Toshiro Heya

Drug delivery using biodegradable microspheres

Abstract Rational delivery systems for leuprorelin acetate, a potent LHRH agonist, have been achieved by developing a microsphere system using biodegradable polymers, poly(lactic/glycolic acid) (PLGA) and polylactic acid, which sustainedly release the drug depending on the biodegradation of polymer used and persistently suppress steroidogenesis for over one and 3 months, respectively, following a single injection. To produce these systems we established a novel microencapsulation technique, the in-water drying method, and microspheres with a high trap ratio and small initial burst were obtained. A microsphere system of TRH prepared using PLGA could also continuously release the drug for 2 or 4 weeks. Using these systems effectively reduced the required dose compared with that needed with daily injection due to more continuous receptor hits on the target organs and could improve patient compliance. Chemoembolization using PLGA microspheres containing an angiogenesis inhibitor, TNP-470, resulted in dramatic regression of VX-2 carcinoma in rabbits. The microsphere system using biod-egradable polymers is very useful in designing controlled release delivery and targeted delivery to attain potent and rational therapy.

Controlled release of LHRH agonist, leuprolide acetate, from microcapsules: serum drug level profiles and pharmacological effects in animals

Abstract— The pharmacokinetic behaviour of leuprolide acetate from a controlled release parenteral dosage form has been studied in rats and dogs. The release of the drug in rats after a single subcutaneous injection exhibited pseudo‐zero‐order kinetics for one month in doses ranging from 0·0135 to 1·35 mg/rat; the release rate at a dose of 1·35 mg/rat was 2·8% of dose/day; after intramuscular injection the response was similar. In rats, the serum leuprolide acetate levels increased sharply immediately after injection by either route as a consequence of the initial release of the drug; subsequently, the levels attained a plateau for two weeks. The serum level profiles in dogs showed essentially the same pattern as those in rats. When the dosage form was injected into rats, the serum testosterone level (a pharmacological index) sharply peaked, abruptly decreased to below the normal level, and then was sustained at a suppressed level for over six weeks at a dose of 1·35 mg/rat (equivalent to 3 mg kg−1) and higher, while the serum testosterone level after an injection of 0·0135 and 0·135 mg/rat was not sufficiently suppressed. The profiles in dogs showed essentially the same pattern as those in rats. With multiple administrations (once every 4 weeks), serum testosterone levels in dogs did not show any sharp rise after the second and third injections. Changes in rat reproductive organ weights agreed well with the serum testosterone profile in the suppression. The results demonstrate that this dosage form releases the drug at a constant rate for one month and has a long‐acting potency.

Pharmacokinetics of once-a-month injectable microspheres of leuprolide acetate.

The pharmacokinetic parameters of leuprolide acetate, a potent analogue of LH-RH, were determined in rats and dogs after i.v. and s.c. dosing with leuprolide solution. The effective human dose of once-a-month injectable microspheres of leuprolide was estimated to be about 3.2 to 8.1 mg analogue/month using these parameters. After microsphere injection at three different doses in rat serum leuprolide concentrations were sustained for over 4 weeks, and the AUCs and mean serum levels were linearly correlated with the dose. The serum levels and urinary excretion of the analogue in rats after repeated s.c. injection of the microspheres every 4 weeks exhibited similar profiles after each injection; no changes of the absorption and excretion of the analogue after the repeated injection could be demonstrated. The serum levels of the analogue metabolite (M-I) were 21% of the intact form 3 hr after injection of the microspheres but very low at the steady state after 1 to 4 weeks.

One-month release injectable microspheres of leuprolide acetate inhibit steroidogenesis and genital organ growth in rats

Abstract We have prepared one-month release injectable microspheres of leuprolide acetate, a highly potent analog of luteinizing hormone-releasing hormone (LH-RH), to treat endocrine-dependent tumors and endometriosis. The drug was encapsulated with a biocompatible and biodegradable polymer, copoly( dl -lactic/glycolic acid) (PLGA), by a novel in-water drying method through a (w/o)/w emulsion. The effects of this sustained-release preparation on maintaining the serum levels of the analog, on serum testosterone, and on the growth of the genital organs were evaluated in rats of different strains (Sprague-Dawley (SD) and Wistar) and ages (6 and 10 weeks). The results were compared with those obtained by constant infusion or daily pulsatile injections of the analog solution. A single injection of the PLGA microspheres sustained effective serum levels of the analog for at least 4 weeks, and persistently inhibited serum testosterone and growth of the genital organs (testis, seminal vesicle, and prostate) over 6 weeks in both strains at both ages. These antagonistic activities were almost identical to those observed after constant infusion of the analog solution, and equal or superior to those after pulsatile daily injections. A single injection of these sustained release injectable microspheres satisfactorily inhibits steroidogenesis and consequently suppresses genital organ growth; its use may eliminate the inconvenience of daily subcutaneous injections, and elevate compliance and efficacy in patients with prostatic cancer.

Sustained Pharmacological Activities in Rats Following Single and Repeated Administration of Once-a-Month Injectable Microspheres of Leuprolide Acetate

Once-a-month injectable microspheres of leuprolide acetate prepared with copoly(DL-lactic/glycolic acid) using an in-water drying method were assessed for duration of the analogue release and pharmacological effects in rats after a single or repeated injection. The periodic challenge test revealed that a single injection of the microspheres caused a dramatic and persistent suppression of the ability of the pituitary–gonadal system to secrete gonadotropin and testosterone for over 5 weeks. The complete recovery of these functions was observed 10 weeks after the injection. The repeated injection of the microspheres at intervals of 2 or 4 weeks achieved persistent suppression of steroidogenesis after an initial transient flare-up and beneficially avoided the “acute-on-chronic response.” This depot formulation is expected to assure patient compliance and produce stronger therapeutic effects than the daily solution.

Effects of a sustained release formulation of thyrotropin-releasing hormone on behavioral abnormalities in senescence-accelerated mice.

Effects of a sustained release formulation of thyrotropin-releasing hormone (TRH-SR) on reduced anxiety-like behavior and learning impairment in senescence-accelerated mice (SAM) were examined. SAMP8/Ta (SAMP8) mice showing age-related emotional changes as well as learning and memory impairments, and SAMR1TA (SAMR1) mice exhibiting normal aging were used at 8 months of age. Subcutaneous injection of TRH-SR (2.8 mg/kg as free TRH) produced a sustained increase in immunoreactive plasma TRH levels up to about 4 weeks after dosing in SAMP8. TRH-SR antagonized the reduced neophobia to novel food in SAMP8 in a dose-dependent manner when tested 10 days but not 3 days after the injection. In the elevated plus-maze test, the SAMP8 control group treated with vehicle had significant increases in the number of entries into open arms and the time spent in open arms in comparison to SAMR1 mice. TRH-SR showed dose-dependent decreases in the number of entries into open arms, and reduced the time spent in open arms in SAMP8 mice. Furthermore, TRH-SR significantly improved the impairment of water maze learning in SAMP8 mice. In contrast, bolus administration of TRH had no significant effects on behavioral abnormalities in SAMP8 even at high doses, implying that long-term and continuous infusion of TRH may be important for amelioration of the behavioral abnormalities. These results suggest that TRH-SR may be useful for treatment of age-related emotional disorders and memory disturbance in dementia.