Overcoming the blood-brain tumor barrier for effective glioblastoma treatment.

Gliomas are the most common primary brain tumors. Particularly in adult patients, the vast majority of gliomas belongs to the heterogeneous group of diffuse gliomas, i.e. glial tumors characterized by diffuse infiltrative growth in the preexistent brain tissue. Unfortunately, glioblastoma, the most aggressive (WHO grade IV) diffuse glioma is also by far the most frequent one. After standard treatment, the 2-year overall survival of glioblastoma patients is approximately only 25%. Advanced knowledge in the molecular pathology underlying malignant transformation has offered new handles and better treatments for several cancer types. Unfortunately, glioblastoma multiforme (GBM) patients have not yet profited as although numerous experimental drugs have been tested in clinical trials, all failed miserably. This grim prognosis for GBM is at least partly due to the lack of successful drug delivery across the blood-brain tumor barrier (BBTB). The human brain comprises over 100 billion capillaries with a total length of 400 miles, a total surface area of 20 m(2) and a median inter-capillary distance of about 50 µm, making it the best perfused organ in the body. The BBTB encompasses existing and newly formed blood vessels that contribute to the delivery of nutrients and oxygen to the tumor and facilitate glioma cell migration to other parts of the brain. The high metabolic demands of high-grade glioma create hypoxic areas that trigger increased expression of VEGF and angiogenesis, leading to the formation of abnormal vessels and a dysfunctional BBTB. Even though the BBTB is considered 'leaky' in the core part of glioblastomas, in large parts of glioblastomas and, even more so, in lower grade diffuse gliomas the BBTB more closely resembles the intact blood-brain barrier (BBB) and prevents efficient passage of cancer therapeutics, including small molecules and antibodies. Thus, many drugs can still be blocked from reaching the many infiltrative glioblastoma cells that demonstrate 'within-organ-metastasis' away from the core part to brain areas displaying a more organized and less leaky BBTB. Hence, drug delivery in glioblastoma deserves explicit attention as otherwise new experimental therapies will continue to fail. In the current review we highlight different aspects of the BBTB in glioma patients and preclinical models and discuss the advantages and drawbacks of drug delivery approaches for the treatment of glioma patients. We provide an overview on methods to overcome the BBTB, including osmotic blood-brain barrier disruption (BBBD), bradykinin receptor-mediated BBTB opening, inhibition of multidrug efflux transporters, receptor-mediated transport systems and physiological circumvention of the BBTB. While our knowledge about the molecular biology of glioma cells is rapidly expanding and is, to some extent, already assisting us in the design of tumor-tailored therapeutics, we are still struggling to develop modalities to expose the entire tumor to such therapeutics at pharmacologically meaningful quantities. Therefore, we must expand our knowledge about the fundamentals of the BBTB as a step toward the design of practical and safe devices and approaches for enhanced drug delivery into the diseased brain area.

Fractionated brain X-irradiation profoundly reduces hippocampal immature neuron numbers without affecting spontaneous behavior in mice.

Whole brain radiotherapy (WBRT) is used to improve tumor control in patients with primary brain tumors, or brain metastasis from various primary tumors to improve tumor control. However, WBRT can lead to cognitive decline in patients. We assessed whether fractionated WBRT (fWBRT) affects spontaneous behavior of mice in automated home cages and cognition (spatial memory) using the Barnes maze. Male C57Bl/6j mice received bi-lateral fWBRT at a dosage of 4 Gy/day on 5 consecutive days. In line with previous reports, immunohistochemical analysis of doublecortin positive cells in the dentate gyrus showed a profound reduction in immature neurons 4 weeks after fWBRT. Surprisingly, spontaneous behavior as measured in automated home cages was not affected. Moreover, learning and memory measured with Barnes maze, was also not affected 4-6 weeks after fWBRT. At 10-11 weeks after fWBRT a significant difference in escape latency during the learning phase, but not in the probe test of the Barnes maze was observed. In conclusion, although we confirmed the serious adverse effect of fWBRT on neurogenesis 4 weeks after fWBRT, we did not find similar profound effects on spontaneous behavior in the automated home cage nor on learning abilities as measured by the Barnes maze. The relationship between the neurobiological effects of fWBRT and cognition seems more complex than often assumed and the choice of animal model, cognitive tasks, neurobiological parameters, and experimental set-up might be important factors in these types of experiments.

A validated HPLC-MS/MS method for simultaneously analyzing curcumin, demethoxycurcumin, bisdemethoxycurcumin, tetra-hydrocurcumin and piperine in human plasma, urine or feces.

Background: The spice curcumin is supposed to have many different beneficial health effects. To understand the complete pharmacokinetics of curcumin we need an analytical method to determine curcumin and its metabolites in human plasma, urine or feces. We have developed an HPLC-MS/MS method for the simultaneous analysis of curcumin, demethoxycurcumin, bisdemethoxycurcumin, tetrahydrocurcumin and piperine in human plasma, urine or feces. Methods: Sample pretreatment involved a simple liquid-liquid extraction with tert-butyl methyl ether. Conjugated curcumin and analogs can be measured after enzymatic hydrolysis. Reversed-phase chromatography with a linear gradient of 50-95% methanol in 0.1% formic acid was used. Total run time is 15 min. The method was validated with regards to stability, specificity, sensitivity, linearity, accuracy, repeatability and reproducibility. The applicability of the method was tested using actual patients samples. Results: The LLOQ in plasma, urine and feces for curcumin, demethoxycurcumin, bisdemethoxycurcumin, tetrahydrocurcumin and piperine ranged from 1 to 5 nM. Whereas all compounds could be quantified on a linear range between 2 and 400 nM. Plasma and feces recovery of curcumin was 97.1 ± 3.7% and 99.4 ± 16.2%, whereas urine showed a recovery of 57.1 ± 9.3%. All compounds had acceptable in-between day or between day variability in the different matrixes. Conclusion: A HPLC-MS/MS method was developed and validated for the simultaneous quantification of curcumin, demethoxycurcumin, bisdemethoxycurcumin, tetrahydrocurcumin and piperine in human plasma, urine or feces. This method will aid in critically verifying the pharmacokinetics of curcumin made by supplement manufacturers and help us to provide insight in the claimed bioavailability of curcumin supplements.

Paclitaxel in self-micro emulsifying formulations: oral bioavailability study in mice.

The anticancer drug paclitaxel is formulated for i.v. administration in a mixture of Cremophor EL and ethanol.Its oral bioavailability is very low due to the action of P-glycoproteinin the gut wall and CYP450 in gut wall and liver.However, proof-of-concept studies using the i.v. formulation diluted in drinking water have demonstrated the feasibility of the oral route as an alternative when given in combination with inhibitors of P-glycoprotein and CYP450. Because of the unacceptable pharmaceutical properties of the drinking solution, a better formulation for oral application is needed.We have evaluated the suitability of various self-micro emulsifying oily formulations (SMEOF's) of paclitaxel for oral application using wild-type and P-glycoprotein knockout mice and cyclosporin A (CsA) as P-glycoprotein and CYP450 inhibitor. The oral bioavailability of paclitaxel in all SMEOF's without concomitant CsA was low in wild-type mice, showing that this vehicle does not enhance intestinal uptake by itself.Paclitaxel (10 mg/kg) in SMEOF#3 given with CsA resulted in plasma levels that were comparable to the Cremophor ELethanol containing drinking solution plus CsA. Whereas the AUC increased linearly with the oral paclitaxel dose in P-glycoprotein knockout mice, it increased less than proportional in wild-type mice given with CsA. In both strains more unchanged paclitaxel was recovered in the feces at higher doses. This observation most likely reflects more profound precipitation of paclitaxel within the gastro-intestinal tract at higher doses. The resulting absolute reduction in absorption of paclitaxel from the gut was possibly concealed by partial saturation of first-pass metabolism when P-glycoprotein was absent. In conclusion, SMEOF's maybe a useful vehicle for oral delivery of paclitaxel in combination with CsA, although the physical stability within the gastro-intestinal tract remains a critical issue, especially when applied at higher dose levels.

Disposition and toxicity of trabectedin (ET-743) in wild-type and mdr1 gene (P-gp) knock-out mice.

Trabectedin is a novel anticancer drug active against soft tissue sarcomas. Trabectedin is a substrate for P-glycoprotein (P-gp), which is encoded by mdr1a/1b in rodents. Plasma and tissue distribution, and excretion of [(14)C]-trabectedin were evaluated in wild-type and mdr1a/1b(-/-) mice. In parallel, we investigated the toxicity profile of trabectedin by serial measurements of blood liver enzymes and general pathology. [(14)C]-trabectedin was extensively distributed into tissues, and rapidly converted into a range of unknown metabolic products. The excretion of radioactivity was similar in both genotypes. The plasma clearance of unchanged trabectedin was not reduced when P-gp was absent, but organs under wild type circumstances protected by P-gp showed increased trabectedin concentrations in mdr1a/1b(-/-) mice. Although hepatic trabectedin concentrations were not increased when P-gp was absent, mdr1a/1b(-/-) mice experienced more severe liver toxicity. P-gp plays a role in the in vivo disposition and toxicology of trabectedin.

Characterisation of tumour vasculature in mouse brain by USPIO contrast-enhanced MRI.

To enhance the success rate of antiangiogenic therapies in the clinic, it is crucial to identify parameters for tumour angiogenesis that can predict response to these therapies. In brain tumours, one such parameter is vascular leakage, which is a response to tumour-derived vascular endothelial growth factor-A and can be measured by Gadolinium-DTPA (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). However, as vascular permeability and angiogenesis are not strictly coupled, tumour blood volume may be another potentially important parameter. In this study, contrast-enhanced MR imaging was performed in three orthotopic mouse models for human brain tumours (angiogenic melanoma metastases and E34 and U87 human glioma xenografts) using both Gd-DTPA to detect vascular leakage and ultrasmall iron oxide particles (USPIO) to measure blood volume. Pixel-by-pixel maps of the enhancement in the transverse relaxation rates (Delta R(2) and Delta R(2)(*)) after injection of USPIO provided an index proportional to the blood volume of the microvasculature and macrovasculature, respectively, for each tumour. The melanoma metastases were characterised by a blood volume and vessel leakage higher than both glioma xenografts. The U87 glioblastoma xenografts displayed higher permeability and blood volume in the rim than in the core. The E34 glioma xenografts were characterised by a relatively high blood volume, accompanied by only a moderate blood-brain barrier disruption. Delineation of the tumour was best assessed on post-USPIO gradient-echo images. These findings suggest that contrast-enhanced MR imaging using USPIOs and, in particular, Delta R(2) and Delta R(2)(*) quantitation, provides important additional information about tumour vasculature.

Absence or pharmacological blocking of placental P-glycoprotein profoundly increases fetal drug exposure.

It was recently shown that naturally occurring Mdr1a mutant fetuses of the CF-1 outbred mouse stock have no placental Mdr1a P-glycoprotein (P-gp) and that this absence is associated with increased sensitivity to avermectin, a teratogenic pesticide. To further define the role of placental drug-transporting P-gp in toxicological protection of the fetus, we used mice with a targeted disruption of the Mdr1a and Mdr1b genes. Mdr1a(+/-)/1b(+/-) females were mated with Mdr1a(+/-)/1b(+/-) males to obtain fetuses of 3 genotypes (Mdr1a(+/+)/1b(+/+), Mdr1a(+/-)/1b(+/-), and Mdr 1a(-/-)/1b(-/-)) in a single mother. Intravenous administration of the P-gp substrate drugs [(3)H]digoxin, [(14)C]saquinavir, or paclitaxel to pregnant dams revealed that 2.4-, 7-, or 16-fold more drug, respectively, entered the Mdr1a(-/-)/1b(-/-) fetuses than entered wild-type fetuses. Furthermore, placental P-gp activity could be completely inhibited by oral administration of the P-gp blockers PSC833 or GG918 to heterozygous mothers. Our findings imply that the placental drug-transporting P-gp is of great importance in limiting the fetal penetration of various potentially harmful or therapeutic compounds and demonstrate that this P-gp function can be abolished by pharmacological means. The latter principle could be applied clinically to improve pharmacotherapy of the unborn child.

Development of luciferase tagged brain tumour models in mice for chemotherapy intervention studies.

The blood-brain barrier (BBB) is considered one of the major causes for the low efficacy of cytotoxic compounds against primary brain tumours. The aim of this study was to develop intracranial tumour models in mice featuring intact or locally disrupted BBB properties, which can be used in testing chemotherapy against brain tumours. These tumours were established by intracranial injection of suspensions of different tumour cell lines. All cell lines had been transfected with luciferase to allow non-invasive imaging of tumour development using a super-cooled CCD-camera. Following their implantation, tumours developed which displayed the infiltrative, invasive or expansive growth patterns that are also found in primary brain cancer or brain metastases. Contrast-enhanced magnetic resonance imaging showed that the Mel57, K1735Br2 and RG-2 lesions grow without disruption of the BBB, whereas the BBB was leaky in the U87MG and VEGF-A-transfected Mel57 lesions. This was confirmed by immunohistochemistry. Bioluminescence measurements allowed the visualisation of tumour burden already within 4 days after injection of the tumour cells. The applicability of our models for performing efficacy studies was demonstrated in an experiment using temozolomide as study drug. In conclusion, we have developed experimental brain tumour models with partly disrupted, or completely intact BBB properties. In vivo imaging by luciferase allows convenient follow-up of tumour growth and these models will be useful for chemotherapeutic intervention studies.

Altered pharmacokinetics of vinblastine in Mdr1a P-glycoprotein-deficient Mice.

BACKGROUND: P-glycoprotein (Pgp) is a membrane protein that acts as an extrusion pump for many cytotoxic drugs. Pgp is expressed in normal tissues, and its (over)expression in tumor cells contributes to their drug resistance. Human Pgp is encoded by the MDR1 gene, In mice, two Pgps (encoded by the mdr1a and mdr1b genes) appear to perform the same function as the single human protein. The simultaneous use of cytotoxic drugs and agents that block Pgp function has raised questions of safety, since a blockade of Pgp in normal tissues could alter drug pharmacokinetics and change the spectrum of toxic side effects. Analysis of the consequences of Pgp blockade has been facilitated by the generation of mice with disrupted mdr1a genes [mdr1a(-/-)]. PURPOSE: We studied the plasma pharmaco-kinetics, tissue distribution, and excretion of the cytotoxic drug vinblastine (VBL) and its metabolites in mdr1a (-/-) mice and in wild-type [mdr1a(+/+)] mice. METHODS: VBL was administered to mice in bolus doses of either 1 or 6 mg/kg body weight by intravenous injection. VBL and its metabolites were quantified in tissue specimens, plasma, feces, and urine by use of high-performance liquid chromatography. Liquid scintillation counting was used to measure radioactivity in specimens from animals that had received [3H]VBL. Pharmacokinetic parameters were calculated by use of noncompartmental methods. Only two-sided P values are reported. RESULTS: The half-life (t1/2) of VBL during its terminal phase of elimination was longer in mdr1a (-/-) mice than in wild-type mice. The t1/2 values with a 1-mg/kg dose were 3.6 hours +/- 0.3 hour (mean +/- standard error) and 2.1 hours +/- 0.3 hour, respectively (P < .05); with a 6-mg/kg dose, the values were 8.6 hours +/- 1.8 hours and 4.2 hours +/- 0.2 hour, respectively (P = .058). Fecal excretion of nonmetabolized VBL was reduced from 20%-25% of the administered dose (either 1 or 6 mg/kg) in wild-type mice to 9.3% (1-mg/kg dose) or 3.4% (6-mg/kg dose) in mdr1a(-/-) mice (both P < .05); the cumulative urinary excretion of VBL was low (< 6% of the administered dose) and not substantially different in the two types of mice. The metabolism of VBL to hydrophilic compounds, a primary mechanism involved in its elimination, was not altered in mdr1a(-/-) mice. The brains of mdr1a(-/-) mice accumulated substantially more VBL than the brains of wild-type mice. In mdr1a(-/-) mice, a few other tissues, such as the heart and the liver, accumulated increased amounts of VBL, but the relative levels of accumulation were lower than those found in the brain. CONCLUSIONS: Mice lacking the Pgp encoded by the mdr1a gene exhibit reduced fecal excretion of VBL, leading to a prolonged elimination t1/2 for this drug. Intact mdr1a function appears to protect the brain against high plasma levels of VBL, but most other tissues are not similarly protected. IMPLICATIONS: Enhanced drug accumulation in nonmalignant tissues after Pgp blockade should be carefully considered in future clinical trials of Pgp modulation.

Nonlinear pharmacokinetics of paclitaxel in mice results from the pharmaceutical vehicle Cremophor EL.

Studies in humans and mice have demonstrated a nonlinear pharmacokinetic behavior of paclitaxel. Because of its poor water solubility, the drug is formulated in a mixture of Cremophor EL and ethanol (1:1, v/v; Taxol). We hypothesized that the substantial amounts of concurrently administered Cremophor EL on the disposition of paclitaxel, female FVB mice received paclitazel by i.v. injection at does levels of 2, 10, and 20 mg/kg by appropriate (standard) dilution of the commercially available formulation of paclitaxel (Taxol) with saline. The drug was also given at 2 mg/kg with supplemental Cremophor EL-ethanol to achieve the same amount of vehicle as by standard administration of 10 mg/kg. Furthermore, paclitaxel formulations in Tween 80-ethanol (1:1, v/v) and dimethylacetamide were tested. Plasma samples were collected between 5 min and 48 h, and tissue specimens were sampled at 1, 4, and 8 h after drug administration. Paclitaxel and metabolites were quantified by high-performance liquid chromatography. Cremophor EL levels were determined by a novel high-performance liquid chromatography procedure. For comparative reasons, Cremophor EL was also assayed in plasma samples from three patients receiving a 3-h i.v. infusion of 175 mg/m2 of paclitaxel. A marked nonlinear pharmacokinetic behavior of paclitaxel was observed when the drug was formulated in Cremophor EL-ethanol. The clearance of 2.37 L/h/kg at 2 mg/kg was reduced to 0.33 and 0.15 L/h/kg at 10 and 20 mg/kg, respectively. When 2 mg/kg were given with an amount of Cremophor EL-ethanol matching that of the 10-mg/kg dose level, the clearance was 0.56 L/h/kg. If administered at 10 mg/kg in Tween 80-ethanol or at 2 and 10 mg/kg in dimethylacetamide, the clearances were 2.66, 2.57, and 2.62 L/h/kg, respectively. Despite the fact that much higher plasma levels of paclitaxel are reached when given in the Cremophor EL-ethanol formulation, the tissue levels were essentially similar with all tested drug preparations. The Cremophor EL levels in patients were in the same order of magnitude as those observed in mice after administration of 2 and 10 mg/kg. These data demonstrate that Cremophor EL has a profound effect on the pharmacokinetics of paclitaxel im mice. Because Cremophor EL also contributes substantially to the nonlinear pharmacokinetic behavior of paclitaxel observed in humans.

Plasma pharmacokinetics of vinblastine and the investigational Vinca alkaloid N-(deacetyl-O-4-vinblastoyl-23)-L-ethyl isoleucinate in mice as determined by high-performance liquid chromatography.

The plasma pharmacokinetics of vinblastine and N-(deacetyl-O-4-vinblastoyl-23)-L-ethyl isoleucinate (VileE) in mice have been studied as part of the preclinical investigations of VileE, a new investigational semisynthetic Vinca alkaloid. Groups of animals received the test compounds through i.v. bolus injection at LD10, 0.5 x LD10, and 0.1 x LD10 doses. VileE has also been administered p.o. Drug plasma levels have been analyzed with a sensitive and selective method using liquid-liquid extraction for sample clean-up and high-performance liquid chromatography combined with fluorescence detection for quantification. Following i.v. injection, plasma kinetics of both vinblastine and VileE can be described adequately by a three-compartment open model. VileE demonstrates nonlinear pharmacokinetics with decreasing clearance and increasing terminal half-lives at increasing doses. Comparison of the plasma concentration versus time curves for vinblastine in humans and mice indicates that the toxicity of these compounds may not be directly related to the drug exposure expressed by the area under curve in plasma but by the terminal half-life and the time that a toxic threshold level is attained. Pharmacokinetically guided dose escalation in coming phase I trials of VileE is, therefore, discouraged.

Comparative pharmacology of the novel cyclopropylpyrroloindole-prodrug carzelesin in mice, rats, and humans.

Carzelesin is a novel cyclopropylpyrroloindole prodrug analogue that has recently been tested in Phase I clinical trials. To increase our understanding in the pharmacology of this new class of cytotoxic drugs, we have compared the pharmacology of this drug in mice, rats, and humans. The mouse was the most tolerant [10% lethal dose (LD10), 500 microg/kg], the rat was intermediate (LD10, 40 microg/kg), and humans were the least tolerant species in this series (maximum tolerated dose, 300 microg/m2 corresponding to 7.5 microg/kg). In both mice and humans, bone marrow toxicity was the primary toxic side effect. Pharmacokinetic studies, using a validated high-performance liquid chromatographic procedure, revealed that differences in drug clearance and conversion to the active drug (U-76,074) could not explain the substantial interspecies differences. The area under the plasma concentration time curve (AUCs) of carzelesin in mice and rats at their LD10s were about 80- and 20-fold higher, respectively, than in humans receiving the maximum tolerated dose, whereas the respective AUCs of U-76,074 in mice and rats were 50- and 10-fold higher. By using a colony-forming assay with bone marrow stem cells from mice and humans, we observed only a 3-fold higher toxicity in the latter. Although some of this discrepancy may be explained by the fact that the in vitro and the in vivo assays probably reflect the toxicity on different populations of colony-forming units, the tolerance of the mouse bone marrow in vivo against the very high drug levels in plasma suggest the presence of a protective mechanism, which is less active in humans. An important consequence of the much higher susceptibility of the human bone marrow for carzelesin is that the target plasma levels in humans are much below active concentrations achieved in mice, and it is clear that this may compromise the successful use of this agent in the clinic. Ultimately, however, the efficacy of this drug will be established in Phase II clinical trials.

Neurobiological changes by cytotoxic agents in mice.

Cognitive deficit is a frequently reported side-effect of adjuvant chemotherapy. A large number of animal studies has been performed to examine the neurobiological mechanisms underlying this phenomenon, however, definite conclusions from these studies are restricted due to differences in experimental set-up. We systematically investigated the effects of 6 cytotoxic agents on various neurobiological parameters. C57Bl/6J mice were treated with cyclophosphamide, docetaxel, doxorubicin, 5-fluorouracil, methotrexate, or topotecan. The animals were sacrificed 3 or 15 weeks after treatment and the effect on neurogenesis, blood vessel density, and neuroinflammation was analyzed using immunohistochemistry. None of the cytostatic agents tested affected neurogenesis (cell survival or cell proliferation). Blood vessel density was increased in the hippocampus and prefrontal cortex 3 weeks after treatment with docetaxel and doxorubicin compared with control animals. A decrease in the number of microglial cells was observed in the prefrontal cortex after treatment with cyclophosphamide, docetaxel, 5-FU, and topotecan compared with control mice. The observed decrease in microglia cells is indicative of inflammation that occurred after treatment. Overall, the magnitude of the effects was relatively modest. Therefore, we conducted a similar study with topotecan in Abcg2;Abcb1a/b knock out and wildtype FVB mice. Animals were sacrificed 3 weeks after treatment and no notable effect was seen in hippocampal cell differentiation (DCX), microglia activation, or blood vessel density. Perhaps the FVB strain is more resistant to the neurotoxic effects of topotecan which makes this not the correct model to study the mechanism of chemotherapy-induced cognitive impairment.

Strategies to target drugs to gliomas and CNS metastases of solid tumors.

The treatment for central nervous system metastases of solid tumors and gliomas is limited as the blood-brain barrier (BBB) is an obstacle to systemic therapy. Here, we review the physiochemical properties of the BBB and both current and new drug strategies to penetrate brain tumors. We focus on targeting receptor- or carrier-mediated transport mechanisms over the BBB used by drug conjugates, nanoparticles, polymer-based nanocarriers, siRNA, and antibodies.

Clinical and pharmacologic study of multidrug resistance reversal with vinblastine and bepridil.

PURPOSE: To achieve an adequate plasma concentration of bepridil, a calcium channel blocker, which reverts multidrug resistance (MDR) in vitro, when administered in combination with vinblastine in patients with advanced colorectal cancer, a tumor characterized by high MDR1 gene expression. To study the pharmacokinetics of both drugs, tolerability and antitumor activity in relation to the MDR1 expression in tumor tissue. PATIENTS AND METHODS: Sixteen colorectal cancer patients entered the study. Bepridil was administered by central venous catheter as 5-mg/kg bolus over 30 minutes, followed by 12 mg/kg for 12 hours and 5 mg/kg for 24 hours. Vinblastine 5 mg/m2 was administered as an intravenous (i.v.) bolus 24.5 hours after the start of bepridil. MDR1/P-glycoprotein (Pgp) expression was assessed in 14 tumor samples by immunohistochemistry and RNase protection assay. RESULTS: The bepridil plasma level was greater than 2 mumol/L at the time of vinblastine administration in all patients investigated. At the dose used in the study, bepridil produced a QTc-prolongation more than 50 ms, which prevented further dose escalation. However, cardiac toxicity was asymptomatic in all treated patients, and other side effects were mild. MDR1/Pgp expression was positive in nine of 14 cases. Of fifteen patients assessable for response, one complete remission of 8 months' duration and 14 progressions were observed. The responding patient attained complete remission again when re-treated on progression with vinblastine alone. CONCLUSION: Bepridil plasma concentrations needed in vitro to modulate MDR could be achieved in this study with tolerable toxicity; however, despite most tumors being MDR1/Pgp-positive, no response was obtained that could be attributed to the drug combination. Mechanisms of drug resistance other than MDR are probably implicated in drug resistance of colorectal cancer.

Phase I and pharmacokinetic study of oral paclitaxel.

PURPOSE: To investigate dose escalation of oral paclitaxel in combination with dose increment and scheduling of cyclosporine (CsA) to improve the systemic exposure to paclitaxel and to explore the maximum-tolerated dose (MTD) and dose-limiting toxicity (DLT). PATIENTS AND METHODS: A total of 53 patients received, on one occasion, oral paclitaxel in combination with CsA, coadministered to enhance the absorption of paclitaxel, and, on another occasion, intravenous paclitaxel at a dose of 175 mg/m(2) as a 3-hour infusion. RESULTS: The main toxicities observed after oral intake of paclitaxel were acute nausea and vomiting, which reached DLT at the dose level of 360 mg/m(2). Dose escalation of oral paclitaxel from 60 to 300 mg/m(2) resulted in significant but less than proportional increases in the plasma area under the concentration-time curve (AUC) of paclitaxel. The mean AUC values +/- SD after 60, 180, and 300 mg/m(2) of oral paclitaxel were 1.65 +/- 0.93, 3.33 +/- 2.39, and 3.46 +/- 1.37 micromol/L.h, respectively. Dose increment and scheduling of CsA did not result in a further increase in the AUC of paclitaxel. The AUC of intravenous paclitaxel was 15.39 +/- 3.26 micromol/L.h. CONCLUSION: The MTD of oral paclitaxel was 300 mg/m(2). However, because the pharmacokinetic data of oral paclitaxel, in particular at the highest doses applied, revealed nonlinear pharmacokinetics with only a moderate further increase of the AUC with doses up to 300 mg/m(2), the oral paclitaxel dose of 180 mg/m(2) in combination with 15 mg/kg oral CsA is considered most appropriate for further investigation. The safety of the oral combination at this dose level was good.

Enhanced oral absorption and decreased elimination of paclitaxel in mice cotreated with cyclosporin A.

Recent experiments in mice have demonstrated that the systemic exposure to p.o. administered paclitaxel is significantly enhanced with coadministration of the P-glycoprotein blocker SDZ PSC 833 (J. van Asperen et al, Br. J. Cancer, 76: 1181-1183, 1997). To facilitate further research on the feasibility of a clinically effective oral formulation of paclitaxel, it is important to know whether cotreatment with a commonly applied and commercially available P-glycoprotein blocker, e.g., cyclosporin A, has a similar effect. Here, we present a detailed study about the effects of cyclosporin A on the pharmacokinetics of p.o. and i.v. administered paclitaxel. Female FVB mice received a combined treatment of 5 or 10 mg/kg paclitaxel (either i.v. or p.o.) plus 0, 10, or 50 mg/kg cyclosporin A (p.o.). The plasma concentrations of paclitaxel were determined at several time points after drug administration using high-performance liquid chromatography. Calculated relative to the area under the plasma concentration-time curve of i.v. administered paclitaxel in mice treated without cyclosporin A, the oral bioavailability of paclitaxel increased from 9.3% up to 67% with coadministration of cyclosporin A. The bioavailability in mice cotreated with 10 or 50 mg/kg cyclosporin A appeared to be similar. The effect of cyclosporin A on the systemic exposure to p.o. administered paclitaxel was the result of both a significantly decreased clearance and an increased uptake. A histological examination revealed that the enhanced absorption was not caused by gastrointestinal toxicity. We conclude that cyclosporin A and SDZ PSC 833 are equally effective in increasing the systemic exposure to p.o. administered paclitaxel. These data are promising for the development of a clinically useful oral formulation of this cytostatic drug and indicate that cyclosporin A is a suitable agent for further research of this concept.

Rapid esterase-sensitive breakdown of polysorbate 80 and its impact on the plasma pharmacokinetics of docetaxel and metabolites in mice.

We have developed and validated an analytical methodology for the quantification of docetaxel and its four major human oxidation metabolites in mouse plasma. We have used this procedure to study the pharmacokinetics and metabolism of docetaxel in female FVB mice, receiving 2.5, 10, or 33 mg/kg of docetaxel by i.v. injection. We have also studied the pharmacokinetics of polysorbate 80, because it was shown previously that the vehicle substance Cremophor EL, which is used in the formulation of paclitaxel, exerts a profound effect on the pharmacokinetics of this compound. Linear pharmacokinetics of docetaxel was observed at dose levels between 2.5 and 10 mg/kg, where plasma levels corresponded to those in patients receiving the maximum tolerated dose. At the highest dose level of 33 mg/kg, a deviation from the linear kinetics was observed. Compared with humans, mice could tolerate much higher plasma levels, suggesting that the toxic side effects are related to a certain plasma threshold concentration instead of area under the curve or Cmax. At the highest dose level, three docetaxel metabolites could be detected in the plasma samples of mice for up to 4 h after drug administration. The hydroxy metabolite of the tert-butoxy group (metabolite II) was the major metabolite, followed by the two epimeric hydroxyoxazolone-type compounds (metabolites I and III). A fourth putative metabolite (e.g., the cyclic oxazolidinedione derivative) was not detected. Because of rapid degradation of polysorbate 80 by esterases in plasma, the concentration of this vehicle substance declined very rapidly. Consequently, this substance was not able to interfere in the disposition of docetaxel.

Increased oral bioavailability of paclitaxel by GF120918 in mice through selective modulation of P-glycoprotein.

Previous studies in mice with disrupted mdr1a P-glycoprotein genes have shown that the oral bioavailability of paclitaxel is very low because of the presence of this drug-transporting protein in the intestinal wall. Additional studies with cyclosporin A have shown that this P-glycoprotein-inhibiting agent is able to increase the bioavailability of paclitaxel in mouse models and in patients. However, the potential immune-suppressive side effects of cyclosporin A renders this compound less suitable for chronic use in cancer patients. In this paper we present the results obtained with GF120918, an experimental P-glycoprotein inhibitor, on the oral bioavailability of paclitaxel in both wild-type and mdrlab knockout mice. GF120918 (25 mg/kg) was administered p.o. by gavage 15 min or 2 h before oral or i.v. dosing of paclitaxel, respectively. Paclitaxel plasma levels were quantified by high-performance liquid chromatography. GF120918 increased the plasma values for areas under the concentration-time curve of oral paclitaxel in wild-type mice by 6.6-fold from 408 to 2701 ng x ml(-1) h. Calculated relative to their respective values for area under the concentration-time curve after i.v. administration, GF120918 increased the oral bioavailability of paclitaxel in wild-type mice from 8.5 to 40.2%. The plasma pharmacokinetics of paclitaxel in mdr1ab knockout mice was not altered by GF120918, whereas the pharmacokinetics of paclitaxel in wild-type mice receiving GF120918 became comparable with mdr1ab knockout mice. This result indicates that GF120918 at this dose-level selectively and completely blocks P-glycoprotein in the intestines and does not notably interfere in the elimination of paclitaxel by metabolism or other transporters. On the basis of this result, GF120918 has been selected for additional study in humans.

Phase I clinical and pharmacokinetic study of carzelesin (U-80244) given daily for five consecutive days.

Carzelesin (U-80244), one of the synthetic DNA minor groove binding cyclopropylpyrroloindole analogues, was selected for clinical development because of its high potency, promising antitumor activity in murine solid tumors and leukemia, and significant therapeutic efficacy against colon and rhabdomyosarcoma xenografts. In this Phase I study, carzelesin was given daily for 5 consecutive days to (a) determine the maximum tolerable dose (MTD) and the pattern of toxicity of this schedule; (b) define the pharmacokinetic profile of the parent, as was done for the intermediate compound U-76073 and the DNA-reactive agent U-76074; and (c) document any antitumor activity observed. Carzelesin was given as a 10-min infusion with a constant-rate infusion pump. Treatment was repeated every 4 weeks or when blood counts had recovered to normal values. The starting dose of 12 microgram/m2/day was escalated by 20-30% increments until the MTD (defined as the dose leading to grade 4 hematological or grade 3 nonhematological toxicity in at least two of six patients) was reached. Pharmacokinetic studies were planned on days 1 and 5 of the first cycle in at least two patients per dose level. Plasma levels of carzelesin, U-76073, and U-76074 were determined by high-performance liquid chromatography with UV detection and a detection limit of 0.5 ng/ml. Twenty-five patients were entered in the study, and 56 cycles were evaluable for hematological toxicity. Subsequent dose levels evaluated were 24, 30, 35, and 40 microgram/m2. Both neutropenia and thrombocytopenia were dose limiting and cumulative, with a high interpatient variability. Neutropenia occurred earlier (median time to neutrophil nadir and recovery, 15 and 29 days, respectively) than thrombocytopenia (median time to platelet nadir and recovery, 25 and >/=26 days, respectively); there were delays of treatment because of persisting thrombocytopenia in all patients treated at the MTD. At the MTD, the peak plasma concentrations of carzelesin were achieved at the end of the infusion and were higher than those found cytotoxic in vitro against tumor cell lines. Carzelesin was detectable up to a maximum of 1 h after the infusion. Smaller amounts of U-76073 were detectable for a maximum of 30 min only at the MTD, whereas U-76074 was never found. An 8-month partial remission was reported in one previously untreated patient with hepatocellular carcinoma at 40 microgram/m2. The MTD was fixed at 40 microgram/m2 daily; 35 and 30 microgram/m2 are the daily doses recommended for Phase II studies in good- and poor-risk patients. The daily regimen for 5 days seems to offer no advantage over the single intermittent schedule that has been selected for the Phase II program in Europe.