LINIFANIB AGAINST RECEPTOR ENZYMES

Introduction: Small molecule multi-kinase receptors

The initiation of signaling cascades in most normal and tumor cell lines begin with the protein receptors on the surface of the cell membrane. Triggering a receptor by extracellular ligands induce dimerization and conformational changes in the trans membrane sub units of the receptor proteins. Such changes reveal tyrosine kinase binding domain within the cytosolic protein segments. Auto-phosphorylation activates the tyrosine kinase which in turn attracts proteins to complex. Phosphorylation of the tyrosine kinase binding domains of the complexed protein triggers release and the signal movement from membrane to cytosole. It his way further downstream targets are attracted, phosphorylated and released passing the signal to specific areas within the cell. The pathway ends when a cellular function such growth, differentiation and proliferation is induced. The two cell membrane receptors VEGFR and PDGFR are two of the most documented proteins. Inhibition of either of these two targets can induce various tumor reduction effects and apoptotic affects.

The Linifanib PDGFR inhibitor is a small molecule inhibitor that has been shown to have sensitivity for some of the isoforms of these pathway molecules. Preclinical and clinical evidence demonstrates significant activity in a variety of different metabolic disorders.

Linifanib: Properties and Availability

The Linifanib RTK inhibitor has been developed by several different compounds in the past and has been known by a variety of different code names, such as A741439, ABT-869 and RG3635. Currently developed by Abbott laboratories this molecule has demonstrated inhibitory ability against a variety of different kinases. The Linifanib structure is relatively simple based on urea with substitution by a fluoro-methyl phenyl and a phenyl indazol. Linifanib IC50 towards receptors FLT1&3 [1;2], CSF-1R [3] and VEGFR2 [4] averages at 4 nM, while sensitivity towards cKIT is slightly higher at 14 nM and PDGFRß at 66 nM. Two remaining activities at 180nM were determined for FLT4 and TIE2.Linifanib stability of the solid powder is specified as only 1 year expiration when stored at -20°C. Linifanib solubility is listed in the MSDS only for DMSO and a saturated solution can be achieved at approximately 20 mg/ml, this is significantly lower in solutions of aqueous buffers (~0.2 mg/ml). Linifanib suppliers market this molecule usually under the code ABT-869 but researchers can buy Linifanib for Linifanib price of approximately $210 for just 10 mg.

Linifanib: Preclinical investigation

Linifanib has been screened in a variety of cell lines demonstrating sensitivity in Endothelial cell and AML cells at an IC50 of approximately 1 nM. At a higher concentration (2-5 µM) sensitivity was observed for Colon , Fibro sarcoma, epidermoid carcinoma, small cell lung carcinoma [5] and breast carcinoma. However, in two varieties of colon and breast carcinoma (MDA-231 and DLD-1) cell lines no activity was seen at all, the two cell lines are related by the mutation of the p53 protein [6]. In addition activity in cell cultures murine and rat models have been used to test anti-tumor activity of Linifanib. Xenografts revealed significant inhibition of VEGFR1 inducing a increase in the apoptosis of tumor cells derived from a AML source [7]. Conversely murine and rodent models demonstrated an adverse effect for Linifanib in that increased hypertension induced cardiovascular damage, treatment with ACE inhibitors prevented hypertension effects but didn’t reduce the anti-tumor efficacy of the molecule [8]. In combination therapy with rapamycin Linifanib demonstrated synergistic effects with highly significant reduction in angiogenesis in hepatocellular carcinoma cell culture [9]. With the most toxicity for this molecule avoidable and much significant responses seen in vitro this molecule was advance to clinical trial status at phase I and II levels.

Linifanib: Clinical status

The Linifanib VEGFR inhibitor was first trialed in refractory solid tumors demonstrating stable diseases in 48% of patients treated. Continuous oral daily dosing demonstrated a highly significant reduction in angiogenesis effects [10]. At phase II level in advabced renal failure and non small cell lung cancer activity was observed to a marginal degree, altered dose scheduling was recommended for improvement to the treatment profile but results for this have not been report at this stage [11;12]. Linifanib clinical trials have been initiated by Abbott in non small cell lung cancer after failure of previous chemotherapy and in combination with carboplatin / paclitaxel. In renal cell carcinoma a phase II trial has been initiated after Sunitinib failure since previous phase I trials indicated a possible benefit to this approach. Further clinical trials have been started in solid tumors, investigating the effects of food / dietary factors on the pharmacokinetics of Linifanib, in acute myeloid leukemia carrying the FTL3-ITD mutated gene since preclinical evidence suggested this would be an effective patient subpopulation.

References

    1.    Zhou J, Khng J et al. In vivo activity of ABT-869, a multi-target kinase inhibitor, against acute myeloid leukemia with wild-type FLT3 receptor. Leuk Res 2008; 32(7):1091-1100.

    2.    Shankar DB, Li J et al. ABT-869, a multitargeted receptor tyrosine kinase inhibitor: inhibition of FLT3 phosphorylation and signaling in acute myeloid leukemia. Blood 2007; 109(8):3400-3408.

    3.    Guo J, Marcotte PA et al. Inhibition of phosphorylation of the colony-stimulating factor-1 receptor (c-Fms) tyrosine kinase in transfected cells by ABT-869 and other tyrosine kinase inhibitors. Mol Cancer Ther 2006; 5(4):1007-1013.

    4.    Zhou J, Goh BC et al. ABT-869, a promising multi-targeted tyrosine kinase inhibitor: from bench to bedside. J Hematol Oncol 2009; 2:33.

    5.    Ikeda AK, Judelson DR et al. ABT-869 inhibits the proliferation of Ewing Sarcoma cells and suppresses platelet-derived growth factor receptor beta and c-KIT signaling pathways. Mol Cancer Ther 2010; 9(3):653-660.

    6.    Albert DH, Tapang P et al. Preclinical activity of ABT-869, a multitargeted receptor tyrosine kinase inhibitor. Mol Cancer Ther 2006; 5(4):995-1006.

    7.    Zhou J, Khng J et al. In vivo activity of ABT-869, a multi-target kinase inhibitor, against acute myeloid leukemia with wild-type FLT3 receptor. Leuk Res 2008; 32(7):1091-1100.

    8.    Franklin PH, Banfor PN et al. Effect of the multitargeted receptor tyrosine kinase inhibitor, ABT-869 [N-(4-(3-amino-1H-indazol-4-yl)phenyl)-N'-(2-fluoro-5-methylphenyl)urea], on blood pressure in conscious rats and mice: reversal with antihypertensive agents and effect on tumor growth inhibition. J Pharmacol Exp Ther 2009; 329(3):928-937.

    9.    Jasinghe VJ, Xie Z et al. ABT-869, a multi-targeted tyrosine kinase inhibitor, in combination with rapamycin is effective for subcutaneous hepatocellular carcinoma xenograft. J Hepatol 2008; 49(6):985-997.

  10.    Wong CI, Koh TS et al. Phase I and biomarker study of ABT-869, a multiple receptor tyrosine kinase inhibitor, in patients with refractory solid malignancies. J Clin Oncol 2009; 27(28):4718-4726.

  11.    Tan EH, Goss GD et al. Phase 2 trial of Linifanib (ABT-869) in patients with advanced non-small cell lung cancer. J Thorac Oncol 2011; 6(8):1418-1425.

  12.    Tannir NM, Wong YN et al. Phase 2 trial of linifanib (ABT-869) in patients with advanced renal cell cancer after sunitinib failure. European Journal of Cancer 2011; 47(18):2706-2714.