Integrated PK/PD Modeling Relates Smoothened Inhibitor Biomarkers to The Heterogeneous Intratumor Disposition of Cetuximab in Pancreatic Cancer Tumor Models.

Therapeutic antibodies have shown little efficacy in the treatment of pancreatic ductal adenocarcinomas (PDAC). Tumor desmoplasia, hypovascularity, and poor perfusion result in insufficient tumor cell exposure, contributing to treatment failure. Smoothened inhibitors of hedgehog signaling (sHHi) increase PDAC tumor permeability, perfusion, and drug delivery, and provide a tool to develop a quantitative, mechanistic understanding as to how the temporal dynamics of tumor priming can impact intratumor distribution of monoclonal antibodies (mAb). A linked pharmacokinetic (PK)/pharmacodynamic (PD) model was developed to integrate the plasma and tumor PK of a sHHi priming agent with its effects upon downstream stromal biomarkers Gli1, hyaluronic acid, and interstitial fluid pressure in PDAC patient-derived xenograft (PDX) tumors. In parallel, in situ tumor concentrations of cetuximab (CTX: anti-epidermal growth factor receptor; EGFR) were quantified as a marker for tumor delivery of mAb or antibody-drug conjugates. A minimal, physiologically-based pharmacokinetic (mPBPK) model was constructed to link sHHi effects upon mechanistic effectors of tumor barrier compromise with the intratumor distribution of CTX, and CTX occupancy of EGFR in tumors. Integration of the mPBPK model of mAb deposition and intratumor distribution with the PK/PD model of tumor responses to priming not only identified physiological parameters that are critical for tumor antibody distribution, but also provides insight into dosing regimens that could achieve maximal tumor disposition of therapeutic antibodies under conditions of transient PDAC tumor permeability barrier compromise that mechanistically-diverse tumor priming strategies may achieve.

SAR of L-ABBA analogs for GGT1 inhibitory activity and L-ABBA's effect on plasma cysteine and GSH species.

Gamma-glutamyl transferase 1 (GGT1) is a critical enzyme involved in the hydrolysis and/or transfer of gamma-glutamyl groups of glutathione, which helps maintain cysteine levels in plasma. In this study, we synthesized L-ABBA analogs to investigate their inhibitory effect on GGT1 hydrolysis and transpeptidase activity, with the goal of defining the pharmacophore of L-ABBA. Our structure-activity relationship (SAR) study revealed that an α-COO- and α-NH3+ group, as well as a two-CH2 unit distance between α-C and boronic acid, are essential for the activity. The addition of an R (alkyl) group at the α-C reduced the activity of GGT1 inhibition, with L-ABBA being the most potent inhibitor among the analogs. Next, we investigated the impact of L-ABBA on plasma levels of cysteine and GSH species, with the expectation of observing reduced cysteine levels and enhanced GSH levels due to its GGT1 inhibition. We administered L-ABBA intraperitoneally and determined the plasma levels of cysteine, cystine, GSH, and GSSG using LCMS. Our results showed time- and dose-dependent L-ABBA changes in total plasma cysteine and GSH levels. This study is the first to demonstrate the regulation of plasma thiol species upon GGT1 inhibition, with plasma cystine levels reduced by up to âˆ¼ 75 % with L-ABBA (0.3 mg/dose). Cancer cells are highly dependent on the uptake of cysteine from plasma for maintaining high levels of intracellular glutathione. Thus, our findings suggest that GGT1 inhibitors, such as L-ABBA, have the potential to be used in GSH reduction thereby inducing oxidative stress in cancer cells and reducing their resistance to many chemotherapeutic agents.

Defining the Intravital Renal Disposition of Fluorescence-Quenched Exenatide.

Despite the understanding that renal clearance is pivotal for driving the pharmacokinetics of numerous therapeutic proteins and peptides, the specific processes that occur following glomerular filtration remain poorly defined. For instance, sites of catabolism within the proximal tubule can occur at the brush border, within lysosomes following endocytosis, or even within the tubule lumen itself. The objective of the current study was to address these limitations and develop methodology to study the kidney disposition of a model therapeutic protein. Exenatide is a peptide used to treat type 2 diabetes mellitus. Glomerular filtration and ensuing renal catabolism have been shown to be its principal clearance pathway. Here, we designed and validated a Förster resonance energy transfer-quenched exenatide derivative to provide critical information on the renal handling of exenatide. A combination of in vitro techniques was used to confirm substantial fluorescence quenching of intact peptide that was released upon proteolytic cleavage. This evaluation was then followed by an assessment of the in vivo disposition of quenched exenatide directly within kidneys of living rats via intravital two-photon microscopy. Live imaging demonstrated rapid glomerular filtration and identified exenatide metabolism occurred within the subapical regions of the proximal tubule epithelia, with subsequent intracellular trafficking of cleaved fragments. These results provide a novel examination into the real-time, intravital disposition of a protein therapeutic within the kidney and offer a platform to build upon for future work.

Unconjugated p-cresol activates macrophage macropinocytosis leading to increased LDL uptake.

Patients with chronic kidney disease (CKD) and end-stage renal disease suffer from increased cardiovascular events and cardiac mortality. Prior studies have demonstrated that a portion of this enhanced risk can be attributed to the accumulation of microbiota-derived toxic metabolites, with most studies focusing on the sulfonated form of p-cresol (PCS). However, unconjugated p-cresol (uPC) itself was never assessed due to rapid and extensive first-pass metabolism that results in negligible serum concentrations of uPC. These reports thus failed to consider the host exposure to uPC prior to hepatic metabolism. In the current study, not only did we measure the effect of altering the intestinal microbiota on lipid accumulation in coronary arteries, but we also examined macrophage lipid uptake and handling pathways in response to uPC. We found that atherosclerosis-prone mice fed a high-fat diet exhibited significantly higher coronary artery lipid deposits upon receiving fecal material from CKD mice. Furthermore, treatment with uPC increased total cholesterol, triglycerides, and hepatic and aortic fatty deposits in non-CKD mice. Studies employing an in vitro macrophage model demonstrated that uPC exposure increased apoptosis whereas PCS did not. Additionally, uPC exhibited higher potency than PCS to stimulate LDL uptake and only uPC induced endocytosis- and pinocytosis-related genes. Pharmacological inhibition of varying cholesterol influx and efflux systems indicated that uPC increased macrophage LDL uptake by activating macropinocytosis. Overall, these findings indicate that uPC itself had a distinct effect on macrophage biology that might have contributed to increased cardiovascular risk in patients with CKD.

Contribution of Monocarboxylate Transporter 6 to the Pharmacokinetics and Pharmacodynamics of Bumetanide in Mice.

Bumetanide, a sulfamyl loop diuretic, is used for the treatment of edema in association with congestive heart failure. Being a polar, anionic compound at physiologic pH, bumetanide uptake and efflux into different tissues is largely transporter-mediated. Of note, organic anion transporters (SLC22A) have been extensively studied in terms of their importance in transporting bumetanide to its primary site of action in the kidney. The contribution of one of the less-studied bumetanide transporters, monocarboxylate transporter 6 (MCT6; SLC16A5), to bumetanide pharmacokinetics (PK) and pharmacodynamics (PD) has yet to be characterized. The affinity of bumetanide for murine Mct6 was evaluated using Mct6-transfected Xenopus laevis oocytes. Furthermore, bumetanide was intravenously and orally administered to wild-type mice (Mct6+/+) and homozygous Mct6 knockout mice (Mct6-/-) to elucidate the contribution of Mct6 to bumetanide PK/PD in vivo. We demonstrated that murine Mct6 transports bumetanide at a similar affinity compared with human MCT6 (78 and 84 µM, respectively, at pH 7.4). After bumetanide administration, there were no significant differences in plasma PK. Additionally, diuresis was significantly decreased by ∼55% after intravenous bumetanide administration in Mct6-/- mice. Kidney cortex concentrations of bumetanide were decreased, suggesting decreased Mct6-mediated bumetanide transport to its site of action in the kidney. Overall, these results suggest that Mct6 does not play a major role in the plasma PK of bumetanide in mice; however, it significantly contributes to bumetanide's pharmacodynamics due to changes in kidney concentrations. SIGNIFICANCE STATEMENT: Previous evidence suggested that MCT6 transports bumetanide in vitro; however, no studies to date have evaluated the in vivo contribution of this transporter. In vitro studies indicated that mouse and human MCT6 transport bumetanide with similar affinities. Using Mct6 knockout mice, we demonstrated that murine Mct6 does not play a major role in the plasma pharmacokinetics of bumetanide; however, the pharmacodynamic effect of diuresis was attenuated in the knockout mice, likely because of the decreased bumetanide concentrations in the kidney.

Comparison of the composition and in vitro activity of polymyxin B products.

A number of companies manufacture polymyxin B using United States Pharmacopeia (USP) metrics, rather than chemical composition, to report biological activity. Given that polymyxin B contains several different components, it is unknown whether pharmacokinetic and pharmacodynamic variability exists between the different brands and whether USP metrics capture this variability. Here we investigated the composition of polymyxin B obtained from four manufacturers (Sigma-Aldrich, AK Scientific, USP and MP Biomedicals) and evaluated their rate and extent of killing against multidrug-resistant Acinetobacter baumannii and Klebsiella pneumoniae using in vitro static time-kill experiments. Ultraviolet (UV) fingerprinting and liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed similarities and differences between component distributions. The significant differences between products, based on UV fingerprinting and LC-MS/MS, did not translate into pharmacodynamic differences at the three concentrations evaluated. The aggregate polymyxin B concentration, rather than that of the individual components, influences overall bacterial killing.

Development and validation of a liquid chromatography tandem mass spectrometry assay for AZD3965 in mouse plasma and tumor tissue: Application to pharmacokinetic and breast tumor xenograft studies.

AZD3965, a pyrole pyrimidine derivative, is a potent and orally bioavailable inhibitor of monocarboxylate transporter 1 (MCT1), currently in a Phase I clinical trial in UK for lymphomas and solid tumors. There is currently no published assay for AZD3965. The objectives of this study were to develop and validate a LC/MS/MS assay for quantifying AZD3965 in mouse plasma and tumor tissue. Protein precipitation with 0.1% formic acid in acetonitrile was used for sample preparation. Chromatographic separation was achieved on a C18 column followed by tandem mass spectrometry detection in multiple reaction monitoring mode with utilizing Atmospheric Pressure Chemical Ionization. AR-C155858 was used as the internal standard. The inter-day and intra-day precision and accuracy of quality control samples evaluated in plasma and tumor tissue were less than ±7% of the nominal concentrations. The extraction recovery, matrix effect and stability values were all within acceptable levels. Sample dilution integrity, accessed by diluting plasma spiked with AZD3965 10-fold with blank plasma, was 101%. The lower limit of quantification (LLOQ) and upper limit of quantification (ULOQ) were 0.15 ng/mL and 12 µg/mL, respectively, in plasma. The assay of AZD3965 in tumor tissue was also validated with good precision and accuracy. The LLOQ was 0.15 ng/mL in tumor tissue. This assay was successfully applied to pharmacokinetic and murine 4T1 breast tumor xenograft studies of AZD3965 in mice.

Cell Signaling Model Connects Vorinostat Pharmacokinetics and Tumor Growth Response in Multiple Myeloma Xenografts.

Multiple myeloma is a fatal hematological malignancy with high rates of drug resistance and relapse. Vorinostat, a histone deacetylase inhibitor, has shown promise in enhancing efficacy when combined with current myeloma therapies. In this study, temporal changes of critical proteins and cell proliferation were measured in myeloma cells exposed to vorinostat. A model linking biomarker dynamics to cell proliferation was developed that captured vorinostat effects on signal transduction and cell viability. The model structure and parameters were fixed to describe tumor dynamics in vivo, and tumor-specific growth and death rate parameters were estimated. The signaling model captured tumor growth inhibition in murine xenografts for a range of dose levels and regimens. This model may be used as a mechanistic bridge to link vorinostat exposure to molecular events and pharmacodynamic (PD) outcomes. It may also provide a translational platform to explore vorinostat activity as a single agent and in combination regimens.

The development and validation of a simple liquid chromatography-tandem mass spectrometry method for polymyxin B1 and B2 quantification in different matrices.

Polymyxin B has resurfaced as a last-line treatment for multi-drug resistant Gram-negative bacteria. Accurate characterization and quantification of polymyxin B components is necessary to optimize this therapy. We developed and validated a robust, straightforward LC-MS/MS method to quantify polymyxin B1 and B2, the primary polymyxin B components, in various matrices (cation-adjusted Mueller-Hinton broth (CAMHB), human and rat plasma). Of sample preparation approaches investigated, two protein precipitation/extraction methods were developed as part of an analytical strategy based upon reverse-phase LC-MS/MS using electrospray ionization in positive multiple-reaction monitoring mode. Both methods were validated over therapeutically and experimentally relevant concentration ranges (CAMHB: 0.1-8.0µg/mL, rat and human plasma: 0.05-4.0µg/mL). Quality control samples spanning a relevant concentration range were employed to assess intra- and inter-day accuracy (relative error (%RSD)) and precision (coefficient of variation (CV%)). For polymyxin B1 and B2 in CAMHB, inter-day standard deviations were 1.18-4.59% and 0.777-1.23%, respectively, and accuracies were 94.2-99.3% and 94.4-99.1%. For rat plasma, inter-day standard deviations were 1.53%-5.64% and 4.07%-8.26%. Accuracies were 100.6-108.9% and 96.1-108.1%. For human plasma, inter-day standard deviations were 2.77-7.32% and 1.55-7.29%. Accuracies were 89.6-96.4% and 92.9-102.0%. Extraction recoveries for all matrices were >93.5%. Adsorption, storage, and long-term stability were assessed and were acceptable. Accuracy, precision, and cost-efficiency make this an ideal approach for quantifying polymyxin B in in vitro and in vivo samples including those from rat and human subjects.

Candida albicans Shed Msb2 and Host Mucins Affect the Candidacidal Activity of Salivary Hst 5.

Salivary Histatin 5 (Hst 5) is an antimicrobial peptide that exhibits potent antifungal activity towards Candida albicans, the causative agent of oral candidiasis. However, it exhibits limited activity in vivo, largely due to inactivation by salivary components of both host and pathogen origin. Proteins secreted by C. albicans during infection such as secreted aspartyl proteases (Saps) and shed mucin Msb2 can reduce Hst 5 activity; and human salivary mucins, while suggested to protect Hst 5 from proteolytic degradation, can entrap peptides into mucin gels, thereby reducing bioavailability. We show here that Sap6 that is secreted during hyphal growth reduces Hst 5 activity, most likely a result of proteolytic degradation of Hst 5 since this effect is abrogated with heat inactivated Sap 6. We further show that just like C. albicans shedding Msb2, mammalian mucins, fetuin and porcine gut mucin (that is related to salivary mucins), also reduce Hst 5 activity. However, we identify mucin-like protein-induced changes in C. albicans cell morphology and aggregation patterns, suggesting that the effect of such proteins on Hst 5 cannot be interpreted independently of their effect on yeast cells.

Simultaneous determination of the flavonoids robinin and kaempferol in human breast cancer cells by liquid chromatography-tandem mass spectrometry.

An accurate, precise and sensitive method was developed and validated for the simultaneous quantification of the flavonoid glycoside robinin, and its algycone kaempferol in human breast cancer MCF-7 cells. The application of liquid chromatography-tandem mass spectrometry (LC/MS/MS) with a TurboIonspray interface in negative mode under multiple reactions monitoring was investigated. Chromatographic separation was achieved on a C(18) column using a mobile phase consisting of (A) water with 0.025% formic acid and 1mM ammonium formate and (B) acetonitrile with 0.025% formic acid. Rutin was used as the internal standard for robinin and fisetin as the internal standard for kaempferol. The assay had a limit of detection of 0.1ng/ml for both compounds when present in cell lysate. The calibration curves were linear from 1 to 250ng/ml (r>0.999) for each compound. The intra- and inter-day coefficients of variation were less than 10% and intra- and inter-day accuracies were within 11%. This assay was successfully applied in a robinin cellular uptake study to determine the intracellular concentrations of robinin in MCF-7 cells.