Ibulocydine is a novel prodrug Cdk inhibitor that effectively induces apoptosis in hepatocellular carcinoma cells

Ibulocydine Inhibits Migration and Invasion of TNBC Cells via MMP-9 Regulation

Triple-negative breast cancer (TNBC) accounts for approximately 15-20% of all breast cancer types, indicating a poor survival prognosis with a more aggressive biology of metastasis to the lung and a short response duration to available therapies. Ibulocydine (IB) is a novel (cyclin-dependent kinase) CDK7/9 inhibitor prodrug displaying potent anti-cancer effects against various cancer cell types. We performed in vitro and in vivo experiments to determine whether IB inhibits metastasis and eventually overcomes the poor drug response in TNBC. The result showed that IB inhibited the growth of TNBC cells by inducing caspase-mediated apoptosis and blocking metastasis by reducing MMP-9 expression in vitro. Concurrently, in vivo experiments using the metastasis model showed that IB inhibited metastasis of MDA-MB-231-Luc cells to the lung. Collectively, these results demonstrate that IB inhibited the growth of TNBC cells and blocked metastasis by regulating MMP-9 expression, suggesting a novel therapeutic agent for metastatic TNBC.

Recent progress in development of cyclin-dependent kinase 7 inhibitors for cancer therapy

Introduction: Cyclin-dependent kinase 7 (CDK7) is a part of the CDK-activating kinase family (CAK) which has a key role in the cell cycle and transcriptional regulation. Several lines of evidence suggest that CDK7 is a promising therapeutic target for cancer. CDK7 selective inhibitors such as SY-5609 and CT7001 are in clinical development. Areas covered: We explore the biology of CDK7 and its role in cancer and follow this with an evaluation of the preclinical and clinical progress of CDK7 inhibitors, and their potential in the clinic. We searched PubMed and ClinicalTrials to identify relevant data from the database inception to 14 October 2020. Expert opinion: CDK7 inhibitors are next generation therapeutics for cancer. However, there are still challenges which include selectively, side effects, and drug resistance. Nevertheless, with ongoing clinical development of these inhibitors and greater analysis of their target, CDK7 inhibitors will become a promising approach for treatment of cancer in the near future.

Novel [(N-alkyl-3-indolylmethylene)hydrazono]oxindoles arrest cell cycle and induce cell apoptosis by inhibiting CDK2 and Bcl-2: synthesis, biological evaluation and in silico studies

As a continuation for our previous work, a novel set of N-alkylindole-isatin conjugates (7, 8a-c, 9 and 10a-e) is here designed and synthesised with the prime aim to develop more efficient isatin-based antitumor candidates. Utilising the SAR outputs from the previous study, our design here is based on appending four alkyl groups with different length (ethyl and n-propyl), bulkiness (iso-propyl) and unsaturation (allyl) on N-1 of indole motif, with subsequent conjugation with different N-unsubstituted isatin moieties to furnish the target conjugates. As planned, the adopted strategy achieved a substantial improvement in the growth inhibitory profile for the target conjugates in comparison to the reported lead VI. The best results were obtained with N-propylindole -5-methylisatin hybrid 8a which displayed broad spectrum anti-proliferative action with efficient sub-panel GI50 (MG-MID) range from 1.33 to 4.23 µM, and promising full-panel GI50 (MG-MID) equals 3.10 µM, at the NCI five-dose assay. Also, hybrid 8a was able to provoke cell cycle disturbance and apoptosis in breast T-47D cells as evidenced by the DNA flow cytometry and Annexin V-FITC/PI assays. Furthermore, hybrid 8a exhibited good inhibitory action against cell cycle regulator CDK2 protein kinase and the anti-apoptotic Bcl-2 protein (IC50= 0.85 ± 0.03 and 0.46 ± 0.02 µM, respectively). Interestingly, molecular docking for hybrid 8a in CDK2 and Bcl-2 active sites unveiled that N-propyl group is involved in significant hydrophobic interactions. Taken together, the results suggested conjugate 8a as a promising lead for further development and optimisation as an efficient antitumor drug.

Role of cyclin-dependent kinases (CDKs) in hepatocellular carcinoma: Therapeutic potential of targeting the CDK signaling pathway

Liver cancer is the fourth leading cause of cancer related mortality in the world, with hepatocellular carcinoma (HCC) representing the most common primary subtype. Two-thirds of HCC patients have advanced disease when diagnosed, and for these patients, treatment strategies remain limited. In addition, there is a high incidence of tumor recurrence after surgical resection with the current treatment regimens. The development of novel and more effective agents is required. Cyclin-dependent kinases (CDKs) constitute a family of 21 different protein kinases involved in regulating cell proliferation, apoptosis, and drug resistance, and are evaluated in preclinical and clinical trials as chemotherapeutics. To summarize and discuss the therapeutic potential of targeting CDKs in HCC, recent published articles identified from PubMed were comprehensively reviewed. The key words included hepatocellular carcinoma, cyclin-dependent kinases, and CDK inhibitors. This review focuses on the emerging evidence from studies describing the genetic and functional aspects of CDKs in HCC. We also present an overview of CDK inhibitors that have shown efficacy in laboratory studies of HCC. Although many of the studies assessing CDK-targeting therapies in HCC are at the preclinical stage, there is significant evidence that CDK inhibitors used alone or in combination with established chemotherapy drugs could have significant applications in HCC.

Inhibition of anaplastic lymphoma kinase promotes apoptosis and suppresses proliferation in human hepatocellular carcinoma

Our study was to examine the roles of crizotinib and ceritinib in hepatocellular carcinoma (HCC) cells and explore the possible mechanisms. MTT assay was employed to examine the proliferation of five HCC cell lines treated with various concentrations of crizotinib or ceritinib. HepG2 and HCCLM3 cells were incubated with 2 nmol/l ceritinib for 1 week, followed by crystal violet staining and cell counting. Protein amounts of t-ALK, p-ALK, t-AKT, p-AKT, t-ERK, p-ERK, Mcl-1, survivin, and XIAP in HepG2 cells under different culture conditions were evaluated by western blot. HepG2 and HCCLM3 cells were treated with vehicle or ceritinib and measured by flow cytometry apoptosis analysis with Annexin-V/propidium iodide staining. MTT assay showed that both crizotinib and ceritinib suppressed the proliferation of various human HCC cells. Crystal violet staining analysis also indicated that ceritinib effectively inhibited human HCC cell proliferation. Western blot analysis indicated that both crizotinib and ceritinib inhibited ALK, AKT, and ERK phosphorylations. In addition, ceritinib reduced antiapoptotic gene expressions in HepG2 cells. Flow cytometry analysis indicated that ceritinib induced HepG2 and HCCLM3 cells apoptosis. ALK inhibitor exhibited antitumor effects by inhibiting ALK activation, repressing AKT and ERK pathways, and suppressing antiapoptotic gene expressions, which subsequently promoted apoptosis and suppressed HCC cell proliferations.

Dysregulation of miRNA in chronic hepatitis B is associated with hepatocellular carcinoma risk after nucleos(t)ide analogue treatment

Hepatitis B virus (HBV) infection is a major cause of hepatocellular carcinoma (HCC). Nucleos(t)ide analogue (NA) therapy effectively reduces the incidence of HCC, but it does not completely prevent the disease. Here, we show that dysregulation of microRNAs (miRNAs) is involved in post-NA HCC development. We divided chronic hepatitis B (CHB) patients who received NA therapy into two groups: 1) those who did not develop HCC during the follow-up period after NA therapy (no-HCC group) and 2) those who did (HCC group). miRNA expression profiles were significantly altered in CHB tissues as compared to normal liver, and the HCC group showed greater alteration than the no-HCC group. NA treatment restored the miRNA expression profiles to near-normal in the no-HCC group, but it was less effective in the HCC group. A number of miRNAs implicated in HCC, including miR-101, miR-140, miR-152, miR-199a-3p, and let-7g, were downregulated in CHB. Moreover, we identified CDK7 and TACC2 as novel target genes of miR-199a-3p. Our results suggest that altered miRNA expression in CHB contributes to HCC development, and that improvement of miRNA expression after NA treatment is associated with reduced HCC risk.

Discovery of 3-Benzyl-1-( trans-4-((5-cyanopyridin-2-yl)amino)cyclohexyl)-1-arylurea Derivatives as Novel and Selective Cyclin-Dependent Kinase 12 (CDK12) Inhibitors

Cyclin-dependent kinase 12 (CDK12) plays a key role in the coordination of transcription with elongation and mRNA processing. CDK12 mutations found in tumors and CDK12 inhibition sensitize cancer cells to DNA-damaging reagents and DNA-repair inhibitors. This suggests that CDK12 inhibitors are potential therapeutics for cancer that may cause synthetic lethality. Here, we report the discovery of 3-benzyl-1-( trans-4-((5-cyanopyridin-2-yl)amino)cyclohexyl)-1-arylurea derivatives as novel and selective CDK12 inhibitors. Structure-activity relationship studies of a HTS hit, structure-based drug design, and conformation-oriented design using the Cambridge Structural Database afforded the optimized compound 2, which exhibited not only potent CDK12 (and CDK13) inhibitory activity and excellent selectivity but also good physicochemical properties. Furthermore, 2 inhibited the phosphorylation of Ser2 in the C-terminal domain of RNA polymerase II and induced growth inhibition in SK-BR-3 cells. Therefore, 2 represents an excellent chemical probe for functional studies of CDK12 and could be a promising lead compound for drug discovery.

Upregulation of Mcl-1 inhibits JQ1-triggered anticancer activity in hepatocellular carcinoma cells

Bromodomains and extra-terminal (BET) proteins inhibitors are promising cancer therapeutic agents. However, tumor cells often develop resistance to BET inhibitors, greatly limiting their therapeutic potential. To study the mechanism underlying the resistance of BET inhibitors in hepatocellular carcinoma (HCC) cells, we herein investigated the impact of BET inhibitor JQ1 on the gene expression of Bcl-2 family members by RNA sequencing analysis, and found that acute treatment with JQ1 triggered upregulation of Mcl-1 in HCCLM3 and BEL7402 cell lines. This JQ1-triggered Mcl-1 upregulation was further confirmed by quantitative reverse transcription polymerase chain reaction and western blotting analysis, both at mRNA and protein levels. Inhibition of Mcl-1 by RNA interference dramatically enhanced JQ1-triggered caspase-3 activation, cleavage of poly (ADP-ribose) polymerase and apoptotic cell death induction in multiple HCC cell lines. Moreover, JQ1 in combination with cyclin-dependent kinase inhibitor flavopiridol at a subtoxic concentration that reduced expression of Mcl-1, triggered massive apoptotic cell death in HCCLM3 and BEL7402 cell lines. Together, these data suggest that Mcl-1 is a major contributor to BET inhibitor-resistance in HCC cells, and that combining drugs capable of down-regulating Mcl-1 may promote therapeutic potential in human HCC.

Pyrrolo[2,3-d]pyrimidine (7-deazapurine) as a privileged scaffold in design of antitumor and antiviral nucleosides

7-Deazapurine (pyrrolo[2,3-d]pyrimidine) nucleosides are important analogues of biogenic purine nucleosides with diverse biological activities. Replacement of the N7 atom with a carbon atom makes the five-membered ring more electron rich and brings a possibility of attaching additional substituents at the C7 position. This often leads to derivatives with increased base-pairing in DNA or RNA or better binding to enzymes. Several types of 7-deazapurine nucleosides with potent cytostatic or cytotoxic effects have been identified. The most promising are 7-hetaryl-7-deazaadenosines, which are activated in cancer cells by phosphorylation and get incorporated both to RNA (causing inhibition of proteosynthesis) and to DNA (causing DNA damage). Mechanism of action of other types of cytostatic nucleosides, 6-hetaryl-7-deazapurine and thieno-fused deazapurine ribonucleosides, is not yet known. Many 7-deazaadenosine derivatives are potent inhibitors of adenosine kinases. Many types of sugar-modified derivatives of 7-deazapurine nucleosides are also strong antivirals. Most important are 2'-C-methylribo- or 2'-C-methyl-2'-fluororibonucleosides with anti-HCV activities (several compounds underwent clinical trials). Some underexplored areas of potential interest are also outlined.

miR-206 inhibits the growth of hepatocellular carcinoma cells via targeting CDK9

miR‐206 plays an important role in regulating the growth of multiple cancer cells. Cyclin‐dependent kinase 9 (CDK9) stimulates the production of abundant prosurvival proteins, leading to impaired apoptosis of cancer cells. However, it is unknown whether CDK9 is involved in the miR‐206‐mediated growth suppression of hepatocellular carcinoma (HCC) cells. In this study, we found that the expression level of miR‐206 was significantly lower in HCC cell lines than that in normal hepatic cell line (L02). Meanwhile, CDK9 was upregulated in HCC cell lines. Moreover, miR‐206 downregulated CDK9 in HCC cells via directly binding to its mRNA 3′ UTR, which resulted in a decrease of RNA PolII Ser2 phosphorylation and Mcl‐1 level. Additionally, miR‐206 suppressed the cell proliferation, and induced cell cycle arrest and apoptosis. Similarly, silence or inhibition of CDK9 also repressed the cell proliferation, and induced cell cycle arrest and apoptosis. Taken together, the results demonstrated that miR‐206 inhibited the growth of HCC cells through targeting CDK9, suggesting that the miR‐206‐CDK9 pathway may be a novel target for the treatment of HCC.

Survivin, a molecular target for therapeutic interventions in squamous cell carcinoma

Squamous cell carcinoma (SCC) is the most common cancer worldwide. The treatment of locally advanced disease generally requires various combinations of radiotherapy, surgery, and systemic therapy. Despite aggressive multimodal treatment, most of the patients relapse. Identification of molecules that sustain cancer cell growth and survival has made molecular targeting a feasible therapeutic strategy. Survivin is a member of the Inhibitor of Apoptosis Protein (IAP) family, which is overexpressed in most of the malignancies including SCC and totally absent in most of the normal tissues. This feature makes survivin an ideal target for cancer therapy. It orchestrates several important mechanisms to support cancer cell survival including inhibition of apoptosis and regulation of cell division. Overexpression of survivin in tumors is also associated with poor prognosis, aggressive tumor behavior, resistance to therapy, and high tumor recurrence. Various strategies have been developed to target survivin expression in cancer cells, and their effects on apoptosis induction and tumor growth attenuation have been demonstrated. In this review, we discuss recent advances in therapeutic potential of survivin in cancer treatment.

Ibulocydine sensitizes human hepatocellular carcinoma cells to TRAIL-induced apoptosis via calpain-mediated Bax cleavage

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) induces apoptosis selectively in cancer cells without affecting the majority of normal human cells. However, hepatocellular carcinoma (HCC) cells often display resistance to TRAIL-induced apoptosis. Ibulocydine (IB) is an isobutyrate ester pro-drug of a novel synthetic Cdk inhibitor that targets Cdk7 and Cdk9. In this study, we show that treatment with subtoxic doses of IB in combination with TRAIL displays potent cytotoxicity in TRAIL-resistant human HCC cells. Combination of IB and TRAIL was found to synergistically induce apoptosis through activation of caspases, which was blocked by a pan-caspase inhibitor (zVAD). Although the expression of Mcl-1 and survivin were reduced by IB plus TRAIL, overexpression of Mcl-1 and survivin did not block the cell death induced by co-treatment. Moreover, overexpression of Bcl-xL did not significantly interfere with the cell death induced by co-treatment of IB and TRAIL. Interestingly, the combination treatment induced cleavage of Bax, which was translocated to mitochondria upon induction of apoptosis. Furthermore, down-regulation of Bax by small interfering RNA effectively reduced the cell death and loss of mitochondrial membrane potential (MMP) caused by co-treatment with IB and TRAIL. Finally, pre-treatment of HCC cells with a calpain inhibitor effectively blocked IB plus TRAIL-induced cleavage of Bax and apoptosis. Collectively, our results demonstrate that IB increases the sensitivity of human HCC cells to TRAIL via mitochondria signaling pathway mediated by calpain-induced cleavage of Bax, suggesting that combined treatment with IB and TRAIL may offer an effective therapeutic strategy for human HCC.

Roscovitine has anti-proliferative and pro-apoptotic effects on glioblastoma cell lines: A pilot study

Purine analogue roscovitine, a cyclin-dependent kinase (CDK) inhibitor, has shown strong anti-proliferative and pro-apoptotic effects in solid and hematologic cancers such as non small-cell lung cancer and lymphomas. It targets CDK2, 7 and 9 preferentially, which are also overexpressed in glioblastoma. Τherefore, the biological effects of roscovitine in glioblastoma cell lines were investigated. Glioblastoma A172 and G28 cell lines were incubated with serial concentrations of roscovitine for 24-120 h. Proliferation was measured using the xCELLigence Real-Time Cell Analyzer, an impedance‑based cell viability system. Cell cycle distribution was assessed by flow cytometry and gene expression was quantified by quantitative RT-PCR and western blot analysis. Roscovitine exhibited a clear dose-dependent anti‑proliferative and pro‑apoptotic effect in the A172 cell line, while G28 cells showed a anti-proliferative effect only at 100 µM. The results of the flow cytometric (FACS) analysis revealed a dose-dependent increase of the G2/M and sub-G1 fractions in A172 cells, while G28 cells responded with an elevated sub-G1 fraction only at the highest concentration. Roscovitine led to a dose‑dependent decrease of transcripts of p53, CDK 7 and cyclins A and E and an increase of >4-fold of p21 in A172 cells. In G28 cells, a dose‑dependent induction of CDK2, p21 and cyclin D was observed between 10 and 50 µM roscovitine after 72 h, however, at the highest concentration of 100 µM, all investigated genes were downregulated. Roscovitine exerted clear dose-dependent anti-proliferative and pro-apoptotic effects in A172 cells and less distinct effects on G28 cells. In A172 cells, roscovitine led to G2/M arrest and induced apoptosis, an effect accompanied by induced p21 and a reduced expression of CDK2, 7 and 9 and cyclins A and E. These effects requre further studies on a larger scale to confirm whether roscovitine can be used as a therapeutic agent against glioblastoma.

Modifications of RNA polymerase II CTD: Connections to the histone code and cellular function

At the onset of transcription, many protein machineries interpret the cellular signals that regulate gene expression. These complex signals are mostly transmitted to the indispensable primary proteins involved in transcription, RNA polymerase II (RNAPII) and histones. RNAPII and histones are so well coordinated in this cellular function that each cellular signal is precisely allocated to specific machinery depending on the stage of transcription. The carboxy-terminal domain (CTD) of RNAPII in eukaryotes undergoes extensive posttranslational modification, called the 'CTD code', that is indispensable for coupling transcription with many cellular processes, including mRNA processing. The posttranslational modification of histones, known as the 'histone code', is also critical for gene transcription through the reversible and dynamic remodeling of chromatin structure. Notably, the histone code is closely linked with the CTD code, and their combinatorial effects enable the delicate regulation of gene transcription. This review elucidates recent findings regarding the CTD modifications of RNAPII and their coordination with the histone code, providing integrative pathways for the fine-tuned regulation of gene expression and cellular function.

Ibulocydine sensitizes human cancers to radiotherapy by induction of mitochondria-mediated apoptosis

BACKGROUND AND PURPOSE

Ibulocydine (IB), a novel prodrug of CDK inhibitor, has been reported to have anti-cancer effect in human hepatoma cells. In order to address its feasibility as a radiosensitizer to improve radiotherapeutic efficacy for human cancers, this study was designed.

MATERIAL AND METHODS

Human cancer cells of lung and colon were treated with IB and/or radiotherapy (RT). The cellular effects were assessed by CCK-8, clonogenic, flow cytometric, and western blotting assays. In vivo radiotherapeutic efficacy was evaluated using the xenograft mouse model.

RESULTS

Combined treatment of IB and RT significantly reduced viability and survival fraction of the cells. Apoptotic cell death accompanied with activation of caspases, decrease in Bcl-2/Bax expression, loss of mitochondrial membrane potential (MMP) leading to release of cytochrome c into cytosol was observed. Recovery of Bcl-2 expression level by introducing Bcl-2 expressing plasmid DNA compromised the loss of MMP and apoptosis induced by IB and RT. In vivo therapeutic efficacy of combined treatment was verified in the xenograft mouse model, in which tumor growth was markedly delayed by RT with IB.

CONCLUSIONS

IB demonstrated the property of sensitizing human cancer cells to RT by induction of mitochondria-mediated apoptosis, suggesting that IB deserves to be applied for chemoradiotherapy.

The cyclin-dependent kinase inhibitor SNS-032 induces apoptosis in breast cancer cells via depletion of Mcl-1 and X-linked inhibitor of apoptosis protein and displays antitumor activity in vivo

Inhibitors of cyclin-dependent kinases (Cdks) have been reported to have activities in many types of cancer cells by inhibiting Cdk7 and Cdk9, which control transcription. SNS-032 is a potent and selective inhibitor of Cdk2, Cdk7 and Cdk9 and has emerged in clinical trials. Here, we examined the viability of MCF-7 and MDA-MB-435 breast cancer cells in the presence of SNS-032 and observed a dose-dependent inhibition of cellular proliferation in both cell lines. SNS-032 had a direct apoptosis-inducing effect through both the extrinsic and intrinsic apoptotic pathways in breast cancer cells as shown by a dose-dependent increase in Annexin V-positive cells and terminal deoxynucleotidyl transferase-mediated dUTP nick?end labeling (TUNEL)-positive cells, as well as activation of caspase-8, -9 and poly(ADP-ribose) polymerase (PARP). At the molecular level, SNS-032 induced a marked dephosphorylation of serine 2 and 5 of RNA polymerase (RNA Pol) II and blocked RNA synthesis. Consistent with the inherently rapid turnover rates of their transcripts and proteins, the anti-apoptotic proteins Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP) were rapidly reduced on exposure to SNS-032. Our results also indicated that SNS-032 suppressed the growth of breast cancer xenografts in mice. These data demonstrate that the use of SNS-032 may be a rational and novel therapeutic strategy for human breast cancer and warrants further clinical investigation.

The basal transcription machinery as a target for cancer therapy

General transcription is required for the growth and survival of all living cells. However, tumor cells require extraordinary levels of transcription, including the transcription of ribosomal RNA genes by RNA polymerase I (RNPI) and mRNA by RNA polymerase II (RNPII). In fact, cancer cells have mutations that directly enhance transcription and are frequently required for cancer transformation. For example, the recent discovery that MYC enhances the transcription of the majority genes in the genome correlates with the fact that several transcription interfering drugs preferentially kill cancer cells. In recent years, advances in the mechanistic studies of the basal transcription machinery and the discovery of drugs that interfere with multiple components of transcription are being used to combat cancer. For example, drugs such as triptolide that targets the general transcription factors TFIIH and JQ1 to inhibit BRD4 are administered to target the high proliferative rate of cancer cells. Given the importance of finding new strategies to preferentially sensitize tumor cells, this review primarily focuses on several transcription inhibitory drugs to demonstrate that the basal transcription machinery constitutes a potential target for the design of novel cancer drugs. We highlight the drugs’ mechanisms for interfering with tumor cell survival, their importance in cancer treatment and the challenges of clinical application.

Increased α-tubulin1b expression indicates poor prognosis and resistance to chemotherapy in hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer deaths worldwide. It is important to understand molecular mechanisms of HCC progression and to develop clinically useful biomarkers for the disease.

AIM

We aimed to investigate the possible involvement of α-tubulin1b (TUBA1B) in HCC pathology.

METHODS

Tissue specimens were obtained from 114 HCC patients during hepatectomy. Immunohistochemistry and western blot analysis were used to detect TUBA1B expression in HCC tissues and cell lines. TUBA1B was knocked down in HCC cells by siRNA transfection. CCK-8 assay and flow cytometry were applied to determine cell proliferation and cell cycle progression, respectively. The efficacy of paclitaxel chemotherapy was evaluated by plate colony formation assay.

RESULTS

TUBA1B was higher expressed in HCC tumor tissues than in adjacent nontumor tissues. TUBA1B and Ki-67 expressions were positively related to each other, and both their expressions were significantly associated with histological grade of HCC patients. Univariate and multivariate survival analyses revealed that TUBA1B was a significant predictor for overall survival of HCC patients. TUBA1B expression was increased in HCC cells during the G1- to S-phase transition. TUBA1B knockout in HCC cells inhibited cell proliferation, and attenuated resistance to paclitaxel.

CONCLUSIONS

Our results indicated that TUBA1B expression was upregulated in HCC tumor tissues and proliferating HCC cells, and an increased TUBA1B expression was associated with poor overall survival and resistance to paclitaxel of HCC patients.

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.