Subacute Toxicities of All-trans-Retinoic Acid Encapsulated in the Poly(D,L-Lactide) Microspheres

All-trans-retinoic acid (RA) plays essential roles in the regulation of differentiation and proliferation. It has been proved that RA is effective in the treatments of epithelial and hematologic malignancies. However, in spite of its pronounced effects, the clinical applications of RA are limited due to the retinoid acute resistance. Although RA induces complete remission in a high proportion of the patients of acute promyelocytic leukemia (APL), the cancer was relapsed in many patients after a brief remission in spite of a continued RA treatment. Patients who relapsed from remission that was initially induced by RA had clinically resistant to further RA treatment. That is, specific cytochrome P450 enzymes in the liver were induced by the continuous oral administration of RA, thereby accelerating the metabolism of RA. To overcome this problem, biodegradable microspheres were proposed by us, previously. And, several microsphere formulations for RA delivery have been prepared and studied on their effectiveness. Recently, poly(D,L-lactide) (PDLLA) microsphere formulation was optimized, And, from the animal studies by using a mouse and a rat, it have appeared to be effective on both the inhibition of tumor growth and chemoprevention of a carcinogenesis. In this study, subacute toxicities of the PDLLA microsphere formulation have been investigated as a preclinical test. For the test, the microspheres was injected subcutaneously into the back site of rats, and body weight change, clinical signs, hematological changes, blood biochemistry were evaluated. As a result, severe toxicities such as mortality were observed at the dose of 100mg RA/kg, and toxicities were not observed at the dose of 50mg RA/kg, which is the effective dose against carcinogenesis. Bone fracture, observed at several rats, might be inhibited by treating them with anti-inflammatory drugs.

아급성 독성 시험으로부터, 미립구내의 레티노익 산을 기준으로 한 투여량이 100mg/kg 일때는 4마리의 치사 개체가 보이는 등의 심각한 독성 효과가 유발되었으며, 25 및 50mg/kg인 경우에 독성 효과가 거의 나타나지 않음을 관찰하였다. 50mg/kg의 투여량의 경우, 일부 동물에서 뼈골절 현상이 나타났지만, 이러한 독성효과는 항염증제를 같이 투여함으로써 극복될 수 있을 것으로 생각되어졌다. 따라서, 앞으로의 실험에서는 항염증제를 이용하여, 가능한 독성을 억제하연서, 보다 빠른 기간 내에 상태가 회복될 수 있도록 하는 연구를 행할 것이다.