Development of new glucocorticosteroids with a very high ratio between topical and systemic activities

The very potent topical anti-inflammatory glucocorticosteroids (GCS) most widely used are either 17 alpha-esters of halogenated 16-methyl-17 alpha-hydroxycorticosteroids (e.g. beclomethasone 17 alpha, 21-dipropionate = BDP) or 16 alpha, 17 alpha-acetals of halogenated 16 alpha, 17 alpha-dihydroxy corticosteroids (e.g. triamcinolone acetonide = TA). The purpose of the present investigation was to increase the ratio between the topical anti-inflammatory (TAIP) and the systemic potencies (SP) of GCS 16 alpha, 17 alpha-acetals, as such compounds are not biotransformed in the lung. Structure-activity investigations in rodents showed that fluoro substituents in positions 6 alpha or 9 alpha or both 6 alpha, 9 alpha 9 alpha increased SP more than TAIP. On the other hand, nonsymmetrical 16 alpha, 17 alpha-acetal substitution increased TAIP more than SP. The best TAIP:SP ratio was obtained with budesonide, which contains this new type of acetal substituent, but has no halogen atoms in the steroid nucleus. In the rat and the mouse budesonide has a 5--10 times better TAIP:SP ratio than 16 alpha, 17 alpha-acetonides, like TA, as well as 17 alpha-ester GCS, like BDP. The improved ratio for budesonide is probably due to a high intrinsic GCS activity at the site of application combined with an effective inactivation by biotransformation after systemic absorption. The importance of the inactivation in the liver was verified by experiments in which the biotransformation capacity of the liver was blocked by SKF-525 A.