Xianhua Cao

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.

Synergistic Antipancreatic Tumor Effect by Simultaneously Targeting Hypoxic Cancer Cells With HSP90 Inhibitor and Glycolysis Inhibitor

Purpose: We sought to examine the synergistic antipancreatic cancer effect by simultaneously targeting hypoxic cancer cells with heat-shock protein 90 (HSP90) inhibitor and blockade of energy production. Experimental Design: The anticancer effects of an HSP90 inhibitor (geldanamycin) in pancreatic cells were investigated in hypoxia and normoxia. A hexokinase II inhibitor, 3-broma-pyruvate (3BrPA), was evaluated for selective glycolysis inhibition in hypoxia as a sensitizer of HSP90 inhibitor against pancreatic cancer. The HSP90 client protein degradation was monitored by Western blot. The synergistic antitumor effect of geldanamycin and 3BrPA was evaluated in a xenograft pancreatic cancer model and monitored by a noninvasive dynamic contrast-enhanced magnetic resonance imaging. Results: Hypoxia enhanced HIF-1α expression by 11-fold in pancreatic cancer cells, and HSP90 inhibitor exhibited a seven- to eightfold higher anticancer effect in hypoxia compared with normoxia via HSP90 client protein degradation. 3BrPA selectively inhibited glycolysis and sensitized geldanamycin against pancreatic cancer cells by 17- to 400-fold through HSP90 client protein degradation. The synergistic anticancer effect of reduced doses of geldanamycin and 3-BrPA was confirmed in xenograft models in vivo by more than 75% tumor growth inhibition. Conclusions: The combination of HSP90 inhibitors and glycolysis inhibitors provides preferential inhibition of cancer cells in hypoxia through HSP90 client protein degradation and selective glycolysis inhibition. This may provide a new therapeutic regimen to battle chemotherapy-resistant pancreatic cancers, by enhancing the synergistic therapeutic efficacy and reducing dose-limiting toxicity.

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.

Dynamic schema for near infrared detection of pressure-induced changes in solid tumors

Differentiation among malignant tumors, benign tumors, and normal tissue is highly important in the diagnosis and treatment of many malignancies. We have proposed a dynamic schema for noninvasive characterization of pressure-induced changes in solid tumors. Our hypothesis has been that the altered neovascularization processes within cancer-bearing tissues may significantly increase vascular resistance and cause a much slower response of hemoglobin concentration during a dynamic compression stimulus. This hypothesis was tested by the evaluation of data generated from human tumor clinical testing and from animal tumor model testing. In the human tumor clinical testing, a unified diagnostic criterion was derived that integrated the relative characteristics of tumor oxygen, hemoglobin, and hemoglobin dynamics. By applying such a unified criterion, we were able to differentiate benign breast lesions and malignant breast tumors with high sensitivity and specificity within a subset of 14 suspicious breast lesions with similar size and depth characteristics. In the animal testing, a stepped compression load was applied to the subcutaneous tumor deposit on an athymic NU/NU nude mouse model with subcutaneous xenograft BxPC-3 cancer. Characteristic differences were observed between the premortem tumor and the postmortem tumor in terms of pressure-induced tumor structural and functional changes.

Monitoring Oxygen Dynamics During Pressure Induced Ischemia on Cancer Xenograft Models

We recently developed a multi-modal test platform for real time, non-invasive monitoring of tumor tissue structural and oxygen dynamic changes during pressure-induced ischemia. The system integrated a clinical ultrasound, a mechanical load frame, and a near infrared tissue oximeter. The system was tested on an athymic NU/NU mouse model with xenograft pancreatic cancer implanted on the back. The preliminary results demonstrated characteristic differences between the premortem tumor and the postmortem tumor in terms of physical and physiological responses to compression stimuli. These differences suggested that it might be possible to characterize suspicious tumors based on their oxygen dynamic responses to pressure-induced ischemia.

Development of a Multi-modal Sensor for in vivo Monitoring of Tumor Oxygen Dynamics

A multi-modal sensor has been developed for noninvasive, real time, in vivo monitoring of oxygen intake, consumption and blood flow dynamics in tumor tissue during ischemia-reperfusion. The sensor head integrated a near infrared tissue oximeter for tissue oxygen saturation and hemoglobin concentration measurement, a laser Doppler for blood flow measurement, and an electron paramagnetic resonance spectroscope (EPRS) for oxygen tension measurement. The sensor has been tested on athymic NU/NU mice with xenograft pancreatic cancer implanted on right legs. Ischemia-reperfusion was introduced by physical ligation of the femur artery. Preliminary results demonstrated technical feasibility of simultaneous tissue oxygen and blood flow measurements. Further data analysis is on the way.