Tandutinib (MLN518), a Potent FLT3 Inhibitor, Synergizes with Cytarabine and/or Daunorubicin in a Sequence-Independent Manner.
Authors: Schittenhelm Marcus M. , Yee Kevin W. , Kampa Kerstin M. , Heinrich Michael C. 
Published: April 2020

Abstract
FLT3 kinase inhibitors display promising pre-clinical efficacy in a variety of in vitro and animal models of FLT3-ITD+ AML. Tandutinib is a 4-piprazinylquinazoline compound that is a potent inhibitor of type III RTKs with a cellular IC50 of ~200 nM for FLT3. In a phase 2 study, Tandutinib demonstrated anti-leukemic activity in approximately half of the evaluable patients, although there were no partial or complete remissions. Therefore, optimal use of like Tandutinib will likely require combination therapy with standard cytotoxic agents such as cytarabine (Cy) and an anthracycline (e.g. daunorubicin, Dn). Notably, single agent Tandutinib has not been associated with myelosuppression, mucositis or cardiac toxicity--the dose limiting toxicities of AML chemotherapy. To determine the feasibility of combining Tandutinib and chemotherapy, we tested Tandutinib in combination with Cy and/or Dn. For our experiments, we utilized three cell lines containing FLT3 ITD mutations: a BaF3 cell line transduced with an ITD mutant FLT3 as well as MV 4–11 and MOLM 14 cell lines which have naturally occurring FLT3 ITD mutations. Data was analyzed using the statistical methods of Chou and Talalay to calculate combination indices (CI) for drug mixtures performed in a fixed dilution pattern. In all cell lines, calculated combination indices for inhibition of cellular proliferation and induction of apoptosis were much less than one, indicating a synergistic effect of combining Tandutinib with Cy or Dn. In addition, the combination of Tandutinib with Cy and Dn was also markedly synergistic. These results were confirmed using primary AML blasts (FLT3 ITD+). All of the above studies were performed using simultaneous treatment with Tandutinib and Cy and/or Dn. Previous in vitro studies utilizing a structurally unrelated FLT3 inhibitor, Lestaurtinib (CEP-701), demonstrated the potential importance of treatment sequencing for optimal killing of AML cells. Notably, treatment with Lestaurtinib with or following chemotherapy was found to be synergistic, whereas treatment with Lestaurtinib followed by chemotherapy was generally antagonistic. Therefore, we next determined whether sequencing of Tandutinib and chemotherapy had any effect on the efficacy of combination therapy. For these experiments, we tested two different sequencing regimens: monotherapy treatment with Tandutinib for 24 hours with the addition of Cy or Dn for an additional 48 hours; ormonotherapy with Cy or Dn for 24 hours with the addition of Tandutinib for an additional 48 hours. Both regimens produced a synergistic effect and had comparable efficacy. Therefore, unlike Lestaurtinib, the synergistic effect of Tandutinib and Cy/Dn appears to be independent of the sequence of drug administration. These data suggest that addition of Tandutinib to agents used in induction chemotherapy for AML could result in enhanced antileukemic effects. Our synergy experiments also suggest that combined use of Tandutinib and chemotherapy may allow dose reduction of chemotherapy (with resultant decreased side effects) without loss of antileukemic activity. Such a combined treatment approach may be particularly desirable for elderly AML patients who often have poor tolerance of standard AML chemotherapy regimens. Currently, the combination of Tandutinib + standard induction chemotherapy is being tested in a phase I/II study for treatment of newly diagnosed AML.