SIE values calculated from this work are in the range 210.03 kcal/mol to 210.67 kcal/mol. Though there is no direct correlation between IC50 and SIE values, it can be observed that their respective values lie within a narrow range. Many patients eventually developed imatinib resistance, usually associated with above mentioned mutations in ABL kinase domain that either directly or indirectly effects the binding affinity of imatinib to ABL. The most common gatekeeper residue mutation T315I that accounts for 15�C20% of clinically observed mutations is completely resistant to imatinib, nilotinib and dasatinib. Native and T315I BCR-ABL kinases complexed with dasatinib are subjected to 25 ns of MD simulations and SIE binding free energies are calculated. The analysis of dasatinib complexed with native and T315I order D-JNKI-1 mutant BCR-ABL kinases revealed that native complex has relatively higher SIE free energy than when complexed with T315I that signifies the greater affinity of dasatinib for native compared to mutant BCR-ABL kinase. The RMSD of BCR-ABL kinase �C CPDA ponatinib complexes shown in Figure 3 indicated that in the native complex, ABL kinase converged from 2.5 ns of MD and ponatinib converged from 1 ns to the end of simulations. The SIE calculated free energy for native complex is 210.41 kcal/mol. The gatekeeper mutant T315I has a longer side chain and the less common gatekeeper mutant T315A has a smaller side chain when compared to Thr315. The calculated free energies correlate with experimentally measured IC50 values and comparably ponatinib has better binding towards the mutation T315A than T315I. The free energy of BCR-ABLT315I complexed with imatinib is 29.89 kcal/mol indicating that ponatinib has higher binding towards T315I mutation compared to imatinib. Table 1 shows the distribution of electrostatic potential and contribution from neighbouring residues during MD simulations that are responsible for this free energy change. The mutation Y253F and Y253H present on the P-loop is in close contact with imidazo pyridazine of ponatinib. The Y253F mutation has 2 fold greater activity than Y253H, although the net SIE values for both complexes do not correlate with observed experimental values. These mutations show decrease in intermolecular coulomb energies compared to
