Lanyan Fang

Why is it Challenging to Predict Intestinal Drug Absorption and Oral Bioavailability in Human Using Rat Model

PurposeTo study the correlation of intestinal absorption for drugs with various absorption routes between human and rat, and to explore the underlying molecular mechanisms for the similarity in drug intestinal absorption and the differences in oral bioavailability between human and rat.Materials and MethodsThe intestinal permeabilities of 14 drugs and three drug-like compounds with different absorption mechanisms in rat and human jejunum were determined by in situ intestinal perfusion. A total of 48 drugs were selected for oral bioavailability comparison. Expression profiles of transporters and metabolizing enzymes in both rat and human intestines (duodenum and colon) were measured using GeneChip analysis.ResultsNo correlation (r2 = 0.29) was found in oral drug bioavailability between rat and human, while a correlation (r2 = 0.8) was observed for drug intestinal permeability with both carrier-mediated absorption and passive diffusion mechanisms between human and rat small intestine. Moderate correlation (with r2 > 0.56) was also found for the expression levels of transporters in the duodenum of human and rat, which provides the molecular mechanisms for the similarity and correlation of drug absorption between two species. In contrast, no correlation was found for the expressions of metabolizing enzymes between rat and human intestine, which indicates the difference in drug metabolism and oral bioavailability in two species. Detailed analysis indicates that many transporters (such as PepT1, SGLT-1, GLUT5, MRP2, NT2, and high affinity glutamate transporter) share similar expression levels in both human and rat with regional dependent expression patterns, which have high expression in the small intestine and low expression in the colon. However, discrepancy was also observed for several other transporters (such as MDR1, MRP3, GLUT1, and GLUT3) in both the duodenum and colon of human and rat. In addition, the expressions of metabolizing enzymes (CYP3A4/CYP3A9 and UDPG) showed 12 to 193-fold difference between human and rat intestine with distinct regional dependent expression patterns.ConclusionsThe data indicate that rat and human show similar drug intestinal absorption profiles and similar transporter expression patterns in the small intestine, while the two species exhibit distinct expression levels and patterns for metabolizing enzymes in the intestine. Therefore, a rat model can be used to predict oral drug absorption in the small intestine of human, but not to predict drug metabolism or oral bioavailability in human.

Glucose uptake inhibitor sensitizes cancer cells to daunorubicin and overcomes drug resistance in hypoxia

AbstractPurposeA high-rate glycolysis is a fundamental property of solid tumors and is associated with an over-expression of glucose transporters and glycolytic enzymes. We hypothesize that over-expression of glucose transporters in tumors prevents apoptosis, promotes cancer cell survival, and confers drug resistance. Inhibition of glucose transporter will preferentially sensitize the anticancer effects of chemotherapeutic drugs to overcome drug resistance in hypoxia.MethodsGlucose transporter expressions were detected in cancer tissues and NCI 60 cancer cells with immunostaining and DNA microarray. Glucose uptake was measured with 3H-2-deoxy-glucose. Cytotoxicity of daunorubicin (DNR) in combination of glucose inhibitor was detected by MTS assay under hypoxic condition. Early stage apoptosis was monitored with Annexin V-FITC staining.ResultsImmunostaining showed that GLUT1 was significantly increased in hypoxic regions of the human colon and breast tumors. The expression profiles of all glucose transporters in NCI 60 cancer cells exhibited distinct expression patterns. Phloretin exhibited more than 60% glucose uptake inhibition. Hypoxia conferred two to fivefold higher drug resistance in SW620 and K562 to DNR. Inhibition of glucose uptake by phloretin sensitized cancer cells to DNR for its anticancer activity and apoptosis to overcome drug resistance only under hypoxia. Conclusion Cancer cells heavily rely on glucose transporters for glucose uptake to facilitate a high-rate glycolysis under hypoxia for their survival and drug resistance. Combination of glucose transporter inhibitors and chemotherapeutic drugs may provide a preferential novel therapeutic strategy to overcome drug resistance in hypoxia.

Histone Deacetylase Inhibitors through Click Chemistry

Histone deacetylase inhibitors (HDACi) are a relatively new class of chemotherapy agents. Herein, we report a click-chemistry based approach to the synthesis of HDACi. Fourteen agents were synthesized from the combination of two alkyne and seven azido precursors. The inhibition of HDAC1 and HDAC8 was then determined by in vitro enzymatic assays, after which the cytotoxicity was evaluated in the NCI human cancer cell line screen. A lead compound 5 g (NSC746457) was discovered that inhibited HDAC1 at an IC(50) value of 104 +/- 30 nM and proved quite potent in the cancer cell line screen with GI(50) values ranging from 3.92 microM to 10 nM. Thus, this click HDACi design has provided a new chemical scaffold that has not only revealed a lead compound, but one which is easily amendable to further structural modifications given the modular nature of this approach.

Population Pharmacokinetics of Humanized Monoclonal Antibody HuCC49ΔCH2 and Murine Antibody CC49 in Colorectal Cancer Patients

To predict the optimal time for surgery after antibody administration, the population pharmacokinetics of 125I‐HuCC49ΔCH2 and 125I‐CC49 were characterized in 55 patients with colorectal cancers. A 2‐compartment linear model was used to fit the pharmacokinetic data. Model stability and performance were assessed using a visual predictive check procedure. Different clinical trial designs were evaluated by simulation in combination with Bayesian estimation method to predict the optimal time for surgery. The results showed that HuCC49ΔCH2 had 65% faster clearance from blood circulation and 24% shorter mean residence time than CC49. Population pharmacokinetic analysis identified body weight as the only covariate to explain between‐subject variability in clearance, intercompartmental flow rate, and volume of distribution. Model predictions indicated a wide interval for the optimal time of surgery, suggesting that it would be beneficial to individualize the time of surgery for each patient by measurement of antibody disposition. Clinical trial designs with at least 3 measurements of antibody disposition were found to be better than an empirical direct observation method for the optimal prediction of surgery time.

Predictive Physiologically Based Pharmacokinetic Model for Antibody-Directed Enzyme Prodrug Therapy

Antibody-directed enzyme prodrug therapy (ADEPT) using anti-TAG-72 antibody and geldanamycin (GA) prodrug were validated in vitro. To understand the complexity and to explore optimal therapeutic regimens for ADEPT in vivo, a physiologically based pharmacokinetic model (PBPK) is applied to analyze each anatomical component/organ. The baseline model predicts that active drug tumor/plasma exposure (AUC) ratio is 2-fold, although antibody-enzyme conjugates (AbE) are distributed into tumors up to 9-fold higher than in plasma. However, the active drug tumor/plasma AUC ratio can be increased up to 100-fold when AbE are depleted from plasma. Similarly, the active drug tumor/plasma AUC ratio can be increased from 2- to 6-fold when the intrinsic clearance of AbE is accelerated by 10-fold. Several sensitive parameters are identified: 1) increasing flow inside tumor (Jiso,tumor) significantly increases active drug tumor/plasma AUC ratio; 2) increasing permeability of prodrug (from range 1.4 × 10–6 to 1.4 × 10–4 cm/s) increases active drug tumor/plasma AUC ratio significantly, whereas active drug permeability enhancement (from range 5 × 10–4 to 5 × 10–2 cm/s) has minimal effect; 3) decreasing Emax and increasing EC50 for converting prodrug to active drug increase tumor/plasma AUC ratio for active drug. The PBPK model predicts that the optimal dosing interval between AbE and prodrug administration is 5 days, the optimal AbE dose is 0.1 Bmax, and the optimal dose for GA prodrug is 60 mg/kg. The current PBPK model successfully identifies sensitive parameters and predicts an optimal dosing regimen for ADEPT.