G4-Selective Ligand Induced Autophagy

Abstract

G-quadruplex (G4) structures have emerged as singular therapeutic targets for cancer and neurodegeneration. Autophagy is a housekeeping cellular homeostatic mechanism and deregulation of autophagy is common in cancer and in neurodegenerative diseases. In this study, we identified the presence of 46 putative G4 sequences in the MTOR gene by use of QGRS mapper tool. We sought to connect these putative G4 sequences to a functional context by leveraging G4-targeting ligands. A G4-selective dimeric carbocyanine dye Bis-4,3 and the porphyrin TMPyP4 were used to affect the replication, transcription and translation of the MTOR gene. The ligand-induced induction of autophagic pathway via MTOR gene regulation was monitored upon treatment of HeLa and SHSY-5Y cells with G4-targeting ligands. The use of Bis-4,3 was compared with the known G4-stabilizing activity of TMPyP4. Our results show that treatment with G4-selective ligands downregulates mTOR activity and leads to the induction of excessive autophagy. This is first report on effect of G4-selective ligands on MTOR regulation and mTOR expression. mTOR being the key negative regulator of autophagy, the current work suggests potential of G4 stabilizing ligands towards induction of autophagy through the downregulation of mTOR.

Therapeutic Use of G4-Ligands in Cancer: State-of-the-Art and Future Perspectives

“…As anticipated, the possibility of targeting cancer cells through the pharmacological stabilization of naturally occurring G4 structures has long been considered by chemists, physicists, biologists, and clinicians as an opportunity for developing molecules that are able to selectively counteract tumor formation and progression. In agreement with this, the number of G4 ligands has significantly grown over the last 25 years, constituting a superfamily of molecules, with up to 3000 different members to date, distinguished for their structure and biological activity (see Figure 3 for notable examples reported in the text) [21,23,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46].…”

“…At the functional level, the alteration of VEGF-R promotes an impairment of vascularization and, consequently, an inhibition of tumor growth and dissemination. Again, a recent study published by Majumder and colleagues demonstrated the capability of TMPyP4 to impair the expression of mTOR, a key factor in the autophagic process [23]. In detail, the development of these novel therapeutic strategies was originally driven by the idea that these molecules, stabilizing G4 structures at telomeres, were able to physically inhibit telomerase activity, consequently impairing the endless replication of cancer cells [11].…”

“…At the functional level, the alteration of VEGF-R promotes an impairment of vascularization and, consequently, an inhibition of tumor growth and dissemination. Again, a recent study published by Majumder and colleagues demonstrated the capability of TMPyP4 to impair the expression of mTOR, a key factor in the autophagic process [23]. During this time, the therapeutic potential of G4s has extended beyond the regulation of gene expression.…”