Targeting nuclear kinases in cancer: development of cell cycle kinase inhibitors

Cellular proliferation is a tightly controlled set of events that is regulated by numerous nuclear protein kinases. The proteins involved include checkpoint kinases (CHK), cyclin-dependent kinases (CDK), which regulate the cell cycle and aurora kinases (AURK) and polo-like kinases (PLK), which regulate mitosis. In cancer, these nuclear kinases are often dysregulated and cause uncontrolled cell proliferation and growth. Much work has gone into developing novel therapeutics that target each of these protein kinases in cancer but none have been approved in patients. In this review we provide an overview of the current compounds being developed clinically to target these nuclear kinases involved in regulating the cell cycle and mitosis.

Targeted approach to metastatic colorectal cancer: what comes beyond epidermal growth factor receptor antibodies and bevacizumab?

The prognosis of patients with cancer remains poor in spite of the advances obtained in recent years with new therapeutic agents, new approaches in surgical procedures and new diagnostic methods. The discovery of a plethora of cellular targets and the rational generation of selective targeting agents has opened an era of new opportunities and extraordinary challenges. The specificity of these agents renders them capable of specifically targeting the inherent abnormalities of cancer cells, potentially resulting in less toxicity than traditional nonselective cytotoxics. Among the many new types of rationally designed agents are therapeutics targeting various strategic facets of growth signal transduction, malignant angiogenesis, survival, metastasis and cell-cycle regulation. The evaluation of these agents is likely to require some changes from the traditional drug development paradigms to realize their full potential. Inhibition of the epidermal growth factor receptor and the vascular endothelial growth factor have provided proof of principle that disruption of signal cascades in patients with colorectal cancer has therapeutic potential. This experience has also taught us that resistance to such rationally developed targeted therapeutic strategies is common. In this article, we review the role of signal transduction in colorectal cancer, introduce promising molecular targets, and outline therapeutic approaches under development.

A phase I dose escalation study of AT9283, a small molecule inhibitor of aurora kinases, in patients with advanced solid malignancies

BACKGROUND

AT9283 is an inhibitor of aurora kinases A and B with antitumor activity in preclinical models. This a First in Human phase I study assessed the safety, tolerability, pharmacokinetic and pharmacodynamic properties and preliminary efficacy of AT9283.

PATIENTS AND METHODS

Patients with advanced tumors received AT9283 as a continuous central venous infusion over 3 days in cohorts of three to six patients starting at 1.5 mg/m(2)/day (equivalent to 4.5 mg/m(2)/72 h). The oral bioavailability of AT9283 was assessed in a cohort of seven patients. Pharmacodynamic analysis of biomarkers included phosphorylation of histone H3 on serine 10, proliferating cell nuclear antigen, Ki67, M30 and M65 in skin and plasma.

RESULTS

Forty patients were included in all analyses. AT9283 was generally well tolerated with main toxic effects of reversible dose-related myelosuppression, gastrointestinal disturbance, fatigue and alopecia. The dose-limiting toxicity of AT9283 was grade 3 febrile neutropenia in two patients at 36 mg/m(2)/72 h and the maximum tolerated dose (MTD) was established at 27 mg/m(2)/72 h. Systemic exposure was dose proportional. The mean oral bioavailability of a 0.9 mg/m(2) dose was 29.4% (range 11.2%-36.7%). Pharmacodynamic analyses indicated antiproliferative and apoptotic activity of AT9283. Four patients with esophageal, non-small-cell lung cancer (n = 2) and colorectal cancer demonstrated RECIST stable disease ≥ 6 months.

CONCLUSION

AT9283 was well tolerated up to the MTD of 27 mg/m(2)/72 h. AT9283 is currently assessed in phase II trials.

Inhibitors targeting mitosis: tales of how great drugs against a promising target were brought down by a flawed rationale

Although they have been advocated with an understandable enthusiasm, mitosis-specific agents such as inhibitors of mitotic kinases and kinesin spindle protein have not been successful clinically. These drugs were developed as agents that would build on the success of microtubule-targeting agents while avoiding the neurotoxicity that encumbers drugs such as taxanes and vinca alkaloids. The rationale for using mitosis-specific agents was based on the thesis that the clinical efficacy of microtubule-targeting agents could be ascribed to the induction of mitotic arrest. However, the latter concept, which has long been accepted as dogma, is likely important only in cell culture and rapidly growing preclinical models, and irrelevant in patient tumors, where interference with intracellular trafficking on microtubules is likely the principal mechanism of action. Here we review the preclinical and clinical data for a diverse group of inhibitors that target mitosis and identify the reasons why these highly specific, myelosuppressive compounds have failed to deliver on their promise.

Mutants of protein kinase A that mimic the ATP-binding site of Aurora kinase

We describe in the present paper mutations of the catalytic subunit α of PKA (protein kinase A) that introduce amino acid side chains into the ATP-binding site and progressively transform the pocket to mimic that of Aurora protein kinases. The resultant PKA variants are enzymatically active and exhibit high affinity for ATP site inhibitors that are specific for Aurora kinases. These features make the Aurora-chimaeric PKA a valuable tool for structure-based drug discovery tasks. Analysis of crystal structures of the chimaera reveal the roles for individual amino acid residues in the binding of a variety of inhibitors, offering key insights into selectivity mechanisms. Furthermore, the high affinity for Aurora kinase-specific inhibitors, combined with the favourable crystallizability properties of PKA, allow rapid determination of inhibitor complex structures at an atomic resolution. We demonstrate the utility of the Aurora-chimaeric PKA by measuring binding kinetics for three Aurora kinase-specific inhibitors, and present the X-ray structures of the chimaeric enzyme in complex with VX-680 (MK-0457) and JNJ-7706621 [Aurora kinase/CDK (cyclin-dependent kinase) inhibitor].

Phase I dose escalation study of MK-0457, a novel Aurora kinase inhibitor, in adult patients with advanced solid tumors

PURPOSE

To assess the maximum-tolerated dose (MTD), dose-limiting toxicity (DLT), safety, and tolerability of the 24-h continuous intravenous (CIV) infusion of MK-0457, a novel pan-Aurora kinase inhibitor, in patients with advanced solid tumors and to determine the bioavailability of an oral dose of 100 mg MK-0457.

STUDY DESIGN

MK-0457 was administered as a 24-h CIV infusion every 21 days. Dose escalation proceeded per toxicity criteria. A 100-mg oral dose was administered to seven patients 48 h prior to the CIV infusion dose of 64 mg/m(2)/h.

RESULTS

Twenty-seven patients received a total of 86 infusions of MK-0457. Dose-limiting toxicity at 96 mg/m(2)/h included grade 4 neutropenia and grade 3 herpes zoster. The MTD was identified as 64 mg/m(2)/h. The most common adverse events were nausea, vomiting, diarrhea, and fatigue. Pharmacokinetic analyses revealed that CIV infusion MK-0457 had an estimated mean terminal half-life of approximately 6.6-10.2 h and that end-of-infusion concentrations and mean AUCs were approximately dose proportional. The estimated mean oral bioavailability of MK-0457 was 7.9%. One patient with advanced ovarian cancer attained prolonged stable disease for 11 months.

CONCLUSIONS

MK-0457 was well tolerated in this schedule. Almost half the patients attained stable disease. Further development of this class of agents will likely occur in combination with other anti-cancer treatments.

Biology of Aurora A kinase: implications in cancer manifestation and therapy

The Aurora A kinase belongs to serine/threonine group of kinases, well known for its role in cell cycle, especially in the regulation of mitosis. Numerous substrates of Aurora A kinase have been identified, which are predominantly related to cell cycle progression while some of them are transcription factors. Aurora A-mediated phosphorylation can either directly or indirectly regulate the function of its substrates. There are overwhelming evidences which report overexpression and gene amplification of Aurora A in several human cancers, and suggest that Aurora A could be a bona fide oncogene involved in tumorigenesis. Hence, Aurora A plays wide-ranging roles in both mitosis and its deregulation manifests in cancer progression. These observations have favored the choice of Aurora kinases as a target for cancer therapy. Recently, numerous small molecules have been discovered against Aurora kinases and many have entered clinical trials. Most of these small-molecule modulators designed are specific against either Aurora A or Aurora B, but some are dual inhibitors targeting the ATP-binding site which is highly conserved among the three human homologues of Aurora kinase. In this review, we discuss the physiological functions of Aurora A, interactions between Aurora A kinase and its cellular substrates, tumorigenesis mediated by Aurora A kinase upon overexpression, and small-molecule modulators of Aurora kinase as targets for cancer therapy.

Influence of pharmacogenetic variability on the pharmacokinetics and toxicity of the aurora kinase inhibitor danusertib

Objectives Danusertib is a serine/threonine kinase inhibitor of multiple kinases, including aurora-A, B, and C. This explorative study aims to identify possible relationships between single nucleotide polymorphisms in genes coding for drug metabolizing enzymes and transporter proteins and clearance of danusertib, to clarify the interpatient variability in exposure. In addition, this study explores the relationship between target receptor polymorphisms and toxicity of danusertib. Methods For associations with clearance, 48 cancer patients treated in a phase I study were analyzed for ABCB1, ABCG2 and FMO3 polymorphisms. Association analyses between neutropenia and drug target receptors, including KDR, RET, FLT3, FLT4, AURKB and AURKA, were performed in 30 patients treated at recommended phase II dose-levels in three danusertib phase I or phase II trials. Results No relationships between danusertib clearance and drug metabolizing enzymes and transporter protein polymorphisms were found. Only, for the one patient with FMO3 18281AA polymorphism, a significantly higher clearance was noticed, compared to patients carrying at least 1 wild type allele. No effect of target receptor genotypes or haplotypes on neutropenia was observed. Conclusions As we did not find any major correlations between pharmacogenetic variability in the studied enzymes and transporters and pharmacokinetics nor toxicity, it is unlikely that danusertib is highly susceptible for pharmacogenetic variation. Therefore, no dosing alterations of danusertib are expected in the future, based on the polymorphisms studied. However, the relationship between FMO3 polymorphisms and clearance of danusertib warrants further research, as we could study only a small group of patients.

Novel targets in esophageal and gastric cancer: beyond antiangiogenesis

Cancers of the stomach, gastroesophageal junction and esophagus are a major cause of cancer-related deaths worldwide. In Western countries, adenocarcinomas of the distal esophagus, gastroesophageal junction and proximal stomach have been increasing in frequency more rapidly than other malignancies. The majority of newly diagnosed patients present with advanced disease and the overall survival remains dismal at approximately 10% at 5 years. Better understanding of tumor biology has led to the development of promising novel therapeutic strategies. There is therefore increasing optimism that some of these approaches will improve the outcomes in these increasingly common cancers. Given the success of antiangiogenesis as a therapeutic strategy in various types of cancer, there are ongoing efforts to investigate the utility of other targeted therapies in the treatment of gastric and esophageal cancers. This review will focus on novel therapeutic targets other than angiogenesis and provide a rationale for the further clinical evaluation of these agents in patients with upper gastrointestinal tract cancers.

Danusertib (formerly PHA-739358)--a novel combined pan-Aurora kinases and third generation Bcr-Abl tyrosine kinase inhibitor

The Aurora kinases belong to a family of highly conserved serine/threonine protein kinases. They play an essential role as key mitotic regulators, controlling entry into mitosis, centrosome function, chromosome assembly, and segregation. As many other regulators of mitosis, Aurora kinases are frequently found to be aberrantly overexpressed in cancer cells. Therefore, these proteins have become an attractive target for the development of new anticancer therapies. In fact, several small-molecule inhibitors of Aurora kinases have already been developed and some of them have shown promising clinical efficacy in a number of human tumors in Phase I and II clinical trials. Among those, one of the most advanced clinical compound currently is Danusertib (formerly PHA-739358), which exhibits inhibitory activity against all known Aurora kinases as well as other cancer-relevant kinases such as the Bcr-Abl tyrosine kinase, including its multidrug-resistant T315I mutant. This mutation is responsible for up to 25% of all clinically observed resistances in CML patients undergoing Imatinib therapy. However, this particular mutation is predicted to play an even more important clinical role in the future, since in addition to Imatinib, it also confers resistance to second-generation Bcr-Abl inhibitors such as Nilotinib, Dasatinib, and Bosutinib. Therefore, combined Aurora and Bcr-Abl inhibition (the latter including high-grade resistance conferring mutations) with compounds such as Danusertib represents a promising new strategy for treatment of Bcr-Abl positive leukemias, especially those in second and third line of treatment.

Phase I pharmacokinetic and pharmacodynamic study of the aurora kinase inhibitor danusertib in patients with advanced or metastatic solid tumors

PURPOSE

Danusertib (PHA-739358) is a small-molecule pan-aurora kinase inhibitor. This phase I dose escalation study was conducted to evaluate safety and tolerability of danusertib with additional pharmacokinetic, biomarker, and efficacy assessments.

PATIENTS AND METHODS

Patients with solid tumors refractory to standard therapies or with no standard therapy available were enrolled. Danusertib was administered intravenously on days 1, 8, and 15 every 28 days in 6-hour or 3-hour infusion schedules (ie, 6-hour IVS or 3-hour IVS). Dose levels from 45 mg/m(2) in the 6-hour IVS, and from 250 mg/m(2) in the 3-hour IVS, were studied.

RESULTS

Fifty patients were treated. For the 6-hour IVS, the most frequently reported adverse effects were neutropenia (55%), nausea (25%), anorexia (23%), fatigue (20%), and diarrhea (18%). In the 3-hour IVS, fatigue (70%), neutropenia (60%), diarrhea (50%), and nausea (30%) were seen. Nonhematologic toxicity was mild to moderate. Neutropenia was dose limiting. The maximum-tolerated dose was 330 mg/m(2) for the 6-hour IVS and was not identified for the 3-hour IVS. The systemic exposure to danusertib increased linearly with dose. The infusion rate did not appear to remarkably influence the pharmacokinetics of danusertib. Biomarker analysis showed inhibition of histone H3 phosphorylation, indicative of aurora B inhibition, at doses of 190 mg/m(2) or greater. Stable disease was observed in 23.7% of evaluable patients, and disease stabilization occurred in 6 or more months in five patients.

CONCLUSION

Dose-limiting toxicity of danusertib is neutropenia, which was short lasting and generally uncomplicated; danusertib administration had limited nonhematologic toxicity. The recommended dose of danusertib for phase II studies is 330 mg/m(2) infused over 6 hours on days 1, 8, and 15 every 28 days.

In vitro anti-myeloma activity of the Aurora kinase inhibitor VE-465

This study characterized the preclinical anti-myeloma activity of VE465, a low molecular weight pan-Aurora kinase inhibitor. After 96-h drug exposure, several multiple myeloma (MM) cell lines were more sensitive to VE465 compared to non-malignant cells. The anti-MM activity of VE465 was maintained in the presence of interleukin-6 and, interestingly, enhanced by co-culture with stromal cells. However, primary MM cells were less responsive than cell lines. Combinations with dexamethasone (Dex), doxorubicin (Doxo) and bortezomib showed no antagonism. Our study highlights the potential role of the tumour microenvironment in modulating the activity of this drug class.

The topoisomerase I poison CPT-11 enhances the effect of the aurora B kinase inhibitor AZD1152 both in vitro and in vivo

PURPOSE

AZD1152 is an Aurora B kinase inhibitor currently in clinical trials. As the topoisomerase I poison CPT-11 induces a G(2) arrest, a mechanistic understanding of the cell cycle interactions between these agents may prove critical for combination therapy.

METHODS

AZD1152 was tested in vitro and in vivo with SN-38 and CPT-11 against HCT-116 cells. Inhibition of clonogenicity, induction of apoptosis, effects on polyploidy, and tumor growth were examined.

RESULTS

AZD1152 alone induced polyploidy of HCT-116 cells at low nanomolar concentrations. The induction of apoptosis required prolonged exposure (48 hours) and higher concentrations of drug. When SN-38 was given before or concomitantly with AZD1152, SN-38 blocked the AZD1152 effect by arresting cells in G(2) and inhibiting cells from undergoing polyploidy. With the reverse combination (AZD1152 followed by SN-38), there was a significant induction of polyploidy and apoptosis, even with shorter exposure (24 hours) of AZD1152. In vivo, AZD1152 alone suppressed HCT-116 xenograft tumor growth in a dose-dependent manner with target inhibition of phosphoH3, induction of multinucleated giant cells, but without induction of apoptosis. In combination, both sequences in vivo (CPT->AZD, AZD->CPT, P = 0.008, AUC/d) proved superior to either single agent therapy. However, AZD->CPT still showed a greater increase in apoptosis and greater suppression of tumor regrowth than CPT->AZD (P = 0.02, AUC/d).

CONCLUSIONS

The results from these studies indicate a promising therapeutic strategy for combining AZD1152 with CPT-11, and suggest that the sequence of drug administration is pivotal when an Aurora B kinase inhibitor is administered with a topoisomerase I poison.

[Inhibitors of aurora kinases]

Aurora kinases (A, B and C) are proteins expressed only in cells which divide actively and their increase is a factor of bad prognosis in cancer. They regulate the maturation of centrosomes, the separation and the condensation of chromosomes, mitotic checkpoint and cytokinesis. The inhibition of aurora kinases, by powerful and selective inhibitors, is due to the formation of abnormal cells which are eliminated by apoptosis. The purpose of this article is to present the role, the antitumor activity and the tolerability of these inhibitors. They can be administered orally or intravenously, on weekly or monthly schedules. In our knowledge, twelve molecules are evaluated at the present time and will be discussed only the most advanced namely: VX-680, ZM 447439, MLN 8054, AZD 1152, PHA 739358, SU 6668 and AT 9283. The main indications are breast, colon, lung, pancreas and bladder cancers as well as hematologic tumors such as leukemia (ALL, AML, CML) and lymphoma. These inhibitors can be associated with other chemotherapies. They seem well tolerated; the reported side effects are digestive disorders (diarrhea), fever, asthenia, alopecia, slumber, neutropenia, myelosuppression and disturbance of the biological markers.

Aurora kinases as anticancer drug targets

The human aurora family of serine-threonine kinases comprises three members, which act in concert with many other proteins to control chromosome assembly and segregation during mitosis. Aurora dysfunction can cause aneuploidy, mitotic arrest, and cell death. Aurora kinases are strongly expressed in a broad range of cancer types. Aurora A expression in tumors is often associated with gene amplification, genetic instability, poor histologic differentiation, and poor prognosis. Aurora B is frequently expressed at high levels in a variety of tumors, often coincidently with aurora A, and expression level has also been associated with increased genetic instability and clinical outcome. Further, aurora kinase gene polymorphisms are associated with increased risk or early onset of cancer. The expression of aurora C in cancer is less well studied. In recent years, several small-molecule aurora kinase inhibitors have been developed that exhibit preclinical activity against a wide range of solid tumors. Preliminary clinical data from phase I trials have largely been consistent with cytostatic effects, with disease stabilization as the best response achieved in solid tumors. Objective responses have been noted in leukemia patients, although this might conceivably be due to inhibition of the Abl kinase. Current challenges include the optimization of drug administration, the identification of potential biomarkers of tumor sensitivity, and combination studies with cytotoxic drugs. Here, we summarize the most recent preclinical and clinical data and discuss new directions in the development of aurora kinase inhibitors as antineoplastic agents.

Tubulin-associated proteins: Aurora and Polo-like kinases as therapeutic targets in cancer

Tubulin is a very important target for cancer-fighting therapies; therefore, the cancer research community continues to adopt new ways of developing the therapeutic potential of tubulin and tubulin-associated proteins. Two families of tubulin-associated kinases, Aurora and Polo-like, have received significant attention regarding how they contribute to tumorigenesis and can be targeted with selective small molecule inhibitors. Aurora and Polo-like kinases play essential roles in centrosome separation, chromosome alignment and segregation, and cytokinesis. Inhibition of any of these kinases results in abnormal mitotic events (which vary depending on the particular family member) and eventually leads to apoptosis. Because of the biological consequences of inhibiting these kinases, several Aurora or Polo-like selective inhibitors have advanced to various stages of preclinical and clinical development; the most advanced are currently in phase 2 clinical trials.

Molecular targeted therapy of head and neck cancer: Review and clinical development challenges

Recently, new targets have been identified in head and neck squamous cell carcinomas (HNSCC) as playing key roles in tumour proliferation and metastases. The first target that has led to the approval of a molecularly based therapy in HNSCC has been the epidermal growth factor receptor (EGFR). Indeed, cetuximab, a monoclonal antibody directed against EGFR, has recently been approved in combination with radiation therapy in patients with locally advanced HNSCC, and in patients with platinum-refractory recurrent or metastatic (R/M) HNSCC. This review discusses novel targeted anticancer agents that do not exclusively target EGFR. The initial assessments of novel agents have typically been in patients with heavily pre-treated R/M HNSCC, with response rates and times to progression that are often disappointing. Evaluation of novel agents in the pre-operative 'window' setting, or as first-line therapy for R/M disease, may offer a more optimal understanding of their molecular and clinical effects.

The new paradigm in the treatment of colorectal cancer: are we hitting the right target?

The treatment of advanced colorectal cancer has definitely advanced in the last 10 years as newer and more active cytotoxic chemotherapy agents have become available. Better understanding of different fundamental molecular changes in carcinogenesis has resulted in the emergence of important therapeutic targets in colon cancer treatment. The era of nihilism has been replaced by a time of optimism with the development of targeted therapy, with the promise of agents with improved activity and a better toxicity profile in the management of colon cancer. This review focuses on novel agents, particularly targeted therapy in both earlier and more advanced phases of clinical investigations.

Targeted anti-mitotic therapies: can we improve on tubulin agents?

The advent of molecularly targeted drug discovery has facilitated the identification of a new generation of anti-mitotic therapies that target proteins with specific functions in mitosis. The exquisite selectivity for mitosis and the distinct ways in which these new agents interfere with mitosis provides the potential to not only overcome certain limitations of current tubulin-targeted anti-mitotic drugs, but to expand the scope of clinical efficacy that those drugs have established. The development of these new anti-mitotic drugs as targeted therapies faces significant challenges; nevertheless, these potential therapies also serve as unique tools to dissect the molecular mechanisms of the mitotic-checkpoint response.

Aurora Kinases: New Targets for Cancer Therapy

The Aurora kinase family is a collection of highly related serine/threonine kinases that functions as a key regulator of mitosis. In mammalian cells, Aurora has evolved into three related kinases known as Aurora-A, Aurora-B, and Aurora-C. These kinases are overexpressed in a number of human cancers, and transfection studies have established Aurora-A as a bone fide oncogene. Because Aurora overexpression is associated with malignancy, these kinases have been targeted for cancer therapy. This article reviews the multiple functions of Aurora kinase in the regulation of mitosis and the mitotic checkpoint, the role of abnormal Aurora kinase activity in the development of cancer, the putative mechanisms of Aurora kinase inhibition and its antitumor effects, the development of the first generation of Aurora kinase inhibitors, and prospects for the future of Aurora kinase inhibition in the treatment of cancer.

Development of new cancer therapeutic agents targeting mitosis

Targeting cellular proliferation persists as a mainstay of cancer therapeutic strategy. Although microtubule-targeting drugs (such as taxanes and vinca alkaloids) have been used successfully in the clinic to treat a variety of cancers, they carry substantial liabilities that have spurred drug companies to aggressively pursue new tubulin-targeting drug candidates with improved efficacy and toxicity profiles. The recent discoveries of new mitotic targets for cancer therapy (such as kinesin spindle protein, Aurora kinases and Polo-like kinase-1) have also stimulated intense work focused on identifying novel antimitotic drugs directed at these new targets. A number of novel antimitotic drugs have demonstrated encouraging activity in preclinical models and have progressed into clinical development. This review focuses on selected new antimitotic drugs under evaluation in clinical trials.