11β-Hydroxysteroid Dehydrogenase Type 1 (11β-HSD1) Inhibitors Still Improve Metabolic Phenotype in Male 11β-HSD1 Knockout Mice Suggesting Off-Target Mechanisms

The enzyme 11 beta-hydroxysteroid dehydrogenase type 1 (11 beta-HSD1) is a target for novel type 2 diabetes and obesity therapies based on the premise that lowering of tissue glucocorticoids will have positive effects on body weight, glycemic control, and insulin sensitivity. An 11 beta-HSD1 inhibitor (compound C) inhibited liver 11 beta-HSD1 by >90% but led to only small improvements in metabolic parameters in high-fat diet (HFD)-fed male C57BL/6J mice. A 4-fold higher concentration produced similar enzyme inhibition but, in addition, reduced body weight (17%), food intake (28%), and glucose (22%). We hypothesized that at the higher doses compound C might be accessing the brain. However, when we developed male brain-specific 11 beta-HSD1 knockout mice and fed them the HFD, they had body weight and fat pad mass and glucose and insulin responses similar to those of HFD-fed Nestin-Cre controls. We then found that administration of compound C to male global 11 beta-HSD1 knockout mice elicited improvements in metabolic parameters, suggesting "off-target" mechanisms. Based on the patent literature, we synthesized another 11 beta-HSD1 inhibitor (MK-0916) from a different chemical series and showed that it too had similar off-target body weight and food intake effects at high doses. In summary, a significant component of the beneficial metabolic effects of these 11 beta-HSD1 inhibitors occurs via 11 beta-HSD1-independent pathways, and only limited efficacy is achievable from selective 11 beta-HSD1 inhibition. These data challenge the concept that inhibition of 11 beta-HSD1 is likely to produce a "step-change" treatment for diabetes and/or obesity.