P688: virtual screening protocol to identify tyrosine kinase inhibitors with a potential to interact with p-glycoprotein and to act as mdr chemosensitizers: a validation study

Background: Resistance to tyrosine kinase inhibitors (TKIs) in chronic myeloid leukemia (CML) has been attributed to both BCR-ABL-dependent pathways - acquisition of point mutations and BCR-ABL-independent ones – drug efflux mediated by ATP-binding cassette proteins. Primary multidrug resistance (MDR) has been mostly attributed to aberrant expression of P-glycoprotein (Pgp). Therefore research efforts have been directed to improving anticancer drug efficacy by co-administration of TKIs as Pgp modulators. Recently novel SRC family kinase (SFK) inhibitors based on the pyrazolol[3,4-d]-pyramidine scaffold were shown to inhibit Pgp in two MDR cancer cell lines with the proforms outlining a stronger potential to modulate Pgp [1]. Aims: In this study we aimed: (i) to validate the in-house developed virtual screening (VS) protocol for TKIs with a potential to interact with Pgp; (ii) to compare the Pgp binding potential of the novel SFK inhibitors (SI306, SI221, pro-SI306, pro-SI221) with that of widely explored TKIs (core group), including those used for treatment of CML - imatinib, nilotinib and dasatinib. Methods: Molecular modelling was performed in MOE software [2]. Two VS protocols were explored in the study: (A) docking without pharmacophore filter and with triangle matching placement; (B) an in-house developed VS protocol based on pharmacophore filter and docking with pharmacophore placement. The following docking settings were applied: (i) rigid receptor / flexible ligand mode; (ii) London dG scoring function applied at both the placement stage and the rescoring stage. VS protocol B is based on an in-house library of 43 TKIs collected from the scientific literature and DrugBank database. The library includes structural identificators of the compounds and experimental data proving their P-gp binding. It is freely available at http://biomed.bas.bg/qsarmm/Tyrosine_kinase_inhibitors.The VS protocols were applied to predict the Pgp binding affinity of the SFK inhibitors SI306, SI221, pro-SI306, and pro-SI221 as well as the core group drugs. Results: The results are presented in Table 1. The pro-forms showed higher interaction energies in the docking simulations compared to their parent ones in agreement with the experimental results pointing to the pro-forms having a stronger potential to modulate Pgp (Table 1) [1]. Further the comparison with the reference compound Dasatinib shows that except for SI221, the novel SFK inhibitors have a similar or even higher potential to interact with P-gp. The comparison with the core group of drugs outlines the following order of predicted P-gp affinity: (i) for VS protocol A: pro-SI306>pro-SI221>Nilotinib; (ii) for VS protocol B: pro-SI221>Lapatinib>pro-SI306>Tepotinib>Nilotinib. In both cases pro-SI306 and pro-SI221 are among the top-ranked P-gp ligands. Image:Summary/Conclusion: In summary, the previously developed VS screening protocol based on pharmacophore filtering and docking was validated on novel SFK inhibitors that were predicted as Pgp ligands in agreement with the experimental results. Further, the VS results outlined their similar or even higher affinity to Pgp compared to Dasatinib, which was used as reference compound due to its dual BCR-ABL and SRC inhibitory activity. Therefore they are suitable lead structures in the design of Pgp modulators able to restore sensitivity to TKIs in resistant tumour cell lines. The presented protocols as well as the investigated compounds might be useful for virtual screening/drug design of TKIs that act as MDR chemosensitizers in a combined anti-cancer therapy.