Fedratinib (TG101348)

TG-101348 also significantly inhibits JAK2 V617F, Flt3, and Ret with IC50 of 3 nM, 15 nM, and 48 nM, respectively. TG101348 has an IC50 ~300-fold higher for the closely related JAK3 and is a less potent inhibitor of the JAK1 and TYK2 family members. TG101348 inhibits proliferation of a human erythroblast leukemia (HEL) cell line that harbors the JAK2V617F mutation, as well as a murine pro-B cell line expressing human JAK2V617F (Ba/F3 JAK2V617F), with IC50 of 305 nM and 270 nM, respectively. TG-101348 also inhibits proliferation of parental Ba/F3 cells to a comparable level, with IC50 of ~420 nM. TG101348 treatment reduces STAT5 phosphorylation at concentrations that parallel the concentrations required to inhibit cell proliferation. TG101348 induces apoptosis in both HEL and Ba/F3 JAK2V617F cells in a dose-dependent manner. TG101348 does not show proapoptotic activity in control normal human dermal fibroblasts at concentrations up to 10 μM, and the antiproliferative IC50 against fibroblasts is >5 μM. ^[1] TG101348 treatment decreases GATA-1 expression, which is associated with erythroid-skewing of JAK2V617F⁺ progenitor differentiation, and inhibits STAT5 as well as GATA S310 phosphorylation. ^[2] TG101348 inhibits the proliferation of HMC-1.1 (KITV560G) cells, with somewhat lower potency than HMC-1.2 (KITD816V, KITV560G) cells, with IC50 of 740 nM and 407 nM, respectively. ^[3]

Approximately 2 × 10³ cells are plated into microtiter-plate wells in 100 μL RPMI-1640 growth media with indicated concentrations of inhibitor. Following 72 hours incubation with TG101348, 50 μL of XTT dye are added to each well and incubated for 4 hours in a CO₂ incubator. The colored formazan product is measured by spectrophotometry at 450 nm with correction at 650 nm. The concentration in which 50% of the effect (i.e., inhibition of proliferation) is observed (IC50) is determined using the GraphPad Prism 4.0 software. All experiments are performed in triplicate, and the results are normalized to growth of untreated cells. Induction of apoptosis of EpoBa/F3 JAK2V617F, Ba/F3p210, HEL, and K562 cells is determined by DNA fragmentation with DMSO and increasing concentrations of TG101348.

TG101348 has potential for efficacious treatment of JAK2V617F-associated myeloproliferative diseases (MPD). In treated animals, there is a statistically significant reduction in hematocrit and leukocyte count, a dose-dependent reduction/elimination of extramedullary hematopoiesis, and, at least in some instances, evidence for attenuation of myelofibrosis, correlated with surrogate endpoints, including reduction/elimination of JAK2V617F disease burden, suppression of endogenous erythroid colony formation, and in vivo inhibition of JAK-STAT signal transduction. There are no apparent toxicities and no effect on T cell number. ^[1] Oral administration of TG101348 (120 mg/kg) significantly inhibits PV progenitor erythroid differentiation in vivo. ^[2]