Development and Preclinical Evaluation of Novel STK3/4 Inhibitors with Anti-Obesity Potential

Obesity is associated with impaired adipocyte metabolism driven in part by mitochondrial dysfunction. Serine/threonine-protein kinase 3 (STK3) and STK4 promote mitophagy, leading to reduced mitochondrial mass in adipose tissue. Thus, inhibition of STK3/4 represents a potential therapeutic strategy for obesity and related metabolic disorders.

Two novel STK3/STK4 inhibitors, LL-M and LL-P, were identified from a focused small-molecule library using a fluorescence-based titration assay. Their effects on STK3/4 signaling and mitophagy were evaluated in C3H10T1/2 adipocytes. In vivo efficacy was assessed in male C57BL/6J mice fed either a normal chow diet or a high-fat diet (HFD), followed by a 2-week treatment with LL-M or LL-P. Metabolic outcomes, including body weight, glucose tolerance, and energy expenditure, were assessed.

In adipocytes, LL-M and LL-P effectively suppressed STK3/4 signaling, reduced BCL2 interacting protein 3 (BNIP3)-mediated mitophagy, and increased mitochondrial metabolic activity. In HFD-fed mice, treatment with either compound attenuated body-weight gain, improved glucose tolerance, and enhanced energy expenditure.

Pharmacological inhibition of STK3/4 by LL-M and LL-P restores mitochondrial function through suppression of BNIP3-mediated mitophagy, leading to improved adipocyte function and metabolic outcomes. These findings support the therapeutic potential of LL-M and LL-P as small-molecule candidates for the treatment of obesity and related metabolic disorders.