The oral route for the administration of cytotoxic drugs: strategies to increase the efficiency and consistency of drug delivery

Self Emulsifying Delivery System of Cissus quadrangularis: Evidence of Enhanced Efficacy and Promising Pharmacokinetic Profile in the Management of Osteoporosis

Treatment therapies used to manage osteoporosis are associated with severe side effects. So worldwide herbs are widely studied to develop alternative safe & effective treatments. Cissus quadrangularis (CQ) has a significant role in bone health and fracture healing. It is documented that its extracts increase osteoblastic differentiation & mineralization. Currently, Cissus quadrangularis is available in the form of tablets in the market for oral delivery. But these conventional forms are associated with poor bioavailability. There is a need for a novel drug delivery system with improving oral bioavailability. Therefore, a Cissus quadrangularis-loaded self-emulsifying drug delivery system (CQ-SEDDS) was developed which disperses rapidly in the gastrointestinal fluids, yielding nano-emulsions containing a solubilized drug. This solubilized form of the drug can be easily absorbed through lymphatic pathways and bypass the hepatic first-pass effect. The emulsification efficiency, zeta potential, globule size, in-vitro dissolution, ex-vivo, in-vivo and bone marker studies were performed to assess the absorption and permeation potential of CQ incorporated in SEDDS. CQ-SEDDS with excipients Tween 80, Cremophor RH40, Transcutol HP & α-Tocopherol acetate had shown about 76% enhancement in the bioavailability of active constituents of CQ. This study provided the pre-clinical data of CQ-SEDDS using osteoporotic rat model studies.

Determination of CYP450 Expression Levels in the Human Small Intestine by Mass Spectrometry-Based Targeted Proteomics

The human small intestine can be involved in the first-pass metabolism of drugs. Under this condition, members of the CYP450 superfamily are expected to contribute to drug presystemic biotransformation. The aim of this study was to quantify protein expression levels of 16 major CYP450 isoforms in tissue obtained from nine human organ donors in seven subsections of the small intestine, i.e., duodenum (one section, N = 7 tissue samples), jejunum (three subsections (proximal, mid and distal), N = 9 tissue samples) and ileum (three subsections, (proximal, mid and distal), N = 9 tissue samples), using liquid chromatography tandem mass spectrometry (LC-MS/MS) based targeted proteomics. CYP450 absolute protein expression levels were compared to mRNA levels and enzyme activities by using established probe drugs. Proteins corresponding to seven of sixteen potential CYP450 isoforms were detected and quantified in various sections of the small intestine: CYP2C9, CYP2C19, CYP2D6, CYP2J2, CYP3A4, CYP3A5 and CYP4F2. Wide inter-subject variability was observed, especially for CYP2D6. CYP2C9 (p = 0.004) and CYP2C19 (p = 0.005) expression levels decreased along the small intestine. From the duodenum to the ileum, CYP2J2 (p = 0.001) increased, and a trend was observed for CYP3A5 (p = 0.13). CYP3A4 expression was higher in the jejunum than in the ileum (p = 0.03), while CYP4F2 expression was lower in the duodenum compared to the jejunum and the ileum (p = 0.005). CYP450 protein levels were better correlated with specific isoform activities than with mRNA levels. This study provides new data on absolute CYP450 quantification in human small intestine that could improve physiologically based pharmacokinetic models. These data could better inform drug absorption profiles while considering the regional expression of CYP450 isoforms.

Probing the new strategy for the oral formulations of taxanes: changing the method with the situation

The first-generation taxanes (including paclitaxel and docetaxel) are widely used for the treatment of various cancers in clinical settings. In the past decade, a series of new-generation taxanes have been developed which are effective in the inhibition of tumor resistance. However, intravenous (i.v.) infusion is still the only route of administration, and may result in serious adverse reactions with respect to the utilization of Cremophor EL or Tween-80 as solvent. Besides, the dosing schedule is also limited. Therefore, oral administration of taxanes is urgently needed to avoid the adverse reactionss and increase dosing frequency. In this review, we first outlined the discovery and development of taxane-based anticancer agents. Furthermore, we summarized the research progress on the oral formulations of taxanes and proposed some thoughts on the future development of oral taxane formulations.

The Pharmacokinetics of Gefitinib in a Chinese Cancer Population Group: A Virtual Clinical Trials Population Study

Gefitinib, a selective inhibitor of the epidermal growth factor receptor (EGFR) tyrosine kinase, is used to treat non-small-cell lung cancer (NSCLC). Lung cancer rates are high in China and are expected to increase over the next decade. CYP 2D6 intermediate metaboliser (IM) phenotypes are more prevalent in the Chinese population compared to Caucasians; the increased risk of drug-drug interactions (DDI) with chemotherapy polypharmacy may lead to different clinical pharmacokinetics outcomes for Chinese patients. This study developed and validated a virtual Chinese cancer population for the pragmatic assessment of gefitinib DDI as a victim drug in Chinese and Caucasian cancer populations. When assessing the impact of 2D6 phenotypes on bupropion mediated CYP 2D6 DDI in Chinese cancer population, we found that AUC increased by at least 60% in extensive metabolizers (EM) and 30% in IM. As a result, fmCYP2D6 was reduced by 15% in IM in the presence of bupropion, translating into > 70% of EM subjects and > 48% of IM subjects with trough concentrations at steady state (Ctrough,ss) below the gefitinib target trough level. The PBPK model predicted that a 500 mg once daily dose in both EM and IM subjects successfully reduced the percent of subjects below the Ctrough,ss. Such changes in Ctrough,ss warrant further investigation and highlight the ability of pharmacokinetic modelling to investigate populations that may be difficult to recruit for traditional clinical studies.

Prevalence and significance of potential drug-drug interactions among cancer patients receiving chemotherapy

Background

Cancer patients often receive multiple drugs to maximize their therapeutic benefit, treat co-morbidities and counter the adverse effects of chemotherapy. Concomitant administration of multiple drugs increases the risk of drug interactions leading to compromised therapeutic efficacy or safety of therapy. The purpose of this study was to identify the prevalence, levels and predictors of potential drug-drug interactions (pDDIs) among cancer patients.

Methods

Six hundred and 78 patients receiving chemotherapy from two tertiary care hospitals were included in this cross-sectional study. Patient medication profiles were screened for pDDIs using the Micromedex® database. Logistic regression analysis was performed to identify the predictors of pDDIs.

Results

The overall prevalence of pDDIs was 78%, majority of patients had 1–2 pDDIs (39.2%). A total of 1843 pDDIs were detected. Major-pDDIs were most frequent (67.3%) whereas, a significant association of pDDIs was found between > 7 all prescribed drugs (p < 0.001) and ≥ 3 anti-cancer drugs (p < 0.001). Potential adverse outcomes of these interactions include reduced therapeutic effectiveness, QT interval prolongation, tendon rupture, bone marrow suppression and neurotoxicity.

Conclusions

Major finding of this study is the high prevalence of pDDIs signifying the need of strict patient monitoring for pDDIs among cancer patients. Patients at higher risk to pDDIs include those prescribed with > 7 any types of drugs or ≥ 3 anticancer drugs. Moreover, list of most frequently identified major and moderate interactions will aid health care professional in timely identification and prevention of pDDIs.

Fabrication, optimization, and in vitro evaluation of docetaxel-loaded nanostructured lipid carriers for improved anticancer activity

Lung cancer is the leading cause of cancer-related deaths in both men and women worldwide. It is the leading cancer killer in both men and women in every Ethnic Group. A major problem associated with chemotherapies against their lung cancer is the lack of selective toxicity, which results in a narrow therapeutic index thereby compromising clinical prognosis. To circumvent these challenges, the present investigation sought to develop a docetaxel-loaded nanostructured lipid carrier system (DTX-NLCS) for the treatment of lung cancer. A 3-factor/3-level Box-Behnken Design was applied to systematically optimize the DTX-NLCS parameters. The amount of drug, emulsifier concentration, and homogenization speed was selected as independent variables, while the particle size and % entrapment efficiency (%EE) were selected as dependent variables. The optimized batch parameters were 29.81 mg drug, 19.97% w/w emulsifier, and 13 200 (rpm) speed of homogenization with a mean particle size of 154.1 ± 3.13 nm and a mean %EE of 86.12 ± 3.48%. The in vitro lipolysis experiments revealed that the optimized DTX-NLCs were stabilized by 10% w/w PEG 4000 mono-stearate and exhibited an anti-lipolytic effect. Furthermore, the in vitro gastrointestinal stability studies (at pH-1.2, pH-4.5, pH-6.8, and pH-7.4) revealed that the optimized developed system could withstand various GI tract media. The in vitro dissolution studies depicted a pH-independent controlled-release consistent with the Weibull model. In vitro cytotoxicity studies using NCI-H460 cell lines further revealed that there was a reduction in IC₅₀ values in the DTX-NLCS treated cells as compared to those treated with the pure drug, indicating an improved efficiency for the developed system.

Design, Synthesis, and SAR of C-3 Benzoic Acid, C-17 Triterpenoid Derivatives. Identification of the HIV-1 Maturation Inhibitor 4-((1 R,3a S,5a R,5b R,7a R,11a S,11b R,13a R,13b R)-3a-((2-(1,1-Dioxidothiomorpholino)ethyl)amino)-5a,5b,8,8,11a-pentamethyl-1-(prop-1-en-2-yl)-2,3,3a,4,5,5a,5b,6,7,7a,8,11,11a,11b,12,13,13a,13b-octadecahydro-1 H-cyclopenta[ a]chrysen-9-yl)benzoic Acid (GSK3532795, BMS-955176)

GSK3532795, formerly known as BMS-955176 (1), is a potent, orally active, second-generation HIV-1 maturation inhibitor (MI) that advanced through phase IIb clinical trials. The careful design, selection, and evaluation of substituents appended to the C-3 and C-17 positions of the natural product betulinic acid (3) was critical in attaining a molecule with the desired virological and pharmacokinetic profile. Herein, we highlight the key insights made in the discovery program and detail the evolution of the structure-activity relationships (SARs) that led to the design of the specific C-17 amine moiety in 1. These modifications ultimately enabled the discovery of 1 as a second-generation MI that combines broad coverage of polymorphic viruses (EC₅₀ <15 nM toward a panel of common polymorphisms representative of 96.5% HIV-1 subtype B virus) with a favorable pharmacokinetic profile in preclinical species.

The Effects of Pharmaceutical Excipients on Gastrointestinal Tract Metabolic Enzymes and Transporters-an Update

Accumulating evidence from the last decade has shown that many pharmaceutical excipients are not pharmacologically inert but instead have effects on metabolic enzymes and/or drug transporters. Hence, the absorption, distribution, metabolism, and elimination (ADME) of active pharmaceutical ingredients (APIs) may be altered due to the modulation of their metabolism and transport by excipients. The impact of excipients is a potential concern for Biopharmaceutics Classification System (BCS)-based biowaivers, particularly as the BCS-based biowaivers have been extended to class 3 drugs in certain dosage forms. The presence of different excipients or varying amounts of excipients between formulations may result in bio-inequivalence. The excipient impact may lead to significant variations in clinical outcomes as well. The aim of this paper is to review the recent findings of excipient effects on gastrointestinal (GI) absorption, focusing on their interactions with the metabolic enzymes and transporters in the GI tract. A wide range of commonly used excipients such as binders, diluents, fillers, solvents, and surfactants are discussed here. We summarized the reported effects of those excipients on GI tract phase I and phase II enzymes, uptake and efflux transporters, and relevant clinical significance. This information can enhance our understanding of excipient influence on drug absorption and is useful in designing pharmacokinetic studies and evaluating the resultant data.

Oral delivery of paclitaxel nanocrystal (PNC) with a dual Pgp-CYP3A4 inhibitor: preparation, characterization and antitumor activity

Several molecular inheritances have severely restrained the peroral delivery of taxanes. The main objective of the present investigation was to develop a paclitaxel (PTX) formulation which can circumvent the hurdles of its extremely poor solubility and permeability, Pgp efflux and high pre-systemic metabolism. Positively charged PTX nanocrystals of 209 nm were prepared by sonoprecipitation with high pressure homogenization technique, wherein an arginine based surfactant was explored as a stabilizer. The BET surface area analysis revealed that the surface area of PNC was 8.53 m(2)/gm, reflecting significant rise in surface area with nanonization of PTX. The DSC and XRD pattern suggested that the PTX is in the form of the most stable dihydrate crystal. The PNC showed very rapid dissolution profile compared to plain PTX in both sinks and non-sink conditions. Clarithromycin (CLM) was evaluated as a better alternative to cyclosporin A in improving PTX permeability. The PNC-CLM showed remarkable enhancement of 453% in relative bioavailability along with maintaining the therapeutic concentration of PTX for 8h. Efficacy data in B16 F10 melanoma tumor bearing mice showed substantial reduction in tumor volume and improvement in percentage survival compared to the control group.

Novel oral anticancer drugs: a review of adverse drug reactions, interactions and patient adherence

Each aspect of oncological care is widely affected by the spread of oral anticancer agents, which raises several questions in terms of safe medication use and patient adherence. Over the past decade targeted therapies have appeared in clinical practice and revolutionized the pharmacological treatment of malignancies. Regular patient – doctor visits and proper patient education is crucial in order to comply with the therapy previously agreed upon with the oncologist, to increase patient adherence, to detect and to treat adverse effects in early stages. Since the information on the new medicines in Hungarian language is sparse it is the intention of the authors to give an overview of the basic knowledge, patient safety issues, adverse effects and interactions. Official drug information summaries and data on pharmacokinetics, interactions and adverse effects from the literature are reviewed as the basis for this overview. Orv. Hetil., 2012, 153, 66–78.

Synthesis and biological evaluation of 2-amino-1-thiazolyl imidazoles as orally active anticancer agents

Designed from a high throughput screened hit compound, novel 2-amino-1-thiazolyl imidazoles were synthesized and demonstrated cytotoxicity against human cancer cells. 1-(4-Phenylthiazol-2-yl)-4-(thiophen-2-yl)-1H-imidazol-2-amine (compound 2), a 2-amino-1-thiazolyl imidazole, inhibited tubulin polymerization, interacted with the colchicine-binding sites of tubulins, and caused cell cycle arrest at the G(2)/M phase in human gastric cancer cells. Disruption of the microtubule structure in cancer cells by compound 2 was also observed. Compound 2 concentration-dependently inhibited the proliferation of cancer cells in histocultured human gastric and colorectal tumors. Given orally, compound 2 prolonged the lifespans of leukemia mice intraperitoneally inoculated with the murine P388 leukemic cells. We report 2-amino-1-thiazolyl imidazoles as a novel class of orally active microtubule-destabilizing anticancer agents.

Modulation of Oral Drug Bioavailability: From Preclinical Mechanism to Therapeutic Application

Currently, more than one fourth of all anticancer drugs are developed as oral formulations, and it is expected that this number will increase substantially in the near future. To enable oral drug therapy, adequate oral bioavailability must be achieved. Factors that have proved to be important in limiting the oral bioavailability are the presence of ATP-binding cassette drug transporters (ABC transporters) and the cytochrome P450 enzymes. We discuss the tissues distribution and physiological function of the ABC transporters in the human body, their expression in tumors, currently known polymorphisms and drugs that are able to inhibit their function as transporter. Furthermore, the role of the ABC transporters and drug-metabolizing enzymes as mechanisms to modulate the pharmacokinetics of anticancer agents, will be reviewed. Finally, some clinical examples of oral drug modulation are discussed. Among these examples are the coadministration of paclitaxel with CsA, a CYP3A4 substrate with P-glycoprotein (P-gp) modulating activity, and topotecan combined with the BCRP/P-gp transport inhibitor elacridar. Both are good examples of improvement of oral drug bioavailability by temporary inhibition of drug transporters in the gut epithelium.

Polymeric micelles in oral chemotherapy

Oral administration of anticancer agents is preferred by patients for its convenience and potential for use in outpatient and palliative setting. In addition, oral administration facilitates a prolonged exposure to the cytotoxic agents. Enhancement of bioavailability of emerging cytotoxic agents is a pre-requisite for successful development of oral modes of cancer treatment. Over the last decade, our studies have focused specifically on the utilization of large (MW>10(5)) and non-degradable polymers in oral chemotherapy. A family of block-graft copolymers of the poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) Pluronic(R) polyethers and poly(acrylic acid) (PAA) bound by carbon-carbon bonds emerged, wherein both polymeric components are generally recognized as safe. Animal studies with Pluronic-PAA copolymers demonstrated that these molecules are excreted when administered orally and do not absorb into the systemic circulation. The Pluronic-PAA copolymers are surface-active and self-assemble, at physiological pH, into intra- and intermolecular micelles with hydrophobic cores of dehydrated PPO and multilayered coronas of hydrophilic PEO and partially ionized PAA segments. These micelles efficiently solubilize hydrophobic drugs such as paclitaxel and steroids and protect molecules such as camptothecins from the hydrolytic reactions. High surface activity of the Pluronic-PAA copolymers in water results in interactions with cell membranes and suppression of the membrane pumps such as P-glycoprotein. The ionizable carboxyls in the micellar corona facilitate mucoadhesion that enhances the residence time of the micelles and solubilized drugs in the gastrointestinal tract. Large payloads of the Pluronic-PAA micelles with weakly basic and water-soluble drugs such as doxorubicin and its analogs, mitomycin C, mitoxantrone, fluorouracil, and cyclophosphamide are achieved through electrostatic interactions with the micellar corona. Mechanical and physical properties of the Pluronic-PAA powders, blends, and micelles allow for formulation procedures where an active is simply dispersed into an aqueous Pluronic-PAA micellar formulation followed by optional lyophilization and processing into a ready dosage form. We review a number of in vivo and in vitro experiments demonstrating that that the oral administration of the cytotoxics formulated with the Pluronic-PAA copolymer micelles results in enhanced drug bioavailability.

The effect of P-glycoprotein and cytochrome P450 3a on the oral bioavailability of vinorelbine in mice

PURPOSE

This study was designed to determine the effects of P-glycoprotein (P-gp) and cytochrome P450 3a metabolism on the oral bioavailability of the vinca alkaloid Vinorelbine (Navelbine; VRL).

METHODS

Pharmacokinetics of VRL were determined in FVB wild-type and mdr1a/1b (-/-) mice after oral and intravenous administration of 10 mg/kg VRL with or without oral ritonavir (5 mg/kg) prior to VRL. Serial blood samples were drawn for a period of up to 48 hours using mice with a cannulated jugular vein. Feces was collected for a period of 96 hours. VRL was determined by ion-exchange HPLC in combination with fluorescence detection.

RESULTS

The oral bioavailability in wild-type was 16.0+/-1.4% (mean+/-SE) and was not significantly higher in mdr1a/1b (-/-) mice (17.9+/-0.7%). Both after intravenous and oral administration, the AUC was not significantly different between wild-type and mdr1a/1b(-/-) mice. When RTV was co-administered the AUC of intravenous VRL increased significantly by 30% (p = 0.012). Because RTV increased the AUC of oral VRL by 83% the oral bioavailability was increased to 22.5+/-2.3% (p = 0.016). The fecal recovery of unchanged VRL was about 34 and 6% of the dose in wild-type and mdr1a/1b(-/-) mice, respectively, and was not altered by RTV.

CONCLUSION

This study shows that P-gp has little effect on the disposition and oral bioavailability of VRL. A substantial fraction of an oral dose of VRL is absorbed from the gut of wild-type mice. Consequently, first-pass metabolism is the most important factor for explaining the modest oral bioavailability, but the results with RTV suggest that cyp3a plays only a modest role in metabolic breakdown in mice. Apparently, other routes of metabolic elimination are more important. These results suggest that also in patients the oral bioavailability may not gain substantially from the co-administration of a potent P-gp and/or Cyp3a inhibitor.

Development of supersaturatable self-emulsifying drug delivery system formulations for improving the oral absorption of poorly soluble drugs

The supersaturatable self-emulsifying drug delivery system (S-SEDDS) represents a new thermodynamically stable formulation approach wherein it is designed to contain a reduced amount of a surfactant and a water-soluble cellulosic polymer (or other polymers) to prevent precipitation of the drug by generating and maintaining a supersaturated state in vivo. The S-SEDDS formulations can result in enhanced oral absorption as compared with the related self-emulsifying drug delivery systems (SEDDS) formulation and the reduced surfactant levels may minimise gastrointestinal surfactant side effects.

Pharmacokinetic variability of anticancer agents

The translation of advances in cancer biology to drug discovery can be complicated by pharmacokinetic variation between individuals and within individuals, and this can result in unpredictable toxicity and variable antineoplastic effects. Previously unrecognized variables (such as genetic polymorphisms) are now known to have a significant impact on drug disposition. How can the pharmacokinetic variability of anticancer agents be reduced? This will require the understanding of correlations between pharmacokinetics and treatment outcomes, the identification of relevant patient parameters, mathematical modelling of individual and population pharmacokinetics, and the development of algorithms that will tailor doses to the individual patient.

Formulation strategies for absorption windows

Absorption windows in the proximal gut can limit the bioavailability of orally administered compounds and can be a major obstacle to the development of controlled release formulations for important drugs. Methods to increase the residence of drug formulations at or above the absorption window are discussed in this review. Two main approaches are presently being explored: (i) bioadhesive microspheres that have a slow intestinal transit; and (ii) the gastroretentive dosage system, which is based on multiparticulates or large single unit systems. A good understanding of gastrointestinal transit in humans and the effect of factors such as food can be helpful in the design of rational systems that will have clinical benefit.

Drug interactions in oncology

Drug interactions are an ongoing concern in treatment of cancer, especially when cytotoxic drugs are being used. However, the clinical relevance of these interactions is not always investigated. Drug interactions can be pharmaceutical, pharmacokinetic, or pharmacodynamic. They can also be wanted (eg, use of ciclosporin to enhance the oral bioavailability of paclitaxel); unwanted (eg, combination of the antiviral agent sorivudine and oral fluorouracil analogues can lead to fatal complications); between cytotoxic drugs, cytotoxic drugs and non-cytotoxic drugs; or with pharmaceutical vehicles. Potential interactions between anticancer drugs and over-the-counter or alternative medicines and herbs should not be underestimated. More attention should be given to the recognition of potential drug interactions in the preclinical and early clinical development phase of a new anticancer drug. Here, we provide a comprehensive overview of drug interactions, with selected examples.

Preclinical Pharmacokinetic Properties of the P-Glycoprotein Inhibitor GF120918A (HCl salt of GF120918, 9,10-Dihydro-5-methoxy-9-oxo-N-[4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]phenyl]-4-acridine-carboxamide) in the Mouse, Rat, Dog, and Monkey

GF120918A, the HCl salt of GF120918 (9,10-dihydro-5-methoxy-9-oxo-N-[4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl) ethyl]phenyl]-4-acridine-carboxamide), has been used both in vitro and in vivo as a tool inhibitor of P-glycoprotein (Pgp) to investigate the role of transporters in the disposition of various test molecules. However, to date, a detailed description of the preclinical pharmacokinetic properties of GF120918A has not been published. This investigation was performed to evaluate in vitro and in vivo pharmacokinetic properties of GF120918A in the mouse, rat, dog, and monkey and to evaluate the in vivo efficacy of GF120918A in modulating absorption and systemic exposure in the monkey. GF120918A demonstrated reasonable absorption and systemic exposure in each of the species studied, however, in rodents, administration of 300 mg/kg afforded a substantially less than linear increase in systemic exposure compared with 30 mg/kg. In accordance with its intestinal and hepatic exposure and potency against P-glycoprotein, GF120918A demonstrated marked modulation of erythromycin systemic exposure in the monkey, with no effect on propranolol, a negative control molecule. In vitro, GF120918A demonstrated high plasma protein binding across species, although a definitive protein binding evaluation was precluded by poor recovery, particularly in buffer and in mouse, rat, and dog plasma. GF120918A did not demonstrate potent inhibition of several human cytochrome P450 enzymes evaluated in vitro, with IC(50) values well above concentrations anticipated to be achieved in vivo. Together, these data confirm the utility of GF120918A as a tool P-glycoprotein inhibitor in preclinical species and offer additional guidance on preclinical dose regimens likely to produce P-glycoprotein-mediated effects.

Effects of Food on the Clinical Pharmacokinetics of Anticancer Agents

Pharmacokinetic interactions between food and orally administered drugs involve changes mainly in the absorption and metabolism of a drug, and may have clinical implications. Such interactions, in particular, may be of major clinical significance for cancer chemotherapy since the majority of anticancer agents are toxic, have a low therapeutic index and are administered long term, most often in combination with other cytotoxic agents. The purpose of this review is to compare the pharmacokinetic profiles of various anticancer drugs, including chemopreventive agents that have been examined previously in fasted and fed conditions, and to discuss the underlying basis/mechanisms of food effect in light of a drug's physicochemical and pharmacokinetic properties. Clinical pharmacokinetic parameters such as maximum concentration, area under the concentration-time curve, time to maximum concentration and half-life for each drug are compared in fasted and fed states, and specific dietary recommendations are summarised accordingly. In addition, the effects of food on the metabolite kinetics and pharmacodynamic responses, and the potential role of food effect in the modulation of oral biovariability and multidrug resistance have been extensively discussed. Overall, this comprehensive pharmacokinetic analysis indicates that a broad spectrum of food effects is seen among anticancer agents because of diverse factors regulating each drug's oral bioavailability and its interactions with food. The consideration of such effects is important, as it could lead to more rational pharmacological monitoring and possibly improve the oral chemotherapy of cancer in children, adults and the elderly.

Development of a supersaturable SEDDS (S‐SEDDS) formulation of paclitaxel with improved oral bioavailability

A new, supersaturable self-emulsifying drug delivery system (S-SEDDS) of paclitaxel was developed employing hydroxypropyl methylcellulose (HPMC) as a precipitation inhibitor with a conventional SEDDS formulation. In vitro dilution of the S-SEDDS formulation results in formation of a microemulsion, followed by slow crystallization of paclitaxel on standing. This result indicates that the system is supersaturated with respect to crystalline paclitaxel, and the supersaturated state is prolonged by HPMC in the formulation. In the absence of HPMC the SEDDS formulation undergoes rapid precipitation, yielding a low paclitaxel solution concentration. A pharmacokinetic study was conducted in male Sprague-Dawley rats to assess exposure after an oral paclitaxel dose of 10 mg/kg in the SEDDS formulations with (S-SEDDS) and without HPMC. The paclitaxel S-SEDDS formulation shows approximately 10-fold higher maximum concentration (C(max)) and five-fold higher oral bioavailability (F approximately 9.5%) compared with that of the orally dosed Taxol formulation (F approximately 2.0%) and the SEDDS formulation without HPMC (F approximately 1%). Coadministration of cyclosporin A (CsA), an inhibitor of P-glycoprotein and CYP 3A4 enzyme, at a dose of 5 mg/kg with the S-SEDDS formulation further increased the oral bioavailability (F approximately 22.6%). This assessment demonstrates that the systemic exposure of paclitaxel following oral administration can be substantially improved via the S-SEDDS approach.

Oral delivery of taxanes

Oral treatment with cytotoxic agents is to be preferred as this administration route is convenient to patients, reduces administration costs and facilitates the use of more chronic treatment regimens. For the taxanes paclitaxel and docetaxel, however, low oral bioavailability has limited development of treatment by the oral route. Preclinical studies with mdr1a P-glycoprotein knock-out mice, which lack functional P-glycoprotein activity in the gut, have shown significant bioavailability of orally administered paclitaxel. Additional studies in wild-type mice revealed good bioavailability after oral administration when paclitaxel was combined with P-glycoprotein blockers such as cyclosporin A or the structurally related compound SDZ PSC 833. Based on the extensive preclinical research, the feasibility of oral administration of paclitaxel and docetaxel in cancer patients was recently demonstrated in our Institute. Co-administration of cyclosporin A strongly enhanced the oral bioavailability of both paclitaxel and docetaxel. For docetaxel in combination with cyclosporin A an oral bioavailability of 90% was achieved with an interpatient variability similar to that after intravenous drug administration; for paclitaxel the oral bioavailability is estimated at approximately 50%. The safety of the oral route for both taxanes is good. A phase II study of weekly oral docetaxel in combination with cyclosporin A is currently ongoing.