Downregulation of Plk1 expression by receptor-mediated uptake of antisense oligonucleotide-loaded nanoparticles

HER2-Targeted, Degradable Core Cross-Linked Micelles for Specific and Dual pH-Sensitive DOX Release

Here, a targeted, dual-pH responsive, and stable micelle nanocarrier is designed, which specifically selects an HER2 receptor on breast cancer cells. Intracellularly degradable and stabilized micelles are prepared by core cross-linking via reversible addition-fragmentation chain-transfer (RAFT) polymerization with an acid-sensitive cross-linker followed by the conjugation of maleimide-doxorubicin to the pyridyl disulfide-modified micelles. Multifunctional nanocarriers are obtained by coupling HER2-specific peptide. Formation of micelles, addition of peptide and doxorubicin (DOX) are confirmed structurally by spectroscopical techniques. Size and morphological characterization are performed by Zetasizer and transmission electron microscope (TEM). For the physicochemical verification of the synergistic acid-triggered degradation induced by acetal and hydrazone bond degradation, Infrared spectroscopy and particle size measurements are used. Drug release studies show that DOX release is accelerated at acidic pH. DOX-conjugated HER2-specific peptide-carrying nanocarriers significantly enhance cytotoxicity toward SKBR-3 cells. More importantly, no selectivity toward MCF-10A cells is observed compared to HER2(+) SKBR-3 cells. Formulations cause apoptosis depending on Bax and Caspase-3 and cell cycle arrest in G2 phase. This study shows a novel system for HER2-targeted therapy of breast cancer with a multifunctional nanocarrier, which has higher stability, dual pH-sensitivity, selectivity, and it can be an efficient way of targeted anticancer drug delivery.

Modelling the Functions of Polo-Like Kinases in Mice and Their Applications as Cancer Targets with a Special Focus on Ovarian Cancer

Polo-like kinases (PLKs) belong to a five-membered family of highly conserved serine/threonine kinases (PLK1-5) that play differentiated and essential roles as key mitotic kinases and cell cycle regulators and with this in proliferation and cellular growth. Besides, evidence is accumulating for complex and vital non-mitotic functions of PLKs. Dysregulation of PLKs is widely associated with tumorigenesis and by this, PLKs have gained increasing significance as attractive targets in cancer with diagnostic, prognostic and therapeutic potential. PLK1 has proved to have strong clinical relevance as it was found to be over-expressed in different cancer types and linked to poor patient prognosis. Targeting the diverse functions of PLKs (tumor suppressor, oncogenic) are currently at the center of numerous investigations in particular with the inhibition of PLK1 and PLK4, respectively in multiple cancer trials. Functions of PLKs and the effects of their inhibition have been extensively studied in cancer cell culture models but information is rare on how these drugs affect benign tissues and organs. As a step further towards clinical application as cancer targets, mouse models therefore play a central role. Modelling PLK function in animal models, e.g., by gene disruption or by treatment with small molecule PLK inhibitors offers promising possibilities to unveil the biological significance of PLKs in cancer maintenance and progression and give important information on PLKs' applicability as cancer targets. In this review we aim at summarizing the approaches of modelling PLK function in mice so far with a special glimpse on the significance of PLKs in ovarian cancer and of orthotopic cancer models used in this fatal malignancy.

Non-mitotic functions of polo-like kinases in cancer cells

Inhibitors of mitotic protein kinases are currently being developed as non-neurotoxic alternatives of microtubule-targeting agents (taxanes, vinca alkaloids) which provide a substantial survival benefit for patients afflicted with different types of solid tumors. Among the mitotic kinases, the cyclin-dependent kinases, the Aurora kinases, the kinesin spindle protein and Polo-like kinases (PLKs) have emerged as attractive targets of cancer therapeutics. The functions of mammalian PLK1-5 are traditionally linked to the regulation of the cell cycle and to the stress response. Especially the key role of PLK1 and PLK4 in cellular growth and proliferation, their overexpression in multiple types of human cancer and their druggability, make them appealing targets for cancer therapy. Inhibitors for PLK1 and PLK4 are currently being tested in multiple cancer trials. The clinical success of microtubule-targeting agents is attributed not solely to the induction of a mitotic arrest in cancer cells, but also to non-mitotic effects like targeting intracellular trafficking on microtubules. This raises the question whether new cancer targets like PLK1 and PLK4 regulate critical non-mitotic functions in tumor cells. In this article we summarize the important roles of PLK1-5 for the regulation of non-mitotic signaling. Due to these functions it is conceivable that inhibitors for PLK1 or PLK4 can target interphase cells, which underscores their attractive potential as cancer drug targets. Moreover, we also describe the contribution of the tumor-suppressors PLK2, PLK3 and PLK5 to cancer cell signaling outside of mitosis. These observations highlight the urgent need to develop highly specific ATP-competitive inhibitors for PLK4 and for PLK1 like the 3rd generation PLK-inhibitor Onvansertib to prevent the inhibition of tumor-suppressor PLKs in- and outside of mitosis. The remarkable feature of PLKs to encompass a unique druggable domain, the polo-box-domain (PBD) that can be found only in PLKs offers the opportunity for the development of inhibitors that target PLKs exclusively. Beyond the development of mono-specific ATP-competitive PLK inhibitors, the PBD as drug target will support the design of new drugs that eradicate cancer cells based on the mitotic and non-mitotic function of PLK1 and PLK4.

α-Santalol functionalized chitosan nanoparticles as efficient inhibitors of polo-like kinase in triple negative breast cancer

Polo-like kinase 1 (PLK-1) is a protein kinase that plays a significant role in the initiation, maintenance, and completion of mitotic processes in the cell cycle.

An Effective Cationic Human Serum Albumin-Based Gene-Delivery Carrier Containing the Nuclear Localization Signal

Considerable effort has been devoted to the development of gene carriers over the years. However, toxicity, immunogenicity, and low transfection efficiency are still major barriers. How to overcome these obstacles has become a burning question in gene delivery. In the present study, a simple cationic human serum albumin (CHSA)-based gene-delivery system containing nuclear localization signals (NLSs) was constructed to conquer the limitations. CHSA/NLS/plasmid DNA (pDNA) complexes were prepared and characterized by Hoechst 33258 intercalation, gel retardation assay, morphological analysis, circular dichroism (CD) spectroscopy, particle size, and zeta potential measurements. Results showed that CHSA/NLS/pDNA complexes were able to condense and protect pDNA with high encapsulation efficiency. The complexes displayed a nutritional effect on cells at a low concentration and there was no significant cytotoxicity or immunogenicity. In addition, CHSA/NLS/pDNA complexes exhibited excellent cellular uptake rates and the mechanism was mainly the clathrin or macropinocytosis-dependent endocytosis pathway. Furthermore, CHSA/NLS/pDNA significantly enhanced gene expression efficiency in vitro. More importantly, CHSA/NLS/pDNA complexes showed a desired antitumor effect in vivo, exhibiting the highest inhibition rate (57.3%) and significant upregulation in p53 protein. All these results confirm that CHSA/NLS/pDNA complexes have a bright future as a safe and effective delivery system for gene therapy.

Horizons of nanotechnology applications in female specific cancers

Female-specific cancers are the most common cancers in women worldwide. Early detection methods remain unavailable for most of these cancers, signifying that most of them are diagnosed at later stages. Furthermore, current treatment options for most female-specific cancers are surgery, radiation and chemotherapy. Although important milestones in molecularly targeted approaches have been achieved lately, current therapeutic strategies for female-specific cancers remain limited, ineffective and plagued by the emergence of chemoresistance, which aggravates prognosis. Recently, the application of nanotechnology to the medical field has allowed the development of novel nano-based approaches for the management and treatment of cancers, including female-specific cancers. These approaches promise to improve patient survival rates by reducing side effects, enabling selective delivery of drugs to tumor tissues and enhancing the uptake of therapeutic compounds, thus increasing anti-tumor activity. In this review, we focus on the application of nano-based technologies to the design of novel and innovative diagnostic and therapeutic strategies in the context of female-specific cancers, highlighting their potential uses and limitations.

Click modified amphiphilic graft copolymeric micelles of poly(styrene-alt-maleic anhydride) for combinatorial delivery of doxorubicin and plk-1 siRNA in cancer therapy

The anti-apoptotic defense mechanism of cancer cells poses a major hurdle which makes chemotherapy less effective. Combinatorial delivery of drugs and siRNAs targeting anti-apoptotic proteins is a vital means for improving therapeutic effects. The present study aims at designing a suitable carrier which can effectively co-deliver doxorubicin and plk1 siRNA to tumor cells. Low molecular weight poly(styrene-alt-maleic anhydride) was chemically modified via a click reaction to obtain a cationic amphiphilic polymer for the co-delivery of therapeutic agents. Short glycol chains were utilized as linker molecules for grafting which in turn imparted a stealth nature and minimized plasma protein adsorption to the polymeric surface. Isonicotinic acid was grafted to the polymer due to its ability to penetrate the endolysosomal membrane and arginine-lysine conjugates were embedded for complexing siRNA. The polymer was able to self-assemble in to smooth, spherical micellar structures with a CMC of ∼3 μg mL^-1. The particle size of the micelles was ∼14-30 nm as depicted using TEM and FESEM. Atomic force microscopic analysis showed an average height of ∼12 nm for the polymeric micelles. An optimum doxorubicin loading of ∼9% w/w was achieved with the micelles using a dialysis method. Effective complexation of siRNA occurred above a polymer/siRNA weight ratio of 10 without any significant change in the particle size. Doxorubicin and fluorescent labeled siRNA loaded micelles exhibited excellent co-localization within the cytoplasm of MCF-7 cells. The synergistic effect of the active agents in inhibiting tumor cell proliferation was depicted using an MTT assay and visualized using calcein/propidium iodide staining of the treated cells. Co-administration of doxorubicin and plk1 siRNA in EAT tumor bearing Swiss albino mice using the cationic micelles significantly enhanced the antitumor efficacy.

Polo-like kinase and its inhibitors: Ready for the match to start?

Polo-like kinases (Plks) plays a central role in the normal cell cycle and their upregulation has been shown to play a role in the pathogenesis of multiple human cancers. Preclinical work demonstrates that targeting Plk has a significant impact on the treatment of both solid and hematologic malignancies in vitro and in vivo. We review here the basic science and clinical work to date with the Plks as well as future directions with this novel class of mitotic inhibitors.

The role of recent nanotechnology in enhancing the efficacy of radiation therapy

Radiation therapy is one of the most commonly used non-surgical interventions in tumor treatment and is often combined with other modalities to enhance its efficacy. Despite recent advances in radiation oncology, treatment responses, however, vary considerably between individual patients. A variety of approaches have been developed to enhance radiation response or to counteract resistance to ionizing radiation. Among them, a relatively novel class of radiation sensitizers comprises nanoparticles (NPs) which are highly efficient and selective systems in the nanometer range. NPs can either encapsulate radiation sensitizing agents, thereby protecting them from degradation, or sensitize cancer cells to ionizing radiation via their physicochemical properties, e.g. high Z number. Moreover, they can be chemically modified for active molecular targeting and the imaging of tumors. In this review we will focus on recent developments in nanotechnology, different classes and modifications of NPs and their radiation sensitizing properties.

Upregulated Polo-Like Kinase 1 Expression Correlates with Inferior Survival Outcomes in Rectal Cancer

BACKGROUND

Human polo-like kinase 1 (PLK1) expression has been associated with inferior outcomes in colorectal cancer. Our aims were to analyse PLK1 in rectal cancer, and its association with clinicopathological variables, overall survival as well as tumour regression to neoadjuvant treatment.

METHODS

PLK1 expression was quantified with immunohistochemistry in the centre and periphery (invasive front) of rectal cancers, as well as in the involved regional lymph nodes from 286 patients. Scores were based on staining intensity and percentage of positive cells, multiplied to give weighted scores from 1-12, dichotomised into low (0-5) or high (6-12).

RESULTS

PLK1 scores in the tumour periphery were significantly different to adjacent normal mucosa. Survival analysis revealed that low PLK1 score in the tumour periphery had a hazard ratio of death of 0.59 in multivariate analysis. Other predictors of survival included age, tumour depth, metastatic status, vascular and perineural invasion and adjuvant chemotherapy. There was no statistically significant correlation between PLK1 score and histological tumour regression in the neoadjuvant cohort.

CONCLUSION

Low PLK1 score was an independent predictor of superior overall survival, adjusting for multiple clinicopathological variables including treatment.

ScFv-decorated PEG-PLA-based nanoparticles for enhanced siRNA delivery to Her2⁺ breast cancer

Patients with Her2-overexpressing (Her2(+)) breast cancers generally have a poorer prognosis due to the high aggressiveness and chemoresistance of the disease. Small interfering RNA (siRNA) targeting the gene encoding polo-like kinase 1 (Plk1; siPlk1) has emerged as an efficient therapeutic agent for Her2(+) breast cancers. Poly(ethylene glycol)-block-poly(D,L-lactide) (PEG-PLA)-based nanoparticles for siRNA delivery were previously developed and optimized. In this study, for targeted delivery of siPlk1 to Her2(+) breast cancer, anti-Her2 single-chain variable fragment antibody (ScFv(Her2))-decorated PEG-PLA-based nanoparticles with si Plk1 encapsulation (ScFv(Her2)-NP(si) Plk1) are developed. With the rationally designed conjugation site, ScFv(Her2)-NP(siRNA) can specifically bind to the Her2 antigen overexpressed on the surface of Her2(+) breast cancer cells. Therefore, ScFv(Her2)-NP(si) Plk1 exhibits improved cellular uptake, promoted Plk1 silencing efficiency, and induced enhanced tumor cell apoptosis in Her2(+) breast cancer cells, when compared with nontargeted NP(si) Plk1. More importantly, ScFv(Her2)-NP(siRNA) markedly enhances the accumulation of siRNA in Her2(+) breast tumor tissue, and remarkably improves the efficacy of tumor suppression. Dose-dependent anti-tumor efficacy further demonstrates that ScFvHer2 -decorated PEG-PLA-based nanoparticles with siPlk1 encapsulation can significantly enhance the inhibition of Her2(+) breast tumor growth and reduce the dose of injected siRNA. These results suggest that ScFvHer2 -decorated PEG-PLA-based nanoparticles show great potential for targeted RNA interference therapy of Her2(+) breast tumor.

Systemic siRNA Delivery via Peptide-Tagged Polymeric Nanoparticles, Targeting PLK1 Gene in a Mouse Xenograft Model of Colorectal Cancer

Polymeric nanoparticles were developed from a series of chemical reactions using chitosan, polyethylene glycol, and a cell-targeting peptide (CP15). The nanoparticles were complexed with PLK1-siRNA. The optimal siRNA loading was achieved at an N : P ratio of 129.2 yielding a nanoparticle size of >200 nm. These nanoparticles were delivered intraperitoneally and tested for efficient delivery, cytotoxicity, and biodistribution in a mouse xenograft model of colorectal cancer. Both unmodified and modified chitosan nanoparticles showed enhanced accumulation at the tumor site. However, the modified chitosan nanoparticles showed considerably, less distribution in other organs. The relative gene expression as evaluated showed efficient delivery of PLK1-siRNA (0.5 mg/kg) with 50.7 ± 19.5% knockdown (P = 0.031) of PLK1 gene. The in vivo data reveals no systemic toxicity in the animals, when tested for systemic inflammation and liver toxicity. These results indicate a potential of using peptide-tagged nanoparticles for systemic delivery of siRNA at the targeted tumor site.

Antitumoral effect of PLK-1-inhibitor BI2536 in combination with cisplatin and docetaxel in squamous cell carcinoma cell lines of the head and neck

Inhibition of the polo-like-kinase-1 (PLK-1) has been shown to be effective in several haematological and solid tumor models. In this systemic in vitro study, the antitumor effect of BI2536, a small molecule inhibitor of PLK-1, in combination with cisplatin and docetaxel was examined in nine squamous cell carcinoma cell lines, most of which had a head and neck origin (SCCHN). Dose escalation studies were conducted with nine SCCHN cell lines using BI2536, cisplatin and docetaxel in cell line-specific concentrations. Growth inhibitory and proapoptotic effects were measured quantitatively using cytohistology and a Human Apoptose Array kit. BI2536 in combination with cisplatin and docetaxel showed a markedly higher antiproliferative and apoptotic activity in the SCCHN cell lines investigated (P≤0.008), compared with single agent cisplatin or docetaxel alone. The findings of this study showed that the addition of PLK-1-inhibitor BI2536 to conventional chemotherapeutic drugs led to a statistically higher antiproliferative and apoptotic effect in SCCHN cell lines compared with cisplatin or docetaxel alone. Inaugurating BI2536 in the clinical setting might enhance the antitumoral activity of conventional drugs, possibly leading to less toxic side effects of cancer therapy.

Cytotoxicity and cellular uptake of tri-block copolymer nanoparticles with different size and surface characteristics

Background

Polymer nanoparticles (PNP) are becoming increasingly important in nanomedicine and food-based applications. Size and surface characteristics are often considered to be important factors in the cellular interactions of these PNP, although systematic investigations on the role of surface properties on cellular interactions and toxicity of PNP are scarce.

Results

Fluorescent, monodisperse tri-block copolymer nanoparticles with different sizes (45 and 90 nm) and surface charges (positive and negative) were synthesized, characterized and studied for uptake and cytotoxicity in NR8383 and Caco-2 cells. All types of PNP were taken up by the cells. The positive smaller PNP₄₅ (45 nm) showed a higher cytotoxicity compared to the positive bigger PNP₉₀ (90 nm) particles including reduction in mitochondrial membrane potential (ΔΨ_m), induction of reactive oxygen species (ROS) production, ATP depletion and TNF-α release. The negative PNP did not show any cytotoxic effect. Reduction in mitochondrial membrane potential (ΔΨ_m), uncoupling of the electron transfer chain in mitochondria and the resulting ATP depletion, induction of ROS and oxidative stress may all play a role in the possible mode of action for the cytotoxicity of these PNP. The role of receptor-mediated endocytosis in the intracellular uptake of different PNP was studied by confocal laser scanning microscopy (CLSM). Involvement of size and charge in the cellular uptake of PNP by clathrin (for positive PNP), caveolin (for negative PNP) and mannose receptors (for hydroxylated PNP) were found with smaller PNP₄₅ showing stronger interactions with the receptors than bigger PNP₉₀.

Conclusions

The size and surface characteristics of polymer nanoparticles (PNP; 45 and 90 nm with different surface charges) play a crucial role in cellular uptake. Specific interactions with cell membrane-bound receptors (clathrin, caveolin and mannose) leading to cellular internalization were observed to depend on size and surface properties of the different PNP. These properties of the nanoparticles also dominate their cytotoxicity, which was analyzed for many factors. The effective reduction in the mitochondrial membrane potential (ΔΨ_m), uncoupling of the electron transfer chain in mitochondria and resulting ATP depletion, induction of ROS and oxidative stress likely all play a role in the mechanisms behind the cytotoxicity of these PNP.

Targeted delivery of PLK1-siRNA by ScFv suppresses Her2+ breast cancer growth and metastasis

A major obstacle to developing small interfering RNAs (siRNAs) as cancer drugs is their intracellular delivery to disseminated cancer cells. Fusion proteins of single-chain fragmented antibodies (ScFvs) and positively charged peptides deliver siRNAs into specific target cells. However, the therapeutic potential of ScFv-mediated siRNA delivery has not been evaluated in cancer. Here, we tested whether Polo-like kinase 1 (PLK1) siRNAs complexed with a Her2-ScFv-protamine peptide fusion protein (F5-P) could suppress Her2(+) breast cancer cell lines and primary human cancers in orthotopic breast cancer models. PLK1-siRNAs transferred by F5-P inhibited target gene expression, reduced proliferation, and induced apoptosis of Her2(+) breast cancer cell lines and primary human cancer cells in vitro without triggering an interferon response. Intravenously injected F5-P/PLK1-siRNA complexes concentrated in orthotopic Her2(+) breast cancer xenografts and persisted for at least 72 hours, leading to suppressed PLK1 gene expression and tumor cell apoptosis. The intravenously injected siRNA complexes retarded Her2(+) breast tumor growth, reduced metastasis, and prolonged survival without evident toxicity. F5-P-mediated delivery of a cocktail of PLK1, CCND1, and AKT siRNAs was more effective than an equivalent dose of PLK1-siRNAs alone. These data suggest that F5-P could be used to deliver siRNAs to treat Her2(+) breast cancer.

Targeting the cell cycle in esophageal adenocarcinoma: An adjunct to anticancer treatment

Esophageal adenocarcinoma is a major cause of cancer death in men in the developed world. Continuing poor outcomes with conventional therapies that predominantly target apoptosis pathways have lead to increasing interest in treatments that target the cell cycle. A large international effort has led to the development of a large number of inhibitors, which target cell cycle kinases, including cyclin-dependent kinases, Aurora kinases and polo-like kinase. Initial phase I/II trials in solid tumors have often demonstrated only modest clinical benefits of monotherapy. This may relate in part to a failure to identify the patient populations that will gain the most clinical benefit. Newer compounds lacking the side effect profile of first-generation compounds may show utility as adjunctive treatments targeted to an individual’s predicted response to treatment.

Dinosaurs and ancient civilizations: reflections on the treatment of cancer

Research efforts in the area of palaeopathology have been seen as an avenue to improve our understanding of the pathogenesis of cancer. Answers to questions of whether dinosaurs had cancer, or if cancer plagued ancient civilizations, have captured the imagination as well as the popular media. Evidence for dinosaurian cancer may indicate that cancer may have been with us from the dawn of time. Ancient recorded history suggests that past civilizations attempted to fight cancer with a variety of interventions. When contemplating the issue why a generalized cure for cancer has not been found, it might prove useful to reflect on the relatively limited time that this issue has been an agenda item of governmental attention as well as continued introduction of an every evolving myriad of manmade carcinogens relative to the total time cancer has been present on planet Earth. This article reflects on the history of cancer and the progress made following the initiation of the "era of cancer chemotherapy."

Albumin nanoshell encapsulation of near-infrared-excitable rare-Earth nanoparticles enhances biocompatibility and enables targeted cell imaging

The use of traditional fluorophores for in vivo imaging applications is limited by poor quantum yield, poor tissue penetration of the excitation light, and excessive tissue autofluorescence, while the use of inorganic fluorescent particles that offer a high quantum yield is frequently limited due to particle toxicity. Rare-earth-doped nanoparticles that utilize near-infrared upconversion overcome the optical limitations of traditional fluorophores, but are not typically suitable for biological application due to their insolubility in aqueous solution, lack of functional surface groups for conjugation of biomolecules, and potential cytotoxicity. A new approach to establish highly biocompatible and biologically targetable nanoshell complexes of luminescent rare-earth-doped NaYF(4) nanoparticles (REs) excitable with 920-980 nm near-infrared light for biomedical imaging applications is reported. The approach involves the encapsulation of NaYF(4) nanoparticles doped with Yb and Er within human serum albumin nanoshells to create water-dispersible, biologically functionalizable composite particles. These particles exhibit narrow size distributions around 200 nm and are stable in aqueous solution for over 4 weeks. The albumin shell confers cytoprotection and significantly enhances the biocompatibility of REs even at concentrations above 200 microg REs mL(-1). Composite particles conjugated with cyclic arginine-glycine-aspartic acid (cRGD) specifically target both human glioblastoma cell lines and melanoma cells expressing alpha(v)beta(3) integrin receptors. These findings highlight the promise of albumin-encapsulated rare-earth nanoparticles for imaging cancer cells in vitro and the potential for targeted imaging of disease sites in vivo.

Polo-like kinase 1 as predictive marker and therapeutic target for radiotherapy in rectal cancer

The ability to predict tumor sensitivity toward radiotherapy may significantly impact the selection of patients for preoperative combined-modality therapy. The aim of the present study was to test the predictive value of Polo-like kinase 1 (PLK1) in rectal cancer patients and to investigate whether PLK1 plays a direct role in mediating radiation sensitivity. PLK1 expression was evaluated by immunohistochemistry (n = 76) or Affymetrix HG133 microarray (n = 20) on pretreatment biopsies of patients with advanced rectal cancer. Expression was correlated with both tumor regression in the resected specimen and long-term clinical outcome. Furthermore, we used small interfering RNAs (siRNAs) to down-regulate PLK1 expression in colorectal cancer cells and analyzed the effects of PLK1-specific siRNAs by Western blot and quantitative real-time PCR analysis, FACScan analysis, caspase 3/7 assays, and colony-forming assays. We observed that increased PLK1 protein expression was significantly related to a poorer tumor regression and a higher risk of local recurrence in uni- and multivariate analysis. A significant decrease of PLK1 expression by siRNAs in combination with ionizing radiation induced an increased percentage of apoptotic cells and increased caspase 3/7 activity. Furthermore, enhanced G(2)-M levels, decreased cellular viability, and reduced clonogenic survival were demonstrated, indicating a radiosensitizing effect of PLK1 depletion. Therefore, PLK1 may be a novel predictive marker for radiation response as well as a promising therapeutic target in rectal cancer patients.

Multifaceted polo-like kinases: drug targets and antitargets for cancer therapy

The polo-like kinase 1 (PLK1) acts in concert with cyclin-dependent kinase 1-cyclin B1 and Aurora kinases to orchestrate a wide range of critical cell cycle events. Because PLK1 has been preclinically validated as a cancer target, small-molecule inhibitors of PLK1 have become attractive candidates for anticancer drug development. Although the roles of the closely related PLK2, PLK3 and PLK4 in cancer are less well understood, there is evidence showing that PLK2 and PLK3 act as tumour suppressors through their functions in the p53 signalling network, which guards the cell against various stress signals. In this article, recent insights into the biology of PLKs will be reviewed, with an emphasis on their role in malignant transformation, and progress in the development of small-molecule PLK1 inhibitors will be examined.

The War on Cancer rages on

In 1971, the "War on Cancer" was launched by the US government to cure cancer by the 200-year anniversary of the founding of the United States of America, 1976. This article briefly looks back at the progress that has been made in cancer research and compares progress made in other areas of human affliction. While progress has indeed been made, the battle continues to rage on.

Polo-like kinase 1 (Plk1) as a novel drug target in chronic myeloid leukemia: overriding imatinib resistance with the Plk1 inhibitor BI 2536

In most patients with chronic myeloid leukemia (CML), the disease can be kept under control using the BCR/ABL kinase inhibitor imatinib. Nevertheless, resistance or intolerance to imatinib and other BCR/ABL inhibitors may occur during therapy. Therefore, CML research is focusing on novel targets and targeted drugs. Polo-like kinase 1 (Plk1) is a serine/threonine kinase that plays an essential role in mitosis. In this study, we examined the expression of Plk1 in CML cells and its potential role as a therapeutic target. Plk1 was found to be expressed in phosphorylated form in the CML cell line K562 as well as in primary CML cells in all patients tested. Inhibition of BCR/ABL by imatinib or nilotinib (AMN107) led to decreased expression of the Plk1 protein in CML cells, suggesting that BCR/ABL promotes Plk1 generation. Silencing of Plk1 in CML cells by a small interfering RNA approach was followed by cell cycle arrest and apoptosis. Furthermore, the Plk1-targeting drug BI 2536 was found to inhibit proliferation of imatinib-sensitive and imatinib-resistant CML cells, including leukemic cells, carrying the T315 mutation of BCR/ABL with reasonable IC(50) values (1-50 nmol/L). The growth-inhibitory effects of BI 2536 on CML cells were found to be associated with cell cycle arrest and apoptosis. Moreover, BI 2536 was found to synergize with imatinib and nilotinib in producing growth inhibition in CML cells. In conclusion, Plk1 is expressed in CML cells and may represent a novel, interesting target in imatinib-sensitive and imatinib-resistant CML.

HER2 targeting as a two-sided strategy for breast cancer diagnosis and treatment: Outlook and recent implications in nanomedical approaches

At present, mammary carcinoma is the second most common type of malignant tumor in adult women after lung cancer, as more than one million women are diagnosed with breast cancer every year. Despite advances in diagnosis and treatment, which have resulted in a decrease in mortality in recent decades, breast cancer remains a major public health problem. One of the most significant unresolved clinical and scientific problems is the occurrence of resistance to clinical treatments and their toxicity (and how to predict, prevent and overcome them). However, the heterogeneity of human breast cancer in terms of genetic features, molecular profiles and clinical behavior represents a constraint obstructing the discovery of a solution to the disease. It is currently considered that the chances of success of therapy may increase if the tumor cells are selectively removed before they can evolve to their mature stages up to metastases production. Therefore, novel and more sensitive diagnostic tools are being developed, with the aim of improving the early and noninvasive detection of rising malignancies and the accuracy of tumor tissue localization. Meanwhile, there is an emerging use of targeted therapies in oncology, depending on the expression of specific proteins or genes present in tumor cells. Among the molecular targets considered for the treatment of breast cancer cells so far, we chose to focus on examples involving overexpression and/or gene amplification of "Human Epidermal growth factor Receptor 2" (HER2) protein. In current studies, various types of nanoparticles conjugated with the anti-HER2 monoclonal antibody, the so-called "trastuzumab", are investigated extensively due to promising results in biological and preclinical applications aimed at improving the treatment of breast cancer. In this paper, we present a critical review of the preparation and use of different kinds of trastuzumab-functionalized nanoparticles, with an emphasis on the therapeutic and diagnostic (theranostic) potential of this generation of hybrid nanoparticles, exploiting the multifaceted mechanisms of action of trastuzumab against malignant cells.

Overexpression of polo-like kinase1 predicts a poor prognosis in hepatocellular carcinoma patients

AIM

To elucidate the role of overexpressed polo-like kinase1 (PLK1) in hepatocellular carcinoma (HCC).

METHODS

We prospectively collected clinicopathological, immunohistochemical and semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) data from 135 HCC patients undergoing successful hepatectomy. The correlations between PLK1 mRNA expression and clinicopathologic variables were analyzed by Mann-Whitney U test. Prognostic factors were identified by univariate and multivariate analyses.

RESULTS

Immunohistochemical results showed overexpression of PLK1 was mainly found in tumor tissues compared with tumor-free tissue. A similar mRNA result was obtained by semi-quantitative RT-PCR. A total of 111 samples were positive for PLK1 mRNA expression. The positive expression was correlated with venous invasion, tumor nodules and Edmondson grade. Furthermore, 1, 3, 5-year survival rates in the positive expression group were significantly lower than the negative control group. Multivariate analysis showed that positive PLK1 expression was an independent risk factor for HCC.

CONCLUSION

PLK1 could be a potential biomarker for diagnosis and therapy for HCC.

Uptake of plasmid-loaded nanoparticles in breast cancer cells and effect on Plk1 expression

The development of nucleic acid-based drugs for cancer therapeutic application has shown promising results in the past. However the delivery of these drugs to target cells is one problem which remains to be resolved. Nanoparticles have been described as promising strategies to deliver drugs into target cells. Human serum albumin (HSA) nanoparticles conjugated to trastuzumab for a cell type-specific targeting of human epidermal growth factor receptor 2 (HER2)-overexpressing cells were developed with incorporated expression plasmids for small hairpin RNAs (shRNAs) targeting polo-like kinase 1 (Plk1). Plk1 is a promising target for such an approach because it is overexpressed in all known cancer types and is a negative prognostic factor. Receptor-mediated uptake of the trastuzumab-modified nanoparticles into HER2-positive cells could be observed leading to reduced Plk1 expression. Taken together, HSA nanoparticles represent promising tools to deliver expression plasmids for shRNAs into target cells and should be further evaluated with regard to a therapeutic application of RNA interference in cancer therapy.

Hypoxia targeting gene expression for breast cancer gene therapy

Gene therapy is a promising strategy to treat various inherited and acquired diseases. However, targeting gene expression to specific tissue is required to minimize side effects of gene therapy. Hypoxia is present in the microenvironment of solid tumors such as breast tumors. A hypoxic tumor targeting gene expression system has been developed for cancer gene therapy. In hypoxic tissues, hypoxia inducible factor (HIF)-1alpha is accumulated and stimulates transcription of the genes that have hypoxia response elements (HREs) in their promoters. Therefore, transcriptional regulation with a hypoxia inducible promoter is the most widely used strategy for hypoxic tumors targeting gene therapy. In breast cancer gene therapy, breast tumor specific promoters in combination with HREs have been used to induce gene expression in hypoxic breast tumors. Post-transcriptional regulation using an untranslated region (UTR) is also a useful strategy to increase gene expression in hypoxic tumor tissue. In addition, post-translational regulation with the oxygen-dependent degradation (ODD) domain is effective to eliminate therapeutic gene products and reduce side effects in normal tissue. In combination with the breast tumor specific promoters, hypoxic tumor targeting strategies will be useful for the development of a safe breast cancer gene therapy.

Trastuzumab-functionalized nanoparticles of biodegradable copolymers for targeted delivery of docetaxel

Aims: We synthesized a novel system of docetaxel-loaded, trastuzumab-functionalized nanoparticles (NPs) of biodegradable copolymers for targeted and synergistic chemotherapy. Materials & Methods: NPs of two component biodegradable copolymers were prepared by a modified solvent extraction/evaporation method with D-α-tocopheryl polyethylene glycol succinate (TPGS) as emulsifier. One component copolymer is poly(lactide)-TPGS, which is of desired hydrophobic–lipophilic balance for cellular adhesion, and another is carboxyl group-terminated TPGS, which facilitates the conjugation of trastuzumab on the NP surface for targeting. Results: In vitro investigation with SK-BR-3 breast cancer cells of HER2 overexpression showed that the trastuzumab-functionalized NPs have great advantages over nude NPs in cellular uptake and cytotoxicity. Conclusion: Trastuzumab conjugated onto the NP surface has two functions: one is to target HER2-overexpressing cancer cells and the other is to enhance the cytotoxicity of docetaxel through synergistic effects. The trastuzumab-functionalized, docetaxel-loaded NPs have great potential for targeted chemotherapy to treat HER2-overexpressing cancer.

Neoplasia: the second decade

This issue marks the end of the 10-year anniversary of Neoplasia where we have seen exciting growth in both number of submitted and published articles in Neoplasia. Neoplasia was first published in 1999. During the past 10 years, Neoplasia has dynamically adapted to the needs of the cancer research community as technologies have advanced. Neoplasia is currently providing access to articles through PubMed Central to continue to facilitate rapid broad-based dissemination of published findings to the scientific community through an Open Access model. This has in part helped Neoplasia to achieve an improved impact factor this past year, demonstrating that the manuscripts published by Neoplasia are of great interest to the overall cancer research community. This past year, Neoplasia received a record number of articles for review and has had a 21% increase in the number of published articles.

The balance of Polo-like kinase 1 in tumorigenesis

Polo-like kinase 1 (Plk1) belongs to a family of conserved serine/threonine kinases with a polo-box domain, which have similar but non-overlapping functions in the cell cycle progression. Plk1 plays a key role to ensure the normal mitosis. Interestingly, overexpression of Plk1 is associated with tumor development and could serve as a prognostic marker for many cancers. Due to Plk1 overexpression, several Plk1 inhibitors have been developed and tested for the cancer treatment. However, in a recent study, it has been suggested that down-regulation of Plk1 could also induce aneuploidy and tumor formation in vivo. Therefore, a normal level of Plk1 is important for mitosis. And caution should be taken when Plk1 inhibitors are used in the clinical trial and their side effects including tumorigenesis should be carefully evaluated.

Effect of trastuzumab-modified antisense oligonucleotide-loaded human serum albumin nanoparticles prepared by heat denaturation

Nanoparticles represent a promising tool for targeted drug delivery to tumour cells and are able to protect drugs against degradation. In our present study we developed targeted nanoparticles loaded with antisense oligonucleotides (ASOs) against Plk1 (polo-like kinase 1) prepared by heat denaturation instead of using glutaraldehyde. Glutaraldehyde can lead to an inactivation of ASOs through chemical crosslinking and is a toxic entity. We examined the ideal preparation conditions and characterised the resulting particles in terms of physico-chemical properties, ASO recovery after enzymatic degradation and stability. Stable monodisperse nanoparticles with an ASO recovery of more than 80% could be prepared at a temperature of 105 degrees C for 10 min. Furthermore we performed quantitative real-time PCR and Western blot to detect an ASO-mediated effect on Plk1 in BT-474 cells. We observed a significant reduction of Plk1 mRNA and protein expression. Thus, this is the first report of ASO-loaded HSA nanoparticles prepared by heat denaturation, where an impact on gene expression could be observed. The data provide the basis for the further development of carrier systems for ASOs to reduce off-target effects evoked by systemically administered ASOs and to achieve a better penetration into primary and metastatic target cells.

Analyzing real-time PCR data by the comparative C(T) method

Two different methods of presenting quantitative gene expression exist: absolute and relative quantification. Absolute quantification calculates the copy number of the gene usually by relating the PCR signal to a standard curve. Relative gene expression presents the data of the gene of interest relative to some calibrator or internal control gene. A widely used method to present relative gene expression is the comparative C(T) method also referred to as the 2 (-DeltaDeltaC(T)) method. This protocol provides an overview of the comparative C(T) method for quantitative gene expression studies. Also presented here are various examples to present quantitative gene expression data using this method.