Pretreatment evaluation of fluorescence resonance energy transfer‐based drug sensitivity test for patients with chronic myelogenous leukemia treated with dasatinib

<jats:p>Tyrosine kinase inhibitors (<jats:styled-content style="fixed-case">TKI</jats:styled-content>) are used for primary therapy in patients with newly diagnosed <jats:styled-content style="fixed-case">CML</jats:styled-content>. However, a reliable method for optimal selection of a <jats:styled-content style="fixed-case">TKI</jats:styled-content> from the viewpoint of drug sensitivity of <jats:styled-content style="fixed-case">CML</jats:styled-content> cells has not been established. We have developed a <jats:styled-content style="fixed-case">FRET</jats:styled-content>‐based drug sensitivity test in which a CrkL‐derived fluorescent biosensor efficiently quantifies the kinase activity of <jats:styled-content style="fixed-case">BCR</jats:styled-content>‐<jats:styled-content style="fixed-case">ABL</jats:styled-content> of living cells and sensitively evaluates the inhibitory activity of a <jats:styled-content style="fixed-case">TKI</jats:styled-content> against <jats:styled-content style="fixed-case">BCR</jats:styled-content>‐<jats:styled-content style="fixed-case">ABL</jats:styled-content>. Here, we validated the utility of the <jats:styled-content style="fixed-case">FRET</jats:styled-content>‐based drug sensitivity test carried out at diagnosis for predicting the molecular efficacy. Sixty‐two patients with newly diagnosed chronic phase <jats:styled-content style="fixed-case">CML</jats:styled-content> were enrolled in this study and treated with dasatinib. Bone marrow cells at diagnosis were subjected to <jats:styled-content style="fixed-case">FRET</jats:styled-content> analysis. The Δ<jats:styled-content style="fixed-case">FRET</jats:styled-content> value was calculated by subtraction of <jats:styled-content style="fixed-case">FRET</jats:styled-content> efficiency in the presence of dasatinib from that in the absence of dasatinib. Treatment response was evaluated every 3 months by the <jats:italic><jats:styled-content style="fixed-case">BCR</jats:styled-content>‐<jats:styled-content style="fixed-case">ABL</jats:styled-content>1</jats:italic> International Scale. Based on the Δ<jats:styled-content style="fixed-case">FRET</jats:styled-content> value and molecular response, a threshold of the Δ<jats:styled-content style="fixed-case">FRET</jats:styled-content> value in the top 10% of <jats:styled-content style="fixed-case">FRET</jats:styled-content> efficiency was set to 0.31. Patients with Δ<jats:styled-content style="fixed-case">FRET</jats:styled-content> value ≥0.31 had significantly superior molecular responses (<jats:styled-content style="fixed-case">MMR</jats:styled-content> at 6 and 9 months and both <jats:styled-content style="fixed-case">MR</jats:styled-content>4 and <jats:styled-content style="fixed-case">MR</jats:styled-content>4.5 at 6, 9, and 12 months) compared with the responses in patients with Δ<jats:styled-content style="fixed-case">FRET</jats:styled-content> value <0.31. These results suggest that the <jats:styled-content style="fixed-case">FRET</jats:styled-content>‐based drug sensitivity test at diagnosis can predict early and deep molecular responses. This study is registered with <jats:styled-content style="fixed-case">UMIN</jats:styled-content> Clinical Trials Registry (<jats:styled-content style="fixed-case">UMIN</jats:styled-content>000006358).</jats:p>