Principles of cancer therapy: oncogene and non-oncogene addiction

Mechanisms of aneuploidy induction by RAS and RAF oncogenes

Most cancers progress with the accumulation of genetic mutations with time and this is frequently associated with the acquisition of genomic instability in the form of whole chromosome changes, chromosomal rearrangements, gene amplifications or smaller changes at the nucleotide level. Whole chromosome instability (W-CIN), characterised by aneuploidy, is a major form of genomic instability observed in human cancers and several lines of evidence now support the argument that W-CIN is a promoter of tumourigenesis rather than being a passenger event. The primary mechanism proposed for evolution of CIN is abnormalities in mitosis/cytokinesis. However, mutations in genes directly involved in controlling mitosis/cytokinesis are rare in human cancers and so the mechanisms underpinning the evolution of CIN in cancers are not currently clear. On the other hand, mutations in RAS or BRAF are frequently found in human cancers, many of which demonstrate CIN, suggesting a possible link between deregulated signaling through the RAS/RAF/MEK/ERK pathway and CIN. In this review, we focus on a potential relationship between deregulated RAS/RAF signaling and CIN, and discuss possible mechanisms connecting the two.

Past, present, and future of molecular and cellular oncology

In the last 20 years, the field of cellular and molecular oncology has been born and has moved its first steps, with an increasingly rapid pace. Hundreds of oncogenic and oncosuppressive signaling cascades have been characterized, facilitating the development of an ever more refined and variegated arsenal of diagnostic and therapeutic weapons. Furthermore, several cancer-specific features and processes have been identified that constitute promising therapeutic targets. For instance, it has been demonstrated that microRNAs can play a critical role in oncogenesis and tumor suppression. Moreover, it turned out that tumor cells frequently exhibit an extensive metabolic rewiring, can behave in a stem cell-like fashion (and hence sustain tumor growth), often constitutively activate stress response pathways that allow them to survive, can react to therapy by engaging in non-apoptotic cell death programs, and sometimes die while eliciting a tumor-specific immune response. In this Perspective article, we discuss the main issues generated by these discoveries that will be in the limelight of molecular and cellular oncology research for the next, hopefully few years.

Synthetic lethality: exploiting the addiction of cancer to DNA repair

Because cancer at its origin must acquire permanent genomic mutations, it is by definition a disease of DNA repair. Yet for cancer cells to replicate their DNA and divide, which is the fundamental phenotype of cancer, multiple DNA repair pathways are required. This produces a paradox for the cancer cell, where its origin is at the same time its weakness. To overcome this difficulty, a cancer cell often becomes addicted to DNA repair pathways other than the one that led to its initial mutability. The best example of this is in breast or ovarian cancers with mutated BRCA1 or 2, essential components of a repair pathway for repairing DNA double-strand breaks. Because replicating DNA requires repair of DNA double-strand breaks, these cancers have become reliant on another DNA repair component, PARP1, for replication fork progression. The inhibition of PARP1 in these cells results in catastrophic double-strand breaks during replication, and ultimately cell death. The exploitation of the addiction of cancer cells to a DNA repair pathway is based on synthetic lethality and has wide applicability to the treatment of many types of malignancies, including those of hematologic origin. There is a large number of novel compounds in clinical trials that use this mechanism for their antineoplastic activity, making synthetic lethality one of the most important new concepts in recent drug development.

Enhancement of dendritic cells as vaccines for cancer

Dendritic cells are the most potent antigen-presenting cells known; owing to their ability to stimulate antigen-specific cytolytic and memory T-cell responses, their use as cancer vaccines is rapidly increasing. While clinical trials provide evidence that dendritic cells vaccines are safe and elicit immunological responses in most patients, few complete tumor remissions have been reported and further technological advances are required. An effective dendritic cell vaccine must possess and maintain several characteristics: it must migrate to lymph nodes, have a mature, Th1-polarizing phenotype expressed stably after infusion and present antigen for sufficient time to produce a T-cell response capable of eliminating a tumor. While dendritic cells are readily matured ex vivo, their phenotype and fate after infusion are rarely evaluable; therefore, strategies to ensure that dendritic cells access lymphoid tissues and retain an immunostimulatory phenotype are required. In order to best exploit dendritic cells as vaccines, they may require genetic modification and combination with other strategies including adoptive T-cell transfer, inhibition of regulatory T cells or modulation of inflammatory pathways.

Functional synergies yet distinct modulators affected by genetic alterations in common human cancers

An important general concern in cancer research is how diverse genetic alterations and regulatory pathways can produce common signaling outcomes. In this study, we report the construction of cancer models that combine unique regulation and common signaling. We compared and functionally analyzed sets of genetic alterations, including somatic sequence mutations and copy number changes, in breast, colon, and pancreatic cancer and glioblastoma that had been determined previously by global exon sequencing and SNP (single nucleotide polymorphism) array analyses in multiple patients. The genes affected by the different types of alterations were mostly unique in each cancer type, affected different pathways, and were connected with different transcription factors, ligands, and receptors. In our model, we show that distinct amplifications, deletions, and sequence alterations in each cancer resulted in common signaling pathways and transcription regulation. In functional clustering, the impact of the type of alteration was more pronounced than the impact of the kind of cancer. Several pathways such as TGF-β/SMAD signaling and PI3K (phosphoinositide 3-kinase) signaling were defined as synergistic (affected by different alterations in all four cancer types). Despite large differences at the genetic level, all data sets interacted with a common group of 65 "universal cancer genes" (UCG) comprising a concise network focused on proliferation/apoptosis balance and angiogenesis. Using unique nodal regulators ("overconnected" genes), UCGs, and synergistic pathways, the cancer models that we built could combine common signaling with unique regulation. Our findings provide a novel integrated perspective on the complex signaling and regulatory networks that underlie common human cancers.

Geraniol inhibits prostate cancer growth by targeting cell cycle and apoptosis pathways

The progression of prostate cancer is associated with escape from cell cycle arrest and apoptosis under androgen-depleted conditions. Here, we found that geraniol, a naturally occurring monoterpene, induces cell cycle arrest and apoptosis in cultured cells and tumor grafted mice using PC-3 prostate cancer cells. Geraniol modulated the expression of various cell cycle regulators and Bcl-2 family proteins in PC-3 cells in vitro and in vivo. Furthermore, we showed that the combination of sub-optimal doses of geraniol and docetaxel noticeably suppresses prostate cancer growth in cultured cells and tumor xenograft mice. Therefore, our findings provide insight into unraveling the mechanisms underlying escape from cell cycle arrest and apoptosis and developing therapeutic strategies against prostate cancer.

Molecular targets of phytochemicals for cancer prevention

Although successful for a limited number of tumour types, the efficacy of cancer therapies, especially for late-stage disease, remains poor overall. Many have argued that this could be avoided by focusing on cancer prevention, which has now entered the arena of targeted therapies. During the process of identifying preventive agents, dietary phytochemicals, which are thought to be safe for human use, have emerged as modulators of key cellular signalling pathways. The task now is to understand how these chemicals perturb these pathways by modelling their interactions with their target proteins.

Pathway-based identification of biomarkers for targeted therapeutics: personalized oncology with PI3K pathway inhibitors

Although we have made great progress in understanding the complex genetic alterations that underlie human cancer, it has proven difficult to identify which molecularly targeted therapeutics will benefit which patients. Drug-specific modulation of oncogenic signaling pathways in specific patient subpopulations can predict responsiveness to targeted therapy. Here, we report a pathway-based phosphoprofiling approach to identify and quantify clinically relevant, drug-specific biomarkers for phosphatidylinositol 3-kinase (PI3K) pathway inhibitors that target AKT, phosphoinositide-dependent kinase 1 (PDK1), and PI3K-mammalian target of rapamycin (mTOR). We quantified 375 nonredundant PI3K pathway-relevant phosphopeptides, all containing AKT, PDK1, or mitogen-activated protein kinase substrate recognition motifs. Of these phosphopeptides, 71 were drug-regulated, 11 of them by all three inhibitors. Drug-modulated phosphoproteins were enriched for involvement in cytoskeletal reorganization (filamin, stathmin, dynamin, PAK4, and PTPN14), vesicle transport (LARP1, VPS13D, and SLC20A1), and protein translation (S6RP and PRAS40). We then generated phosphospecific antibodies against selected, drug-regulated phosphorylation sites that would be suitable as biomarker tools for PI3K pathway inhibitors. As proof of concept, we show clinical translation feasibility for an antibody against phospho-PRAS40(Thr246). Evaluation of binding of this antibody in human cancer cell lines, a PTEN (phosphatase and tensin homolog deleted from chromosome 10)-deficient mouse prostate tumor model, and triple-negative breast tumor tissues showed that phospho-PRAS40(Thr246) positively correlates with PI3K pathway activation and predicts AKT inhibitor sensitivity. In contrast to phosphorylation of AKT(Thr308), the phospho-PRAS40(Thr246) epitope is highly stable in tissue samples and thus is ideal for immunohistochemistry. In summary, our study illustrates a rational approach for discovery of drug-specific biomarkers toward development of patient-tailored treatments.

Heterogeneous sensitivity of human acute myeloid leukemia to β-catenin down-modulation

Dysregulation of the Wnt/ß-catenin pathway has been observed in various malignancies, including acute myeloid leukemia (AML), where the over-expression of ß-catenin is an independent adverse prognostic factor. ß-catenin was found up-regulated in the vast majority of AML samples and more frequently localized in the nucleus of leukemic stem cells compared to normal bone marrow CD34⁺ cells. The knockdown of ß-catenin, using a short hairpin RNA (shRNA) lentiviral approach, accelerates ATRA-induced differentiation and impairs the proliferation of HL60 leukemic cell line. Using in vivo quantitative tracking of these cells, we observed a reduced engraftment potential after xenotransplantation when ß-catenin was silenced. However when studying primary AML cells, despite effective down-regulation of ß-catenin we did not observe any impairment of their in vitro long-term maintenance on MS-5 stroma nor of their engraftment potential in vivo. Altogether, these results demonstrate that despite a frequent ß-catenin up-regulation in AML, leukemia initiating cells might not be ‘addicted’ to this pathway and thus targeted therapy against ß-catenin might not be successful in all patients.

Principles and current strategies for targeting autophagy for cancer treatment

Autophagy is an evolutionarily conserved, intracellular self-defense mechanism in which organelles and proteins are sequestered into autophagic vesicles that are subsequently degraded through fusion with lysosomes. Cells, thereby, prevent the toxic accumulation of damaged or unnecessary components, but also recycle these components to sustain metabolic homoeostasis. Heightened autophagy is a mechanism of resistance for cancer cells faced with metabolic and therapeutic stress, revealing opportunities for exploitation as a therapeutic target in cancer. We summarize recent developments in the field of autophagy and cancer and build upon the results presented at the Cancer Therapy Evaluation Program (CTEP) Early Drug Development meeting in March 2010. Herein, we describe our current understanding of the core components of the autophagy machinery and the functional relevance of autophagy within the tumor microenvironment, and we outline how this knowledge has informed preclinical investigations combining the autophagy inhibitor hydroxychloroquine (HCQ) with chemotherapy, targeted therapy, and immunotherapy. Finally, we describe ongoing clinical trials involving HCQ as a first generation autophagy inhibitor, as well as strategies for the development of novel, more potent, and specific inhibitors of autophagy.

Pharmacologic modulation of serine/threonine phosphorylation highly sensitizes PHEO in a MPC cell and mouse model to conventional chemotherapy

Background

The failure of cytotoxic cancer regimens to cure the most drug-resistant, well-differentiated solid tumors has been attributed to the heterogeneity of cell types that differ in their capacities for growth, differentiation, and metastases. We investigated the effect of LB1, a small molecule inhibitor of serine/threonine protein phosphatase 2A (PP2A), on its ability to inhibit a low growth fraction and highly drug-resistant solid neuroendocrine tumor, such as metastatic pheochromocytoma (PHEO). Subsequently, we evaluated the increased efficacy of chemotherapy combined with LB1.

Methodology/Principal Findings

The effect of LB1 and temozolomide (TMZ), a standard chemotherapeutic agent that alone only transiently suppressed the growth and regression of metastatic PHEO, was evaluated in vitro on a single PHEO cell line and in vivo on mouse model of metastatic PHEO. In the present study, we show that metastatic PHEO, for which there is currently no cure, can be eliminated by combining LB1, thereby inhibiting PP2A, with TMZ. This new treatment approach resulted in long term, disease-free survival of up to 40% of animals bearing multiple intrahepatic metastases, a disease state that the majority of patients die from. Inhibition of PP2A was associated with prevention of G1/S phase arrest by p53 and of mitotic arrest mediated by polo-like kinase 1 (Plk-1).

Conclusions/Significance

The elimination of DNA damage-induced defense mechanisms, through transient pharmacologic inhibition of PP2A, is proposed as a new approach for enhancing the efficacy of non-specific cancer chemotherapy regimens against a broad spectrum of low growth fraction tumors very commonly resistant to cytotoxic drugs.

Heat shock protein Hsp72 plays an essential role in Her2-induced mammary tumorigenesis

The major heat shock protein Hsp72 is expressed at elevated levels in many human cancers and its expression correlates with tumor progression. Here we investigated the role of Hsp72 in Her2 oncogene-induced neoplastic transformation and tumorigenesis. Expression of Her2 in untransformed MCF10A mammary epithelial cells caused transformation, as judged by foci formation in culture and tumorigenesis in xenografts. However, expression of Her2 in Hsp72-depleted cells failed to induce transformation. The anti-tumorigenic effects of Hsp72 downregulation were associated with cellular senescence due to accumulation of p21 and depletion of survivin. Accordingly, either knockdown of p21 or expression of survivin reversed this senescence process. Further, we developed an animal model of Hsp72-dependent breast cancer associated with expression of Her2. Knockout of Hsp72 almost completely suppressed tumorigenesis in the MMTVneu breast cancer mouse model. In young Hsp72 KO mice, expression of Her2 instead of mammary tissue hyperplasia led to suppression of duct development and blocked alveolar budding. These effects were due to massive cell senescence in mammary tissue, which was associated with upregulation of p21 and downregulation of survivin. Therefore Hsp72 plays an essential role in Her2-induced tumorigenesis by regulating oncogene-induced senescence pathways.

Targeting the mitotic checkpoint for cancer therapy with NMS-P715, an inhibitor of MPS1 kinase

MPS1 kinase is a key regulator of the spindle assembly checkpoint (SAC), a mitotic mechanism specifically required for proper chromosomal alignment and segregation. It has been found aberrantly overexpressed in a wide range of human tumors and is necessary for tumoral cell proliferation. Here we report the identification and characterization of NMS-P715, a selective and orally bioavailable MPS1 small-molecule inhibitor, which selectively reduces cancer cell proliferation, leaving normal cells almost unaffected. NMS-P715 accelerates mitosis and affects kinetochore components localization causing massive aneuploidy and cell death in a variety of tumoral cell lines and inhibits tumor growth in preclinical cancer models. Inhibiting the SAC could represent a promising new approach to selectively target cancer cells.

Anticancer activity of Celastrol in combination with ErbB2-targeted therapeutics for treatment of ErbB2-overexpressing breast cancers

The receptor tyrosine kinase ErbB2 is overexpressed in up to a third of breast cancers, allowing targeted therapy with ErbB2-directed humanized antibodies such as Trastuzumab. Concurrent targeting of ErbB2 stability with HSP90 inhibitors is synergistic with Trastuzumab, suggesting that pharmacological agents that can inhibit HSP90 as well as signaling pathways activated by ErbB2 could be useful against ErbB2-overexpressing breast cancers. The triterpene natural product Celastrol inhibits HSP90 and several pathways relevant to ErbB2-dependent oncogenesis including the NFκB pathway and the proteasome, and has shown promising activity in other cancer models. Here, we demonstrate that Celastrol exhibits in vitro antitumor activity against a panel of human breast cancer cell lines with selectivity towards those overexpressing ErbB2. Celastrol strongly synergized with ErbB2-targeted therapeutics Trastuzumab and Lapatinib, producing higher cytotoxicity with substantially lower doses of Celastrol. Celastrol significantly retarded the rate of growth of ErbB2-overexpressing human breast cancer cells in a mouse xenograft model with only minor systemic toxicity. Mechanistically, Celastrol not only induced the expected ubiquitinylation and degradation of ErbB2 and other HSP90 client proteins, but it also increased the levels of reactive oxygen species (ROS). Our studies show that the Michael Acceptor functionality in Celastrol is important for its ability to destabilize ErbB2 and exert its bioactivity against ErbB2-overexpressing breast cancer cells. These studies suggest the potential use of Michael acceptor-containing molecules as novel therapeutic modalities against ErbB2-driven breast cancer by targeting multiple biological attributes of the driver oncogene.

Apoptosis and oncogenesis: give and take in the BCL-2 family

The mitochondrial pathway of apoptosis constitutes one of the main safeguards against tumorigenesis. The BCL-2 family includes the central players of this pathway that regulate cell fate through the control of mitochondrial outer membrane permeabilization (MOMP), and important progress has been made in understanding the dynamic interactions between pro-apoptotic and anti-apoptotic BCL-2 proteins. In particular, recent studies have delineated a stepwise model for the induction of MOMP. BCL-2 proteins are often dysregulated in cancer, leading to increased survival of abnormal cells; however, recent studies have paradoxically shown that apoptosis induction can under some circumstances drive tumor formation, perhaps by inducing compensatory proliferation under conditions of cellular stress. These observations underline the complexity of BCL-2 protein function in oncogenesis.

Protein homeostasis and the phenotypic manifestation of genetic diversity: principles and mechanisms

Changing a single nucleotide in a genome can have profound consequences under some conditions, but the same change can have no consequences under others. Indeed, organisms can be surprisingly robust to environmental and genetic perturbations. Yet, the mechanisms underlying such robustness are controversial. Moreover, how they might affect evolutionary change remains enigmatic. Here, we review the recently appreciated central role of protein homeostasis in buffering and potentiating genetic variation and discuss how these processes mediate the critical influence of the environment on the relationship between genotype and phenotype. Deciphering how robustness emerges from biological organization and the mechanisms by which it is overcome in changing environments will lead to a more complete understanding of both fundamental evolutionary processes and diverse human diseases.

Targeting nonhomologous end-joining through epidermal growth factor receptor inhibition: rationale and strategies for radiosensitization

DNA double-strand breaks (DSBs) are the most lethal type of DNA damage induced by ionizing radiation or chemotherapeutic drugs used to eradicate cancer cells. The ability of cancer cells to effectively repair DSBs significantly influences the outcome of therapeutic regimens. Therefore, a new and important area of clinical cancer research is the development of DNA repair inhibitors that can be used as radio- or chemosensitizers. Nonhomologous end joining (NHEJ) is the predominant pathway for the repair of radiation-induced DSBs. A series of recent reports indicates that the epidermal growth factor receptor (EGFR) or its downstream components may modulate NHEJ through direct interaction with the DNA repair enzyme, DNA-dependent protein kinase. Because EGFR is overexpressed or activated in many cancers, these findings provide a compelling rationale for combining radiotherapy with therapies that block EGFR or its downstream signaling components. In this review, we delineate how these novel connections between a cell-surface receptor (EGFR) and a predominantly nuclear event (NHEJ) provide vulnerable nodes that can be selectively targeted to improve cancer therapy.

Integrated computational model of cell cycle and checkpoint reveals different essential roles of Aurora-A and Plk1 in mitotic entry

Understanding the regulation of mitotic entry is one of the most important goals of modern cell biology, and computational modeling of mitotic entry has been a subject of several recent studies. However, there are still many regulation mechanisms that remain poorly characterized. Two crucial aspects are how mitotic entry is controlled by its upstream regulators Aurora-A and Plk1, and how mitotic entry is coordinated with other biological events, especially G2/M checkpoint. In this context, we reconstructed a comprehensive computational model that integrates the mitotic entry network and the G2/M checkpoint system. Computational simulation of this model and subsequent experimental verification revealed that Aurora-A and Plk1 are redundant to the activation of cyclin B/Cdk1 during normal mitotic entry, but become especially important for cyclin B/Cdk1 activation during G2/M checkpoint recovery. Further analysis indicated that, in response to DNA damage, Chk1-mediated network rewiring makes cyclin B/Cdk1 more sensitive to the down-regulation of Aurora-A and Plk1. In addition, we demonstrated that concurrently targeting Aurora-A and Plk1 during G2/M checkpoint recovery achieves a synergistic effect, which suggests the combinational use of Aurora-A and Plk1 inhibitors after chemotherapy or radiotherapy. Thus, the results presented here provide novel insights into the regulation mechanism of mitotic entry and have potential value in cancer therapy.

DNA damage and DNA replication stress in yeast models of aging

DNA damage DNA damage is an important factor in aging in all eukaryotes. Although connections between DNA damage DNA damage and aging have been extensively investigated in complex organisms, only a relatively few studies have investigated DNA damage DNA damage as an aging factor in the model organism S. cerevisiae. Several of these studies point to DNA replication stress DNA replication stress as a cause of age-dependent DNA damage DNA damage in the replicative model of aging, which measures how many times budding yeast cells divide before they senesce and die. Even fewer studies have investigated how DNA damage DNA damage contributes to aging in the chronological aging chronological aging model, which measures how long cells in stationary phase cultures retain reproductive capacity. DNA replication stress DNA replication stress also has been implicated as a factor in chronological aging chronological aging . Since cells in stationary phase are generally considered to be "post-mitotic" and to reside in a quiescent G0/G1 state, the notion that defects in DNA replication might contribute to chronological aging chronological aging appears to be somewhat paradoxical. However, the results of recent studies suggest that a significant fraction of cells in stationary phase cultures are not quiescent, especially in experiments that employ defined medium, which is frequently employed to assess chronological lifespan. Most cells that fail to achieve quiescence remain in a viable, but non-dividing state until they eventually die, similar to the senescent state in mammalian cells. In this chapter we discuss the role of DNA damage DNA damage and DNA replication stress DNA replication stress in both replicative and chronological aging chronological aging in S. cerevisiae. We also discuss the relevance of these findings to the emerging view that DNA damage DNA damage and DNA replication stress DNA replication stress are important components of the senescent state that occurs at early stages of cancer.

The integration of a Stat3 specific peptide aptamer into the thioredoxin scaffold protein strongly enhances its inhibitory potency

We are characterizing peptides which are able to interact with functional domains of oncoproteins and thus inhibit their activity. The yeast two-hybrid system was used to derive a peptide sequence which specifically interacts with the dimerization domain of the transcription factor Stat3. The activated form of Stat3 is required for the survival of many transformed cells and Stat3 inhibition can cause tumor cell death. The genetic selection of specific peptide sequences from random peptide libraries requires the integration into a scaffold protein and the expression in yeast cells. The scaffold protein, a variant of the human thioredoxin protein, has previously been optimized and also allows for effective bacterial expression of the recombinant protein and the cellular uptake of the purified, recombinant protein. We investigated the contributions of the scaffold protein to the inhibitory properties of rS3-PA. For this purpose we compared rS3-PA in which the ligand peptide is embedded within the thioredoxin scaffold protein with a minimal Stat3-interacting peptide sequence. sS3-P45 is a synthetic peptide of 45 amino acids in length and consists only of the Stat3-binding sequence of 20 amino acids, a protein transduction domain (PTD) and a Flag-tag. Both, the recombinant rS3-PA of 19.3 kDa and the synthetic sS3-P45 of 5.1 kDa, were taken up into the cytoplasm of cells by the PTD-mediated transduction process, inhibited Stat3 target gene expression and caused the death of Stat3-dependent tumor cells. Stat3-independent normal cells were unaffected. rS3-PA effectively inhibited Stat3 function at 2 μM, however, sS3-P45 was required at a concentration of 100 μM to exert the same effects. The more potent action of rS3-PA is most probably due to a conformational stabilization of the Stat3-interacting peptide in the context of the scaffold protein.

Discovery and SAR of 5-(3-chlorophenylamino)benzo[c][2,6]naphthyridine-8-carboxylic acid (CX-4945), the first clinical stage inhibitor of protein kinase CK2 for the treatment of cancer

Herein we chronicle the discovery of CX-4945 (25n), a first-in-class, orally bioavailable ATP-competitive inhibitor of protein kinase CK2 in clinical trials for cancer. CK2 has long been considered a prime cancer drug target because of the roles of deregulated and overexpressed CK2 in cancer-promoting prosurvival and antiapoptotic pathways. These biological properties as well as the suitability of CK2's small ATP binding site for the design of selective inhibitors, led us to fashion novel therapeutic agents for cancer. The optimization leading to 25n (K(i) = 0.38 nM) was guided by molecular modeling, suggesting a strong binding of 25n resulting from a combination of hydrophobic interactions, an ionic bridge with Lys68, and hydrogen bonding with the hinge region. 25n was found to be highly selective, orally bioavailable across species (20-51%) and efficacious in xenograft models. The discovery of 25n will allow the therapeutic targeting of CK2 in humans for the first time.

Targeted therapies in cancer - challenges and chances offered by newly developed techniques for protein analysis in clinical tissues

In recent years, new anticancer therapies have accompanied the classical approaches of surgery and radio- and chemotherapy. These new forms of treatment aim to inhibit specific molecular targets namely altered or deregulated proteins, which offer the possibility of individualized therapies.The specificity and efficiency of these new approaches, however, bring about a number of challenges. First of all, it is essential to specifically identify and quantify protein targets in tumor tissues for the reasonable use of such targeted therapies. Additionally, it has become even more obvious in recent years that the presence of a target protein is not always sufficient to predict the outcome of targeted therapies. The deregulation of downstream signaling molecules might also play an important role in the success of such therapeutic approaches. For these reasons, the analysis of tumor-specific protein expression profiles prior to therapy has been suggested as the most effective way to predict possible therapeutic results. To further elucidate signaling networks underlying cancer development and to identify new targets, it is necessary to implement tools that allow the rapid, precise, inexpensive and simultaneous analysis of many network components while requiring only a small amount of clinical material.Reverse phase protein microarray (RPPA) is a promising technology that meets these requirements while enabling the quantitative measurement of proteins. Together with recently developed protocols for the extraction of proteins from formalin-fixed, paraffin-embedded (FFPE) tissues, RPPA may provide the means to quantify therapeutic targets and diagnostic markers in the near future and reliably screen for new protein targets.With the possibility to quantitatively analyze DNA, RNA and protein from a single FFPE tissue sample, the methods are available for integrated patient profiling at all levels of gene expression, thus allowing optimal patient stratification for individualized therapies.

L3MBTL1 polycomb protein, a candidate tumor suppressor in del(20q12) myeloid disorders, is essential for genome stability

The l3mbtl1 gene is located on the long arm of chromosome 20 (q12), within a region commonly deleted in several myeloid malignancies. L3MBTL1 is a human homolog of the Drosophila polycomb L(3)MBT tumor suppressor protein and thus a candidate tumor suppressor in del(20q12) myeloid disorders. We used the loss-of-function approach to explore the possible tumor suppressive mechanism of L3MBTL1 and found that depletion of L3MBTL1 from human cells causes replicative stress, DNA breaks, activation of the DNA damage response, and genomic instability. L3MBTL1 interacts with Cdc45, MCM2-7 and PCNA, components of the DNA replication machinery, and is required for normal replication fork progression, suggesting that L3MBTL1 causes DNA damage, at least in part, by perturbing DNA replication. An activated DNA damage response and genomic instability are common features in tumorigenesis and a consequence of overexpression of many oncogenes. We propose that the loss of L3MBTL1 contributes to the development of 20q(-) hematopoietic malignancies by inducing replicative stress, DNA damage, and genomic instability.

Autophagy is essential to suppress cell stress and to allow BCR-Abl-mediated leukemogenesis

Hematopoietic cells normally require cell extrinsic signals to maintain metabolism and survival. In contrast, cancer cells can express constitutively active oncogenic kinases such as BCR-Abl that promote these processes independent of extrinsic growth factors. When cells receive insufficient growth signals or when oncogenic kinases are inhibited, glucose metabolism decreases and the self-digestive process of autophagy is elevated to degrade bulk cytoplasm and organelles. While autophagy has been proposed to provide a cell-intrinsic nutrient supply for mitochondrial oxidative metabolism and to maintain cellular homeostasis through degradation of damaged organelles or protein aggregates, its acute role in growth factor deprivation or inhibition of oncogenic kinases remains poorly understood. We therefore developed a growth factor-dependent hematopoietic cell culture model in which autophagy can be acutely disrupted through conditional Cre-mediated excision of the autophagy-essential gene Atg3. Treated cells rapidly lost their ability to perform autophagy and underwent cell cycle arrest and apoptosis. While Atg3 was essential for optimal upregulation of mitochondrial oxidative pathways in growth factor withdrawal, this metabolic contribution of autophagy did not appear critical for cell survival, as provision of exogenous pyruvate or lipids could not completely rescue Atg3-deficiency. Instead, autophagy suppressed a stress response that otherwise led to p53 phosphorylation and upregulation of p21 and the pro-apoptotic Bcl-2 family protein Puma. Importantly, BCR-Abl-expressing cells had low basal levels of autophagy but were highly dependent on this process, and rapidly underwent apoptosis upon disruption of autophagy through Atg3 deletion or treatment with chemical autophagy inhibitors. This dependence on autophagy extended in vivo, as Atg3 deletion also prevented BCR-Abl-mediated leukemogenesis in a cell transfer model. Together these data demonstrate a critical role for autophagy to mitigate cell stress, and that cells expressing the oncogenic kinase BCR-Abl appear particularly dependent on autophagy for cell survival and leukemogenesis.

MicroRNA functions in stress responses

MicroRNAs (miRNAs) are a class of ∼22 nucleotide short noncoding RNAs that play key roles in fundamental cellular processes, including how cells respond to changes in environment or, broadly defined, stresses. Responding to stresses, cells either choose to restore or reprogram their gene expression patterns. This decision is partly mediated by miRNA functions, in particular by modulating the amount of miRNAs, the amount of mRNA targets, or the activity/mode of action of miRNA-protein complexes. In turn, these changes determine the specificity, timing, and concentration of gene products expressed upon stresses. Dysregulation of these processes contributes to chronic diseases, including cancers.

The DNA damage response: making it safe to play with knives

Damage to our genetic material is an ongoing threat to both our ability to faithfully transmit genetic information to our offspring as well as our own survival. To respond to these threats, eukaryotes have evolved the DNA damage response (DDR). The DDR is a complex signal transduction pathway that has the ability to sense DNA damage and transduce this information to the cell to influence cellular responses to DNA damage. Cells possess an arsenal of enzymatic tools capable of remodeling and repairing DNA; however, their activities must be tightly regulated in a temporal, spatial, and DNA lesion-appropriate fashion to optimize repair and prevent unnecessary and potentially deleterious alterations in the structure of DNA during normal cellular processes. This review will focus on how the DDR controls DNA repair and the phenotypic consequences of defects in these critical regulatory functions in mammals.

PROBING CANCER SIGNALING WITH RESONANT WAVEGUIDE GRATING BIOSENSORS

IMPORTANCE OF THE FIELD: Cancer is a collection of diseases that arise from the progressive accumulation of genetic alterations in somatic cells. Genomic approaches have identified a great variety of genetic abnormalities associated with tumorigenesis, and molecular imaging and quantification assays have further elucidated the complex interactions within or between pathways. It is acknowledged that it is proteins, rather than genes, to fulfill most cellular functions; and signaling proteins largely operate through a large and complex network. To this end, cancer is mostly a pathway dysregulated disease - a small number of core pathways are dominate in aberrant cell growth leading to cancer. Thus, understanding the functional consequences of dysregulated and/or mutant signaling proteins in the context of native signaling networks is the frontier in cancer research. AREAS COVERED IN THIS REVIEW: This article reviews why resonant waveguide grating (RWG) biosensor cellular assays are considered to be integrative in nature, and how RWG biosensor can be used for mining the surface markers of cancer cells, and discovering core pathway(s) of cancer receptor signaling. WHAT THE READER WILL GAIN: The reader will gain an overview of cancer biology from pathway perspective, and have a glimpse of potential implications of integrative cellular assays, as promised by RWG biosensor, in cancer research and diagnosis. TAKE HOME MESSAGE: Successful approaches for developing next-generation anti-cancer therapies and diagnostic protocols should take into account that the dysregulation of oncogenic pathways is central to tumorigenesis. The biosensor cellular assays offer unprecedented advantage in characterizing cancer biology. However, significant challenges are also presented in deconvoluting and validating cellular mechanisms identified in cancer receptor signaling using these assays.

Invasive three-dimensional organotypic neoplasia from multiple normal human epithelia

Refined cancer models are required to assess the burgeoning number of potential targets for cancer therapeutics within a rapid and clinically relevant context. Here we utilize tumor-associated genetic pathways to transform primary human epithelial cells from epidermis, oropharynx, esophagus, and cervix into genetically defined tumors within a human 3-dimensional (3-D) tissue environment incorporating cell-populated stroma and intact basement membrane. These engineered organotypic tissues recapitulated natural features of tumor progression, including epithelial invasion through basement membrane, a complex process critically required for biologic malignancy in 90% of human cancers. Invasion was rapid, and potentiated by stromal cells. Oncogenic signals in 3-D tissue, but not 2-D culture, resembled gene expression profiles from spontaneous human cancers. Screening well-characterized signaling pathway inhibitors in 3-D organotypic neoplasia helped distil a clinically faithful cancer gene signature. Multi-tissue 3-D human tissue cancer models may provide an efficient and relevant complement to current approaches to characterize cancer progression.

Synthetic lethality: general principles, utility and detection using genetic screens in human cells

Synthetic lethality occurs when the simultaneous perturbation of two genes results in cellular or organismal death. Synthetic lethality also occurs between genes and small molecules, and can be used to elucidate the mechanism of action of drugs. This area has recently attracted attention because of the prospect of a new generation of anti-cancer drugs. Based on studies ranging from yeast to human cells, this review provides an overview of the general principles that underlie synthetic lethality and relates them to its utility for identifying gene function, drug action and cancer therapy. It also identifies the latest strategies for the large-scale mapping of synthetic lethalities in human cells which bring us closer to the generation of comprehensive human genetic interaction maps.

Molecular biology and anticancer drug discovery

The profound impact of molecular biology on the philosophy of how one should seek new cancer therapeutics cannot be overstated. It has enabled the discovery of unique drugs as well as the identification of new drug targets and biomarkers and the creation of powerful animal models. Nevertheless, the process of cancer drug discovery remains inherently complex and inefficient. This is partially a consequence of the requirement of any successful therapy to show differential effects toward tumor cells relative to nonmalignant cells. The goal of this chapter is to outline the impact of molecular biology on modern approaches to anticancer drug discovery and to highlight the continuing challenges.

KRIBB11 inhibits HSP70 synthesis through inhibition of heat shock factor 1 function by impairing the recruitment of positive transcription elongation factor b to the hsp70 promoter

Heat shock factor 1 (HSF1) is the master switch for heat shock protein (HSP) expression in eukaryotes. A synthetic chemical library was screened to identify inhibitors of HSF1 using a luciferase reporter under the control of a heat shock element. A compound named KRIBB11 (N(2)-(1H-indazole-5-yl)-N(6)-methyl-3-nitropyridine-2,6-diamine) was identified for its activity in abolishing the heat shock-induced luciferase activity with an IC(50) of 1.2 μmol/liter. When the cells were exposed to heat shock in the presence of KRIBB11, the induction of HSF1 downstream target proteins such as HSP27 and HSP70 was blocked. In addition, treatment of HCT-116 cells with KRIBB11 induced growth arrest and apoptosis. Markers of apoptosis, such as cleaved poly(ADP-ribose) polymerase, were detected after KRIBB11 treatment. Biotinyl-KRIBB11 was synthesized as an affinity probe for the identification of KRIBB11 target proteins. Using affinity chromatography and competition assays, KRIBB11 was shown to associate with HSF1 in vitro. Chromatin immunoprecipitation analysis showed that KRIBB11 inhibited HSF1-dependent recruitment of p-TEFb (positive transcription elongation factor b) to the hsp70 promoter. Finally, intraperitoneal treatment of nude mice with KRIBB11 at 50 mg/kg resulted in a 47.4% (p < 0.05) inhibition of tumor growth without body weight loss. Immunoblotting assays showed that the expression of HSP70 was lower in KRIBB11-treated tumor tissue than in control tissues. Because HSPs are expressed at high levels in a wide range of tumors, these results strengthen the rationale for targeting HSF1 in cancer therapy.

Sulf-2: an extracellular modulator of cell signaling and a cancer target candidate

IMPORTANCE OF THE FIELD

Sulf-1 and Sulf-2 are sulfatases that edit the sulfation status of heparan sulfate proteoglycans (HSPGs) on the outside of cells and regulate a number of critical signaling pathways. The Sulfs are dysregulated in many cancers with Sulf-2 in particular implicated as a driver of carcinogenesis in NSCLC, pancreatic cancer and hepatocellular carcinoma.

AREAS COVERED IN THIS REVIEW

This review describes the novel activity of the Sulfs in altering the sulfation pattern of HSPG chains on the outside of cells. Thereby, the Sulfs can change the binding of growth factors to these chains and can either promote (e.g., Wnt) or inhibit (e.g., fibroblast growth factor-2) signaling. The review focuses on the widespread upregulation of both Sulfs in cancers and summarizes the evidence that Sulf-2 promotes the transformed behavior of several types of cancer cells in vitro as well as their tumorigenicity in vivo.

WHAT THE READER WILL GAIN

Sulf-2 is a bonafide candidate as a cancer-causing agent in NSCLC and other cancers in which it is upregulated.

TAKE HOME MESSAGE

Sulf-2 is an extracellular enzyme and as such would be an attractive therapeutic target for the treatment of NSCLC and other cancers.

Global downstream pathway analysis reveals a dependence of oncogenic NF-E2-related factor 2 mutation on the mTOR growth signaling pathway

In multicellular organisms, adaptive responses to oxidative stress are regulated by NF-E2-related factor 2 (NRF2), a master transcription factor of antioxidant genes and phase II detoxifying enzymes. Aberrant activation of NRF2 by either loss-of-function mutations in the Keap1 gene or gain-of-function mutations in the Nrf2 gene occurs in a wide range of human cancers, but details of the biological consequences of NRF2 activation in the cancer cells remain unclear. Here, we report that mutant NRF2 induces epithelial cell proliferation, anchorage-independent growth, and tumorigenicity and metastasis in vivo. Genome-wide gene expression profiling revealed that mutant NRF2 affects diverse molecular pathways including the mammalian target of rapamycin (mTOR) pathway. Mutant NRF2 upregulates RagD, a small G-protein activator of the mTOR pathway, which was also overexpressed in primary lung cancer. Consistently, Nrf2-mutated lung cancer cells were sensitive to mTOR pathway inhibitors (rapamycin and NVP-BEZ235) in both in vitro and an in vivo xenograft model. The gene expression signature associated with mutant NRF2 was a marker of poor prognosis in patients with carcinoma of the head and neck region and lung. These results show that oncogenic Nrf2 mutation induces dependence on the mTOR pathway during carcinogenesis. Our findings offer a rationale to target NRF2 as an anticancer strategy, and they suggest NRF2 activation as a novel biomarker for personalized molecular therapies or prognostic assessment.

Translating cancer research into targeted therapeutics

The emphasis in cancer drug development has shifted from cytotoxic, non-specific chemotherapies to molecularly targeted, rationally designed drugs promising greater efficacy and less side effects. Nevertheless, despite some successes drug development remains painfully slow. Here, we highlight the issues involved and suggest ways in which this process can be improved and expedited. We envision an increasing shift to integrated cancer research and biomarker-driven adaptive and hypothesis testing clinical trials. The goal is the development of specific cancer medicines to treat the individual patient, with treatment selection being driven by a detailed understanding of the genetics and biology of the patient and their cancer.

Immunopathogenesis of lymphoma: focus on CCR4

Evading immune surveillance is one of the common hallmarks of cancer. Herein we describe two major evasion mechanisms in lymphoma, focusing on regulatory T (Treg) cells and C-C chemokine receptor 4 (CCR4) expressed on these cells. First, the tumor cells themselves function as Treg cells, characterized by expression of CCR4, contributing to tumor survival by downregulating host immunity. Second, CCR4 ligands are produced by tumor cells, which attract other CCR4(+) Treg cells to the vicinity of the tumor. CCR4(+) adult T-cell leukemia//lymphoma is an example of the former phenomenon, and Hodgkin lymphoma of the latter, for which an almost identical immunopathogenesis has been reported in many types of cancer. Awareness of the importance of CCR4 allows the rational design of more effective cancer treatments. Accordingly, we have developed a defucosylated anti-CCR4 mAb, the first therapeutic agent targeting CCR4 to be used clinically for cancer. The therapeutic anti-CCR4 mAb represents a promising treatment method for patients with CCR4(+) neoplasms by directly killing the cancer cells, but could also be used as a novel treatment strategy for many types of CCR4(-) cancers to overcome the suppressive effect of CCR4(+) Treg cells.

Loss of thioredoxin reductase 1 renders tumors highly susceptible to pharmacologic glutathione deprivation

Tumor cells generate substantial amounts of reactive oxygen species (ROS), engendering the need to maintain high levels of antioxidants such as thioredoxin (Trx)- and glutathione (GSH)-dependent enzymes. Exacerbating oxidative stress by specifically inhibiting these types of ROS-scavenging enzymes has emerged as a promising chemotherapeutic strategy to kill tumor cells. However, potential redundancies among the various antioxidant systems may constrain this simple approach. Trx1 and thioredoxin reductase 1 (Txnrd1) are upregulated in numerous cancers, and Txnrd1 has been reported to be indispensable for tumorigenesis. However, we report here that genetic ablation of Txnrd1 has no apparent effect on tumor cell behavior based on similar proliferative, clonogenic, and tumorigenic potential. This finding reflects widespread redundancies between the Trx- and GSH-dependent systems based on evidence of a bypass to Txnrd1 deficiency by compensatory upregulation of GSH-metabolizing enzymes. Because the survival and growth of Txnrd1-deficient tumors were strictly dependent on a functional GSH system, Txnrd1-/- tumors were highly susceptible to experimental GSH depletion in vitro and in vivo. Thus, our findings establish for the first time that a concomitant inhibition of the two major antioxidant systems is highly effective in killing tumor, highlighting a promising strategy to combat cancer.

Cell cycle and cell death in disease: past, present and future

Cell division and cell death are the two predominant physiological processes that regulate tissue homeostasis in the adult organism. The importance of dysregulation of these processes in the pathogenesis of major diseases, such as cancer, myocardial infarction, stroke, atherosclerosis, infection, inflammation and neurodegenerative disorders, is becoming increasingly evident. Hence, attempts to find modulators of the cell cycle and cell death programmes are being made with the hope of creating novel therapeutic approaches to the treatment of these diseases. It is clear that improved understanding of how cells balance life-and-death processes is crucial for this development. In view of this, a Nobel Symposium entitled 'The Cell Cycle and Apoptosis in Disease' was organized in conjunction with the celebration of the 200-year anniversary of the Karolinska Institute in 2010. The symposium focused on the importance of dysregulation of cell cycle/cell death programmes in the pathogenesis of human disease. Three comprehensive reviews based on presentations at this symposium are presented in this issue of the Journal of Internal Medicine. They include a discussion of autophagy in anticancer therapy, the description of a role for type 2 transglutaminase in Huntington's disease and the proposal that 'redox-sensing' mechanisms might act as an orthogonal control in cell cycle and apoptosis signalling.

Exploration of synthetic lethal interactions as cancer drug targets

In cancer research the quest continues to identify the Achilles’ heel of cancer. The ideal cancer drug targets are those that are essential in tumor cells but not in normal cells. Such targets are defined as cancer-specific vulnerabilities or as synthetic lethal interactions with cancer-specific genetic lesions. The search for synthetic lethal interactions focuses on proteins that are frequently mutated but elude pharmacological inhibition, for example, RAS, or proteins that are lost in cancer cells and by definition cannot be targeted, such as the tumor suppressor genes p53, APC and RB. These genetic interactions could yield alternative, effective targets for cancer treatment. However, it remains very difficult to predict or extrapolate these synthetic lethal interactions based on existing knowledge. With the discovery of RNAi, unbiased large-scale functional genomic screens for the identification of such targets have become possible potentially leading to major advances in the treatment of cancers. In this review we will discuss the biological basis of synthetic lethal interactions in relation to existing targeted therapeutics, lessons taught by targeted therapeutics already used in the clinic and the implementation of RNAi as tool to identify such synthetic lethal interactions.

Modeling human osteosarcoma in the mouse: From bedside to bench

Osteosarcoma (OS) is the most common primary tumour of bone, occurring predominantly in the second decade of life. High-dose cytotoxic chemotherapy and surgical resection have improved prognosis, with long-term survival for patients with localized (non-metastatic) disease approaching 70%. At presentation approximately 20% of patients have metastases and almost all patients with recurrent OS have metastatic disease and cure rates for patients with metastatic or recurrent disease remain poor (<20% survival). Over the past 20 years, considerable progress has been made in the understanding of OS pathogenesis, yet these insights have not translated into substantial therapeutic advances and clinical outcomes. Further progress is essential in order to develop molecularly based therapies that target both primary lesions as well as metastatic disease. The increasing sophistication with which gene expression can be modulated in the mouse, both positively and negatively in addition to temporally, has allowed for the recent generation of more faithful OS models than have previously been available. These murine OS models can recapitulate all aspects of the disease process, from initiation and establishment to invasion and dissemination to distant sites. The development and utilisation of murine models that faithfully recapitulate human osteosarcoma, complementing existing approaches using human and canine disease, holds significant promise in furthering our understanding of the genetic basis of the disease and, more critically, in advancing pre-clinical studies aimed at the rational development and trialing of new therapeutic approaches.

Fractionated radiation therapy can induce a molecular profile for therapeutic targeting

To examine the possibility of using fractionated radiation in a unique way with molecular targeted therapy, gene expression profiles of prostate carcinoma cells treated with 10 Gy radiation administered either as a single dose or as fractions of 2 Gy × 5 and 1 Gy × 10 were examined by microarray analysis. Compared to the single dose, the fractionated irradiation resulted in significant increases in differentially expressed genes in both cell lines, with more robust changes in PC3 cells than in DU145 cells. The differentially expressed genes (>twofold change; P < 0.05) were clustered and their ontological annotations evaluated. In PC3 cells genes regulating immune and stress response, cell cycle and apoptosis were significantly up-regulated by multifractionated radiation compared to single-dose radiation. Ingenuity Pathway Analysis (IPA) of the differentially expressed genes revealed that immune response and cardiovascular genes were in the top functional category in PC3 cells and cell-to-cell signaling in DU145 cells. RT-PCR analysis showed that a flexure point for gene expression occurred at the 6th-8th fraction and AKT inhibitor perifosine produced enhanced cell killing after 1 Gy × 8 fractionated radiation in PC3 and DU145 cells compared to single dose. This study suggests that fractionated radiation may be a uniquely exploitable, non-oncogene-addiction stress pathway for molecular therapeutic targeting.

Roles of fibroblast growth factor receptors in carcinogenesis

The fibroblast growth factor receptors (FGFR) play essential roles both during development and in the adult. Upon ligand binding, FGFRs induce intracellular signaling networks that tightly regulate key biological processes, such as cell proliferation, survival, migration, and differentiation. Deregulation of FGFR signaling can thus alter tissue homeostasis and has been associated with several developmental syndromes as well as with many types of cancer. In human cancer, FGFRs have been found to be deregulated by multiple mechanisms, including aberrant expression, mutations, chromosomal rearrangements, and amplifications. In this review, we will give an overview of the main FGFR alterations described in human cancer to date and discuss their contribution to cancer progression.

Preclinical evaluation of AMG 900, a novel potent and highly selective pan-aurora kinase inhibitor with activity in taxane-resistant tumor cell lines

In mammalian cells, the aurora kinases (aurora-A, -B, and -C) play essential roles in regulating cell division. The expression of aurora-A and -B is elevated in a variety of human cancers and is associated with high proliferation rates and poor prognosis, making them attractive targets for anticancer therapy. AMG 900 is an orally bioavailable, potent, and highly selective pan-aurora kinase inhibitor that is active in taxane-resistant tumor cell lines. In tumor cells, AMG 900 inhibited autophosphorylation of aurora-A and -B as well as phosphorylation of histone H3 on Ser(10), a proximal substrate of aurora-B. The predominant cellular response of tumor cells to AMG 900 treatment was aborted cell division without a prolonged mitotic arrest, which ultimately resulted in cell death. AMG 900 inhibited the proliferation of 26 tumor cell lines, including cell lines resistant to the antimitotic drug paclitaxel and to other aurora kinase inhibitors (AZD1152, MK-0457, and PHA-739358), at low nanomolar concentrations. Furthermore, AMG 900 was active in an AZD1152-resistant HCT116 variant cell line that harbors an aurora-B mutation (W221L). Oral administration of AMG 900 blocked the phosphorylation of histone H3 in a dose-dependent manner and significantly inhibited the growth of HCT116 tumor xenografts. Importantly, AMG 900 was broadly active in multiple xenograft models, including 3 multidrug-resistant xenograft models, representing 5 tumor types. AMG 900 has entered clinical evaluation in adult patients with advanced cancers and has the potential to treat tumors refractory to anticancer drugs such as the taxanes.

Profiling the cancer genome

Cancer profiling studies have had a profound impact on our understanding of the biology of cancers in a number of ways, including providing insights into the biological heterogeneity of specific cancer types, identification of novel oncogenes and tumor suppressors, and defining pathways that interact to drive the growth of individual cancers. Several large-scale genomic studies are underway that aim to catalog all biologically significant mutational events in each cancer type, and these findings will allow researchers to understand how mutational networks function within individual tumors. The identification of molecular predictive and prognostic tools to facilitate treatment decisions is an important step for individualized patient therapy and, ultimately, in improving patient outcomes. Whereas there are still significant challenges to implementing genomic testing and targeted therapy into routine clinical practice, rapid technological advancements provide hope for overcoming these obstacles.