6-(2-Aminoethyl)-6H-indolo[2,3-b]quinoxalines as Promising Compounds Capable of Binding to FLT3 (D835V) Kinase

Indolo[2,3-b]quinoxalines, along with their N-substituted derivatives, exhibit pronounced anticancer activity, although the mechanisms of their biological action may vary. Herein, a panel of sixty-five 6-(2-aminoethyl)-6H-indolo[2,3-b]quinoxaline derivatives comprising eight series with distinct amine moieties connected to the tetracyclic indoloquinoxaline core via a dimethylene linker was evaluated as drug-like candidates for kinase binding and cytotoxic activity. The ADME (Absorption, Distribution, Metabolism, and Excretion) properties of the compounds included in this set were preliminarily determined using the SwissADME tool. Analysis revealed that the library of quinoxaline derivatives largely complies with the drug-likeness rule for kinase-targeted compounds. As part of the biological screening, the compounds were initially tested on two cell lines MonoMac-6 and THP-1 (both derived from patients with acute monocytic leukemia) using sunitinib, a known antitumor agent acting as a multi-target receptor tyrosine kinase inhibitor, as a reference compound. Compound 3g, which demonstrated the highest activity in the cytotoxicity analysis (IC50 = 1.9 and 3.5 μM for the MonoMac-6 and THP-1 cell lines, respectively), was screened using the Eurofins DiscoverX scanEDGE panel, comprising 97 distinct kinases representing all known kinase families. Subsequently, the compound was tested using the Eurofins DiscoverX scanTK™ panel, covering 135 distinct receptor and non-receptor tyrosine kinases. Based on initial screening results, compound 3g exhibits relatively high binding activity against fourteen tyrosine kinases, including TYK2, ZAP70, eight mutant forms of ABL1, two mutant forms of FLT3, and one mutant form of ALK, and demonstrates relatively high binding selectivity with respect to non-mutant tyrosine kinases (S-score: 0.024). Secondary screening of nine selected analogs of compound 3g led to the identification of compound 3h, which demonstrates relatively high binding affinity for FLT3 (D835V) (Kd = 0.41 μM). Molecular modeling suggested modes of binding interaction of the compounds 3h and 3g in the FLT3 (D835V) catalytic site. Our results demonstrate that 6-(2-aminoethyl)-6H-indolo[2,3-b]quinoxaline derivatives could be potential candidates for developing anticancer drugs.