ABSTRACT: Activation of Sirtuin (silent mating type information regulation 2 homolog) 1, or SIRT1, is an unexplored therapeutic approach for treatment of inflammatory diseases. The goal of this study was to evaluate the clinical activity and tolerability of multiple doses of SRT2104, a selective activator of SIRT1, in patients with moderate to severe psoriasis after day 84 of treatment. Forty patients were randomized 4:1 to three escalating doses of SRT2104 (250, 500, 1000 mg/d SRT2104 or placebo). Across all SRT2104 groups, 34.6% of patients (9 out of 26; 90% CI 18.0%-54.2%, p<0.0001) achieved good to excellent histological improvement based on skin biopsies taken at baseline and day 84. To evaluate the changes in expression profile with treatment and to identify pathways involved in histological improvement, a subset of 22 Pre and Post treatment biopsies from 11 patients (4 Placebo, 7 Active Treatment) were hybridized to hgu133plus2 chips. Improvement in histology was associated with modulation of IL-17 and TNF-_ signaling pathways and keratinocyte differentiation target genes. Various studies suggest a crucial role of TNF_ and IL-17 in psoriasis pathogenesis and IL-17/TNF_ synergism induces a strong induction of differentially expressed genes in psoriasis, thus advocating a crucial role of IL-17/TNF_ combination in the molecular basis of disease (Chiricozzi et al., 2010). In the current study, broad scale gene expression profiling revealed that SRT2104 significantly reduced known IL-17 and TNF_ responsive genes including SERPINB4, S100A12, SERPINB3, kynu etc. even though the sample size for this analysis was small. One of the most highly modulated genes by SRT2104 included Kynu, a gene that regulates tryptophan metabolism, known to confer antibacterial effector functions (Daubener and MacKenzie, 1999). Interestingly kynu is part of the etanercept residual genomic profile that is not modulated by etanercept therapy even though clinical efficacy is achieved. Possibly, SRT2104 may be modulating the lipid barrier of the epidermis of psoriatic skin via modulation of keratinocyte diferentiation genes, which would be consistent with the observed improvement in skin histology. These results indicate a combinatorial effect of SRT2104 on TNF_, and IL-17 inflammatory signaling pathways and keratinocyte differentiation that could be a contributing factor towards improvement in clinical scores by the SIRT1 activator, SRT2104.
