Effects of the FLT3 Inhibitor PKC 412 in Combination with Cytostatic Drugs In Vitro in Acute Myeloid Leukemia.

FLT3 is a member of the class III tyrosine kinase receptor family. Interaction with its ligand results in reactions that involve different signalling pathways in the cell. A majority of acute myeloid leukemias (AML) express FLT3. FLT3 is mutated and activated in about 30% of all patients with AML. The new compound PKC412 was found to specifically an potently inhibit the growth of leukemic cell lines with a FLT3 mutation.

In the first part of this study the primary objective was to evaluate the in vitro effect of the combination of PKC412 and ara-C focusing on the timing of the two drugs. Samples from 21 patients with AML have been included. IC50 curves for PKC 412 curves were obtained to find appropriate concentrations for the study. Two different in vitro models were used. In the 4+3 model the incubation time for the first drug was 4 days and the second drug was added after 1 day. In the 2+2 model the cells were incubated for 2 days with the first drug, then centrifuged and resuspended and incubated with the second drug for another 2 days. The FLT3 status was analysed with PCR and the ATP bioluminiscens method was used to determine viable cells after the incubations.

The preliminary results show that most of the possible combinations of the 2 drugs had an additive effect. In the 2+2 model 2 days with ara-C 0,5 m M followed by 2 days with PKC 0,2 m M resulted in a synergistic effect in the AML patient cells with FLT3-ITD. We also found a synergistic effect in the FLT3 mutated cells when PKC412 0,2 m M and daunorubicin 0,15 m M was combined in a 4 days incubation

Our results suggest that the timing of PKC412 in combination with cytostatic drugs can influence the effect. The timing of the drugs may be of importance in the designing of future clinical trials of PKC412 in AML patients.