Design and synthesis of novel human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) dual inhibitors bearing a pyrrolo[3,2-d]pyrimidine scaffold

Dual inhibitors of human epidermal growth factor receptor 2 (HER2) and epidermal growth factor receptor (EGFR) have been investigated for breast, lung, gastric, prostate, and other cancers; one, lapatinib, is currently approved for breast cancer. To develop novel HER2/EGFR dual kinase inhibitors, we designed and synthesized pyrrolo[3,2-d]pyrimidine derivatives capable of fitting into the receptors' ATP binding site. Among the prepared compounds, 34e showed potent HER2 and EGFR (HER1) inhibitory activities as well as tumor growth inhibitory activity. The X-ray cocrystal structures of 34e with both HER2 and EGFR demonstrated that 34e interacts with the expected residues in their respective ATP pockets. Furthermore, reflecting its good oral bioavailability, 34e exhibited potent in vivo efficacy in HER2-overexpressing tumor xenograft models. On the basis of these findings, we report 34e (TAK-285) as a promising candidate for clinical development as a novel HER2/EGFR dual kinase inhibitor.     

Second-generation epidermal growth factor tyrosine kinase inhibitors in non-small cell lung cancer

Inhibiting the tyrosine kinase activity of the epidermal growth factor receptor (EGFR) has an established role in the treatment of advanced non-small cell lung cancer. The first-generation EGFR inhibitors erlotinib and gefitinib have been approved for treatment in the second- and third-line setting. Second-generation EGFR tyrosine kinase inhibitors are now in development aiming to improve efficacy and overcome primary and secondary resistance to the first-generation drugs. The two most common strategies being used to achieve these aims are irreversible binding of drug to target and kinase multi-targeting. This is an overview of the early clinical development of selected second-generation tyrosine kinase inhibitors focusing on the treatment of non-small cell lung cancer.     

Monoclonal antibodies targeting the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR, HER1) autocrine pathway contributes to a number of highly relevant processes in cancer development and progression, including cell proliferation, regulation of apoptotic cell death, angiogenesis and metastatic spread. The crucial role that EGFR plays in human cancers has led to an extensive search for selective inhibitors of its signaling pathway. The results of a large body of preclinical studies and clinical trials thus far conducted suggest that targeting the EGFR could bring a significant contribution to cancer therapy. A variety of different approaches are currently being used to target the EGFR. The most promising strategies in clinical development include monoclonal antibodies, to prevent ligand binding, and small molecules inhibitors of the tyrosine kinase enzymatic activity, that inhibit autophosphorylation and downstream intracellular signaling. Several blocking monoclonal antibodies against the EGFR have been developed. Among these, IMC-225 is a chimeric human-mouse monoclonal IgG1 antibody that has been the first anti-EGFR targeted therapy to enter clinical evaluation in cancer patients in Phase II and III studies, alone or in combination with conventional radiotherapy and chemotherapy. However, other antibodies against EGFR have demonstrated antitumor activity in several preclinical models of human cancer and are currently under investigation in the clinical setting, such as ICR62, ABX-EGF and EMD72000. This review will focus on all the preclinical data available on monoclonal antibodies engineered against the EGF receptor.     

Patent status of histone deacetylase inhibitors

Histone deacetylase (HDAC) has emerged as an important therapeutic target for the treatment of cancer and other diseases. Several HDAC inhibitors that target class I and II HDACs are currently in clinical trials. The initial results from these studies indicate that HDAC inhibitors show great promise for the treatment of cancer. To date, more than 30 research organisations are named as applicants on published patent applications claiming structures of HDAC inhibitors. This review summarises the patent literature published from mid-2002 to early 2004 containing claims directed towards HDAC inhibitor structures, together with discussion of the related primary literature.     

Design and synthesis of pyrrolo[3,2-d]pyrimidine human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) dual inhibitors: exploration of novel back-pocket binders

To develop novel human epidermal growth factor receptor 2 (HER2)/epidermal growth factor receptor (EGFR) kinase inhibitors, we explored pyrrolo[3,2-d]pyrimidine derivatives bearing bicyclic fused rings designed to fit the back pocket of the HER2/EGFR proteins. Among them, the 1,2-benzisothiazole (42m) ring was selected as a suitable back pocket binder because of its potent HER2/EGFR binding and cell growth inhibitory (GI) activities and pseudoirreversibility (PI) profile as well as good bioavailability (BA). Ultimately, we arrived at our preclinical candidate 51m by optimization of the N-5 side chain to improve CYP inhibition and metabolic stability profiles without a loss of potency (HER2/EGFR inhibitory activity, IC(50), 0.98/2.5 nM; and GI activity BT-474 cells, GI(50), 2.0 nM). Reflecting the strong in vitro activities, 51m exhibited potent tumor regressive efficacy against both HER2- and EGFR-overexpressing tumor (4-1ST and CAL27) xenograft models in mice at oral doses of 50 mg/kg and 100 mg/kg.     

Non-hydroxamate histone deacetylase inhibitors

A number of histone deacetylase (HDAC) inhibitors have been developed as anticancer agents and most of them are hydroxamic acid derivatives, typified by suberoylanilide hydroxamic acid (SAHA), Trichostatin A (TSA) and NVP-LAQ824. However, hydroxamic acids have been associated with poor pharmacokinetics and severe toxicity. In addition, although isozyme-selective HDAC inhibitors are considered useful not only as tools for probing the biology of an enzyme but as drugs with low toxicity, many of the hydroxamate HDAC inhibitors do not distinguish well among the HDAC isozymes. Thus, there has been considerable interest in developing non-hydroxamate HDAC inhibitors. To date, small fatty acids, o-aminoanilides, electrophilic ketones, N-formyl hydroxylamines, thiols and mercaptoamides have been reported as non-hydroxamate HDAC inhibitors, and some of them show antiproliferative activity comparable to hydroxamates. Interestingly, hydroxamate HDAC inhibitors such as SAHA and TSA do not discriminate well among the HDAC isozymes whereas many non-hydroxamate HDAC inhibitors have shown selectivity. These non-hydroxamate HDAC inhibitors should pave the way for the development of tools for biological research and new medicines with few side effects. In this review, we introduce non-hydroxamate HDAC inhibitors describing their design, enzyme inhibition, cancer cell growth inhibition and isozyme selectivity.     

2-aroylindoles and 2-aroylbenzofurans with N-hydroxyacrylamide substructures as a novel series of rationally designed histone deacetylase inhibitors

Histone deacetylase (HDAC) inhibitors are considered to be drugs for targeted cancer therapy and second-generation HDIs are currently being tested in clinical trials. Here, we report on the synthesis and biological evaluation of a novel HDAC inhibitor scaffold with the hydroxamate Zn(2+) complexing headgroup, selected from the 2-aroylindol motif. Inhibition of nuclear extract HDAC and recombinant HDAC 1 as well as induction of histone H3K(9+14) hyperacetylation mediated by E-N-hydroxy-(2-aroylindole)acrylamides or E-N-hydroxy-(2-aroylbenzofuran)acrylamides were studied. Moreover, the cytotoxic activity, the effects on the cell cycle, and histone H3S(10) phosphorylation of selected compounds were determined. By use of a panel of 24 different human tumor cell lines, mean IC(50) values of the most potent analogues 6c and 7b were 0.75 and 0.65 microM, respectively. The novel compounds were shown to be no substrates of the P-glycoprotein drug transporter. Comparable to N(1)-hydroxy-N(8)-phenyloctanediamide "2 (SAHA)", cells in the S phase of the cell cycle are depleted, with partial arrest in G1 and G2/M and finally induction of massive apoptosis.     

Small molecule inhibitors of histone deacetylase

This patent deals with novel histone deacetylase (HDAC) inhibitors and methods of their use for treating cell proliferative diseases or conditions, such as cancer, restenosis and psoriasis. Claimed herein are pharmaceutical compositions comprising small molecule HDAC inhibitors as the active ingredient, optionally combined with the use of an antisense oligonucleotide that inhibits HDAC expression. The claimed compounds were synthesised according to given reaction schemes and tested for their inhibition of HDAC enzymatic activity using nuclear extracts from cancer cells (pooled HDACs) and recombinant human HDAC1. An exemplified compound is stated to have caused a significant reduction in tumour weight and volume relative to saline-treated controls in BALB/c nude mice subcutaneously bearing A549 human lung carcinoma cells.     

Residues in the 11 A channel of histone deacetylase 1 promote catalytic activity: implications for designing isoform-selective histone deacetylase inhibitors

Histone deacetylase 1 (HDAC1) has been linked to cell growth and cell cycle regulation, which makes it a widely recognized target for anticancer drugs. Whereas variations of the metal-binding and capping groups of HDAC inhibitors have been studied extensively, the role of the linker region is less well known, despite the potency of inhibitors with diverse linkers, such as MS-275. To facilitate a drug design that targets HDAC1, we assessed the influence of residues in the 11 A channel of the HDAC1 active site on activity by using an alanine scan. The mutation of eight channel residues to alanine resulted in a substantial reduction in deacetylase activity. Molecular dynamics simulations indicated that alanine mutation results in significant movement of the active-site channel, which suggests that channel residues promote HDAC1 activity by influencing substrate interactions. With little characterization of HDAC1 available, the combined experimental and computational results define the active-site residues of HDAC1 that are critical for substrate/inhibitor binding and provide important insight into drug design.     

Romidepsin: a novel histone deacetylase inhibitor for cancer

Introduction: Romidepsin is a novel histone deacetylase (HDAC) inhibitor, with a recent approval for treatment of cutaneous T-cell lymphoma (CTCL). HDAC inhibitors represent a novel approach to anti-tumor therapy. In contrast to traditional cytotoxic chemotherapy, HDAC inhibitors target underlying epigenetic changes leading to malignant transformation. Further study of romidepsin and similar agents in solid and hematologic malignancies is ongoing. Areas covered: This review discusses the development of romidepsin, its mechanism of action, pivotal clinical trials, drug toxicity and its recent approval for CTCL treatment. Key clinical trials covered include Phase I/II testing of romidepsin in solid and hematologic malignancies. In addition, the Phase II trial in CTCL leading to FDA approval of romidepsin is reviewed in detail. Literature search was performed using PubMed; keywords and concepts used included romidepsin, T-cell lymphoma and HDAC inhibitors. Expert opinion: Romidepsin is a potent HDAC inhibitor with demonstrable activity in T-cell lymphoma. In contrast to vorinostat, romidepsin is approved as second-line therapy. Current approval only includes CTCL; promising results have been demonstrated in Phase II testing of peripheral T-cell lymphoma subtypes. Future directions include expanded indications in T-cell lymphomas as well as novel combinations with other HDAC inhibitors and other therapeutic agents.     

Evodiamine-inspired dual inhibitors of histone deacetylase 1 (HDAC1) and topoisomerase 2 (TOP2) with potent antitumor activity

A great challenge in multi-targeting drug discovery is to identify drug-like lead compounds with therapeutic advantages over single target inhibitors and drug combinations. Inspired by our previous efforts in designing antitumor evodiamine derivatives, herein selective histone deacetylase 1 (HDAC1) and topoisomerase 2 (TOP2) dual inhibitors were successfully identified, which showed potent in vitro and in vivo antitumor potency. Particularly, compound 30a was orally active and possessed excellent in vivo antitumor activity in the HCT116 xenograft model (TGI = 75.2%, 150 mg/kg, p.o.) without significant toxicity, which was more potent than HDAC inhibitor vorinostat, TOP inhibitor evodiamine and their combination. Taken together, this study highlights the therapeutic advantages of evodiamine-based HDAC1/TOP2 dual inhibitors and provides valuable leads for the development of novel multi-targeting antitumor agents.     

Cutaneous reactions to epidermal growth factor receptor inhibitors

Cutaneous toxicities are the most common adverse effects of antineoplastic therapy with epidermal growth factor receptor (EGFR) inhibitors. Skin reactions to this class of agents usually present as papular and/or pustular follicular eruptions developing within two weeks of treatment onset. Other manifestations include generalized xerosis and pruritus, as well as abnormalities of the hair and nails. For most EGFR inhibitors, the incidence and severity of cutaneous toxicity are associated with clinical benefit. At the same time, cutaneous toxic effects may detract substantially from health-related quality of life, leading to interruption, discontinuation or dose reduction of EGFR inhibitor therapy in significantly affected patients. Current recommendations for treatment of EGFR inhibitor-induced eruptions are based primarily on anecdotal evidence from published case series and physicians' own experiences, and include antibiotics, corticosteroids and retinoids. Randomized controlled trials are needed to enable the development of evidence-based paradigms for the treatment of EGFR inhibitor-induced skin eruptions.     

Current patent status of histone deacetylase inhibitors

Histone deacetylases (HDACs) alter the acetylation status of the amino terminal region of histone proteins, which are complexed with DNA in the nucleosome. This acetylation status determines DNA accessibility and, in turn, influences gene expression. The inappropriate recruitment of HDACs may be one mechanism by which oncogenes can alter gene expression in favour of excessive proliferation and this makes inhibition of HDACs a potential target for the development of small molecule anticancer agents. There are several HDAC inhibitors currently in cancer clinical trials and approximately twenty research organisations with ongoing programmes in this field. This review examines the HDAC patent literature from 1997 to mid-2002 with some discussion of primary literature and older citations when appropriate. The review is divided into the structural classes of known HDAC inhibitors that include the non-peptidic hydroxamic acids, cyclic peptides, benzamides, butyric acid analogues and electrophilic ketones.     

From natural products to small molecule ketone histone deacetylase inhibitors: development of new class specific agents

Histone deacetylases (HDACs) are one of two counteracting enzyme families whose activity controls the acetylation state of lysine protein residues, notably those contained in the N-terminal extensions of the core histones. Deregulation of the acetylation state of specific lysine residues has been implicated in a multitude of biologic processes, notably cancer, where HDACs are known to be involved in the control of cell cycle progression, cell survival and differentiation. HDAC inhibitors are being developed as anti-neoplastic agents. Nature has led the way in the development of these compounds, with trichostatin A being the first hydroxamic acid HDAC inhibitor identified. Likewise, the disulfide depsipeptide Romidepsin is currently in clinical trials, while an array of cyclic tetrapeptides HDAC inhibitors have been reported. Rational drug design has allowed these cyclic tetrapeptide to be transformed into equally potent small molecule inhibitors selective for either class I or class II HDACs. While acyclic alkyl ketones have been demonstrated to be selective HDAC 1, 2 and 3 inhibitors with efficacy in xenograft models, trifluoromethyl ketones have been shown to be selective inhibitors for class II HDACs and recently have been revealed to bind in the active site of the enzyme in their hydrated form.     

Emerging drugs targeting human epidermal growth factor receptor 2 (HER2) in the treatment of breast cancer

Introduction: Human epidermal growth factor 2 (HER2) overexpression is present in 20% of breast cancer patients. It is associated with more aggressive disease and worse clinical outcome. New drugs are thus needed. Approved and future treatments will be discussed in this review.

Areas covered: The monoclonal antibodies trastuzumab and pertuzumab, the tyrosine kinase inhibitor lapatinib and the antibody-drug conjugate trastuzmab emtansine are approved for HER2 positive breast cancer. The combination of trastuzumab, pertuzumab and docetaxel is currently the first-line treatment in the metastatic setting. New therapies are still needed due to frequent relapse and resistance. These include mammalian target of rapamycin inhibitors, heat shock protein 90 inhibitors, pan-HER2 tyrosine kinase inhibitors, antibody-drug conjugates, immunotherapy agents (antibodies and vaccines), radioimmunotherapy and HER2 specific affinity proteins. Possible developmental issues are the complexity of the molecular biology of the HER2 positive cancer cell, the occurrence of resistance, toxicity and the high cost.

Expert opinion: The determination of the right sequence of use of old and new therapies remains a challenging issue. The selection of patients who do or don’t benefit from potentially toxic chemotherapy is also difficult. Central nervous system metastases are a common problem in HER2 positive breast cancer that needs to be addressed in future trials.     

Selective histone deacetylase inhibitors

Histone deacetylases (HDACs) are a family of conserved metalloproteases which play a key role in the development of cancer. They can be divided into 18 subtypes according to their structural diversity. Histone deacetylase inhibitors are considered as potential anti-cancer agents and a lot of pan-HDAC inhibitors have entered clinical trials. Selective HDAC inhibitors targeting only one member or one class subtype are less exploited at present and regarded less toxic as well as more tolerable than pan-HDAC inhibitors. Certain structural modifications or new moieties may help to acquire isoform selectivity. In this review, we will focus on each member of HDACs and selective HDAC inhibitors as well as the relationship between structure and selectivity.     

Anticancer activities of histone deacetylase inhibitors

Histone deacetylases (HDACs) are enzymes involved in the remodelling of chromatin, and have a key role in the epigenetic regulation of gene expression. In addition, the activity of non-histone proteins can be regulated through HDAC-mediated hypo-acetylation. In recent years, inhibition of HDACs has emerged as a potential strategy to reverse aberrant epigenetic changes associated with cancer, and several classes of HDAC inhibitors have been found to have potent and specific anticancer activities in preclinical studies. However, such studies have also indicated that the effects of HDAC inhibitors could be considerably broader and more complicated than originally understood. Here we summarize recent advances in the understanding of the molecular events that underlie the anticancer effects of HDAC inhibitors, and discuss how such information could be used in optimizing the development and application of these agents in the clinic, either as monotherapies or in combination with other anticancer drugs.