Selective PI3Kδ inhibitors,a review of the patent literature

Introduction: Phosphatidylinositol 3-kinase (PI3K), a lipid kinase, is the first kinase involved in, and a key component of, the PI3K/Akt/mTOR signalling pathway, and is significantly upregulated in many cancers. However, four distinct isoforms of PI3K are known with different expression patterns and different pathophysiological roles. The PI3Kδ isoform is expressed in leukocytes and has been implicated as a potential target in the development of selective inhibitors for the treatment of haematological malignancies and various inflammatory diseases.

Areas covered: This review briefly covers the understanding of the four PI3K isoforms and their roles and the inhibitors selective for either one or two isoforms that have been identified to date. It then focuses upon progress in the identification of selective PI3Kδ inhibitors focusing upon the original efforts at ICOS/Calistoga that led to the initial clinical candidates such as CAL-101. After assessing the patent filings from these companies, it considers filings from other players and how they have sought to explore similar, and structurally distinct, scaffolds in their search for selective inhibitors, and how different companies appear focused on either oncological or anti-inflammatory uses for their inhibitors.

Expert opinion: The impact of the work at ICOS is highlighted by the fact that prior to their disclosure of selective leads, no patent applications claiming selective PI3Kδ inhibitors had been filed by other companies. This disclosure, followed by the first filings by Piramed, led to an upsurge in interest with a large cluster of filings published in 2008 while half the relevant applications were published in 2010 or 2011. These efforts, and the initial clinical data on CAL-101, the leading PI3Kδ inhibitors, have also prompted a number of commercially significant deals. In addition to an increasing number of filings, the entry into the clinical development of more selective PI3Kδ inhibitors should stimulate a better understanding of the role of this specific kinase isoform.     

Bruton’s tyrosine kinase (BTK) inhibitors in treating cancer: a patent review (2010-2018)

Introduction: Bruton’s tyrosine kinase (BTK) plays a critical role in the regulation of survival, proliferation, activation and differentiation of B-lineage cells. It participates by regulating multiple cellular signaling pathways, including B cell receptor and FcR signaling cascades. BTK is abundantly expressed and constitutively active in the pathogenesis of B cell hematological malignancies, as well as several autoimmune diseases. Therefore, BTK is considered as an attractive target for treatment of B-lineage lymphomas, leukemias, and some autoimmune diseases. Many industry and academia efforts have been made to explore small molecular BTK inhibitors.

Areas covered: This review aims to provide an overview of the patented BTK inhibitors for the treatment of cancer from 2010 to 2018.

Expert opinion: BTK inhibitors attract much interest for their therapeutic potential in the treatment of cancers and autoimmune diseases, especially for B cell hematological malignancies. In 2013, ibrutinib was approved by the FDA as the first-in-class BTK inhibitors for the treatment of mantle cell lymphoma (MCL) and chronic lymphocytic leukemia (CLL), and now it is also undergoing clinical evaluation for other indications in either single or combined therapy. It is clear that BTK inhibitors can provide a promising clinical benefit in treating B-lineage lymphomas and leukemias.     

Inhibitors of the bone morphogenetic protein (BMP) signaling pathway: a patent review (2008-2015)

Introduction: The bone morphogenetic protein (BMP) is a critical signaling pathway and plays a diverse role in embryonic pattern formation and is implicated in a variety of disease processes, including anemia, bone formation, atherosclerosis, skin diseases, and cancers, among others.

Areas covered: This review covers small molecule inhibitors/antagonists of BMP in patent applications between 2008 – 2015, along with brief synopses of the disclosed inhibitors in the primary literature.

Expert opinion: The development of potent and selective BMP inhibitors is ongoing with most of the work centered around improving the selectivity and pharmacokinetic profile. Early work was for the treatment of the rare and neglected disease, fibrodysplasia ossificans progressiva (FOP). Recently, however, there has been increased interest in their use in a number of other diseases such as cancer, atherosclerosis, and anemia of chronic disease, to name a few. Although the primary participants in the early work were from academic laboratories, recently a significant surge from the pharmaceutical industry has elevated the interest in the development of BMP inhibitors for a wide-range of therapeutic indications. Due to this, expect a number of new approaches such as repurposing of other kinase inhibitors to be brought into clinical trials in the near future.     

Caspase inhibitors: a review of recently patented compounds (2013-2015)

Introduction: Although many caspase inhibitors have been patented, caspase inhibitors have not entered the market due to their toxicity and poor pharmacokinetic profile.

Areas covered: In this article, we review patents (2013–2015) for peptide and non-peptide caspase inhibitors and their compositions.

Expert opinion: Noteworthy patents include a peptidic caspase-2 inhibitor for nasal administration and a peptidomimetic caspase-6 inhibitor that can be administered via several routes for the treatment of neurodegenerative diseases. Furthermore, caspase-1 inhibitors for contact dermatitis and inflammation, cardiovascular diseases, and liver diseases and a caspase-3 inhibitor for cerebral stroke have been patented. Of particular interest is the novel use of tyrosine kinase inhibitors (sunitinib and its derivatives) for the prevention and treatment of age-related ocular diseases via inhibition of the caspase-3, dual-leucine zipper kinase (DLK) and leucine zipper-bearing kinase (LZK) pathways. However, for effective clinical application of caspase inhibitors, novel peptidic and nonpeptidic caspase inhibitors with lower toxicity and improved efficacy should be developed via structural modifications, and further animal studies and preclinical and clinical trials are needed. In addition, the poor pharmacokinetic properties of classic caspase inhibitors may be improved by using advanced drug delivery systems that employ liposomes, polymers, and nanoparticles through effective administration routes.     

The possible involvement of glycogen synthase kinase-3 (GSK-3) in diabetes, cancer and central nervous system diseases

Glycogen synthase kinase (GSK-3) is a key enzyme in multiple cell processes. Since many pharmacological compounds that have effects on common metabolic pathways may have uses in many different diseases, we review here the possible involvement of glycogen synthase kinase 3 in diabetes, cancer and CNS diseases. Moreover, diabetes has recently been strongly linked to CNS diseases such as schizophrenia and bipolar illness. GSK-3 is both directly and indirectly inhibited by lithium, a key compound for treatment of bipolar disorder. Several antipsychotic drugs also affect the GSK-3 mediated pathways and postmortem study of brain in schizophrenia led to reports of alterations of GSK-3 activity or mRNA message. However, other reports are contradictory. Development of GSK-3 inhibitors for CNS diseases is complicated by the importance of GSK-3 in glucose metabolism and pancreas function and the possible effect of GSK-3 inhibition to be oncogenic. Further development of GSK-3 inhibitors for clinical trials should be approached with caution.     

Inhibitors of interleukin-1 receptor-associated kinase 4 (IRAK4): a patent review (2012-2015)

Introduction: IRAK4 is located proximal to TLR/IL-1 receptors, and in preclinical studies, inhibits downstream signaling from these receptors. The development of novel small molecule inhibitors of this kinase has the potential to lead to new therapeutics to treat diseases such as rheumatoid arthritis, lupus, and lymphomas.

Areas covered: The aim of this review is to summarize the recent patent literature (2012–2015) surrounding small molecule inhibitors of IRAK4. Specific examples of the chemical matter from each patent will be discussed, including any data that are presented for the examples highlighted.

Expert opinion: There are currently many examples of highly potent and kinase selective IRAK4 inhibitors and some have been tested in various in vivo disease models, demonstrating robust pre-clinical efficacy. Several compounds appear to have the ‘drug-like’ properties to advance to the clinic, with Pfizer having already initiated several phase I studies.     

MEK inhibitors in oncology: a patent review (2015-Present)

Introduction: The RAS/RAF/MEK/ERK and PI3K/AKT/mTOR signaling pathways have been identified as promising therapeutic targets for cancer therapy. Over-activation of these pathways and their components including gene mutations has been considered as one of the major causes of melanoma. Mitogen-activated protein kinase (MEK) is a downstream kinase of RAS pathway found in two different forms MEK1/2. The MEK inhibitors in combination with other kinase/mutant gene inhibitors have shown promising results in patients with metastatic melanoma.

Areas covered: A comprehensive review of the patent literature (2015 – Present) on MEK inhibitors, their combinations with other kinase inhibitors and structural insights has been highlighted.

Expert opinion: Recently mitogen-activated protein kinase (MEK) inhibitors have attracted considerable interest in oncology especially in melanoma. The MEK inhibitors showed promising results in patients with metastatic melanoma harboring mutant genes such as BRAF, KRAS. The MEK1/2 inhibitors in combination with BRAF, KRAS and/or PI3K inhibitors showed promising results in mutated colorectal, pancreatic adenocarcinoma, solid tumor, and relapsed/refractory melanoma. The combination delays the onset of acquired resistance, resulting in increased progression-free and overall survival. The combination and/or multi-targeted kinase/mutant gene inhibitors may be a therapeutic option for the personalized cancer treatment of patients with relapsed or refractory multiple myeloma.     

Itk inhibitors: a patent review

Importance of field: IL-2 inducible T-cell kinase (Itk) is a non-receptor tyrosine kinase of the Tec family. It plays an important role in T cell signaling and the production of various pro-inflammatory cytokines such as IL-2, IL-4, IL-5, IL-10 and IL-13. Inhibition of Itk has been a target for the treatment of diseases related to inflammation disorders such as psoriasis and allergic asthma. Rich resources on the structural information for Itk made discovery of novel selective Itk inhibitors blossom in the past decade.

Areas covered in this review: In this report, distinct structural classes of specific Itk inhibitors are summarized and their in vitro/in vivo properties are discussed.

What the reader will gain: A summary of 21 patents including 16 different chemical structure classes of Itk inhibitors. The in vivo efficacies of some of the inhibitors in animal models are also discussed.

Take home message: Although some of the inhibitors show efficacy in different animal models, which implies potential for therapeutic use in human, there is not yet a chemical entity reported in clinical trials. The prospects for Itk inhibitors will rely on the quality of the compound and the validity of the target in patients within the selected therapeutic area.     

Targeting protein kinase-b3 (akt3) signaling in melanoma

Introduction: Deregulated Akt activity leading to apoptosis inhibition, enhanced proliferation and drug resistance has been shown to be responsible for 35–70% of advanced metastatic melanomas. Of the three isoforms, the majority of melanomas have elevated Akt3 expression and activity. Hence, potent inhibitors targeting Akt are urgently required, which is possible only if (a) the factors responsible for the failure of Akt inhibitors in clinical trials is known; and (b) the information pertaining to synergistically acting targeted therapeutics is available.

Areas covered: This review provides a brief introduction of the PI3K-Akt signaling pathway and its role in melanoma development. In addition, the functional role of key Akt pathway members such as PRAS40, GSK3 kinases, WEE1 kinase in melanoma development are discussed together with strategies to modulate these targets. Efficacy and safety of Akt inhibitors is also discussed. Finally, the mechanism(s) through which Akt leads to drug resistance is discussed in this expert opinion review.

Expert opinion: Even though Akt play key roles in melanoma tumor progression, cell survival and drug resistance, many gaps still exist that require further understanding of Akt functions, especially in the (a) metastatic spread; (b) circulating melanoma cells survival; and (c) melanoma stem cells growth.     

Specific delivery of kinase inhibitors in nonmalignant and malignant diseases

Introduction: Kinase inhibitors have been hailed as a breakthrough in the treatment of cancer. Extensive research is now being devoted to the development of kinase inhibitors as a treatment for many nonmalignant diseases. However, the use of kinase inhibitors in both malignant and nonmalignant diseases is also associated with side effects and the development of resistance. It may be worthwhile to explore whether cell-specific delivery of kinase inhibitors improves therapeutic efficacy and reduces side effects.

Areas covered: This review aims to provide an overview of the preclinical studies performed to examine the specific targeting of kinase inhibitors in vitro and in vivo. It gives an introduction to kinase signaling pathways induced during disease, along with the possible problems associated with their inhibition. It also discusses the studies on specific delivery and shows that altering the specificity of kinase inhibitors by targeting methods improves their effectivity and safety.

Expert opinion: Compared with the delivery of cytotoxic compounds, the specific delivery of kinase inhibitors has not yet been studied extensively. The studies discussed in this review provide an insight into methods used to target kinase inhibitors to different organs. The targeting of different kinase inhibitors has improved their therapeutic possibilities, but many questions still remain to be studied.     

A patent review of Monoacylglycerol Lipase (MAGL) inhibitors (2013-2017)

Introduction: Monoacylglycerol lipase is a serine hydrolase that plays a major role in the degradation of the endocannabinoid 2-arachidonoylglycerol. Because of this key role, selective inactivation of MAGL represents an interesting approach to obtain desirable effects in several diseases. Furthermore, MAGL is upregulated in cancer cells and primary tumors and its inhibition in aggressive breast, ovarian, and melanoma cancer cells impairs cell migration, invasiveness, and tumorigenicity.

Areas covered: This review covers patent literature on MAGL inhibitors and their applications published from 2013 to 2017.

Expert opinion: MAGL inhibition has gained considerable importance in many therapeutic fields and one compound has been subjected to Phase I studies. Even if a reasonable number of patents have been recently reported, novel MAGL inhibitors are still required, especially novel chemical classes displaying a reversible mechanism of action.     

Cathepsin B and L inhibitors: a patent review (2010 - present)

Introduction: Cathepsins play an important role in protein degradation and processing. Aberrant cathepsin B or L is closely associated with many serious diseases such as cancer, osteoporosis and autoimmune disorders. Therefore, development of potent and selective cathepsin B and L inhibitors has aroused much attention in recent years. Although several classes of cathepsin inhibitors are presently available, there are still some problems to solve, such as broad-spectrum inhibition to protease, specially cysteine proteases, which lead to unpredictable side effects in clinical trials. Therefore, it is very necessary to discovery new scaffolds and new application of cathepsin B and L inhibitors for developing therapeutic agents for treating diseases mediated by cathepsin B or L.

Areas covered: This updated review summarizes new patents on cathepsin B and L inhibitors from 2010 to present.

Expert opinion: The review gives the latest development in the area of inhibitors of cathepsin B and L, which have been considered key therapeutic targets for the development of drugs treating related diseases. This review puts emphasis on the discovery of novel small molecule inhibitors of cathepsin B and L, as well as their new application as new therapeutic agents.     

Autotaxin inhibitors: a patent review (2012-2016)

Introduction: Autotaxin (ATX) is a secreted enzyme that hydrolyzes lysophosphatidylcholine to lysophosphatidic acid (LPA) and choline. The ATX/LPA axis has received increasing interest in recent years because both the enzyme ATX and the bioactive lipid LPA are involved in various pathological conditions such as tumor progression and metastasis, fibrotic diseases, autoimmune diseases, arthritis, chronic hepatitis, obesity and impaired glucose homeostasis. Thus, a great effort has been devotd in developing synthetic ATX inhibitors as new agents to treat various diseases including cancer and fibrotic diseases.

Areas covered: This review article summarizes the autotaxin inhibitors presented in patent literature from October 2012 to August 2016 and their biological evaluation, discussing their activities in vitro and in vivo.

Expert opinion: During the recent years, there has been an intensive effort on the discovery of potent and selective ATX inhibitors. Although various synthetic inhibitors have been developed, only limited studies for their in vivo activity have been reported so far. A decade after the first claim of synthetic ATX inhibitors in 2006, one inhibitor has been in clinical trials for idiopapthic pulmonary fibrosis. The use of ATX inhibitors seems an attractive strategy to produce novel medicinal agents, for example anticancer agents.     

LSD1 inhibitors: a patent review (2010-2015)

Introduction: Lysine demethylase 1 (LSD1) plays an important role in mediating the expression of genes involved in cancer and non-cancer diseases such as viral infections, cardiovascular and neurodegenerative disorders. It is involved in a number of processes from adipogenesis to cell adhesion to viral latency, regulating several cell pathways related with proliferation, development, and cell cycle control. Numerous chemical entities have been studied in recent years and some of them entered the clinical arena.

Areas covered: This review summarizes recent efforts in the drug development of LSD1 inhibitors reported in the patent literature covering the 2010-2015 period, including their potential use as therapeutics in cancerous, neurological, inflammatory, cardiovascular, and viral diseases.

Expert opinion: The development of novel potent and selective LSD1 inhibitors is ongoing, in order to improve their potency and selectivity against specific types of cancer or non-cancer diseases. More in-depth studies are required to assess the role of LSD1 inhibitors in the expression of LSD1 target genes, for a better assessment of the biochemistry underlying their efficacy, and to provide evidence for any possible side effects. Furthermore, an interesting therapeutic approach is the use of LSD1 inhibitors in conjunction with other epidrugs to combine their therapeutic potential, leading to innovative, personalized treatments.     

c-Met kinase inhibitors: an update patent review (2014-2017)

Introduction: The receptor tyrosine kinase c-Met is involved in the formation, metastasis and invasion of various malignant tumors thus it has been an attractive target for anti-tumor drug designing. Many compositions targeting c-Met have been developed in pharmaceutical industry for cancer therapy and some of them are in clinical study now. Among them, Crizotinib was the first small molecular inhibitor approved by FDA in 2011.

Areas covered: This review briefly summarizes the signal transduction pathway about c-Met, its role in oncogenesis, most recent patents of small-molecule inhibitors and antibodies of c-Met from 2014 to 2017.

Expert opinion: To date, some c-Met inhibitors have been launched in the market. In addition, their clinical performances have shown encouraging value in cancer therapy. Many potential agents are still in preclinical or clinical study now and achieve some promising progressions. Some patients have developed resistance to c-Met inhibitors which results in the need to develop inhibitors with novel structures. Development of several potent drugs also tends to be pharmacodynamically active against multiple targets.     

An overview of investigational antiapoptotic drugs with potential application for the treatment of neurodegenerative disorders

Importance of the field: The increase in life expectancy in developed countries has given rise to several emerging social problems. Of particular note is the dramatic rise in the incidence of neurodegenerative diseases. Given this new social scenario, there is a need to identify therapeutic strategies to delay the advance of these pathologies, for which no effective treatment is currently available.

Areas covered in this review: The present review discusses some of the drugs that are now under development with antiapoptotic activity or currently on the market that may have a potential application for the treatment of neurodegenerative diseases. Moreover, we also comment on potential compounds such as resveratrol and melatonin. Despite the lack of information from clinical trials on these two compounds, they are attracting considerable attention because of their natural origin and antioxidant and antiapoptotic action. Furthermore, they do not show toxicity in humans. In addition, we discuss the potential application of several compounds, such as NMDA antagonists, JNK inhibitors and GSK-3 inhibitors, for the treatment of neurodegenerative disorders.

What the reader will gain: This article will review recent developments in the field of apoptosis inhibitors, which might provide future tools for the treatment of the neurodegenerative diseases.

Take home message: The treatment of neurodegenerative diseases is a major challenge in medicine. This is partly because the incidence of these disorders is expected to rise in the coming years. New developments in the field of apoptosis inhibitors may provide future tools for the treatment of the aforementioned neurodegenerative diseases.     

VEGFR-2 inhibitors and the therapeutic applications thereof: a patent review (2012-2016)

Introduction: Angiogenesis is an important component of certain normal physiological processes, but aberrant angiogenesis contributes to some pathological disorders and in particular to tumor growth. Activation of vascular endothelial growth factor receptor-2 (VEGFR-2) by vascular endothelial growth factor (VEGF) is a critical step in the signal transduction pathway that initiates tumor angiogenesis. Inhibition of angiogenesis via blocking VEGF/VEGFR-2 signaling pathway has emerged as a potential approach to anticancer therapy. Indeed, this approach has recently been clinically validated with the approvals of VEGFR-2 inhibitors.

Areas covered: This review accounts for small-molecule inhibitors and antibodies of VEGFR-2 reported in the patent literature covering between January 2012 and June 2016, and their potential use as therapeutics for cancers, angiogenesis-related disorders and inflammatory diseases.

Expert opinion: Despite the attractiveness of anti-angiogenic therapy by VEGF inhibition alone, several issues may limit this approach. VEGF expression levels can be elevated by numerous diverse stimuli such as the activation of other RTK signaling transduction pathway. Therefore, the development of multi-targeted tyrosine kinase inhibitors and the strategy of using these agents in conjunction with other anti-cancer agents are recent interesting therapeutic approaches that could give promising results.     

Interleukin-1 receptor-associated kinase 4 (IRAK4) inhibitors: an updated patent review (2016-2018)

Introduction: Interleukin-1 receptor-associated kinase 4 (IRAK4) is the most upstream kinase in Toll/Interleukin-1 receptor (TIR) signaling. Human and rodent genetics support the role of IRAK4 in immune function and the involvement of IRAK4-dependent signaling in certain cancers is hypothesized. The accumulating evidence has motivated the discovery of IRAK4 inhibitors that could be used therapeutically.

Areas covered: This review summarizes patents published in 2016–2018 claiming IRAK4 inhibitors. Representative analogues from each patent are presented with a focus on compounds that have been profiled in cellular and in vivo assays.

Expert opinion: The last three years have seen an increased number of IRAK4 inhibitors with which to assess the therapeutic potential of the target. At least 5 companies are believed to have advanced to the clinic. Pfizer is in phase II for rheumatoid arthritis (RA). The outcomes of these studies should inform on the therapeutic potential in autoimmune disease and cancer.