Updated project metadata. Abnormalities in the FLT3 signaling pathway play an integral role in AML disease relapse and drug resistance. Developing new and specific FLT3 tyrosine kinase inhibitors for use in combination to induction therapy is an important step to reduce disease relapse and achieve clinical remission. To develop potent FLT3 TKI requires sensitive in vitro assay that depended on efficient FLT3 artificial substrates, which there are none reported for FLT3 WT and kinase variants. The kinase assay linked with phosphoproteomics was applied as a high throughput technique to increase the known FLT3 kinase substrates (WT, ITD and D835Y) that were used to identify the FLT3 kinase variant’s preferred kinase sequence using the KINATEST-ID substrate predictive pipeline. The identified substrate sequence was used to synthesize and validate pan-FLT3 artificial substrates to monitor in vitro kinase activity in the presence of clinically relevant FLT3 TKI.