Synthesis and In Vitro Evaluation of Tetrahydroquinoline Derivatives as Antiproliferative Compounds of Breast Cancer via Targeting the GPER

Abstract

Background: Some reports have demonstrated the role of the G Protein-coupled Estrogen Receptor (GPER) in growth and proliferation of breast cancer cells. Objective: In an effort to develop new therapeutic strategies against breast cancer, we employed an in silico study to explore the binding modes of tetrahydroquinoline 2 and 4 to be compared with the reported ligands G1 and G1PABA. Methods: This study aimed to design and filter ligands by in silico studies determining their Lipinski's rule, toxicity and binding properties with GPER to achieve experimental assays as anti-proliferative compounds of breast cancer cell lines. Results: In silico studies suggest as promissory two tetrahydroquinoline 2 and 4 which contain a carboxyl group instead of the acetyl group (as is needed for G1 synthesis), which add low (2) and high hindrance (4) chemical moieties to explore the polar, hydrophobic and hindrance effects. Docking and molecular dynamics simulations of the target compounds were performed with GPER to explore their binding mode and free energy values. In addition, the target small molecules were synthesized and assayed in vitro using breast cancer cells (MCF-7 and MDA-MB-231). Experimental assays showed that compound 2 decreased cell proliferation, showing IC50 values of 50µM and 25µM after 72h of treatment of MCF-7 and MDA-MB-231 cell lines, respectively. Importantly, compound 2 showed a similar inhibitory effect on proliferation as G1 compound in MDA-MB-231 cells, suggesting that both ligands reach the GPER-binding site in a similar way, as was demonstrated through in silico studies. Conclusion: A concentration-dependent inhibition of cell proliferation occurred with compound 2 in the two cell lines regardless of GPER.

Computational Approaches for the Discovery of GPER Targeting Compounds

“…It is the case of G1-PABA ( 54 ), a compound part of a small series of G1 analogs, in which the acetyl moiety is replaced with a carboxyl group. The same pharmacophore core was further used to obtain a G1-PABA methylester and L -proline derivative, with similar structural and energetic binding properties ( 55 ). All these newly synthesized compounds were validated in vitro in experimental assays using breast cancer cell lines.…”

Modifications on the Tetrahydroquinoline Scaffold Targeting a Phenylalanine Cluster on GPER as Antiproliferative Compounds against Renal, Liver and Pancreatic Cancer Cells

“…G1-PABA ( 1 ) and the tert-butyl derivative (compound 7 ) were obtained following the previous method reported by our research group [ 22 , 23 ].…”

“…The second chemical modification was to obtain a molecule with a tert-butyl group off the piperidine ring (compound 7 ), seeking to increase the hydrophobic environment that can establish interactions with the aforementioned cluster of aromatic residues. Thus, we started with a G1 analog previously prepared by our research group [ 22 ], which is subsequently referred to as G1-PABA. The chemical synthesis of G1-PABA involved modification of the p -amino acetophenone of G1 using p -aminobenzoic acid, which has shown inhibitory activity against breast cancer cells [ 22 , 23 ].…”

“…Thus, we started with a G1 analog previously prepared by our research group [ 22 ], which is subsequently referred to as G1-PABA. The chemical synthesis of G1-PABA involved modification of the p -amino acetophenone of G1 using p -aminobenzoic acid, which has shown inhibitory activity against breast cancer cells [ 22 , 23 ]. Once G1-PABA was synthetized, compounds 4 , 5 and 7 were synthesized and tested in renal, liver and pancreatic cancer cells.…”

GPER and Testicular Germ Cell Cancer

“…However, G-15 exhibits a partial cross-reactivity with ERα explaining why G-36 is mainly used in the study of GPER/GPR30 ( 102 ). Other pharmacological ligands were synthetized (GPER/GPR30-L1 and GPER/GPR30-L2) ( 102 , 103 ) but they exhibit variable affinities for GPER/GPR30 and potential cross-reactivity with classical ERs, explaining why they cannot be considered as therapeutic tools at this time ( 104 ). These small molecules were used especially in vitro , as we did with seminoma cells; in our model, G-1 was able to mimic the proliferative effect of BPA while G-15 neutralized this effect and reduced cell proliferation in the presence of BPA ( 71 ).…”