NEU3 x NEU4

There is increasing interest in carbohydrate analogs for drug development, and the polar nature of these targets presents a challenge for medicinal chemistry. Multiple substrate hydroxy groups are typically required for enzyme active site recognition. Not all of these polar groups will have the same importance in recognition. A common strategy is to replace or remove these groups and compare the activity of the resulting analogs. If hydroxy groups are non-essential, or if their removal results in increased potency they may form the basis of improved inhibitors or substrates. In our studies of human neuraminidase enzymes (NEU), we have identified modifications at the C5 and C9 positions of the 2-deoxy-2,3-didehydro-N-acetyl neuraminic (DANA) scaffold that provide potent and selective inhibitors. In this study, we sought to test the requirements of each of the four human NEU isoenzymes for the presence of O4, O7, O8, or O9 hydroxy groups found in DANA. We synthesized the corresponding mono- (4, 7, 8, and 9) and di-deoxy (7,9; 7,8; and 8,9) analogs of DANA and tested their potency against human NEU. We found that 8-deoxy compounds increased potency against NEU2 and NEU3. Additionally, several di-deoxy analogs were tolerated by NEU1, NEU2, and NEU3. Finally, we generated known selective inhibitors of NEU3 and NEU4 and tested their 8-deoxy analogs. Combination of these features did not improve overall potency, suggesting deoxygenated analogs will require additional optimization.

Human neuraminidases play critical roles in many physiological and pathological processes. Humans have four isoenzymes of NEU, making selective inhibitors important tools to investigate the function of individual isoenzymes. A typical scaffold for NEU inhibitors is 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (DANA) where C9 modifications can be critical for potency and selectivity against human NEU. To design improved DANA analogues, we generated a library of compounds with either a short alkyl chain or a biphenyl substituent linked to the C9 position through one of six amide bioisosteres. Bioisostere linkers included triazole, urea, thiourea, carbamate, thiocarbamate, and sulfonamide groups. Within this library, we identified a C9 biphenyl carbamate derivative (963) that showed high selectivity and potency for NEU3 (K_i = 0.12 ± 0.01 μM). In contrast, NEU1 and NEU4 isoenzymes preferred amide and triazole linkers, respectively. Finally, analogues with urea, sulfonamide, and amide linkers showed enhanced inhibitory activity for a bacterial NEU, NanI from Clostridium perfringens.

Aim of the study: Sialidases, also called neuraminidases, are enzymes that cleave terminal sialic acids from glycoconjugates. In humans and mice, lung fibrosis is associated with desialylation of glycoconjugates and upregulation of sialidases. There are four mammalian sialidases, and it is unclear when the four mammalian sialidases are elevated over the course of inflammatory and fibrotic responses, whether tissue resident and inflammatory cells express different sialidases, and if sialidases are differentially expressed in male and females. Materials and Methods: To determine the time course of sialidase expression and the identity of sialidase expressing cells, we used the bleomycin model of pulmonary fibrosis in mice to examine levels of sialidases during inflammation (days 3 - 10) and fibrosis (days 10 - 21). Results: Bleomycin aspiration increased sialidase NEU1 at days 14 and 21 in male mice and day 10 in female mice. NEU2 levels increased at day 7 in male and day 10 in female mice. NEU3 appears to have a biphasic response in male mice with increased levels at day 7 and then at days 14 and 21, whereas in female mice NEU3 levels increased over 21 days. In control mice, the sialidases were mainly expressed by EpCAM positive epithelial cells, but after bleomycin, epithelial cells, CD45 positive immune cells, and alveolar cells expressed NEU1, NEU2, and NEU3. Sialidase expression was higher in male compared to female mice. There was little expression of NEU4 in murine lung tissue. Conclusions: These results suggest that sialidases are dynamically expressed following bleomycin, that sialidases are differentially expressed in male and females, and that of the four sialidases only NEU3 upregulation is associated with fibrosis in both male and female mice.