Utility of CYP3A4 and PXR-CAR-CYP3A4/3A7 Transgenic Mouse Models To Assess the Magnitude of CYP3A4 Mediated Drug-Drug Interactions.

Species differences in the expression, activity, regulation, and substrate specificity of metabolizing enzymes preclude the use of animal models to predict clinical drug-drug interactions (DDIs). The objective of this work is to determine if the transgenic (Tg) Cyp3a-/-Tg-3A4Hep/Int and Nr1i2/Nr1i3-/--Cyp3a-/-Tg-PXR-CAR-3A4/3A7Hep/Int (PXR-CAR-CYP3A4/3A7) mouse models could be used to predict in vivo DDI of 10 drugs; alprazolam, bosutinib, crizotinib, dasatinib, gefitinib, ibrutinib, regorafenib, sorafenib, triazolam, and vandetinib (as victims); with varying magnitudes of reported CYP3A4 clinical DDI. As an assessment of the effect of CYP3A4 inhibition, these drugs were coadministered to Cyp3a-/-Tg-3A4Hep/Int mice with the CYP3A inhibitor, itraconazole. For crizotinib, regorafenib, sorafenib, and vandetanib, there was no significant increase of AUC observed; with alprazolam, bosutinib, ibrutinib, dasatinib, and triazolam, pretreatment with itraconazole resulted in a 2-, 4-, 17-, 7-, and 15-fold increase in AUC, respectively. With the exception of gefinitib for which the DDI effect was overpredicted (12-fold in Tg-mice vs 2-fold in the clinic), the magnitude of AUC increase observed in this study was consistent (within 2-fold) with the clinical DDI observed following administration with itraconazole/ketoconazole. As an assessment of CYP3A4 induction, following rifampin pretreatment to PXR-CAR-3A4/3A7Hep/Int mice, an 8% decrease in vandetanib mean AUC was observed; 39-52% reduction in AUC were observed for dasatinib, ibrutinib, regorafenib, and sorafenib compared to vehicle treated mice. The greatest effect of rifampin induction was observed with alprazolam, bosutinib, crizotinib, gefitinib, and triazolam where 72-91% decrease in AUC were observed. With the exception of vandetanib for which rifampin induction was under-predicted, the magnitude of induction observed in this study was consistent (within 2-fold) with clinical observations. These data sets suggest that, with two exceptions, these transgenic mice models were able to exclude or capture the magnitude of CYP3A4 clinical inhibition and induction. Data generated in transgenic mice may be used to gain confidence and complement in vitro and in silico methods for assessing DDI potential/liability.

Use of transgenic mouse models to understand the oral disposition and drug-drug interaction potential of cobimetinib, a MEK inhibitor.

Data from the clinical absolute bioavailability (F) study with cobimetinib suggested that F was lower than predicted based on its low hepatic extraction and good absorption. The CYP3A4 transgenic (Tg) mouse model with differential expression of CYP3A4 in the liver (Cyp3a(-/-)Tg-3A4Hep) or intestine (Cyp3a(-/-)Tg-3A4Int) and both liver and intestine (Cyp3a(-/-)Tg-3A4Hep/Int) were used to study the contribution of intestinal metabolism to the F of cobimetinib. In addition, the effect of CYP3A4 inhibition and induction on cobimetinib exposures was tested in the Cyp3a(-/-)Tg-3A4Hep/Int and PXR-CAR-CYP3A4/CYP3A7 mouse models, respectively. After i.v. administration of 1 mg/kg cobimetinib to wild-type [(WT) FVB], Cyp3a(-/-)Tg-3A4Hep, Cyp3a(-/-)Tg-3A4Int, or Cyp3a(-/-)Tg-3A4Hep/Int mice, clearance (CL) (26-35 ml/min/kg) was similar in the CYP3A4 transgenic and WT mice. After oral administration of 5 mg/kg cobimetinib, the area under the curve (AUC) values of cobimetinib in WT, Cyp3a(-/-)Tg-3A4Hep, Cyp3a(-/-)Tg-3A4Int, or Cyp3a(-/-)Tg-3A4Hep/Int mice were 1.35, 3.39, 1.04, and 0.701 µM⋅h, respectively. The approximately 80% lower AUC of cobimetinib in transgenic mice when intestinal CYP3A4 was present suggested that the intestinal first pass contributed to the oral CL of cobimetinib. Oxidative metabolites observed in human circulation were also observed in the transgenic mice. In drug-drug interaction (DDI) studies using Cyp3a(-/-)Tg-3A4Hep/Int mice, 8- and 4-fold increases in oral and i.v. cobimetinib exposure, respectively, were observed with itraconazole co-administration. In PXR-CAR-CYP3A4/CYP3A7 mice, rifampin induction decreased cobimetinib oral exposure by approximately 80%. Collectively, these data support the conclusion that CYP3A4 intestinal metabolism contributes to the oral disposition of cobimetinib and suggest that under certain circumstances the transgenic model may be useful in predicting clinical DDIs.

A reversed sulfonamide series of selective RORc inverse agonists.

The identification of a new series of RORc inverse agonists is described. Comprehensive structure-activity relationship studies of this reversed sulfonamide series identified potent RORc inverse agonists in biochemical and cellular assays which were also selective against a panel of nuclear receptors. Our work has contributed a compound that may serve as a useful in vitro tool to delineate the complex biological pathways involved in signalling through RORc. An X-ray co-crystal structure of an analogue with RORc has also provided useful insights into the binding interactions of the new series.

Pharmacokinetics and Safety of Firsocostat, an Acetyl-Coenzyme A Carboxylase Inhibitor, in Participants with Mild, Moderate, and Severe Hepatic Impairment.

Firsocostat is an oral, liver-targeted inhibitor of acetyl-coenzyme A carboxylase in development for the treatment of metabolic dysfunction-associated steatohepatitis. Hepatic organic anion transporting polypeptides play a significant role in the disposition of firsocostat with minimal contributions from uridine diphospho-glucuronosyltransferase and cytochrome P450 3A enzymes. This phase 1 study evaluated the pharmacokinetics and safety of firsocostat in participants with mild, moderate, or severe hepatic impairment. Participants with stable mild, moderate, or severe hepatic impairment (Child-Pugh A, B, or C, respectively [n = 10 per cohort]) and healthy matched controls with normal hepatic function (n = 10 per cohort) received a single oral dose of firsocostat (20 mg for mild and moderate hepatic impairment; 5 mg for severe hepatic impairment) with intensive pharmacokinetic sampling over 96 h. Safety was monitored throughout the study. Firsocostat plasma exposure (AUCinf) was 83%, 8.7-fold, and 30-fold higher in participants with mild, moderate, and severe hepatic impairment, respectively, relative to matched controls. Firsocostat was generally well tolerated, and all reported adverse events were mild in nature. Dose adjustment is not necessary for the administration of firsocostat in patients with mild hepatic impairment. However, based on the observed increases in firsocostat exposure, dose adjustment should be considered for patients with moderate or severe hepatic impairment, and additional safety and efficacy data from future clinical trials will further inform dose adjustment.

Effect of Renal Impairment on the Pharmacokinetics of Firsocostat, an Acetyl-Coenzyme A Carboxylase Inhibitor, and Cilofexor, a Selective Nonsteroidal Farnesoid X Receptor Agonist.

Firsocostat, a liver-targeted acetyl-coenzyme A carboxylase inhibitor, and cilofexor, a nonsteroidal farnesoid X receptor agonist, are being developed in combination for treatment of nonalcoholic steatohepatitis. This phase 1 study evaluated firsocostat and cilofexor pharmacokinetics and tolerability in participants with severe renal impairment (SRI) and healthy matched controls (HMCs). Ten participants with SRI (estimated glomerular filtration rate by Modification of Diet in Renal Disease <30 mL/min/1.73 m2 ), and 10 HMCs received single oral doses of firsocostat (20 mg) on day 1 and cilofexor (100 mg) on day 7 in a fasted state. Plasma concentrations of firsocostat (and nonactive metabolite GS-834773) and cilofexor (and nonactive metabolites GS-716070 and GS-1056756) were collected over 96 hours and quantified; plasma exposures (area under the concentration-time curve [AUC] and peak concentration [Cmax ]) and plasma protein binding were characterized. Firsocostat AUC was ≈40% higher in SRI versus HMC, while Cmax was 8% lower. Observed exposures of the firsocostat metabolite were ≈4.6-fold higher in SRI participants versus HMC. Exposures (AUC and Cmax ) of cilofexor and metabolites and percentages of protein binding of all analytes were similar between SRI and HMC groups. Treatment-emergent adverse events were generally mild and not considered related to study drug. A <50% increase in firsocostat exposure was observed among SRI participants but was deemed not clinically relevant. There was no apparent effect of SRI on cilofexor exposure. Based on this trial, firsocostat and cilofexor dosing are not expected to require modification in patients who are renally impaired.

Plasma Protein Binding Determination for Unstable Ester Prodrugs: Remdesivir and Tenofovir Alafenamide.

Remdesivir (RDV) and tenofovir alafenamide (TAF) are prodrugs designed to be converted to their respective active metabolites. Plasma protein binding (PPB) determination of these prodrugs is important for patients with possible alteration of free fraction of the drugs due to plasma protein changes in renal impairment, hepatic impairment, or pregnancy. However, the prodrugs' instability in human plasma presents a challenge for accurate PPB determination. In this research work, two approaches were used in the method development and qualification for PPB assessment of RDV and TAF. For RDV, dichlorvos was used to inhibit esterase activity to stabilize the prodrug in plasma during equilibrium dialysis (ED). The impact of dichlorvos on protein binding was evaluated and determined to be insignificant by comparing the unbound fraction (fu) determined by the ED method with dichlorvos present and the fu determined by an ultrafiltration method without dichlorvos. In contrast to RDV, TAF degradation in plasma is ∼3-fold slower, and TAF stability cannot be improved by dichlorvos. Fit-for-purpose acceptance criteria for the TAF PPB method were chosen, and an ED method was developed based on these criteria. These two methods were then qualified and applied for PPB determinations in clinical studies.

Evaluation of the potential drug interactions mediated through P-gp, OCT2, and MATE1/2K with filgotinib in healthy subjects.

Filgotinib, a preferential Janus Kinase-1 inhibitor, is approved in Europe and Japan for treatment of rheumatoid arthritis and is being developed for treatment of other chronic inflammatory diseases. Three drug-drug interactions studies were conducted in healthy subjects to evaluate the effect of P-glycoprotein (P-gp) modulation (study 1: P-gp inhibition by itraconazole and study 2: P-gp induction by rifampin) on filgotinib pharmacokinetics and the potential of filgotinib to impact exposure of metformin, an organic cation transporter (OCT) 2 and multidrug and toxin extrusion (MATE) 1/2K substrate (study 3). Co-administration of filgotinib with itraconazole increased filgotinib exposure (maximum concentration [Cmax ] by 64% and area under the curve to infinity [AUCinf ] by 45%) but had no effect on the exposure of GS-829845, filgotinib's primary metabolite. Rifampin moderately reduced exposures of filgotinib and GS-829845 (Cmax by 26% and AUCinf by 27% for filgotinib; Cmax by 19% and AUCinf by 38% for GS-829845). The data confirmed that filgotinib is a P-gp substrate. However, the magnitude of change in filgotinib/GS-829845 exposure by P-gp modulators is not deemed to be clinically relevant based on filgotinib exposure-response analyses in subjects with rheumatoid arthritis. Filgotinib did not alter metformin exposures, indicating that filgotinib and GS-829845 do not inhibit OCT2 and MATE1/2K at the clinical doses. Filgotinib was generally well-tolerated when administered alone or with the co-administered drugs in the studies. Results from these studies were the basis to enable the use of P-gp modulators and substrates of OCT2, MATE1, and MATE2K with filgotinib without the need for dose modifications in the current approved rheumatoid arthritis population.

Highly selective c-Jun N-terminal kinase (JNK) 3 inhibitors with in vitro CNS-like pharmacokinetic properties II. Central core replacement.

In this Letter, we describe the evolution of selective JNK3 inhibitors from 1, that routinely exhibit >10-fold selectivity over JNK1 and >1000-fold selectivity over related MAPKs. Strong SAR was found for substitution of the naphthalene ring, as well as for inhibitors adopting different central scaffolds. Significant potency gains were appreciated by inverting the polarity of the thione of the parent triazolothione 1, resulting in potent compounds with attractive pharmacokinetic profiles.

Highly selective c-Jun N-terminal kinase (JNK) 2 and 3 inhibitors with in vitro CNS-like pharmacokinetic properties prevent neurodegeneration.

In this Letter, we describe the discovery of selective JNK2 and JNK3 inhibitors, such as 10, that routinely exhibit >10-fold selectivity over JNK1 and >1000-fold selectivity over related MAPKs, p38α and ERK2. Substitution of the naphthalene ring affords an isoform selective JNK3 inhibitor, 30, with approximately 10-fold selectivity over both JNK1 and JNK2. A naphthalene ring penetrates deep into the selectivity pocket accounting for the differentiation amongst the kinases. Interestingly, the gatekeeper Met146 sulfide interacts with the naphthalene ring in a sulfur-π stacking interaction. Compound 38 ameliorates neurotoxicity induced by amyloid-ß in human cortical neurons. Lastly, we demonstrate how to install propitious in vitro CNS-like properties into these selective inhibitors.

Lack of Drug-Drug Interaction Between Filgotinib, a Selective JAK1 Inhibitor, and Oral Hormonal Contraceptives Levonorgestrel/Ethinyl Estradiol in Healthy Volunteers.

Filgotinib (FIL) is a potent and selective JAK1 inhibitor in clinical development for treatment of severe inflammatory diseases. A drug-drug interaction study to evaluate the potential effect of FIL on the pharmacokinetics (PK) of the oral contraceptive levonorgestrel (LEVO)/ethinyl estradiol (EE) was conducted. This was a phase 1, open-label, randomized, crossover study in healthy female subjects (N = 24). Subjects received a single dose of LEVO (150 µg)/EE (30 µg) alone (reference), or in combination with multiple-dose FIL (200 mg once daily for 15 days; test). Intensive PK sampling was conducted, and safety was assessed throughout the study. PK interactions were evaluated using 90% confidence intervals of the geometric least squares mean ratios of the test versus reference treatments. All 24 subjects enrolled completed study treatments. Coadministration of FIL with the oral contraceptive did not alter the PK of LEVO and EE; the 90% confidence intervals of the geometric least squares mean ratios were contained within bioequivalence bounds (80%-125%). Exposures of FIL were consistent with observed clinical exposure data. Study treatments were generally well tolerated. All adverse events were mild. Coadministration with FIL did not alter the PK of LEVO/EE, and hormonal contraceptives can serve as an effective contraception method for subjects on FIL treatment.

Organic Anion Transporting Polypeptide Inhibition Dramatically Increases Plasma Exposure but not Pharmacodynamic Effect nor Inferred Hepatic Intracellular Exposure of Firsocostat.

Firsocostat (FIR: previously GS-0976), a highly sensitive OATP substrate, reduces hepatic de novo lipogenesis (DNL) by inhibiting acetyl-CoA carboxylases (ACC). Measuring the pharmacodynamic (PD) efficacy of FIR on DNL provides a unique opportunity to determine optimal dosing strategies for liver-targeted OATP substrates in settings of altered OATP function. A randomized, four-way crossover drug-drug interaction study was conducted. Hepatic DNL, a marker for ACC activity, was measured in 28 healthy volunteers after reference, single dose FIR 10 mg, FIR 10 mg plus the OATP inhibitor rifampin (RIF) 300 mg i.v., or RIF 300 mg i.v. (control for DNL effect of RIF), each separated by a 7-day washout. Samples were collected for pharmacokinetic (PK) and PD assessments through 24 hours after each treatment. Hepatic DNL and its inhibition by FIR were assessed. Twenty-four subjects completed the study. All adverse events were mild. RIF alone increased hepatic DNL area under the effect curve from time of administration up to the time of the last quantifiable concentration (AUEClast ; 35.7%). Despite a 5.2-fold increase in FIR plasma exposure (area under the concentration-time curve from zero to infinity (AUCinf )) when administered with RIF, FIR alone, and FIR + RIF had the same hepatic PD effect, 37.1% and 34.9% reduction in DNL AUEClast , respectively, compared with their respective controls. These findings indicate that large decreases in OATP activity do not alter hepatic intracellular exposure (as inferred by no change in PD) for drugs that are primarily eliminated hepatically and permeability rate-limited, such as FIR. These results support PK theory that has been difficult to test and provide practical guidance on administration of liver-targeted drugs in settings of reduced OATP function.

Filgotinib, a JAK1 Inhibitor, Has No Effect on QT Interval in Healthy Subjects.

Filgotinib, a selective inhibitor of Janus kinase 1, is being developed for the treatment of chronic inflammatory diseases. Electrocardiograms evaluated the effect of filgotinib on the corrected QT (QTc) interval in 52 healthy subjects who received each of 4 treatments: filgotinib 200 mg (therapeutic dose), 450 mg (supratherapeutic dose), and placebo, each administered once daily for 7 days, and a single dose of moxifloxacin 400 mg (positive control). Plasma samples were collected for pharmacokinetic analysis. The QTc interval was calculated using Fridericia's correction factor (QTcF) or an individual correction factor (QTcI). The relationship between plasma concentrations of filgotinib and its major metabolite and time-matched, baseline-adjusted, placebo-corrected QTc (ΔΔQTc) was evaluated. Filgotinib did not prolong QTcF or QTcI and using an appropriate mixed-effect model, the upper limit of the 2-sided 90% confidence interval for ΔΔQTc for each filgotinib dose (200 and 450 mg) remained below 10 milliseconds at all postdose time points. There were no clinically relevant relationships between QTc interval and plasma concentrations of filgotinib or its major metabolite. Filgotinib, administered at 200 or 450 mg, was generally well tolerated. Results of this thorough QT study demonstrate that filgotinib and its major metabolite are not associated with QTc interval prolongation.

The Relative Bioavailability and Effects of Food and Acid-Reducing Agents on Filgotinib Tablets in Healthy Subjects.

Filgotinib is a potent, selective Janus kinase-1 inhibitor being developed to treat chronic inflammatory diseases. This phase 1 study in healthy subjects evaluated the relative bioavailability of filgotinib maleate tablets versus the reference tablet (filgotinib hydrochloride) and effects of food and acid-reducing agents (ARAs) on the pharmacokinetics of filgotinib and its major metabolite. Noncompartmental pharmacokinetic parameters of filgotinib and its major metabolite were compared between the 2 tablets at 100- and 200-mg doses and with or without food or ARAs. Filgotinib maleate tablets resulted in equivalent plasma exposures (area under concentration-time curve to infinity [AUC∞ ] and maximum concentration [Cmax ]) of filgotinib and its metabolite as the reference tablet (90%CIs of geometric least-squares mean ratios were within the prespecified no-effect boundary of 70% to 143%). Food intake had no effect on filgotinib AUC∞ , but a high-fat meal reduced Cmax by 20%. Coadministration of filgotinib with omeprazole or famotidine had no effect on filgotinib AUC∞ , but omeprazole decreased Cmax by 27%. Neither food nor ARAs affected metabolite exposure. Single-dose filgotinib 100 or 200 mg was well tolerated. This study supports evaluation of filgotinib maleate tablets, administered without regard to food or ARAs, in future clinical studies.

Discovery of (S)-1-(1-(4-Chloro-3-fluorophenyl)-2-hydroxyethyl)-4-(2-((1-methyl-1H-pyrazol-5-yl)amino)pyrimidin-4-yl)pyridin-2(1H)-one (GDC-0994), an Extracellular Signal-Regulated Kinase 1/2 (ERK1/2) Inhibitor in Early Clinical Development.

The extracellular signal-regulated kinases ERK1/2 represent an essential node within the RAS/RAF/MEK/ERK signaling cascade that is commonly activated by oncogenic mutations in BRAF or RAS or by upstream oncogenic signaling. While targeting upstream nodes with RAF and MEK inhibitors has proven effective clinically, resistance frequently develops through reactivation of the pathway. Simultaneous targeting of multiple nodes in the pathway, such as MEK and ERK, offers the prospect of enhanced efficacy as well as reduced potential for acquired resistance. Described herein is the discovery and characterization of GDC-0994 (22), an orally bioavailable small molecule inhibitor selective for ERK kinase activity.

Collagenase as an effective tool for drug quantitation in tissues.

BACKGROUND: In early drug-discovery research, traditional techniques to analyze drug concentrations in tissues for bioanalytical needs include bead beaters and probe homogenization devices, but are not as effective for tough fibrous tissues. To prepare these tissues, the enzyme collagenase was used to digest the collagen fibers present in epithelial and connective tissue. RESULTS: The benefits of tissue homogenization using a bead beater following collagenase treatment of samples, as opposed to using bead beating alone, was investigated. Matrix effect, recovery factor and stability with and without collagenase were assessed. CONCLUSION: Little to no effects on the quality and reliability of collagenase treated samples were observed. This enzymatic approach is a feasible and effective tool for tissue homogenization and subsequent analysis by LC-MS/MS.

Nanosuspension delivery of paclitaxel to xenograft mice can alter drug disposition and anti-tumor activity.

Paclitaxel is a common chemotherapeutic agent that is effective against various cancers. The poor aqueous solubility of paclitaxel necessitates a large percentage of Cremophor EL:ethanol (USP) in its commercial formulation which leads to hypersensitivity reactions in patients. We evaluate the use of a crystalline nanosuspension versus the USP formulation to deliver paclitaxel to tumor-bearing xenograft mice. Anti-tumor efficacy was assessed following intravenous administration of three 20 mg/kg doses of paclitaxel. Paclitaxel pharmacokinetics and tissue distribution were evaluated, and differences were observed between the two formulations. Plasma clearance and tissue to plasma ratio of mice that were dosed with the nanosuspension are approximately 33- and 11-fold higher compared to those of mice that were given the USP formulation. Despite a higher tumor to plasma ratio for the nanosuspension treatment group, absolute paclitaxel tumor exposure was higher for the USP group. Accordingly, a higher anti-tumor effect was observed in the xenograft mice that were dosed with the USP formulation (90% versus 42% tumor growth inhibition). This reduction in activity of nanoparticle formulation appeared to result from a slower than anticipated dissolution in vivo. This study illustrates a need for careful consideration of both dose and systemic solubility prior utilizing nanosuspension as a mode of intravenous delivery.

Measuring NAD(+) levels in mouse blood and tissue samples via a surrogate matrix approach using LC-MS/MS.

BACKGROUND: NAD(+) is an endogenous analyte and is unstable during blood sample collection, both of which present obstacles for quantitation. Moreover, current procedures for NAD(+) sample collection require onsite treatment with strong acid to stabilize the NAD(+) in mouse blood cells. RESULTS: NAD(+) can be stabilized by addition of acid before the frozen mouse blood sample was thawed. A simple sample collection procedure was proposed to facilitate the analysis of NAD(+) in mouse blood and tissue samples. A LC-MS/MS method was developed for quantifying NAD(+) in mouse blood and various tissue samples. The described method was used to measure endogenous NAD(+) levels in mouse blood following oral administration of the nicotinamide phosphoribosyltransferase inhibitor GNE-617. CONCLUSION: This study presents a suitable assay and sample collection procedure for high throughput screening of NAD(+) samples in preclinical discovery studies.

In vitro and in vivo evaluation of amorphous solid dispersions generated by different bench-scale processes, using griseofulvin as a model compound.

Drug polymer-based amorphous solid dispersions (ASD) are widely used in the pharmaceutical industry to improve bioavailability for poorly water-soluble compounds. Spray-drying is the most common process involved in the manufacturing of ASD material. However, spray-drying involves a high investment of material quantity and time. Lower investment manufacturing processes such as fast evaporation and freeze-drying (lyophilization) have been developed to manufacture ASD at the bench level. The general belief is that the overall performance of ASD material is thermodynamically driven and should be independent of the manufacturing process. However, no formal comparison has been made to assess the in vivo performance of material generated by different processes. This study compares the in vitro and in vivo properties of ASD material generated by fast evaporation, lyophilization, and spray-drying methods using griseofulvin as a model compound and hydroxypropyl methylcellulose acetate succinate as the polymer matrix. Our data suggest that despite minor differences in the formulation release properties and stability of the ASD materials, the overall exposure is comparable between the three manufacturing processes under the conditions examined. These results suggest that fast evaporation and lyophilization may be suitable to generate ASD material for oral evaluation. However, caution should be exercised since the general applicability of the present findings will need to be further evaluated.

Supplementation of nicotinic acid with NAMPT inhibitors results in loss of in vivo efficacy in NAPRT1-deficient tumor models.

Nicotinamide adenine dinucleotide (NAD) is a metabolite essential for cell survival and generated de novo from tryptophan or recycled from nicotinamide (NAM) through the nicotinamide phosphoribosyltransferase (NAMPT)-dependent salvage pathway. Alternatively, nicotinic acid (NA) is metabolized to NAD through the nicotinic acid phosphoribosyltransferase domain containing 1 (NAPRT1)-dependent salvage pathway. Tumor cells are more reliant on the NAMPT salvage pathway making this enzyme an attractive therapeutic target. Moreover, the therapeutic index of NAMPT inhibitors may be increased by in NAPRT-deficient tumors by NA supplementation as normal tissues may regenerate NAD through NAPRT1. To confirm the latter, we tested novel NAMPT inhibitors, GNE-617 and GNE-618, in cell culture- and patient-derived tumor models. While NA did not protect NAPRT1-deficient tumor cell lines from NAMPT inhibition in vitro, it rescued efficacy of GNE-617 and GNE-618 in cell culture- and patient-derived tumor xenografts in vivo. NA co-treatment increased NAD and NAM levels in NAPRT1-deficient tumors to levels that sustained growth in vivo. Furthermore, NAM co-administration with GNE-617 led to increased tumor NAD levels and rescued in vivo efficacy as well. Importantly, tumor xenografts remained NAPRT1-deficient in the presence of NA, indicating that the NAPRT1-dependent pathway is not reactivated. Protection of NAPRT1-deficient tumors in vivo may be due to increased circulating levels of metabolites generated by mouse liver, in response to NA or through competitive reactivation of NAMPT by NAM. Our results have important implications for the development of NAMPT inhibitors when considering NA co-treatment as a rescue strategy.

Evaluation of homogenization techniques for the preparation of mouse tissue samples to support drug discovery.

BACKGROUND: In early drug-discovery research, understanding the tissue distribution of drug at the site of action can help to predict the toxicity, efficacy and exposure level of the drug. The bottleneck of tissue analysis by LC-MS/MS is the time-consuming homogenization step. RESULTS: Both mechanical and enzymatic techniques for mouse tissue homogenization were evaluated, which included bead beater, polytron and enzymatic digestion. Brain, bone marrow, kidney, spleen and liver tissues can be homogenized effectively using the bead beater alone. Lung and heart tissues were best treated with collagenase first and then homogenized by the bead beater. CONCLUSION: Homogenization conditions for seven mouse tissues have been evaluated and optimized. These findings will expedite the preparation of tissue samples for analysis.