Is Fingolimod Cell Cycle inhibitor Worth The Bucks?

The consensus at this time is to treat patient in a multidisciplinary approach based on biopsy margin, tumor size, mitotic rate, site, immunohistochemical staining, and mutational status. Most GIST patients will achieve the clinical benets with imatinib, but an estimated 10% will progress within 3 to 6 months of initiating therapy.

In the cases reviewed, 1 out of 5 GISTs in the stomach and the small intestine developed resistance/relapse to imatinib treatment within two years. Primary imatinib resistance is observed in roughly 10% of all genotypic subtypes of GIST. Most cases that show primary resistance are kit and PDGFRA wild type, those with kit exon 9 mutations Cell Cycle inhibitor and those with PDGFRA D824V mutation. Imatinib only binds to the inactive form of PDGFRA. Furthermore, the D824V mutation of PDGFRA results in change in the kinase activation loop which favors active conformation, thereby making it resistant to imatinib. In patients who do not harbor the PDGFRA or kit mutation, the mechanism of resistance is potentially a mutation in another alternate signaling pathway.

The median progression free survival and overall survival with sunitinib were signicantly longer for patients with secondary kit mutations in exon 13 or 14 than Cell Cycle inhibitor those with secondary kit mutations in exon 17 or 18. This correlates that sunitinib potentially inhibits the phosphorylation of KIT double mutation in ATP binding site but not in mutations of the activating loop. Sunitinib also has increased potency against imatinib resistant ATP binding pocket mutation but inferior potency against the activation loop. No case report of sunitinib resistance was reported in our review. Newer monoclonal antibodies are being developed for treatment of imitinib/sunitinib resistance GISTs. These include nilotinib, sorafenib, dovitinib, crenolanib, pazopanib, and dasatinib.

Dasatinib is structurally unrelated to imatinib, possibly demonstrating a higher anity to KIT. It inhibits Cell Cycle inhibitor KIT autophosphorylation and KIT dependent activation of downstream pathways. Preclinical cell studies indicate that dasatinib may inhibit the KIT D816V mutation that is resistant to imatinib.