Targeting mitotic exit with hyperthermia or APC/C inhibition to increase paclitaxel efficacy

Suppressing Anaphase-Promoting Complex/Cyclosome-Cell Division Cycle 20 Activity to Enhance the Effectiveness of Anti-Cancer Drugs That Induce Multipolar Mitotic Spindles

Paclitaxel induces multipolar spindles at clinically relevant doses but does not substantially increase mitotic indices. Paclitaxel's anti-cancer effects are hypothesized to occur by promoting chromosome mis-segregation on multipolar spindles leading to apoptosis, necrosis and cyclic-GMP-AMP Synthase-Stimulator of Interferon Genes (cGAS-STING) pathway activation in daughter cells, leading to secretion of type I interferon (IFN) and immunogenic cell death. Eribulin and vinorelbine have also been reported to cause increases in multipolar spindles in cancer cells. Recently, suppression of Anaphase-Promoting Complex/Cyclosome-Cell Division Cycle 20 (APC/C-CDC20) activity using CRISPR/Cas9 mutagenesis has been reported to increase sensitivity to Kinesin Family 18a (KIF18a) inhibition, which functions to suppress multipolar mitotic spindles in cancer cells. We propose that a way to enhance the effectiveness of anti-cancer agents that increase multipolar spindles is by suppressing the APC/C-CDC20 to delay, but not block, anaphase entry. Delaying anaphase entry in genomically unstable cells may enhance multipolar spindle-induced cell death. In genomically stable healthy human cells, delayed anaphase entry may suppress the level of multipolar spindles induced by anti-cancer drugs and lower mitotic cytotoxicity. We outline specific combinations of molecules to investigate that may achieve the goal of enhancing the effectiveness of anti-cancer agents.

Deciphering the Molecular Mechanisms behind Drug Resistance in Ovarian Cancer to Unlock Efficient Treatment Options

Ovarian cancer is a highly lethal form of gynecological cancer. This disease often goes undetected until advanced stages, resulting in high morbidity and mortality rates. Unfortunately, many patients experience relapse and succumb to the disease due to the emergence of drug resistance that significantly limits the effectiveness of currently available oncological treatments. Here, we discuss the molecular mechanisms responsible for resistance to carboplatin, paclitaxel, polyadenosine diphosphate ribose polymerase inhibitors, and bevacizumab in ovarian cancer. We present a detailed analysis of the most extensively investigated resistance mechanisms, including drug inactivation, drug target alterations, enhanced drug efflux pumps, increased DNA damage repair capacity, and reduced drug absorption/accumulation. The in-depth understanding of the molecular mechanisms associated with drug resistance is crucial to unveil new biomarkers capable of predicting and monitoring the kinetics during disease progression and discovering new therapeutic targets.

Distinct effects of heat shock temperatures on mitotic progression by influencing the spindle assembly checkpoint

Heat shock is a physiological and environmental stress that leads to the denaturation and inactivation of cellular proteins and is used in hyperthermia cancer therapy. Previously, we revealed that mild heat shock (42 °C) delays the mitotic progression by activating the spindle assembly checkpoint (SAC). However, it is unclear whether SAC activation is maintained at higher temperatures than 42 °C. Here, we demonstrated that a high temperature of 44 °C just before mitotic entry led to a prolonged mitotic delay in the early phase, which was shortened by the SAC inhibitor, AZ3146, indicating SAC activation. Interestingly, mitotic slippage was observed at 44 °C after a prolonged delay but not at 42 °C heat shock. Furthermore, the multinuclear cells were generated by mitotic slippage in 44 °C-treated cells. Immunofluorescence analysis revealed that heat shock at 44 °C reduces the kinetochore localization of MAD2, which is essential for mitotic checkpoint activation, in nocodazole-arrested mitotic cells. These results indicate that 44 °C heat shock causes SAC inactivation even after full activation of SAC and suggest that decreased localization of MAD2 at the kinetochore is involved in heat shock-induced mitotic slippage, resulting in multinucleation. Since mitotic slippage causes drug resistance and chromosomal instability, we propose that there may be a risk of cancer malignancy when the cells are exposed to high temperatures.

CDC20: a novel therapeutic target in cancer

Cell division cycle protein 20 (Cdc20) is a member of the cell cyclin family. In the early stage of mitosis, it activates the anaphase-promoting complex (APC) and forms the E3 ubiquitin ligase complex APC^Cdc20, which destroys key regulators of the cell cycle and promotes mitosis. Cdc20 serves as a target for the spindle checkpoint, ensuring proper chromosome segregation. As an oncoprotein, Cdc20 is highly expressed in a variety of malignant tumors, and Cdc20 overexpression is associated with poor prognosis of these tumors. This review aims to dissect the tumorigenic role of Cdc20 in human malignancies and its targeting strategies.

Inhibition of Mps1 kinase enhances taxanes efficacy in castration resistant prostate cancer

Androgen ablation therapy is the standard of care for newly diagnosed prostate cancer (PC) patients. PC that relapsed after hormonal therapy, referred to as castration-resistant PC (CRPC), often presents with metastasis (mCRPC) and is the major cause of disease lethality. The few available therapies for mCRPC include the Taxanes Docetaxel (DTX) and Cabazitaxel (CBZ). Alas, clinical success of Taxanes in mCRPC is limited by high intrinsic and acquired resistance. Therefore, it remains essential to develop rationally designed treatments for managing therapy-resistant mCRPC disease. The major effect of Taxanes on microtubule hyper-polymerization is a prolonged mitotic block due to activation of the Spindle Assembly Checkpoint (SAC). Taxane-sensitive cells eventually inactivate SAC and exit mitosis by mitotic catastrophe, resulting in genome instability and blockade of proliferation. Resistant cells remain in mitotic block, and, upon drug decay, resume mitosis and proliferation, underlying one resistance mechanism. In our study we explored the possibility of forced mitotic exit to elevate Taxane efficacy. Inactivation of the SAC component, mitotic checkpoint kinase Mps1/TTK with a small molecule inhibitor (Msp1i), potentiated efficacy of Taxanes treatment in both 2D cell culture and 3D prostasphere settings. Mechanistically, Mps1 inhibition forced mitotic catastrophe in cells blocked in mitosis by Taxanes. Androgen receptor (AR), the main driver of PC, is often mutated or truncated in mCRPC. Remarkably, Mps1i significantly potentiated CBZ cytotoxicity regardless of AR status, in both AR-WT and in AR-truncated CRPC cells. Overall, our data demonstrate that forced mitotic exit by Mps1 inhibition potentiates Taxanes efficacy. Given that several Mps1i's are currently in different stages of clinical trials, our results point to Mps1 as a new therapeutic target to potentiate efficacy of Taxanes in mCRPC patients.

The Role of the APC/C and Its Coactivators Cdh1 and Cdc20 in Cancer Development and Therapy

To sustain genomic stability by correct DNA replication and mitosis, cell cycle progression is tightly controlled by the cyclic activity of cyclin-dependent kinases, their binding to cyclins in the respective phase and the regulation of cyclin levels by ubiquitin-dependent proteolysis. The spindle assembly checkpoint plays an important role at the metaphase-anaphase transition to ensure a correct separation of sister chromatids before cytokinesis and to initiate mitotic exit, as an incorrect chromosome distribution may lead to genetically unstable cells and tumorigenesis. The ubiquitin ligase anaphase-promoting complex or cyclosome (APC/C) is essential for these processes by mediating the proteasomal destruction of cyclins and other important cell cycle regulators. To this end, it interacts with the two regulatory subunits Cdh1 and Cdc20. Both play a role in tumorigenesis with Cdh1 being a tumor suppressor and Cdc20 an oncogene. In this review, we summarize the current knowledge about the APC/C-regulators Cdh1 and Cdc20 in tumorigenesis and potential targeted therapeutic approaches.

Prognostic and clinical significance of subcellular CDC27 for patients with rectal adenocarcinoma treated with adjuvant chemotherapy

Rectal adenocarcinoma (READ) constitutes one-third of newly diagnosed colorectal cancer cases. Surgery, chemotherapy and concurrent chemoradiotherapy are the main treatments to improve patient outcomes for READ. However, patients with READ receiving these treatments eventually relapse, leading to a poor survival outcome. The present study collected surgical specimens from patients with READ and determined that cytoplasmic cell division cycle 27 (CDC27) expression was associated with the risk of lymph node metastasis and distant metastasis. Nuclear CDC27 expression was negatively associated with 5-year disease-free survival (DFS) and 5-year overall survival (OS) rates. Multivariate Cox proportional regression analysis showed that nuclear CDC27 was an independent prognostic factor in the patients with READ, especially in those treated with adjuvant chemotherapy. High nuclear CDC27 expression was significantly associated with poorer 5-year DFS (HR, 2.106; 95% CI, 1.275-3.570; P=0.003) and 5-year OS (HR, 2.369; 95% CI, 1.270-4.6810; P=0.005) rates. The data indicated that cytoplasmic CDC27 expression could affect tumor progression and that it plays an important role in metastasis. Nuclear CDC27 expression was markedly associated with poorer survival outcomes and was an independent prognostic factor in patients with postoperative adjuvant chemotherapy-treated READ. Thus, CDC27 expression serves as a potential prognostic marker for rectal tumor progression and chemotherapy treatment.

Hyperthermia Treatment as a Promising Anti-Cancer Strategy: Therapeutic Targets, Perspective Mechanisms and Synergistic Combinations in Experimental Approaches

Despite recent developments in diagnosis and treatment options, cancer remains one of the most critical threats to health. Several anti-cancer therapies have been identified, but further research is needed to provide more treatment options that are safe and effective for cancer. Hyperthermia (HT) is a promising treatment strategy for cancer because of its safety and cost-effectiveness. This review summarizes studies on the anti-cancer effects of HT and the detailed mechanisms. In addition, combination therapies with anti-cancer drugs or natural products that can effectively overcome the limitations of HT are reviewed because HT may trigger protective events, such as an increase of heat shock proteins (HSPs). In the 115 reports included, the mechanisms related to apoptosis, cell cycle, reactive oxygen species, mitochondrial membrane potential, DNA damage, transcription factors and HSPs were considered important. This review shows that HT is an effective inducer of apoptosis. Moreover, the limitations of HT may be overcome using combined therapy with anti-cancer drugs or natural products. Therefore, appropriate combinations of such agents with HT will exert maximal effects to treat cancer.

Targeting mitotic exit in solid tumors

Targeting mitosis by taxanes is one of the most common chemotherapeutic approaches in various malignant solid tumors, but cancer cells may survive antimitotic treatment with attainable in vivo concentrations due to mitotic slippage with a residual activity of the ubiquitin ligase anaphase-promoting complex (APC/C) and a continuous slow ubiquitin-proteasome-dependent cyclin B-degradation leading to mitotic exit. Therefore, blocking cyclin B-proteolysis via additional proteasome (PI) or APC/C-inhibition may have the potential to enhance tumor cell eradication by inducing a more robust mitotic block and mitotic cell death. Here, we analyzed this approach in different cell lines and more physiological patient-derived xenografts (PDX) from lung and breast cancer. The sequential combination of paclitaxel with the PI bortezomib enhanced cell death, but in contrast to the hypothesis during interphase and not in mitosis in both lung and breast cancer. APC/C-inhibition alone or in sequential combination with paclitaxel led to strong mitotic cell death in lung cancer. But in breast cancer, with high expression of the anti-apoptotic regulator Mcl-1, cell death in interphase was induced. Here, combined APC/C- and Mcl-1-inhibition with or without paclitaxel was highly lethal but still resulted in interphase cell death. Taken together, the combination of antimitotic agents with a clinically approved PI or inhibitors of the APC/C and Mcl-1 is a promising approach to improve treatment response in different solid tumors, even though they act entity-dependent at different cell cycle phases.

Future prospects for mitosis-targeted antitumor therapies

Dysregulation of cell cycle progression is a hallmark of cancer cells. In recent years, efforts have been devoted to the development of new therapies that target proteins involved in cell cycle regulation and mitosis. Novel targeted antimitotic drugs include inhibitors of aurora kinase family, polo-like kinase 1, Mps1, Eg5, CENP-5 and the APC/cyclosome complex. While certain new inhibitors reached the clinical trial stage, most were discontinued due to negative results. However, these therapies should not be readily dismissed. Based on recent advances concerning their mechanisms of action, new strategies could be devised to increase their efficacy and promote further clinical trials. Here we discuss three main lines of action to empower these therapeutic approaches: increasing cell death signals during mitotic arrest, targeting senescent cells and facilitating antitumor immune response through immunogenic cell death (ICD).

The Negative Cross-Talk between SAG/RBX2/ROC2 and APC/C E3 Ligases in Regulation of Cell Cycle Progression and Drug Resistance

Anaphase-promoting complex/cyclosome (APC/C) is a well-characterized E3 ligase that couples with UBE2C and UBE2S E2s for substrate ubiquitylation by the K11 linkage. Our recent data show that SAG/RBX2/ROC2, a RING component of Cullin-RING E3 ligase, also complexes with these E2s for K11-linked substrate polyubiquitylation. Whether these two E3s cross-talk with each other was previously unknown. Here, we report that SAG competes with APC2 for UBE2C/UBE2S binding to act as a potential endogenous inhibitor of APC/C, thereby regulating the G2-to-M progression. As such, SAG knockdown triggers premature activation of APC/C, leading to mitotic slippage and resistance to anti-microtubule drugs. On the other hand, SAG itself is a substrate of APC/C^CDH1 for targeted degradation at the G1 phase. The degradation-resistant mutant of SAG-R98A/L101A accelerates the G1-to-S progression. Our study reveals that the negative cross-talk between SAG and APC/C is likely a mechanism to ensure the fidelity of cell cycle progression.

Zhang et al. provide a mechanistic insight of how negative cross-talk between E3 ligases SAG and APC/C ensures proper cell cycle progression. SAG knockdown prematurely activates APC/C to promote mitotic progression and trigger anti-microtubule drugs resistance, whereas SAG degradation by APC/C^CDH1 mainly occurs in G1 phase for proper G1-to-S transition.

Hyperthermia induced disruption of mechanical balance leads to G1 arrest and senescence in cells

Human body temperature limits below 40°C during heat stroke or fever. The implications of prolonged exposure to the physiologically relevant temperature (40°C) on cellular mechanobiology is poorly understood. Here, we have examined the effects of heat stress (40°C for 72 h incubation) in human lung adenocarcinoma (A549), mouse melanoma (B16F10), and non-cancerous mouse origin adipose tissue cells (L929). Hyperthermia increased the level of ROS, γ-H2AX and HSP70 and decreased mitochondrial membrane potential in the cells. Heat stress impaired cell division, caused G1 arrest, induced cellular senescence, and apoptosis in all the tested cell lines. The cells incubated at 40°C for 72 h displayed a significant decrease in the f-actin level and cellular traction as compared with cells incubated at 37°C. Also, the cells showed a larger focal adhesion area and stronger adhesion at 40°C than at 37°C. The mitotic cells at 40°C were unable to round up properly and displayed retracting actin stress fibers. Hyperthermia down-regulated HDAC6, increased the acetylation level of microtubules, and perturbed the chromosome alignment in the mitotic cells at 40°C. Overexpression of HDAC6 rescued the cells from the G1 arrest and reduced the delay in cell rounding at 40°C suggesting a crucial role of HDAC6 in hyperthermia mediated responses. This study elucidates the significant role of cellular traction, focal adhesions, and cytoskeletal networks in mitotic cell rounding and chromosomal misalignment. It also highlights the significance of HDAC6 in heat-evoked senile cellular responses.

Taxanes in cancer treatment: Activity, chemoresistance and its overcoming

Since 1984, when paclitaxel was approved by the FDA for the treatment of advanced ovarian carcinoma, taxanes have been widely used as microtubule-targeting antitumor agents. However, their historic classification as antimitotics does not describe all their functions. Indeed, taxanes act in a complex manner, altering multiple cellular oncogenic processes including mitosis, angiogenesis, apoptosis, inflammatory response, and ROS production. On the one hand, identification of the diverse effects of taxanes on oncogenic signaling pathways provides opportunities to apply these cytotoxic drugs in a more rational manner. On the other hand, this may facilitate the development of novel treatment modalities to surmount anticancer drug resistance. In the latter respect, chemoresistance remains a major impediment which limits the efficacy of antitumor chemotherapy. Taxanes have shown impact on key molecular mechanisms including disruption of mitotic spindle, mitosis slippage and inhibition of angiogenesis. Furthermore, there is an emerging contribution of cellular processes including autophagy, oxidative stress, epigenetic alterations and microRNAs deregulation to the acquisition of taxane resistance. Hence, these two lines of findings are currently promoting a more rational and efficacious taxane application as well as development of novel molecular strategies to enhance the efficacy of taxane-based cancer treatment while overcoming drug resistance. This review provides a general and comprehensive picture on the use of taxanes in cancer treatment. In particular, we describe the history of application of taxanes in anticancer therapeutics, the synthesis of the different drugs belonging to this class of cytotoxic compounds, their features and the differences between them. We further dissect the molecular mechanisms of action of taxanes and the molecular basis underlying the onset of taxane resistance. We further delineate the possible modalities to overcome chemoresistance to taxanes, such as increasing drug solubility, delivery and pharmacokinetics, overcoming microtubule alterations or mitotic slippage, inhibiting drug efflux pumps or drug metabolism, targeting redox metabolism, immune response, and other cellular functions.

Mitotic checkpoint defects: en route to cancer and drug resistance

Loss of mitosis regulation is a common feature of malignant cells that leads to aberrant cell division with inaccurate chromosome segregation. The mitotic checkpoint is responsible for faithful transmission of genetic material to the progeny. Defects in this checkpoint, such as mutations and changes in gene expression, lead to abnormal chromosome content or aneuploidy that may facilitate cancer development. Furthermore, a defective checkpoint response is indicated in the development of drug resistance to microtubule poisons that are used in treatment of various blood and solid cancers for several decades. Mitotic slippage and senescence are important cell fates that occur even with an active mitotic checkpoint and are held responsible for the resistance. However, contradictory findings in both the scenarios of carcinogenesis and drug resistance have aroused questions on whether mitotic checkpoint defects are truly responsible for these dismal outcomes. Here, we discuss the possible contribution of the faulty checkpoint signaling in cancer development and drug resistance, followed by the latest research on this pathway for better outcomes in cancer treatment.

Mechanisms of Taxane Resistance

The taxane family of chemotherapy drugs has been used to treat a variety of mostly epithelial-derived tumors and remain the first-line treatment for some cancers. Despite the improved survival time and reduction of tumor size observed in some patients, many have no response to the drugs or develop resistance over time. Taxane resistance is multi-faceted and involves multiple pathways in proliferation, apoptosis, metabolism, and the transport of foreign substances. In this review, we dive deeper into hypothesized resistance mechanisms from research during the last decade, with a focus on the cancer types that use taxanes as first-line treatment but frequently develop resistance to them. Furthermore, we will discuss current clinical inhibitors and those yet to be approved that target key pathways or proteins and aim to reverse resistance in combination with taxanes or individually. Lastly, we will highlight taxane response biomarkers, specific genes with monitored expression and correlated with response to taxanes, mentioning those currently being used and those that should be adopted. The future directions of taxanes involve more personalized approaches to treatment by tailoring drug-inhibitor combinations or alternatives depending on levels of resistance biomarkers. We hope that this review will identify gaps in knowledge surrounding taxane resistance that future research or clinical trials can overcome.

Paradoxical mitotic exit induced by a small molecule inhibitor of APC/CCdc20

The anaphase-promoting complex/cyclosome (APC/C) is a ubiquitin ligase that initiates anaphase and mitotic exit. APC/C is activated by Cdc20 and inhibited by the mitotic checkpoint complex (MCC), which delays mitotic exit when the spindle assembly checkpoint (SAC) is activated. We previously identified apcin as a small molecule ligand of Cdc20 that inhibits APC/C^Cdc20 and prolongs mitosis. Here we find that apcin paradoxically shortens mitosis when SAC activity is high. These opposing effects of apcin arise from targeting of a common binding site in Cdc20 required for both substrate ubiquitination and MCC-dependent APC/C inhibition. Furthermore, we found that apcin cooperates with p31^comet to relieve MCC-dependent inhibition of APC/C. Apcin therefore causes either net APC/C inhibition, prolonging mitosis when SAC activity is low, or net APC/C activation, shortening mitosis when SAC activity is high, demonstrating that a small molecule can produce opposing biological effects depending on regulatory context.

Effects of tosyl-l-arginine methyl ester (TAME) on the APC/c subunits: An in silico investigation for inhibiting cell cycle

The anaphase-promoting complex/cyclosome (APC/c) is requisite for controlling mitosis, which is activated by Cdh1 and Cdc20 activators. Dysregulation of APC/c is observed in many cancers and is known as a targeted drug particularly in cancer drug resistance. It was shown that tosyl-l-arginine methyl ester (TAME), via mimicking isoleucine-arginine (IR) tail of co-activators, inhibits APC/c functions. However, structure details and interaction of TAME with APC/c are poorly defined. In the current study, a well-established set of computational methods was used to identify the best binding pocket in order to inhibit APC activity. Therefore, the interaction of IR tail and Cbox of co-activators, as well as TAME as an inhibitor, as an inhibitor, with APC3 and APC8 subunits of APC/c were analyzed, regarding structure, molecular docking, molecular dynamics, and free binding energy. The results indicated that TAME bound to APC3 with a higher binding affinity (∼-7.3 kcal/mol) than APC8 (∼-5.7 kcal/mol). Also, the binding free energy value obtained for the APC3-TAME was -22.25 ± 1.12 kcal/mol. According to binding free energies, van der Waals energy was the major favorable contributor to the ligand binding. These results offer that TAME had more affinity to interact with the APC3 subunit, at the IR binding pocket than the APC8 subunit at the Cbox binding pocket. In conclusion, IR binding pocket can serve as an appropriate potential target for TAME as an inhibitor of APC/c.

Imbalance of the spindle-assembly checkpoint promotes spindle poison-mediated cytotoxicity with distinct kinetics

Disrupting microtubule dynamics with spindle poisons activates the spindle-assembly checkpoint (SAC) and induces mitotic cell death. However, mitotic exit can occur prematurely without proper chromosomal segregation or cytokinesis by a process termed mitotic slippage. It remains controversial whether mitotic slippage increases the cytotoxicity of spindle poisons or the converse. Altering the SAC induces either mitotic cell death or mitotic slippage. While knockout of MAD2-binding protein p31^comet strengthened the SAC and promoted mitotic cell death, knockout of TRIP13 had the opposite effect of triggering mitotic slippage. We demonstrated that mitotic slippage prevented mitotic cell death caused by spindle poisons, but reduced subsequent long-term survival. Weakening of the SAC also reduced cell survival in response to spindle perturbation insufficient for triggering mitotic slippage, of which mitotic exit was characterized by displaced chromosomes during metaphase. In either mitotic slippage or mitotic exit with missegregated chromosomes, cell death occurred only after one cell cycle following mitotic exit and increased progressively during subsequent cell cycles. Consistent with these results, transient inhibition of the SAC using an MPS1 inhibitor acted synergistically with spindle perturbation in inducing chromosome missegregation and cytotoxicity. The specific temporal patterns of cell death after mitotic exit with weakened SAC may reconcile the contradictory results from many previous studies.

Mitotic Catastrophe Induced in HeLa Tumor Cells by Photodynamic Therapy with Methyl-aminolevulinate

Photodynamic therapy (PDT) constitutes a cancer treatment modality based on the administration of a photosensitizer, which accumulates in tumor cells. The subsequent irradiation of the tumoral area triggers the formation of reactive oxygen species responsible for cancer cell death. One of the compounds approved in clinical practice is methyl-aminolevulinate (MAL), a protoporphyrin IX (PpIX) precursor intermediate of heme synthesis. We have identified the mitotic catastrophe (MC) process after MAL-PDT in HeLa human carcinoma cells. The fluorescence microscopy revealed that PpIX was located mainly at plasma membrane and lysosomes of HeLa cells, although some fluorescence was also detected at endoplasmic reticulum and Golgi apparatus. Cell blockage at metaphase-anaphase transition was observed 24 h after PDT by phase contrast microscopy and flow cytometry. Mitotic apparatus components evaluation by immunofluorescence and Western blot indicated: multipolar spindles and disorganized chromosomes in the equatorial plate accompanied with dispersion of centromeres and alterations in aurora kinase proteins. The mitotic blockage induced by MAL-PDT resembled that induced by two compounds used in chemotherapy, taxol and nocodazole, both targeting microtubules. The alterations in tumoral cells provided evidence of MC induced by MAL-PDT, resolving mainly by apoptosis, directly or through the formation of multinucleate cells.

Targeting mitosis exit: A brake for cancer cell proliferation

The transition from mitosis to interphase, referred to as mitotic exit, is a critical mitotic process which involves activation and inactivation of multiple mitotic kinases and counteracting protein phosphatases. Loss of mitotic exit checkpoints is a common feature of cancer cells, leading to mitotic dysregulation and confers cancer cells with oncogenic characteristics, such as aberrant proliferation and microtubule-targeting agent (MTA) resistance. Since MTA resistance results from cancer cells prematurely exiting mitosis (mitotic slippage), blocking mitotic exit is believed to be a promising anticancer strategy. Moreover, based on this theory, simultaneous inhibition of mitotic exit and additional cell cycle phases would likely achieve synergistic antitumor effects. In this review, we divide the molecular regulators of mitotic exit into four categories based on their different regulatory functions: 1) the anaphase-promoting complex/cyclosome (APC/C, a ubiquitin ligase), 2) cyclin B, 3) mitotic kinases and phosphatases, 4) kinesins and microtubule-binding proteins. We also review the regulators of mitotic exit and propose prospective anticancer strategies targeting mitotic exit, including their strengths and possible challenges to their use.

The Anaphase Promoting Complex/Cyclosome (APC/C): A Versatile E3 Ubiquitin Ligase

In the present chapter we discuss the essential roles of the human E3 ubiquitin ligase Anaphase Promoting Complex/Cyclosome (APC/C) in mitosis as well as the emerging evidence of important APC/C roles in cellular processes beyond cell division control such as regulation of genomic integrity and cell differentiation of the nervous system. We consider the potential incipient role of APC/C dysregulation in the pathophysiology of the neurological disorder Alzheimer's disease (AD). We also discuss how certain Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) viruses take control of the host's cell division regulatory system through harnessing APC/C ubiquitin ligase activity and hypothesise the plausible molecular mechanisms underpinning virus manipulation of the APC/C. We also examine how defects in the function of this multisubunit protein assembly drive abnormal cell proliferation and lastly argue the potential of APC/C as a promising therapeutic target for the development of innovative therapies for the treatment of chronic malignancies such as cancer.

Heat shock-induced mitotic arrest requires heat shock protein 105 for the activation of spindle assembly checkpoint

Heat shock causes proteotoxic stress that induces various cellular responses, including delayed mitotic progression and the generation of an aberrant number of chromosomes. In this study, heat shock delayed the onset of anaphase by increasing the number of misoriented cells, accompanied by the kinetochore localization of budding uninhibited by benzimidazole-related (BubR)1 in a monopolar spindle (Mps)1-dependent manner. The mitotic delay was canceled by knockdown of mitotic arrest defect (Mad)2. Knockdown of heat shock protein (Hsp)105 partially abrogated the mitotic delay with the loss of the kinetochore localization of BubR1 under heat shock conditions and accelerated mitotic progression under nonstressed conditions. Consistent with this result, Hsp105 knockdown increased the number of anaphase cells with lagging chromosomes, through mitotic slippage, and decreased taxol sensitivity more than Mad2 knockdown. Hsp105 was coprecipitated with cell division cycle (Cdc)20 in an Mps1-dependent manner; however, its knockdown did not affect coprecipitation of Mad2 and BubR1 with Cdc20. We propose that heat shock delays the onset of anaphase via the activation of the spindle assembly checkpoint (SAC). Hsp105 prevents abnormal cell division by contributing to SAC activation under heat shock and nonstressed conditions by interacting with Cdc20 but not affecting formation of the mitotic checkpoint complex.-Kakihana, A., Oto, Y., Saito, Y., Nakayama, Y. Heat shock-induced mitotic arrest requires heat shock protein 105 for the activation of spindle assembly checkpoint.

Mitosis inhibitors in anticancer therapy: When blocking the exit becomes a solution

Current microtubule-targeting agents (MTAs) remain amongst the most important antimitotic drugs used against a broad range of malignancies. By perturbing spindle assembly, MTAs activate the spindle assembly checkpoint (SAC), which induces mitotic arrest and subsequent apoptosis. However, besides toxic side effects and resistance, mitotic slippage and failure in triggering apoptosis in various cancer cells are limiting factors of MTAs efficacy. Alternative strategies to target mitosis without affecting microtubules have, thus, led to the identification of small molecules, such as those that target spindle Kinesins, Aurora and Polo-like kinases. Unfortunately, these so-called second-generation of antimitotics, encompassing mitotic blockers and mitotic drivers, have failed in clinical trials. Our recent understanding regarding the mechanisms of cell death during a mitotic arrest pointed out apoptosis as the main variable, providing an opportunity to control the cell fates and influence the effectiveness of antimitotics. Here, we provide an overview on the second-generation of antimitotics, and discuss possible strategies that exploit SAC activity, mitotic slippage/exit and apoptosis induction, in order to improve the efficacy of anticancer strategies that target mitosis.

Inhibition of kinesin family member 20B sensitizes hepatocellular carcinoma cell to microtubule-targeting agents by blocking cytokinesis

Kinesin family member 20B (KIF20B, also known as MPHOSPH1) is a kinesin protein that plays a critical role in cytokinesis. Previously, we and others have demonstrated the oncogenic role of KIF20B in several cancers; however, the exact mechanisms underlying its tumorigenic effects remain unclear. Herein, we showed overexpression of KIF20B in human hepatocellular carcinoma (HCC) and reported a negative correlation between KIF20B level and prognosis of patients. Mechanistically, reducing KIF20B blockades mitotic exit of HCC cells at telophase in a spindle assembly checkpoint independent way. Importantly, reducing KIF20B acts synergistically with three microtubule-associated agents (MTA) to p53- or p14ARF-dependently suppress p53-wt or p53-null HCC cells. In addition to taxol, reducing KIF20B also enhanced the toxicity of two chemotherapeutic drugs, hydroxycamptothecin and mitomycin C. In conclusion, we found a novel mechanism in that blocking cytokinesis by KIF20B inhibition increases the efficacy of MTA; our results thus suggested a dual-mitotic suppression approach against HCC by combining MTA with KIF20B inhibition, which simultaneously blocks mitosis at both metaphase and telophase.

Magnetic nanoparticle hyperthermia potentiates paclitaxel activity in sensitive and resistant breast cancer cells

Introduction

Overcoming resistance to antimitotic drugs, such as paclitaxel (PTX), would represent a major advance in breast cancer treatment. PTX induces mitotic block and sensitive cells exit mitosis dying by mitotic catastrophe. Resistant cells remain in block and continue proliferation after drug decay, denoting one of the PTX resistance mechanisms. Mild hyperthermia (HT) triggers mitotic exit of PTX-pretreated cells, overcoming PTX resistance and suggesting HT-forced mitotic exit as a promising strategy to potentiate PTX.

Methods and results

Superparamagnetic iron oxide nanoparticles (SPIONs) were used to deliver mild HT at 42°C in PTX-pretreated breast adenocarcinoma MCF-7 cells sensitive and resistant to PTX. To evaluate mechanism of cell death, cells were classified based on nuclear morphology into interphase, mitotic, micronucleated, and apoptotic. The combined PTX→SPION treatment resulted in an increase in the percentage of micronucleated cells, an indication of forced mitotic exit. Importantly, in PTX-resistant cells, the combination therapy using SPION HT helps to overcome resistance by reducing the number of cells relative to the control.

Conclusion

SPION HT potentiates PTX by significantly reducing cell survival, suggesting potential of combined treatment for future clinical translation.

Peptide inhibitors of the anaphase promoting-complex that cause sensitivity to microtubule poison

There is an interest in identifying Anaphase Promoting-Complex/Cyclosome (APC/C) inhibitors that lead to sensitivity to microtubule poisons as a strategy for targeting cancer cells. Using budding yeast Saccharomyces cerevisiae, peptides derived from the Mitotic Arrest Deficient 2 (Mad2)-binding motif of Cell Division Cycle 20 (Cdc20) were observed to inhibit both Cdc20- and CDC20 Homology 1 (Cdh1)-dependent APC/C activity. Over expression of peptides in vivo led to sensitivity to a microtubule poison and, in a recovery from a microtubule poison arrest, delayed degradation of yeast Securin protein Precocious Dissociation of Sisters 1 (Pds1). Peptides with mutations in the Cdc20 activating KILR-motif still bound APC/C, but lost the ability to inhibit APC/C in vitro and lost the ability to induce sensitivity to a microtubule poison in vivo. Thus, an APC/C binding and activation motif that promotes mitotic progression, namely the Cdc20 KILR-motif, can also function as an APC/C inhibitor when present in excess. Another activator for mitotic progression after recovery from microtubule poison is p31^comet, where a yeast predicted open-reading frame YBR296C-A encoding a 39 amino acid predicted protein was identified by homology to p31^comet, and named Tiny Yeast Comet 1 (TYC1). Tyc1 over expression resulted in sensitivity to microtubule poison. Tyc1 inhibited both APC/C^Cdc20 and APC/C^Cdh1 activities in vitro and bound to APC/C. A homologous peptide derived from human p31^comet bound to and inhibited yeast APC/C demonstrating evolutionary retention of these biochemical activities. Cdc20 Mad2-binding motif peptides and Tyc1 disrupted the ability of the co-factors Cdc20 and Cdh1 to bind to APC/C, and co-over expression of both together in vivo resulted in an increased sensitivity to microtubule poison. We hypothesize that Cdc20 Mad2-binding motif peptides, Tyc1 and human hp31 peptide can serve as novel molecular tools for investigating APC/C inhibition that leads to sensitivity to microtubule poison in vivo.

Integrated analysis highlights APC11 protein expression as a likely new independent predictive marker for colorectal cancer

After a diagnosis of colorectal cancer (CRC), approximately 50% of patients will present distant metastasis. Although significant progress has been made in treatments, most of them will die from the disease. We investigated the predictive and prognostic potential of APC11, the catalytic subunit of APC/C, which has never been examined in the context of CRC. The expression of APC11 was assessed in CRC cell lines, in tissue microarrays (TMAs) and in public datasets. Overexpression of APC11 mRNA was associated with chromosomal instability, lymphovascular invasion and residual tumor. Regression models accounting for the effects of well-known protein markers highlighted association of APC11 protein expression with residual tumor (odds ratio: OR = 6.51; 95% confidence intervals: CI = 1.54–27.59; P = 0.012) and metastasis at diagnosis (OR = 3.87; 95% CI = 1.20–2.45; P = 0.024). Overexpression of APC11 protein was also associated with worse distant relapse-free survival (hazard ratio: HR = 2.60; 95% CI = 1.26–5.37; P = 0.01) and worse overall survival (HR = 2.69; 95% CI = 1.31–5.51; P = 0.007). APC11 overexpression in primary CRC thus represents a potentially novel theranostic marker of metastatic CRC.

Reducing protein regulator of cytokinesis 1 as a prospective therapy for hepatocellular carcinoma

Proteins that bind to microtubule are important for cell cycle, and some of these proteins show oncogenic characteristics with mechanisms not fully understood. Herein we demonstrate overexpression of protein regulator of cytokinesis 1 (PRC1), a microtubule-associated regulator of mitosis, in human hepatocellular carcinoma (HCC). Moreover, upregulated PRC1 is associated with lower survival rates of HCC patients. Mechanistically, reducing PRC1 blocks mitotic exit of HCC cells at telophase in a spindle assembly checkpoint independent manner, and acts synergistically with microtubule-associated agents (MTAs) to suppress p53-wt or p53-null HCC cells in a p53- or p14ARF-dependent manner; while overexpressing PRC1 increases the resistance of HCC to taxol. A combined treatment of taxol/shPRC1 results in 90% suppression of tumor growth in subcutaneous HCC xenograft models. In orthotopic xenograft mice, reducing PRC1 significantly alleviates HCC development and hepatic injury. Together, our results suggest a dual-mitotic suppression approach against HCC by combining MTAs with cytokinesis inhibition, which blocks mitosis at both metaphase and telophase.

Dual PI3K/mTOR inhibitor BEZ235 as a promising therapeutic strategy against paclitaxel-resistant gastric cancer via targeting PI3K/Akt/mTOR pathway

Paclitaxel (PTX) is widely used in the front-line chemotherapy for gastric cancer (GC), but resistance limits its use. Due to the lack of proper models, mechanisms underlying PTX resistance in GC were not well studied. Using established PTX-resistant GC cell sublines HGC-27R, we for the first time integrated biological traits and molecular mechanisms of PTX resistance in GC. Data revealed that PTX-resistant GC cells were characterized by microtubular disorders, an EMT phenotype, reduced responses to antimitotic drugs, and resistance to apoptosis (marked by upregulated β-tubulin III, vimentin, attenuated changes in G₂/M molecules or pro-apoptotic factors in response to antimitotic drugs or apoptotic inducers, respectively). Activation of the phosphoinositide 3-kinase, the serine/threonine kinase Akt and mammalian target of rapamycin (PI3K/Akt/mTOR) and mitogen-activated protein kinase (MAPK) pathways were also observed, which might be the reason for above phenotypic alternations. In vitro data suggested that targeting these pathways were sufficient to elicit antitumor responses in PTX-resistant GC, in which the dual PI3K/mTOR inhibitor BEZ235 displayed higher therapeutic efficiency than the mTOR inhibitor everolimus or the MEK inhibitor AZD6244. Antitumor effects of BEZ235 were also confirmed in mice bearing HGC-27R tumors. Thus, these data suggest that PI3K/Akt/mTOR and MAPK pathway inhibition, especially PI3K/mTOR dual blockade, might be a promising therapeutic strategy against PTX-resistant GC.

Activation of anaphase-promoting complex by p53 induces a state of dormancy in cancer cells against chemotherapeutic stress

Cancer dormancy is a stage in tumor progression in which residual disease remains occult and asymptomatic for a prolonged period. Cancer cell dormancy is the main cause of cancer recurrence and failure of therapy. However, cancer dormancy is poorly characterized and the mechanisms of how cancer cells develop dormancy and relapse remain elusive. In this study, 5- fluorouracil (5-FU) was used to induce cancer cell dormancy. We found that cancer cells escape the cytotoxicity of 5-FU by becoming “dormant”. After exposure to 5-FU, residual non-small cell lung cancer (NSCLC) cells underwent epithelial-mesenchymal transition (EMT), followed by mesenchymal-epithelial transition (MET). These EMT-transformed NSCLC cells were in the state of cell quiescence where cells were not dividing and were arrested in the cell cycle in G0-G1. The dormant cells underwent an EMT showed characteristics of cancer stem cells. P53 is strongly accumulated in response to 5-FU-induced dormant cells through the activation of ubiquitin ligase anaphase-promoting complex (APC/C) and TGF-β/Smad signaling. In contrast to the EMT-transformed cells, MET-transformed cells showed an increased ability to proliferate, suggesting that dormant EMT cells were reactivated in the MET process. During the EMT-MET process, DNA repair including nonhomologous end joining (NHEJ) and homologous recombination (HR) is critical to dormant cell reactivation. Our findings provide a mechanism to unravel cancer cell dormancy and reactivation of the cancer cell population.

Taming the Beast: Control of APC/CCdc20-Dependent Destruction

The anaphase-promoting complex/cyclosome (APC/C) is a large multisubunit ubiquitin ligase that triggers the metaphase-to-anaphase transition in the cell cycle by targeting the substrates cyclin B and securin for destruction. APC/C activity toward these two key substrates requires the coactivator Cdc20. To ensure that cells enter mitosis and partition their duplicated genome with high accuracy, APC/C^Cdc20 activity must be tightly controlled. Here, we discuss the mechanisms that regulate APC/C^Cdc20 activity both before and during mitosis. We focus our discussion primarily on the chromosomal pathways that both accelerate and delay APC/C activation by targeting Cdc20 to opposing fates. The findings discussed provide an overview of how cells control the activation of this major cell cycle regulator to ensure both accurate and timely cell division.

Inhibitor of H3K27 demethylase JMJD3/UTX GSK-J4 is a potential therapeutic option for castration resistant prostate cancer

Androgen receptor (AR) mediates initiation and progression of prostate cancer (PCa); AR-driven transcription is activated by binding of androgens to the ligand-binding domain (LBD) of AR. Androgen ablation therapy offers only a temporary relief of locally advanced and metastatic PCa, and the disease eventually recurs as a lethal castration-resistant PCa (CRPC) as there is no effective treatment for CRPC patients. Thus, it is critical to identify novel targeted and combinatorial regimens for clinical management of CRPC. Reduction of the repressive epigenetic modification H3K27me2/3 correlates with PCa aggressiveness, while corresponding demethylases JMJD3/UTX are overexpressed in PCa. We found that JMJD3/UTX inhibitor GSK-J4 reduced more efficiently proliferation of AR-ΔLBD cells (CRPC model) compared with isogenic AR-WT cells. Inhibition of JMJD3/UTX protects demethylation of H3K27Me2/3, thus reducing levels of H3k27Me1. We observed that the reduction dynamics of H3K27Me1 was faster and achieved at lower inhibitor concentrations in AR-ΔLBD cells, suggesting that inhibition of JMJD3/UTX diminished proliferation of these cells by hindering AR-driven transcription. In addition, we observed synergy between GSK-J4 and Cabazitaxel, a taxane derivative that is approved for CRPC treatment. Collectively, our results point at the H3K27 demethylation pathway as a new potential therapeutic target in CRPC patients.

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.

Cell Division Cycle 6 Promotes Mitotic Slippage and Contributes to Drug Resistance in Paclitaxel-Treated Cancer Cells

Paclitaxel (PTX) is an antimitotic drug that possesses potent anticancer activity, but its therapeutic potential in the clinic has been hindered by drug resistance. Here, we report a mechanism by which cancer cells can exit from the PTX-induced mitotic arrest, i.e. mitotic slippage, and avoid subsequent death resulting in drug resistance. In cells experiencing mitotic slippage, Cdc6 protein level was significantly upregulated, Cdk1 activity was inhibited, and Cohesin/Rad21 was cleaved as a result. Cdc6 depletion by RNAi or Norcantharidin inhibited PTX-induced Cdc6 up-regulation, maintained Cdk1 activity, and repressed Cohesin/Rad21 cleavage. In all, this resulted in reduced mitotic slippage and reversal of PTX resistance. Moreover, in synchronized cells, the role of Cdc6 in mitotic exit under PTX pressure was also confirmed. This study indicates that Cdc6 may promote mitotic slippage by inactivation of Cdk1. Targeting of Cdc6 may serve as a promising strategy for enhancing the anticancer activity of PTX.

Insights into APC/C: from cellular function to diseases and therapeutics

Anaphase-promoting complex/cyclosome (APC/C) is a multifunctional ubiquitin-protein ligase that targets different substrates for ubiquitylation and therefore regulates a variety of cellular processes such as cell division, differentiation, genome stability, energy metabolism, cell death, autophagy as well as carcinogenesis. Activity of APC/C is principally governed by two WD-40 domain proteins, Cdc20 and Cdh1, in and beyond cell cycle. In the past decade, the results based on numerous biochemical, 3D structural, mouse genetic and small molecule inhibitor studies have largely attracted our attention into the emerging role of APC/C and its regulation in biological function, human diseases and potential therapeutics. This review will aim to summarize some recently reported insights into APC/C in regulating cellular function, connection of its dysfunction with human diseases and its implication of therapeutics.

Effects of hyperthermia as a mitigation strategy in DNA damage-based cancer therapies

Utilization of thermal therapy (hyperthermia) is defined as the application of exogenous heat induction and represents a concept that is far from new as it goes back to ancient times when heat was used for treating various diseases, including malignancies. Such therapeutic strategy has gained even more popularity (over the last few decades) since various studies have shed light into understanding hyperthermia's underlying molecular mechanism(s) of action. In general, hyperthermia is applied as complementary (adjuvant) means in therapeutic protocols combining chemotherapy and/or irradiation both of which can induce irreversible cellular DNA damage. Furthermore, according to a number of in vitro, in vivo and clinical studies, hyperthermia has been shown to enhance the beneficial effects of DNA targeting therapeutic strategies by interfering with DNA repair response cascades. Therefore, the continuously growing evidence supporting hyperthermia's beneficial role in cancer treatment can also encourage its application as a DNA repair mitigation strategy. In this review article, we aim to provide detailed information on how hyperthermia acts on DNA damage and repair pathways and thus potentially contributing to various adjuvant therapeutic protocols relevant to more efficient cancer treatment strategies.

Chelidonine induces mitotic slippage and apoptotic-like death in SGC-7901 human gastric carcinoma cells

The aim of the present study was to investigate the effect of chelidonine on mitotic slippage and apoptotic-like death in SGC-7901 human gastric cancer cells. The MTT assay was performed to detect the antiproliferative effect of chelidonine. Following treatment with chelidonine (10 µmol/l), the ultrastructure changes in SGC-7901, MCF-7 and HepG2 cells were observed by transmission electron microscopy. The effects of chelidonine on G2/M phase arrest and apoptosis of SGC-7901 cells were determined by flow cytometry. Indirect immunofluorescence assay and laser scanning confocal microscopy (LSCM) were used to detect the phosphorylation level of histone H3 (Ser10) and microtubule formation was detected using LSCM following immunofluorescent labeling. Subsequent to treatment with chelidonine (10 µmol/l), expression levels of mitotic slippage-associated proteins, including BUB1 mitotic checkpoint serine/threonine kinase B (BubR1), cyclin-dependent kinase 1 (Cdk1) and cyclin B1, and apoptosis-associated protein, caspase-3 were examined by western blotting at 24, 48 and 72 h. The half maximal inhibitory concentration of chelidonine was 23.13 µmol/l over 48 h and chelidonine induced G2/M phase arrest of cells. The phosphorylation of histone H3 at Ser10 was significantly increased following treatment with chelidonine for 24 h, indicating that chelidonine arrested the SGC-7901 cells in the M phase. Chelidonine inhibited microtubule polymerization, destroyed microtubule structures and induced cell cycle arrest in the M phase. Giant cells were observed with multiple micronuclei of varying sizes, which indicated that following a prolonged arrest in the M phase, the cells underwent mitotic catastrophe. Western blotting demonstrated that the protein expression levels of BubR1, cyclin B1 and Cdk1 decreased significantly between 48 and 72 h. Low expression levels of BubR1 and inactivation of the cyclin B1-Cdk1 complex results in the cells being arrested at mitosis and leads to mitotic slippage. In addition, apoptotic morphological changes in multinucleated cells were observed, the apoptosis rates increased gradually with administration of chelidonine in a time-dependent manner and the protein levels of caspase-3 increased significantly between 24 and 72 h. Thus, chelidonine induces mitotic slippage, and apoptotic-like death occurs in SGC-7901 cells undergoing mitotic catastrophe. Gastric cancer is a common malignancy, and ranks second in overall cancer-associated mortalities worldwide. The present study demonstrated that chelidonine induces M phase arrest and mitotic slippage of SGC-7901 human gastric carcinoma cells via downregulating the expression of BubR1, Cdk1 and cyclin B1 proteins. With the prolongation of chelidonine treatment, the giant cells with multiple micronuclei underwent mitotic slippage and were maintained in the G1 phase and did not survive. A number of multinucleated cells underwent apoptosis via a caspase-dependent signaling pathway. The current study proposes that chelidonine induces mitotic slippage and apoptotic-like death of SGC-7901 cells.

Protein kinase A type II-α regulatory subunit regulates the response of prostate cancer cells to taxane treatment

In the last decade taxane-based therapy has emerged as a standard of care for hormone-refractory prostate cancer. Nevertheless, a significant fraction of tumors show no appreciable response to the treatment, while the others develop resistance and recur. Despite years of intense research, the mechanisms of taxane resistance in prostate cancer and other malignancies are poorly understood and remain a topic of intense investigation. We have used improved mutagenesis via random insertion of a strong promoter to search for events, which enable survival of prostate cancer cells after Taxol exposure. High-throughput mapping of the integration sites pointed to the PRKAR2A gene, which codes for a type II-α regulatory subunit of protein kinase A, as a candidate modulator of drug response. Both full-length and N-terminally truncated forms of the PRKAR2A gene product markedly increased survival of prostate cancer cells lines treated with Taxol and Taxotere. Suppression of protein kinase A enzymatic activity is the likely mechanism of action of the overexpressed proteins. Accordingly, protein kinase A inhibitor PKI (6-22) amide reduced toxicity of Taxol to prostate cancer cells. Our findings support the role of protein kinase A and its constituent proteins in cell response to chemotherapy.

Effects of hyperthermia on DNA repair pathways: one treatment to inhibit them all

The currently available arsenal of anticancer modalities includes many DNA damaging agents that can kill malignant cells. However, efficient DNA repair mechanisms protect both healthy and cancer cells against the effects of treatment and contribute to the development of drug resistance. Therefore, anti-cancer treatments based on inflicting DNA damage can benefit from inhibition of DNA repair. Hyperthermia – treatment at elevated temperature – considerably affects DNA repair, among other cellular processes, and can thus sensitize (cancer) cells to DNA damaging agents. This effect has been known and clinically applied for many decades, but how heat inhibits DNA repair and which pathways are targeted has not been fully elucidated. In this review we attempt to summarize the known effects of hyperthermia on DNA repair pathways relevant in clinical treatment of cancer. Furthermore, we outline the relationships between the effects of heat on DNA repair and sensitization of cells to various DNA damaging agents.

Protein kinase C β inhibition by enzastaurin leads to mitotic missegregation and preferential cytotoxicity toward colorectal cancer cells with chromosomal instability (CIN)

Enzastaurin is a selective inhibitor of protein kinase C β and a potent inhibitor of tumor angiogenesis. In addition, enzastaurin shows direct cytotoxic activity toward a subset of tumor cells including colorectal cancer cells (CRC). In spite of promising results in animal models, the clinical activity of enzastaurin in CRC patients has been disappointing although a subset of patients seems to derive benefit. In the present study we investigated the biological and cytotoxic activities of enzastaurin toward a panel of well-characterized CRC cell lines in order to clarify the mechanistic basis for the cytotoxic activity. Our results show that enzastaurin is significantly more cytotoxic toward CRC cells with chromosome instability (CIN) compared to cells with microsatellite instability (MSI). Since CIN is usually attributed to mitotic dysfunction, the influence of enzastaurin on cell cycle progression and mitotic transit was characterized for representative CIN and MSI cell lines. Enzastaurin exposure was accompanied by prolonged metaphase arrest in CIN cells followed by the appearance of tetraploid and micronuclei-containing cells as well as by increased apoptosis, whereas no detectable mitotic dysfunctions were observed in MSI cells exposed to isotoxic doses of enzastaurin. Our study identifies enzastaurin as a new, context dependent member of a heterogeneous group of anticancer compounds that induce "mitotic catastrophe," that is mitotic dysfunction accompanied by cell death. These data provide novel insight into the mechanism of action of enzastaurin and may allow the identification of biomarkers useful to identify CRC patients particularly likely, or not, to benefit from treatment with enzastaurin.

Stressing mitosis to death

The final stage of cell division (mitosis), involves the compaction of the duplicated genome into chromatid pairs. Each pair is captured by microtubules emanating from opposite spindle poles, aligned at the metaphase plate, and then faithfully segregated to form two identical daughter cells. Chromatids that are not correctly attached to the spindle are detected by the constitutively active spindle assembly checkpoint (SAC). Any stress that prevents correct bipolar spindle attachment, blocks the satisfaction of the SAC, and induces a prolonged mitotic arrest, providing the cell time to obtain attachment and complete segregation correctly. Unfortunately, during mitosis repairing damage is not generally possible due to the compaction of DNA into chromosomes, and subsequent suppression of gene transcription and translation. Therefore, in the presence of significant damage cell death is instigated to ensure that genomic stability is maintained. While most stresses lead to an arrest in mitosis, some promote premature mitotic exit, allowing cells to bypass mitotic cell death. This mini-review will focus on the effects and outcomes that common stresses have on mitosis, and how this impacts on the efficacy of mitotic chemotherapies.