Utilizing targeted cancer therapeutic agents in combination: novel approaches and urgent requirements

A synergetic screening approach with companion effector for combination therapy: application to retinoblastoma

For many cancers, the lack of potency and the toxicity of current drugs limits the dose achievable in patients and the efficacy of treatment. Among them, retinoblastoma is a rare cancer of the eye for which better chemotherapeutic options are needed. Combination therapy is a compelling approach to enhance the efficacy of current treatment, however clinical trials to test rationally designed combinations of approved drugs are slow and expensive, and limited by our lack of in-depth knowledge of drug specificity. Since many patients already turn to nutraceuticals in hopes of improving their condition, we hypothesized that certain approved drugs could potentially synergize with widely consumed supplements. Following this hypothesis, we devised an alternative screening strategy aimed at taking advantage of a bait compound such as a nutraceutical with potential therapeutic benefits but low potency, by screening chemical libraries for approved drugs that synergize with this companion effector. As a proof of concept, we sought to identify approved drugs with synergetic therapeutic effects toward retinoblastoma cells in combination with the antioxidant resveratrol, popular as a supplement. We systematically tested FDA-approved drugs and known bioactives seeking to identify such pairs, which led to uncovering only a few additive combinations; but to our surprise, we identified a class of anticancer drugs widely used in the clinic whose therapeutic effect is antagonized with resveratrol. Our observations could explain in part why some patients do not respond well to treatment. Our results validate this alternative approach, and we expect that our companion effector strategy could significantly impact both drug discovery and the nutraceutical industry.

Development of therapeutic combinations targeting major cancer signaling pathways

Signaling networks play key homeostatic processes in living organisms but are commonly hijacked in oncogenesis. Prominent examples include genetically altered receptor tyrosine kinases and dysregulated intracellular signaling molecules. The discovery and development of targeted therapies against such oncogenic proteins has imparted clinical benefit. Nevertheless, concerns remain about the limited single-agent efficacy and narrow therapeutic indices of many of these antitumor agents. Moreover, it is apparent that oncogenic proteins comprise complex signaling networks that interact through crosstalk and feedback loops, which modify therapeutic vulnerability. These complexities mandate the study of drug combinations, which will also become necessary to reverse tumor drug resistance. Here, we outline the challenges associated with rational drug codevelopment strategies, with a focus on the importance of analytically validated biomarkers for patient selection and pharmacokinetic-pharmacodynamic (PK-PD) studies. Overall, the most informative clinical studies of novel combinations will have the following characteristics: robust scientific hypotheses leading to their selection; supportive preclinical data from contextually appropriate preclinical model systems; sufficient preclinical PK data to inform on the risk of drug-drug interactions; and detailed PD studies to determine the biologically active dose range for each agent. Toward this end, several novel clinical trial designs may be envisioned to accelerate successful drug combination development while minimizing the risk of late drug combination attrition. Although considerable challenges remain, these efforts may enable important steps to be taken toward more durable therapeutic control of many cancers.

KRAS mutant tumor subpopulations can subvert durable responses to personalized cancer treatments

KRAS mutations in colorectal and lung cancers predict failure to respond to therapies that target the EGFR. Significant percentages of patients with KRAS wild-type tumors also fail to respond to these therapies. Relapse occurs in patients with KRAS wild-type and mutant tumors, with moderately longer progression-free survival in patients with KRAS wild-type tumors. Colon and lung tumors frequently carry KRAS mutant tumor subpopulations not detected by DNA sequencing. This suggests detected and undetected KRAS mutant subpopulations in colon and lung tumors are undermining the efficacy of anti-EGFR therapies. Therefore, consideration should be given to combining therapies that target KRAS mutant cells with those that downregulate EGFR signaling. As tumors are frequently polyclonal in origin and comprised of distinct clonal populations carrying complementing genetic and/or epigenetic lesions, preclinical models that assess the efficacy of combination therapies in the context of heterogeneous tumor cell populations will be essential for progress in this area.

Systems biology for molecular life sciences and its impact in biomedicine

Modern systems biology is already contributing to a radical transformation of molecular life sciences and biomedicine, and it is expected to have a real impact in the clinical setting in the next years. In this review, the emergence of systems biology is contextualized with a historic overview, and its present state is depicted. The present and expected future contribution of systems biology to the development of molecular medicine is underscored. Concerning the present situation, this review includes a reflection on the "inflation" of biological data and the urgent need for tools and procedures to make hidden information emerge. Descriptions of the impact of networks and models and the available resources and tools for applying them in systems biology approaches to molecular medicine are provided as well. The actual current impact of systems biology in molecular medicine is illustrated, reviewing two cases, namely, those of systems pharmacology and cancer systems biology. Finally, some of the expected contributions of systems biology to the immediate future of molecular medicine are commented.

Design and conduct of early clinical studies of two or more targeted anticancer therapies: recommendations from the task force on Methodology for the Development of Innovative Cancer Therapies

The Methodology for the Development of Innovative Cancer Therapies (MDICT) task force considered aspects of the design and conduct of early (phase I and II) studies of combinations of molecular targeted agents during their 2012 meeting. The task force defined necessary non-clinical data, such as evidence of additive or synergistic effects in multiple molecularly credentialed and validated models, and appropriate pharmacodynamic marker development. A robust hypothesis was considered critical while non-clinical pharmacokinetic studies were also considered valuable. Clinical trials should include clear objectives that will prove or disprove the hypothesis. Predictive biomarkers/classifiers should be explored in phase I studies, rather than used to select patients. Trial design should be efficient and flexible rather than based on a strict progression from phase I to II to III; researchers could consider phase I studies with an expansion cohort, Phase I/II designs or phase II studies with a safety run in. Pharmacokinetics are recommended when interactions or overlapping toxicity is expected. Pharmacodynamic evaluations should be considered especially in a subset of patients closest to the recommended dose; an attempt should be made to validate surrogate tissues to enable inclusion for all patients. Schedule and or dose should be formally explored for e.g. with a randomised or an adaptive design. Data and knowledge sharing was strongly recommended, including the creation of formal or informal consortia of laboratories with individual expertise in pathway or target based models, collaboration between companies to ensure that agents which are 'best in class' are combined, and the development of databases which will be able to inform the development of future recommendations/guidelines.

Safety and feasibility of targeted agent combinations in solid tumours

The plethora of novel molecular-targeted agents (MTAs) has provided an opportunity to selectively target pathways involved in carcinogenesis and tumour progression. Combination strategies of MTAs are being used to inhibit multiple aberrant pathways in the hope of optimizing antitumour efficacy and to prevent development of resistance. While the selection of specific agents in a given combination has been based on biological considerations (including the role of the putative targets in cancer) and the interactions of the agents used in combination, there has been little exploration of the possible enhanced toxicity of combinations resulting from alterations in multiple signalling pathways in normal cell biology. Owing to the complex networks and crosstalk that govern normal and tumour cell proliferation, inhibiting multiple pathways with MTA combinations can result in unpredictable disturbances in normal physiology. This Review focuses on the main toxicities and the lack of tolerability of some common MTA combinations, particularly where evidence of enhanced toxicity compared to either agent alone is documented or there is development of unexpected toxicity. Toxicities caused by MTA combinations highlight the need to introduce new preclinical testing paradigms early in the drug development process for the assessment of chronic toxicities resulting from such combinations.

Assessing the efficacy of molecularly targeted agents on cell line-based platforms by using system identification

Background

Molecularly targeted agents (MTAs) are increasingly used for cancer treatment, the goal being to improve the efficacy and selectivity of cancer treatment by developing agents that block the growth of cancer cells by interfering with specific targeted molecules needed for carcinogenesis and tumor growth. This approach differs from traditional cytotoxic anticancer drugs. The lack of specificity of cytotoxic drugs allows a relatively straightforward approach in preclinical and clinical studies, where the optimal dose has usually been defined as the "maximum tolerated dose" (MTD). This toxicity-based dosing approach is founded on the assumption that the therapeutic anticancer effect and toxic effects of the drug increase in parallel as the dose is escalated. On the contrary, most MTAs are expected to be more selective and less toxic than cytotoxic drugs. Consequently, the maximum therapeutic effect may be achieved at a "biologically effective dose" (BED) well below the MTD. Hence, dosing study for MTAs should be different from cytotoxic drugs. Enhanced efforts to molecularly characterize the drug efficacy for MTAs in preclinical models will be valuable for successfully designing dosing regimens for clinical trials.

Results

A novel preclinical model combining experimental methods and theoretical analysis is proposed to investigate the mechanism of action and identify pharmacodynamic characteristics of the drug. Instead of fixed time point analysis of the drug exposure to drug effect, the time course of drug effect for different doses is quantitatively studied on cell line-based platforms using system identification, where tumor cells' responses to drugs through the use of fluorescent reporters are sampled over a time course. Results show that drug effect is time-varying and higher dosages induce faster and stronger responses as expected. However, the drug efficacy change along different dosages is not linear; on the contrary, there exist certain thresholds. This kind of preclinical study can provide valuable suggestions about dosing regimens for the in vivo experimental stage to increase productivity.

Managing drug resistance in cancer: lessons from HIV therapy

Drug resistance is a common cause of treatment failure for HIV infection and cancer. The high mutation rate of HIV leads to genetic heterogeneity among viral populations and provides the seed from which drug-resistant clones emerge in response to therapy. Similarly, most cancers are characterized by extensive genetic, epigenetic, transcriptional and cellular diversity, and drug-resistant cancer cells outgrow their non-resistant peers in a process of somatic evolution. Patient-specific combination of antiviral drugs has emerged as a powerful approach for treating drug-resistant HIV infection, using genotype-based predictions to identify the best matched combination therapy among several hundred possible combinations of HIV drugs. In this Opinion article, we argue that HIV therapy provides a 'blueprint' for designing and validating patient-specific combination therapies in cancer.

Combination Agents Versus Multi-Targeted Agents – Pros and Cons

Cancer, in all its various forms, is perhaps the archetypical multi-factorial disease and it is therefore not surprising that single-target drugs are rarely useful as anti-cancer agents when used on their own. Traditional cancer therapy has relied on effective drug combinations and the more recent emergence of compounds that simultaneously modulate multiple targets has added to the oncology armoury and raised the question as to which approach, drug combinations or single compound multi-targeted drug, is to be preferred. This chapter reviews the basis for combining existing drugs and how these combinations are selected, and compares these with multi-targeted drugs (MTDs) such as sunitinib, a broad-spectrum kinase inhibitor that inhibits a range of growth factors. Whether using physical combinations or MTDs, or indeed combinations of MTDs, the choice of which targets and which pathways to attack is crucial and the rationale for selecting these is discussed in detail. The NCI Cancer Therapy Evaluation Program, designed to facilitate trials of novel combinations, will aid in the rational selection of targets and pathways to combine in future MTDs. The pros and cons of combinations and MTDs in terms of the relative challenges in clinical development are examined, and the systematic use of biomarkers, better approaches to patient selection, and improved design of trials to take account of the heightened potential for acute and delayed on- and off-target toxicities are highlighted.

Moving molecular targeted drug therapy towards personalized medicine: issues related to clinical trial design

With the event of new Molecular targets, clinical trial design requirements to perform these trials are changing. This paper discusses some of the considerations that need to be taken into account when designing a trial, including those trials that assess combinations of targets.

Combined inhibition of EGFR and CK2 augments the attenuation of PI3K-Akt-mTOR signaling and the killing of cancer cells

Ser/Thr protein kinase CK2 regulates multiple processes that play important roles in the sensitivity of cancer to epidermal growth factor receptor targeting therapeutics, including PI3K-Akt-mTOR signaling, Hsp90 activity, and inhibition of apoptosis. We hypothesized that top-down inhibition of EGFR, combined with lateral suppression of multiple oncogenic pathways by targeting CK2, would create a pharmacologic synthetic lethal event and result in an improved cancer therapy compared to EGFR inhibition alone. This hypothesis was tested by combining CX-4945, a first-in-class clinical stage inhibitor of CK2, with the EGFR tyrosine kinase inhibitor, erlotinib, in vitro and in vivo in models of non-small cell lung carcinoma, NCI-H2170, and squamous cell carcinoma, A431. Our results demonstrate that combination of CX-4945 with erlotinib results in enhanced attenuation of the PI3K-Akt-mTOR pathway. We also observed an increase in apoptosis, synergistic killing of cancer cells in vitro, as well as improved antitumor efficacy in vivo. Taken together, these data position CK2 as a valid pharmacologic target for drug combinations and support further evaluation of CX-4945 in combination with EGFR targeting agents.

Synergistic activity of the Hsp90 inhibitor ganetespib with taxanes in non-small cell lung cancer models

Systemic chemotherapy using two-drug platinum-based regimens for the treatment of advanced stage non-small cell lung cancer (NSCLC) has largely reached a plateau of effectiveness. Accordingly, efforts to improve survival and quality of life outcomes have more recently focused on the use of molecularly targeted agents, either alone or in combination with standard of care therapies such as taxanes. The molecular chaperone heat shock protein 90 (Hsp90) represents an attractive candidate for therapeutic intervention, as its inhibition results in the simultaneous blockade of multiple oncogenic signaling cascades. Ganetespib is a non-ansamycin inhibitor of Hsp90 currently under clinical evaluation in a number of human malignancies, including NSCLC. Here we show that ganetespib potentiates the cytotoxic activity of the taxanes paclitaxel and docetaxel in NSCLC models. The combination of ganetespib with paclitaxel, docetaxel or another microtubule-targeted agent vincristine resulted in synergistic antiproliferative effects in the H1975 cell line in vitro. These benefits translated to improved efficacy in H1975 xenografts in vivo, with significantly enhanced tumor growth inhibition observed in combination with paclitaxel and tumor regressions seen with docetaxel. Notably, concurrent exposure to ganetespib and docetaxel improved antitumor activity in 5 of 6 NSCLC xenograft models examined. Our data suggest that the improved therapeutic indices are likely to be mechanistically multifactorial, including loss of pro-survival signaling and direct cell cycle effects resulting from Hsp90 modulation by ganetespib. Taken together, these findings provide preclinical evidence for the use of this combination to treat patients with advanced NSCLC.

Intermittent administration of MEK inhibitor GDC-0973 plus PI3K inhibitor GDC-0941 triggers robust apoptosis and tumor growth inhibition

Combinations of MAP/ERK kinase (MEK) and phosphoinositide 3-kinase (PI3K) inhibitors have shown promise in preclinical cancer models, leading to the initiation of clinical trials cotargeting these two key cancer signaling pathways. GDC-0973, a novel selective MEK inhibitor, and GDC-0941, a class I PI3K inhibitor, are in early stage clinical trials as both single agents and in combination. The discovery of these selective inhibitors has allowed investigation into the precise effects of combining inhibitors of two major signaling branches downstream of RAS. Here, we investigated multiple biomarkers in the mitogen-activated protein kinase (MAPK) and PI3K pathway to search for points of convergence that explain the increased apoptosis seen in combination. Using washout studies in vitro and alternate dosing schedules in mice, we showed that intermittent inhibition of the PI3K and MAPK pathway is sufficient for efficacy in BRAF and KRAS mutant cancer cells. The combination of GDC-0973 with the PI3K inhibitor GDC-0941 resulted in combination efficacy in vitro and in vivo via induction of biomarkers associated with apoptosis, including Bcl-2 family proapoptotic regulators. Therefore, these data suggest that continuous exposure of MEK and PI3K inhibitors in combination is not required for efficacy in preclinical cancer models and that sustained effects on downstream apoptosis biomarkers can be observed in response to intermittent dosing.

A 71-gene signature of TRAIL sensitivity in cancer cells

TNF-related apoptosis inducing ligand (TRAIL) is a promising anticancer agent because of its ability to selectively induce apoptosis in cancer cells but not in most normal cells. However, some cancer cells are resistant to TRAIL cytotoxicity thereby limiting its therapeutic efficacy. Using genome-wide mRNA expression profiles from the NCI60 panel and their differential sensitivities to TRAIL-induced apoptosis, we have identified 71 genes whose expression levels are systemically higher in TRAIL-sensitive cell lines than resistant lines. The elevated expression of the 71 genes was able to accurately predict TRAIL sensitivity in the NCI60 training set and two test sets consisting of a total of 95 human cancer cell lines. Interestingly, the 71-gene signature is dominated by two functionally related gene families-interferon (IFN)-induced genes and the MHC genes. Consistent with this result, treatment with IFN-γ augmented TRAIL-induced apoptosis. The 71-gene signature could be evaluated clinically for predicting tumor response to TRAIL-related therapies.

Epigenetic drug discovery: targeting DNA methyltransferases

Epigenetic modification of DNA leads to changes in gene expression. DNA methyltransferases (DNMTs) comprise a family of nuclear enzymes that catalyze the methylation of CpG dinucleotides, resulting in an epigenetic methylome distinguished between normal cells and those in disease states such as cancer. Disrupting gene expression patterns through promoter methylation has been implicated in many malignancies and supports DNMTs as attractive therapeutic targets. This review focuses on the rationale of targeting DNMTs in cancer, the historical approach to DNMT inhibition, and current marketed hypomethylating therapeutics azacytidine and decitabine. In addition, we address novel DNMT inhibitory agents emerging in development, including CP-4200 and SGI-110, analogs of azacytidine and decitabine, respectively; the oligonucleotides MG98 and miR29a; and a number of reversible inhibitors, some of which appear to be selective against particular DNMT isoforms. Finally, we discuss future opportunities and challenges for next-generation therapeutics.

New approaches for pediatric rhabdomyosarcoma drug discovery: targeting combinatorial signaling

INTRODUCTION

Rhabdomyosarcomas (RMS) are rare heterogeneous pediatric tumors that are treated by surgery, chemotherapy and irradiation. New therapeutic approaches are needed, especially in the advanced stages to target the pro-oncogenic signals. Exploring the molecular interactions of the regulatory signals and their roles in the developmental aspects of different subtypes of RMS is essential to identify potential targets and develop new therapeutic drugs.

AREAS COVERED

Insights into different drug discovery approaches are discussed with specific emphasis on gene expression profiling, fusion protein, role of small interfering RNA (siRNA)- and microRNA (miRNA)-based discovery approaches, targeting cancer stem cells, and in vitro and in vivo model systems. Targeting some overexpressed signals along with the possibilities of combination therapy of validated drug targets is discussed. Additionally, methods to overcome the limitations of discovery-based research are briefly discussed.

EXPERT OPINION

Due to drug resistance, ineffective therapy in advanced stages and relapse, there is a demand to explore new drug targets and discovery approaches. Implementing miRNA-based profiling would reveal the extent of miR-based regulation, various biomarkers and potential targets in RMS. A suitable combination of innovative techniques and the use of model systems might assist the identification and validation of novel targets and drug discovery methods. Combining specific drugs along with type-specific target inhibition of overexpressed mRNAs through siRNA approaches would enable the development of personalized therapy.

Anti-VEGF and beyond: shaping a new generation of anti-angiogenic therapies for cancer

The anti-angiogenic class of drugs is one of the few where representatives have gained international approval for clinical use in oncology during the past decade. Most of the biological and clinical activity of the currently available generation of anti-angiogenic drugs targets vascular endothelial growth factor (VEGF) and its related pathways. However, the clinical benefits associated with the use of these drugs have, so far, been limited. There is, therefore, an unmet need for biomarkers that can be used to identify patients who are most likely to benefit therapeutically and also to predict the best schedule and dosage for these drugs. Here, we discuss some of the emerging new combination strategies involving the approved anti-angiogenic drugs, some of the emerging targets associated with neoplastic angiogenesis and some novel agents used as a paradigm of the next generation of anti-angiogenic drugs.

Opportunities and challenges in the development of experimental drug combinations for cancer

It is becoming increasingly evident that cancers are dependent on a number of altered molecular pathways and can develop diverse mechanisms of resistance to therapy with single agents. Therefore, combination regimens may provide the best hope for effective therapies with durable effects. Despite preclinical data to support this notion, there are many challenges to the development of targeted combinations including scientific, economic, legal, and regulatory barriers. A discussion of these challenges and identification of models and best practices are presented with intent of aiding the research community in addressing real and perceived barriers to the development of combination therapies for cancer.

[Sleep and its pharmacologic treatment]

Background

The discovery of novel anticancer drugs is critical for the pharmaceutical research and development, and patient treatment. Repurposing existing drugs that may have unanticipated effects as potential candidates is one way to meet this important goal. Systematic investigation of efficient anticancer drugs could provide valuable insights into trends in the discovery of anticancer drugs, which may contribute to the systematic discovery of new anticancer drugs.

Results

In this study, we collected and analyzed 150 anticancer drugs approved by the US Food and Drug Administration (FDA). Based on drug mechanism of action, these agents are divided into two groups: 61 cytotoxic-based drugs and 89 target-based drugs. We found that in the recent years, the proportion of targeted agents tended to be increasing, and the targeted drugs tended to be delivered as signal drugs. For 89 target-based drugs, we collected 102 effect-mediating drug targets in the human genome and found that most targets located on the plasma membrane and most of them belonged to the enzyme, especially tyrosine kinase. From above 150 drugs, we built a drug-cancer network, which contained 183 nodes (150 drugs and 33 cancer types) and 248 drug-cancer associations. The network indicated that the cytotoxic drugs tended to be used to treat more cancer types than targeted drugs. From 89 targeted drugs, we built a cancer-drug-target network, which contained 214 nodes (23 cancer types, 89 drugs, and 102 targets) and 313 edges (118 drug-cancer associations and 195 drug-target associations). Starting from the network, we discovered 133 novel drug-cancer associations among 52 drugs and 16 cancer types by applying the common target-based approach. Most novel drug-cancer associations (116, 87%) are supported by at least one clinical trial study.

Conclusions

In this study, we provided a comprehensive data source, including anticancer drugs and their targets and performed a detailed analysis in term of historical tendency and networks. Its application to identify novel drug-cancer associations demonstrated that the data collected in this study is promising to serve as a fundamental for anticancer drug repurposing and development.