Farnesyl transferase inhibitors impair chromosomal maintenance in cell lines and human tumors by compromising CENP-E and CENP-F function

A farnesyl-dependent structural role for CENP-E in expansion of the fibrous corona

Correct chromosome segregation during cell division depends on proper connections between spindle microtubules and kinetochores. During prometaphase, kinetochores are temporarily covered with a dense protein meshwork known as the fibrous corona. Formed by oligomerization of ROD/ZW10/ZWILCH-SPINDLY (RZZ-S) complexes, the fibrous corona promotes spindle assembly, chromosome orientation, and spindle checkpoint signaling. The molecular requirements for formation of the fibrous corona are not fully understood. Here, we show that the fibrous corona depends on the mitotic kinesin CENP-E and that poorly expanded fibrous coronas after CENP-E depletion are functionally compromised. This previously unrecognized role for CENP-E does not require its motor activity but instead is driven by farnesyl modification of its C-terminal kinetochore- and microtubule-binding domain. We show that in cells, CENP-E binds Spindly and recruits RZZ-S complexes to ectopic locations in a farnesyl-dependent manner. CENP-E is recruited to kinetochores following RZZ-S, and-while not required for RZZ-S oligomerization per se-promotes subsequent fibrous corona expansion. Our comparative genomics analyses suggest that the farnesylation motif in CENP-E orthologs emerged alongside the full RZZ-S module in an ancestral lineage close to the fungi-animal split (Obazoa), revealing potential conservation of the mechanisms for fibrous corona formation. Our results show that proper spindle assembly has a potentially conserved non-motor contribution from the kinesin CENP-E through stabilization of the fibrous corona meshwork during its formation.

Deciphering the Prognostic and Therapeutic Significance of Cell Cycle Regulator CENPF: A Potential Biomarker of Prognosis and Immune Microenvironment for Patients with Liposarcoma

Liposarcoma (LPS) is one of the most common subtypes of sarcoma with a high recurrence rate. CENPF is a regulator of cell cycle, differential expression of which has been shown to be related with various cancers. However, the prognostic value of CENPF in LPS has not been deciphered yet. Using data from TCGA and GEO datasets, the expression difference of CENPF and its effects on the prognosis or immune infiltration of LPS patients were analyzed. As results show, CENPF was significantly upregulated in LPS compared to normal tissues. Survival curves illustrated that high CENPF expression was significantly associated with adverse prognosis. Univariate and multivariate analysis suggested that CENPF expression could be an independent risk factor for LPS. CENPF was closely related to chromosome segregation, microtubule binding and cell cycle. Immune infiltration analysis elucidated a negative correlation between CENPF expression and immune score. In conclusion, CENPF not only could be considered as a potential prognostic biomarker but also a potential malignant indicator of immune infiltration-related survival for LPS. The elevated expression of CENPF reveals an unfavorable prognostic outcome and worse immune score. Thus, therapeutically targeting CENPF combined with immunotherapy might be an attractive strategy for the treatment of LPS.

Expression of SnoRNA U50A Is Associated with Better Prognosis and Prolonged Mitosis in Breast Cancer

Simple Summary

SnoRNAs are essential for fundamental cellular processes. However, emerging evidence shows that snoRNAs play regulatory roles during cancer progression. The snoRNA U50A (U50A) is a newly-identified putative tumor suppressor, but its clinical and mechanistic impacts in breast cancer remain elusive. In this study, we quantified the copy number of U50A in breast cancer patient tissues and found that a higher level of U50A expression is correlated with better overall survival in breast cancer patients. By utilizing transcriptomic analysis, we demonstrated that U50A prolongs mitosis and reduces colony-forming ability through downregulating mitosis-related genes. Consistent with these in vitro results, breast cancer tissues expressing higher U50A significantly exhibited accumulated mitotic tumor cells and were associated with reduced tumor size. Altogether, this is the first study showing the clinical, cellular, and regulatory impacts of snoRNA U50A in human breast cancer.

Abstract

Small nucleolar RNAs (snoRNAs) are small noncoding RNAs generally recognized as housekeeping genes. Genomic analysis has shown that snoRNA U50A (U50A) is a candidate tumor suppressor gene deleted in less than 10% of breast cancer patients. To date, the pathological roles of U50A in cancer, including its clinical significance and its regulatory impact at the molecular level, are not well-defined. Here, we quantified the copy number of U50A in human breast cancer tissues. Our results showed that the U50A expression level is correlated with better prognosis in breast cancer patients. Utilizing RNA-sequencing for transcriptomic analysis, we revealed that U50A downregulates mitosis-related genes leading to arrested cancer cell mitosis and suppressed colony-forming ability. Moreover, in support of the impacts of U50A in prolonging mitosis and inhibiting clonogenic activity, breast cancer tissues with higher U50A expression exhibit accumulated mitotic tumor cells. In conclusion, based on the evidence from U50A-downregulated mitosis-related genes, prolonged mitosis, repressed colony-forming ability, and clinical analyses, we demonstrated molecular insights into the pathological impact of snoRNA U50A in human breast cancer.

Leaving no-one behind: how CENP-E facilitates chromosome alignment

Chromosome alignment and biorientation is essential for mitotic progression and genomic stability. Most chromosomes align at the spindle equator in a motor-independent manner. However, a subset of polar kinetochores fail to bi-orient and require a microtubule motor-based transport mechanism to move to the cell equator. Centromere Protein E (CENP-E/KIF10) is a kinesin motor from the Kinesin-7 family, which localizes to unattached kinetochores during mitosis and utilizes plus-end directed microtubule motility to slide mono-oriented chromosomes to the spindle equator. Recent work has revealed how CENP-E cooperates with chromokinesins and dynein to mediate chromosome congression and highlighted its role at aligned chromosomes. Additionally, we have gained new mechanistic insights into the targeting and regulation of CENP-E motor activity at the kinetochore. Here, we will review the function of CENP-E in chromosome congression, the pathways that contribute to CENP-E loading at the kinetochore, and how CENP-E activity is regulated during mitosis.

2-methoxyestradiol sensitizes breast cancer cells to taxanes by targeting centrosomes

Centrosomes amplification is a hallmark of cancer. We hypothesize that 2-methoxyestradiol (2-ME) sensitizes breast cancer (BC) cells to taxanes by targeting amplified centrosomes. We assessed the extent by which 2-ME together with paclitaxel (PTX) induces centrosome alterations with subsequent mitotic catastrophe in different BC subtypes. 2-ME induced a significant reduction in PTX IC₅₀ values in all cells tested ranging from 28–44% (P < 0.05). Treatment with both PTX and 2-ME significantly increased the number of misaligned metaphases compared to PTX alone (34%, 100% and 52% for MCF7, MDA-MB231 and SUM149, respectively; P < 0.05). The number of cells with multipolar spindle formation was significantly increased (81%, 220% and 285% for MCF7, MDA-MB231 and SUM 149, respectively; P < 0.05). PTX and 2-ME treatment significantly increased interphase declustering in cancer cells (56% for MCF7, 208% for MDA-MB231 and 218% for SUM149, respectively; P < 0.05) and metaphase declustering (1.4-fold, 1.56-fold and 2.48-fold increase for MCF7, MDA-MB231 and SUM149, respectively; P < 0.05). This report is the first to document centrosome declustering as a mechanism of action of 2-ME and provides a potential approach for reducing taxane toxicity in cancer treated patients.

Weighted gene coexpression network analysis identifies a new biomarker of CENPF for prediction disease prognosis and progression in nonmuscle invasive bladder cancer

BACKGROUND

The dreadful prognosis of nonmuscle invasive bladder cancer mainly results from the delay in recognition of individuals with a high risk of progression. Thus, the emphasis of this work lies in developing valuable biomarkers that is conducive to accurately predicting the progression of NMIBC.

METHODS

Microarray data from GSE32894 including 209 NMIBC samples were performed by weighted gene coexpression network analysis (WGCNA), which could find modules of highly correlated genes and relate modules to external sample traits. Besides, we constructed a protein-protein interaction to facilitate screening the hub gene. At last, we used RNA-seq and microarray data and clinical information from ArrayExpress (E-MTAB-4321) and GSE13507 to select and validate the candidate gene.

RESULTS

In current paper, blue module of 13 gene coexpression clusters we identified was selected as the key modules. Seven genes namely: CDCA8, CENPF, MCM6, MELK, PRC1, STIL, and TPX2 have been identified as candidate genes. Notably, among them, only elevated CENPF in NIMBC tissue was closely associated with low progression-free survival (PFS) and overall survival (OS) rate in three datasets and had a large area under receiver operating characteristic (ROC) curve. Finally, CENPF was identified as an effective biomarker in NMIBC.

CONCLUSION

Therefore, our findings submit a new progressive and prognostic molecular marker and therapeutic target for NMIBC. Moreover, these genes that deserve to be further researched may improve the comprehension about the occurrence and development of superficial bladder cancer.

Loss of CENPF leads to developmental failure in mouse embryos

Aneuploidy caused by abnormal chromosome segregation during early embryo development leads to embryonic death or congenital malformation. Centromere protein F (CENPF) is a member of centromere protein family that regulates chromosome segregation during mitosis. However, its necessity in early embryo development has not been fully investigated. In this study, expression and function of CENPF was investigated in mouse early embryogenesis. Detection of CENPF expression and localization revealed a cytoplasm, spindle and nuclear membrane related dynamic pattern throughout mitotic progression. Farnesyltransferase inhibitor (FTI) was employed to inhibit CENPF farnesylation in zygotes. The results showed that CENPF degradation was inhibited and its specific localization on nuclear membranes in morula and blastocyst vanished after FTI treatment. Also, CAAX motif mutation leads to failure of CENPF-C630 localization in morula and blastocyst. These results indicate that farnesylation plays a key role during CENPF degradation and localization in early embryos. To further assess CENPF function in parthenogenetic or fertilized embryos development, morpholino (MO) and Trim-Away were used to disturb CENPF function. CENPF knockdown in Metaphase II (MII) oocytes, zygotes or embryos with MO approach resulted in failure to develop into morulae and blastocysts, revealing its indispensable role in both parthenogenetic and fertilized embryos. Disturbing of CENPF with Trim-Away approach in zygotes resulted in impaired development of 2-cell and 4-cell, but did not affect the morula and blastocyst formation because of the recovered expression of CENPF. Taken together, our data suggest CENPF plays an important role during early embryonic development in mice. Abbreviation: CENPF: centromere protein F; MO: morpholino; FTI: Farnesyltransferase inhibitor; CENPE: centromere protein E; IVF: in vitro fertilization; MII: metaphase II; SAC: spindle assembly checkpoint; Mad1: mitotic arrest deficient 1; BUB1: budding uninhibited by benzimidazole 1; BUBR1: BUB1 mitotic checkpoint serine/threonine kinase B; Cdc20: cell division cycle 20.

Miro-dependent mitochondrial pool of CENP-F and its farnesylated C-terminal domain are dispensable for normal development in mice

CENP-F is a large, microtubule-binding protein that regulates multiple cellular processes including chromosome segregation and mitochondrial trafficking at cytokinesis. This multiplicity of functions is mediated through the binding of various partners, like Bub1 at the kinetochore and Miro at mitochondria. Due to the multifunctionality of CENP-F, the cellular phenotypes observed upon its depletion are difficult to interpret and there is a need to genetically separate its different functions by preventing binding to selected partners. Here we engineer a CENP-F point-mutant that is deficient in Miro binding and thus is unable to localize to mitochondria, but retains other localizations. We introduce this mutation in cultured human cells using CRISPR/Cas9 system and show it causes a defect in mitochondrial spreading similar to that observed upon Miro depletion. We further create a mouse model carrying this CENP-F variant, as well as truncated CENP-F mutants lacking the farnesylated C-terminus of the protein. Importantly, one of these truncations leads to ~80% downregulation of CENP-F expression. We observe that, despite the phenotypes apparent in cultured cells, mutant mice develop normally. Taken together, these mice will serve as important models to study CENP-F biology at organismal level. In addition, because truncations of CENP-F in humans cause a lethal disease termed Strømme syndrome, they might also be relevant disease models.

Mechanisms of kinesin-7 CENP-E in kinetochore-microtubule capture and chromosome alignment during cell division

Chromosome congression is essential for faithful chromosome segregation and genomic stability in cell division. Centromere-associated protein E (CENP-E), a plus-end-directed kinesin motor, is required for congression of pole-proximal chromosomes in metaphase. CENP-E accumulates at the outer plate of kinetochores and mediates the kinetochore-microtubule capture. CENP-E also transports the chromosomes along spindle microtubules towards the equatorial plate. CENP-E interacts with Bub1-related kinase, Aurora B and core kinetochore components during kinetochore-microtubule attachment. In this review, we introduce the structures and mechanochemistry of kinesin-7 CENP-E. We highlight the complicated interactions between CENP-E and partner proteins during chromosome congression. We summarise the detailed roles and mechanisms of CENP-E in mitosis and meiosis, including the kinetochore-microtubule capture, chromosome congression/alignment in metaphase and the regulation of spindle assembly checkpoint. We also shed a light on the roles of CENP-E in tumourigenesis and CENP-E's specific inhibitors.

The kinetochore proteins CENP-E and CENP-F directly and specifically interact with distinct BUB mitotic checkpoint Ser/Thr kinases

The segregation of chromosomes during cell division relies on the function of the kinetochores, protein complexes that physically connect chromosomes with microtubules of the spindle. The metazoan proteins, centromere protein E (CENP-E) and CENP-F, are components of a fibrous layer of mitotic kinetochores named the corona. Several of their features suggest that CENP-E and CENP-F are paralogs: they are very large (comprising ∼2700 and 3200 residues, respectively), contain abundant predicted coiled-coil structures, are C-terminally prenylated, and are endowed with microtubule-binding sites at their termini. Moreover, CENP-E contains an ATP-hydrolyzing motor domain that promotes microtubule plus end–directed motion. Here, we show that both CENP-E and CENP-F are recruited to mitotic kinetochores independently of the main corona constituent, the Rod/Zwilch/ZW10 (RZZ) complex. We identified specific interactions of CENP-F and CENP-E with budding uninhibited by benzimidazole 1 (BUB1) and BUB1-related (BUBR1) mitotic checkpoint Ser/Thr kinases, respectively, paralogous proteins involved in mitotic checkpoint control and chromosome alignment. Whereas BUBR1 was dispensable for kinetochore localization of CENP-E, BUB1 was stringently required for CENP-F localization. Through biochemical reconstitution, we demonstrated that the CENP-E/BUBR1 and CENP-F/BUB1 interactions are direct and require similar determinants, a dimeric coiled-coil in CENP-E or CENP-F and a kinase domain in BUBR1 or BUB1. Our findings are consistent with the existence of structurally similar BUB1/CENP-F and BUBR1/CENP-E complexes, supporting the notion that CENP-E and CENP-F are evolutionarily related.

Progerin impairs chromosome maintenance by depleting CENP-F from metaphase kinetochores in Hutchinson-Gilford progeria fibroblasts

Hutchinson-Gilford progeria syndrome (HGPS, OMIM 176670) is a rare premature aging disorder that leads to death at an average age of 14.7 years due to myocardial infarction or stroke. The most common mutation in HGPS is at position G608G (GGC>GGT) within exon 11 of the LMNA gene. This mutation results in the deletion of 50 amino acids at the carboxyl-terminal tail of prelamin A, producing a truncated farnesylated protein called progerin. Lamins play important roles in the organization and structure of the nucleus. The nuclear build-up of progerin causes severe morphological and functional changes in interphase HGPS cells. In this study, we investigated whether progerin elicits spatiotemporal deviations in mitotic processes in HGPS fibroblasts. We analyzed the nuclear distribution of endogenous progerin during mitosis in relation to components of the nuclear lamina, nuclear envelope (NE) and nuclear pores. We found that progerin caused defects in chromosome segregation as early as metaphase, delayed NE reformation and trapped lamina components and inner NE proteins in the endoplasmic reticulum at the end of mitosis. Progerin displaced the centromere protein F (CENP-F) from metaphase chromosome kinetochores, which caused increased chromatin lagging, binucleated cells and genomic instability. This accumulation of progerin-dependent defects with each round of mitosis predisposes cells to premature senescence.

Synergistic effect of farnesyl transferase inhibitor lonafarnib combined with chemotherapeutic agents against the growth of hepatocellular carcinoma cells

Hepatocellular carcinoma (HCC) is a common and deadly cancer worldwide and is often refractory to chemotherapy due to the development of multidrug resistance. Lonafarnib is an orally active and potent non-peptidomimetic inhibitor of farnesyl transferase. Here, using in vitro HCC cell models, we demonstrated that lonafarnib inhibited tumor proliferation and reduced the activity of mitogen-activated protein kinases pathways. In addition, lonafarnib caused G1 to S phase arrest through the downregulation of Cyclin D1, CDK6 and SKP2, while it induced cellular apoptosis by promoting the cleavage and activation of Caspase-3 and PARP. When combined with doxorubicin and sorafenib, lonafarnib was able to increase the sensitivity of HCC cells to chemotherapy. Furthermore, we also constructed ABCB1-overexpressing HCC cells and found that lonafarnib decreased chemoresistance by inhibiting ABCB1-mediated drug efflux activity. These results suggest that lonafarnib may be a promising synergistic agent for improving the treatment of drug-resistant HCC.

Targeting mitotic pathways for endocrine-related cancer therapeutics

A colossal amount of basic research over the past few decades has provided unprecedented insights into the highly complex process of cell division. There is an ever-expanding catalog of proteins that orchestrate, participate and coordinate in the exquisite processes of spindle formation, chromosome dynamics and the formation and regulation of kinetochore microtubule attachments. Use of classical microtubule poisons has still been widely and often successfully used to combat a variety of cancers, but their non-selective interference in other crucial physiologic processes necessitate the identification of novel druggable components specific to the cell cycle/division pathway. Considering cell cycle deregulation, unscheduled proliferation, genomic instability and chromosomal instability as a hallmark of tumor cells, there lies an enormous untapped terrain that needs to be unearthed before a drug can pave its way from bench to bedside. This review attempts to systematically summarize the advances made in this context so far with an emphasis on endocrine-related cancers and the avenues for future progress to target mitotic mechanisms in an effort to combat these dreadful cancers.

Mechanism for G2 phase-specific nuclear export of the kinetochore protein CENP-F

Centromere protein F (CENP-F) is a component of the kinetochore and a regulator of cell cycle progression. CENP-F recruits the dynein transport machinery and orchestrates several cell cycle-specific transport events, including transport of the nucleus, mitochondria and chromosomes. A key regulatory step for several of these functions is likely the G2 phase-specific export of CENP-F from the nucleus to the cytosol, where the cytoplasmic dynein transport machinery resides; however, the molecular mechanism of this process is elusive. Here, we have identified 3 phosphorylation sites within the bipartite classical nuclear localization signal (cNLS) of CENP-F. These sites are specific for cyclin-dependent kinase 1 (Cdk1), which is active in G2 phase. Phosphomimetic mutations of these residues strongly diminish the interaction of the CENP-F cNLS with its nuclear transport receptor karyopherin α. These mutations also diminish nuclear localization of the CENP-F cNLS in cells. Notably, the cNLS is phosphorylated in the -1 position, which is important to orient the adjacent major motif for binding into its pocket on karyopherin α. We propose that localization of CENP-F is regulated by a cNLS, and a nuclear export pathway, resulting in nuclear localization during most of interphase. In G2 phase, the cNLS is weakened by phosphorylation through Cdk1, likely resulting in nuclear export of CENP-F via the still active nuclear export pathway. Once CENP-F resides in the cytosol, it can engage in pathways that are important for cell cycle progression, kinetochore assembly and the faithful segregation of chromosomes into daughter cells.

Mechanisms of Chromosome Congression during Mitosis

Chromosome congression during prometaphase culminates with the establishment of a metaphase plate, a hallmark of mitosis in metazoans. Classical views resulting from more than 100 years of research on this topic have attempted to explain chromosome congression based on the balance between opposing pulling and/or pushing forces that reach an equilibrium near the spindle equator. However, in mammalian cells, chromosome bi-orientation and force balance at kinetochores are not required for chromosome congression, whereas the mechanisms of chromosome congression are not necessarily involved in the maintenance of chromosome alignment after congression. Thus, chromosome congression and maintenance of alignment are determined by different principles. Moreover, it is now clear that not all chromosomes use the same mechanism for congressing to the spindle equator. Those chromosomes that are favorably positioned between both poles when the nuclear envelope breaks down use the so-called "direct congression" pathway in which chromosomes align after bi-orientation and the establishment of end-on kinetochore-microtubule attachments. This favors the balanced action of kinetochore pulling forces and polar ejection forces along chromosome arms that drive chromosome oscillatory movements during and after congression. The other pathway, which we call "peripheral congression", is independent of end-on kinetochore microtubule-attachments and relies on the dominant and coordinated action of the kinetochore motors Dynein and Centromere Protein E (CENP-E) that mediate the lateral transport of peripheral chromosomes along microtubules, first towards the poles and subsequently towards the equator. How the opposite polarities of kinetochore motors are regulated in space and time to drive congression of peripheral chromosomes only now starts to be understood. This appears to be regulated by position-dependent phosphorylation of both Dynein and CENP-E and by spindle microtubule diversity by means of tubulin post-translational modifications. This so-called "tubulin code" might work as a navigation system that selectively guides kinetochore motors with opposite polarities along specific spindle microtubule populations, ultimately leading to the congression of peripheral chromosomes. We propose an integrated model of chromosome congression in mammalian cells that depends essentially on the following parameters: (1) chromosome position relative to the spindle poles after nuclear envelope breakdown; (2) establishment of stable end-on kinetochore-microtubule attachments and bi-orientation; (3) coordination between kinetochore- and arm-associated motors; and (4) spatial signatures associated with post-translational modifications of specific spindle microtubule populations. The physiological consequences of abnormal chromosome congression, as well as the therapeutic potential of inhibiting chromosome congression are also discussed.

Anti-mitotic agents: Are they emerging molecules for cancer treatment?

Mutations in cancer cells frequently result in cell cycle alterations that lead to unrestricted growth compared to normal cells. Considering this phenomenon, many drugs have been developed to inhibit different cell-cycle phases. Mitotic phase targeting disturbs mitosis in tumor cells, triggers the spindle assembly checkpoint and frequently results in cell death. The first anti-mitotics to enter clinical trials aimed to target tubulin. Although these drugs improved the treatment of certain cancers, and many anti-microtubule compounds are already approved for clinical use, severe adverse events such as neuropathies were observed. Since then, efforts have been focused on the development of drugs that also target kinases, motor proteins and multi-protein complexes involved in mitosis. In this review, we summarize the major proteins involved in the mitotic phase that can also be targeted for cancer treatment. Finally, we address the activity of anti-mitotic drugs tested in clinical trials in recent years.

Autoantibodies directed to centromere protein F in a patient with BRCA1 gene mutation

Background

Autoantibodies directed to centromere protein F were first reported in 1993 and their association with malignancy has been well documented.

Case

We present the case of a 48-year-old Caucasian female with a BRCA1 gene mutation associated with bilateral breast cancer. Antinuclear autoantibody immunofluorescence performed for workup of possible inflammatory arthropathy showed a high titre cell cycle related nuclear speckled pattern, with subsequent confirmation by addressable laser bead immunoassay of the target antigen as an immunodominant epitope at the C-terminus of centromere protein F.

Conclusion

Here we review the current literature on centromere protein F, its association with breast cancer and present the first case of this antibody being identified in a person with a BRCA1 gene mutation.

A novel role of farnesylation in targeting a mitotic checkpoint protein, human Spindly, to kinetochores

The mitotic checkpoint protein Spindly is farnesylated in vivo and this modification is required for its interaction with the RZZ complex and its localization to kinetochores.

Kinetochore (KT) localization of mitotic checkpoint proteins is essential for their function during mitosis. hSpindly KT localization is dependent on the RZZ complex and hSpindly recruits the dynein–dynactin complex to KTs during mitosis, but the mechanism of hSpindly KT recruitment is unknown. Through domain-mapping studies we characterized the KT localization domain of hSpindly and discovered it undergoes farnesylation at the C-terminal cysteine residue. The N-terminal 293 residues of hSpindly are dispensable for its KT localization. Inhibition of farnesylation using a farnesyl transferase inhibitor (FTI) abrogated hSpindly KT localization without affecting RZZ complex, CENP-E, and CENP-F KT localization. We showed that hSpindly is farnesylated in vivo and farnesylation is essential for its interaction with the RZZ complex and hence KT localization. FTI treatment and hSpindly knockdown displayed the same mitotic phenotypes, indicating that hSpindly is a key FTI target in mitosis. Our data show a novel role of lipidation in targeting a checkpoint protein to KTs through protein–protein interaction.

Preventing farnesylation of the dynein adaptor Spindly contributes to the mitotic defects caused by farnesyltransferase inhibitors

The kinetochore-specific dynein adaptor Spindly is identified as a novel substrate of farnesyltransferase in human cells. Farnesylation is required for Spindly accumulation at kinetochores, and nonfarnesylated Spindly delays chromosome congression, providing new mechanistic insight into the biological effect of farnesyltransferase inhibitors.

The clinical interest in farnesyltransferase inhibitors (FTIs) makes it important to understand how these compounds affect cellular processes involving farnesylated proteins. Mitotic abnormalities observed after treatment with FTIs have so far been attributed to defects in the farnesylation of the outer kinetochore proteins CENP-E and CENP-F, which are involved in chromosome congression and spindle assembly checkpoint signaling. Here we identify the cytoplasmic dynein adaptor Spindly as an additional component of the outer kinetochore that is modified by farnesyltransferase (FTase). We show that farnesylation of Spindly is essential for its localization, and thus for the proper localization of dynein and its cofactor dynactin, to prometaphase kinetochores and that Spindly kinetochore recruitment is more severely affected by FTase inhibition than kinetochore recruitment of CENP-E and CENP-F. Molecular replacement experiments show that both Spindly and CENP-E farnesylation are required for efficient chromosome congression. The identification of Spindly as a new mitotic substrate of FTase provides insight into the causes of the mitotic phenotypes observed with FTase inhibitors.

Mitosis as an anti-cancer drug target

Suppression of cell proliferation by targeting mitosis is one potential cancer intervention. A number of existing chemotherapy drugs disrupt mitosis by targeting microtubule dynamics. While efficacious, these drugs have limitations, i.e. neuropathy, unpredictability and development of resistance. In order to overcome these issues, a great deal of effort has been spent exploring novel mitotic targets including Polo-like kinase 1, Aurora kinases, Mps1, Cenp-E and KSP/Eg5. Here we summarize the latest developments in the discovery and clinical evaluation of new mitotic drug targets.

LKB1 represses focal adhesion kinase (FAK) signaling via a FAK-LKB1 complex to regulate FAK site maturation and directional persistence

Liver kinase β1 (LKB1, also known as STK11) is a serine/threonine kinase that has multiple cellular functions including the regulation of cell polarity and motility. Murine proteomic studies show that LKB1 loss causes aberrant adhesion signaling; however, the mechanistic underpinnings of this relationship are unknown. We show that cells stably depleted of LKB1 or its co-activator STRADα have increased phosphorylation of focal adhesion kinase (FAK) at Tyr(397)/Tyr(861) and enhanced adhesion to fibronectin. LKB1 associates in a complex with FAK and LKB1 accumulation at the cellular leading edge is mutually excluded from regions of activated Tyr(397)-FAK. LKB1-compromised cells lack directional persistence compared with wild-type cells, but this is restored through subsequent pharmacological FAK inhibition or depletion, showing that cell directionality is mediated through LKB1-FAK signaling. Live cell confocal imaging reveals that LKB1-compromised cells lack normal FAK site maturation and turnover, suggesting that defects in adhesion and directional persistence are caused by aberrant adhesion dynamics. Furthermore, re-expression of full-length wild-type or the LKB1 N-terminal domain repressed FAK activity, whereas the kinase domain or C-terminal domain alone did not, indicating that FAK suppression is potentially regulated through the LKB1 N-terminal domain. Based upon these results, we conclude that LKB1 serves as a FAK repressor to stabilize focal adhesion sites, and when LKB1 function is compromised, aberrant FAK signaling ensues, resulting in rapid FAK site maturation and poor directional persistence.

Oncogenic role of kinesin proteins and targeting kinesin therapy

The kinesin superfamily (KIF) is a group of proteins that share a highly conserved motor domain. Except for some members, many KIF proteins have adenosine triphosphatase activity and microtubule-dependent plus-end motion ability. Kinesins participate in several essential cellular functions, including mitosis, meiosis and the transport of macromolecules. Increasing evidence indicates kinesin proteins play critical roles in the genesis and development of human cancers. Some kinesin proteins are associated with maligancy as well as drug resistance of solid tumor. Thus, targeting KIF therapy seems to be a promising anticancer strategy. Inhibitors of KIF such as kinesin spindle protein (KSP/Eg5) have entered clinical trials for monotherapy or in combination with other drugs, and kinesins other than Eg5 with various potential anticancer target characteristics are also constantly being discovered and studied. Here, we summarize the oncogenic roles of kinesin proteins and potential cancer therapy strategies that target KIF.

Regulatory mechanisms of kinetochore-microtubule interaction in mitosis

Interaction of microtubules with kinetochores is fundamental to chromosome segregation. Kinetochores initially associate with lateral surfaces of microtubules and subsequently become attached to microtubule ends. During these interactions, kinetochores can move by sliding along microtubules or by moving together with depolymerizing microtubule ends. The interplay between kinetochores and microtubules leads to the establishment of bi-orientation, which is the attachment of sister kinetochores to microtubules from opposite spindle poles, and subsequent chromosome segregation. Molecular mechanisms underlying these processes have been intensively studied over the past 10 years. Emerging evidence suggests that the KNL1-Mis12-Ndc80 (KMN) network plays a central role in connecting kinetochores to microtubules, which is under fine regulation by a mitotic kinase, Aurora B. However, a growing number of additional molecules are being shown to be involved in the kinetochore-microtubule interaction. Here I overview the current range of regulatory mechanisms of the kinetochore-microtubule interaction, and discuss how these multiple molecules contribute cooperatively to allow faithful chromosome segregation.

Mitosis-targeted anti-cancer therapies: where they stand

The strategy of clinically targeting cancerous cells at their most vulnerable state during mitosis has instigated numerous studies into the mitotic cell death (MCD) pathway. As the hallmark of cancer revolves around cell-cycle deregulation, it is not surprising that antimitotic therapies are effective against the abnormal proliferation of transformed cells. Moreover, these antimitotic drugs are also highly selective and sensitive. Despite the robust rate of discovery and the development of mitosis-selective inhibitors, the unpredictable complexities of the human body's response to these drugs still herald the biggest challenge towards clinical success. Undoubtedly, the need to bridge the gap between promising preclinical trials and effective translational bedside treatment prompts further investigations towards mapping out the mechanistic pathways of MCD, understanding how these drugs work as medicine in the body and more comprehensive target validations. In this review, current antimitotic agents are summarized with particular emphasis on the evaluation of their clinical efficacy as well as their limitations. In addition, we discuss the basis behind the lack of activity of these inhibitors in human trials and the potential and future directions of mitotic anticancer strategies.

Integrating image analysis algorithms in a web interface for the quantification of microtubule dynamics

We present improvements to a web interface and an integrated computational tracking algorithm for quantitative analysis of microtubule dynamics in live-cell microscopy images. Based on a previously implemented system, more new functionalities have been added to the interface. The system also integrates a computational tracking algorithm to aid the analysis. The analysis workflow of the proposed interface is made similar to the current manual analysis workflow in order to make the interface intuitive to use. We show the workflow of the computer analysis algorithm and how it is used to aid the existing analysis workflow. We also demonstrate how to re-evaluate existing data in a case study using real imaging data. Lastly, we show the added functionalities of the interface including how to share image data and analysis results.

Treatment of human pre-B acute lymphoblastic leukemia with the Aurora kinase inhibitor PHA-739358 (Danusertib)

BACKGROUND

Treatment of Philadelphia chromosome-positive acute lymphoblastic leukemias (Ph-positive ALL) with clinically approved inhibitors of the Bcr/Abl tyrosine kinase frequently results in the emergence of a leukemic clone carrying the T315I mutation in Bcr/Abl, which confers resistance to these drugs. PHA-739358, an Aurora kinase inhibitor, was reported to inhibit the Bcr/Abl T315I mutant in CML cells but no preclinical studies have examined this in detail in human ALL.

RESULTS

We compared the sensitivity of human Bcr/Abl T315I, Bcr/Abl wild type and non-Bcr/Abl ALL cells to this drug. PHA-739358 inhibited proliferation and induced apoptosis independently of Bcr/Abl, the T315I mutation, or presence of the tumor suppressor p53, but the degree of effectiveness varied between different ALL samples. Since short-term treatment with a single dose of drug only transiently inhibited proliferation, we tested combination treatments of PHA-739358 with the farnesyltransferase inhibitor Lonafarnib, with vincristine and with dasatinib. All combinations reduced viability and cell numbers compared to treatment with a single drug. Clonogenic assays showed that 25 nM PHA-739358 significantly reduced the colony growth potential of Ph-positive ALL cells, and combined treatment with a second drug abrogated colony growth in this assay. PHA-739358 further effectively blocked Bcr/Abl tyrosine kinase activity and Aurora kinase B in vivo, and mice transplanted with human Bcr/Abl T315I ALL cells treated with a 3x 7-day cycle of PHA-739358 as mono-treatment had significantly longer survival.

CONCLUSIONS

PHA-739358 represents an alternative drug for the treatment of both Ph-positive and negative ALL, although combined treatment with a second drug may be needed to eradicate the leukemic cells.

AMPK regulates mitotic spindle orientation through phosphorylation of myosin regulatory light chain

The proper orientation of the mitotic spindle is essential for mitosis; however, how these events unfold at the molecular level is not well understood. AMP-activated protein kinase (AMPK) regulates energy homeostasis in eukaryotes, and AMPK-null Drosophila mutants have spindle defects. We show that threonine(172) phosphorylated AMPK localizes to the mitotic spindle poles and increases when cells enter mitosis. AMPK depletion causes a mitotic delay with misoriented spindles relative to the normal division plane and a reduced number and length of astral microtubules. AMPK-depleted cells contain mitotic actin bundles, which prevent astral microtubule-actin cortex attachments. Since myosin regulatory light chain (MRLC) is an AMPK downstream target and mediates actin function, we investigated whether AMPK signals through MRLC to control spindle orientation. Mitotic levels of serine(19) phosphorylated MRLC (pMRLC(ser19)) and spindle pole-associated pMRLC(ser19) are abolished when AMPK function is compromised, indicating that AMPK is essential for pMRLC(ser19) spindle pole activity. Phosphorylation of AMPK and MRLC in the mitotic spindle is dependent upon calcium/calmodulin-dependent protein kinase kinase (CamKK) activity in LKB1-deficient cells, suggesting that CamKK regulates this pathway when LKB1 function is compromised. Taken together, these data indicate that AMPK mediates spindle pole-associated pMRLC(ser19) to control spindle orientation via regulation of actin cortex-astral microtubule attachments.

Lonafarnib for cancer and progeria

INTRODUCTION

Lonafarnib is a non-peptidomimetic inhibitor of farnesyl transferase, an enzyme responsible for the post-translational lipid modification of a wide variety of cellular proteins that are involved in the pathogenic pathways of various diseases including cancer and progeria. Although extensive clinical research indicates limited activity of lonafarnib in solid tumors, there is recent interest in combinations of farnesyl transferase inhibitors with imatinib or bortezomib in hematological malignancies and to investigate the role of lonafarnib in progeria.

AREAS COVERED

This review examines the in vitro and in vivo pharmacology of lonafarnib and the available clinical data for lonafarnib monotherapy and combination therapy in the treatment of solid and hematological malignancies as well as progeria, using studies identified from the PubMed database supplemented by computerized search of relevant abstracts from major cancer and hematology conferences.

EXPERT OPINION

There is no evidence to support the use of lonafarnib in solid tumors. There is ongoing interest to explore lonafarnib for progeria and to investigate other farnesyl transferase inhibitors for chronic and acute leukemias.

Killing cells by targeting mitosis

Cell cycle deregulation is a common feature of human cancer. Tumor cells accumulate mutations that result in unscheduled proliferation, genomic instability and chromosomal instability. Several therapeutic strategies have been proposed for targeting the cell division cycle in cancer. Whereas inhibiting the initial phases of the cell cycle is likely to generate viable quiescent cells, targeting mitosis offers several possibilities for killing cancer cells. Microtubule poisons have proved efficacy in the clinic against a broad range of malignancies, and novel targeted strategies are now evaluating the inhibition of critical activities, such as cyclin-dependent kinase 1, Aurora or Polo kinases or spindle kinesins. Abrogation of the mitotic checkpoint or targeting the energetic or proteotoxic stress of aneuploid or chromosomally instable cells may also provide further benefits by inducing lethal levels of instability. Although cancer cells may display different responses to these treatments, recent data suggest that targeting mitotic exit by inhibiting the anaphase-promoting complex generates metaphase cells that invariably die in mitosis. As the efficacy of cell-cycle targeting approaches has been limited so far, further understanding of the molecular pathways modulating mitotic cell death will be required to move forward these new proposals to the clinic.

The kinetochore protein Cenp-F is a potential novel target for zoledronic acid in breast cancer cells

The anti-resorptive agent zoledronic acid inhibits key enzymes in the mevalonate pathway, disrupting post-translational modification and thereby correct protein localization and function. Inhibition of prenylation may also be responsible for the reported anti-tumour effects of zoledronic acid, but the specific molecular targets have not been identified. Cenp-F/mitosin, a kinetochore-associated protein involved in the correct separation of chromosomes during mitosis, has been shown to undergo post-translational prenylation and may therefore be a novel target contributing to the anti-tumour effects of zoledronic acid. We investigated whether zoledronic acid causes loss of Cenp-F from the kinetochore in breast cancer cells, to determine if the reported anti-tumour effects may be mediated by impairing correct chromosome separation. MDA-MB-436, MDA-MB-231 and MCF-7 breast cancer cells and MCF-10A non-malignant breast epithelial cells were treated with zoledronic acid in vitro, and the effect on Cenp-F localization was analysed by immunoflourescence microscopy. Zoledronic acid caused loss of Cenp-F from the kinetochore, accompanied by an increase in the number of cells in pro-, /prometa- and metaphase in all of the cancer cell lines. There was also a significant increase in the number of lagging chromosomes in mitotic cells. The effects of zoledronic acid could be reversed by inclusion of an intermediary of the mevalonate pathway, showing that the loss of Cenp-F from the kinetochore was caused by the inhibition of farnesylation. In contrast, no effect was seen on Cenp-F in non-malignant MCF-10A cells. This is the first report showing a specific effect of zoledronic acid on a protein involved in the regulation of chromosome segregation, identifying Cenp-F as a potential new molecular target for NBPs in tumour cells.

Discovery and SAR of methylated tetrahydropyranyl derivatives as inhibitors of isoprenylcysteine carboxyl methyltransferase (ICMT)

A series of tetrahydropyranyl (THP) derivatives has been developed as potent inhibitors of isoprenylcysteine carboxyl methyltransferase (ICMT) for use as anticancer agents. Structural modification of the submicromolar hit compound 3 led to the potent 3-methoxy substituted analogue 27. Further SAR development around the THP ring resulted in an additional 10-fold increase in potency, exemplified by analogue 75 with an IC(50) of 1.3 nM. Active and potent compounds demonstrated a dose-dependent increase in Ras cytosolic protein. Potent ICMT inhibitors also reduced cell viability in several cancer cell lines with growth inhibition (GI(50)) values ranging from 0.3 to >100 μM. However, none of the cellular effects observed using ICMT inhibitors were as pronounced as those resulting from a farnesyltransferase inhibitor.

Withaferin A inhibits breast cancer invasion and metastasis at sub-cytotoxic doses by inducing vimentin disassembly and serine 56 phosphorylation

Withaferin A (WFA) is purified from the plant Withania somnifera and inhibits the vimentin cytoskeleton. Vimentin overexpression in cancer correlates with metastatic disease, induction of epithelial to mesenchymal transition and reduced patient survival. As vimentin functions in cell motility, we wanted to test the hypothesis that WFA inhibits cancer metastasis by disrupting vimentin function. These data showed that WFA had weak cytotoxic and apoptotic activity at concentrations less than or equal to 500 nM, but retained potent anti-invasive activity at these low doses. Imaging of breast cancer cell lines revealed that WFA induces perinuclear vimentin accumulation followed by rapid vimentin depolymerization. A concomitant induction of vimentin ser56 phosphorylation was observed, which is consistent with vimentin disassembly. Structure activity relationships were established using a set of chemically modified WFA analogs and showed that the predicted vimentin-binding region of WFA is necessary to induce vimentin ser56 phosphorylation and for its anti-invasive activity. Pharmacokinetic studies in mice revealed that WFA reaches peak concentrations up to 2 μM in plasma with a half-life of 1.36 hr following a single 4 mg/kg dose. In a breast cancer metastasis mouse model, WFA showed dose-dependent inhibition of metastatic lung nodules and induced vimentin ser56 phosphorylation, with minimal toxicity to lung tissue. Based upon these studies, we conclude that WFA is a potent breast cancer anti-metastatic agent and the anti-metastatic activity of WFA is, at least in part, mediated through its effects on vimentin and vimentin ser56 phosphorylation.

Protein farnesylation inhibitors cause donut-shaped cell nuclei attributable to a centrosome separation defect

Despite the success of protein farnesyltransferase inhibitors (FTIs) in the treatment of certain malignancies, their mode of action is incompletely understood. Dissecting the molecular pathways affected by FTIs is important, particularly because this group of drugs is now being tested for the treatment of Hutchinson-Gilford progeria syndrome. In the current study, we show that FTI treatment causes a centrosome separation defect, leading to the formation of donut-shaped nuclei in nontransformed cell lines, tumor cell lines, and tissues of FTI-treated mice. Donut-shaped nuclei arise during chromatin decondensation in late mitosis; subsequently, cells with donut-shaped nuclei exhibit defects in karyokinesis, develop aneuploidy, and are often binucleated. Binucleated cells proliferate slowly. We identified lamin B1 and proteasome-mediated degradation of pericentrin as critical components in FTI-induced "donut formation" and binucleation. Reducing pericentrin expression or ectopic expression of nonfarnesylated lamin B1 was sufficient to elicit donut formation and binucleated cells, whereas blocking proteasomal degradation eliminated FTI-induced donut formation. Our studies have uncovered an important role of FTIs on centrosome separation and define pericentrin as a (indirect) target of FTIs affecting centrosome position and bipolar spindle formation, likely explaining some of the anticancer effects of these drugs.

Farnesyl transferase expression determines clinical response to the docetaxel-lonafarnib combination in patients with advanced malignancies

BACKGROUND

Lonafarnib (LNF) is a protein farnesyl transferase (FTase) inhibitor that has shown synergistic activity with taxanes in preclinical models and early stage clinical trials. Preclinical findings suggested tubulin acetylation and FTase expression levels may be important determinants of drug sensitivity that would help identify patient populations more likely to benefit from this regimen. This pilot study evaluated the biological effects of LNF and docetaxel (DTX) combination therapy in refractory solid tumors by comparing pretreatment and post-treatment tumor biopsies.

METHODS

Patients with histologically confirmed locally advanced or metastatic solid malignancies refractory to standard therapies or with no effective therapies available were eligible. Patients were randomized to 1 of 4 dosing cohorts: 1) 30 mg/m², 100 mg; 2) 36 mg/m², 100 mg; 3) 30 mg/m², 150 mg; or 4) 36 mg/m², 150 mg of DTX intravenously weekly, LNF orally twice daily, respectively.

RESULTS

Of the 38 patients enrolled, 36 were treated, and 29 were evaluable for toxicity and response assessment. The combination of LNF and DTX was tolerated in all cohorts with the exception of a 28% incidence of grade 3/4 diarrhea, which was manageable with aggressive antidiarrheal regimens. Seven patients derived clinically meaningful benefit from this combination treatment; these patients had significantly lower basal FTase-beta mRNA expression levels than the mean study population level (P < .05). Correlation of clinical benefit with tubulin acetylation content as well as basal acetyl-tubulin content were evaluated. However, no significant correlation was found.

CONCLUSIONS

Despite the small number of patients, these findings support our preclinical mechanistic studies and warrant further clinical investigations using FTase-beta mRNA expression as a potential predictive biomarker to select for an enriched patient population to study the effects of taxane and FTase inhibitor combination therapies.

Mitosis as an anti-cancer target

Most of the current drugs used to treat cancer can be classified as anti-proliferative drugs. These drugs perturb the proliferative cycle of tumor cells at diverse stages of the cell cycle. Examples of such drugs are DNA-damaging agents and inhibitors of cyclin-dependent kinases that arrest cell cycle progression at different stages of interphase. Another class of anti-proliferative drugs is the so-called anti-mitotic drugs, which selectively perturb progression through mitosis. Mitosis is the shortest and final stage in the cell cycle and has evolved to accurately divide the duplicated genome over the two daughter cells. This review deals with the different strategies that are currently considered to perturb mitotic progression in the treatment of cancer.

The role of kinesin family proteins in tumorigenesis and progression: potential biomarkers and molecular targets for cancer therapy

The kinesin superfamily contains a conserved class of microtubule-dependent molecular motor proteins that possess an adenosine triphosphatase activity and motion characteristics. The active movement of kinesins supports several cellular functions, including mitosis, meiosis, and the transport of macromolecules. Mitosis is a process of eukaryotic cell division that involves the division of nuclei, cytoplasm, organelles, and the cell membrane into 2 daughter cells with roughly equivalent portions of these cellular components. Any errors in this process could result in cell death, abnormality (such as gene deletion, chromosome translocation, or duplication), and cancer. Because mitosis is complex and highly regulated, alteration of kinesin expression or function could lead to carcinogenesis. Moreover, because human cancer is a gene-related disease involving abnormal cell growth, targeting kinesins may create a novel strategy for the control of human cancer. Indeed, several such drugs are being tested successfully in the clinic. In this review, the authors discuss in detail the structure and function of kinesins, the correlation of kinesin expression with tumorigenesis and progression, and the development of biomarkers and cancer-targeted therapy involving the kinesin family proteins.

Substrate-specific regulation of ubiquitination by the anaphase-promoting complex

By orchestrating the sequential degradation of a large number of cell cycle regulators, the ubiquitin ligase anaphase-promoting complex (APC/C) is essential for proliferation in all eukaryotes. The correct timing of APC/C-dependent substrate degradation, a critical feature of progression through mitosis, was long known to be controlled by mechanisms targeting the core APC/C-machinery. Recent experiments, however, have revealed an important contribution of substrate-specific regulation of the APC/C to achieve accurate cell division. In this perspective, we describe different mechanisms of substrate-specific APC/C-regulation and discuss their importance for cell division.

CAMP (C13orf8, ZNF828) is a novel regulator of kinetochore-microtubule attachment

Proper attachment of microtubules to kinetochores is essential for accurate chromosome segregation. Here, we report a novel protein involved in kinetochore-microtubule attachment, chromosome alignment-maintaining phosphoprotein (CAMP) (C13orf8, ZNF828). CAMP is a zinc-finger protein containing three characteristic repeat motifs termed the WK, SPE, and FPE motifs. CAMP localizes to chromosomes and the spindle including kinetochores, and undergoes CDK1-dependent phosphorylation at multiple sites during mitosis. CAMP-depleted cells showed severe chromosome misalignment, which was associated with the poor resistance of K-fibres to the tension exerted upon establishment of sister kinetochore bi-orientation. We found that the FPE region, which is responsible for spindle and kinetochore localization, is essential for proper chromosome alignment. The C-terminal region containing the zinc-finger domains negatively regulates chromosome alignment, and phosphorylation in the FPE region counteracts this regulation. Kinetochore localization of CENP-E and CENP-F was affected by CAMP depletion, and by expressing CAMP mutants that cannot functionally rescue CAMP depletion, placing CENP-E and CENP-F as downstream effectors of CAMP. These data suggest that CAMP is required for maintaining kinetochore-microtubule attachment during bi-orientation.

Prognostic significance and therapeutic implications of centromere protein F expression in human nasopharyngeal carcinoma

Background

Our recent cDNA microarray data showed that centromere protein F (CENP-F) is significantly upregulated in primary cultured nasopharyngeal carcinoma (NPC) tumor cells compared with normal nasopharyngeal epithelial cells. The goal of this study was to further investigate the levels of CENP-F expression in NPC cell lines and tissues to clarify the clinical significance of CENP-F expression in NPC as well as the potential therapeutic implications of CENP-F expression.

Methods

Real-time RT-PCR and western blotting were used to examine CENP-F expression levels in normal primary nasopharyngeal epithelial cells (NPEC), immortalized nasopharyngeal epithelial cells and NPC cell lines. Levels of CENP-F mRNA were determined by real-time RT-PCR in 23 freshly frozen nasopharyngeal biopsy tissues, and CENP-F protein levels were detected by immunohistochemistry in paraffin sections of 202 archival NPC tissues. Statistical analyses were applied to test for prognostic associations. The cytotoxicities of CENP-F potential target chemicals, zoledronic acid (ZOL) and FTI-277 alone, or in combination with cisplatin, in NPC cells were determined by the MTT assay.

Results

The levels of CENP-F mRNA and protein were higher in NPC cell lines than in normal and immortalized NPECs. CENP-F mRNA level was upregulated in nasopharyngeal carcinoma biopsy tissues compared with noncancerous tissues. By immunohistochemical analysis, CENP-F was highly expressed in 98 (48.5%) of 202 NPC tissues. Statistical analysis showed that high expression of CENP-F was positively correlated with T classification (P < 0.001), clinical stage (P < 0.001), skull-base invasion (P < 0.001) and distant metastasis (P = 0.012) inversely correlated with the overall survival time in NPC patients. Multivariate analysis showed that CENP-F expression was an independent prognostic indicator for the survival of the patient. Moreover, we found that ZOL or FTI-277 could significantly enhance the chemotherapeutic sensitivity of NPC cell lines (HONE1 and 6-10B) with high CENP-F expression to cisplatin, although ZOL or FTI-277 alone only exhibited a minor inhibitory effect to NPC cells.

Conclusion

Our data suggest that CENP-F protein is a valuable marker of NPC progression, and CENP-F expression is associated with poor overall survival of patients. In addition, our data indicate a potential benefit of combining ZOL or FTI-277 with cisplatin in NPC suggesting that CENP-F expression may have therapeutic implications.

A yeast-based genomic strategy highlights the cell protein networks altered by FTase inhibitor peptidomimetics

Background

Farnesyltransferase inhibitors (FTIs) are anticancer agents developed to inhibit Ras oncoprotein activities. FTIs of different chemical structure act via a conserved mechanism in eukaryotic cells. They have low toxicity and are active on a wide range of tumors in cellular and animal models, independently of the Ras activation state. Their ultimate mechanism of action, however, remains undetermined. FTase has hundred of substrates in human cells, many of which play a pivotal role in either tumorigenesis or in pro-survival pathways. This lack of knowledge probably accounts for the failure of FTIs at clinical stage III for most of the malignancies treated, with the notable exception of haematological malignancies. Understanding which cellular pathways are the ultimate targets of FTIs in different tumor types and the basis of FTI resistance is required to improve the efficacy of FTIs in cancer treatment.

Results

Here we used a yeast-based cellular assay to define the transcriptional changes consequent to FTI peptidomimetic administration in conditions that do not substantially change Ras membrane/cytosol distribution. Yeast and cancer cell lines were used to validate the results of the network analysis. The transcriptome of yeast cells treated with FTase inhibitor I was compared with that of untreated cells and with an isogenic strain genetically inhibited for FTase activity (Δram1). Cells treated with GGTI-298 were analyzed in a parallel study to validate the specificity of the FTI response. Network analysis, based on gene ontology criteria, identified a cell cycle gene cluster up-regulated by FTI treatment that has the Aurora A kinase IPL1 and the checkpoint protein MAD2 as hubs. Moreover, TORC1-S6K-downstream effectors were found to be down-regulated in yeast and mammalian FTI-treated cells. Notably only FTIs, but not genetic inhibition of FTase, elicited up-regulation of ABC/transporters.

Conclusions

This work provides a view of how FTIs globally affect cell activity. It suggests that the chromosome segregation machinery and Aurora A association with the kinetochore as well as TORC1-S6K downstream effectors are among the ultimate targets affected by the transcriptional deregulation caused by FTI peptidomimetics. Moreover, it stresses the importance of monitoring the MDR response in patients treated with FTIs.

RNA interference (RNAi) screening approach identifies agents that enhance paclitaxel activity in breast cancer cells

Introduction

Paclitaxel is a widely used drug in the treatment of patients with locally advanced and metastatic breast cancer. However, only a small portion of patients have a complete response to paclitaxel-based chemotherapy, and many patients are resistant. Strategies that increase sensitivity and limit resistance to paclitaxel would be of clinical use, especially for patients with triple-negative breast cancer (TNBC).

Methods

We generated a gene set from overlay of the druggable genome and a collection of genomically deregulated gene transcripts in breast cancer. We used loss-of-function RNA interference (RNAi) to identify gene products in this set that, when targeted, increase paclitaxel sensitivity. Pharmacological agents that targeted the top scoring hits/genes from our RNAi screens were used in combination with paclitaxel, and the effects on the growth of various breast cancer cell lines were determined.

Results

RNAi screens performed herein were validated by identification of genes in pathways that, when previously targeted, enhanced paclitaxel sensitivity in the pre-clinical and clinical settings. When chemical inhibitors, CCT007093 and mithramycin, against two top hits in our screen, PPMID and SP1, respectively, were used in combination with paclitaxel, we observed synergistic growth inhibition in both 2D and 3D breast cancer cell cultures. The transforming growth factor beta (TGFβ) receptor inhibitor, LY2109761, that targets the signaling pathway of another top scoring hit, TGFβ1, was synergistic with paclitaxel when used in combination on select breast cancer cell lines grown in 3D culture. We also determined the relative paclitaxel sensitivity of 22 TNBC cell lines and identified 18 drug-sensitive and four drug-resistant cell lines. Of significance, we found that both CCT007093 and mithramycin, when used in combination with paclitaxel, resulted in synergistic inhibition of the four paclitaxel-resistant TNBC cell lines.

Conclusions

RNAi screening can identify druggable targets and novel drug combinations that can sensitize breast cancer cells to paclitaxel. This genomic-based approach can be applied to a multitude of tumor-derived cell lines and drug treatments to generate requisite pre-clinical data for new drug combination therapies to pursue in clinical investigations.

Cdc20 is required for the post-anaphase, KEN-dependent degradation of centromere protein F

Progression through mitosis and cytokinesis requires the sequential proteolysis of several cell-cycle regulators. This proteolysis is mediated by the ubiquitin-proteasome system, with the E3 ligase being the anaphase-promoting complex, also known as the cyclosome (APC/C). The APC/C is regulated by two activators, namely Cdc20 and Cdh1. The current view is that prior to anaphase, the APC/C is activated by Cdc20, but that following anaphase, APC/C switches to Cdh1-dependent activation. However, here we present an analysis of the kinetochore protein Cenp-F that is inconsistent with this notion. Although it has long been appreciated that Cenp-F is degraded sometime during or after mitosis, exactly when and how has not been clear. Here we show that degradation of Cenp-F initiates about six minutes after anaphase, and that this is dependent on a C-terminal KEN-box. Although these two observations are consistent with Cenp-F being a substrate of Cdh1-activated APC/C, Cenp-F is degraded normally in Cdh1-null cells. By contrast, RNAi-mediated repression of APC/C subunits or Cdc20 does inhibit Cenp-F degradation. These findings therefore suggest that the APC/C does not simply 'switch' upon anaphase onset; rather, our observations indicate that Cdc20 also contributes to post-anaphase activation of the APC/C. We also show that the post-anaphase, KEN-box-dependent degradation of Cenp-F requires it to be farnesylated, a post-translational modification usually linked to membrane association. Because so many of the behaviours of Cenp-F are farnesylation-dependent, we suggest that this modification plays a more global role in Cenp-F function.

Continuous and intermittent dosing of lonafarnib potentiates the therapeutic efficacy of docetaxel on preclinical human prostate cancer models

Lonafarnib is a potent, selective farnesyltransferase inhibitor (FTI) undergoing clinical studies for the treatment of solid tumors and hematological malignancies. Preclinically, a number of FTIs, including lonafarnib, interact with taxanes to inhibit cancer cell growth in an additive/synergistic manner. These observations provided rationale for investigating the effects of combining lonafarnib and docetaxel on preclinical prostate cancer models. To date, docetaxel is the only chemotherapeutic agent in clinical use for hormone-refractory prostate cancer. In vitro experiments with 22Rv1, LNCaP, DU-145, PC3 and PC3-M prostate cancer cell lines showed significantly enhanced inhibition of cell proliferation and apoptosis when lonafarnib was added to docetaxel. In human tumor xenograft models, continuous coadministration of lonafarnib with docetaxel caused marked tumor regressions (24-47%) in tumors from all of the cell types as well as parental CWR22 xenografts. Intermittent dosing of lonafarnib (5 days on then 5 days off) coadministered with docetaxel produced similar regressions in hormone-refractory 22Rv1 tumors. 22Rv1 tumors progressing on docetaxel treatment also responded to treatment with intermittent lonafarnib (5 days on then 5 days off). Moreover, animals did not exhibit any signs of toxicity during coadministration of lonafarnib and docetaxel. In conclusion, coadministration of continuous and intermittent lonafarnib enhanced the antitumor activity of docetaxel in a panel of prostate cancer models. An intermittent dosing schedule of lonafarnib coadministered with docetaxel may allow enhanced efficacy to that of continuous dosing by improving the tolerability of higher doses of lonafarnib.

Traffic control: regulation of kinesin motors

Kinesins are a family of molecular motors that use the energy of ATP hydrolysis to move along the surface of, or destabilize, microtubule filaments. Much progress has been made in understanding the mechanics and functions of the kinesin motors that play important parts in cell division, cell motility, intracellular trafficking and ciliary function. How kinesins are regulated in cells to ensure the temporal and spatial fidelity of their microtubule-based activities is less well understood. Recent work has revealed molecular mechanisms that control kinesin autoinhibition and subsequent activation, binding to cargos and microtubule tracks, and localization at specific sites of action.

Kinesin motor proteins as targets for cancer therapy

The process of mitosis is a validated point of intervention in cancer therapy and a variety of anti-mitotic drugs are successfully being used in the clinic. To date, all approved antimitotics target the spindle microtubules, thus interfering with spindle dynamics, leading to mitotic arrest and apoptosis. While effective, these drugs are also associated with a variety of side effects, including neurotoxicity. In recent years, mitotic kinesins have attracted significant attention in the search for novel, alternative mitotic drug targets. Due to their specific function in mitosis, targeting these proteins creates an opportunity for the development of more selective antimitotics with an improved side effect profile. In addition, kinesin inhibitors may overcome resistance to microtubule targeting drugs. Drug discovery efforts in this area have initially focused on the plus-end directed kinesin spindle protein (KSP) and a variety of compounds are currently undergoing clinical testing.

Working together: Farnesyl transferase inhibitors and statins block protein prenylation

Farnesyl transferase inhibitors (FTIs) have so far proved to have limited value as single agents in clinical trials. This PharmSight will focus on the use of a novel group of FTIs that are most effective in vitro when used in combination with the "statin" class of anti-hypercholesterolemic agents, which also block protein prenylation. We recently showed that these novel FTIs in combination with lovastatin reduce Ras prenylation and induce an apoptotic response in malignant peripheral nerve sheath cells. The combination of statins with these new FTIs may produce profound synergistic cytostatic and cytotoxic effects against a variety of tumors and other proliferative disorders. Since statins are well tolerated in the clinic, we suggest that this combination approach should be tested in in vivo models.

Centromere-associated protein E: a motor that puts the brakes on the mitotic checkpoint

Cell cycle checkpoints have long been recognized as important nodes for regulating cell proliferation and maintaining genomic integrity. These checkpoints are often altered in cancer and represent promising points for therapeutic intervention. Until recently, direct targeting of the mitotic checkpoint has been an untapped area for cancer drug discovery. Regulation of the mitotic checkpoint is complex, but many of the critical players have been identified and functionally characterized. A substantial number of these proteins can be localized to the kinetochore, a structure located at the centromeric region of each mitotic chromosome. The kinetochore mediates chromosome attachment to spindle microtubules and subsequent chromosome movement. The mitotic checkpoint monitors microtubule attachment and chromosome position on the mitotic spindle, inhibiting progression into anaphase until proper attachment and metaphase positioning is achieved. Centromere-associated protein E is a kinesin microtubule motor protein that plays an essential role in integrating the mechanics of microtubule-chromosome interactions with mitotic checkpoint signaling, and has emerged as a novel target for cancer therapy.