A Potent Chemotherapeutic Strategy for Bladder Cancer: ( S )-Methoxy-Trityl-L-Cystein, a Novel Eg5 Inhibitor

Eg5 Overexpression Is Predictive of Poor Prognosis in Hepatocellular Carcinoma Patients

Eg5 (kinesin spindle protein) plays an essential role in mitosis. Inhibition of Eg5 function results in cell cycle arrest at mitosis, which leads to cell death. To date, Eg5 expression and its prognostic significance have not been studied in hepatocellular carcinoma (HCC). In this study, 26 freshly frozen HCC tissue samples and matched peritumoral tissue samples were evaluated with a one-step qPCR test and immunohistochemical (IHC) analysis was conducted on 156 HCC samples to investigate the relationships among Eg5 expression, clinicopathological factors, and prognosis. Eg5 mRNA and protein expression levels were significantly higher in HCC tissues relative to matched noncancerous tissues (p < 0.05). High Eg5 protein expression was significantly related to liver cirrhosis (p = 0.038) and TNM stage (p = 0.008). Kaplan-Meier survival and Cox regression analyses revealed that Eg5 overexpression (p = 0.001), liver cirrhosis (p = 0.009), and TNM stage (p = 0.025) were independent prognostic factors for overall survival. These findings indicate that Eg5 expression can be used as a biomarker of poor prognosis and as a novel therapeutic target for HCC.

Ubiquitin ligase RNF20/40 facilitates spindle assembly and promotes breast carcinogenesis through stabilizing motor protein Eg5

Whether transcriptional regulators are functionally involved in mitosis is a fundamental question in cell biology. Here we report that the RNF20/40 complex, a major ubiquitin ligase catalysing histone H2B monoubiquitination, interacts with the motor protein Eg5 during mitosis and participates in spindle assembly. We show that the RNF20/40 complex monoubiquitinates and stabilizes Eg5. Loss of RNF20/40 results in spindle assembly defects, cell cycle arrest and apoptosis. Consistently, depletion of either RNF20/40 or Eg5 suppresses breast cancer in vivo. Significantly, RNF20/40 and Eg5 are concurrently upregulated in human breast carcinomas and high Eg5 expression is associated with poorer overall survival of patients with luminal A, or B, breast cancer. Our study uncovers an important spindle assembly role of the RNF20/40 complex, and implicates the RNF20/40-Eg5 axis in breast carcinogenesis, supporting the pursuit of these proteins as potential targets for breast cancer therapeutic interventions.

Eg5 has a role in spindle assembly and has been associated with tumorigenesis but it is not clear how its activity is regulated. Here, the authors show that the E3 ligase RNF20/40 regulates mitotic spindle assembly by regulating the stability of Eg5 through mono-ubiquitination of K745.

A Potent Chemotherapeutic Strategy with Eg5 Inhibitor against Gemcitabine Resistant Bladder Cancer

Development of resistance to gemcitabine is a major concern in bladder cancer therapy, and the mechanism remains unclear. Eg5 has been recently identified as an attractive target in cancer chemotherapy, so novel targeted chemotherapy with Eg5 inhibitor is expected to improve the anticancer effect in gemcitabine-resistant bladder cancer. In this research, RT112-Gr cells were 350-fold less sensitive to gemcitabine than the parental cell lines, while KU7-Gr cells were 15-fold less sensitive to gemcitabine than the parental cell lines. Human OneArray Microarray analysis was performed to obtain broad spectrum information about the genes differentially expressed in RT112 and RT112-Gr cells. The anti-proliferative activity of S(MeO)TLC, an Eg5 inhibitor, was analyzed in RT112-Gr cell lines using a cell viability assay. Furthermore, the inhibitory effect was evaluated in vivo using subcutaneous xenograft tumor model. According to the result of Human OneArray® GeneChip, RRM1 and RRM2 were up-regulated, while there was no significant change in Eg5. Trypan blue staining confirmed that in S(MeO)TLC and Gemcitabine combining S(MeO)TLC group cell viability were significantly decreased in RT112-Gr cells as compared with other groups. S(MeO)TLC and S(MeO)TLC+gemcitabine groups prominently suppressed tumor growth in comparison with other groups’ in vivo. There were no significant differences in S(MeO)TLC and gemcitabine+S(MeO)TLC group in the effect of inhibition of bladder cancer in vivo and in vitro. Our data collectively demonstrated that S(MeO)TLC represents a novel strategy for the treatment of gemcitabine resistant bladder cancer.

Successful imatinib therapy for neuroendocrine carcinoma with activating Kit mutation: a case study

Neuroendocrine tumors (NET) and gastrointestinal stromal tumors (GIST) are believed to originate from the cells of Cajal that are randomly dispersed along the aerodigestive tract. Despite their distinct morphologic appearance, NET and GIST may share oncogenic mechanisms. Often presenting in the metastatic setting, treatment options for patients with NET are limited. This case report presents a patient with refractory metastatic NET that did not respond conventional chemotherapy. The patient was treated with a KIF11 inhibitor in a phase I clinical trial and experienced a prolonged and clinically meaningful partial response. On progression at 20 months, the patient's tumor was sequenced to reveal a KIT exon 11 mutation. Institution of imatinib therapy achieved a rapid and sustained antitumor effect with profound clinical benefit. Despite previously reported KIT expression in NET, this is the first documented case of an activating KIT mutation in NET and of successful treatment with both a KIF11 inhibitor and imatinib, each of which was elucidated through molecular profiling of the patient's tumor. Imatinib may be a valuable therapy in NET harboring activating KIT mutations.

Kinesin spindle protein inhibitors with diaryl amine scaffolds: crystal packing analysis for improved aqueous solubility

Diaryl amine derivatives have been designed and synthesized as novel kinesin spindle protein (KSP) inhibitors based on planar carbazole-type KSP inhibitors with poor aqueous solubility. The new generation of inhibitors was found to show comparable inhibitory activity and high selectivity for KSP, and this was accompanied with improved solubility. Kinetic analysis and molecular modeling studies suggested that these inhibitors work in an ATP-competitive manner via binding to the secondary allosteric site formed by α4 and α6 helices of KSP. Comparative structural investigations on a series of compounds revealed that the higher solubility of diaryl amine-type inhibitors was attributed to fewer van der Waals interactions in the crystal packing and the hydrogen-bond acceptor nitrogen of the aniline moiety for favorable solvation.

Eg5 inhibitor, a novel potent targeted therapy, induces cell apoptosis in renal cell carcinoma

Eg5 is critical for mitosis and overexpressed in various malignant tumors, which has now been identified as a promising target in cancer therapy. However, the anti-cancer activity of Eg5 inhibitor in renal cell carcinoma (RCC) remains an open issue. In this paper, we evaluated, for the first time, the therapeutic benefit of blocking Eg5 by S-(methoxytrityl)-L-cysteine (S(MeO)TLC) in RCC both in vitro and vivo. The expression of Eg5 was examined in clinical tissue samples and various kidney cell lines, including 293T, 786-0, and OS-RC-2. The anti-proliferative activity of Eg5 inhibitors, (S)-trityl-L-cysteine (STLC) and S(MeO)TLC, was evaluated by a cell viability assay. An apoptosis assay with Hoechst nuclear staining and flow cytometry was applied to investigate the efficacy of the S(MeO)TLC, which is more potent than STLC. Immunofluorescence was used to research the possible mechanism. Furthermore, in vivo studies were performed by using subcutaneous xenograft models, which were used to confirm its role as a potential anti-neoplastic drug. The Eg5 expression was detected in kidney cell lines and RCC tissues, which was low in normal kidney samples. STLC and S(MeO)TLC exhibited their optimal anti-proliferative activity in 72 h, and cells treated with S(MeO)TLC presented characteristic monoastral spindle phenotype in 24 h and apoptotic cells in 48 h. In vivo, S(MeO)TLC effectively suppressed tumor growth in subcutaneous xenograft models. Inhibition of Eg5 represses the proliferation of RCC in vitro and in vivo. All these findings collectively demonstrate that S(MeO)TLC, a potent Eg5 inhibitor, is a promising anti-cancer agent for the treatment of RCC.

Kinesin spindle protein inhibitors in cancer: a patent review (2008 - present)

INTRODUCTION

Inhibition of kinesin spindle protein (KSP) has emerged as a novel and validated therapeutic strategy against cancers. A lot of new KSP inhibitors have been identified in recent years and some of them have entered clinical trials. This may provide more selections in future cancer therapy.

AREAS COVERED

In the present review, the authors will describe the most recent classes of KSP inhibitors by reviewing about 96 literatures in which 24 patent applications were included from 2008 to now.

EXPERT OPINION

Many new KSP inhibitors have been discovered that act either by binding in an allosteric site of KSP or by ATP competitive inhibition. There are several ATP non-competitive KSP inhibitors entering clinical investigation. Although they were both well tolerated and showed acceptable pharmacokinetic profiles, limited clinical response was always the problem. Mutation of the binding pocket was also a hindrance in the development of these allosteric inhibitors. The appearance of ATP competitive KSP inhibitors was considered to be able to overcome mutation-mediated resistance to the allosteric inhibitors, which could be a new approach for the development of novel KSP inhibitors.

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.

The expression of Eg5 predicts a poor outcome for patients with renal cell carcinoma

Eg5 is a member of the kinesin family of proteins, which associates with bipolar spindle formation in dividing tumor cells during mitosis. The aim of our study is to investigate the prognostic role of Eg5 expression in patients with renal cell carcinoma (RCC). RCC tissue specimens from 164 consecutively treated patients who underwent surgery between 2005 and 2011 were evaluated. The Eg5 expression was determined by immunohistochemistry, and correlated with clinicopathological parameters. The prognostic significance of Eg5 expression was explored using the univariate and multivariate survival analysis of 164 patients who were followed; one hundred and sixty-four tissue specimens "of patients" who were regularly followed with the mean 35.8 months (from 5 to 80 months). The expression of Eg5 was significantly associated with tumor nuclear grade (P = 0.019) and stage (P = 0.007), as well as tumor size (P = 0.033). In univariate analysis, Eg5 overexpression showed unfavorable influence on recurrence-free survival with statistical significance (P = 0.003). Clinical stage, nuclear grade and tumor size also showed strong statistical relation with adverse recurrence-free survival (P < 0.001). Multivariate analysis revealed that tumor stage, nuclear grade and Eg5 reactivity (P < 0.001, P = 0.002, P = 0.032) were identified as independent prognostic factors for recurrence-free survival in patients with RCC. In our opinion, the result of this study proved the relationship between Eg5 expression and worse clinical outcome in RCC. This finding suggested that Eg5 served as a prognostic factor, which could be useful to predict cancer evolution and provide appropriate treatments for RCC patients.

Downregulation of Ral GTPase-activating protein promotes tumor invasion and metastasis of bladder cancer

The small GTPase Ral is known to be highly activated in several human cancers, such as bladder, colon and pancreas cancers. It is reported that activated Ral is involved in cell proliferation, migration and metastasis of bladder cancer. This protein is activated by Ral guanine nucleotide exchange factors (RalGEFs) and inactivated by Ral GTPase-activating proteins (RalGAPs), the latter of which consist of heterodimers containing a catalytic α1 or α2 subunit and a common β subunit. In Ras-driven cancers, such as pancreas and colon cancers, constitutively active Ras mutant activates Ral through interaction with RalGEFs, which contain the Ras association domain. However, little is known with regard to the mechanism that governs aberrant activation of Ral in bladder cancer, in which Ras mutations are relatively infrequent. Here, we show that Ral was highly activated in invasive bladder cancer cells due to reduced expression of RalGAPα2, the dominant catalytic subunit in bladder, rather than increased expression of RalGEFs. Exogenous expression of wild-type RalGAPα2 in KU7 bladder cancer cells with invasive phenotype, but not mutant RalGAPα2-N1742K lacking RalGAP activity, resulted in attenuated cell migration in vitro and lung metastasis in vivo. Furthermore, genetic ablation of Ralgapa2 promoted tumor invasion in a chemically-induced murine bladder cancer model. Importantly, immunohistochemical analysis of human bladder cancer specimens revealed that lower expression of RalGAPα2 was associated with advanced clinical stage and poor survival of patients. Collectively, these results are highly indicative that attenuated expression of RalGAPα2 leads to disease progression of bladder cancer through enhancement of Ral activity.

Triphenylbutanamines: kinesin spindle protein inhibitors with in vivo antitumor activity

The human mitotic kinesin Eg5 represents a novel mitotic spindle target for cancer chemotherapy. We previously identified S-trityl-l-cysteine (STLC) and related analogues as selective potent inhibitors of Eg5. We herein report on the development of a series of 4,4,4-triphenylbutan-1-amine inhibitors derived from the STLC scaffold. This new generation systematically improves on potency: the most potent C-trityl analogues exhibit K_i^app ≤ 10 nM and GI₅₀ ≈ 50 nM, comparable to results from the phase II clinical benchmark ispinesib. Crystallographic studies reveal that they adopt the same overall binding configuration as S-trityl analogues at an allosteric site formed by loop L5 of Eg5. Evaluation of their druglike properties reveals favorable profiles for future development and, in the clinical candidate ispinesib, moderate hERG and CYP inhibition. One triphenylbutanamine analogue and ispinesib possess very good bioavailability (51% and 45%, respectively), with the former showing in vivo antitumor growth activity in nude mice xenograft studies.

A potent chemotherapeutic strategy in prostate cancer: S-(methoxytrityl)-L-cysteine, a novel Eg5 inhibitor

Docetaxel-based combination chemotherapy remains the predominant treatment for castration-resistant prostate cancer. However, taxane-related drug resistance and neurotoxicity have prompted us to develop substitute treatment strategies. Eg5 (kinesin spindle protein), which is crucial for bipolar spindle formation and duplicated chromosome separation during the early phase of mitosis, has emerged as an attractive target for cancer chemotherapy. The aim of this study was to investigate the anticancer efficacy of S-(methoxytrityl)-L-cysteine (S(MeO)TLC), a novel Eg5 inhibitor in prostate cancer. Eg5 expression was examined in human prostate cancer cell lines and tissue microarrays were constructed from clinical specimens. Antiproliferative activity of S(MeO)TLC in prostate cancer cells was assessed by a cell viability assay. The anticancer effect and inhibitory mechanism of S(MeO)TLC in prostate cancer cells was further explored by Hoechst staining, flow cytometry and immunofluorescence. In addition, the antitumor effect of S(MeO)TLC on subcutaneous xenograft models was assessed. Eg5 expression was identified in PC3, DU145 and LNCaP cells. More than half of prostate cancer clinical specimens displayed Eg5 expression. S(MeO)TLC exhibited more powerful anticancer activity in prostate cancer cells compared with the other four Eg5 inhibitors tested. S(MeO)TLC induced cell death after arresting dividing cells at mitosis with distinct monopolar spindle formation. S(MeO)TLC exhibited its significant inhibitory activity (P<0.05) on subcutaneous xenograft models also through induction of mitotic arrest. We conclude that Eg5 is a good target for prostate cancer chemotherapy, and S(MeO)TLC is a potent promising anticancer agent in prostate cancer.