Novel approaches to the development of tyrosine kinase inhibitors and their role in the fight against cancer

Identification of novel c-Kit inhibitors from natural sources using virtual screening and molecular dynamics simulations

The Mast/Stem cell growth factor receptor Kit (c-Kit), a Proto-oncogene c-Kit, is a tyrosine-protein kinase involved in cell differentiation, proliferation, migration, and survival. Its role in developing certain cancers, particularly gastrointestinal stromal tumors (GISTs) and acute myeloid leukemia (AML), makes it an attractive therapeutic target. Several small molecule inhibitors targeting c-Kit have been developed and approved for clinical use. Recent studies have focused on identifying and optimizing natural compounds as c-Kit inhibitors employing virtual screening. Still, drug resistance, off-target side effects, and variability in patient response remain significant challenges. From this perspective, phytochemicals could be an important resource for discovering novel c-Kit inhibitors with less toxicity, improved efficacy, and high specificity. This study aimed to uncover possible c-Kit inhibitors by utilizing a structure-based virtual screening of active phytoconstituents from Indian medicinal plants. Through the screening stages, two promising candidates, Anilinonaphthalene and Licoflavonol, were chosen based on their drug-like features and ability to bind to c-Kit. These chosen candidates were subjected to all-atom molecular dynamics (MD) simulations to evaluate their stability and interaction with c-Kit. The selected compounds Anilinonaphthalene from Daucus carota and Licoflavonol from Glycyrrhiza glabra showed their potential to act as selective binding partners of c-Kit. Our results suggest that the identified phytoconstituents could serve as a starting point to develop novel c-Kit inhibitors for developing new and effective therapies against multiple cancers, including GISTs and AML. The use of virtual screening and MD simulations provides a rational approach to discovering potential drug candidates from natural sources.Communicated by Ramaswamy H. Sarma.

Current progress and open challenges for applying tyrosine kinase inhibitors in osteosarcoma

Osteosarcoma (OS) is a mesenchymal-origin tumor that constitutes the most common primary malignant bone tumor. The survival rate of the patients has significantly improved since the introduction of neoadjuvant chemotherapy and extensive resection, but it has stagnated in recent 40 years. Tyrosine kinase inhibitors (TKIs) have played a key part in the treatment of malignant tumors. In advanced OS, TKIs including anlotinib, apatinib, sorafenib, etc. have significantly improved the progression-free survival of patients, while the overall survival remains unchanged. The main reason is the rapid and inevitable progress of acquired drug resistance of OS. However, as the application of TKIs in OS and other tumors is still in the exploratory phase, its drug resistance mechanism and corresponding solutions are rarely reported. Hence, in this review, we summarize knowledge of the applications of TKIs, the mechanism of TKIs resistance, and the attempts to overcome TKIs resistance in OS, which are the three potentially novel insights of TKIs in OS. Because most evidence is derived from studies using animal and cell models, we also reviewed clinical trials and related bioinformatics data available in public databases, which partially improved our understanding of TKIs applications.

Role of inflammation and oxidative stress in chemotherapy-induced neurotoxicity

Chemotherapeutic agents may adversely affect the nervous system, including the neural precursor cells as well as the white matter. Although the mechanisms are not completely understood, several hypotheses connecting inflammation and oxidative stress with neurotoxicity are now emerging. The proposed mechanisms differ depending on the class of drug. For example, toxicity due to cisplatin occurs due to activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), which alters hippocampal long-term potentiation. Free radical injury is also involved in the cisplatin-mediated neurotoxicity as dysregulation of nuclear factor erythroid 2-related factor 2 (Nrf2) has been seen which protects against the free radical injury by regulating glutathione S-transferases and hemeoxygenase-1 (HO-1). Thus, correcting the imbalance between NF-κB and Nrf2/HO-1 pathways may alleviate cisplatin-induced neurotoxicity. With newer agents like bortezomib, peripheral neuropathy occurs due to up-regulation of TNF-α and IL-6 in the sensory neurons. Superoxide dismutase dysregulation is also involved in bortezomib-induced neuropathy. This article reviews the available literature on inflammation and oxidative stress in neurotoxicity caused by various classes of chemotherapeutic agents. It covers the conventional medicines like platinum compounds, vinca alkaloids, and methotrexate, as well as the newer therapeutic agents like immunomodulators and immune checkpoint inhibitors. A better understanding of the pathophysiology will lead to further advancement in strategies for management of chemotherapy-induced neurotoxicity.

Recently approved treatment options for patients with metastatic triple-negative and HER2-neu-positive breast cancer

Breast cancer (BC) is the most common cancer affecting women worldwide. In 2021, the estimated number of new breast cancer cases was 281 550 and about 43 500 women died from metastatic breast cancer (mBC). For women aged 20-59 years, mBC remains the leading cause of cancer death and is, therefore, an important public health concern. Only 5% of women initially present with metastatic disease. Approximately 20% of patients presenting with local or locoregional disease progress to mBC despite adjuvant therapy. Inspite of all the medicosurgical advancements, the overall prognosis for patients diagnosed with mBC remains poor, with median overall survival of approximately 31 months, although this varies based on tumor biology. In recent years, there has been significant progress in developing immunotargeted therapies such as antihuman epidermal growth factor receptor 2 (anti-HER2) or check point inhibitors that confirmed to have dramatically improve the prognosis of mBC, a historically unfavorable disease subset. Even with the major progress that has been made in understanding the biology of BC, challenges such as resistance frequency to therapies, unknown efficacy, concerns for safety of drug combination and toxicities still remain high. Therefore, a new targeted and more selective treatment approaches are the need of the hour. In this review, we aim to outline the most recently approved medications in treatment of Her2-positive and triple-negative breast cancers.

A concise review on tyrosine kinase targeted cancer therapy

Abstract:

The tyrosine kinase (TK) family is considered one of the important family members of the kinase family due to its important role in various cellular processes like cell growth, cell differentiation, apoptosis, etc. Mutation, overexpression, and dysfunction of tyrosine kinase receptors lead to the development of malignancy; thus, they are considered as one of the important targets for the development of anti-cancer molecules. The tyrosine kinase family is majorly divided into two classes; receptor and non-receptor tyrosine kinase. Both of the classes have an important role in the development of tumour cells. Currently, there are more than 40 FDA-approved tyrosine kinase inhibitors, which are used in the treatment of various types of cancers. Tyrosine kinase inhibitors mainly block the phosphorylation of tyrosine residue of the corresponding kinase substrate and so activation of downstream signalling pathways can be inhibited. The promising results of tyrosine kinase inhibitors in solid tumours provide a revolution in oncology research. In this article, we had summarized the role of some important members of the tyrosine kinase family in the development and progression of tumour cells and the significance of tyrosine kinase inhibitors in the treatment of various types of cancer.

Identification of tyrosine kinase inhibitors from Panax bipinnatifidus and Panax pseudoginseng for RTK-HER2 and VEGFR2 receptors, by in silico approach

Breast and stomach cancer is reported as a leading cause for human mortality across the world. The overexpression of receptor tyrosine kinase (RTK) proteins, namely the human epidermal growth factor receptor2 (HER2) and the vascular endothelial growth factor receptor2 (VEGFR2), is reported to be responsible for development and metastasis of breast and stomach cancer. Although several synthetic tyrosine kinase inhibitors (TKIs) as drug candidates targeting RTK-HER2 and VEGFR2 are currently available in the market, these are expensive with the reported side effects. This confers an opportunity for development of alternative novel tyrosine kinase inhibitors (TKIs) for RTK-HER2 and VEGFR2 receptors from the botanical sources. In the present study, we characterized 47 bioactive phytocompounds from the methanol extracts of the rhizomes of Asiatic traditional medicinal herbs-Panax bipinnatifidus and Panax pseudoginseng, of Indian Himalayan landraces using HPLC, GC-MS and high-sensitivity LC-MS tools. We performed molecular docking and molecular dynamics simulation analysis using Schrödinger suite 2020-3 to confirm the TKI phytocompounds showing the best binding affinity towards RTK-HER2 and VEGFR2 receptors. The results of molecular docking studies confirmed that the phytocompound (ligand) luteolin 7-O-glucoside (IHP15) showed the highest binding affinity towards receptor HER2 (PDB ID: 3PP0) with docking score and Glide g score (G-Score) of - 13.272, while chlorogenic acid (IHP12) showed the highest binding affinity towards receptor VEGFR2 (PDB ID: 4AGC) with docking score and Glide g score (G-Score) of - 10.673. Molecular dynamics (MD) simulation analysis carried out for 100 ns has confirmed strong binding interaction between the ligand and receptor complex [luteolin 7-O-glucoside (IHP15) and HER2 (PDB ID: 3PP0)] and is found to be stabilized within 40 to 100 ns of MD simulation, whereas ligand-receptor complex [chlorogenic acid (IPH12) and VEGFR2 (PDB ID: 4AGC)] also showed strong binding interaction and is found to be stabilized within 18-30 ns but slightly deviated during 100 ns of MD simulation. In silico ADME-Tox study using SwissADME revealed that the ligands luteolin 7-O-glucoside (IHP15) and chlorogenic acid (IHP12) have passed majority parameters of the common drug discovery rules. The present study has confirmed luteolin 7-O-glucoside (IHP15) and chlorogenic acid (IHP12) as potential tyrosine kinase inhibitors (TKIs) which were found to inhibit RTKs-HER2 and VEGFR2 receptor proteins, and thus paving the way for development of alternative potential TKIs (drug molecules) for treatment of HER2- and VEGFR2-positive breast and stomach cancer.

Recent advances in development of hetero-bivalent kinase inhibitors

Identifying a pharmacological agent that targets only one of more than 500 kinases present in humans is an important challenge. One potential solution to this problem is the development of bivalent kinase inhibitors, which consist of two connected fragments, each bind to a dissimilar binding site of the bisubstrate enzyme. The main advantage of bivalent (type V) kinase inhibitors is generating more interactions with target enzymes that can enhance the molecules' selectivity and affinity compared to single-site inhibitors. Earlier type V inhibitors were not suitable for the cellular environment and were mostly used in in vitro studies. However, recently developed bivalent compounds have high kinase affinity, high biological and chemical stability in vivo. This review summarized the hetero-bivalent kinase inhibitors described in the literature from 2014 to the present. We attempted to classify the molecules by serine/threonine and tyrosine kinase inhibitors, and then each target kinase and its hetero-bivalent inhibitor was assessed in depth. In addition, we discussed the analysis of advantages, limitations, and perspectives of bivalent kinase inhibitors compared with the monovalent kinase inhibitors.

Tyrosine kinase inhibitors for solid tumors in the past 20 years (2001-2020)

Tyrosine kinases are implicated in tumorigenesis and progression, and have emerged as major targets for drug discovery. Tyrosine kinase inhibitors (TKIs) inhibit corresponding kinases from phosphorylating tyrosine residues of their substrates and then block the activation of downstream signaling pathways. Over the past 20 years, multiple robust and well-tolerated TKIs with single or multiple targets including EGFR, ALK, ROS1, HER2, NTRK, VEGFR, RET, MET, MEK, FGFR, PDGFR, and KIT have been developed, contributing to the realization of precision cancer medicine based on individual patient's genetic alteration features. TKIs have dramatically improved patients' survival and quality of life, and shifted treatment paradigm of various solid tumors. In this article, we summarized the developing history of TKIs for treatment of solid tumors, aiming to provide up-to-date evidence for clinical decision-making and insight for future studies.

Hif-1α Inhibitors Could Successfully Inhibit the Progression of Differentiated Thyroid Cancer in Vitro

Hypoxia-inducible factor (HIF)-1α plays an important role in cancer progression. In various cancers, including thyroid cancer, overexpression of HIF-1α is related to poor prognosis or treatment response. However, few studies have investigated the role of HIF-1α inhibition in thyroid cancer progression. We evaluated the utility of the HIF-1α inhibitor IDF-11774 in vitro utilizing two thyroid cancer cell lines, K1 and BCPAP. Both cell lines were tested to elucidate the effects of IDF-11774 on cell proliferation and migration using soft agar and invasion assays. Here, we found that a reduction of HIF-1α expression in BCPAP cells was observed after treatment with IDF-11774 in a dose-dependent manner. Moreover, cell proliferation, migration, and anchorage-independent growth were effectively inhibited by IDF-11774 in BCPAP cells but not in K1 cells. Additionally, invasion of BCPAP but not K1 cells was controlled with IDF-11774 in a dose-dependent manner. Our findings suggest that promoting the degradation of HIF-1α could be a strategy to manage progression and that HIF-1α inhibitors are potent drugs for thyroid cancer treatment.

Pharmacokinetic Modeling of Targeted Ultrasound Contrast Agents for Quantitative Assessment of Anti-Angiogenic Therapy: a Longitudinal Case-Control Study in Colon Cancer

PURPOSE

To evaluate quantitative and semi-quantitative ultrasound molecular imaging (USMI) for antiangiogenic therapy monitoring in human colon cancer xenografts in mice.

PROCEDURES

Colon cancer was established in 17 mice by injection of LS174T (N_r = 9) or CT26 (N_n = 8) cancer cells to simulate clinical responders and non-responders, respectively. Antiangiogenic treatment (bevacizumab; N_rt = N_nt = 5) or control treatment (saline; N_rc = 4, N_nc = 3) was administered at days 0, 3, and 7. Three-dimensional USMI was performed by injection at days 0, 1, 3, 7, and 10 of microbubbles targeted to the vascular endothelial growth factor receptor 2 (VEGFR2). Microbubble binding rate (k_b), estimated by first-pass binding model fitting, and semi-quantitative parameters late enhancement (LE) and differential targeted enhancement (dTE) were compared at each day to evaluate their ability to assess and predict the response to therapy. Correlation analysis with the ex-vivo immunohistological quantification of VEGFR2 expression and the percentage blood vessel area was also performed.

RESULTS

Significant changes in the USMI parameters during treatment were observed only in the responders treated with bevacizumab (p-value < 0.05). Prediction of the response to therapy as early as 1 day after treatment was achieved by the quantitative parameter k_b (p-value < 0.01), earlier than possible by tumor volume quantification. USMI parameters could significantly distinguish between clinical responders and non-responders (p-value << 0.01) and correlated well with the ex-vivo quantification of VEGFR2 expression and the percentage blood vessels area (p-value << 0.01).

CONCLUSION

USMI (semi)quantitative parameters provide earlier assessment of the response to therapy compared to tumor volume, permit early prediction of non-responders, and correlate well with ex-vivo angiogenesis biomarkers.

Transport of a graphene nanosheet sandwiched inside cell membranes

The transport of nanoparticles at bio-nano interfaces is essential for many cellular responses and biomedical applications. How two-dimensional nanomaterials, such as graphene and transition-metal dichalcogenides, diffuse along the cell membrane is, however, unknown, posing an urgent and important issue to promote their applications in the biomedical area. Here, we show that the transport of graphene oxides (GOs) sandwiched inside cell membranes varies from Brownian to Lévy and even directional dynamics. Specifically, experiments evidence sandwiched graphene-cell membrane superstructures in different cells. Combined simulations and analysis identify a sandwiched GO-induced pore in cell membrane leaflets, spanning unstable, metastable, and stable states. An analytical model that rationalizes the regimes of these membrane-pore states fits simulations quantitatively, resulting in a mechanistic interpretation of the emergence of Lévy and directional dynamics. We finally demonstrate the applicability of sandwiched GOs in enhanced efficiency of membrane-specific drug delivery. Our findings inform approaches to programming intramembrane transport of two-dimensional nanomaterials toward advantageous biomedical applications.

Combining a QSAR Approach and Structural Analysis to Derive an SAR Map of Lyn Kinase Inhibition

Lyn kinase, a member of the Src family of protein tyrosine kinases, is mainly expressed by various hematopoietic cells, neural and adipose tissues. Abnormal Lyn kinase regulation causes various diseases such as cancers. Thus, Lyn represents, a potential target to develop new antitumor drugs. In the present study, using 176 molecules (123 training set molecules and 53 test set molecules) known by their inhibitory activities (IC50) against Lyn kinase, we constructed predictive models by linking their physico-chemical parameters (descriptors) to their biological activity. The models were derived using two different methods: the generalized linear model (GLM) and the artificial neural network (ANN). The ANN Model provided the best prediction precisions with a Square Correlation coefficient R² = 0.92 and a Root of the Mean Square Error RMSE = 0.29. It was able to extrapolate to the test set successfully (R² = 0.91 and RMSE = 0.33). In a second step, we have analyzed the used descriptors within the models as well as the structural features of the molecules in the training set. This analysis resulted in a transparent and informative SAR map that can be very useful for medicinal chemists to design new Lyn kinase inhibitors.

Ethacrynic acid improves the antitumor effects of irreversible epidermal growth factor receptor tyrosine kinase inhibitors in breast cancer

Prolonged treatment of breast cancer with epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) often results in acquired resistance and a narrow therapeutic index. One strategy to improve the therapeutic effects of EGFR TKIs is to combine them with drugs used for other clinical indications. Ethacrynic acid (EA) is an FDA approved drug that may have antitumor effects and may enhance the cytotoxicity of chemotherapeutic agents by binding to glutathione and inhibiting WNT signaling. While the α,β-unsaturated-keto structure of EA is similar to that of irreversible TKIs, the mechanism of action of EA when combined with irreversible EGFR TKIs in breast cancer remains unknown. We therefore investigated the combination of irreversible EGFR TKIs and EA. We found that irreversible EGFR TKIs and EA synergistically inhibit breast cancer both in vitro and in vivo. The combination of EGFR TKIs and EA induces necrosis and cell cycle arrest and represses WNT/β-catenin signaling as well as MAPK-ERK1/2 signaling. We conclude that EA synergistically enhances the antitumor effects of irreversible EGFR TKIs in breast cancer.

Synthesis, crystal structure and activity evaluation of novel 3,4-dihydro-1-benzoxepin-5(2H)-one derivatives as protein-tyrosine kinase (PTK) inhibitors

Four new 3,4-dihydro-1-benzoxepin-5(2H)-one derivatives, namely (E)-4-(5-bromo-2-hydroxybenzylidene)-6,8-dimethoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (7), (E)-4-[(E)-3-(5-bromo-2-hydroxyphenyl)allylidene]-6,8-dimethoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (8), (E)-4-(5-bromo-2-hydroxybenzylidene)-6-hydroxy-8-methoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, C₁₈H₁₅BrO₅, (9), and (E)-4-[(E)-3-(5-bromo-2-hydroxyphenyl)allylidene]-6-hydroxy-8-methoxy-3,4-dihydrobenzo[b]oxepin-5(2H)-one, (10), have been synthesized and characterized by FT-IR, NMR and MS. The structure of (9) was confirmed by single-crystal X-ray diffraction. Crystal structure analysis shows that molecules of (9) are connected into a one-dimensional chain in the [010] direction through classical hydrogen bonds and these chains are further extended into a three-dimensional network via C-H...O interactions. The inhibitory activities of these compounds against protein-tyrosine kinases (PTKs) show that 6-hydroxy-substituted compounds (9) and (10) are more effective for inhibiting ErbB1 and ErbB2 than are 6-methoxy-substituted compounds (7) and (8). This may be because (9) and (10) could effectively bind to the active pockets of the protein through intermolecular interactions.

Novel Anthraquinone-based Derivatives as Potent Inhibitors for Receptor Tyrosine Kinases

The influence of new derivatives of 9,10-anthraquinone with benzoylthiourea, thiazole, triazole and amino acid fragments on the activity of membrane-associated tyrosine kinases was investigated. Inhibitors of protein tyrosine kinase activity of the membrane fraction, as promising agents to search for new potential anticancer agents among the studied compounds, were discovered.

Synthesis of 6,8,9 poly-substituted purine analogue libraries as pro-apoptotic inducers of human leukemic lymphocytes and DAPK-1 inhibitors

A 18-member library of 6,8,9-poly-substituted purines was prepared from pyrimidines, primary alcohols, and N,N-dimethylamides under basic conditions via a novel one-pot synthetic pathway controlled by amide sizes and the novel analogues were tested against two leukemia cell lines: Jurkat (acute T cell leukemia) and K562 (chronic erythroleukemia) cells. Compounds having a benzoxy group at C6 position of the aromatic ring exhibited antiproliferative activity in Jurkat cells whereas all compounds induced a lower effect on K562 cells. Analysis of cell cycle, Annexin-V staining, and cleavage of initiator caspases assays showed that the active purine analogues induce cell death by apoptosis. Based on these results, a new purine derivative was synthesized, 6-benzyloxy-9-tert-butyl-8-phenyl-9H-purine (6d), which displayed the highest activity of the series against Jurkat cell lines. Finally, (33)P-radiolabeled kinase assays using 96 recombinant human kinases known to be involved in apoptotic events were performed. Just one of the kinases tested, DAPK-1, was inhibited 50% or more by the phenotypic hits at 10 μM, suggesting that the inhibition of this target could be responsible for the induction of cell death by apoptosis. In agreement with the phenotypic results, the most active antiproliferative agent, 6d, displayed also the lowest IC50 value against recombinant DAPK1 (2.5 μM), further supporting the potential role of this protein on the observed functional response. DAPK-1 inhibition led by 6d together with its pro-apoptotic properties against the Jurkat line makes it an interesting candidate to further investigate the role of DAPK1 kinase in triggering apoptosis in cancer cells, a role which is attracting recent interest.

Recent advances in the development of dual VEGFR and c-Met small molecule inhibitors as anticancer drugs

Vascular endothelial growth factor receptor (VEGFR) is a very important receptor tyrosine kinase (RTK) that can induce angiogenesis, increase cell growth and metastasis, reduce apoptosis, alter cytoskeletal function, and affect other biologic changes. Moreover, it is identified to be deregulated in varieties of human cancers. Therefore, VEGFR turn out to be a remarkable target of significant types of anticancer drugs in clinical trials. On the other side, c-Met is the receptor of hepatocyte growth factor (HGF) and a receptor tyrosine kinase. Previous studies have shown that c-Met elicits many different signaling pathways mediating cell proliferation, migration, differentiation, and survival. Furthermore, the correlation between aberrant signaling of the HGF/c-Met pathway and aggressive tumor growth, poor prognosis in cancer patients has been established. Recent reports had shown that c-Met/HGF and VEGFR/VEGF (vascular endothelial growth factor) can act synergistically in the progression of many diseases. They were also found to be over expressed in many human cancers. Thus, in a variety of malignancies, VEGFR and c-Met receptor tyrosine kinases have acted as therapeutic targets. With the development of molecular biology techniques, further understanding of the human tumor disease pathogenesis and interrelated signaling pathways known to tumor cells, using a single target inhibitors have been difficult to achieve the desired therapeutic effect. At this point, with respect to the combination of two inhibitors, a single compound which is able to inhibit both VEGFR and c-Met may put forward the advantage of raising anticancer activity. With the strong interest in these compounds, this review represents a renewal of previous works on the development of dual VEGFR and c-Met small molecule inhibitors as novel anti-cancer agents. Newly collection derivatives have been mainly describing in their biological profiles and chemical structures.

Elucidation of the molecular mechanisms underlying adverse reactions associated with a kinase inhibitor using systems toxicology

BACKGROUND/OBJECTIVES

Targeted kinase inhibitors are an important class of agents in anticancer therapeutics, but their limited tolerability hampers their clinical performance. Identification of the molecular mechanisms underlying the development of adverse reactions will be helpful in establishing a rational method for the management of clinically adverse reactions. Here, we selected sunitinib as a model and demonstrated that the molecular mechanisms underlying the adverse reactions associated with kinase inhibitors can efficiently be identified using a systems toxicological approach.

METHODS

First, toxicological target candidates were short-listed by comparing the human kinase occupancy profiles of sunitinib and sorafenib, and the molecular mechanisms underlying adverse reactions were predicted by sequential simulations using publicly available mathematical models. Next, to evaluate the probability of these predictions, a clinical observation study was conducted in six patients treated with sunitinib. Finally, mouse experiments were performed for detailed confirmation of the hypothesized molecular mechanisms and to evaluate the efficacy of a proposed countermeasure against adverse reactions to sunitinib.

RESULTS

In silico simulations indicated the possibility that sunitinib-mediated off-target inhibition of phosphorylase kinase leads to the generation of oxidative stress in various tissues. Clinical observations of patients and mouse experiments confirmed the validity of this prediction. The simulation further suggested that concomitant use of an antioxidant may prevent sunitinib-mediated adverse reactions, which was confirmed in mouse experiments.

CONCLUSIONS

A systems toxicological approach successfully predicted the molecular mechanisms underlying clinically adverse reactions associated with sunitinib and was used to plan a rational method for the management of these adverse reactions.

The azaindole framework in the design of kinase inhibitors

This review article illustrates the growing use of azaindole derivatives as kinase inhibitors and their contribution to drug discovery and innovation. The different protein kinases which have served as targets and the known molecules which have emerged from medicinal chemistry and Fragment-Based Drug Discovery (FBDD) programs are presented. The various synthetic routes used to access these compounds and the chemical pathways leading to their synthesis are also discussed. An analysis of their mode of binding based on X-ray crystallography data gives structural insights for the design of more potent and selective inhibitors.

The preclinical development of regorafenib for the treatment of colorectal cancer

INTRODUCTION

The RAS-RAF-MEK-ERK pathway is one of the best characterized kinase cascades. During the exploration of small molecules that inhibit RAF1 kinase, regorafenib (BAY 73-4506) was discovered as a multikinase inhibitor which demonstrated anti-cancer, anti-angiogenic, and apoptotic activities in metastatic colorectal cancer. This was not the first multikinase inhibitor discovered for the disease; indeed, before regorafenib was approved by FDA as a multikinase inhibitor for metastatic colorectal cancer in 2012, sorafenib (BAY 43-9006) had already been developed to be the first in the world as a multikinase inhibitor for malignancy. Indeed, the only difference between the two compounds is fluorine bound to its proximal phenyl ring although the end result is a considerably different profile, both as a kinase inhibitor as well as in its clinical application.

AREAS COVERED

In this drug discovery case history, the authors review the design, discovery, and development of both regorafenib and sorafenib from back in the 1990s. Furthermore, the authors highlight the drug's anti-cancer and anti-angiogenic properties as well as its efficacy, safety pharmacology and toxicology based on FDA documents.

EXPERT OPINION

In order to better predict the efficacy of kinase inhibitors and to utilize them more efficiently, our understanding of drug discovery, the approaches for kinase profiling, and technologies needed for their development are paramount. Indeed, the authors believe that the field should better explore the use of predictive biomarkers that might be able to better assess these therapeutics. Pharmaceutical scientists must also consider the cost effectiveness of the targeted agents developed as a number of the drugs developed are very expensive.