AUTHOR=Alcaro Stefano , Bolognesi Maria Laura , GarcĂ­a-Sosa Alfonso T. , Rapposelli Simona TITLE=Editorial: Multi-Target-Directed Ligands (MTDL) as Challenging Research Tools in Drug Discovery: From Design to Pharmacological Evaluation JOURNAL=Frontiers in Chemistry VOLUME=7 YEAR=2019 URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2019.00071 DOI=10.3389/fchem.2019.00071 ISSN=2296-2646