Immunogenicity and safety of booster CYD-TDV dengue vaccine after alternative primary vaccination schedules in healthy individuals aged 9-50 years: a randomised, controlled, phase 2, non-inferiority study

BACKGROUND

Dengue is endemic in many countries throughout the tropics and subtropics, and the disease causes substantial morbidity and health-care burdens in these regions. We previously compared antibody responses after one-dose, two-dose, or three-dose primary regimens with the only approved dengue vaccine CYD-TDV (Dengvaxia; Sanofi Pasteur, Lyon, France) in individuals aged 9 years and older with previous dengue exposure. In this study, we assessed the need for a CYD-TDV booster after these primary vaccination regimens.

METHODS

In this randomised, controlled, phase 2, non-inferiority study, healthy individuals aged 9-50 years recruited from three sites in Colombia and three sites in the Philippines (excluding those with the usual contraindications to vaccinations) were randomly assigned 1:1:1 via a permuted block method with stratification by site and by age group using an independent voice response system to receive, at 6-month intervals, three doses of CYD-TDV (three-dose group), one dose of placebo followed by two doses of CYD-TDV (two-dose group), or two doses of placebo followed by one dose of CYD-TDV (one-dose group). Participants were also randomly assigned (1:1) to receive a CYD-TDV booster at 1 year or 2 years after the last primary dose. Each CYD-TDV dose was 0·5 mL and administered subcutaneously in the deltoid region of the upper arm. The investigators and sponsor, study staff interacting with the investigators, and participants and their parents or legally acceptable representatives were masked to group assignment. Neutralising antibodies were measured by 50% plaque reduction neutralisation testing, and geometric mean titres (GMTs) were calculated. Due to a change in study protocol, only participants who were dengue seropositive at baseline in the Colombian cohort received a booster vaccination. The primary outcome was to show non-inferiority of the booster dose administered at 1 year or 2 years after the two-dose and three-dose primary regimens; non-inferiority was shown if the lower limit of the two-sided adjusted 95% CI of the between-group (day 28 post-booster dose GMT from the three-dose or two-dose group vs day 28 GMT post-dose three of the three-dose primary regimen [three-dose group]) geometric mean ratio (GMR) was higher than 0·5 for each serotype. Non-inferiority of the 1-year or 2-year booster was shown if all four serotypes achieved non-inferiority. Safety was assessed among all participants who received the booster. This trial is registered with ClinicalTrials.gov, NCT02628444, and is closed to accrual.

FINDINGS

Between May 2 and Sept 16, 2016, we recruited and enrolled 1050 individuals who received either vaccine or placebo. Of the 350, 348, and 352 individuals randomly assigned to three-dose, two-dose, and one-dose groups, respectively, 108, 115, and 115 from the Colombian cohort were dengue seropositive at baseline and received a booster; 55 and 53 in the three-dose group received a booster after 1 year and 2 years, respectively, as did 59 and 56 in the two-dose group, and 62 and 53 in the one-dose group. After the three-dose primary schedule, non-inferiority was shown for serotypes 2 (GMR 0·746; 95% CI 0·550-1·010) and 3 (1·040; 0·686-1·570) but not serotypes 1 (0·567; 0·399-0·805) and 4 (0·647; 0·434-0·963) for the 1-year booster, and again for serotypes 2 (0·871; 0·673-1·130) and 3 (1·150; 0·887-1·490) but not serotypes 1 (0·688; 0·479-0·989) and 4 (0·655; 0·471-0·911) for the 2-year booster. Similarly, after the two-dose primary schedule, non-inferiority was shown for serotypes 2 (0·809; 0·505-1·300) and 3 (1·19; 0·732-1·940) but not serotypes 1 (0·627; 0·342-1·150) and 4 (0·499; 0·331-0·754) for the 1-year booster, and for serotype 3 (0·911; 0·573-1·450) but not serotypes 1 (0·889; 0·462-1·710), 2 (0·677; 0·402-1·140), and 4 (0·702; 0·447-1·100) for the 2-year booster. Thus, non-inferiority of the 1-year or 2-year booster was not shown after the three-dose or two-dose primary vaccination regimen in dengue-seropositive participants. No safety concerns occurred with the 1-year or 2-year CYD-TDV booster.

INTERPRETATION

CYD-TDV booster 1 year or 2 years after the two-dose or three-dose primary vaccination regimen does not elicit a consistent, meaningful booster effect against all dengue serotypes in participants who are seropositive for dengue at baseline.

FUNDING

Sanofi Pasteur.

TRANSLATION

For the Spanish translation of the abstract see Supplementary Materials section.

CYD Tetravalent Dengue Vaccine Performance by Baseline Immune Profile (Monotypic/Multitypic) in Dengue-Seropositive Individuals

Background

The immune profile of dengue-experienced individuals is a determinant of dengue reinfection severity risk. Individuals with a single prior dengue infection (monotypic) are at highest risk for severe disease, while individuals with ≥ 2 prior dengue infections (multitypic) are at lower risk. The tetravalent dengue vaccine (CYD-TDV) has shown efficacy in the prevention of dengue in individuals with prior dengue infection. We estimated efficacy in individuals with monotypic or multitypic immune profiles.

Methods

Participants enrolled in the immunogenicity subsets of 2 randomized placebo-controlled phase 3 studies (CYD14, NCT01373281; CYD15, NCT01374516) were classified as either monotypic or multitypic, based on measured baseline dengue plaque reduction neutralization test. Vaccine efficacy (VE) against symptomatic virologically confirmed dengue (VCD) was assessed over 25 months and against VCD hospitalization over 6 years.

Results

Of 3927 participants in the immunogenicity subsets, 496 and 257 in the CYD-TDV and placebo groups, respectively, were classified as monotypic immune, and 1227 and 612, respectively, as multitypic immune. VE against symptomatic VCD was 77.4% (95% CI, 56.4%–88.2%) for monotypic and 89.2% (95% CI, 71.5%–95.9%) for multitypic profiles, with corresponding absolute risk reductions (ARRs) of 4.48% (95% CI, 2.32%–6.65%) for monotypics and 1.67% (95% CI, .89%–2.46%) for multitypics. VE against hospitalized VCD was 75.3% (95% CI, 42.7%–90.2%) in monotypics and 81.2% (95% CI, 21.7%–96.8%) in multitypics, with ARRs of 0.95% (95% CI, .37%–1.53%) for monotypics and 0.18% (95% CI, .02%–.34%) for multitypics.

Conclusions

CYD-TDV benefits individuals with monotypic and multitypic immune profiles. Larger public health benefit is expected to derive from the protection of individuals with a monotypic immune profile.

Immunogenicity and safety of simplified vaccination schedules for the CYD-TDV dengue vaccine in healthy individuals aged 9-50 years (CYD65): a randomised, controlled, phase 2, non-inferiority study

BACKGROUND

Three doses of the licensed tetravalent dengue vaccine CYD-TDV (Dengvaxia, Sanofi Pasteur, Lyon France) are immunogenic and effective against symptomatic dengue in individuals aged 9 years and older who are dengue seropositive. Previous trials have provided some evidence that antibody responses elicited after just one dose or two doses of CYD-TDV might be similar to those elicited after three doses. We compared antibody responses following one-dose, two-dose, and three-dose vaccination regimens in individuals who were dengue seropositive at baseline up to 1 year after the last injection.

METHODS

In this randomised, controlled, phase 2, non-inferiority study (CYD65), healthy individuals aged 9-50 years were recruited from the community in three sites in Colombia and three sites in the Philippines. Participants were randomly assigned (1:1:1), using a permuted block method with stratification by site and age group, to receive, at 6-month intervals (on day 0, month 6, and month 12), three doses of CYD-TDV (three-dose group), one dose of placebo (on day 0) and two doses of CYD-TDV (at months 6 and 12; two-dose group), or two doses of placebo (on day 0 and month 6) and one dose of CYD-TDV (at month 12; one-dose group). Each dose of CYD-TDV was 0·5 mL, administered subcutaneously into the deltoid of the upper arm. Participants, study staff, investigators, and the funder were masked to group assignment. The co-primary endpoints were geometric mean titres (GMTs) of neutralising antibodies against each dengue virus serotype at 28 days and 1 year after the last vaccine injection. After a protocol amendment during the conduct of the study, the original co-primary objectives of non-inferiority of the one-dose and two-dose groups to the three-dose group were altered to include non-inferiority of the two-dose group to the three-dose group only, to be assessed in individuals who were dengue seropositive at baseline. Non-inferiority was shown if the lower limit of the 95% CI for the ratio of GMTs (GMR) at 28 days and 1 year between groups was more than 0·5 for each serotype. The analysis of the coprimary objectives was done in the per-protocol analysis dataset, which included all participants who had been vaccinated, had no protocol deviations, and had a valid serology test result for at least one dengue serotype at 28 days after the third injection. Safety was assessed throughout in all participants who received at least one injection of study drug, regardless of serostatus. This trial is registered with ClinicalTrials.gov, NCT02628444, and is closed to accrual.

FINDINGS

Between May 2, 2016, and Sept 16, 2016, we recruited and enrolled 1050 individuals, of whom 1048 received at least one injection and 993 had at least one blood sample taken (full-analysis dataset; 333 in three-dose group, 328 in two-dose group, and 332 in one-dose group). 860 (86·6%) of 993 participants in the full-analysis dataset were dengue seropositive at baseline. Non-inferiority (two dose vs three dose) was shown for each serotype at both 28 days and 1 year among dengue-seropositive participants (number of participants assessed: 272 [two-dose group], 265 [three-dose group] at 28 days; and 190 [two-dose group], 185 [three-dose group] at 1 year). At 28 days after the last injection, neutralising antibody GMTs were 899 (95% CI 752-1075) in the two-dose group versus 822 (700-964) in the three dose group against dengue serotype 1 (GMR 1·09 [95% CI 0·86-1·39]); 869 (754-1002) versus 875 (770-995) against serotype 2 (GMR 0·99 [0·82-1·20]); 599 (524-685) versus 610 (535-694) against serotype 3 (GMR 0·98 [0·82-1·18]); and 510 (453-575) versus 531 (470-601) against serotype 4 (GMR 0·96 [0·81-1·14]). At year 1, GMTs had decreased but remained above baseline for all serotypes: 504 (95% CI 403-630) in the two-dose group versus 490 (398-604) in the three-dose group against serotype 1 (GMR 1·03 [0·76-1·40]); 737 (611-888) versus 821 (704-957) against serotype 2 (GMR 0·90 [0·71-1·14]); 437 (368-519) versus 477 (405-561) against serotype 3 (GMR 0·92 [0·72-1·16]); and 238 (205-277) versus 270 (235-310) against serotype 4 (GMR 0·88 [0·72-1·09]). Reactogenicity profiles were similar across treatment groups. Most unsolicited adverse events after any injection were non-serious and systemic in nature. During the study, 60 serious adverse events were reported in 58 participants (14 in three-dose group, 26 in two-dose group, 18 in one-dose group), mostly infection and infestations or injury, poisoning, and procedural complications. No serious adverse events of special interest or admissions to hospital for dengue occurred. Two deaths occurred, unrelated to study treatment.

INTERPRETATION

A two-dose CYD-TDV regimen might be an alternative to the licensed three-dose regimen in individuals who are dengue seropositive at baseline and aged 9 years and older. Vaccination with a reduced number of doses could lead to improved vaccine compliance and coverage, especially in low-resource settings.

FUNDING

Sanofi Pasteur.

Prospective cohort study with active surveillance for fever in four dengue endemic countries in Latin America

To prepare for a Phase III dengue vaccine efficacy trial, 20 investigational sites were selected for this observational study to identify dengue infections in a closed cohort (N = 3,000 children 9-16 years of age). Of 255 acute febrile episodes experienced by 235 children, 50 (21.3%) were considered serologically probable dengue, and 18 (7.7%) were considered virologically confirmed (i.e., dengue NS1 antigen positive) dengue cases. Considering the disease-free and at-risk period from study start to onset of symptoms, the overall incidence density of acute febrile episodes was 17.7 per 100 person-years of follow-up, ranging from 15.3 in Colombia to 22.0 in Puerto Rico. This study showed that all sites were capable of capturing and following up acute febrile episodes within a specific timeframe among the established cohort and to detect dengue cases.

Assessing the interest to participate in a dengue vaccine efficacy trial among residents of Puerto Rico

Dengue, endemic in Puerto Rico, is a major public health problem. Vaccines are thought the best means to prevent dengue because vector control alone has been largely ineffective. We implemented qualitative studies in 2006 and 2010 to determine the acceptability of conducting placebo-controlled dengue vaccine efficacy trials in Puerto Rican children. Key informant interviews and focus groups with parents and children were conducted in municipalities with high dengue incidence. We used structured open-ended questions to determine motivators and attitudes regarding vaccine trial participation. Knowledge about dengue risk and prevention, and knowledge, attitudes, and beliefs regarding vaccines and vaccine trials were assessed. Using grounded theory, we conducted content analysis and established categories and sub-categories of participant responses. All participants were knowledgeable about dengue prevention and perceived children as most affected age groups. Participants were aware of vaccines benefits and they thought a vaccine could prevent dengue. However, most would not allow their children to participate in a placebo-controlled vaccine trial. Barriers included lack of trust in new vaccines and vaccine trial procedures; fear of developing dengue or side effects from the vaccine and lack of information about candidate dengue vaccines. Participants thought information, including results of previous trials might overcome barriers to participation. Motivators for participation were altruism, protection from dengue, free medical attention, and compensation for transportation and participation. Parents would consider children participation if accurate vaccine trial information is provided.

Phase II, randomized, double-blind, placebo-controlled, multicenter study to investigate the immunogenicity and safety of a West Nile virus vaccine in healthy adults

BACKGROUND

ChimeriVax-WN02 is a live, attenuated chimeric vaccine for protection against West Nile virus. This Phase II, randomized, double-blind, placebo-controlled, multicenter study assessed the immunogenicity, viremia, and safety of the ChimeriVax-WN02 vaccine.

METHODS

The 2-part study included adults in general good health. In part 1, subjects aged 18-40 years were randomized to 1 of 4 treatment groups: ChimeriVax-WN02 3.7- × -10(5) plaque-forming units (PFU), 3.7 × 10(4) PFU, 3.7 × 10(3) PFU, or placebo. In part 2, subjects aged 41-64 and ≥ 65 years were randomized to receive ChimeriVax-WN02 3.7 × 10(5) PFU or placebo.

RESULTS

In both part 1 and part 2, seroconversion was achieved at day 28 by >96% of subjects in active treatment groups. In part 1, neutralizing antibody titers at day 28 were higher and viremia levels lower with the highest dose, whereas the adverse event profile was similar between the dose groups. In part 2, antibody titers and viremia levels were higher in subjects aged ≥ 65 years, and more subjects in the 41-64 years cohort experienced adverse events.

CONCLUSIONS

The ChimeriVax-WN02 vaccine was highly immunogenic in younger adults and the elderly, and it was well tolerated at all dose levels and in all age groups investigated. Clinical Trials.gov identifier: NCT00442169.

Effectiveness of previous mumps vaccination during a summer camp outbreak

OBJECTIVES

Mumps is a vaccine-preventable disease that may cause outbreaks. In July 2005, an outbreak of mumps occurred during a children's summer camp in upstate New York. An investigation was initiated to describe the cases and evaluate vaccine effectiveness.

METHODS

A retrospective cohort study was conducted among 541 children from the United States and abroad who attended a 1- or 2-month overnight summer camp. Patients with mumps were interviewed; serologic analysis was conducted for 6 case patients. Vaccine effectiveness was calculated by retrospective review of immunization records for 507 attendees who were eligible for vaccination and had verified immunization history.

RESULTS

Thirty-one camp attendees were identified as having mumps (attack rate: 5.7%); 5 (83%) of 6 patients tested had positivity for mumps immunoglobulin M. Of the 507 participants (including 29 patients) with available immunization history, 440 (including 16 [87%] patients) were 2-dose recipients of mumps vaccine (attack rate: 3.6%); 46 participants (including 4 [9%] patients) were 1-dose recipients (attack rate: 8.7%); and 21 (including 9 [4%] patients) were unvaccinated (attack rate: 42.9%). Vaccine effectiveness was 92% for 2 doses and 80% for 1 dose.

CONCLUSIONS

Outbreaks of mumps in settings such as summer camps can occur despite high vaccination rates. Vaccine effectiveness for 2 mumps vaccinations was greater than vaccine effectiveness for 1 mumps vaccination. Therefore, recommendation of 2 mumps vaccinations for summer camp participants continues to be appropriate. Control of mumps disease relies on broad vaccination coupled with correct clinical diagnosis and strict control measures.

Identical genotype B3 sequences from measles patients in 4 countries, 2005

Surveillance of measles virus detected an epidemiologic link between a refugee from Kenya and a Dutch tourist in New Jersey, USA. Identical genotype B3 sequences from patients with contemporaneous cases in the United States, Canada, and Mexico in November and December 2005 indicate that Kenya was likely to have been the common source of virus.

A limited measles outbreak in a highly vaccinated US boarding school

OBJECTIVES

We investigated a measles outbreak that began in March 2003 in a Pennsylvania boarding school with >600 students to identify all cases, including the source; implement outbreak control measures; and evaluate vaccine effectiveness.

METHODS

Measles was suspected in any person at the school with a generalized rash and fever during March 21 to May 28, 2003 and investigated with serologic testing. We reviewed vaccination history from school records and conducted a survey to determine country of measles vaccination. Vaccine effectiveness was calculated using the cohort method.

RESULTS

We identified 9 laboratory-confirmed cases at the school: 8 students and 1 staff member. Among them, 2 had never received any doses of measles-containing vaccine (MCV), 1 received 1 dose of MCV, and 6 received 2 doses of MCV. Three of the 6 who received 2 doses of MCV received both doses outside the United States. The source case had been infected in Lebanon. Two laboratory-confirmed spread cases were identified in New York City. Measles virus of genotype D4 was isolated in cases from the school and New York City. Of the 663 students in the school, 8 (1.2%) had never received any doses of MCV, 26 (3.9%) had received 1 dose, and 629 (94.9%) had received 2 doses before the outbreak. Vaccine effectiveness among students who had received 2 doses of MCV was 98.6%. However, students who received both doses outside the United States had a higher attack rate (3 of 75) than those who received both doses in the United States (3 of 509; rate ratio: 6.8; 95% confidence interval: 1.4-33.0).

CONCLUSIONS

This is the largest measles outbreak to occur in a school in the United States since 1998, but it was limited to only 9 cases in a boarding school with >600 students. The limited extent of this outbreak highlights the high level of population immunity achieved in the United States through widespread implementation of a 2-dose measles-mumps-rubella vaccination strategy in school-aged children. States and schools should continue to enforce strictly the 2-dose measles-mumps-rubella vaccination requirement and, in an outbreak setting, consider revaccinating students who received measles vaccine outside of the United States. Continued vigilance by health care providers is needed to recognize measles cases.

[Multidrug resistance in uveal melanoma]

In spite of important progress in the local treatment of uveal melanoma, the most frequent primitive intraocular tumor, 15%-30% of patients still die because of tumor metastasis. This tumor is characterized by constitutive chemoresistance, thwarting any attempt to control it using the usual chemotherapy protocols. The chemoresistance of uveal melanoma is mainly due to the typical multidrug resistance phenotype (MDR), which is linked to overexpression of membrane proteins that actively extrude anticancer drugs from the cell. Typical MDR is particularly complex in this tumor since several chemoresistance-related proteins are simultaneously produced. The negative prognostic significance of the overexpression of P-glycoprotein, the main representative among the typical MDR-related proteins, was shown in uveal melanoma. The atypical MDR phenotype, which refers to other chemoresistance mechanisms such as resistance to apoptosis also contributes to the chemoresistance of uveal melanoma. Thanks to the recent progress in molecular biology, the chemosensitization strategies of gene therapy approaches, which aim at weakening the pathological activity of MDR genes in cancer cells, are currently on the rise. This approach will disrupt current therapeutic strategies and necessarily improve and standardize the methods used to characterize the chemoresistance profile of this cancer. Indeed, we will have to know the genes to be targeted for each melanoma in order to induce cell chemosensitivity.

Données cytogénétiques actuelles : vers la monosomie du chromosme 3 comme principal facteur pronostique du mélanome uvéal

Uveal melanoma is the most frequent intraocular cancer. The recent development of new technologies such as microsatellite analysis and comparative genomic hybridization have elucidated both the cytogenetics and the natural history of this disease. Fifty to 60% of uveal melanomas are linked to monosomy 3, which appears as an early and determinant event in tumor progression. Tumors with this anomaly have a very poor prognosis. Recent work suggests that this category of uveal melanomas represents a distinct pathological entity from that associated with normal disomy 3. Chromosome 6 aberrations probably make up a second entry point into the process of carcinogenesis, while gains in 8q seem to appear later in the natural history of uveal melanoma because of their higher frequency in larger tumors. Progress in genome analysis has identified regions in chromosomes 3, 6, and 8 as those most probably involved in tumorigenesis. It is to be hoped that this will soon lead to the discovery of the genes responsible.

RU49953: a non-hormonal steroid derivative that potently inhibits P-glycoprotein and reverts cellular multidrug resistance

Progesterone and the antiprogestin RU38486 have been reported as non-transported modulators of P-glycoprotein-mediated drug efflux. However, their hormonal properties limit their potential for clinical trials. The present work shows that some derivatives from either progesterone/RU38486 or estradiol, displaying differential interaction with hormone receptors, bind to P-glycoprotein and chemosensitize the growth of MDR1-transfected cells to vinblastine more strongly than does RU38486. Structure comparison of the compounds indicates that the highly hydrophobic estradiol derivative RU49953, which does not interact with any hormone receptor, inhibits P-glycoprotein-mediated drug efflux very efficiently, as monitored by flow cytometry, and prevents drug site photoaffinity labeling by azidopine. It induces a much higher chemosensitization than the well-known P-glycoprotein modulator verapamil, which is itself more efficient than RU38486. RU49953 therefore constitutes a promising new lead for steroid-type modulators of multidrug resistance.

Modulation by flavonoids of cell multidrug resistance mediated by P-glycoprotein and related ABC transporters

Cancer cell resistance to chemotherapy is often mediated by overexpression of P-glycoprotein, a plasma membrane ABC (ATP-binding cassette) transporter which extrudes cytotoxic drugs at the expense of ATP hydrolysis. P-glycoprotein (ABCB1, according to the human gene nomenclature committee) consists of two homologous halves each containing a transmembrane domain (TMD) involved in drug binding and efflux, and a cytosolic nucleotide-binding domain (NBD) involved in ATP binding and hydrolysis, with an overall (TMD-NBD)2 domain topology. Homologous ABC multidrug transporters, from the same ABCB family, are found in many species such as Plasmodiumfalciparum and Leishmania spp. protozoa, where they induce resistance to antiparasitic drugs. In yeasts, some ABC transporters involved in resistance to fungicides, such as Saccharomyces cerevisiae Pdr5p and Snq2p, display a different (NBD-TMD)2 domain topology and are classified in another family, ABCG. Much effort has been spent to modulate multidrug resistance in the different species by using specific inhibitors, but generally with little success due to additional cellular targets and/or extrusion of the potential inhibitors. This review shows that due to similarities in function and maybe in three-dimensional organization of the different transporters, common potential modulators have been found. An in vitro 'rational screening' was performed among the large flavonoid family using a four-step procedure: (i) direct binding to purified recombinant cytosolic NBD and/or full-length transporter, (ii) inhibition of ATP hydrolysis and energy-dependent drug interaction with transporter-enriched membranes, (iii) inhibition of cell transporter activity monitored by flow cytometry and (iv) chemosensitization of cell growth. The results indicate that prenylated flavonoids bind with high affinity, and strongly inhibit drug interaction and nucleotide hydrolysis. As such, they constitute promising potential modulators of multidrug resistance.

P-glycoprotein-mediated resistance to chemotherapy in cancer cells: using recombinant cytosolic domains to establish structure-function relationships

Resistance to chemotherapy in cancer cells is mainly mediated by overexpression of P-glycoprotein (Pgp), a plasma membrane ATP-binding cassette (ABC) transporter which extrudes cytotoxic drugs at the expense of ATP hydrolysis. Pgp consists of two homologous halves each containing a transmembrane domain and a cytosolic nucleotide-binding domain (NBD) which contains two consensus Walker motifs, A and B, involved in ATP binding and hydrolysis. The protein also contains an S signature characteristic of ABC transporters. The molecular mechanism of Pgp-mediated drug transport is not known. Since the transporter has an extraordinarily broad substrate specificity, its cellular function has been described as a "hydrophobic vacuum cleaner". The limited knowledge about the mechanism of Pgp, partly due to the lack of a high-resolution structure, is well reflected in the failure to efficiently inhibit its activity in cancer cells and thus to reverse multidrug resistance (MDR). In contrast to the difficulties encountered when studying the full-length Pgp, the recombinant NBDs can be obtained in large amounts as soluble proteins. The biochemical and biophysical characterization of recombinant NBDs is shown here to provide a suitable alternative route to establish structure-function relationships. NBDs were shown to bind ATP and analogues as well as potent modulators of MDR, such as hydrophobic steroids, at a region close to the ATP site. Interestingly, flavonoids also bind to NBDs with high affinity. Their binding site partly overlaps both the ATP-binding site and the steroid-interacting region. Therefore flavonoids constitute a new promising class of bifunctional modulators of Pgp.

Correlation between the affinity of flavonoids binding to the cytosolic site of Leishmania tropica multidrug transporter and their efficiency to revert parasite resistance to daunomycin

The C-terminal nucleotide-binding domain (NBD2) of a P-glycoprotein-like transporter, encoded by the ltrmdr1 gene in Leishmania tropica and involved in parasite multidrug resistance (MDR), was overexpressed in Escherichia coli as a hexahistidine tagged protein and purified. The L. tropica recombinant domain efficiently bound fluorescent derivatives of ATP, the hydrophobic steroid analogue RU 486, and different classes of flavonoids with the following efficiency: flavone > flavanone > isoflavone > glucorhamnosyl-flavone > chromone. The affinity for flavones was dependent on the presence of hydroxyl groups at positions 5 and 3 and was further increased by a hydrophobic 1,1-dimethylallyl substituent at position 8. When flow cytometry was used to measure daunomycin accumulation in a MDR L. tropica line, a reversing effect was observed with flavones such as dimethylallyl-kaempferide at low concentration or apigenin at higher concentration, but neither with the glucorhamnosyl derivative rutin nor with the isoflavone genistein. The in vivo reversing effect of dimethylallyl-kaempferide was correlated to a high inhibition of MDR cell growth in the presence of daunomycin. The results suggest that flavone inhibition of both daunomycin efflux and parasite growth in the presence of the drug correlates to direct binding of the compound to cytosolic domain of the P-glycoprotein-like transporter.

Flavonoids: a class of modulators with bifunctional interactions at vicinal ATP- and steroid-binding sites on mouse P-glycoprotein

A hexahistidine-tagged C-terminal nucleotide-binding domain (H6-NBD2) from mouse P-glycoprotein was designed, overexpressed, and purified as a highly soluble recombinant protein. Intrinsic fluorescence of its single tryptophan residue allowed monitoring of high-affinity binding of 2'(3')-N-methylanthraniloyl-ATP (MANT-ATP), a fluorescent ATP derivative that induces a marked quenching correlated to fluorescence resonance-energy transfer. H6-NBD2 also bound all flavonoids known to modulate the multidrug resistance phenotype of P-glycoprotein-positive cancer cells, with similar affinities and relative efficiencies. Flavones (like quercetin or apigenin) bound more strongly than flavanones (naringenin), isoflavones (genistein), or glycosylated derivatives (rutin). Kaempferide, a 4'-methoxy 3,5,7-trihydroxy flavone, was even more reactive and induced a complete quenching of H6-NBD2 intrinsic fluorescence. Kaempferide binding was partly prevented by preincubation with ATP, or partly displaced upon ATP addition. Interestingly, kaempferide was also able to partly prevent the binding of the antiprogestin RU 486 to a hydrophobic region similar to that recently found, close to the ATP site, in the N-terminal cytosolic domain. Conversely, RU 486 partly prevented kaempferide binding, the effect being additive to the partial prevention by ATP. Furthermore, MANT-ATP binding, which occurred at the ATP site and extended to the vicinal steroid-interacting hydrophobic region, was completely prevented or displaced by kaempferide. All results indicate that flavonoids constitute a new class of modulators with bifunctional interactions at vicinal ATP-binding site and steroid-interacting region within a cytosolic domain of P-glycoprotein.

Binding of steroid modulators to recombinant cytosolic domain from mouse P-glycoprotein in close proximity to the ATP site

We recently found that recombinant NBD1 cytosolic domain corresponding to segment 395-581 of mouse mdr1 P-glycoprotein bound fluorescent 2'(3')-N-methylanthraniloyl-ATP (MANT-ATP) with high affinity [Dayan, G., Baubichon-Cortay, H., Jault, J.-M., Cortay, J. -C., Deléage, G., & Di Pietro, A. (1996) J. Biol. Chem. 271, 11652-11658]. The present work shows that a longer 371-705 domain (extended-NBD1), including tryptophan-696 as an intrinsic probe, which bound MANT-ATP with identical affinity, also interacted with steroids known to modulate anticancer drug efflux from P-glycoprotein-positive multidrug-resistant cells. Progesterone, which is not transported, its hydrophobic derivatives medroxyprogesterone acetate and megestrol acetate, and Delta6-progesterone produced nearly a 50% saturating quenching of the domain intrinsic fluorescence, with dissociation constants ranging from 53 to 18 microM. The even more hydrophobic antiprogestin RU 486 produced a complete quenching of tryptophan-696 fluorescence, in contrast to more hydrophilic derivatives of progesterone containing hydroxyl groups at positions 11, 16, 17, and 21 and known to be transported, which produced very little quenching. A similar differential interaction was observed with full-length purified P-glycoprotein. The steroid-binding region within extended-NBD1 appeared distinct from the nucleotide-binding site as the RU 486-induced quenching was neither prevented nor reversed by high ATP concentrations. In contrast, MANT-ATP binding was efficiently prevented or displaced by RU 486, suggesting that the hydrophobic MANT group of the bound nucleotide analogue overlaps, at least partially, the adjacent steroid-binding region revealed by RU 486.

Recombinant N-terminal nucleotide-binding domain from mouse P-glycoprotein. Overexpression, purification, and role of cysteine 430

Varying length cDNAs encoding the N-terminal nucleotide-binding domain (NBD1) from mouse mdr1 P-glyco- protein were prepared on the basis of structure predictions. Corresponding recombinant proteins were overexpressed in Escherichia coli, and the shortest one containing amino acids 395-581 exhibited the highest solubility. Insertion of an N-terminal hexahistidine tag allowed domain purification by nickel-chelate affinity chromatography. NBD1 efficiently interacted with nucleotides. Fluorescence methods showed that ATP bound at millimolar concentrations and its 2',3'-O-(2,4,6-trinitrophenyl) derivative at micromolar concentrations, while the 2'(3')-N-methylanthraniloyl derivative had intermediate affinity. Photoaffinity labeling was achieved upon irradiation with 8-azido-ATP. The domain exhibited ATPase activity with a Km for MgATP in the millimolar range, and ATP hydrolysis was competitively inhibited by micromolar 2',3'-O-(2,4,6-trinitrophenyl)-ATP. NBD1 contained a single cysteine residue, at position 430, that was derivatized with radiolabeled N-ethylmaleimide. Cysteine modification increased 6-fold the Kd for 2'(3')-N-methylanthraniloyl-ATP and prevented 8-azido-ATP photolabeling. ATPase activity was inhibited with a 5-fold increase in the Km for MgATP. The results suggest that chemical modification of Cys-430 is involved in the N-ethylmaleimide inhibition of whole P-glycoprotein by altering substrate interaction.

Overexpression and purification of the carboxyl-terminal nucleotide-binding domain from mouse P-glycoprotein. Strategic location of a tryptophan residue

The cDNA encoding the C-terminal nucleotide-binding domain (NBD2) from mouse P-glycoprotein involved in multidrug resistance was obtained from adrenal cell mRNA and amplified by reverse transcriptase polymerase chain reaction. NBD2 was highly overexpressed in Escherichia coli in fusion with glutathione S-transferase and could be purified after efficient thrombin cleavage. Both fused and purified NBD2 bound TNP (2',3'-O-(2,4,6-trinitrophenyl))- derivatives of nucleotides with high affinity. TNP-ATP or TNP-ADP binding at micromolar concentrations produced a characteristic blue-shifted enhancement of extrinsic fluorescence and was specifically prevented or chased by ATP or ADP at millimolar concentrations. A similar affinity binding was monitored by quenching of intrinsic fluorescence. The spectrum of fusion protein, containing 5 tryptophan residues, was maximally quenched at 328 nm upon interaction with TNP-nucleotides. TNP-GTP exhibited a lower affinity than TNP-ATP but produced a higher maximal quenching (44% instead of 28%). The intrinsic fluorescence of purified NBD2, containing a single tryptophan residue, exhibited a narrow spectrum with a maximum at 328 nm characteristic of a hydrophobic tryptophan environment. A high quenching was observed upon nucleotide interaction with similar affinity. The results put forward a functional role for the tryptophan-containing sequence of P-glycoprotein NBD2 that was not detected up to now.