A phase I-II trial of everolimus (RAD001) at a dose of 2.5 mg in combination with imatinib 600 mg daily achieved a progression-free survival of at least 4 months in imatinib-resistant GIST patients after first- and second line-treatment failure . Sirolimus, another mTOR inhibitor, in association with TKIs (PKC412 or imatinib) showed an antitumor
activity in three GIST patients harbouring exon 18 PDGFRA-D842V mutation, that is well known to confer resistance to imatinib in vitro and in vivo [15, 16]. This combination is interesting because it simultaneously inhibits two different molecules of the same signaling pathway (KIT-PDGFRA/PI3-K/AKT/mTOR) that mTOR tumor impacts on cancer cell growth, survival, motility and metabolism . Nilotinib is a second-generation multi-TKI inhibitor that showed 7 to 10-fold higher intracellular concentrations HMPL-504 research buy than imatinib in vitro . This feature may be important to overcome the reduced affinity of the binding between imatinib PLX3397 and TK due to the acquisition of new mutations and to avoid the problem of an up-regulation
of efflux transporters. Nilotinib achieved a median progression-free survival of 12 weeks and a median overall survival of 34 weeks in a small series of patients pre-treated with imatinib and sunitinib . An in vitro and in vivo study on V561D-PDGFRA and D842V-PDGFRA mutants demonstrated that the combinations of nilotinib, imatinib and PKC412 could have a cooperative anti-proliferative activity due to their synergic effects on multiple targets . A clinical study reported that nilotinib alone or in combination with imatinib was well tolerated overall and showed clinical activity in 53 imatinib-resistant GIST patients in terms of median progression-free survival (203 days vs 168 days) and median duration of disease control (259 Molecular motor vs 158
days) . A large phase III trial on nilotinib as monotherapy in pre-treated GIST patients has been completed and, moreover, a large phase III trial comparing imatinib versus nilotinib in untreated metastatic patients is still ongoing [10, 31]. In our experiment, nilotinib as a single agent showed the same results as imatinib in tumor volume control, but it also led to a good reduction of FDG uptake reduction over time. However, the combination with imatinib is superior to the single agent alone. Moreover, nilotinib combined with imatinib showed the same results as the regimen imatinib and everolimus, but tumor metabolism after treatment was stable and hence the FDG uptake reduction was less evident than with imatinib and everolimus. In general our report confirms the effect of nilotinib in GIST treatment, and no further preclinical studies of nilotinib as a single agent or combined with imatinib are necessary.