Predictive Value Tools as an Aid in Chemopreventive Agent Development.
ABSTRACT: Over 25 years, the National Cancer Institute's Division of Cancer Prevention has entered some 800 agents into a chemopreventive agent testing program. Two critical steps involve: 1) in vitro/in vivo morphologic assays and 2) animal tumor assays (incidence/multiplicity reduction). We sought to determine how accurately the earlier-stage (morphologic) assays predict efficacy in the later-stage (animal tumor) assays.Focusing on 210 agents tested in both morphologic and animal tumor assays, we carried out statistical modeling of how well the six most commonly used morphologic assays predicted drug efficacy in animal tumor assays. Using multimodel inference, three statistical models were generated to evaluate the ability of these six morphologic assays to predict tumor outcomes in three different sets of animal tumor assays: 1) all tumor types, 2) mammary cancer only, and 3) colon cancer only. Using this statistical modeling approach, each morphologic assay was assigned a value reflecting how strongly it predicted outcomes in each of the three different sets of animal tumor assays.We demonstrated differences in the predictive value of specific morphologic assays for positive animal tumor assay results. Some of the morphologic assays were strongly predictive of meaningful positive efficacy outcomes in animal tumor assays representing specific cancer types, particularly the aberrant crypt focus (ACF) assay for colon cancer. Moreover, less strongly predictive assays can be combined and sequenced, resulting in enhanced composite predictive ability.Predictive models such as these could be used to guide selection of preventive agents as well as morphologic and animal tumor assays, thereby improving the efficiency of our approach to chemopreventive agent development.
Project description:Cancer prevention research has drawn much attention worldwide. It is believed that some types of cancer can be prevented by following a healthy life style. Cancer chemoprevention by either natural or synthetic agents is a promising route towards lowering cancer incidence. In recent years, the concept of cancer chemoprevention has evolved greatly. Experimental studies in animal models demonstrate that the reversal or suppression of premalignant lesions by chemopreventive agents is achievable. Natural occurring agents such as dietary phytochemicals, tea polyphenols and resveratrol show chemopreventive activity in animal models. Moreover, clinical trials for testing the safety and efficacy of a variety of natural agents in preventing or treating human malignancy have been ongoing. Here, we summarize experimental data on the chemopreventive or tumor suppressive effects of several natural compounds including curcumin, (-)-epigallocatechin-3-gallate, resveratrol, indole-3-carbinol, and vitamin D.
Project description:Pancreatic cancer has a poor prognosis and is often diagnosed at an advanced stage, which makes it difficult to treat. The low survival rate of patients with pancreatic cancer points towards an increased need for novel therapeutic and chemopreventive strategies and also early detection of this disease. Increased consumption of fruits and vegetables has been associated with a reduced risk of pancreatic cancer. Synthetic and natural, diet-derived bioactive compounds have been evaluated as pancreatic cancer chemopreventive agents and have demonstrated various degrees of efficacy in cellular and in vivo animal models. Some chemopreventive agents (for example, curcumin or resveratrol) have also been reported to sensitize pancreatic cancer cells to standard chemotherapeutic drugs (for example, gemcitabine or erlotinib), which suggests that chemopreventive agents could potentially be used as potentiators of standard chemotherapy. Few clinical trials of pancreatic cancer chemopreventive agents have been completed and some are in early phases. Further development of pancreatic cancer chemopreventive agents may prove to be tremendously valuable for individuals at high risk of developing pancreatic cancer and patients who present with premalignant lesions. This Review discusses the current state of the pancreatic cancer chemoprevention field and highlights the challenges ahead.
Project description:Compared to the current knowledge on cancer chemotherapeutic agents, only limited information is available on the ability of organic compounds, such as drugs and/or natural products, to prevent or delay the onset of cancer. In order to evaluate chemical chemopreventive potentials and design novel chemopreventive agents with low to no toxicity, we developed predictive computational models for chemopreventive agents in this study. First, we curated a database containing over 400 organic compounds with known chemoprevention activities. Based on this database, various random forest and support vector machine binary classifiers were developed. All of the resulting models were validated by cross validation procedures. Then, the validated models were applied to virtually screen a chemical library containing around 23,000 natural products and derivatives. We selected a list of 148 novel chemopreventive compounds based on the consensus prediction of all validated models. We further analyzed the predicted active compounds by their ease of organic synthesis. Finally, 18 compounds were synthesized and experimentally validated for their chemopreventive activity. The experimental validation results paralleled the cross validation results, demonstrating the utility of the developed models. The predictive models developed in this study can be applied to virtually screen other chemical libraries to identify novel lead compounds for the chemoprevention of cancers.
Project description:Nonsteroidal anti-inflammatory drugs (NSAIDs) are effective cancer chemopreventive agents. However, chronic administration of NSAIDs is associated with significant side effects, mainly of the gastrointestinal tract. Given these limitations, we synthesized phospho-sulindac (P-S; OXT-328), a novel sulindac derivative.Here, we evaluated the safety and efficacy of P-S in preclinical models, including its mechanism of action with human colon cancer cell (HCCC) lines and animal tumor models.(1) Compared with sulindac, P-S is much more potent in inhibiting the growth of cultured HCCCs and more efficacious in preventing the growth of HT-29 xenografts in nude mice. P-S also prevents the growth of intestinal tumors in Apc/Min mice. (2) In combination with difluoromethylornithine (DFMO), P-S reduced tumor multiplicity in Apc/Min mice by 90%. (3) P-S is much safer than sulindac as evidenced by its in vitro toxicologic evaluation and animal toxicity studies. Mechanistically, P-S increases the intracellular levels of reactive oxygen and nitrogen species, which are key early mediators of its chemopreventive effect. Moreover, P-S induces spermidine/spermine N(1)-acetyltransferase enzymatic activity, and together with DFMO it reduces polyamine levels in vitro and in vivo.P-S displays considerable safety and efficacy, two pharmacologic properties that are essential for a potential cancer chemopreventive agent, and thus merits further evaluation.
Project description:In the current paradigm of anticancer drug development, candidate compounds are evaluated by testing their in vitro potency against molecular targets relevant to carcinogenesis, their effect on cultured cancer cells, and their ability to inhibit cancer growth in animal models. We discuss the key assumptions inherent in these approaches. In recent years, great emphasis has been placed on selecting for development compounds with nanomolar in vitro potency, expecting that they will be efficacious and safer based on the assumption that they can be used at lower doses ("the nanomolar rule"). However, this rule ignores critical parameters affecting efficacy and toxicity such as physiochemical and absorption, distribution, metabolism and excretion properties, off-target effects, and multitargeting activities. Thus, uncritical application of the nanomolar rule may reject efficacious compounds or select ineffective or toxic compounds. We present examples of efficacious chemotherapeutic (alkylating agents, hormonal agents, antimetabolites, thalidomide, and valproic acid) and chemopreventive (aspirin and sulindac) agents having millimolar potency and compounds with nanomolar potency (cyclooxygenase-2 inhibitors) that, nevertheless, failed or proved to be unsafe. The effect of candidate drugs on animal models of cancer is a better predictor of human drug efficacy; particularly useful are tumor xenografts. Given the cost of failure at clinical stages, it is imperative to keep in mind the limitations of the nanomolar rule and use relevant in vivo models early in drug discovery to prioritize candidates. Although in vivo models will continue having a major role in cancer drug development, more robust approaches that combine high predictive ability with simplicity and low cost should be developed.
Project description:In recent years, not only has the role of miRNAs in cancer become increasingly clear but also their utilization as potential biomarkers and therapeutic targets has gained ground. Although the importance of dietary stilbenes such as resveratrol and pterostilbene as anti-cancer agents is well recognized, our understanding of their miRNA-targeting capabilities is still limited. In our previous study, we reported that resveratrol downregulates PTEN-targeting members of the oncogenic miR-17 family, which are overexpressed in prostate cancer. This study investigates the resveratrol and pterostilbene induced miRNA-mediated regulation of PTEN in prostate cancer. Here, we show that both compounds decrease the levels of endogenous as well as exogenously expressed miR-17, miR-20a and miR-106b thereby upregulating their target PTEN. Using functional luciferase reporter assays, we demonstrate that ectopically expressed miR-17, miR-20a and miR-106b directly target PTEN 3'UTR to reduce its expression, an effect rescued upon treatment with resveratrol and pterostilbene. Moreover, while stable lentiviral expression of miR-17/106a significantly decreased PTEN mRNA and protein levels and conferred survival advantage to the cells, resveratrol and more so pterostilbene was able to dramatically suppress these effects. Further, pterostilbene through downregulation of miR-17-5p and miR-106a-5p expression both in tumors and systemic circulation, rescued PTEN mRNA and protein levels leading to reduced tumor growth in vivo. Our findings implicate dietary stilbenes as an attractive miRNA-mediated chemopreventive and therapeutic strategy, and circulating miRNAs as potential chemopreventive and predictive biomarkers for clinical development in prostate cancer.
Project description:Tetraploidy constitutes a genomically metastable state that can lead to aneuploidy and genomic instability. Tetraploid cells are frequently found in preneoplastic lesions, including intestinal cancers arising due to the inactivation of the tumor suppressor adenomatous polyposis coli (APC). Using a phenotypic screen, we identified resveratrol as an agent that selectively reduces the fitness of tetraploid cells by slowing down their cell cycle progression and by stimulating the intrinsic pathway of apoptosis. Selective killing of tetraploid cells was observed for a series of additional agents that indirectly or directly stimulate AMP-activated protein kinase (AMPK) including salicylate, whose chemopreventive action has been established by epidemiological studies and clinical trials. Both resveratrol and salicylate reduced the formation of tetraploid or higher-order polyploid cells resulting from the culture of human colon carcinoma cell lines or primary mouse epithelial cells lacking tumor protein p53 (TP53, best known as p53) in the presence of antimitotic agents, as determined by cytofluorometric and videomicroscopic assays. Moreover, oral treatment with either resveratrol or aspirin, the prodrug of salicylate, repressed the accumulation of tetraploid intestinal epithelial cells in the Apc(Min/+) mouse model of colon cancer. Collectively, our results suggest that the chemopreventive action of resveratrol and aspirin involves the elimination of tetraploid cancer cell precursors.
Project description:PURPOSE:Metastasis is responsible for the death of most cancer patients, yet few therapeutic agents are available which specifically target the molecular events that lead to metastasis. We recently showed that inactivating mutations in the tumor suppressor gene BAP1 are closely associated with loss of melanocytic differentiation in uveal melanoma (UM) and metastasis. The purpose of this study was to identify therapeutic agents that reverse the phenotypic effects of BAP1 loss in UM. EXPERIMENTAL DESIGN:In silico screens were done to identify therapeutic compounds predicted to differentiate UM cells using Gene Set Enrichment Analysis and Connectivity Map databases. Valproic acid (VPA), trichostatin A, LBH-589, and suberoylanilide hydroxamic acid were evaluated for their effects on UM cells using morphologic evaluation, MTS viability assays, bromodeoxyuridine incorporation, flow cytometry, clonogenic assays, gene expression profiling, histone acetylation and ubiquitination assays, and a murine xenograft tumorigenicity model. RESULTS:Histone deacetylase (HDAC) inhibitors induced morphologic differentiation, cell-cycle exit, and a shift to a differentiated, melanocytic gene expression profile in cultured UM cells. VPA inhibited the growth of UM tumors in vivo. CONCLUSIONS:These findings suggest that HDAC inhibitors may have therapeutic potential for inducing differentiation and prolonged dormancy of micrometastatic disease in UM.
Project description:Preclinical studies have shown that gefitinib, licofelone, atorvastatin, and ?-difluoromethylornithine (GLAD) are promising colon cancer chemopreventive agents. Because low-dose combination regimens can offer potential additive or synergistic effects without toxicity, GLAD combination was tested for toxicity and chemopreventive efficacy for suppression of intestinal tumorigenesis in adenomatous polyposis coli (APC)(Min/+) mice. Six-week-old wild-type and APC(Min/+) mice were fed modified American Institute of Nutrition 76A diets with or without GLAD (25 + 50 + 50 + 500 ppm) for 14 weeks. Dietary GLAD caused no signs of toxicity based on organ pathology and liver enzyme profiles. GLAD feeding strongly inhibited (80-83%, P < .0001) total intestinal tumor multiplicity and size in APC(Min/+) mice (means ± SEM tumors for control vs GLAD were 67.1 ± 5.4 vs. 11.3 ± 1.1 in males and 72.3 ± 8.9 vs 14.5 ± 2.8 in females). Mice fed GLAD had >95% fewer polyps with sizes of >2 mm compared with control mice and showed 75% and 85% inhibition of colonic tumors in males and females, respectively. Molecular analyses of polyps suggested that GLAD exerts efficacy by inhibiting cell proliferation, inducing apoptosis, decreasing ?-catenin and caveolin-1 levels, increasing caspase-3 cleavage and p21, and modulating expression profile of inflammatory cytokines. These observations demonstrate that GLAD, a novel cocktail of chemopreventive agents at very low doses, suppresses intestinal tumorigenesis in APC(Min/+) mice with no toxicity. This novel strategy to prevent colorectal cancer is an important step in developing agents with high efficacy without unwanted side effects.