Biphasic burst and sustained transdermal delivery in vivo using an AI-optimized 3D-printed MN patch.

The objective of the present study was to fabricate microneedles for delivering lipophilic active ingredients (APIs) using digital light processing (DLP) printing technology and quality by design (QbD) supplemented by artificial intelligence (AI) algorithms. In the present study, dissolvable microneedle (MN) patches using ibuprofen (IBU) as a model drug were successfully fabricated with DLP printing technology at âˆ¼ 750 µm height, ∼250 µm base diameter, and tip with radius of curvature (RoC) of âˆ¼ 15 µm. MN patches were comprised of IBU, photoinitiator, Lithium phenyl (2,4,6-trimethylbenzoyl) phosphinate (LAP), polyethylene glycol dimethacrylate (PEGDAMA)550 and distilled water and were developed using the QbD optimization approach. Optimization of print fidelity and needle morphology were achieved using AI implementing a semi-supervised machine learning approach. Mechanical strength tests demonstrated that IBU MNs formed pores both on Parafilm M® and human cadaver skin. IBU-MNs consisting of 0.23 %w/v and 0.49 %w/v LAP with 10 %w/v water showed âˆ¼ 2 mg/cm2 sustained drug permeation at 72 h in skin permeation experiments with flux of âˆ¼ 40 µg/cm2/h. Pharmacokinetic studies in rats displayed biphasic rapid first-order absorption with sustained zero-order input of Ko = 150ug/hr, AUC0-48h = 62812.02 ± 11128.39 ng/ml*h, Tmax = 2.66 ± 1.12 h, and Cmax = 3717.43 ± 782.25 ng/ml (using 0.23 %w/v LAP IBU MN patch). An in vitro in vivo relation (IVIVR) was conducted identifying a polynomial relationship between patch release and fraction absorbed in vivo. This study demonstrates fabrication of dissolvable DLP-printed microneedle patches for lipophilic API delivery with biphasic rapid first-order and sustained zero-order release.

Cost-Effectiveness Model Shows Superiority of Wireless Spinal Cord Stimulation Implantation Without a Separate Trial.

OBJECTIVE: We evaluated the cost-effectiveness of wireless spinal cord stimulation (Wireless SCS) with single stage "direct to permanent" implantation vs. screening with temporary electrodes and an external pulse generator followed by implantation of a system for long-term use (IPG SCS). MATERIALS AND METHODS: We created a cost model that takes a 2019 United States (U.S.) payer perspective and is based on IPG SCS cost models for subjects with chronic back and/or leg pain. Our six-month decision tree includes the screening trial period (success ≥50% relief) and leads to various levels of pain relief with or without complications for IPG SCS and Wireless SCS and without complications for conventional medical management (CMM). Every three months in the follow-on 15-year Markov model (with costs and quality-adjusted life years discounted 3.5% annually), subjects remain stable or transition to deteriorated health or death. Subjects who fail SCS receive CMM. After 60 Markov cycles, a 100,000-sample simulation reveals the impact of maximum willingness-to-pay (WTP) from $10,000 to $100,000 per quality-adjusted life year on net monetary benefit (NMB). Sensitivity analyses considered the impact of the Wireless SCS screening success rate, Wireless SCS device cost, and IPG SCS device longevity. RESULTS: Compared with IPG SCS, Wireless SCS offers higher clinical effectiveness at a lower cost and a higher NMB for our WTP thresholds and is, thus, dominant. Wireless SCS is also cost-effective compared with CMM. Results remain robust with 1) Wireless SCS screening success rates as low as 85% (dominant), 2) the cost of the Wireless SCS devices as high as $55,000 (cost-effective), and 3) IPG SCS devices lasting 12 years (dominant). CONCLUSIONS: In this model, compared with IPG SCS or with CMM, Wireless SCS is a superior strategy.

Genome-wide analysis of clopidogrel active metabolite levels identifies novel variants that influence antiplatelet response.

Clopidogrel is one of the most commonly used therapeutics for the secondary prevention of cardiovascular events in patients with acute coronary syndromes. However, considerable interindividual variation in clopidogrel response has been documented, resulting in suboptimal therapy and an increased risk of recurrent events for some patients. In this investigation, we carried out the first genome-wide association study of circulating clopidogrel active metabolite levels in 513 healthy participants to directly measure clopidogrel pharmacokinetics. We observed that the CYP2C19 locus was the strongest genetic determinant of active metabolite formation (P=9.5×10). In addition, we identified novel genome-wide significant variants on chromosomes 3p25 (rs187941554, P=3.3×10) and 17q11 (rs80343429, P=1.3×10), as well as six additional loci that showed suggestive evidence of association (P≤1.0×10). Four of these loci showed nominal associations with on-clopidogrel ADP-stimulated platelet aggregation (P≤0.05). Evaluation of clopidogrel active metabolite concentration may help identify novel genetic determinants of clopidogrel response, which has implications for the development of novel therapeutics and improved antiplatelet treatment for at-risk patients in the future.

Formulation, Pharmacokinetic, and Efficacy Studies of Mannosylated Self-Emulsifying Solid Dispersions of Noscapine.

PURPOSE: To formulate hydroxypropyl methylcellulose-stabilized self-emulsifying solid dispersible carriers of noscapine to enhance oral bioavailability. METHODS: Formulation of noscapine (Nos) self-emulsifying solid dispersible microparticles (SESDs) was afforded by emulsification using an optimized formula of Labrafil M1944, Tween-80, and Labrasol followed by spray-drying with hydroxypropyl methylcellulose (HPMC), with and without mannosamine (Mann-Nos_SESDs and Nos_SESDs respectively); self-microemulsifying liquid dispersions (SMEDDs) with and without mannosamine (Mann-Nos_SMEDDs and Nos_SMEDDs respectively) were also prepared. SMEDDs and SESDs were characterized for size, polydispersity, surface charge, entrapment efficiency, in vitro permeability, in vitro release kinetics, and oral pharmacokinetics in Sprague-Dawley rats (10 mg/kg p.o). The antitumor efficacy of Mann-Nos_SESDs on the basis of chemosensitization to cisplatin (2.0 mg/kg, i.v.) was investigated in a chemorefractory lung tumor Nu/Nu mouse model up to a maximal oral dose of 300 mg/kg. RESULTS: The oil/surfactant/co-surfactant mixture of Labrafil M1944, Tween-80, and Labrasol optimized at weight ratios of 62.8:9.30:27.90% produced stable self-microemulsifying dispersions (SMEDDs) at a SMEDD to water ratio of 1-3:7-9 parts by weight. SMEDDs had hydrodynamic diameters between 231 and 246 nm; surface charges ranged from -16.50 to -18.7 mV; and entrapment efficiencies were between 32 and 35%. SESDs ranged in size between 5.84 and 6.60 µm with surface charges from -10.62 to -12.40 mV and entrapment efficiencies of 30.96±4.66 and 32.05±3.72% (Nos_SESDs and Mann-Nos_SESDs respectively). Mann-Nos_SESDs exhibited saturating uptake across Caco-2 monolayers (Papp = 4.94±0.18 × 10(-6) cm/s), with controlled release of 50% of Nos in 6 hr at pH 6.8 following Higuchi kinetics. Mann-Nos_ SESDs was 40% more bioavailable compared to Nos_SESDs; and was effective in sensitizing H1650 SP cells to Cisplatin in vitro and in an orthotopic lung tumor model of H1650 SP origin. CONCLUSIONS: Mannosylated noscapine self-emulsifying solid dispersions (Mann-Nos_SESDs) are bioavailable and potentiate the antineoplastic effect of cisplatin-based chemotherapy in cisplatin-resistant NSCLC.

A novel uHPLC-MS/MS method for the quantitation of AZD7451 (AZ12607092) in human plasma.

Tropomyosin-related kinases (Trk) are tyrosine kinase receptors implicated in tumor proliferation, invasion, and survival signaling across a number of tumors, making them potentially attractive targets for the treatment of cancer. AZD7451 is a potent and selective inhibitor of Trk kinases currently undergoing a Phase I dose escalation in glioblastoma multiforme at the National Cancer Institute. A key part of early clinical testing for AZD7451 involves demonstrating that pharmacokinetic half-life and clinical exposures of AZD7451 are sufficient to inhibit Trk receptors in preclinical models. To address this need, an ultra sensitive analytical method was developed to measure the AZD7451 profile in human plasma. A liquid-liquid extraction recovered >80% of AZD7451 before quantitative analysis by ultra HPLC-MS/MS. A Varian Polaris(®) C18-A column and a mass transition of m/z 383.5→340.5 (m/z 389.6→342.0 for the internal standard [(2)H6]-AZD7451) was used, and a dynamic calibration range of 0.5-1000ng/mL was established, which provided a sensitive (<8.5% deviation), and precise (<6%) quantitative assay for AZD7451. AZD7451 demonstrated stability in human plasma at room temperature for 24h (<7% change) and after extraction at 4°C for 24h (<8% change), and was stable through 4 freeze/thaw cycles (<8% change). This method was used to measure AZD7451 plasma levels in clinical samples to confirm the sensitivity at several time points following AZD7451 treatment in subjects with glioblastoma.

Phase II clinical trial of cediranib in patients with metastatic castration-resistant prostate cancer.

OBJECTIVE: To assess the efficacy and toxicity of cediranib, a highly potent inhibitor of vascular endothelial growth factor receptor tyrosine kinases, in patients with metastatic castration-resistant prostate cancer (CRPC) previously treated with docetaxel-based therapy. PATIENTS AND METHODS: The study used a Simon two-stage trial design, which required at least two of 12 patients in the first cohort to be progression-free at 6 months. We enrolled a total of 35 evaluable patients who all received cediranib 20 mg orally daily. In a second cohort, 23 additional patients received prednisone 10 mg daily with cediranib. Endpoints included tumour response, progression-free survival (PFS), overall survival (OS), vascular permeability via dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), and toxicity. RESULTS: A total of 59 patients were enrolled, of whom 67% had received two or more previous chemotherapy regimens. Six of 39 patients with measurable disease had confirmed partial responses and one had an unconfirmed partial response. At 6 months, 43.9% of patients were progression-free; the median PFS and OS periods for all patients were 3.7 months and 10.1 months, respectively. We found that the DCE-MRI variables baseline transport constant (Ktrans ) and rate constant at day 28 were significantly associated with PFS in univariate analyses, but only baseline Ktrans remained significant when considered jointly. The most frequent toxicities were hypertension, fatigue, anorexia and weight loss; the addition of prednisone reduced the incidence of constitutional toxicities. CONCLUSION: This study demonstrated that cediranib was generally well tolerated with some anti-tumour activity in highly pretreated patients with metastatic CRPC who had progressive disease after docetaxel-based therapy.

A rapid ultra HPLC-MS/MS method for the quantitation and pharmacokinetic analysis of 3-deazaneplanocin A in mice.

3-Deazaneplanocin A (DZNep) has been shown to have anti-cancer activity in numerous cancer types and its continued preclinical, and eventual clinical, drug development will require rapid and sensitive bioanalytical methods in order to quantitate this drug for pharmacokinetic analyses. The ultra HPLC with positive thermospray tandem mass spectrometric (LC-MS/MS) detection affords the most sensitive (limit of quantitation 5ng/mL) and rapid (3min run time) bioanalytical method to date for DZNep. Due to the polar nature of this drug and the internal standard (tubercidin), a hydrophilic-interaction column (HILIC) was used. The method was accurate, with less than 10% deviation from nominal values, as well as precise, where both within-day and between-day precisions were less than 15%. A liquid-liquid extraction procedure was able to recover ∼90% of drug from a small volume (50µL) of mouse plasma. This method was successfully applied to a pharmacokinetic study in mice intravenously injected with DZNep.

Are race-specific ERCC1 haplotypes in melanoma cases versus controls related to the predictive and prognostic value of ERCC1 N118N?

OBJECTIVES: Although it does not alter the ERCC1 phenotype, the ERCC1 500C>T (rs11615) polymorphism has undergone a myriad of investigations into its role as a marker for nucleotide excision repair (NER) function in different races, diseases and treatment outcomes. The goal of our study was to test the hypothesis that 500C>T is in linkage disequilibrium (LD) with causative alleles, and that these haplotypes are more frequent in Caucasians with melanoma than in healthy Caucasians or African Americans. DESIGN: In this case-control study, we selected race-specific ERCC1 single-nucleotide polymorphism (SNPs), conducted LD analysis with ERCC1 500C>T and compared the frequency of ERCC1 diplotypes in Caucasians with melanoma (n=165), healthy Caucasians (n=150) and healthy African Americans (n=159). The haplotype was further studied using a fusion gene containing multiple ERCC1 SNPs. SETTING: Large cancer institute in the USA. PARTICIPANTS: A total of 165 Caucasian melanoma patients, 159 healthy Caucasian controls and 159 African American healthy controls. Men and women were enrolled in the clinical trial; however, since the screening trial included prostate cancer screening in addition to screening for other cancers, only male controls were available. OUTCOME MEASURES: The outcome measures were melanoma risk in Caucasians, and LD between ERCC1 SNP, N118N and other race-specific allelic variants. RESULTS: When compared to ERCC1 500C>T alone, a race-specific three-SNP variant haplotype in ERCC1 (comprised of rs11615, rs3212950 and rs3212948) was even more frequent in Caucasians with melanoma than in healthy Caucasians (p=0.0034) or African Americans (p<0.0001). A plasmid containing the variant haplotype was not differentially expressed. CONCLUSIONS: We demonstrate that ERCC1 500C>T participates in a previously characterised cancer-risk haplotype found more frequently in Caucasians, while LD is weak in African Americans; this haplotype appears to also be related to melanoma. It is therefore likely that ERCC1 500C>T is only a valid NER, disease or treatment outcome marker in Caucasians.

The functional G143E variant of carboxylesterase 1 is associated with increased clopidogrel active metabolite levels and greater clopidogrel response.

INTRODUCTION: Carboxylesterase 1 (CES1) is the primary enzyme responsible for converting clopidogrel into biologically inactive carboxylic acid metabolites. METHODS: We genotyped a functional variant in CES1, G143E, in participants of the Pharmacogenomics of Anti-Platelet Intervention (PAPI) study (n=566) and in 350 patients with coronary heart disease treated with clopidogrel, and carried out an association analysis of bioactive metabolite levels, on-clopidogrel ADP-stimulated platelet aggregation, and cardiovascular outcomes. RESULTS: The levels of clopidogrel active metabolite were significantly greater in CES1 143E-allele carriers (P=0.001). Consistent with these findings, individuals who carried the CES1 143E-allele showed a better clopidogrel response as measured by ADP-stimulated platelet aggregation in both participants of the PAPI study (P=0.003) and clopidogrel-treated coronary heart disease patients (P=0.03). No association was found between this single nucleotide polymorphism and baseline measures of platelet aggregation in either cohort. CONCLUSION: Taken together, these findings suggest, for the first time, that genetic variation in CES1 may be an important determinant of the efficacy of clopidogrel.

Phase 1 trial of IL-15 trans presentation blockade using humanized Mikß1 mAb in patients with T-cell large granular lymphocytic leukemia.

In the present study, Hu-Mikß1, a humanized mAb directed at the shared IL-2/IL-15Rß subunit (CD122) was evaluated in patients with T-cell large granular lymphocytic (T-LGL) leukemia. Hu-Mikß1 blocked the trans presentation of IL-15 to T cells expressing IL-2/IL-15Rß and the common γ-chain (CD132), but did not block IL-15 action in cells that expressed the heterotrimeric IL-15 receptor in cis. There was no significant toxicity associated with Hu-Mikß1 administration in patients with T-LGL leukemia, but no major clinical responses were observed. One patient who had previously received murine Mikß1 developed a measurable Ab response to the infused Ab. Nevertheless, the safety profile of this first in-human study of the humanized mAb to IL-2/IL-15Rß (CD122) supports its evaluation in disorders such as refractory celiac disease, in which IL-15 and its receptor have been proposed to play a critical role in the pathogenesis and maintenance of disease activity.

Racial disparities in the association between variants on 8q24 and prostate cancer: a systematic review and meta-analysis.

Recent studies implicate single nucleotide polymorphisms (SNPs) within the 8q24 region as a risk factor for prostate cancer (PCa). New developments suggest that 8q24 encodes regulators of the nearby MYC gene, a known oncogene. In order to better understand the implications of SNPs in this region, we performed meta-analyses, stratified by race, of seven SNPs and one microsatellite marker previously identified as risk loci on the 8q24 region of the genome. In addition, we reviewed the literature examining the possible associations between these polymorphisms and clinicopathological features of PCa. The results of the meta-analyses indicate that rs6983267, rs1447295, rs6983561, rs7837688, rs16901979, and DG8S737 are significantly associated with a higher risk for PCa for at least one race, whereas the variants rs13254738 and rs7000448 are not. The degree of association and frequency of the causative allele varied among men of different races. Though several studies have demonstrated an association between certain 8q24 SNPs and clinicopathological features of the disease, review of this topic revealed conflicting results.

Pharmacokinetic evaluation and in vitro-in vivo correlation (IVIVC) of novel methylene-substituted 3,3' diindolylmethane (DIM).

PURPOSE: 3,3'-Diindolylmethane (DIM) is the major in vivo product of the acid-catalyzed oligomerization of indole-3-carbinol present in cruciferous vegetables. 1, 1-bis (3'-indolyl)-1-(p-substituted phenyl) methanes [C-substituted diindolylmethanes (C-DIMs)] are a new class of anticancer compounds derived from indole 3-carbinol. Despite rapidly increasing knowledge regarding mechanisms responsible for the chemopreventive properties of DIM-C-pPhC6H5, there have been relatively few studies determining the absorption and pharmacokinetic properties of DIM-C-pPhC6H5 to explore its clinical utility. METHODS: In this study, we assessed the solubility, lipophilicity and Caco-2 cell permeability of methylene-substituted DIM. Pharmacokinetic properties in rats were determined following i.v. and oral administration of a novel analog of DIM. Pharmacokinetic parameters were determined using non-compartmental and compartmental techniques with WinNonlin® 5.0 software. To explore potential In Vitro-In Vivo Correlation (IVIVC) between the in vitro permeability values, and the oral absorption pharmacokinetics, we employed deconvolution of i.v. and oral data using a three compartment Exact Loo-Riegelman method. RESULTS: The oral absorption and disposition were described by a three compartment model with combined zero-order/Michaelis-Menten limited systemic uptake using differential equations, at physiologically relevant doses. The saturation model obtained accounts for a nonlinear change in C(max)/Dose, and the absolute bioavailability (0.13±0.06) was also dose dependent. The absorption rate profile of DIM-C-pPhC6H5 across Caco-2 cells was significantly different than in vivo. CONCLUSIONS: The pharmacokinetic absorption model presented represents a useful basis for obtaining plasma level predictability for poorly bioavailable, highly lipophilic drugs, such as the DIM analog DIM-C-pPhC6H5.

Quantification of irinotecan, SN38, and SN38G in human and porcine plasma by ultra high-performance liquid chromatography-tandem mass spectrometry and its application to hepatic chemoembolization.

An analytical method was developed and validated for the quantitative determination of irinotecan, its active metabolite SN38, and glucuronidated SN38 (SN38-G) in both porcine and human plasma. Calibration curves were linear within the concentration range of 0.5-100 ng/mL for SN38 and SN38-G, and 5-1000 ng/mL for irinotecan. Sample pretreatment involved solid-phase extraction of 0.1 mL aliquots of plasma. Irinotecan, SN38, SN38-G, and the internal standards, irinotecan-d10, tolbutamide, and camptothecin, respectively, were separated on a Waters ACQUITY UPLC BEH RP18 column (2. 1mm × 50 mm, 1.7 µm), using a mobile phase composed of methanol and 0.1% formic acid. Accuracy of quality control samples in human plasma ranged from 98.5 to 110.3%, 99.5 to 101.7% and 96.2 to 98.9% for irinotecan, SN38, and SN38-G, respectively. Precision of the three analytes in the same order ranged from 0.8 to 2.8%, 2.4 to 5.7%, and 2.4 to 2.8%. All three analytes proved stable in plasma through four freeze/thaw cycles, as well as through 6h in whole blood at room temperature. The method was likewise validated in porcine plasma with comparable accuracies and precisions also within the generally acceptable range. The validated method was applied to both preclinical and clinical trials involving hepatic chemoembolization of irinotecan drug-eluting beads to study the pharmacokinetics of the three analytes.

A sensitive and rapid ultra HPLC-MS/MS method for the simultaneous detection of clopidogrel and its derivatized active thiol metabolite in human plasma.

A sensitive, selective, and rapid ultra-high performance liquid chromatography-tandem mass spectrometry (uHPLC-MS/MS) was developed for the simultaneous quantification of clopidogrel (Plavix(®)) and its derivatized active metabolite (CAMD) in human plasma. Derivatization of the active metabolite in blood with 2-bromo-3'-methoxy acetophenone (MPB) immediately after collection ensured metabolite stability during sample handling and storage. Following addition of ticlopidine as an internal standard and simple protein precipitation, the analytes were separated on a Waters Acquity UPLC™ sub-2 µm-C(18) column via gradient elution before detection on a triple-quadrupole MS with multiple-reaction-monitoring via electrospray ionization. The method was validated across the clinically relevant concentration range of 0.01-50 ng/mL for parent clopidogrel and 0.1-150 ng/mL (r(2)=0.99) for CAMD, with a fast run time of 1.5 min to support pharmacokinetic studies using 75, 150, or 300 mg oral doses of clopidogrel. The analytical method measured concentrations of clopidogrel and CAMD with accuracy (%DEV) <±12% and precision (%CV) of <±6%. The method was successfully applied to measure the plasma concentrations of clopidogrel and CAMD in three subjects administered single oral doses of 75, 150, and 300 mg clopidogrel. It was further demonstrated that the derivatizing agent (MPB) does not affect clopidogrel levels, thus from one aliquot of blood drawn clinically, this method can simultaneously quantify both clopidogrel and CAMD with sensitivity in the picogram per mL range.

Multihistology, target-driven pilot trial of oral topotecan as an inhibitor of hypoxia-inducible factor-1α in advanced solid tumors.

PURPOSE: Hypoxia-inducible factor 1 (HIF-1) α is frequently overexpressed in human tumors and is associated with angiogenesis and metastasis. Topotecan, a topoisomerase I inhibitor, has been shown to inhibit HIF-1α expression in preclinical models. We designed a pilot trial to measure HIF-1α inhibition in tumor biopsies from patients with advanced solid tumors overexpressing HIF-1α, after treatment with oral topotecan. EXPERIMENTAL DESIGN: Topotecan was administered orally at 1.6 mg/m(2) once daily for 5 days/week for 2 weeks, in 28-day cycles. Objectives were to determine inhibition of expression of HIF-1α and HIF-1 target genes in tumor; to assess tumor blood flow by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI); and to measure pharmacokinetics. Tumor biopsies were collected at baseline and during the second cycle of treatment. RESULTS: Sixteen patients were enrolled. The dose of topotecan was reduced to 1.2 mg/m(2)/day due to myelosuppression. Seven patients had paired tumor biopsies. In 4 patients, HIF-1α nuclear staining became undetectable after treatment (7.5%-50% staining at baseline). Decreased levels of VEGF and GLUT-1 mRNA were measured in 4 patients; the changes were concordant with reduction in HIF-1α in 3 patients. Decreased tumor blood flow and permeability were observed by DCE-MRI in 7 of 10 patients after 1 cycle. One patient had a partial response accompanied by inhibition of HIF-1α in tumor and reduction in tumor blood flow on DCE-MRI. CONCLUSIONS: This multihistology, target assessment trial of a small molecule inhibitor of HIF-1α showed that topotecan could decrease HIF-1α expression in advanced solid tumors.

Simultaneous RP-HPLC-DAD quantification of bromocriptine, haloperidol and its diazepane structural analog in rat plasma with droperidol as internal standard for application to drug-interaction pharmacokinetics.

A simple and rapid RP-HPLC-DAD method was developed and validated for simultaneous determination of the dopamine antagonists haloperidol, its diazepane analog, and the dopamine agonist bromocriptine in rat plasma, to perform pharmacokinetic drug-interaction studies. Samples were prepared for analysis by acetonitrile (22.0 microg/mL) plasma protein precipitation with droperidol as an internal standard, followed by a double-step liquid-liquid extraction with hexane : chloroform (70:30) prior to C-18 separation. Isocratic elution was achieved using a 0.1% (v/v) trifluoroacetic acid in deionized water, methanol and acetonitrile (45/27.5/27.5, v/v/v). Triple-wavelength diode-array detection at the lambda(max) of 245 nm for haloperidol, 254 nm for the diazepane analog and droperidol, and 240 nm for bromocriptine was carried out. The LLOQ of DAL, HAL, and BCT were 45.0, 56.1, and 150 ng/mL, respectively. In rats, the estimated pharmacokinetic parameters (i.e., t(1/2), CL, and V(ss)) of HAL when administered with DAL and BCT were t(1/2) = 16.4 min, V(ss) = 0.541 L/kg for HAL, t(1/2) = 28.0 min, V(ss) = 2.00 L/kg for DAL, and t(1/2) = 24.0 min, V(ss) = 0.106 L/kg for BCT. The PK parameters for HAL differed significantly from those previously reported, which may be an indication of a drug-drug interaction.

Isothermal titration calorimetric study of RNase-A kinetics (cCMP --> 3'-CMP) involving end-product inhibition.

PURPOSE: Isothermal titration calorimetry (ITC) and progress curve analysis was used to measure the enzyme kinetic parameters (KM and kcat) of the hydrolysis of cCMP by RNase-A, a reaction that includes end-product competitive inhibition by 3'-CMP. METHODS: The heat generated from injection of 9-15 microl cCMP (20 mM) into bovine pancreatic RNase-A (600 nM) in 50 mM Na+ acetate buffer (pH 5.5; 37 degrees C) was monitored for 1500-2000 s. Thermal power (dQ/dt), equal to (1)/deltaH(app) x d(cCMP)/dt was recorded every 1 s. The end-product inhibition constant (Kp) and enthalpy of the inhibitor binding interaction was obtained from the saturation data of 60 sequential injections of 3'-CMP (1.2 mM) into 0.05 mM RNase-A. The data of the plot of -d[cCMP]/dt against [cCMP] were fitted to kinetic equations incorporating Kp to yield KM and kcat. RESULTS: DeltaH(app) for each run was obtained by integration of the progress curve. The plot of -d[cCMP]/dt against [cCMP] yielded the kinetic parameters KM = 105.3 microM, 121.6 microM, and 131.3 microM; kcat = 1.63 s(-1), 1.56 s(-1), and 1.71 s(-1). The end-product bound with 1:1 stoichiometry and Kp = 53.2 microM. CONCLUSIONS: The combination of progress curve analysis and ITC allowed rapid and facile measurement of the kinetic parameters for catalytic conversion of cCMP to 3'-CMP by RNase-A, a reaction complicated by end-product inhibition.

Protonation effect on drug affinity.

Pharmacologic ligand-macromolecule interactions are commonly characterized by affinity (dissociation) constants such as K(d) or K(i) without regard to the protonation effect of the buffer used in the measurement. The protonation effect is demonstrated here using isothermal titration microcalorimetry measurements of the competitive inhibitor binding of cytidine 2'-monophosphate (2'-CMP) to RNase-A as a model system in buffers of different ionization Delta H(buffer). The results demonstrate the importance of protonation in measures of affinity.

Toward RNase inhibitors: thermodynamics of 2'-CMP/RNase-A binding in multi-ion buffer.

Certain ribonucleases (RNases), such as eosinophil-derived neurotoxin, are associated with pathological conditions (e.g. asthma and inflammatory bowel disease) and can even be overtly cyto(neuro)toxic. It has been proposed that small-molecule inhibitors should have therapeutic utility. We used isothermal titration microcalorimetry to characterize reversible inhibitor cytidine 2'-monophosphate (2'-CMP) binding to RNase-A in a multi-ion buffer at 37 degrees as a representative system. The estimated parameters were: K(d)=13.9 microM; DeltaG degrees =-6.90 kcal/mol; DeltaH degrees =-15.7 kcal/mol; and DeltaS degrees =-0.028 kcal/mol-K ('enthalpy-driven' interaction). These data should assist drug design of small-molecule inhibitors of homologous RNase catalytic domains.