Differential activity of Cremophor EL and paclitaxel in patients' tumor cells and human carcinoma cell lines in vitro

Measurement of ex vivo resistance to proteasome inhibitors, IMiDs, and daratumumab during multiple myeloma progression

The oncogenic drivers and progression factors in multiple myeloma (MM) are heterogeneous and difficult to target therapeutically. Many different MM drugs have emerged, however, that attack various phenotypic aspects of malignant plasma cells. These drugs are administered in numerous, seemingly interchangeable combinations. Although the availability of many treatment options is useful, no clinical test capable of optimizing and sequencing the treatment regimens for an individual patient is currently available. To overcome this problem, we developed a functional ex vivo approach to measure patients' inherent and acquired drug resistance. This method, which we termed myeloma drug sensitivity testing (My-DST), uses unselected bone marrow mononuclear cells with a panel of drugs in clinical use, followed by flow cytometry to measure myeloma-specific cytotoxicity. We found that using whole bone marrow cultures helped preserve primary MM cell viability. My-DST was used to profile 55 primary samples at diagnosis or at relapse. Sensitivity or resistance to each drug was determined from the change in MM viability relative to untreated control samples. My-DST identified progressive loss of sensitivity to immunomodulatory drugs, proteasome inhibitors, and daratumumab through the disease course, mirroring the clinical development of resistance. Prospectively, patients' ex vivo drug sensitivity to the drugs subsequently received was sensitive and specific for clinical response. In addition, treatment with <2 drugs identified as sensitive by My-DST led to inferior depth and duration of clinical response. In summary, ex vivo drug sensitivity is prognostically impactful and, with further validation, may facilitate more personalized and effective therapeutic regimens.

Paclitaxel-eluting silicone airway stent for preventing granulation tissue growth and lung cancer relapse in central airway pathologies

BACKGROUND

Airway stents are used to treat obstructive central airway pathologies including palliation of lung cancer, but face challenges with granulation tissue growth. Paclitaxel is a chemotherapy drug that also suppresses growth of granulation tissue. Yet, side effects arise from administration with toxic solubilizers. By incorporating paclitaxel in silicone stents, delivery of paclitaxel can be localized, and side effects minimized.

METHODS

Paclitaxel was incorporated into Liquid Silicone Rubber (LSR) containing polydimethylsiloxane, either as a powder or solution, prior to curing. Drug release study was compared in vitro at 37°C over 10 days. Drug release was quantified using HPLC, and bronchial cell lines were grown on LSR to investigate drug cytotoxicity, and expression of inflammatory markers, specifically interleukin-6 and interleukin-8.

RESULTS

Release rate of paclitaxel incorporated into silicone rubber was consistent with the Korsmeyer and Weibull models (R² > 0.96). Paclitaxel exposure reduced IL-8 levels in cancer cell lines, whilst no cytotoxic effect was observed in all cell lines at treatment concentration levels (≤ 0.1% (w/v) paclitaxel in silicone).

CONCLUSIONS

Incorporating paclitaxel into a silicone matrix for future use in a tracheobronchial stent was investigated. Drug release from silicone was observed and is a promising avenue for future treatments of central airway pathologies.

Enhanced anti-tumor efficacy and safety with metronomic intraperitoneal chemotherapy for metastatic ovarian cancer using biodegradable nanotextile implants

The objective of this study was to evaluate intraperitoneal (IP) metronomic chemotherapy using sustained release paclitaxel (PTX) delivery from electrospun biodegradable polymeric yarns woven into suturable nanotextiles. Following confirmation of in vitro PTX efficacy in ID8-VEGF epithelial ovarian cancer cells, in vivo studies were performed upon surgical peritoneal implantation of nanotextile implants in orthotopic, syngeneic ID8-VEGF tumor-bearing C57BL/6 mice. In comparison to the clinical PTX-solution, there was a significant enhancement of anti-tumor efficacy and safety with PTX-nanotextiles. After 35-days, the peritoneum of tumor-bearing mice with PTX-nanotextiles was completely devoid of tumor nodules and ascitic fluid. Additionally, VEGF levels measured in peritoneal lavage fluid were 300-fold lower compared to PTX-solution and 600-fold lower as compared to untreated tumor-bearing animals. PTX-solution treated group also developed severe metastatic lesions and progressive ascitic fluid buildup. More importantly, no signs of systemic/ organ toxicity were observed in PTX-nanotextile implanted mice, unlike the systemic toxic effects induced by PTX-solution. Collectively, our results show the therapeutic and safety advantages offered by combining clinically translatable metronomic low-dose chemotherapy and IP pharmacokinetics using biodegradable nanotextile implants in addressing the challenges of late-stage ovarian cancer.

Lx2-32c-loaded polymeric micelles with small size for intravenous drug delivery and their inhibitory effect on tumor growth and metastasis in clinically associated 4T1 murine breast cancer

Lx2-32c is a novel taxane derivative with a strong antitumor activity. In this study, we developed Lx2-32c–loaded polymeric micelles (Lx2-32c-PMs) with small size and investigated their antitumor efficacy against tumor growth and metastasis on 4T1 murine breast cancer cell line with Cremophor EL–based Lx2-32c solution as the control. In this study, copolymer monomethoxy polyethylene glycol₂₀₀₀–polylactide₁₃₀₀ was used to prepare Lx2-32c-PMs by film hydration method, and their physicochemical properties were characterized as well, according to morphology, particle size, zeta potential, in vitro drug release, and reconstitution stability. Under confocal laser scanning microscopy, it was observed that Lx2-32c-PMs could be effectively taken up by 4T1 cells in a time-dependent manner. Cell Counting Kit-8 assay showed that the IC₅₀ of Lx2-32c-PMs was 0.3827 nM. Meanwhile, Lx2-32c-PMs had better ability to promote apoptosis and induce G₂/M cycle block and polyploidy formation, compared with Lx2-32c solution. More importantly, in vivo animal studies showed that compared to Lx2-32c solution, Lx2-32c-PMs possessed better ability not only to effectively inhibit the tumor growth, but also to significantly suppress spontaneous and postoperative metastasis to distant organs in 4T1 orthotopic tumor-bearing mice. Consequently, Lx2-32c-PMs have significantly prolonged the survival lifetime of tumor-bearing mice. Thus, our study reveals that Lx2-32c-PMs had favorable antitumor activity and exhibited a good prospect for application in the field of antitumor therapy.

Review : Cremophor: Pharmacological activity of an "inert" solubiliser

Objective. To provide an overview of the known pharmacological activity of the solvent for pacli taxel, Cremophor, and the implications for therapy with paclitaxel.

Data Sources. Following an outline of the chemistry of Cremophor and its potential to cause hypersensitivity, we present a summary of our own results from studies on the effect of Cremophor as an MDR modulator.

Data Extraction. The pharmacokinetic inter actions of paclitaxel and Cremophor are discussed, with reference to our own preclinical and clinical studies of Cremophor, and literature reports of altered drug disposition following combination therapy with paclitaxel are examined.

Data Synthesis. Cremophor is not an inert solubiliser. Cremophor may contribute to drug interactions by altering drug disposition, and it has the ability to modulate multidrug resistance. As a consequence of the presence of Cremophor in the paclitaxel formulation, the use of paclitaxel should be considered as the administration of two agents.

Stabilization of Double Stranded Homologous Poly(dA)·Poly(dT) by Taxol

Abstract The nucleic acid activity of taxol and paclitaxel was investigated with synthetic and natural oligo- and polynucleotides. The polynucleotides poly(dA)·poly(dT), poly(dG)·poly(dC), poly [d(A-T)]·poly[d(A-T)], poly[d(G-C)]·poly[d(G-C)] and calf thymus DNA were used. The oligonucleotides are 24-mers with d(purine)(24)·d(pyrimidine)(24) strands, as well as d[(purine)(x)-(pyrimidine)(x)]·d[(purine)(x)-(pyrimidine)(x)] sequences. The study was performed with spectroscopic and calorimetric methods in dilute and condensed DNA-solutions. In a recent study, taxol and paclitaxel showed molecular recognition of AT nucleotides with a high affinity to homologous (dA)·(dT) sequences; no interaction with GC nucleotides could be observed. An astonishing stabilization of the DNA duplex up to ΔT(m) = 25°C was measured by thermal denaturation with poly(dA)·poly(dT)/paclitaxel complexes. Circular dichroism signals of DNA (24-mer) containing homologous (dA)·(dT) tracts increased with increasing amount of the drug; for the other oligo- and polynucleotides no change in the spectra could be found. Contrary to this findings, circular dichroism (CD) spectra of poly(dA)·poly(dT)/paclitaxel complexes displayed reduced intensities of the signals at increasing drug concentrations. These findings in dilute solutions were complemented by differential scanning calorimetric investigations in condensed states (only calf thymus DNA tested). Increasing enthalpies by increasing amount of the drug point to a stabilization. Simple phosphate backbone interaction in the narrow groove of (dA)·(dT) tracts could be a sufficient explanation for all the results. Hydrophilic side groups of the drug interact with the phosphate and clip the strands together, while the hydrophobic parts of the molecule may disturb the polynucleobase formation.

Water-Soluble Derivatives of Octanuclear Iron-Oxo-Pyrazolato Complexes; An Experimental and Computational Study

Two water-soluble iron-pyrazolato complexes, [Fe8], have been prepared by the introduction of twelve hydroxyalkyl groups to the periphery of the approximately spherical octanuclear molecule and they are contrasted with their two organosoluble chloroalkyl analogues. All four new complexes, 1 - 4, have been characterized in solution by 1H-NMR and electrospray ionization mass spectroscopy. The one-electron reduction product of the water-soluble 3, [Fe8]-, has been structurally characterized by single crystal diffraction methods. In aqueous media, the four terminal Fe-Cl bonds of [Fe8] are partially hydrolysed and the resulting chloro/aqua/hydroxo species form supramolecular nanoscale aggregates, as determined by dynamic light scattering and electron microscopy. Preliminary computational studies by density functional theory methods have been employed in order to model the H-bonding interactions controlling the competing solvation and aggregation processes.

Nanoparticle albumin-bound paclitaxel: a novel Cremphor-EL®-free formulation of paclitaxel

Standard formulation paclitaxel requires the use of solvents, such as Cremphor-EL®, which contribute to some of the toxicities commonly associated with paclitaxel-based therapy. Nanoparticle albumin-bound paclitaxel (nab™-paclitaxel) is a novel solvent-free formulation of paclitaxel. The formulation is prepared by high-pressure homogenization of paclitaxel in the presence of serum albumin into a nanoparticle colloidal suspension. The human albumin-stabilized paclitaxel particles have an average size of 130 nm. Nab-paclitaxel has several practical advantages over Cremphor-EL-paclitaxel, including a shorter infusion time (30 min) and no need for premedications for hypersensitivity reactions. The nab-paclitaxel formulation eliminates the impact of Cremphor-EL on paclitaxel pharmacokinetics and utilizes the endogenous albumin transport mechanisms to concentrate nab-paclitaxel within the tumor. A recent Phase III trial compared nab- and Cremphor-EL-paclitaxel in patients with metastatic breast cancer. Patients treated with nab-paclitaxel experienced a higher response, longer time to tumor progression and, in patients receiving second-line or greater therapy, a longer median survival. Patients treated with nab-paclitaxel had a significantly lower rate of severe neutropenia and a higher rate of sensory neuropathy. The preclinical and clinical data indicate that the nab-paclitaxel formulation has significant advantages over Cremphor-EL-paclitaxel.

Oxidative stress induced by Cremophor EL is not accompanied by changes in NF-kappaB activation or iNOS expression

The effects of polyoxyethylenglycerol triricinoleate 35 (Cremophor EL, CrEL) on markers of oxidative stress, nuclear factor kappa B (NF-kappaB) activation and inducible nitric oxide synthase (iNOS) expression were studied in the liver of male Wistar rats. Animals were randomly divided into three groups. Group Cr1 received, i.p., CrEL at 0.046ml/kg daily for 7 days, group Cr2 received CrEL at 0.33ml/kg and the controls were injected with CrEL vehicle (saline solution with 25% ethanol). Both alanine transaminase (ALT) and aspartate transaminase (AST) serum activities were significantly increased in the Cr2 group (+16% and +25%, respectively). AST activity was also higher in the Cr1 group when compared to control animals (+20%). The cytosolic concentration of thiobarbituric acid reactive substances (TBARS) increased in both groups of rats receiving CrEL (Cr1: +24%; Cr2: +33%). Reduced glutathione (GSH) concentration was not significantly modified at any of the CrEL doses, but both the hepatic concentration of oxidised glutathione (GSSG) (Cr1: +37%; Cr2: +84%) and the GSH/GSSG ratio (Cr1: -21%; Cr2: -45%) were significantly modified. CrEL induced no significant NF-kappaB activation, changes in p50 and p65 NF-kappaB subunits or induction of iNOS protein. Data obtained indicate that although high doses of CrEL cause oxidative stress, this is not enough to induce changes in NF-kappaB activation or iNOS expression.

Improvement of paclitaxel therapeutic index by derivatization and association to a cholesterol-rich microemulsion: in vitro and in vivo studies

A cholesterol-rich microemulsion or nanoparticle termed LDE concentrates in cancer tissues after injection into the bloodstream. Here the cytotoxicity, pharmacokinetics, toxicity to animals and therapeutic action of a paclitaxel lipophilic derivative associated to LDE is compared with those of the commercial paclitaxel. Results show that LDE-paclitaxel oleate is stable. The cytostatic activity of the drug in the complex is diminished compared with the commercial paclitaxel due to the cytotoxicity of the vehicle Cremophor EL used in the commercial formulation. Competition experiments in neoplastic cultured cells show that paclitaxel oleate and LDE are internalized together by the LDL receptor pathway. LDE-paclitaxel oleate arrests the G(2)/M phase of cell cycle, similarly to commercial paclitaxel. Tolerability to mice is remarkable, such that the lethal dose (LD(50)) was ninefold greater than that of the commercial formulation (LD(50) = 326 microM and 37 microM, respectively). LDE concentrates paclitaxel oleate in the tumor roughly fourfold relative to the normal adjacent tissues. At equimolar doses, the association of paclitaxel oleate with LDE results in remarkable changes in the drug pharmacokinetic parameters when compared to commercial paclitaxel (t(1/2)=218 min and 184 min, AUC=1,334 microg h/ml and 707 microg h/ml and CL=0.125 ml/min and 0.236 ml/min, respectively). Finally, the therapeutic efficacy of the complex is pronouncedly greater than that of the commercial paclitaxel, as indicated by the reduction in tumor growth, increase in survival rates and % cure of treated mice. In conclusion, LDE-paclitaxel oleate is a stable complex and compared with paclitaxel toxicity is considerably reduced and activity is enhanced, which may lead to improved therapeutic index in clinical use.

Cytotoxic activity of a new paclitaxel formulation, Pacliex, in vitro and in vivo

BACKGROUND

The paclitaxel formulation, Taxol (Bristol-Myers Squibb), is one of the most effective anticancer agents used today. However; it is associated with serious side effects believed to be caused by the Cremophor EL used for its formulation.

AIM

To evaluate the cytotoxic activity of a new paclitaxel formulation, Pacliex (developed by Oasmia Pharmaceutical, Uppsala, Sweden), a mixed micelles preparation in which an amphiphilic synthetic derivative of retinoic acid replaced Cremophor EL/ethanol vehicle.

METHOD

In this study, three model systems were used to evaluate the cytotoxic activity of Pacliex and other paclitaxel preparations. The cytotoxic activities of Pacliex, Taxol and paclitaxel in ethanol were investigated against a panel of ten human tumor cell lines using the fluorometric microculture cytotoxicity assay (FMCA). Low- and high- proliferating in vitro hollow fiber model of two cell lines, the leukemia CCRF-CEM and the myeloma RPMI 8226/S cell lines, were used to assess the cytotoxic activity of the three formulations. The in vivo hollow fiber model of the two cell lines was used for assessment of Pacliex and Taxol activity. The [3-4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assay was utilized to analyze the in vitro and in vivo hollow fiber data.

RESULT

Pacliex was somewhat more effective than Taxol in the more sensitive cell lines. The activity of Taxol was more pronounced in the resistant cell lines due to an additive effect of the vehicle used. The three formulations showed similar activity in both the low- and high-proliferating in vitro hollow fiber cultures. The in vivo hollow fiber cytotoxic activity of Pacliex was similar to that of Taxol. Putting all the results together, it was found that all the three formulations had similar in vitro and in vivo activity.

CONCLUSION

The three in vitro and in vivo models confirmed the similarity of the cytotoxic activities of Pacliex and Taxol. Considering the above, Pacliex could be an interesting alternative Cremophor EL-free formulation of paclitaxel.

Pharmacological effects of formulation vehicles : implications for cancer chemotherapy

The non-ionic surfactants Cremophor EL (CrEL; polyoxyethyleneglycerol triricinoleate 35) and polysorbate 80 (Tween) 80; polyoxyethylene-sorbitan-20-monooleate) are widely used as drug formulation vehicles, including for the taxane anticancer agents paclitaxel and docetaxel. A wealth of recent experimental data has indicated that both solubilisers are biologically and pharmacologically active compounds, and their use as drug formulation vehicles has been implicated in clinically important adverse effects, including acute hypersensitivity reactions and peripheral neuropathy.CrEL and Tween 80 have also been demonstrated to influence the disposition of solubilised drugs that are administered intravenously. The overall resulting effect is a highly increased systemic drug exposure and a simultaneously decreased clearance, leading to alteration in the pharmacodynamic characteristics of the solubilised drug. Kinetic experiments revealed that this effect is primarily caused by reduced cellular uptake of the drug from large spherical micellar-like structures with a highly hydrophobic interior, which act as the principal carrier of circulating drug. Within the central blood compartment, this results in a profound alteration of drug accumulation in erythrocytes, thereby reducing the free drug fraction available for cellular partitioning and influencing drug distribution as well as elimination routes. The existence of CrEL and Tween 80 in blood as large polar micelles has also raised additional complexities in the case of combination chemotherapy regimens with taxanes, such that the disposition of several coadministered drugs, including anthracyclines and epipodophyllotoxins, is significantly altered. In contrast to the enhancing effects of Tween 80, addition of CrEL to the formulation of oral drug preparations seems to result in significantly diminished drug uptake and reduced circulating concentrations. The drawbacks presented by the presence of CrEL or Tween 80 in drug formulations have instigated extensive research to develop alternative delivery forms. Currently, several strategies are in progress to develop Tween 80- and CrEL-free formulations of docetaxel and paclitaxel, which are based on pharmaceutical (e.g. albumin nanoparticles, emulsions and liposomes), chemical (e.g. polyglutamates, analogues and prodrugs), or biological (e.g. oral drug administration) strategies. These continued investigations should eventually lead to more rational and selective chemotherapeutic treatment.

Utility of technetium-99m methoxyisobutyl isonitrile uptake analysis for prediction of the response to chemotherapy in advanced and relapsed breast cancer

BACKGROUND

Technetium-99m methoxyisobutyl isonitrile (Tc-SESTAMIBI) is a substrate of P-glycoprotein and multidrug-resistance associated protein in drug-resistant cells. To assess the clinical effectiveness of Tc-SESTAMIBI for predicting the chemotherapy response to treatment with anthracyclines and vinca alkaloids, we retrospectively evaluated the relationship between the accumulation of Tc-SESTAMIBI and the tumor response.

METHODS

Thirteen patients, including 12 advanced cases and 1 relapsed case, were investigated, all of whom had been treated with anthracyclines or a vinca alkaloid regimen. The accumulation of Tc-SESTAMIBI was compared at 10 min and 2 h after Tc-SESTAMIBI administration. The relationship between the accumulation of Tc-SESTAMIBI and the tumor response following treatment with anthracyclines and vinca alkaloids was assessed.

RESULTS

Eight of 13 patients responded to treatment with anthracyclines and vinca alkaloids, whereas 5 patients did not respond to treatment. At 10 min, 6 (75.0% ) of the 8 responding patients had a high accumulation of Tc-SESTAMIBI, whereas 4 (80.0% ) of the 5 non-responding patients had a low accumulation of Tc-SESTAMIBI. The overall predictive value was 76.9%. The relationship was not statistically significant (Fisher's test). The difference in the decrease of accumulation of Tc-SESTAMIBI between 10 min and 2 h was not associated with tumor response to treatment in 6 of the responding patients with high accumulation. Two false negative cases and one false positive case were observed, suggesting the presence of another factor contributing to drug sensitivity in tumor response, such as apoptosis-related genes.

CONCLUSIONS

Assessment of the initial accumulation of Tc-SESTAMIBI can be a predictive marker of tumor response to treatment with anthracyclines and vinca alkaloids in patients with advanced and relapsed breast cancer. Further studies are required to explore other factors involved in the tumor response to treatment with anthracyclines and vinca alkaloids.

Use of a cholesterol-rich emulsion that binds to low-density lipoprotein receptors as a vehicle for paclitaxel

A cholesterol-rich emulsion (LDE) is taken up by malignant cells which over-express low-density lipoprotein (LDL) receptors and thus may be used as a carrier for drugs directed against neoplastic cells. In this study, we associated the antineoplastic agent paclitaxel to LDE and analysed the new formulation's incorporation efficiency, chemical and physical stability, cellular uptake and cytostatic activity against a neoplastic cell line and the acute toxicity to rats. A paclitaxel incorporation efficiency of approximately 75% was achieved when paclitaxel was mixed with LDE at a 6:1 lipid-to-drug molar ratio. The association of paclitaxel with LDE increased by 54% the mean diameter of the emulsion particles but did not damage the paclitaxel chemical structure as analysed by HPLC. Results from gradient ultracentrifugation and Sephadex G25 gel filtration indicated that the binding of the drug to the emulsion was stable. It was shown that the cellular uptake and the cytotoxic activity of LDE-paclitaxel by a neoplastic cell line (NCI-H292 cells) was indeed mediated by the LDL receptors. The antiproliferative activity of LDE-paclitaxel against NCI-H292 cells was less than that of a commercial paclitaxel preparation (50% inhibitory concentration, IC50 = 2.60 and 0.45 microM, respectively). This difference, however, can be ascribed to the in-vitro anti-proliferative activity of the commercial paclitaxel vehicle Cremophor EL; when Cremophor EL was added to the cultures with LDE-paclitaxel, the IC50 value was reduced to 0.45 microM, attaining that of the commercial paclitaxel preparation. The tolerability of LDE-paclitaxel in rats was remarkable, such that its lethal dose (LD50) was ten-fold greater than that of the commercial formulation (LD50 = 324 and 31.8 mg kg(-1), respectively). Therefore, LDE-paclitaxel association is stable and the cytostatic activity of the drug is preserved while its toxicity to rats is small. By diminishing the side effects and directing paclitaxel to neoplastic tissues, LDE may be useful as adjuvant in chemotherapy with this drug.

Cremophor EL: the drawbacks and advantages of vehicle selection for drug formulation

Cremophor EL (CrEL) is a formulation vehicle used for various poorly-water soluble drugs, including the anticancer agent paclitaxel (Taxol). In contrast to earlier reports, CrEL is not an inert vehicle, but exerts a range of biological effects, some of which have important clinical implications. Its use has been associated with severe anaphylactoid hypersensitivity reactions, hyperlipidaemia, abnormal lipoprotein patterns, aggregation of erythrocytes and peripheral neuropathy. The pharmacokinetic behaviour of CrEL is dose-independent, although its clearance is highly influenced by duration of the infusion. This is particularly important since CrEL can affect the disposition of various drugs by changing the unbound drug concentration through micellar encapsulation. In addition, it has been shown that CrEL, as an integral component of paclitaxel chemotherapy, modifies the toxicity profile of certain anticancer agents given concomitantly, by mechanisms other than kinetic interference. A clear understanding of the biological and pharmacological role of CrEL is essential to help oncologists avoid side-effects associated with the use of paclitaxel or other agents using this vehicle. With the present development of various new anticancer agents, it is recommended that alternative formulation approaches should be pursued to allow a better control of the toxicity of the treatment and the pharmacological interactions related to the use of CrEL.

Assessment of neurotoxicity following repeated cremophor/ethanol injections in rats

As the mixture cremophor/ethanol is known to have side-effects affecting the peripheral nervous system, we have assessed its behavioural and morphological neurotoxicity after repeated intraperitoneal injections in male Sprague Dawley rats. Clinical status of the animals was good throughout the experiment and no motor deficits were observed. Nevertheless, sensory testing demonstrated an hyperalgesia and an allodynia to mechanical stimuli, associated to peripheral axon degeneration.

Role of formulation vehicles in taxane pharmacology

The non-ionic surfactants Cremophor EL (CrEL) and Tween 80, both used as formulation vehicles of many (anticancer) agents including paclitaxel and docetaxel, are not physiological inert compounds. We describe their biological properties, especially the toxic side effects, and their pharmacological properties, such as modulation of P-glycoprotein activity. In detail, we discuss their influence on the disposition of the solubilized drugs, with focus on CrEL and paclitaxel, and of concomitantly administered drugs. The ability of the surfactants to form micelles in aqueous solution as well as biological fluids (e.g. plasma) appears to be of great importance with respect to the pharmacokinetic behavior of the formulated drugs. Due to drug entrapment in the micelles, plasma concentrations and clearance of free drug change significant leading to alteration in pharmacodynamic characteristics. We conclude with some perspectives related to further investigation and development of alternative methods of administration.

Cremophor EL pharmacokinetics in a phase I study of paclitaxel (Taxol) and carboplatin in non-small cell lung cancer patients

The purpose of our study was to investigate the pharmacokinetics of Cremophor EL following administration of escalating doses of Taxol (paclitaxel dissolved in Cremophor EL/ethanol) to non-small cell lung cancer (NSCLC) patients. Patients with NSCLC stage IIIb or IV without prior chemotherapy treatment were eligible for treatment with paclitaxel and carboplatin in a dose-finding phase I study. The starting dose of paclitaxel was 100 mg/m2 and doses were escalated with steps of 25 mg/m2, which is equal to a starting dose of Cremophor EL of 8.3 ml/m2 with dose increments of 2.1 ml/m2. Carboplatin dosages were 300, 350 or 400 mg/m2. Pharmacokinetic sampling was performed during the first and the second course, and the samples were analyzed using a validated high-performance liquid chromatographic assay. A total of 39 patients were included in this pharmacokinetic part of the study. The doses of paclitaxel were escalated up to 250 mg/m2 (20.8 ml/m2 Cremophor EL). Pharmacokinetic analyses revealed a low elimination-rate of Cremophor EL (CI=37.8-134 ml/h/m2; t 1/2=34.4-61.5 h) and a volume of distribution similar to the volume of the central blood compartment (Vss=4.96-7.85 l). In addition, a dose-independent clearance of Cremophor EL was found indicating linear kinetics. Dose adjustment using the body surface area, however, resulted in a non-linear increase in systemic exposure. The use of body surface area in calculations of Cremophor EL should therefore be re-evaluated.

Relationship between diagnosis-specific activity of cytotoxic drugs in fresh human tumour cells ex vivo and in the clinic

The aim of this investigation was to evaluate the relationship between the disease-specific activity of cytotoxic drugs in the clinic and in fresh human tumour cells from patients, as detected by a non-clonogenic cytotoxicity assay. The activity of 18 different cytotoxic drugs in fresh human tumour cells ex vivo was analysed in up to 15 samples from each of 13 different diagnoses using the fluorometric microculture cytotoxicity assay (FMCA). For each drug and diagnosis, relative activity indices (RAIs) were calculated, defined as the fraction of samples within the diagnosis having a survival index (SI) less than the median SI for the drug in all tested samples. Clinical response rates for the drug in the same diagnoses were collected from published phase II trials and were compared with the RAIs using Spearman's rank correlation (Rho) and Pearson's correlation coefficient (R). Correlation coefficients could be calculated for 12 drugs. The coefficients varied between 0.02 and 0.92 (Rho) and between 0.07 and 0.91 (R), but for most drugs the correlation between RAI and clinical response rates was good, with Rho > 0.6 and R > 0.7. Weak correlations were observed for cyclophosphamide and vincristine (Rho = 0.32 and 0.16, respectively), which might be due to old clinical data, and for paclitaxel (Rho = 0.02), which perhaps could be explained by in vitro activity of the solvent, Cremophor EL. The 18 drugs were also categorised according to their suggested clinical use in solid or haematological tumours, and were then compared regarding the activity in solid compared with haematological tumours ex vivo, expressed as the ratio between the number of responders among solid and haematological tumours (S/H ratio). The mean ex vivo S/H ratios in the group of drugs registered for use in haematological tumours was only 0.09 and was significantly different (P = 0.05) from the mean S/H ratios for the drugs used in both haematological and solid tumours (0.31) and in solid tumours only (0.47). Furthermore, the FMCA could identify the 50% most and least sensitive diagnoses with respect to clinical phase II activity with 74% (78/106) correct classifications. The results indicate that the relative activity of cytotoxic drugs in different diagnoses may be detected by the FMCA. Thus, 'phase II trials ex vivo' using non-clonogenic cytotoxicity assays might be used to make clinical trials more effective by targeting trials to diagnoses in which a new agent is most likely to be active.

Effects of paclitaxel with or without cremophor EL on cellular clonogenic survival and apoptosis

Paclitaxel is currently formulated in a vehicle of 50% ethanol and 50% polyethoxylated surfactant cremophor EL. Cremophor EL has been reported to reverse P-glycoprotein-mediated multidrug resistance (MDR) at doses which are clinically achievable. It has also been reported to have a cytotoxic effect per se. In this study we used two different methods to evaluate the survival of cells exposed to paclitaxel with or without cremophor EL and the vehicle alone. Two laryngeal SCC cell lines (UT-SCC-19A and UT-SCC-29) and two ovarian adenocarcinoma cell lines (UT-OC-3 and UT-OC-5) established in our laboratory were investigated. Northern hybridisation was used to study the mdr-1 mRNA expression of the cell lines. With sensitive Northern analyses, these four lines yielded mdr-1 mRNA signals of the expected 4.5 kb size and of variable intensity, generally at higher levels than those in the positive control cell line KB. The 96-well plate clonogenic assay was used to obtain the fraction survival data and apoptosis was recorded by time-lapse video microscopy. Both methods indicate that cremophor EL alone has no effect on cellular survival. Consequently, paclitaxel without cremophor EL is as active as paclitaxel with cremophor EL in vitro.