Quizartinib (AC220) is an orally bioavailable, small molecule receptor tyrosine kinase inhibitor that is being developed by Daiichi Sankyo Company (previously Ambit Biosciences) and Astellas Pharma as a treatment for acute myeloid leukaemia (AML), acute lymphoblastic leukaemia (ALL) and advanced solid tumours. The highest affinity target identified for Quizartinib was FLT3. The only other kinases with binding constants within 10-fold that for FLT3 were the closely related receptor tyrosine kinases KIT, PDGFRA, PDGFRB, RET, and CSF1R. Kinase inhibition of (mutant) KIT, PDGFR and FLT3 isoforms by quizartinib leads to potent inhibition of cellular proliferation and induction of apoptosis in in vitro leukemia models as well as in native leukemia blasts treated ex vivo.

Ripretinib (DCC-2618) is an investigational, orally available switch control kinase inhibitor being developed for the treatment of gastrointestinal stromal tumors (GIST), advanced systemic mastocytosis (ASM), gliomas, and other solid tumors driven by tyrosine-protein kinase KIT (KIT) or platelet-derived growth factor alpha (PDGFRα) kinase. Ripretinib acts by forcing the activation loop (or activation "switch") of kinases into an inactive conformation and is a type II kinase inhibitor demonstrated to broadly inhibit activation loop mutations in KIT and PDGFRA, previously thought only achievable with type I inhibitor. Ripretinib is developed by the company Deciphera and is being investigated in phase 3 clinical trials for the treatment of GIST, ASM and other tumors.

Pazopanib (VOTRIENT) is an orally bioavailable multi-targeted tyrosine kinase receptor inhibitor. Pazopanib inhibits vascular endothelial growth factor receptor (VEGFR)-1, VEGFR-2, VEGFR-3, platelet-derived growth factor receptor (PDGFR)-α and -β, fibroblast growth factor receptor (FGFR) -1 and -3, cytokine receptor (Kit), interleukin-2 receptor inducible T-cell kinase (Itk), leukocyte-specific protein tyrosine kinase (Lck), and transmembrane glycoprotein receptor tyrosine kinase (c-Fms). In an vitro study, pazopanib exerted anti-tumor effect through mechanisms including the Raf-MAPK/ERK (MEK)-extracellular signal-regulated kinase (ERK) pathway. It has good oral exposure and inhibits angiogenesis and tumor growth in mice. Pazopanib (VOTRIENT) was developed by GlaxoSmithKline for the treatment of solid tumours and age-related macular degeneration. However, Novartis acquired all the rights to the drug from GlaxoSmithKline. Pazopanib (VOTRIENT) is indicated for the treatment of patients with advanced renal cell carcinoma and advanced soft tissue sarcoma.

Sunitinib (marketed as Sutent by Pfizer, and previously known as SU11248) is an oral, small-molecule, multi-targeted receptor tyrosine kinase inhibitor that was approved by the FDA for the treatment of renal cell carcinoma (RCC) and imatinib-resistant gastrointestinal stromal tumor. Sunitinib was evaluated for its inhibitory activity against a variety of kinases and was identified as an inhibitor of platelet-derived growth factor receptors (PDGFRa and PDGFRb), vascular endothelial growth factor receptors (VEGFR1, VEGFR2, and VEGFR3), stem cell factor receptor (KIT), Fms-like tyrosine kinase-3 (FLT3), colony-stimulating factor receptor Type 1 (CSF-1R), and the glial cell-line derived neurotrophic factor receptor (RET). Sunitinib adverse events are considered somewhat manageable and the incidence of serious adverse events low. The most common adverse events associated with sunitinib therapy are fatigue, diarrhea, nausea, anorexia, hypertension, yellow skin discoloration, hand-foot skin reaction, and stomatitis. In the placebo-controlled Phase III GIST study, adverse events which occurred more often with sunitinib than placebo included diarrhea, anorexia, skin discoloration, mucositis/stomatitis, asthenia, altered taste, and constipation. Dose reductions were required in 50% of the patients studied in RCC in order to manage the significant toxicities of this agent.

Imatinib (GLEEVEC®) is a tyrosine kinase inhibitor and antineoplastic agent that inhibits the BCR-ABL tyrosine kinase, the constitutive abnormal tyrosine kinase created by the Philadelphia chromosome abnormality in chronic myeloid leukaemia (CML). It inhibits proliferation and induces apoptosis in BCR-ABL positive cell lines as well as fresh leukemic cells from Philadelphia chromosome positive CML. Imatinib (GLEEVEC®) inhibits colony formation in assays using ex vivo peripheral blood and bone marrow samples from CML patients. It is also an inhibitor of the receptor tyrosine kinases for platelet-derived growth factor (PDGF) and stem cell factor (SCF), c-kit, and inhibits PDGF- and SCF-mediated cellular events. In vitro, imatinib (GLEEVEC®) inhibits proliferation and induces apoptosis in gastrointestinal stromal tumor (GIST) cells, which express an activating c-kit mutation.

Telatinib (Bay-579352) developed by Bayer is an orally available and highly potent inhibitor of tyrosine kinases VEGFR2,VEGFR3, PDGFR and c-Kit. Telatinib is a potent inhibitor of angiogenesis. Telatinib caused a significant decrease in endothelium-dependent and endothelium-independent vasodilation. Telatinib demonstrates anti-tumor activity in various cancer models. Telatinib is ready for phase III clinical trials for the treatment of gastric cancer. In 2010, it has been granted orphan drug status by the FDA. Most frequent adverse events were pain, nausea, voice changes and fatigue.

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.

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.

Lucitanib (E-3810) is a novel multi-kinase inhibitor currently in clinical trials for its anti-angiogenic and anti-tumor activity. A Phase I/IIa clinical trial of lucitanib was initiated in 2010 and has demonstrated multiple objective responses in FGFR1 gene-amplified breast cancer patients, and objective responses were also observed in patients with tumors often sensitive to VEGFR inhibitors, such as renal cell and thyroid cancer. Lucitanib is an oral, potent inhibitor of the tyrosine kinase activity of fibroblast growth factor receptors 1 through 3 (FGFR1-3), vascular endothelial growth factor receptors 1 through 3 (VEGFR1-3) and platelet-derived growth factor receptors alpha and beta (PDGFR alpha-beta). The most common adverse events were hypertension, asthenia, and proteinuria.

Amuvatinib (formerly known as MP470) is an oral multi-targeted tyrosine kinase inhibitor, which play critical roles in transducing growth signals to cancer cells. It suppresses c-MET, c-RET and the mutant forms of cKIT, PDGFR and FLT3. It also disrupts DNA repair likely through suppression of homologous recombination protein Rad51, an important survival pathway in many human cancers. In vitro and in vivo data have demonstrated amuvatinib synergy with DNA damaging agents including etoposide and doxorubicin. Overall, in the amuvatinib clinical development program, over 200 subjects were exposed to at least one dose of amuvatinib. In the Phase 1b clinical study in combination with carboplatin and etoposide, responses in small cell lung cancer (SCLC), neuroendocrine as well as other tumor types were observed. Human pharmacokinetic data suggest that co-administration of amuvatinib did not alter exposures of standard of care agents including carboplatin, etoposide, doxorubicin, paclitaxel, topotecan or erlotinib as measured by overall exposure. In the first-in-human study, durable clinical benefit was observed in the gastrointestinal stromal tumors (GIST) with modulation of Rad51 observed in skin punch biopsies. In clinical trials, amuvatinib has demonstrated a wide therapeutic window and shows minimal toxicity in the expected therapeutic dose range, despite suppressing several signaling pathways within cells. However, in spite of this, this drug was discontinued, because it was not pre-specified primary endpoints in the clinical proof of concept (cPOC) stage. But the combination of MP470 and Erlotinib, which target the HER family/PI3K/Akt pathway may represent a novel therapeutic strategy for prostate cancer.