Yuji Horikiri

A novel preparation method for PLGA microspheres using non-halogenated solvents.

We investigated a new preparation method for microspheres based on an Oil/Water type emulsion solvent evaporation method using non-halogenated solvents. This method is based on phase separation between acetone and aqueous glycerol. For the preparation of microspheres by this method, a solution of poly(DL-lactic-co-glycolic acid) (PLGA) in acetone and aqueous glycerol containing poly(vinyl alcohol) were used asthe dispersed and continuous phases in the emulsification process, respectively. Vitamin B12 was used as the model drug. The formation of PLGA microspheres was observed above 60% glycerol in the continuous phase. The yield and encapsulation efficiency of the PLGA microspheres was about 80%, which was the maximum yield obtained with 70% glycerol. The release of vitamin B12 lasted for three weeks.

Anti-tumor effect of intraperitoneal administration of cisplatin-loaded microspheres to human tumor xenografted nude mice

This study evaluates the anti-tumor effect of cisplatin-loaded microspheres (CDDP-MS) against peritoneal carcinomatosis using human tumor xenografts. The incorporated CDDP was released from CDDP-MS for 3 weeks in vivo as well as in vitro. CDDP-MS at a dose of 35 mg/kg (at maximal tolerable dose (MTD)) showed effective anti-tumor activity (tumor growth inhibition rate (IR)=70.3%) against Li-7 (human liver cancer) xenografts transplanted into the peritoneal cavity. This procedure also resulted in increased life span (ILS (%)=47.2%), whereas CDDP dissolved in saline solution (CDDP-SOL) at a dose of 8 mg/kg (at MTD) was ineffective (IR=15.7%, ILS=2.6%). Likewise, CDDP-MS (35 mg/kg) significantly prolonged the mean survival time (ILS=50.8%) compared with a CDDP-SOL group (8 mg/kg) (ILS=13.1%) in the mice with Li-7 xenografts transplanted into the spleen. Furthermore, CDDP-MS showed markedly effective anti-tumor activity (IR=82.2%) against H-154 (human stomach cancer) xenografts, in which CDDP-SOL was effective (IR=69.5%) at the MTDs. The suppressive effect of CDDP-MS on accumulation of malignant ascites was intimately related to unchanged CDDP concentration in ascites. These results demonstrated that the administration of CDDP-MS resulted in an unchanged CDDP concentration in ascites, and induced a sustained tumor growth inhibition along with a prolonged survival time.

Enhancement of nasal absorption of large molecular weight compounds by combination of mucolytic agent and nonionic surfactant

For improving the nasal absorption of poorly absorbable hydrophilic compounds, the suitability of a combination of a mucolytic agent, N-acetyl-L-cysteine (NAC), and a nonionic surfactant, polyoxyethylene (C25) lauryl ether (laureth-25), was examined. Rat studies with fluorescent isothiocyanate-labeled dextran (molecular weight ca. 4.4 kDa, FD-4) as a model hydrophilic compound revealed dramatic enhancement of nasal absorption when NAC and laureth-25 were simultaneously applied. The nasal bioavailability of FD-4 in saline solution was 8.2+/-0.6% but increased to 40.0+/-5.5% when 5% NAC and 5% laureth-25 were added. This synergistic enhancement could result from the mucolytic activity of NAC in reducing mucous viscosity by which the accessibilities of FD-4 and laureth-25 to the epithelial membrane were increased. Further rat studies proved that this formulation increased nasal absorption of salmon calcitonin. Absolute bioavailability from saline solution containing 5% NAC and 1% laureth-25 was 26.8+/-2.2%, 3.5 times that of the commercial calcitonin nasal spray Miacalcin (7.7+/-2.1%). The potential of the new formulation to cause tissue damage in terms of hemolytic activity and liberation of phospholipid from the nasal membranes was nil or slight. The combination of NAC and laureth-25 appears suitable for use in development of nasal products for poorly absorbable drugs, especially peptide and protein drugs.

Organ distribution of cisplatin after intraperitoneal administration of cisplatin-loaded microspheres

The aim of this study was to clarify the organ distribution of cisplatin (CDDP) after intraperitoneal (i.p.) administration of cisplatin-loaded microspheres (CDDP-MS). The distribution of CDDP to normal organs lying in the peritoneal cavity after i.p. administration of CDDP-MS was assessed by comparing with subcutaneous administration to non-cancerous mice. The organ distribution of CDDP after i.p. administration of CDDP-MS shows that CDDP released from microspheres was distributed to the organs lying in the peritoneal cavity and in the retroperitoneum. These are mainly from the systemic circulation, but are not directly from the organ surface. The distribution of CDDP to tumors was evaluated in sarcoma180 tumor-bearing mice by comparing with a bolus injection. The CDDP-MS delivered CDDP to tumors more effectively than did bolus injection. The distribution of CDDP-MS in the peritoneal cavity was in accord with the tumor distribution. This concordance and sustained exposure of CDDP to the tumors might play a critical role in enhancing the CDDP accumulation in tumors. It is concluded that CDDP-MS have a distinct regional pharmacokinetic advantage for peritoneal carcinomatosis, and that i.p. administration of CDDP-MS is an effective treatment for peritoneal carcinomatosis.

Relation between dissolution profiles and toxicity of cisplatin-loaded microspheres.

The aim of this study is to evaluate and compare the dissolution profiles of cisplatin-loaded microspheres (CDDP-MS) in vitro and in vivo, and to determine the relationship between the dissolution profiles in vitro and systemic toxicity. For this purpose, three types of CDDP-MS that release the CDDP for 1, 2 and 5 weeks without a large amount of initial release in phosphate buffered saline (pH 7.4) were prepared. The dissolution profiles of these formulations in vivo were well correlated with in vitro studies, and resulted in well-controlled plasma platinum concentration. The systemic toxicity of the CDDP-MS and CDDP dissolved in saline (CDDP-SOL) were assessed by intraperitoneal administration in mice. The maximal tolerable dose (MTD) of CDDP-SOL was 13.4 mg/kg, whereas the CDDP-MS of 1, 2 and 5-week types were 34.6, 44.2, 62.6 mg/kg, respectively. The MTD of CDDP increased proportionally when 50% of CDDP had been released from MS in vitro (MTD (mg/kg)=5.22 x T(50(day)) + 13.2, R(2)=0.9935). We demonstrate that the systemic toxicity of CDDP-MS can be predicted by evaluation of the dissolution rate in vitro since in vivo dissolution was correlated with the in vitro.