Screening of Stereochemically Defined 2,5-Diketopiperazines Identifies Autophagy Inducers without mTORC1 Suppression
This study identifies four DKPs that can increase autophagic flux without inhibiting mTORC1, suggesting a potential new avenue for autophagy modulation.
Where it sits
this study against the rest of the cyclic glycine-proline (cgp) corpusSummary and findings
This study evaluated the autophagy-inducing effects of stereochemically defined 2,5-diketopiperazines (DKPs) in Caco-2 cells. Four DKPs were identified that increased autophagic flux without reducing mTORC1 signaling. The findings suggest potential for DKPs in autophagy modulation without the adverse effects associated with mTORC1 inhibition.
Abstract
Modulating autophagy has emerged as a potential strategy for treating age-related diseases. However, commonly used pharmacological approaches to induce autophagy, particularly inhibition of mechanistic target of rapamycin complex 1 (mTORC1), can be associated with adverse effects, including immunosuppression and insulin resistance. This has prompted interest in autophagy modulators that act without directly inhibiting mTORC1. 2,5-Diketopiperazines (DKPs) are bioactive cyclic dipeptide scaffolds with diverse biological activities. However, systematic evaluation of their structure-activity relationships has been hindered by racemization during conventional chemical synthesis, leaving the contribution of stereochemistry to autophagy regulation poorly understood. Here, we used a stereoselective one-pot chemoenzymatic synthesis based on the adenylation domain of tyrocidine synthetase A to generate a DKP library with defined stereochemistry. Phenotypic screening in Caco-2 cells stably expressing the GFP-LC3-RFP autophagic flux probe identified four DKPs that increased autophagic flux: c(DW-DP), c(DW-LP), c(DF-DP), and c(DM-LP). Structure-activity analysis revealed stereochemistry-dependent effects associated with amino acid side-chain properties: D-configured residues were favored among DKPs containing aromatic amino acids or methionine, whereas L-configured residues were favored among those containing branched-chain amino acids. Substitution of the proline residue further altered activity, with glycine substitution tending to increase autophagic flux in some DKP scaffolds. Importantly, the active DKPs did not detectably reduce the phosphorylation of the mTORC1 downstream targets p70 S6K and 4EBP1, indicating that their autophagy-inducing effects do not require detectable suppression of canonical mTORC1 signaling. These findings establish stereochemically defined DKPs as candidate scaffolds for the development of autophagy inducers that act through mechanisms distinct from direct mTORC1 inhibition.
Background
The study appears to address the identification of compounds that can induce autophagy without suppressing mTORC1, which is a key regulator of cell growth and metabolism. This is significant because autophagy is a crucial cellular process involved in the degradation and recycling of cellular components, and its dysregulation is implicated in various diseases. Understanding how to modulate autophagy without affecting mTORC1 could have therapeutic implications.
Methods
Not reported in abstract.
Results
Not reported in abstract.
Interpretation
Not reported in abstract.
Limitations
- Not reported in abstract.