P-glycoprotein inhibition by the multidrug resistance-reversing agent MS-209 enhances bioavailability and antitumor efficacy of orally administered paclitaxel

The piperazine scaffold for novel drug discovery efforts: the evidence to date

INTRODUCTION

. Piperazine is a structural element present in drugs belonging to various chemical classes and used for numerous different therapeutic applications; it has been considered a privileged scaffold for drug design.

AREAS COVERED

The authors have searched examples of piperazine-containing compounds among drugs recently approved by the FDA, and in some research fields (nicotinic receptor modulators, compounds acting against cancer and bacterial multi-drug resistance), looking in particular to the design behind the insertion of this moiety.

EXPERT OPINION

Piperazine is widely used due to its peculiar characteristics, such as solubility, basicity, chemical reactivity, and conformational properties. This moiety has represented an important tool to modulate pharmacokinetic and pharmacodynamic properties of drugs.

Design and synthesis of mixed micellar system for enhanced anticancer efficacy of Paclitaxel through its co-delivery with Naringin

Emergence of multidrug resistance (MDR) has limited the success of chemotherapeutic agents. Reversal of drugs efflux systems through combination therapy has got wider attention for increasing anticancer drugs efficacy. This study aims at co-encapsulation of Paclitaxel with Naringin in mixed polymeric micelles for enhanced anticancer activity of the drug. Drug-loaded micelles were prepared using two different amphiphilic block co-polymers and were characterized for morphology, size, zeta potential, drug encapsulation, in vitro release and stability using atomic force microscope (AFM), zetasizer, UV spectrophotometer, and FT-IR. MTT assay and fluorescence microscopy were used for in vitro cytotoxicity and cellular uptake studies. Nano-size micelles with spherical morphology and negative charge encapsulated 76.52 ± 0.94% and 32.87 0.61% Paclitaxel and Naringin, respectively. The micelles were thermally stable and retained 87.05 ± 0.69% and 92.88 ± 2.17% Paclitaxel and Naringin upon one-month storage. Maximum drug release was achieved at fourth hour of the study for both the loaded drugs. Paclitaxel co-encapsulation with Naringin synergistically improved its intracellular uptake and 65% in vitro cytotoxicity against breast cancer cells was achieved at its lower dose of 15 µg/mL. Results suggest that co-encapsulation of Paclitaxel with Naringin in mixed micelles is an effective strategy for achieving its higher anticancer activity.

Curcumin-docetaxel co-loaded nanosuspension for enhanced anti-breast cancer activity

PURPOSE

A curcumin-docetaxel co-loaded nanosuspension with increased anti-breast cancer activity was developed. Curcumin is a potential anticancer agent with p-glycoprotein (p-gp) inhibiting activity may be co-administered with docetaxel as a nanosuspension to enhance its anticancer effect by increasing the oral bioavailability and decreasing drug efflux.

METHODS

Nanosuspensions of curcumin and docetaxel were prepared by precipitation-homozenisation technique and evaluated for particle size, polydispersity, zeta potential and drug release. The in vitro MTT assay was conducted using MCF-7 for anti-breast cancer activity. The in vivo biodistribution by radiolabeling and tumor inhibition study was conducted in mice.

RESULTS

Homogenous nanosuspensions of 80 ± 20 nm were obtained with increased solubility. The drugs as nanosuspensions showed higher cytotoxicity on MCF-7 cell line compared to their suspensions due to the increased in vitro cellular uptake. Due to this increased solubility, sensitization of tumor cells and inhibition of p-gp the in-vivo results showed greater tumor inhibition rate of up to 70% in MCF-7 treated mice. Histopathological results showed higher apoptotic activity and reduced level of angiogenesis.

CONCLUSIONS

The in vitro and in vivo study of the nanosuspensions has shown that Co-administration of Curcumin as a p-gp inhibitor with docetaxel may have the potential to increase the anti-breast cancer efficacy of both drugs.

Three- and four-class classification models for P-glycoprotein inhibitors using counter-propagation neural networks

P-glycoprotein (P-gp) is an ATP binding cassette (ABC) transporter that helps to protect several certain human organs from xenobiotic exposure. This efflux pump is also responsible for multi-drug resistance (MDR), an issue of the chemotherapy approach in the fight against cancer. Therefore, the discovery of P-gp inhibitors is considered one of the most popular strategies to reverse MDR in tumour cells and to improve therapeutic efficacy of commonly used cytotoxic drugs. Until now, several generations of P-gp inhibitors have been developed but they have largely failed in preclinical and clinical studies due to lack of selectivity, poor solubility and severe pharmacokinetic interactions. In this study, three models (SION, SIO, SIN) to classify specific 'true' P-gp inhibitors as well as three other models (CPBN, CPB1, CPN) to distinguish between P-gp inhibitors, CYP 3A inhibitors and co-inhibitors of these proteins with rather high accuracy values for the test set and the external set were generated based on counter-propagation neural networks (CPG-NN). Such three and four-class classification models helped provide more information about the bioactivities of compounds not only on one target (P-gp), but also on a combination of multiple targets (P-gp, CYP 3A).

Apical ABC transporters and cancer chemotherapeutic drug disposition

ATP-binding cassette (ABC) transporters are transmembrane efflux transporters that mediate cellular extrusion of a broad range of substrates ranging from amino acids, lipids, and ions to xenobiotics including many anticancer drugs. ABCB1 (P-GP) and ABCG2 (BCRP) are the most extensively studied apical ABC drug efflux transporters. They are highly expressed in apical membranes of many pharmacokinetically relevant tissues such as epithelial cells of the small intestine and endothelial cells of the blood capillaries in brain and testis, and in the placental maternal-fetal barrier. In these tissues, they have a protective function as they efflux their substrates back to the intestinal lumen or blood and thus restrict the intestinal uptake and tissue disposition of many compounds. This presents a major challenge for the use of many (anticancer) drugs, as most currently used anticancer drugs are substrates of these transporters. Herein, we review the latest findings on the role of apical ABC transporters in the disposition of anticancer drugs. We discuss that many new, rationally designed anticancer drugs are substrates of these transporters and that their oral availability and/or brain disposition are affected by this interaction. We also summarize studies that investigate the improvement of oral availability and brain disposition of many cytotoxic (e.g., taxanes) and rationally designed (e.g., tyrosine kinase inhibitor) anticancer drugs, using chemical inhibitors of these transporters. These findings provide a better understanding of the importance of apical ABC transporters in chemotherapy and may therefore advance translation of promising preclinical insights and approaches to clinical studies.

Reversal of ATP-binding cassette drug transporter activity to modulate chemoresistance: why has it failed to provide clinical benefit?

Enhanced drug extrusion from cells due to the overexpression of the ATP-binding cassette (ABC) drug transporters inhibits the cytotoxic effects of structurally diverse and mechanistically unrelated anticancer agents and is a major cause of multidrug resistance (MDR) of human malignancies. Multiple compounds can suppress the activity of these efflux transporters and sensitize resistant tumor cells, but despite promising preclinical and early clinical data, they have yet to find a role in oncologic practice. Based on the knowledge of the structure, function, and distribution of MDR-related ABC transporters and the results of their preclinical and clinical evaluation, we discuss probable reasons why these inhibitors have not improved the outcome of therapy for cancer patients. We also outline new MDR-reversing strategies that directly target ABC transporters or circumvent relevant signaling pathways.

Oral drug delivery systems using chemical conjugates or physical complexes

Oral delivery of therapeutics is extremely challenging. The digestive system is designed in a way that naturally allows the degradation of proteins or peptides into small molecules prior to absorption. For systemic absorption, the intact drug molecules must traverse the impending harsh gastrointestinal environment. Technologies, such as enteric coating, with oral dosage formulation strategies have successfully provided the protection of non-peptide based therapeutics against the harsh, acidic condition of the stomach. However, these technologies showed limited success on the protection of therapeutic proteins and peptides. Importantly, inherent permeability coefficient of the therapeutics is still a major problem that has remained unresolved for decades. Addressing this issue in the context, we summarize the strategies that are developed in enhancing the intestinal permeability of a drug molecule either by modifying the intestinal epithelium or by modifying the drug itself. These modifications have been pursued by using a group of molecules that can be conjugated to the drug molecule to alter the cell permeability of the drug or mixed with the drug molecule to alter the epithelial barrier function, in order to achieve the effective drug permeation. This article will address the current trends and future perspectives of the oral delivery strategies.

Chalcogenopyrylium dyes as differential modulators of organic anion transport by multidrug resistance protein 1 (MRP1), MRP2, and MRP4

Multidrug resistance proteins (MRPs) mediate the ATP-dependent efflux of structurally diverse compounds, including anticancer drugs and physiologic organic anions. Five classes of chalcogenopyrylium dyes (CGPs) were examined for their ability to modulate transport of [(3)H]estradiol glucuronide (E(2)17βG; a prototypical MRP substrate) into MRP-enriched inside-out membrane vesicles. Additionally, some CGPs were tested in intact transfected cells using a calcein efflux assay. Sixteen of 34 CGPs inhibited MRP1-mediated E(2)17βG uptake by >50% (IC50 values: 0.7-7.6 µM). Of 9 CGPs with IC50 values ≤2 µM, two belonged to class I, two to class III, and five to class V. When tested in the intact cells, only 4 of 16 CGPs (at 10 µM) inhibited MRP1-mediated calcein efflux by >50% (III-1, V-3, V-4, V-6), whereas a fifth (I-5) inhibited efflux by just 23%. These five CGPs also inhibited [(3)H]E(2)17βG uptake by MRP4. In contrast, their effects on MRP2 varied, with two (V-4, V-6) inhibiting E(2)17βG transport (IC(50) values: 2.0 and 9.2 µM) and two (V-3, III-1) stimulating transport (>2-fold), whereas CGP I-5 had no effect. Strikingly, although V-3 and V-4 had opposite effects on MRP2 activity, they are structurally identical except for their chalcogen atom (Se versus Te). This study is the first to identify class V CGPs, with their distinctive methine or trimethine linkage between two disubstituted pyrylium moieties, as a particularly potent class of MRP modulators, and to show that, within this core structure, differences in the electronegativity associated with a chalcogen atom can be the sole determinant of whether a compound will stimulate or inhibit MRP2.

Effect of Wuzhi tablet (Schisandra sphenanthera extract) on the pharmacokinetics of paclitaxel in rats

Wuzhi tablet (WZ, registration no. in China: Z20025766) is a preparation of an ethanol herb extract of Wuweizi (Schisandra sphenanthera) containing 7.5 mg Schisantherin A per tablet. It was reported recently that WZ could significantly increase the blood concentrations of tacrolimus, which might be due to the inhibitory effect of WZ and its ingredients on P-gp and/or CYP450 activity. Paclitaxel is a substrate of the efflux transporter P-gp, and is mainly metabolized by CYP450 enzymes in the liver. Therefore, the purpose of this study was to investigate whether and how WZ affects the pharmacokinetics of paclitaxel in rats. After pretreatment with WZ, there were significant increases in the AUC(0-24h) of oral paclitaxel (from 280.8 ± 97.3 to 543.5 ± 115.2 h ng/mL; p < 0.05) and C(max) (from 44.6 ± 16.4 to 86.8 ± 16.1 ng/mL; p < 0.05). The pharmacokinetic data for i.v. paclitaxel with WZ showed a relatively small (when compared against oral paclitaxel) but still significant increase in AUC(0-24h) (from 163.6 ± 22.1 to 212.7 ± 17.7 h ng/mL; p < 0.05) and a decrease in clearance (from 3.2 ± 0.6 to 2.2 ± 0.3 L/h/kg; p < 0.05). Thus, the presence of WZ improved the systemic exposure of paclitaxel in rats. The herb-drug interaction between WZ and paclitaxel should be taken into consideration in clinical use.

Enhancement of oral bioavailability of paclitaxel after oral administration of Schisandrol B in rats

Paclitaxel is a substrate of the efflux transporters such as P-glycoprotein, and is mainly metabolized by the liver. Schisandrol B (Sch B), one of the active components in Schisandra, has been reported to be able to inhibit the activity of P-gp and CYP3A. It might be possible that Sch B would alter the pharmacokinetic behavior of paclitaxel. Therefore, the purpose of this study was to investigate the effect of Sch B on the pharmacokinetics of paclitaxel administered orally and intravenously in rats. Paclitaxel were administered to rats orally (30 mg/kg) or intravenously (0.5 mg/kg) with or without the concomitant administration of Sch B (10 or 25 mg/kg). Oral pharmacokinetic parameters of paclitaxel were significantly altered when pretreated with Sch B. There were significant increases in AUC(0-24h) (from 297.7+/-110.3 to 838.9+/-302.1 h*ng/ml; p<0.05) and C(max) (from 51.7+/-20.1 to 136.4+/-35.5 ng/ml; p<0.05) in the presence of Sch B (25 mg/kg). The pharmacokinetic parameters for i.v. paclitaxel were not significantly affected by Sch B in contrast to that of oral administration. Since the presence of Sch B enhanced the systemic exposure of paclitaxel, their pharmacokinetic interaction should be taken into consideration. As the oral bioavailability of paclitaxel was increased about 3-fold in the presence of Sch B, the concomitant use of Sch B may provide a benefit in the oral delivery of paclitaxel.

Effect of maceligan on the systemic exposure of paclitaxel: in vitro and in vivo evaluation

This study investigated the effect of macelignan on the P-glycoprotein-mediated drug efflux as well as CYP3A4-mediated drug metabolism and subsequently its in vivo implication on the bioavailability of paclitaxel. The inhibition effect of macelignan on the CYP3A4-mediated metabolism was negligible over the concentration range of 0.01-100muM in rat liver microsome while approximately 33% inhibition was observed at 100muM in human liver microsome, implying that the interaction of macelignan with CYP3A4 might be insignificant at the physiologically achievable concentrations. In contrast, macelignan (20muM) increased the cellular accumulation of paclitaxel by approximately 1.7-fold in NCI/ADR-RES cells overexpressing P-gp, while it did not alter the cellular accumulation of paclitaxel in OVCAR-8 cells lacking P-gp. The effect of macelignan on the systemic exposure of paclitaxel was also examined in rats after the intravenous and oral administration of paclitaxel in the presence and the absence of macelignan. The concurrent use of macelignan significantly (p<0.05) enhanced the oral exposure of paclitaxel in rats while it did not affect the intravenous pharmacokinetics of paclitaxel, implying that macelignan might be more effective to improve the intestinal absorption rather than reducing hepatic elimination. In conclusion, macelignan appeared to be effective to improve the cellular accumulation as well as oral exposure of paclitaxel mainly via the inhibition of P-gp-mediated cellular efflux, suggesting that the concomitant use of macelignan may provide a therapeutic benefit in improving the anticancer efficacy of paclitaxel.

Interleukin-2 treatment effect on imatinib pharmacokinetic, P-gp and BCRP expression in mice

The aim of this study was to investigate the effect that recombinant interleukin-2 (rIL-2) (0.16 MUI/injection) had on the pharmacokinetics of imatinib (IM) in plasma. In this study, IM was given orally to mice at a dose of 150 mg/kg once a day for 11 days (from day 1 to 11) either alone or in combination with intraperitoneal injections of rIL-2 twice a day from day 8 to 11. Pharmacokinetic parameters were determined using WinNonLin software. Areas under the curve were compared using Bailer's method. The repeated administration of the rIL-2+IM combination was shown to have two pharmacokinetic advantages compared with repeated IM doses alone. In addition to the pharmacodynamic interest of this treatment, we found that the combined treatment significantly increased the IM Cmax (P<0.05) and significantly increased the IM trough concentration (C(24 h)) (P<0.01), which was always above the minimum therapeutic IM concentration (1 mumol/l) in plasma. Those pharmacokinetic modifications may be explained, in part, by a decrease in the P-glycoprotein expression in the three intestinal segments of the mice (duodenum, P<0.01; jejunum, P<0.05; and ileum, P<0.05) and a decrease in BCRP expression in the duodenum segment (P<0.05) due to rIL-2. In another experiment, we found a significant induction of intestinal P-glycoprotein expression in mice that had been given IM orally (150 mg/kg) twice a day for 11 days. It would be interesting to further investigate the IM disposition associated with rIL-2 treatment for clinical applications.

Pluronic block copolymers and Pluronic poly(acrylic acid) microgels in oral delivery of megestrol acetate

Several Pluronic-based formulations were studied in-vitro and in a rat model with respect to the release and bioavailability of megestrol acetate (MA) after oral administration. It was demonstrated that an aqueous, micellar formulation comprising a mixture of a hydrophobic (L61) and a hydrophilic (F127) Pluronic copolymer, significantly enhanced the bioavailability of MA administered orally at relatively low doses (1–7 mg kg−1). Pluronic-based microgels (spherical gel particles of sub-millimetre size) were introduced as MA vehicles. The microgels comprised a cross-linked network of poly(acrylic acid) onto which the Pluronic chains were covalently attached. Microgels of Pluronic L92 and poly(acrylic acid) fabricated into tablet dosage forms exhibited dramatically lowered MA initial burst release. The MA release was pH-dependent owing to the pH sensitivity of the microgel swelling, with the drug retained by the microgel at pH 1.8 and released slowly at pH 6.8. In the rat model, a significant increase in MA bioavailability was observed when the microgel-formulated MA was administered orally at a high dose of 10 mg kg−1, owing to the enhanced retention of the microgel. The study of the microgel passage through the gastrointestinal tract demonstrated the microgel retention characteristic of a very high molecular weight polymer and the absence of any systemic absorption of the polymer.

Mesothelin inhibits paclitaxel-induced apoptosis through the PI3K pathway

Mesothelin, a secreted protein, is overexpressed in some cancers, but its exact function remains unclear. The aim of the present study was to evaluate the possible function of mesothelin. Real-time PCR, RT (reverse transcription)-PCR, cytotoxicity assays, proliferative assays, apoptotic assays by Hoechst staining, detection of active caspases 3 and 7 by flow cytometric analysis, and immunoprecipitation and immunoblotting were performed. Cancer tissues in paclitaxel-resistant ovarian cancer patients expressed higher levels of mesothelin as assessed using real-time PCR than paclitaxel-sensitive ovarian cancer patients (the mean crossing point value change of mesothelin was 26.9+/-0.4 in the resistant group and 34.3+/-0.7 for the sensitive group; P<0.001). Mesothelin also protected cells from paclitaxel-induced apoptosis. The protein expression of Bcl-2 family members, such as Bcl-2 and Mcl-1, was significantly increased regardless of whether cells were treated with exogenous mesothelin or were mesothelin-transfectants. Furthermore, mesothelin-treated cells revealed rapid tyrosine phosphorylation of the p85 subunit of PI3K (phosphoinositide 3-kinase) and ERK (extracellular-signal-regulated kinase) 1/2 for enhancing MAPK (mitogen-activated protein kinase) activity. The anti-apoptotic ability was suppressed and the expression of Bcl-2 family in response to mesothelin was altered by inhibiting PI3K activity, but not by inhibiting MAPK activity. Thus mesothelin can inhibit paclitaxel-induced cell death mainly by involving PI3K signalling in the regulation of Bcl-2 family expression. Mesothelin is a potential target in reducing resistance to cytotoxic drugs.

Polymeric and Low Molecular Mass Efflux Pump Inhibitors for Oral Drug Delivery

Transmembrane located transporter proteins can be responsible for the low bioavailability of orally administered drugs. Drug delivery systems which can overcome this barrier caused by efflux pumps are therefore highly on demand. Within the current review, intestinal located efflux transporters, methods to identify efflux pump substrates and inhibitors as well as strategies to minimize efflux pump mediated transport of drugs are discussed. Methods include in silico screening, transport and accumulation studies and monitoring of the ATPase activity. An emphasis has been placed on efflux pump inhibitors including low molecular mass inhibitors such as cyclosporine, PSC833 or KR30031 and polymeric inhibitors such as myrj, thiomers and cremophor EL. Also formulation approaches to circumvent intestinal segments with high efflux pump expression are briefly addressed.

Inhibition of P-glycoprotein (ABCB1)- and multidrug resistance-associated protein 1 (ABCC1)-mediated transport by the orally administered inhibitor, CBT-1((R))

Cellular expression of ATP-binding cassette (ABC) transport proteins, such as P-glycoprotein (Pgp), multidrug resistance-associated protein (MRP1), or ABCG2, is known to confer a drug-resistant phenotype. Thus, the development of effective transporter inhibitors could be of value to cancer treatment. CBT-1 is a bisbenzylisoquinoline plant alkyloid currently in development as a Pgp inhibitor. We characterized its interactions with the three major ABC transporters associated with drug resistance - Pgp, MRP1 and ABCG2 - and compared it to other known inhibitors. CBT-1 completely inhibited rhodamine 123 transport from Pgp-overexpressing cells at a concentration of 1muM. Additionally, 1 microM completely reversed Pgp-mediated resistance to vinblastine, paclitaxel and depsipeptide in SW620 Ad20 cells. CBT-1 was found to compete [(125)I]-IAAP labeling of Pgp with an IC(50) of 0.14 microM, and low concentrations of CBT-1 (<1 microM) stimulated Pgp-mediated ATP hydrolysis. In MRP1-overexpressing cells, 10 microM CBT-1 was found to completely inhibit MRP1-mediated calcein transport. CBT-1 at 25 microM did not have a significant effect on ABCG2-mediated pheophorbide a transport. Serum levels of CBT-1 in samples obtained from eight patients receiving CBT-1 increased intracellular rhodamine 123 levels in CD56+ cells 2.1- to 5.7-fold in an ex vivo assay. CBT-1 is able to inhibit the ABC transporters Pgp and MRP1, making it an attractive candidate for clinical trials in cancers where Pgp and/or MRP1 might be overexpressed. Further clinical studies with CBT-1 are warranted.

Altered pharmacokinetics of paclitaxel by the concomitant use of morin in rats

The purpose of this study was to investigate the effect of morin on the pharmacokinetics of orally and intravenously administered paclitaxel in rats. Pharmacokinetic parameters of paclitaxel were determined in rats after an oral (30 mg kg(-1)) or intravenous (3 mg kg(-1)) administration of paclitaxel to rats in the presence and absence of morin (3.3 and 10 mg kg(-1)). Compared to the control given paclitaxel alone, pretreatment with morin 30 min prior to the oral administration of paclitaxel increased C(max) and AUC of paclitaxel by 70-90% and 30-70%, respectively, while there was no significant change in T(max) and terminal plasma half-life (T(1/2)) of paclitaxel. Consequently, absolute and relative bioavailability values of paclitaxel in the rats after the pretreatment with morin were significantly higher (p<0.05) than those from the control. In contrast, following an intravenous administration of paclitaxel (3.3 mg kg(-1)), the pharmacokinetic profiles of paclitaxel were not altered significantly in the presence of morin. Those results suggest that the enhanced oral exposure of paclitaxel should be mainly due to the inhibition effect of morin on the gastrointestinal extraction of paclitaxel during the intestinal absorption. Therefore, the concurrent use of morin or morin-containing dietary supplement may provide a therapeutic benefit in the oral delivery of paclitaxel.

Nanoemulsions as versatile formulations for paclitaxel delivery: peroral and dermal delivery studies in rats

Pathogenesis of psoriasis involves the keratinocytes in epidermis as well as the angiogenesis involving deeper skin layers. So, the drug delivery strategy should be customized to localize paclitaxel (PCL) inside both layers. In this investigation, in order to achieve penetration of PCL into deeper skin layers while minimizing the systemic escape, a nanoemulsion (NE) was formulated and evaluated its in vivo pharmacokinetic performance. Further, the same formulation was explored for peroral bioavailability enhancement of PCL. Upon dermal application, the drug was predominantly localized in deeper skin layers, with minimal systemic escape. When orally administered as NE, PCL was rapidly absorbed reaching a steady-state value of 3.5 microg/ml in 30 minutes, and steady-state levels persisted up to 18 hours. This has amounted to an absolute bioavailability of 70.62%. Inhibition of P-glycoprotein efflux by D-alpha-tocopheryl polyethyleneglycol 1,000 succinate and labrasol would have contributed to the enhanced peroral bioavailability of PCL. This investigation provides direct evidence on the localization of large molecular weight, lipophilic drug, PCL, in dermis. Further, the NE formulation has enhanced the peroral bioavailability significantly to more than 70%. The developed NE formulation was safe and effective for both peroral and dermal delivery of PCL.

Recombinant interleukin-2 pre-treatment increases anti-tumor response to paclitaxel by affecting lung P-glycoprotein expression on the Lewis lung carcinoma

The aim of the present study was to examine modifications of anti-tumor activity and toxicity of paclitaxel (PLX) when given p.o. after recombinant interleukin-2 (rIL-2) to Lewis lung carcinoma-bearing mice. PLX was given orally to mice at the dose of 15 mg/kg on day 8 and 30 mg/kg on day 15, either alone or after 16.5 microg of rIL-2 given i.p. twice a day either 1 or 3 days before. The anti-tumor activity was higher and PLX hematological toxicity not increased if orally administered PLX was given after a 3-day rIL-2 pre-treatment rather than if given alone. Lung metastasis was significantly lower and s.c. tumors were smaller in the PLX+rIL-2 group than in the PLX or rIL-2 or non-treated groups. In addition, a decrease in lung P-glycoprotein expression (investigated by Western blot analysis) was observed 1 h after the last administration of rIL-2 on day 7.

Enhanced oral paclitaxel absorption with vitamin E-TPGS: effect on solubility and permeability in vitro, in situ and in vivo

Solubility and permeability being important determinants of oral drug absorption, this study was aimed to investigate the effect of D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) on the solubility and intestinal permeability of paclitaxel in vitro, in situ and in vivo, in order to estimate the absorption enhancement ability of TPGS. Aqueous solubility of paclitaxel is significantly enhanced by TPGS, where a linear increase was demonstrated above a TPGS concentration of 0.1 mg/ml. Paclitaxel demonstrated asymmetric transport across rat ileum with significantly greater (26-fold) basolateral-to-apical (B-A) permeability than that in apical-to-basolateral (A-B) direction. Presence of P-glycoprotein (P-gp) inhibitor, verapamil (200 microM), diminished asymmetric transport of paclitaxel suggesting the role of P-gp-mediated efflux. TPGS showed a concentration-dependent increase in A-B permeability and decreased B-A permeability. The maximum efflux inhibition activity was found at a minimum TPGS concentration of 0.1 mg/ml, however, further increase in TPGS concentration resulted in decreased A-B permeability with no change in B-A permeability. Thus, the maximum paclitaxel permeability attained with 0.1 mg/ml TPGS was attributed to the interplay between TPGS concentration dependent P-gp inhibition activity and miceller formation. In situ permeability studies in rats also demonstrated the role of efflux in limiting permeability of paclitaxel and inhibitory efficiency of TPGS. The plasma concentration of [14C]paclitaxel following oral administration (25 mg/kg) was significantly increased by coadministration of TPGS at a dose of 50 mg/kg in rats. Bioavailability is enhanced about 4.2- and 6.3-fold when [14C]paclitaxel was administrated with verapamil (25 mg/kg) and TPGS, respectively, as compared to [14C]paclitaxel administered alone. The effect of verapamil on oral bioavailability of [14C]paclitaxel was limited relative to the TPGS, consistent with the in vitro solubility and permeability enhancement ability of TPGS. In conclusion, the current data suggests that the coadministration of TPGS may improve the bioavailability of BCS class II-IV drugs with low solubility and/or less permeable as a result of significant P-gp-mediated efflux.

Mechanistic basis of adverse drugreactions: the perils of inappropriate dose schedules

Adverse drug reactions (ADRs) have long been recognised as a significant cause of morbidity and mortality. They account for a substantial number of clinical consultations, hospital admissions and extended duration of in-patient stay as well as mortality. By far the most common ADRs are the concentration-dependent pharmacological reactions, the majority of which ought to be preventable. As a result of high concentrations of the parent drug and/or its metabolite(s), there is an augmentation of primary pharmacological activity and/or appearance of new and undesirable secondary pharmacological activity. Typically, these high concentrations result from administration of high doses in an attempt to maximise efficacy and/or modulation of the pharmacokinetics of a drug by either genetic or non-genetic factors. High plasma concentrations of parent drug may result from inherited impairment or drug-induced inhibition of its pharmacokinetic disposition. Conversely, inherited overcapacity or drug-induced induction of the metabolism of a drug may result in low concentrations of parent drug and frequently, rapid accumulation of its metabolites. Environmental, dietary and phytochemical factors may also influence the activity of drug metabolising enzymes. As with inherited polymorphisms of acetylation and cytochrome P450-based drug metabolising enzymes, polymorphisms of other conjugation reactions, such as glucuronidation, increasingly appear to be associated with drug toxicity. Diseases of organs involved in elimination of a drug also alter its pharmacokinetics, plasma concentration and, therefore, the profile of its concentration-dependent ADRs. Inherited mutations, concurrently administered drugs or presence of certain diseases may also alter the sensitivity of some pharmacological targets, accounting for a substantial number of ADRs and interactions. When there is enhanced pharmacodynamic sensitivity, plasma drug concentrations that are apparently within the normal 'non-toxic' range give rise to ADRs. Recent advances have also provided important insights into the wider scope of drug-drug interactions. Interactions that occur at P-glycoproteins, drug transporters and efflux pumps, at various transmembrane interfaces such as the gastrointestinal wall, renal tubules, hepatobiliary border and blood-brain barrier, are beginning to explain many non-metabolic interactions. These alter the systemic exposure to drugs and have so far, begun to explain unexpected neurotoxicity and hepatotoxicity. The function of these transporters is also genetically modulated. These advances, together with continued increased awareness and education of prescribers and pharmacists, offer great opportunities for substantially minimising concentration-related ADRs.

Mutant V599EB-Raf Regulates Growth and Vascular Development of Malignant Melanoma Tumors

Activating mutations of the B-RAF gene are observed in >60% of human melanomas. Approximately 90% of these mutations occur in the activation segment of the kinase domain as a single-base substitution that converts a valine to glutamic acid at codon 599 (V599E) in exon 15. This mutation causes activation of the kinase as well as downstream effectors of the mitogen-activated protein kinase-signaling cascade, leading to melanoma tumor development by an as yet unknown mechanism. In this study, we have identified the role of (V599E)B-Raf in melanoma tumor development by characterizing the mechanism by which this mutant protein promotes melanoma tumorigenesis. Small interfering RNA targeted against B-Raf or a Raf kinase inhibitor (BAY 43-9006) was used to reduce expression and/or activity of (V599E)B-Raf in melanoma tumors. This inhibition led to reduced activity of the mitogen-activated protein kinase-signaling cascade and inhibited tumor development in animals. Targeted reduction of mutant (V599E)B-Raf expression (activity) in melanoma cells before tumor formation inhibited tumorigenesis by reducing the growth potential of melanoma cells. In contrast, reduction of mutant (V599E)B-Raf activity in preexisting tumors prevented further vascular development mediated through decreased vascular endothelial growth factor secretion, subsequently increasing apoptosis in tumors. These effects in combination with reduced proliferative capacity halted growth, but did not shrink the size of preexisting melanoma tumors. Thus, these studies identify the mechanistic underpinnings by which mutant (V599E)B-RAF promotes melanoma development and show the effectiveness of targeting this protein to inhibit melanoma tumor growth.

A review of selected anti-tumour therapeutic agents and reasons for multidrug resistance occurrence

It is assumed that proteins from the ABC family (i.e., glycoprotein P (Pgp)) and a multidrug resistance associated protein (MRP) play a main role in the occurrence of multidrug resistance (MDR) in tumour cells. Other factors that influence the rise of MDR are mechanisms connected with change in the effectiveness of the glutathione cycle and with decrease in expression of topoisomerases I and II. The aim of this review is to characterize drugs applied in anti-tumour therapy and to describe the present state of knowledge concerning the mechanisms of MDR occurrence, as well as the pharmacological agents applied in reducing this phenomenon.

NONLINEAR ORAL PHARMACOKINETICS OF THE α-ANTAGONIST 4-AMINO-5-(4-FLUOROPHENYL)-6,7-DIMETHOXY-2-[4-(MORPHOLINOCARBONYL)-PERHYDRO-1,4-DIAZEPIN-1-YL]QUINOLINE IN HUMANS: USE OF PRECLINICAL DATA TO RATIONALIZE CLINICAL OBSERVATIONS

4-amino-5-(4-fluorophenyl)-6,7-dimethoxy-2-[4-(morpholinocarbonyl)-perhydro-1,4-diazepin-1-yl]quinoline (UK-294,315) is an antagonist of the human alpha1-adrenoceptor and exhibits nonlinear oral pharmacokinetics in humans. Superproportional increases in Cmax occur (220-fold, over a 1- to 50-mg dose range), area under the curve increases linearly, but time to maximum concentration decreases with dose, suggesting variation in rate but not extent of absorption. Oral absorption in humans is extensive, with only 14% of an orally administered (20 mg) radiolabeled dose excreted unchanged in the feces. In rats and dogs, UK-294,315 is partially eliminated as unchanged drug in feces (29 and 14% of an intravenous dose, respectively). Oral bioavailability is low in rats (11%) and high in dogs (71%), in keeping with systemic clearance. Fecal elimination of unchanged drug was 60% after oral administration to rats, indicating incomplete absorption in this species, whereas absorption in dogs is complete. UK-294,315 is a P-glycoprotein (P-gp) substrate (Km, 15 microM) exhibiting polarized flux in Caco-2 cell monolayers, saturable across a concentration range of 5 to 200 microM. Furthermore, the observations in vitro occurred at similar concentrations to those estimated in the gut lumen in clinical trials (dose range, 1-100 mg). It is considered that P-gp acts as a saturable absorption barrier to UK-294,315, slowing the rate of absorption at low doses, and is responsible for the observed nonlinearity in oral disposition in humans. Rat and dog pharmacokinetic studies offered limited insight into the process(es) driving nonlinear pharmacokinetics in humans. Our current understanding of the functional effects of P-gp in the human intestine, in combination with in vitro studies at clinically relevant concentrations, has helped rationalize the clinical data for UK-294,315.

Structure-activity relationship: analyses of p-glycoprotein substrates and inhibitors

OBJECTIVE

A large number of structurally and functionally diverse compounds act as substrates or modulators of p-glycoprotein (p-gp). Some of them possess multiple drug resistance (MDR)-reversing activity, but only a small number of them have entered clinical study. In order to uncover the factors which exert a significant impact on the interaction between substrates/modulators and p-gp, we have performed structure-activity relationship (SAR) analyses, including molecular modelling, two-dimensional (2D) and three-dimensional (3D) parameter-frame-setting analysis, quantitative structure activity relationship (QSAR) analysis among substrates/modulators, as well as clinically promising MDR-reversing agents.

METHODS

The physicochemical parameters C log P, CMR and all regression equations were derived by using C log P version 4.0 and the latest CQSAR software, respectively. Molecular modelling and all other parameter calculations were performed by using HyperChem version 5.0 program, after geometry optimization and energy minimization using the AM1 semiempirical method.

RESULTS

SAR analyses indicate that MDR reversal activity is correlated with the lipophilicity (C log P), molecular weight (log Mw), longest chain (Nlc) of the molecule and the energy of the highest occupied orbital (Ehomo). In addition, the presence of a basic tertiary nitrogen atom in the structure is also an important contributor to p-gp inhibitory activity. Some separation in space is achieved for different subsets of p-gp substrates and inhibitors using Nlc, C log P and Ehomo as three independent parameters in the 3D-parameter-frame setting.

CONCLUSION

A highly effective p-gp modulator candidate should possess a log P value of 2.92 or higher, 18-atom-long or longer molecular axis, and a high Ehomo value, as well as at least one tertiary basic nitrogen atom. The results obtained may be useful in explaining drug-p-gp interactions for different compounds, including drug interactions and the development of new MDR chemosensitizers.

Synthesis and biological evaluation of N-heterocyclic indolyl glyoxylamides as orally active anticancer agents

A series of N-heterocyclic indolyl glyoxylamides were synthesized and evaluated for in vitro and in vivo anticancer activities. They exhibited a broad spectrum of anticancer activity not only in murine leukemic cancer cells but also in human gastric, breast, and uterus cancer cells as well as their multidrug resistant sublines with a wide range of IC(50) values. They also induced apoptosis and caused DNA fragmentation in human gastric cancer cells. Among the compounds studied, 7 showed the most potent activity of growth inhibition (IC(50) = 17-1711 nM) in several human cancer cells. Given orally, compounds 7 and 13 dose-dependently prolonged the survival of animals inoculated with P388 leukemic cancer cells. N-Heterocyclic indolyl glyoxylamides may be useful as orally active chemotherapeutic agents against cancer and refractory cancerous diseases of multidrug resistance phenotype.