Inhibition of insulin-like growth factor I receptor autophosphorylation by novel 6-5 ring-fused compounds

Novel 5,6-disubstituted pyrrolo[2,3-d]pyrimidine derivatives as broad spectrum antiproliferative agents: Synthesis, cell based assays, kinase profile and molecular docking study

Two new series of 5-subtituted and 5,6-disubstituted pyrrolo[2,3-d]pyrimidine octamides (4a-o and 6a-g) and their corresponding free amines 5a-m and 7a-g have been synthesized and biologically evaluated for their antiproliferative activity against three human cancer cell lines. The 5,6-disubstituted octamides 6d-g as well as the amine derivative 7b have shown the best anticancer activity with single digit micromolar GI₅₀ values over the tested cancer cells, and low cytotoxic effects (GI₅₀ > 10.0 µM) against HFF-1 normal cell. A structure activity relationship (SAR) study has been established and disclosed that terminal octamide moiety at C2 as well as disubstitution with fluorobenzyl piperazines at C5 and C6 of pyrrolo[2,3-d]pyrimidine are the key structural features prerequisite for best antiproliferative activity. Moreover, the most active member 6f was tested for its antiproliferative activity over a panel of 60 cancer cell lines at NCI, and exhibited distinct broad spectrum anticancer activity with submicromolar GI₅₀ and TGI values over multiple cancer cells. Kinase profile of compound 6f over 53 oncogenic kinases at 10 µM concentration showed its highly selective inhibitory activity towards FGFR4, Tie2 and TrkA kinases. The observed activity of 6f against TrkA (IC₅₀ = 2.25 µM), FGFR4 (IC₅₀ = 6.71 µM) and Tie2 (IC₅₀ = 6.84 µM) was explained by molecular docking study, which also proposed that 6f may be a type III kinase inhibitor, binding to an allosteric site rather than kinase hinge region. Overall, compound 6f may serve as a promising anticancer lead compound that could be further optimized for development of potent anticancer agents.

Factors influencing the inhibition of protein kinases

The protein kinase field is a very active research area in the pharmaceutical industry and many activities are ongoing to identify inhibitors of these proteins. The design of new chemical entities with improved pharmacological properties requires a deeper understanding of the factors that modulate inhibitor-kinase interactions. In this report, we studied the effect of two of these factors--the magnesium ion cofactor and the protein substrate--on inhibitors of the type I insulin-like growth factor receptor. Our results show that the concentration of magnesium ion influences the potency of adenosine triphosphate (ATP) competitive inhibitors, suggesting an explanation for the observation that such compounds retain their nanomolar potency in cells despite the presence of millimolar levels of ATP. We also showed that the peptidic substrate affects the potency of these inhibitors in a different manner, suggesting that the influence of this substrate on compound potency should be taken into consideration during drug discovery.

Marine algae: natural product source for gastrointestinal cancer treatment

Among marine organisms, marine algae are rich sources of structurally diverse bioactive compounds with various biological activities. In order to survive in a highly competitive environment, freshwater or marine algae have to develop defense strategies that result in a tremendous diversity of compounds from different metabolic pathways. Recently, their importance as a source of novel bioactive substances is growing rapidly and many reports have been published about isolated compounds from algae with biological activities. Many researchers reported anticancer activity of the compounds isolated from marine algae. Gastrointestinal tract cancer is one of the most frequent death causes of cancer in men and women. Especially stomach cancer and colon cancer are the second and third common cancer type in the world after lung cancer. Hence investigation of bioactive compounds against gastrointestinal cancer cells has recently become an important field for researchers.

Allosteric IGF-1R Inhibitors

Targeting allosteric protein sites is a promising approach to interfere selectively with cellular signaling cascades. We have discovered a novel class of allosteric insulin-like growth factor-I receptor (IGF-1R) inhibitors. 3-Cyano-1H-indole-7-carboxylic acid {1-[4-(5-cyano-1H-indol-3-yl)butyl]piperidin-4-yl}amide (10) was found with nanomolar biochemical, micromolar, cellular IGF-1R activity and no relevant interference with cellular insulin receptor signaling up to 30 μM. The allosteric binding site was characterized by X-ray crystallographic studies, and the structural information was used to explain the unique mode of action of this new class of inhibitors.

Design, synthesis and biological evaluation of substituted pyrrolo[2,3-d]pyrimidines as multiple receptor tyrosine kinase inhibitors and antiangiogenic agents

Direct and indirect involvement of receptor tyrosine kinases (RTKs) in tumor growth and metastasis makes them ideal targets for anticancer therapy. A paradigm shift from inhibition of single RTK to inhibition of multiple RTKs has been recently demonstrated. We designed and synthesized eight N(4)-phenylsubstituted-6-(2-phenylethylsubstituted)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamines as homologated series of our previously published RTK inhibitors. We reasoned that increased flexibility of the side chain, which determines potency and selectivity, would improve the spectrum of RTK inhibition. These compounds were synthesized using a bis-electrophilic cyclization to afford substituted pyrrolo[2,3-d]pyrimidines followed by chlorination and substitution at the 4-position with various anilines. Five additional compounds of this series were previously reported by Gangjee et al.(1) with activities against IGFR only. Their synthesis, characterization and biological activities against a variety of other RTKs are reported in this study for the first time. The biological evaluation, in whole cell assays, showed several analogs had remarkable inhibitory activity against epithelial growth factor receptor (EGFR), vascular endothelial growth factor receptor-1 (VEGFR-1), platelet-derived growth factor receptor-beta (PDGFR-beta), the growth of A431 cells in culture, and in the chicken embryo chorioallantoic membrane (CAM) angiogenesis assay. The inhibitory data against the RTKs in this study demonstrate that variation of the 6-ethylaryl substituents as well as the N(4)-phenyl substituents of these analogs does indeed control both the potency and specificity of inhibitory activity against RTKs. In addition, homologation of the chain length of the 6-substituent from a methylene to an ethyl increases the spectrum of RTK inhibition. New multi-RTK inhibitors (8, 12) and potent inhibitors of angiogenesis (15, 19) were identified with the best compound, N(4)-(3-trifluromethylphenyl)-6-(2-phenylethyl)-7H-pyrrolo[2,3-d]pyrimidine-2,4-diamine (15), with an IC(50) value of 30nM in the CAM angiogenesis inhibition assay.

Reactivation of the insulin-like growth factor-II signaling pathway in human hepatocellular carcinoma

Constitutive activation of the insulin-like growth factor (IGF)-signaling axis is frequently observed in human hepatocellular carcinoma (HCC). Especially the overexpression of the fetal growth factor IGF-II, IGF-Ireceptor (IGF-IR), and cytoplasmic downstream effectors such as insulin-receptor substrates (IRS) contribute to proliferation, anti-apoptosis, and invasive behavior. This review focuses on the relevant alterations in this signaling pathway and independent in vivo models that support the central role IGF-II signaling during HCC development and progression. Since this pathway has become the center of interest as a target for potential anti-cancer therapy in many types of malignancies, various experimental strategies have been developed, including neutralizing antibodies and selective receptor kinase inhibitors, with respect to the specific and efficient reduction of oncogenic IGF-II/IGF-IR-signaling.

1,3-Disubstituted-imidazo[1,5-a]pyrazines as insulin-like growth-factor-I receptor (IGF-IR) inhibitors

A series of novel 8-amino-1,3-disubstituted-imidazo[1,5-a]pyrazines was designed and synthesized as IGF-IR inhibitors.

Proliferating endothelial cell-specific expression of IGF-I receptor ribozyme inhibits retinal neovascularization

Insulin-like growth factor-I (IGF-I) and its receptor (IGF-IR) are essential for normal ocular development and are expressed in numerous ocular cell types including lens epithelial cells, retinal pigment epithelial cells, Müller cells and endothelial cells. Endothelial cell proliferation is a common feature of proliferative retinopathies and involves abnormal growth of blood vessels within and on the surface of the retina. In an effort to inhibit the formation of these aberrant blood vessels, we cloned an IGF-IR ribozyme into an expression vector that limits expression of the ribozyme to proliferating endothelial cells. An endothelin enhancer and Cdc6 promoter chimera drives expression of the IGF-IR ribozyme. This promoter limited retinal expression of the reporter gene to proliferating endothelial cells in two mouse models of proliferative retinopathy. In addition, expression of the IGF-IR ribozyme by this promoter inhibited aberrant retinal angiogenesis in both models while preserving normal vessels. These results demonstrate the feasibility of IGF-IR ribozyme expression in a selective manner for safer treatment of abnormal angiogenesis associated with retinopathy.

Role of the activation loop tyrosines in regulation of the insulin-like growth factor I receptor-tyrosine kinase

The tyrosine kinase activity of insulin-like growth factor I receptor (IGF1R) is under tight control. Ligand binding to the extracellular portion of IGF1R stimulates autophosphorylation at three sites (Tyr1131, Tyr1135, and Tyr1136) in the activation loop within the tyrosine kinase catalytic domain. Autophosphorylation at all three sites is required for maximum enzyme activity, and for IGF1-stimulated cellular activity of the receptor. Previous studies have not clarified the contributions of the individual tyrosines to enzymatic activation. Here, we produced single Tyr-to-Phe mutations at these positions, and compared activities of the purified kinase domains (unphosphorylated and phosphorylated) with wild-type IGF1R. Rates of autophosphorylation of the three mutants were more rapid than for wild-type IGF1R; this was most apparent for the Y1135F mutant. Substrate phosphorylation studies on the unphosphorylated forms of IGF1R confirmed that the value of Vmax for Y1135F was elevated relative to wild-type IGF1R, consistent with a disruption of an autoinhibitory interaction. In contrast, activity measurements on the fully phosphorylated enzymes indicated that kcat/Km values were lowered relative to wild-type IGF1R; this effect was most dramatic for Y1136F. We confirmed these findings using limited proteolysis and tryptophan fluorescence experiments. The results demonstrate that Tyr1135 plays a particularly important role in stabilizing the autoinhibited conformation of the activation loop, while Tyr1136 plays the key role in stabilizing the open, activated conformation of IGF1R.

Blocking the insulin-like growth factor-I receptor as a strategy for targeting cancer

Clear links between cancer and cellular signaling triggered by the insulin-like growth factor-I (IGF-I) receptor (IGF-IR) and its cognate ligands (IGF-I and IGF-II) have been reported throughout the past two decades. Experimental results suggest that the pharmaceutical targeting of this signaling pathway could be beneficial for the treatment of cancer. Here, more recent advances towards potentially clinically viable strategies to interfere with the function of IGF-IR will be discussed.