novartis Pharmaceuticals. Study concept and design were contributed by DeMuro, Barrett, Bal, and Hogue. Brogan and Hogue took the lead in data collection, assisted by DeMuro and Bal. Data interpretation was performed by Brogan and Hogue, assisted by the other authors. The manuscript was written by D'Alessio and Brogan, along with the other authors, and revised primarily by Brogan, along with Hogue and assisted by the other authors. The abstract for this article was presented as a research poster at the following meetings: Hogue SL, Brogan A P, De Muro C, D'Alessio D, Bal V. Patient-reported outcomes (PRO) in post-progression oncology: implications in health technology assessments and payer decision making. Poster presented at the ISPOR 18th Annual European Meeting; November 7-11, 2015. Milan, Italy. Hogue SL, Brogan AP, De Muro C, D'Alessio D, Bal V. Influence of patient-reported outcomes (PRO) on market access decisions in markets with centralized healthcare systems. Poster presented at the ISPOR 18th Annual European Meeting; November 7-11, 2015. Milan, Italy. Hogue SL, Brogan AP, De Muro C, Barrett A, D'Alessio D, Bal V. Influence of patient-reported outcomes on market access decisions in decentralized markets (Brazil, Italy, Spain and the United States). Poster presented at the ISPOR 20th Annual Meeting; May 16-20, 2015. Philadelphia PA. Hogue SL, Brogan A P, De Muro C, Barrett A, McLeod L, D'Alessio D, et al. Payer Perspectives of Patient-Reported Outcomes Data: An Online Assessment. Poster presented at the ISOQOL 22nd Annual Meeting; October 21-24, 2015. Vancouver, British Columbia, Canada.

Model-based cost-effectiveness analyses for prostate cancer chemoprevention : a review and summary of challenges.

BACKGROUND AND PURPOSE: Decision-analytic modelling is often used to examine the economics associated with using a specific treatment. As a result, it is important to understand structural and methodological approaches used in published decision-analytic models for examining the cost effectiveness of 5α-reductase inhibitors (5ARIs) for prostate cancer (PCa) chemoprevention. This understanding allows us to provide recommendations for using decision modelling in future economic evaluations of chemoprevention for PCa. METHODS: A review of the published literature was performed using MEDLINE and the Cochrane Library to identify studies involving mathematical decision models that evaluated 5ARIs for PCa chemoprevention. Published articles were reviewed and key modelling components were extracted and summarized. Recommendations for developing future decision models to examine the economic consequences of PCa chemoprevention were presented. RESULTS: We identified seven published models of PCa chemoprevention. All the models identified used a Markov framework with time horizons ranging from 4 years to lifetime. Due to the wide range of patient risk groups examined, PCa risk data were taken from the Surveillance, Epidemiology, and End Results (SEER) and other databases or estimates published in relevant clinical trials. Treatment effects included change in the incidence of high- and low-grade PCa and impacts on benign prostate hyperplasia. Adverse events were considered to affect compliance, discontinuation and quality of life. Quality-of-life impacts were similar among studies. Examination of modelling parameter sensitivities was comprehensive. CONCLUSIONS: Published models have examined the cost effectiveness of PCa chemoprevention; however, limitations exist. Decision models should take into account the full PCa clinical pathway when compiling health states. The time horizon should be long enough to consider the full benefit of chemoprevention while allowing actual time receiving the drug to occur from the start of the model until a man's life expectancy is less than 10 years. Baseline PCa risk should be specific to the population of concern. Models should examine the impact on both low- and high-grade tumours and account for the impact of 5ARIs on benign prostatic hyperplasia. Because chemoprevention has an upfront effect, the structure of the model should be constructed so that the downstream effect of avoiding or delaying recurrence can be considered. Adverse events due to chemoprevention should be considered through compliance, discontinuation or quality-of-life impact, and understanding the impact of avoiding PCa and benign prostatic hyperplasia events are important model properties.

Antibody-catalyzed oxidation of delta(9)-tetrahydrocannabinol.

Marijuana abuse continues to plague society and the lack of effective treatments warrants concern. Catalytic antibodies capable of oxidatively degrading the major psychoactive component of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), are presented. The antibodies generate reactive oxygen species from singlet oxygen (1O2*), using riboflavin (vitamin B2) and visible light as the 1O2* source. Cannabitriol was identified as the major degradation product of this reaction, demonstrating the ability of an antibody to catalyze a complex chemical transformation with therapeutic implications for treating marijuana abuse.

Nornicotine-organocatalyzed aqueous reduction of alpha,beta-unsaturated aldehydes.

Nornicotine, a native component of tobacco and minor nicotine metabolite, was found to catalyze the chemoselective reduction of alpha,beta-unsaturated aldehydes under homogeneous aqueous conditions.

N-(3-oxo-acyl)homoserine lactones signal cell activation through a mechanism distinct from the canonical pathogen-associated molecular pattern recognition receptor pathways.

Innate immune system receptors function as sensors of infection and trigger the immune responses through ligand-specific signaling pathways. These ligands are pathogen-associated products, such as components of bacterial walls and viral nuclear acids. A common response to such ligands is the activation of mitogen-activated protein kinase p38, whereas double-stranded viral RNA additionally induces the phosphorylation of eukaryotic translation initiation factor 2alpha (eIF2alpha). Here we have shown that p38 and eIF2alpha phosphorylation represent two biochemical markers of the effects induced by N-(3-oxo-acyl)homoserine lactones, the secreted products of a number of Gram-negative bacteria, including the human opportunistic pathogen Pseudomonas aeruginosa. Furthermore, N-(3-oxo-dodecanoyl)homoserine lactone induced distension of mitochondria and the endoplasmic reticulum as well as c-jun gene transcription. These effects occurred in a wide variety of cell types including alveolar macrophages and bronchial epithelial cells, requiring the structural integrity of the lactone ring motif and its natural stereochemistry. These findings suggest that N-(3-oxo-acyl)homoserine lactones might be recognized by receptors of the innate immune system. However, we provide evidence that N-(3-oxo-dodecanoyl)homoserine lactone-mediated signaling does not require the presence of the canonical innate immune system receptors, Toll-like receptors, or two members of the NLR/Nod/Caterpillar family, Nod1 and Nod2. These data offer a new understanding of the effects of N-(3-oxo-dodecanoyl)homoserine lactone on host cells and its role in persistent airway infections caused by P. aeruginosa.

Structure of the Escherichia coli quorum sensing protein SdiA: activation of the folding switch by acyl homoserine lactones.

The three-dimensional structure of a complex between the N-terminal domain of the quorum sensing protein SdiA of Escherichia coli and a candidate autoinducer N-octanoyl-L-homoserine lactone (C8-HSL) has been calculated in solution from NMR data. The SdiA-HSL system shows the "folding switch" behavior that has been seen for quorum-sensing factors produced by other bacterial species. In the presence of C8-HSL, a significant proportion of the SdiA protein is produced in a folded, soluble form in an E.coli expression system, whereas in the absence of acyl homoserine lactones, the protein is expressed into insoluble inclusion bodies. In the three-dimensional structure, the autoinducer molecule is sequestered in a deep pocket in the hydrophobic core, forming an integral part of the core packing of the folded SdiA. The NMR spectra of the complex show that the bound C8-HSL is conformationally heterogeneous, either due to motion within the pocket or to heterogeneity of the bound structure. The C8-HSL conformation is defined by NOEs to the protein only at the terminal methyl group of the octanoyl chain. Unlike other well-studied bacterial quorum sensing systems such as LuxR of Vibrio fischeri and TraR of Agrobacterium tumefaciens, there is no endogenous autoinducer for SdiA in E.coli: the E.coli genome does not contain a gene analogous to the LuxI and TraI autoinducer synthetases. We show that two other homoserine lactone derivatives are also capable of acting as a folding-switch autoinducers for SdiA. The observed structural heterogeneity of the bound C8-HSL in the complex, together with the variety of autoinducer-type molecules that can apparently act as folding switches in this system, are consistent with the postulated biological function of the SdiA protein as a detector of the presence of other species of bacteria.

Altered retinoid homeostasis catalyzed by a nicotine metabolite: implications in macular degeneration and normal development.

Retinoids (vitamin A) serve two distinct functions in higher animals: light absorption for vision and gene regulation for growth and development. Cigarette smoking is a contributing factor for diseases that affect vision such as age-related macular degeneration and increases the risk of birth defects; however, altered retinoid homeostasis has received little attention as a potential mechanism for smoking-associated toxicities. Herein, we demonstrate that nornicotine, a nicotine metabolite and component of cigarette smoke, catalyzes the Z-to-E alkene isomerization of unsaturated aldehydes and ketones, including retinals. Despite the recent explosion in the use of organic compounds as chemical catalysts, minimal effort has been devoted to biologically relevant organocatalysis. Our study demonstrates a system in which a lowest unoccupied molecular orbital-lowering intermediate similar to the endogenous protein rhodopsin effectively catalyzes isomerization under biologically relevant conditions. The product of retinal isomerization is all-E-retinal, which in the eye is a biosynthetic precursor to N-retinylidene-N-retinylethanolamine, a hallmark of age-related macular degeneration. Furthermore, 9-Z- and all-E-retinal isomers are biosynthetic precursors to 9-Z- and all-E-retinoic acids, ligands that mediate specific cellular responses by binding to transcriptional regulatory proteins critical in growth and development. Strict maintenance of retinal isomer composition is essential for proper transcriptional regulation. Nornicotine-catalyzed retinal isomerization implies an underlying molecular mechanism for age-related macular degeneration, the birth defects associated with smoking, and other smoking-associated abnormalities that stem from disruption of retinoid metabolism.

Hammett correlation of nornicotine analogues in the aqueous aldol reaction: implications for green organocatalysis.

[reaction: see text] A series of meta- and para-substituted 2-arylpyrrolidines were synthesized and examined for their ability to catalyze an aqueous aldol reaction under buffered conditions. Kinetic analysis of arylpyrrolidine-catalyzed reactions displayed a linear Hammett correlation with rho = 1.14 (R(2) = 0.996), indicating that the reaction is accelerated by electron-withdrawing aryl rings. These results show promise for the development of a synthetically viable aqueous organo-catalyst.

Bismuth-dithiol inhibition of the Escherichia coli rho transcription termination factor.

Bismuth-dithiol mixtures are proven antimicrobial agents with unknown mechanism(s) of action. We show that select bismuth-dithiol solutions inhibit the Escherichia coli rho transcription termination factor. Rho is an essential enzyme in most Gram-negative prokaryotes and without rho function the cells are not viable. Bismuth complexes with 2,3-dimercapto-1-propanol (BiBAL) (3:1 solutions) functioned as a noncompetitive inhibitor with respect to ATP in the rho poly(C)-dependent ATPase assay (I50=60 microM) and as a competitive inhibitor with respect to ribo(C)10 in the poly(dC)-ribo(C)10-dependent ATPase assay. The minimum inhibitory concentration (MIC) of bacterial growth for BiBAL (3:1) in the liquid culture assay using E. coli W3350 was 16 microM. Using the tnaA/lacZ fusion reporter assay we showed that sublethal amounts (3 microM) of BiBAL (3:1 solution) led to a small increase (37%) in in vivo beta-galactosidase activity in E. coli SVS1144, which corresponds to antitermination of the tna operon as a result of rho inhibition. We concluded that BiBAL was a potent in vitro rho inhibitor but its effect on in vivo rho processes was modest indicating that other mechanisms contributed to the antibacterial activity of BiBAL. Our study suggests that structural changes in the dithiol unit that provide greater bismuth binding may improve rho specificity, a macromolecular target not previously recognized for bismuth therapy.

Development of a technique to determine bicyclomycin-rho binding and stoichiometry by isothermal titration calorimetry and mass spectrometry.

Bicyclomycin (1) is the only natural product inhibitor of the transcription termination factor rho. Rho is a hexameric helicase that terminates nascent RNA transcripts utilizing ATP hydrolysis and is an essential protein for many bacteria. The paucity of information concerning the 1-rho interaction stems from the weak binding affinity of 1. We report a novel technique using imine formation with rho to enhance the affinity of a bicyclomycin analogue and determine the binding stoichiometry by isothermal titration calorimetry (ITC) and mass spectrometry (MS). Our designed bicyclomycin ligand, 5a-(3-formyl-phenylsulfanyl)-dihydrobicyclomycin (2) (apparent I(50) = 4 muM), inhibits rho an order of magnitude more efficiently than 1 (I(50) = 60 muM). MS shows that 2 selectively forms an imine with K181 in rho. We found that despite the heterogeneity of ATP binding (three tight and three weak) imposed on the rho hexamer, the nearby bicyclomycin binding pocket is not affected, and both 1 and 2 bind with equal affinity to all six subunits.

Structural mechanism of inhibition of the Rho transcription termination factor by the antibiotic bicyclomycin.

Rho is a hexameric RNA/DNA helicase/translocase that terminates transcription of select genes in bacteria. The naturally occurring antibiotic, bicyclomycin (BCM), acts as a noncompetitive inhibitor of ATP turnover to disrupt this process. We have determined three independent X-ray crystal structures of Rho complexed with BCM and two semisynthetic derivatives, 5a-(3-formylphenylsulfanyl)-dihydrobicyclomycin (FPDB) and 5a-formylbicyclomycin (FB) to 3.15, 3.05, and 3.15 A resolution, respectively. The structures show that BCM and its derivatives are nonnucleotide inhibitors that interact with Rho at a pocket adjacent to the ATP and RNA binding sites in the C-terminal half of the protein. BCM association prevents ATP turnover by an unexpected mechanism, occluding the binding of the nucleophilic water molecule required for ATP hydrolysis. Our data explain why only certain elements of BCM have been amenable to modification and serve as a template for the design of new inhibitors.

Revisiting quorum sensing: Discovery of additional chemical and biological functions for 3-oxo-N-acylhomoserine lactones.

Bacteria use small diffusible molecules to exchange information in a process called quorum sensing. An important class of autoinducers used by Gram-negative bacteria is the family of N-acylhomoserine lactones. Here, we report the discovery of a previously undescribed nonenzymatically formed product from N-(3-oxododecanoyl)-L-homoserine lactone; both the N-acylhomoserine and its novel tetramic acid degradation product, 3-(1-hydroxydecylidene)-5-(2-hydroxyethyl)pyrrolidine-2,4-dione, are potent antibacterial agents. Bactericidal activity was observed against all tested Gram-positive bacterial strains, whereas no toxicity was seen against Gram-negative bacteria. We propose that Pseudomonas aeruginosa utilizes this tetramic acid as an interference strategy to preclude encroachment by competing bacteria. Additionally, we have discovered that this tetramic acid binds iron with comparable affinity to known bacterial siderophores, possibly providing an unrecognized mechanism for iron solubilization. These findings merit new attention such that other previously identified autoinducers be reevaluated for additional biological functions.

Bicyclomycin fluorescent probes: synthesis and biochemical, biophysical, and biological properties.

Bicyclomycin (1) is a commercially available antibiotic whose primary site of action in Escherichia coli is the transcription termination factor rho. Key aspects of the 1.rho interaction-K(d), stoichiometry for 1.rho binding, and whether 1 and ATP binding induce conformational changes in rho-remain unknown. In this study, the design, synthesis, and characterization of a series of bicyclomycin fluorescent probes (BFP) constructed to sense the 1.rho interaction are described and their use documented. We show that dihydrobicyclomycins with medium-to-large C(5a)-substituents afforded excellent inhibitory activities exceeding those of 1 in the poly(C)-dependent ATPase assay. The utility of BFP in bicyclomycin-rho binding studies was documented through the use of 5a-(phenazin-2-ylmethylsulfanyl)dihydrobicyclomycin (15). Excitation (290 nm) of W381 in wild-type rho in the presence of 15 and ATP led to fluorescence resonance energy transfer (FRET) and gave a K(d) (15) of 9.9 microM. Using ADP in place of ATP or excluding nucleotide did not result in energy transfer, which suggests that ATP binding induced a conformational change in rho. FRET measurements provided an approximate weighted average distance (23 A) between W381 and 15 in the presence of bound ATP. The K(d) value for 15.rho was correlated with ATP binding at the 3 tight ATP binding (K(d)(ATP) = 95 nM) sites in wild-type rho.