Dovitinib is an orally active small molecule that exhibits potent inhibitory activity against multiple receptor tyrosine kinases (RTK) involved in tumor growth and angiogenesis. Dovitinib strongly binds to fibroblast growth factor receptor 3 (FGFR3) and inhibits its phosphorylation, which may result in the inhibition of tumor cell proliferation and the induction of tumor cell death. In addition, this agent may inhibit other members of the RTK superfamily, including the vascular endothelial growth factor receptor; fibroblast growth factor receptor 1; platelet-derived growth factor receptor type 3; FMS-like tyrosine kinase 3; stem cell factor receptor (c-KIT); and colony-stimulating factor receptor 1; this may result in an additional reduction in cellular proliferation and angiogenesis, and the induction of tumor cell apoptosis. There are several ongoing Phase I/III clinical trials for dovitinib.

G749 is a Fms-like tyrosine receptor kinase 3 (FLT3) inhibitor and a promising next-generation drug candidate for the treatment of relapsed and refractory acute myeloid leukemia (AML) patients with various FLT3-ITD/FLT3-TKD mutants that shows the ability to overcome drug resistance. It demonstrated potent and sustained inhibition of the FLT3 wild type and mutants including FLT3-ITD, FLT3-D835Y, FLT3-ITD/N676D, and FLT3-ITD/F691L in cellular assays. G749 retained its inhibitory potency in various drug-resistance milieus such as patient plasma, FLT3 ligand surge, and stromal protection. It also displayed potent antileukemic activity in bone marrow blasts from AML patients regardless of FLT3 mutation status, including those with little or only minor responses to AC220 or PKC412. Oral administration of G749 yielded complete tumor regression and increased life span in animal models.

Famitinib, an orally active, small molecule, is a tyrosine kinase inhibitor against multiple targets, including vascular endothelial growth factor receptor 2/3, platelet-derived growth factor receptor, and stem cell factor receptor (c-kit). Jiangsu Hengrui Medicine Co is developing famitinib against a wide variety of advanced-stage solid cancers. Famitinib is participating in phase III clinical trials to evaluate its safety and efficacy in patients with advanced colorectal adenocarcinoma. The other phase III clinical trial for patients with non-squamous non-small cell lung cancer was terminated because of the difficulty in recruitment. In addition, the drug is involved in phase II clinical trials for the treatment of cervical cancer, endometrial cancer, fallopian tube cancer, gastrointestinal stromal tumors, nasopharyngeal cancer, and neuroendocrine tumors.

Crenolanib is an orally active, highly selective, small molecule, next generation inhibitor of platelet-derived growth factor receptor (PDGFR) tyrosine kinase. Crenolanib, manufactured by Arog Pharmaceuticals in Dallas, is taken orally with chemotherapy. The compound is currently being evaluated for safety and efficacy in clinical trials for various types of cancer, including acute myeloid leukemia (AML), gastrointestinal stromal tumor (GIST), and glioma. Crenolanib is an orally bioavailable, selective small molecule inhibitor of type III tyrosine kinases with nanomolar potencies against platelet-derived growth factor receptors (PDGFR) (isoforms PDGFRα and PDGFRβ) and Fms-related tyrosine kinase 3 (FLT3). Besides PDGFR and FLT3, crenolanib does not inhibit any other known receptor tyrosine kinase (RTK) (e.g. VEGFR and FGFR) or any other serine/threonine kinase (e.g., Abl, Raf) at clinically achievable concentrations. Preclinical trials have shown Crenolanib to be active in inhibiting both wild-type and mutant FLT3. Crenolanib is cytotoxic to the FLT3/ITD-expressing leukemia cell lines Molm14 and MV411, with IC50s of 7 nM and 8 nM, respectively. In immunoblots, crenolanib inhibited phosphorylation of both the wild-type FLT3 receptor (in SEMK2 cells) and the FLT3/ITD receptor (in Molm14 cells) in culture medium with IC50s of 1-3 nM. Importantly, the IC50 of crenolanib against the D835Y mutated form of FLT3 was 8.8 nM in culture medium. Furthermore, crenolanib had cytotoxic activity against primary samples that were obtained from patients who had developed D835 mutations while receiving FLT3 TKIs. In vitro, the IC50 of crenolanib for inhibition of FLT3/ITD in plasma was found to be 34 nM, indicating a relatively low degree of plasma protein binding. From pharmacokinetic studies of crenolanib in solid tumor patients, steady state trough plasma levels of roughly 500 nM were found to be safe and tolerable, suggesting that crenolanib could potentially inhibit the target in vivo. Crenolanib has no significant activity against c-KIT, which may be an advantage in that myelosuppression can be avoided.1Furthermore, there was no evidence of QTc prolongation in patients treated with crenolanib. In summary, crenolanib offers a number of advantages over other FLT3 TKIs. Clinical trials of crenolanib in AML patients with FLT3 activating mutations are being planned.