Kinesins and cancer

Kinesin spindle protein (KSP) inhibitors in combination with chemotherapeutic agents for cancer therapy

A diverse group of proteins, the activities of which are precisely orchestrated during mitosis, have emerged as targets for cancer therapeutics; these include the Aurora kinases (AKs), Polo-like kinases (PLKs), and the kinesin spindle protein (KSP). KSP is essential for the proper separation of spindle poles during mitosis. Agents that target KSP selectively act on cells undergoing cell division, which means that KSP inhibitors are mitosis-specific drugs, and have demonstrated remarkable activities in vitro. However, a significant obstacle to the success of KSP inhibitors is that these compounds, with tremendous efficacy in vitro, have demonstrated little or even no antitumor activity in vivo. Accumulated data suggest that a combination of KSP inhibitors with various cytostatic drugs will result in a more powerful tumor-killing effect than monotherapy. Combination therapies might predominate and represent the next frontier in the discovery research of KSP inhibitors as potential anticancer drugs. Few published studies have reviewed combination therapy using KSP inhibitors. Herein we provide a comprehensive review of the literature on KSP inhibitor monotherapy and therapeutic combinations. The current state and problems are also discussed.

Kinesin-5: cross-bridging mechanism to targeted clinical therapy

Kinesin motor proteins comprise an ATPase superfamily that works hand in hand with microtubules in every eukaryote. The mitotic kinesins, by virtue of their potential therapeutic role in cancerous cells, have been a major focus of research for the past 28 years since the discovery of the canonical Kinesin-1 heavy chain. Perhaps the simplest player in mitotic spindle assembly, Kinesin-5 (also known as Kif11, Eg5, or kinesin spindle protein, KSP) is a plus-end-directed motor localized to interpolar spindle microtubules and to the spindle poles. Comprised of a homotetramer complex, its function primarily is to slide anti-parallel microtubules apart from one another. Based on multi-faceted analyses of this motor from numerous laboratories over the years, we have learned a great deal about the function of this motor at the atomic level for catalysis and as an integrated element of the cytoskeleton. These data have, in turn, informed the function of motile kinesins on the whole, as well as spearheaded integrative models of the mitotic apparatus in particular and regulation of the microtubule cytoskeleton in general. We review what is known about how this nanomotor works, its place inside the cytoskeleton of cells, and its small-molecule inhibitors that provide a toolbox for understanding motor function and for anticancer treatment in the clinic.

Antimitotic drugs in cancer chemotherapy: promises and pitfalls

Cancer cells usually display higher proliferation rates than normal cells. Some currently used antitumor drugs, such as vinca alkaloids and taxanes, act by targeting microtubules and inhibiting mitosis. In the last years, different mitotic regulators have been proposed as drug target candidates for antitumor therapies. In particular, inhibitors of Cdks, Chks, Aurora kinase and Polo-like kinase have been synthesized and evaluated in vitro and in animal models and some of them have reached clinical trials. However, to date, none of these inhibitors has been still approved for use in chemotherapy regimes. We will discuss here the most recent preclinical information on those new antimitotic drugs, as well as the possible molecular bases underlying their lack of clinical efficiency. Also, advances in the identification of other mitosis-related targets will be also summarized.

Targeted deletion of Kif18a protects from colitis-associated colorectal (CAC) tumors in mice through impairing Akt phosphorylation

Kinesins are a superfamily of molecular motors involved in cell division or intracellular transport. They are becoming important targets for chemotherapeutic intervention of cancer due to their crucial role in mitosis. Here, we demonstrate that the kinesin-8 Kif18a is overexpressed in murine CAC and is a crucial promoter during early CAC carcinogenesis. Kif18a-deficient mice are evidently protected from AOM-DSS-induced colon carcinogenesis. Kif18A is responsible for proliferation of colonic tumor cells, while Kif18a ablation in mice promotes cell apoptosis. Mechanistically, Kif18a is responsible for induction of Akt phosphorylation, which is known to be associated with cell survival regulation. In conclusion, Kif18a is critical for colorectal carcinogenesis in the setting of inflammation by mechanisms of increased PI3K-AKT signaling. Inhibition of Kif18A activity may be useful in the prevention or chemotherapeutic intervention of CAC.

Beyond taxol: microtubule-based treatment of disease and injury of the nervous system

Contemporary research has revealed a great deal of information on the behaviours of microtubules that underlie critical events in the lives of neurons. Microtubules in the neuron undergo dynamic assembly and disassembly, bundling and splaying, severing, and rapid transport as well as integration with other cytoskeletal elements such as actin filaments. These various behaviours are regulated by signalling pathways that affect microtubule-related proteins such as molecular motor proteins and microtubule severing enzymes, as well as a variety of proteins that promote the assembly, stabilization and bundling of microtubules. In recent years, translational neuroscientists have earmarked microtubules as a promising target for therapy of injury and disease of the nervous system. Proof-of-principle has come mainly from studies using taxol and related drugs to pharmacologically stabilize microtubules in animal models of nerve injury and disease. However, concerns persist that the negative consequences of abnormal microtubule stabilization may outweigh the positive effects. Other potential approaches include microtubule-active drugs with somewhat different properties, but also expanding the therapeutic toolkit to include intervention at the level of microtubule regulatory proteins.

Kinesin-12 differentially affects spindle assembly depending on its microtubule substrate

BACKGROUND

During mitosis, the microtubule (MT) cytoskeleton rearranges into a bipolar spindle that drives chromosome segregation. Two kinesin subtypes, kinesin-5 and kinesin-12, help build this bipolar array by separating the spindle poles. However, unlike kinesin-5, the kinesin-12 mechanism is not well understood.

RESULTS

At physiologically normal protein levels, we demonstrate that the human kinesin-12 Kif15 acts predominantly on kinetochore fibers to regulate their lengths. This activity limits the extent to which spindle poles separate, leading to transient spindle length instabilities when the motor is absent. Using a novel cell line wherein Kif15 usurps kinesin-5 function, we further show that Kif15 can assume a commanding role in spindle pole separation as a consequence of its mislocalization to nonkinetochore MTs. This Kif15-dependent mechanism is inefficient, however, as spindles assemble through a perilous monopolar intermediate.

CONCLUSIONS

By examining Kif15 activity in two cellular contexts, we found that Kif15 bound to kinetochore fibers antagonizes centrosome separation while Kif15 bound to nonkinetochore MTs mediates centrosome separation. Our work demonstrates that Kif15 acts on parallel MT arrays and clarifies its role under both normal and pathological conditions.

Synthetic studies of centromere-associated protein-E (CENP-E) inhibitors: 1.Exploration of fused bicyclic core scaffolds using electrostatic potential map

Centromere-associated protein-E (CENP-E), a mitotic kinesin that plays an important role in mitotic progression, is an attractive target for cancer therapeutic drugs. For the purpose of developing novel CENP-E inhibitors as cancer therapeutics, we investigated a fused bicyclic compound identified by high throughput screening, 4-oxo-4,5-dihydrothieno[3,4-c]pyridine-6-carboxamide 1a. Based on this scaffold, we designed inhibitors for efficient binding at the L5 site in CENP-E utilizing homology modeling as well as electrostatic potential map (EPM) analysis to enhance CENP-E inhibitory activity. This resulted in a new lead, 5-bromoimidazo[1,2-a]pyridine 7, which showed potent CENP-E enzyme inhibition (IC50: 50nM) and cellular activity with accumulation of phosphorylated histone H3 in HeLa cells. Our homology model and EPM analysis proved to be useful tools for the rational design of CENP-E inhibitors.

Mitosis-targeting therapies: a troubleshooting guide

Several mitotic kinases and kinesins are currently considered as cancer targets based on their critical role during the cell division cycle and their significant level of expression in human tumors. Yet, their use is limited by the lack of selectivity against tumor cells, the low percentage of mitotic cells in many human tumors, and dose-limiting side-effects. As a consequence, initial clinical trials have shown limited responses. Despite these drawbacks, inhibiting mitosis is a promising strategy that deserves further development. Future advances will benefit from more specific inhibitors with better pharmacodynamic properties, a clear physiological characterization and cell-type-specific requirements of old and new mitotic targets, and rational strategies based on synthetic lethal interactions to improve selectivity against tumor cells.

High expression of KIF26B in breast cancer associates with poor prognosis

To date, a great number of studies have demonstrated that altered expression of kinesins is associated with development and progression of various human cancers. Kinesin family member 26B (KIF26B), a member of the kinesin superfamily proteins (KIFs), is essential for kidney development. However, the role of KIF26B during tumorigenesis and progression is limited. Here, we demonstrate that both KIF26B mRNA and protein are overexpression in breast cancer tissues by RT-qPCR and western blot. Immunohistochemistry revealed that KIF26B expression significantly correlated with clinicopathological factors, including tumor size (P = 0.011), grade (P = 0.017), lymph node status (P = 0.009) and ER status (P = 0.012). Moreover, the Kaplan-Meier analysis indicated that breast cancer patients with high KIF26B expression had a shorter survival than those with low KIF26B expression. In addition, multivariate analysis indicated that KIF26B is an independent prognostic for outcome in breast cancer (HR, 2.356; 95%CI, 1.268–4.378; P = 0.007). Collectively, our study demonstrated that KIF26B was overexpression in breast cancer and could be served as a potential prognostic marker.

Optimized S-trityl-L-cysteine-based inhibitors of kinesin spindle protein with potent in vivo antitumor activity in lung cancer xenograft models

The mitotic kinesin Eg5 is critical for the assembly of the mitotic spindle and is a promising chemotherapy target. Previously, we identified S-trityl-l-cysteine as a selective inhibitor of Eg5 and developed triphenylbutanamine analogues with improved potency, favorable drug-like properties, but moderate in vivo activity. We report here their further optimization to produce extremely potent inhibitors of Eg5 (K_i^app < 10 nM) with broad-spectrum activity against cancer cell lines comparable to the Phase II drug candidates ispinesib and SB-743921. They have good oral bioavailability and pharmacokinetics and induced complete tumor regression in nude mice explanted with lung cancer patient xenografts. Furthermore, they display fewer liabilities with CYP-metabolizing enzymes and hERG compared with ispinesib and SB-743921, which is important given the likely application of Eg5 inhibitors in combination therapies. We present the case for this preclinical series to be investigated in single and combination chemotherapies, especially targeting hematological malignancies.

Functional genetic screens identify genes essential for tumor cell survival in head and neck and lung cancer

PURPOSE

Despite continuous improvement of treatment regimes, the mortality rates for non-small cell lung cancer (NSCLC) and head and neck squamous cell carcinoma (HNSCC) remain disappointingly high and novel anticancer agents are urgently awaited.

EXPERIMENTAL DESIGN

We combined the data from genome-wide siRNA screens on tumor cell lethality in a lung and a head and neck cancer cell line.

RESULTS

We identified 71 target genes that seem essential for the survival of both cancer types. We identified a cluster of 20 genes that play an important role during G2-M phase transition, underlining the importance of this cell-cycle checkpoint for tumor cell survival. Five genes from this cluster (CKAP5, KPNB1, RAN, TPX2, and KIF11) were evaluated in more detail and have been shown to be essential for tumor cell survival in both tumor types, but most particularly in HNSCC. Phenotypes that were observed following siRNA-mediated knockdown of KIF11 (kinesin family member 11) were reproduced by inhibition of KIF11 using the small-molecule inhibitor ispinesib (SB-715992). We showed that ispinesib induces a G2 arrest, causes aberrant chromosome segregation, and induces cell death in HNSCC in vitro, whereas primary keratinocytes are less sensitive. Furthermore, growth of HNSCC cells engrafted in immunodeficient mice was significantly inhibited after ispinesib treatment.

CONCLUSION

This study identified a wide array of druggable genes for both lung and head and neck cancer. In particular, multiple genes involved in the G2-M checkpoint were shown to be essential for tumor cell survival, indicating their potential as anticancer targets.

New insights into the mechanism of force generation by kinesin-5 molecular motors

Kinesin-5 motors are members of a superfamily of microtubule-dependent ATPases and are widely conserved among eukaryotes. Kinesin-5s typically form homotetramers with pairs of motor domains located at either end of a dumbbell-shaped molecule. This quaternary structure enables cross-linking and ATP-driven sliding of pairs of microtubules, although the exact molecular mechanism of this activity is still unclear. Kinesin-5 function has been characterized in greatest detail in cell division, although a number of interphase roles have also been defined. The kinesin-5 ATPase is tuned for slow microtubule sliding rather than cellular transport and-in vertebrates-can be inhibited specifically by allosteric small molecules currently in cancer clinical trials. The biophysical and structural basis of kinesin-5 mechanochemistry is being elucidated and has provided further insight into kinesin-5 activities. However, it is likely that the precise mechanism of these important motors has evolved according to functional context and regulation in individual organisms.

Profiling of ileal carcinoids

Identification of common molecular mechanisms is needed to facilitate the development of new treatment options for patients with ileal carcinoids.

PURPOSE OF REVIEW

Recent profiling studies on ileal carcinoids were examined to obtain a comprehensive view of risk factors, genetic aberrations, and transcriptional alterations. Special attention was paid to mechanisms that could provide novel targets for therapy.

RESULTS

Genome-wide association studies have shown that single nucleotide polymorphisms (SNPs) at IL12A and DAD1 are associated with an increased risk of ileal carcinoids. Genomic profiling revealed distinct patterns of copy-number alterations in ileal carcinoids. Two groups of carcinoids could be identified by hierarchical clustering. A major group of tumors was characterized by loss on chromosome 18 followed by additional losses on chromosomes 3p, 11q, and 13. Three minimal common regions of deletions were identified at 18q21.1-q21.31, 18q22.1-q22.2, and 18q22.3-q23. A minor group of tumors was characterized by clustered gains on chromosomes 4, 5, 7, 14, and 20. Expression profiling identified three groups of ileal carcinoids by principal component analysis. Tumor progression was associated with changes in gene expression including downregulation of MIR133A. Candidate genes for targeted therapy included ERBB2/HER2, DAD1, PRKCA, RYBP, CASP1, CASP4, CASP5, VMAT1, RET, APLP1, OR51E1, GPR112, SPOCK1, RUNX1, and MIR133A.

CONCLUSION

Profiling of ileal carcinoids has revealed recurrent genetic alterations and distinct patterns of gene expression. Frequent alterations in cellular pathways and genes were identified, suggesting novel targets for therapy. Translational studies are needed to validate suggested molecular targets.