'Piperazining' the catalytic gatekeepers: unraveling the pan-inhibition of SRC kinases; LYN, FYN and BLK by masitinib.

Blocking oncogenic signaling of B-cell receptor (BCR) has been explored as a viable strategy in the treatment of diffuse large B-cell lymphoma. Masitinib is shown to multitarget LYN, FYN and BLK kinases that propagate BCR signals to downstream effectors. However, the molecular mechanisms of its selectivity and pan-inhibition remain elusive. This study therefore employed molecular dynamics simulations coupled with advanced post-molecular dynamics simulation techniques to unravel the structural mechanisms that inform the reported multitargeting ability of masitinib. Molecular dynamics simulations revealed initial selective targeting of catalytic residues (Asp334/Glu335 - LYN; Asp130/Asp148/Glu54 - FYN; Asp89 - BLK) by masitinib, with high-affinity interactions via its piperazine ring at the entrance of the ATP-binding pockets, before systematic access into the hydrophobic deep pocket grooves. Identification of these 'gatekeeper' residues could open up a novel paradigm of structure-based design of highly selective pan-inhibitors of BCR signaling in the treatment of diffuse large B-cell lymphoma.