Novel dual Src/Abl inhibitors for hematologic and solid malignancies

Importance of the field: c-Src and Bcr-Abl are two non-receptor or cytoplasmic tyrosine kinases (TKs) that play important roles in the development of solid and hematological malignancies. Indeed, Src is overexpressed or hyperactivated in a variety of solid tumors, while Bcr-Abl is the causative agent of chronic myeloid leukemia (CML), where Src is also involved. The two enzymes share significant sequence homology and remarkable structural resemblance.

Areas covered in this review: ATP-competitive compounds originally developed as Src inhibitors, showed to be also potent Abl inhibitors. Dasatinib, the first dual Src/Abl inhibitor approved by the US FDA in 2006 for the treatment of imatinib-resistant CML, is currently being tested in several clinical trials for the treatment of different solid tumors. SKI-606 and AZD0530 are two other important dual Src/Abl inhibitors extensively tested in animal models and in clinical trials, but not entered into therapy yet.

What the reader will gain: In this review we will report the latest results regarding dasatinib, SKI-606 and AZD0530, but also the knowledge on new compounds that have appeared in the literature in the last few years, including AP24163, AP24534, XL228, DC2036. We will focus on the most recent clinical trials or on preclinical studies that are in progress on these small-molecule TK inhibitors that represent a targeted therapy with high potential against cancer.

Take home message: Molecularly targeted therapies, including the inhibition of specific TKs hyperactivated or overexpressed in many human cancers, could be less toxic than the classical non-specific cytotoxic chemotherapeutic agents; they could offer important therapeutic effects, especially if used in association with other agents such as monoclonal antibodies.     

Analogs,formulations and derivatives of imatinib: a patent review

Introduction: The Bcr-Abl inhibitor imatinib was approved in 2001 for chronic myeloid leukemia therapy, and dramatically changed the lives of patients affected by this disease. Since it also inhibits platelet derived growth factor receptor (PDGFR) and c-Kit, imatinib is used for various other tumors caused by abnormalities of one or both these two enzymes.

Areas covered: This review presents an overview on imatinib formulations and derivatives, synthetic methodologies and therapeutic uses that have appeared in the patent literature since 2008.

Expert opinion: Innovative imatinib formulations, such as nanoparticles containing the drug, will improve its bioavailability. Moreover, oral solutions or high imatinib content tablets or capsules will improve patient compliance. Some solid formulations and innovative syntheses that have appeared in the last few years will reduce the cost of the drug, offering big advantages for poor countries. Some recently patented efficacious imatinib derivatives are in preclinical studies and could enter clinical trials in the next few years. Overall, Bcr-Abl inhibitors constitute a very appealing research field that can be expected to expand further.     

Pyrrolo[2,3-d]pyrimidines active as Btk inhibitors

Introduction: Btk is a tyrosine kinase dysregulated in several B-cell malignancies and autoimmune diseases, and this has given rise to a search for Btk inhibitors. Nevertheless, only one Btk inhibitor, ibrutinib, has been approved to date, although other compounds are currently being evaluated in clinical trials or in preclinal stages.

Area covered: This review, after a brief introduction on Btk and its inhibitors already in clinical trials, focusses on pyrrolo[2,3-d]pyrimidine derivatives patented in the last five years as Btk inhibitors. Indeed, the pyrrolo[2,3-d]pyrimidine scaffold, being a deaza-isostere of adenine, the nitrogenous base of ATP, is an actively pursued target for Btk inhibitors. The patent literature since 2012 have been extensively investigated, pointing out the general features of the patented compounds and, when it is possible, their mechanism of action.

Expert opinion: The recently patented pyrrolo[2,3-d]pyrimidines, acting as reversible or irreversible inhibitors, showed a very interesting in vitro activity. For this reason, the development of compounds endowed with this scaffold could afford a significant impact in the search for drug candidates for the treatment of immune diseases or B-cell malignancies.     

Current concerns of undertreatment and overtreatment in chronic myeloid leukemia based on European LeukemiaNet 2013 recommendations

Introduction: The aim of this paper is to indicate optimal tyrosine kinase inhibitor (TKI) administration practices based on European LeukemiaNet (ELN) 2013 recommendations for chronic myeloid leukemia (CML). Likewise, current concerns of undertreatment and overtreatment with TKIs during the long-term clinical course of CML will be outlined.

Areas covered: Currently available TKIs for the management of CML are reviewed. The survival benefit of TKIs (imatinib, dasatinib, nilotinib, bosutinib, ponatinib) for the CML is excellent. The CML and TKI literature search was made in PubMed with particular focus on the clinical trials, recommendations, guidelines and expert opinions, as well as the ELN CML 2013 recommendations.

Expert opinion: Initial TKI treatment for low-risk chronic phase CML is imatinib 400 mg; high-Sokal risk and/or CML patients with complex karyotypic abnormalities would require more powerful second-generation TKIs (dasatinib 100 mg or nilotinib 600 mg). Absence of early molecular response after 6 months, complete cytogenetic response after 12 months and major molecular response after 18 months may require a more powerful TKI switch. If one of the two second-generation TKIs (nilotinib or dasatinib) was used as first-line therapy and failed, the other (dasatinib or nilotinib) could be administered.     

The expanding role of nilotinib in chronic myeloid leukemia

Importance of the field: Several therapeutic options, including tyrosine kinase inhibitors, exist for the treatment of patients with Philadelphia chromosome (Ph)-positive chronic myeloid leukemia (CML). Despite impressive results, there is room for improvement for those patients who are either resistant or intolerant to imatinib.

Areas covered in this review: An overview is given on the clinical results with nilotinib, a rationally designed second-generation tyrosine kinase inhibitor, as first- and second-line therapy in patients with Ph-positive CML. Important factors in predicting resistance to nilotinib and guiding therapeutic decisions are addressed.

What the reader will gain: Knowledge on the clinical efficacy and safety of nilotinib after imatinib failure and as first-line treatment. Point mutations in the kinase domain (KD) of BCR-ABL1 are important determinants of clinical sensitivity to currently available tyrosine kinase inhibitors, including nilotinib. Information on specific BCR-ABL1 KD mutations and safety profiles assist in therapeutic decision making.

Take home message: Nilotinib is a highly effective and well-tolerated therapeutic option in patients with Ph-positive CML after imatinib failure. Early evidence demonstrating increased efficacy has allowed expanding nilotinib to previously untreated patients in chronic phase. Insights into mechanisms of resistance to tyrosine kinase inhibitors and predictive factors for response will allow for a more individualized use of these agents.     

A safety evaluation of omacetaxine mepesuccinate for the treatment of chronic myeloid leukemia

ABSTRACT

Introduction: Therapy of chronic myeloid leukemia (CML) has been completely transformed by the development of tyrosine kinase inhibitors (TKIs). However, a subset of patients will fail TKI therapy due to resistance or intolerance. Omacetaxine mepesuccinate (OM), a protein translation inhibitor, is currently the only approved therapy that does not directly target the kinase domain. It has activity for CML patients irrespective of the phase or underlying kinase domain mutation status.

Areas covered: We searched the MEDLINE database for articles published in English on homoharringtonine or omacetaxine from 1970 to present. This article reviews the pharmacokinetics of OM and its clinical evolution for the treatment of CML pre- and post TKI development. Toxicity profile, drug administration and future directions are also discussed.

Expert opinion: OM represents a unique addition to the CML therapeutic armamentarium with its distinct mechanism of action and activity. The adverse event profile is manageable and with subcutaneous administration at the approved dose, cardiac toxicity is no longer a concern. The recent approval of home administration will facilitate access to this therapy and increase patient compliance. We conclude with specific scenarios where OM use should be considered in CP and AP-CML patients in the era of TKI therapy.     

Gilteritinib for the treatment of relapsed and/or refractory FLT3-mutated acute myeloid leukemia

ABSTRACT

Introduction: The receptor tyrosine kinase FLT3 is the most commonly mutated gene in acute myeloid leukemia (AML). FLT3-internal tandem duplication mutations are associated with an increased risk of relapse, and a number of small molecule inhibitors of FLT3 have been developed. The highly potent and selective FLT3 kinase inhibitor gilteritinib is the first tyrosine kinase inhibitor approved as monotherapy for the treatment of relapsed and/or refractory FLT3-mutated AML.

Areas covered: We review the biology and prognostic significance of FLT3 mutations in AML and discuss the pharmacology, clinical efficacy, and toxicity profile of gilteritinib. We also summarize important differences among the various FLT3 inhibitors that are currently approved or under development and highlight areas of ongoing research.

Expert opinion: Gilteritinib has been shown to improve survival compared to salvage chemotherapy in relapsed and/or refractory FLT3-mutated AML. Gilteritinib is orally available with a favorable toxicity profile and as such is quickly becoming the standard of care for this patient population. Ongoing clinical trials are evaluating gilteritinib in combination with frontline chemotherapy, in combination with other agents such as venetoclax and azacitidine for patients who are ineligible for standard induction therapy, and as a maintenance agent.     

Novel inhibitors in development for hepatocellular carcinoma

Importance of the field: The multikinase inhibitor sorafenib was the first agent to demonstrate a survival benefit for patients with locally advanced or metastatic hepatocellular carcinoma (HCC). Although sorafenib represents a landmark in the treatment of HCC and proved molecularly targeted therapy to be effective in this disease, it represents just the first step towards an improvement in systemic therapy. Since then, novel inhibitors have been evaluated in early clinical trials, showing potential activity.

Areas covered in this review: This article aims to review novel inhibitors emerging in the field of advanced HCC. An Internet-based search was performed to identify abstracts, clinical trials (www.clinicaltrials.gov, last accessed 30 November 2009), and original research and review articles.

What the reader will gain: Readers will gain a comprehensive survey of current molecularly targeted therapy approaches in advanced HCC. In addition, challenges such as the design of clinical trials, the assessment of radiological response, the role of combination therapy, and future developments in molecularly targeted therapy are discussed.

Take home message: Sorafenib is the standard of care in patients with advanced HCC. However, promising novel inhibitors are under investigation. Combined molecularly targeted therapies according to an individual genomic and proteomic profiling will probably lead to more personalised medicine in advanced HCC.     

Tyrosine kinase inhibitors in acute and chronic leukemias

Introduction: Since the initial approval of imatinib much has been learned about its resistance mechanisms, and efforts have continued to improve upon BCR-ABL tyrosine kinase inhibitor therapy. Targeted therapy with TKIs has continued to be an area of active research and development in the care of acute and chronic leukemia patients.

Areas covered: This article reviews current approved and investigational TKI treatments for chronic myelogenous leukemia (CML), Philadelphia-chromosome positive acute lymphoblastic leukemia (Ph + ALL) and acute myelogenous leukemia (AML).

Expert opinion: There are now more potent BCR-ABL TKIs approved, which allow for additional options when determining front-line and second-line CML and Ph + ALL treatments. The T315I mutation is an ever-present challenge. Ponatinib, a pan BCR-ABL TKI, while still under investigation, is very hopeful with its ability to overcome T315I mutations in resistant CML and Ph + ALL patients. Because nilotinib and dasatinib have not been directly compared, at present we recommend selecting one or the other based on the side-effect profile, drug interactions, patient comorbidities, and mutational status. FLT-3 inhibition is of particular interest in AML patients with FLT-3 internal tandem duplication mutations; this type of targeted therapy continues to be studied.     

EGFR targeting drugs in the treatment of head and neck squamous cell carcinoma

Importance of the field: Head and neck cancer is the sixth most common cancer worldwide. Despite intense efforts to improve different treatment modalities, mortality rates in advanced cases remain high.

Areas covered in the review: EGFR targeting mAb cetuximab (Erbitux) has been approved for the treatment of locally advanced head and neck squamous cell carcinoma (HNSCC) in combination with radiotherapy and for recurrent or metastatic HNSCC. Here, we review recent scientific advances, as well as future research goals regarding EGFR inhibitors in the treatment of HNSCC. Information was compiled by searching the PubMed, Web of Knowledge and American Society of Clinical Oncology databases for articles published before October 2009. The search terms included ‘head and neck cancer’, ‘EGFR’, ‘cetuximab’, ‘panitumumab’, ‘zalutumumab’, ‘nimotuzumab’, ‘erlotinib’, ‘gefitinib’ and ‘lapatinib’. The National Institutes of Health registry of clinical trials (www.clinicaltrials.gov) was used to search for clinical trials in HNSCC.

What the reader will gain: The background scientific rationale, clinical efficacy and development of EGFR inhibitors in HNSCC are discussed.

Take home message: Cetuximab significantly improves survival of patients with locally advanced or metastatic HNSCC. Treatment strategies combining EGFR inhibitors with multimodality approaches may eventually increase cure rate in HNSCC.     

An evaluation of brigatinib as a promising treatment option for non-small cell lung cancer

ABSTRACT

Introduction: Brigatinib is a second-line inhibitor for the treatment of rearranged anaplastic lymphoma kinase (ALK) in lung cancer patients which has significant activity against brain metastases. This tyrosine kinase inhibitor (TKI) overcomes a wide range of ALK mutations which confer therapeutic resistance and is increasingly applied in first-line therapy due to improved benefit for patients compared to crizotinib, the current standard of care.

Areas covered: The authors review the development and characteristics of brigatinib and discuss the optimal clinical use and sequence of the application of ALK inhibitors in patients progressing under therapy.

Expert opinion: ALK-rearranged NSCLC can be treated with a broad range of approved and novel inhibitors at various stages of therapy, including the second-line therapeutic brigatinib. Besides this TKI, the second-line ALK inhibitors alectinib and ceritinib, as well as the third-line lorlatinib are approved for the treatment of ALK-positive NSCLC patients. The main challenge is to find sequences and combinations of ALK inhibitors which provide the best benefit for the patients.     

Treatment options for chronic myeloid leukemia

Introduction : The bcr-abl tyrosine kinase inhibitors (TKIs) are the cornerstone treatment for chronic myeloid leukemia (CML). However, there are many topics related to therapy that remain debated.

Areas covered : The aim of this paper is to give the reader a comprehensive review of how to treat CML at diagnosis, how to monitor the disease and a brief read of special populations and case scenarios. It describes the first-line (imatinib) and second-line (nilotinib and dasatinib) TKIs currently used for the treatment of CML, including landmark studies proving their efficacy, side effect profile, dosage and use in special populations. It also reviews the current guidelines regarding treatment and monitoring of the disease while on TKIs, along with an overview of treatment in advanced stages, the role of allogeneic stem cell transplantation and investigational drugs.

Expert opinion : Although imatinib represented a mayor therapeutic advancement over conventional chemotherapy, second-generation TKIs offer higher rates of optimal response and should be used as the frontline therapy. Patients with the T315I mutation carry a worse prognosis and should be offered allogeneic stem cell transplantation. The treatment in advanced stages of CML remains suboptimal and bench, translational and clinical research is encouraged.     

Nilotinib for the treatment of Philadelphia-chromosome-positive chronic myeloid leukemia

Importance of the field: Although the introduction of imatinib revolutionized the management of chronic myeloid leukemia (CML), some patients exhibit resistance or intolerance to the drug. Nilotinib induces high and rapid rates of cytogenetic and molecular responses. With recent approval for newly diagnosed patients with chronic phase CML, the current algorithm for treatment will probably be transformed.

Areas covered in this review: This review will describe evaluations of nilotinib in all phases of CML from 1995 to the present. Early preclinical data and Phase I, Phase II and Phase III evaluations will demonstrate the role of nilotinib in newly diagnosed CML, as well as in imatinib-resistant or imatinib-intolerant disease.

What the reader will gain: Mutations in the BCR-ABL kinase domain are responsible for the majority of resistance to imatinib. In comparison with imatinib, nilotinib displays increased selectivity and potency at inhibiting proliferation of BCR-ABL expressing cells. Although several mutations, including T315I, remain resistant to nilotinib, activity in all phases of CML has been reported.

Take home message: Nilotinib induces high and rapid rates of cytogenetic and molecular response, with less progression to advanced forms of disease compared with imatinib. Considering that the rapid achievement of these clinical milestones has been associated with positive long-term outcomes, nilotinib as initial therapy in patients with CML in chronic phase represents the future in CML treatment. Longer follow-up is necessary to recognize survival advantages.     

Investigational FMS-like tyrosine kinase 3 inhibitors in treatment of acute myeloid leukemia

Introduction: Outcomes for the majority of patients with acute myeloid leukemia (AML) remain poor. Over the past decade, significant progress has been made in the understanding of the cytogenetic and molecular determinants of AML pathogenesis. One such advance is the identification of recurring mutations in the FMS-like tyrosine kinase 3 gene (FLT3). Currently, this marker, which appears in approximately one-third of all AML patients, not only signifies a poorer prognosis but also identifies an important target for therapy. FLT3 inhibitors have now undergone clinical evaluation in Phase I, II and III clinical trials, as both single agents and in combination with chemotherapeutics. Unfortunately, to date, none of the FLT3 inhibitors have gained FDA approval for the treatment of patients with AML. Yet, several promising FLT3 inhibitors are being evaluated in all phases of drug development.

Areas covered: This review aims to highlight the agents furthest along in their development. It also focuses on those FLT3 inhibitors that are being evaluated in combination with other anti-leukemia agents.

Expert opinion: The authors believe that the field of research for FLT3 inhibitors remains promising, despite the historically poor prognosis of this subgroup of patients with AML. The most promising areas of research will likely be the elucidation of the mechanisms of resistance to FLT3 inhibitors, and development of potent FLT3 inhibitors alone or in combination with hypomethylating agents, cytotoxic chemotherapy or with other targeted agents.     

Dasatinib in solid tumors

Importance of the field: Dasatinib is an oral, potent adenosine triphosphate-competitive inhibitor of multiple tyrosine kinases including BCR-ABL, c-KIT, platelet-derived growth factor receptor, and Src family kinases (SFKs). It has gained much attention for its use in chronic myeloid leukemia and for the treatment of adults with Philadelphia chromosome-positive acute lymphoblastic leukemia. However, dasatinib is also being explored in solid tumors in ongoing Phase I and II clinical trials.

Areas covered in this review: The clinical efficacy of dasatinib in a wide variety of solid tumors and important Phase I/II studies utilizing dasatinib and the optimal dosage used in solid tumors. A literature search was conducted using PubMed/MEDLINE, www.clinicaltrials.gov, and the American Society of Clinical Oncology websites to find relevant Phase I/II clinical trials during 1987 – 2009.

What the reader will gain: The understanding that the biology and mechanism of Src activation in tumors are not well understood and finding the optimal use of SFK inhibitors in the clinical setting requires further investigation.

Take home message: In reviewing the clinical safety data of dasatinib in its current use as a Src inhibitor in a wide variety of solid malignancies, dasatinib appears to be safe and is a promising agent for the treatment of metastatic solid tumors refractory to standard therapies.     

Small molecule c-Met kinase inhibitors: a review of recent patents

Importance of the field: c-Met kinase is the receptor for hepatocyte growth factor. Primarily expressed on epithelial and mesenchymal cells its normal function is associated with wound healing, liver regeneration and embryo development. However, dysregulation of c-Met through overexpression, gene amplification, mutation or a ligand-dependent autocrine/paracrine loop is associated with tumorigenesis. c-Met dysregulation in human cancer patients is typically associated with a poor prognosis, aggressive disease, increased metastasis and shortened patient survival. Targeting the hepatocyte growth factor/c-Met signalling pathway as a means of cancer therapy has, therefore, become increasingly popular with a number of different therapeutic approaches undergoing clinical trials.

Areas covered by this review: This review covers the patent applications for small molecule c-Met kinase inhibitors since 2007, attempts to place them in context from a structural point of view and examines their potential applications in cancer therapy.

What the reader will gain: Readers will gain an overview of the structural types of c-Met inhibitors, the major players in the field and an insight into what is progressing into the clinic.

Take home message: This area is developing rapidly and the results of the various ongoing clinical trials will generate an increased understanding of the potential benefits and pitfalls of c-Met inhibitors as therapeutic agents.     

An overview of quinoline as a privileged scaffold in cancer drug discovery

Introduction: The concept of privileged structures is well known and is often used in the process of drug design and development. Although its assumptions are not clear, its overall usefulness remains high. Various substructures have been identified as privileged and quinoline is a prime example of such a structure.

Areas covered: Quinoline drugs that are currently approved or under clinical investigation were reviewed based on a literature search. Their modes of action and outcomes during clinical research are discussed.

Expert opinion: Undoubtedly, quinoline-based compounds have a significant impact on anticancer drugs. Although topoisomerase and kinase inhibitors are the only two different classes of agents that are currently approved for anticancer therapy, more than twenty different drug candidates are being tested on humans. The quinoline moiety offers an easily accessible, well-understood scaffold for designing new drugs. It is also a very druggable molecule with the potency for structure optimization through established synthetic pathways. For these reasons, quinoline-based anticancer drugs have a strong position in modern medicinal chemistry.     

Emerging drugs for the treatment of gastrointestinal stromal tumour

Introduction: Tyrosine kinase inhibitors (TKIs) have transformed the treatment landscape for patients with gastrointestinal stromal tumors (GIST). Unfortunately, resistance to the currently approved TKIs poses a huge challenge, and patients are in need of additional therapeutic options. Fortunately, many novel therapeutic approaches are being tested in treatment of GIST to overcome resistance to the approved TKIs

Areas covered: We performed an extensive literature (PUBMED) search to identify emerging drugs being tested in treatment of GIST in early phase clinical trials. We discuss recent ongoing research and emerging novel inhibitors of KIT and PDGFRA receptors, inhibitors in downstream signaling pathways (mTOR and PIK3 inhibitors), inhibitors of other potential targets including ETV1/MEK, MET, FGFR, IGF1R, histone deacetylase inhibitors, heat shock protein 90 inhibitors, cyclin-dependent kinase inhibitors and immune checkpoint inhibitors in treatment of GIST

Expert opinion: Multiple agents are under evaluation; those that benefit GIST patients with imatinib resistant mutations, or those with benefit in patients refractory to approved agents are most likely to be developed in this disease. The role of immunotherapy for GIST is still investigational.     

Emerging protein kinase inhibitors for the treatment of multiple myeloma

ABSTRACT

Introduction: Significant advances have been made during the last two decades in terms of new therapeutic options but also of innovative approaches to diagnosis and management of multiple myeloma (MM). While patient survival has been significantly prolonged, most patients relapse. Including the milestone approval of the first kinase inhibitor imatinib mesylate for CML in 2001, 48 small molecule protein kinase (PK) inhibitors have entered clinical practice until now. However, no PK inhibitor has been approved for MM therapy yet.

Areas covered: This review article summarizes up-to-date knowledge on the pathophysiologic role of PKs in MM. Derived small molecules targeting receptor tyrosine kinases (RTKs), the Ras/Raf/MEK/MAPK- pathway, the PI3K/Akt/mTOR- pathway as well as Bruton tyrosine kinase (BTK), Aurora kinases (AURK), and cyclin-dependent kinases (CDKs) are most promising. Preclinical as well as early clinical data focusing on these molecules will be presented and critically reviewed.

Expert opinion: Current MM therapy is directed against general vulnerabilities. Novel therapeutic strategies, inhibition of PKs in particular, are directed to target tumor-specific driver aberrations such as genetic abnormalities and microenvironment-driven deregulations. Results of ongoing Precision Medicine trials with PK inhibitors alone or in combination with other agents are eagerly awaited and hold the promise of once more improving MM patient outcome.     

Investigational platelet-derived growth factor receptor kinase inhibitors in breast cancer therapy

Introduction: Aberrant regulation of platelet-derived growth factors (PDGFs) and their receptors (PDGFR) has been shown to be involved in many solid tumors, including breast cancer. PDGFR-α and PDGFR-β expressions were documented in breast cancer and are correlated with tumor aggressiveness and metastasis. Preclinical evidence further suggests tumor stimulatory roles of PDGFRs expressed by tumor stroma cells and indicates a deleterious effect of stromal PDGFRs on intratumoral drug uptake.

Areas covered: This review summarizes the present understanding of PDGF signaling in breast cancer based on experimental studies and available clinical trials. It also provides a critical discussion of selected ongoing clinical trials in patients with breast cancer involving PDGFR inhibition with tyrosine kinase inhibitors, specifically in endocrine responsive breast cancer.

Expert opinion: An increased molecular understanding of response and resistance mechanisms to endocrine therapy will be essential for therapeutic advances in PDGFR-directed cancer therapy. Future developments in the field will rely on clinical studies where prospective analyses of target expression in breast cancer cells and in the tumor stroma are included. More selective PDGFR inhibitors with reduced side effects will be crucial for combinatorial therapies. Development of sensitive diagnostics is of critical importance for patient selection and monitoring of therapeutic effects.