Flt-1 (IC50 = 4 nM); KDR (IC50 = 20 nM); PDGFRα (IC50 = 4 nM); FGFR1 (IC50 = 2 nM)
XL999 targets a spectrum of receptor tyrosine kinases (RTKs) involved in tumor angiogenesis and proliferation. It inhibits VEGFR2/KDR (IC₅₀ = 4 nM), Flt-1/VEGFR1 (IC₅₀ = 20 nM), FGFR1 (IC₅₀ = 4 nM), and PDGFRα (IC₅₀ = 2 nM). It also inhibits FGFR3, PDGFRβ, KIT, FLT3, FLT4, and SRC.

The source of tyrosine kinase-IN-1 was compound 8K [1].

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In vitro, XL999 is a multi-target tyrosine kinase inhibitor with potent activity against key RTKs. It has IC₅₀ values of 4 nM for KDR and FGFR1, 20 nM for Flt-1, and 2 nM for PDGFRα. The compound demonstrates excellent activity in target-specific cellular functional assays.

The PK profile of tyrosine kinase-IN-1 was reasonable (AUC(0–∞)=1.9, t1/2=4.6 h). In rats, it has a high oral bioavailability (F=63%) [1].

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In vivo activity data for XL999 are limited in the available literature. As a Spectrum Selective Kinase Inhibitor (SSKI), it inhibits RTKs implicated in the development and maintenance of tumor vasculature and in the proliferation of some tumor cells. Its multi-target profile suggests potential for anti-angiogenic and anti-tumor activity.

In vitro kinase inhibition assays for XL999 are performed using purified kinase enzymes. Kinase activity is measured using radiometric, fluorometric, or ELISA-based methods with peptide or protein substrates. The compound is incubated with the kinase and ATP, and the extent of phosphorylation is measured. IC₅₀ values are calculated from concentration-response curves.

In vitro cellular assays for XL999 are performed using cancer cell lines or endothelial cells. Cells are treated with the compound, and RTK-mediated signaling (e.g., phosphorylation of VEGFR, FGFR, or PDGFR) is measured by Western blotting. Cell proliferation, migration, and tube formation assays are used to assess the compound's anti-angiogenic and anti-proliferative effects.

In vivo animal experiments for XL999 are not extensively documented. As a potential anti-cancer agent, in vivo studies would typically involve administration to mouse xenograft models. The compound would be administered via intraperitoneal or oral routes, and efficacy would be assessed by measuring tumor volume reduction, angiogenesis markers, and RTK phosphorylation in tumor tissues.

The pharmacokinetic properties of XL999 have been characterized in part. The compound has a molecular weight of 445.53 and molecular formula C₂₆H₂₈FN₅O. It is soluble in DMSO but not in water. It has a purity of 99.01%. Further PK details, including half-life, bioavailability, and tissue distribution, are available from the manufacturer's data sheets.

Toxicological data for XL999 are not extensively reported. As a research-use compound, its safety profile has not been formally evaluated in comprehensive preclinical toxicology studies. The compound is intended for research purposes only and is not approved for human therapeutic use. Standard laboratory safety precautions should be followed when handling this compound.

[1]. The design, synthesis, and biological evaluation of potent receptor tyrosine kinase inhibitors. Bioorganic & Medicinal Chemistry Letters 22 (2012) 4979–4985.

XL999 holds promise for patients with lung cancer and acute myeloid leukemia. XL999 is a novel compound that inhibits multiple receptor tyrosine kinases (RTKs) with pro-growth and angiogenic properties, including FGFR 1/3, PDGFRα/β, VEGFR2/KDR, KIT, and FLT3. XL999 also inhibits FLT4 and SRC. XL999 has the potential to inhibit tumor growth—both directly through its novel effects on tumor cell proliferation and indirectly through inhibition of host angiogenesis. XL999 induces cell cycle arrest through a mechanism distinct from previously known mechanisms and exhibits broad antitumor activity in xenograft models.
XL999, an FGFR/VEGFR/PDGFR/FLT3/SRC inhibitor, is a small molecule inhibitor that inhibits multiple tyrosine kinases (TKs), including fibroblast growth factor receptor (FGFR), vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR), FMS-associated tyrosine kinase 3 (FLT3), and SRC, exhibiting potential antitumor activity. Upon administration, XL999 binds to these TKs and inhibits their activity, thereby preventing the activation of downstream signaling pathways and the proliferation of tumor cells overexpressing these TKs. FGFR, VEGFR, PDGFR, FLT-3, and SRC are upregulated in various cancer cell types and play key roles in tumor cell proliferation, angiogenesis, and metastasis.
Pharmaceutical Indications
Investigated for the treatment of cancer/tumor (not specified), lung cancer, and solid tumors.

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Mechanism of Action
XL999 is a potent receptor tyrosine kinase inhibitor. These kinases are involved in tumor angiogenesis and maintenance, as well as the proliferation of certain tumor cells. It inhibits FGFR1, FGFR3, RET, VEGFR2, and PDGFR, and is also a potent inhibitor of FLT3, an important driver of leukemia cell proliferation in some acute myeloid leukemia (AML) patients. XL999 exhibits excellent activity in target-specific cell function assays.

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XL999 is also known as Tyrosine kinase-IN-1. It is a multi-target receptor tyrosine kinase inhibitor with IC₅₀ values of 4 nM (KDR, FGFR1), 20 nM (Flt-1), and 2 nM (PDGFRα). It also inhibits FLT3, KIT, FGFR3, PDGFRβ, FLT4, and SRC. It is used in cancer research to study angiogenesis and tumor growth.

C26H28FN5O

445.5424

445.227

C, 70.09; H, 6.33; F, 4.26; N, 15.72; O, 3.59

705946-27-6

705946-27-6

10433653

Light brown to brown solid powder

1.3±0.1 g/cm3

1.652

2.59

3

5

5

33

736

0

N1C2=C(C=C(NC3CCN(CC)CC3)C=C2)/C(=C(\C2=CC=CC(F)=C2)/C2NC(C)=CN=2)/C1=O

DMQYDVBIPXAAJA-VHXPQNKSSA-N

InChI=1S/C26H28FN5O/c1-3-32-11-9-19(10-12-32)30-20-7-8-22-21(14-20)24(26(33)31-22)23(25-28-15-16(2)29-25)17-5-4-6-18(27)13-17/h4-8,13-15,19,30H,3,9-12H2,1-2H3,(H,28,29)(H,31,33)/b24-23-

(3Z)-5-[(1-ethylpiperidin-4-yl)amino]-3-[(3-fluorophenyl)-(5-methyl-1H-imidazol-2-yl)methylidene]-1H-indol-2-one

XL999; XL-999; XL 999

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

DMSO: ≥ 62.5 mg/mL (~140.3 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (4.67 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.08 mg/mL (4.67 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 20.8 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.

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 (Please use freshly prepared in vivo formulations for optimal results.)