The adenosine monophosphate (AMP)-activated protein kinase (AMPK) is a central regulator of metabolic pathways. Increasing AMPK activity is an attractive therapeutic target. Fbxo48 is an orphan ubiquitin E3 ligase subunit protein. Fbxo48 targets the active p-AMPKα for polyubiquitylation and proteasomal degradation. Especially, Fbxo48 inhibitors prevent pAMPKα degradation and ameliorate insulin resistance. BC1618 is a potent Fbxo48 inhibitory compound.

BC1618 stimulates AMPK-dependent signaling greatly exceeds AICAR or Metformin. In particular, BC1618 increases the biological activity of AMPK not by stimulating the activation of AMPK, but rather by preventing activated pAmpkα from Fbxo48-mediated degradation. BC1618 promotes mitochondrial fission, facilitates autophagy, and improves hepatic insulin sensitivity in high-fat-diet-induced obese mice.

BC1618 exhibits substantially better potency compared to all other SAR compounds and the original hit molecule BC1583 towards increased p-AMPKα protein, measured by an in-cell enzyme-linked immunosorbent assay (ELISA). Moreover, BC1618 enhances p-AMPKα protein stability during Cycloheximide treatment. BC1618 displays more than a 1,000-fold enhanced activity to stimulate pAMPKα in cells, compared with Metformin. Besides, BC1618 induces a dose- and time-dependent increase in p-AMPKα and pACC protein levels in human primary-like hepatocytes. BC1618 (1 µM) effectively disrupts the interaction between Fbxo48 and p-AMPKα. Furthermore, BC1618 directly interacts with Fbxo48 but not Fbxo30 (negative control).

BC1618 facilitates mitochondrial fission and autophagy. Specifically, BC1618 induces phosphorylation of the mTORC1 associated protein Raptor, reducing pS6 levels, all consistent with the known mTOR inhibitory effects exerted by activated AMPK. In addition, BC1618 improves hepatic insulin sensitivity in mice fed a high-fat diet. BC1618 improves hepatic insulin sensitivity in diet-induced obese mice.

All in all, BC1618, an orally active Fbxo48 inhibitor, stimulates Ampk-dependent signaling. BC1618 promotes mitochondrial fission, facilitates autophagy, and improves hepatic insulin sensitivity.

Yuan Liu, et al. A Fbxo48 inhibitor prevents pAMPKα degradation and ameliorates insulin resistance. Nat Chem Biol. 2021 Mar;17(3):298-306.