Novel 5-HT₆R modulators as mTOR-dependent neuronal autophagy inductors

Autophagy is a natural process in which the cell degrades substances through the lysosomal pathway. One of the most studied mechanisms for regulating autophagy is the mTOR signaling pathway. Recent research has shown that the 5-HT₆ receptor is linked to the mTOR pathway and can affect cognition in various neurodevelopmental models. Therefore, developing 5-HT₆ receptor antagonists could improve cognition by inducing autophagy through the inhibition of the mTOR pathway. Our study reports two in-house-designed 5-HT₆R antagonists, PUC-10 and its indazole analogue PUC-55, that induce mTOR-dependent autophagy. PUC-10, an indole-based 5-HT₆ receptor antagonist with high binding affinity (K_i = 14.6 nM) and antagonist potency (IC₅₀ = 32 nM), demonstrated more than 90% at 25 µM cellular viability and a high capacity to induce autophagy in the neuroblastoma SH-SY5Y cell line. Similarly, its indazole analogue, PUC-55 (K_i = 37.5 nM), exhibited high cellular viability and potent autophagy-inducing activity. Both compounds induced overexpression of the 5-HT₆ receptor after 24 h of stimulation, contrasting with the effects observed with Rapamycin (100 nM), a well-known mTOR inhibitor. Additionally, the signaling pathway was characterized, showing that both PUC-10 and PUC-55 induce autophagy by inhibiting the mTOR pathway, suggesting their potential therapeutic applications for neurological disorders.