Weiping yu1, xingguo mei2, qinwei jiang2 and christopher d
THERMOSENSITIVE DOCETAXEL LIPOSOMES
Xingguo Mei1, Qinwei Jiang1, Weiping Yu2 and Christopher D.V. Black2
1Beijing Institute of Pharmacology and Toxicology, 27, Taiping Road, Beijing, PRC 100850
2Celsion Corporation, 10220-L Old Columbia Road, Columbia, MD 21046. USA.
We have developed a liposome preparation containing docetaxel that is designed to release its
contents when subjected to mild hyperthermia (42-43℃). This lyophilized formulation is stable
on storage at 4℃ for at least 12 months and easily reconstituted to give 100 nm single bilayer vesicles in phosphate buffered saline.
The thermal release of docetaxel from the liposome was assayed biologically by injecting two groups of anesthetized mice intravenously with the same amount (75mg docetaxel/m2) of either thermosensitive liposomal docetaxel or non-liposomal docetaxel (formulated for injection according to the manufacturer’s instructions with polysorbate 80 and ethanol/water). Immediately following injection the right hind leg of each mouse was immersed in a thermostatically-controlled water bath at 43°C. After 30 minutes, the mice were sacrificed and both hind legs were surgically excised, weighed and frozen at -70°C. Muscle samples were removed from each leg, weighed, and homogenized. Docetaxel was extracted from the homogenates with methyl tertiary-butyl ether using norethisterone as an internal-standard and quantified by a HPLC-UV method.
Table 1shows the amount of docetaxel extracted per gram of leg muscle as a percentage of the amount of internal standard recovered from both heated and unheated legs. The amount non-liposomal docetaxel recovered is approximately the same whether the leg is heated or not and is very similar to the amount of liposomal drug extracted from the unheated leg. However, in the heated legs from mice treated with liposomal docetaxel, the amount of drug extracted is significantly higher (p = <0.01) i.e., more than twice the amount of docetaxel reaches the heated leg from the thermosensitive docetaxel liposomes.
DOCETAXEL RECOVERED FROM LEG MUSCLE Heated Leg Unheated Leg
In order to test the efficacy of the thermal delivery of liposomal docetaxel we designed another docetaxel liposome with almost the same lipid composition and lipid ratio but which would not release the drug in response to mild hyperthermia. The efficacy of these two liposomal formulations was compared to non-liposomal docetaxel and to saline in mice tumored in the
upper leg with Lewis lung cells. Once the tumors had reached 0.1-0.15 cm3 in volume, mice were stratified by tumor volume and randomized to one of the 4 treatment groups. Each group of 8 animals was treated with six doses of (75mg docetaxel/m2) calculated from body weight over the course of 13 days. The control group received an equal volume of saline. Treatment consisted of intraperitoneal barbiturate anesthesia followed by a slow intravenous injection of test compound after which the tumored leg was warmed for 0.5 hour in a thermostatically-controlled water bath at 43°C. Animals were followed until day 20 or until three times the initial tumor volume was reached whichever was the sooner (tumors grew well and no animals reached the 20 day limit). On day 13, tumor volumes were measured for the last time and the mice were euthanized. The graph shows mean tumor volumes in each treatment group during the treatment period.
Mouse Tumor Volumes
Thermally Sensitive LiposomesNon- Thermal Liposomes
an (± SE 0.4
By the end of the study, tumor volumes of the saline-treated control group were significantly (Mann-Whitney: p<0.001) larger than all the docetaxel treated groups. The inhibition of tumor growth was most obvious in the animals treated with thermosensitive docetaxel liposomes which had significantly (p<0.005) smaller tumor volumes than animals treated with the non-thermally sensitive liposomes or with docetaxel. There was no difference at any time between the tumor volumes of the non-thermally sensitive liposome group and those of the docetaxel-treated group. These tumor inhibition results were confirmed in a second, independent, experiment.
Changes in body weight were used to grossly measure overall drug toxicity in animals during the course of the experiment. All the docetaxel-containing formulations reduced the normal increase
in body weight seen in the saline treated animals but none of these formulations appeared to be more toxic than another.
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