Estriol dissolving microneedle patches for protection against ionizing radiation-induced injury

Estriol can be used to treat radiation-induced leukopenia by increasing peripheral blood leukocytes and therefore it plays an important role in radiation protection. However, only high-dose injectable suspensions are available when estriol is used to combat against ionizing radiation-induced injury. Intramuscular (i.m.) administration of estriol is very painful and inconvenient, and the lack of timely self-administered formulation greatly limits the wide application of estriol. This will facilitate quick response under emergent conditions in complementary with the available estriol formulations. Herein, we prepared estriol microneedle (MNs) patches for the convenient and efficient treatment of radiation-induced injury. A biocompatible polymer, polyvinylpyrrolidone K90, was dissolved in an estriol solution of methanol and cast into a mold to obtain conical-shaped MNs. N-vinyl pyrrolidone was poured on the base of the MNs and photocured to enhance the mechanical strength of estriol MNs (EMNs). EMNs were easily pierced 200 μm into the mouse skin. More importantly, the EMNs tips were dissolved very quickly within 5 min so that the drugs could permeate across skin. Mouse models of ionizing radiation-induced injury were established with 6.5 Gy radiation of ⁶⁰Co γ ray. Moreover, EMNs increased peripheral blood leukocytes in irradiated mice, protected the bone marrow hematopoietic system, and improved the survival rate of the irradiated mice to 80%. EMNs are a promising transdermal drug delivery system that allows for easy, rapid administration and protects the body from damage caused by ionizing radiation.