The ATR inhibitor ceralasertib potentiates cancer checkpoint immunotherapy by regulating the tumor microenvironment

The Ataxia telangiectasia and Rad3-related (ATR) inhibitor ceralasertib in combination with the PD-L1 antibody durvalumab demonstrated encouraging clinical benefit in melanoma and lung cancer patients who progressed on immunotherapy. Here we show that modelling of intermittent ceralasertib treatment in mouse tumor models reveals CD8+ T-cell dependent antitumor activity, which is separate from the effects on tumor cells. Ceralasertib suppresses proliferating CD8+ T-cells on treatment which is rapidly reversed off-treatment. Ceralasertib causes up-regulation of type I interferon (IFNI) pathway in cancer patients and in tumor-bearing mice. IFNI is experimentally found to be a major mediator of antitumor activity of ceralasertib in combination with PD-L1 antibody. Improvement of T-cell function after ceralasertib treatment is linked to changes in myeloid cells in the tumor microenvironment. IFNI also promotes anti-proliferative effects of ceralasertib on tumor cells. Here, we report that broad immunomodulatory changes following intermittent ATR inhibition underpins the clinical therapeutic benefit and indicates its wider impact on antitumor immunity.

Relevance of ATM Status in Driving Sensitivity to DNA Damage Response Inhibitors in Patient-Derived Xenograft Models

Ataxia-telangiectasia mutated gene (ATM) is a key component of the DNA damage response (DDR) and double-strand break repair pathway. The functional loss of ATM (ATM deficiency) is hypothesised to enhance sensitivity to DDR inhibitors (DDRi). Whole-exome sequencing (WES), immunohistochemistry (IHC), and Western blotting (WB) were used to characterise the baseline ATM status across a panel of ATM mutated patient-derived xenograft (PDX) models from a range of tumour types. Antitumour efficacy was assessed with poly(ADP-ribose)polymerase (PARP, olaparib), ataxia- telangiectasia and rad3-related protein (ATR, AZD6738), and DNA-dependent protein kinase (DNA-PK, AZD7648) inhibitors as a monotherapy or in combination to associate responses with ATM status. Biallelic truncation/frameshift ATM mutations were linked to ATM protein loss while monoallelic or missense mutations, including the clinically relevant recurrent R3008H mutation, did not confer ATM protein loss by IHC. DDRi agents showed a mixed response across the PDX's but with a general trend toward greater activity, particularly in combination in models with biallelic ATM mutation and protein loss. A PDX with an ATM splice-site mutation, 2127T > C, with a high relative baseline ATM expression and KAP1 phosphorylation responded to all DDRi treatments. These data highlight the heterogeneity and complexity in describing targetable ATM-deficiencies and the fact that current patient selection biomarker methods remain imperfect; although, complete ATM loss was best able to enrich for DDRi sensitivity.

Ex vivo explant model of adenoma and colorectal cancer to explore mechanisms of action and patient response to cancer prevention therapies

Colorectal cancer (CRC) is the second leading cause of cancer death in the UK. Novel therapeutic prevention strategies to inhibit the development and progression of CRC would be invaluable. Potential contenders include low toxicity agents such as dietary-derived agents or repurposed drugs. However, in vitro and in vivo models used in drug development often do not take into account the heterogeneity of tumours or the tumour microenvironment. This limits translation to a clinical setting. Our objectives were to develop an ex vivo method utilizing CRC and adenoma patient-derived explants (PDEs) which facilitates screening of drugs, assessment of toxicity, and efficacy. Our aims were to use a multiplexed immunofluorescence approach to demonstrate the viability of colorectal tissue PDEs, and the ability to assess immune cell composition and interactions. Using clinically achievable concentrations of curcumin, we show a correlation between curcumin-induced tumour and stromal apoptosis (P < .001) in adenomas and cancers; higher stromal content is associated with poorer outcomes. B cell (CD20+ve) and T cell (CD3+ve) density of immune cells within tumour regions in control samples correlated with curcumin-induced tumour apoptosis (P < .001 and P < .05, respectively), suggesting curcumin-induced apoptosis is potentially predicted by baseline measures of immune cells. A decrease in distance between T cells (CD3+ve) and cytokeratin+ve cells was observed, indicating movement of T cells (CD3+ve) towards the tumour margin (P < .001); this change is consistent with an immune environment associated with improved outcomes. Concurrently, an increase in distance between T cells (CD3+ve) and B cells (CD20+ve) was detected following curcumin treatment (P < .001), which may result in a less immunosuppressive tumour milieu. The colorectal tissue PDE model offers significant potential for simultaneously assessing multiple biomarkers in response to drug exposure allowing a greater understanding of mechanisms of action and efficacy in relevant target tissues, that maintain both their structural integrity and immune cell compartments.

Optimization of an Imidazo[1,2-a]pyridine Series to Afford Highly Selective Type I1/2 Dual Mer/Axl Kinase Inhibitors with In Vivo Efficacy

Inhibition of Mer and Axl kinases has been implicated as a potential way to improve the efficacy of current immuno-oncology therapeutics by restoring the innate immune response in the tumor microenvironment. Highly selective dual Mer/Axl kinase inhibitors are required to validate this hypothesis. Starting from hits from a DNA-encoded library screen, we optimized an imidazo[1,2-a]pyridine series using structure-based compound design to improve potency and reduce lipophilicity, resulting in a highly selective in vivo probe compound 32. We demonstrated dose-dependent in vivo efficacy and target engagement in Mer- and Axl-dependent efficacy models using two structurally differentiated and selective dual Mer/Axl inhibitors. Additionally, in vivo efficacy was observed in a preclinical MC38 immuno-oncology model in combination with anti-PD1 antibodies and ionizing radiation.

Inhibition of DNA-PK with AZD7648 Sensitizes Tumor Cells to Radiotherapy and Induces Type I IFN-Dependent Durable Tumor Control

PURPOSE

Combining radiotherapy (RT) with DNA damage response inhibitors may lead to increased tumor cell death through radiosensitization. DNA-dependent protein kinase (DNA-PK) plays an important role in DNA double-strand break repair via the nonhomologous end joining (NHEJ) pathway. We hypothesized that in addition to a radiosensitizing effect from the combination of RT with AZD7648, a potent and specific inhibitor of DNA-PK, combination therapy may also lead to modulation of an anticancer immune response.

EXPERIMENTAL DESIGN

AZD7648 and RT efficacy, as monotherapy and in combination, was investigated in fully immunocompetent mice in MC38, CT26, and B16-F10 models. Immunologic consequences were analyzed by gene expression and flow-cytometric analysis.

RESULTS

AZD7648, when delivered in combination with RT, induced complete tumor regressions in a significant proportion of mice. The antitumor efficacy was dependent on the presence of CD8+ T cells but independent of NK cells. Analysis of the tumor microenvironment revealed a reduction in T-cell PD-1 expression, increased NK-cell granzyme B expression, and elevated type I IFN signaling in mice treated with the combination when compared with RT treatment alone. Blocking of the type I IFN receptor in vivo also demonstrated a critical role for type I IFN in tumor growth control following combined therapy. Finally, this combination was able to generate tumor antigen-specific immunologic memory capable of suppressing tumor growth following rechallenge.

CONCLUSIONS

Blocking the NHEJ DNA repair pathway with AZD7648 in combination with RT leads to durable immune-mediated tumor control.

Abstract 3511: Exploration of pre-clinical relationships between pharmacokinetics, pharmacodynamics and tumor volume for the novel DNA-PK inhibitor AZD7648

AZD7648 is a potent and highly selective inhibitor of DNA-dependent protein kinase (DNA-PK) that has been nominated for clinical development. DNA-PK is a nuclear serine/threonine protein kinase complex involved in DNA damage repair, and a key component of the non-homologous end joining repair mechanism of double strand breaks (DSBs). This work aimed to explore the relationships between pharmacokinetics (PK), pharmacodynamics (PD) and xenograft tumor volume from pre-clinical studies, in order to define PD requirements for pre-clinical efficacy, and to estimate a target clinical dose for AZD7648 in combination with DSB-inducing agents such as olaparib or pegylated liposomal doxorubicin (PLD). A population-based modelling approach was used to explore the PK of AZD7648 in mice. The PK model was developed using data from full PK profiles (multiple longitudinal samples per mouse), and validated against terminal sample PK data. The potential influences of strain-dependence, time non-linearity, and interaction with olaparib on the pharmacokinetics of AZD7648 were investigated. Direct and indirect inhibition PD models were fitted to the responses of biomarkers describing target engagement (pDNA-PK) or proximal downstream effects (pRPA32 (S4/8) and γH2AX). A compartmental model accurately described AZD7648 PK in mice, with rapid absorption, dose-proportional PK across the range of doses tested, time-independent parameters and no effect of olaparib co-dosing on AZD7648 PK. The PD of proximal target engagement biomarkers were best described with an Imax model with very rapid turnover (&lt;10 minutes), which showed there was negligible delay (due to tumor distribution or pharmacology) and effectively a direct relationship between systemic PK and xenograft biomarker inhibition. Across a number of FaDu ATM KO and BT474c xenograft tumor studies, the duration of cover over IC90 correlated with efficacy in combination with olaparib or PLD, demonstrating the importance of inhibiting DNA-PK for an extended duration in each dosing period. This result was applied to define a target level and duration of PD inhibition, and, when combined with predicted human PK behaviour, a target clinical dose for AZD7648 in combination with DSB-inducing agents to inform the clinical investigation of AZD7648.

Citation Format: Michael Davies, Joost de Jongh, Emma Dean, Jacquelline H. Fok, Frederick W. Goldberg, Neil James, Ankur Karmokar, Antonio Ramos-Montoya, Anna Staniszewska, Andy Sykes, Tamara van Steeg, Elaine Cadogan. Exploration of pre-clinical relationships between pharmacokinetics, pharmacodynamics and tumor volume for the novel DNA-PK inhibitor AZD7648 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3511.

Abstract 3506: AZD7648, a potent and selective inhibitor of DNA-PK, potentiates activity of the PARP inhibitor olaparib resulting in sustained anti-tumour activity in xenograft and PDX models

DNA-dependent kinase (DNA-PK) is a nuclear serine/threonine protein kinase complex and a key component of the non-homologous end joining (NHEJ) process. DNA-PK plays an important role in the cellular response to DNA damage through the detection and repair of double strand breaks (DSB). DSB can be induced by a range of agents, including chemotherapy and radiation. The PARP inhibitor olaparib has also been shown to induce DSB as a consequence of trapping PARP proteins at sites of damaged DNA. Therefore, we hypothesised that DNA-PK inhibitors may combine therapeutically with PARP inhibitors. AZD7648 is a highly potent and selective inhibitor of DNA-PK (pDNA-PK cell IC50 = 92 nM) The combination treatment of AZD7648 with olaparib for 10 - 12 days in vitro leads to at least 20% greater cell growth inhibition compared with either agents as monotherapies in a panel of cell lines with deficiencies in the ATM pathway (e.g. cells lacking ATM protein or where ATM substrates are not phosphorylated after exposure to DSB inducing agents). This effect is also seen in isogenic ATM knock-out (KO) FaDu head and neck and A549 non-small cell lung cancer cell lines. At concentrations of AZD7648 (0.6 - 2 µM) and olaparib (1 µM) that have monotherapy activity in the ATM KO cells but not in their wild-type counterparts (WT), the combination treatment enhanced the G2/M cell cycle arrest caused by olaparib and led to greater levels of micronuclei formation as detected using high-content immunofluorescece assays (mean per cell: FaDu WT = 0.1, FaDu ATM KO = 0.4). This was associated with a larger quantity of chromosomal aberrations in the ATM KO versus WT cells following combination treatment detected by metaphase spread analysis (mean per cell: FaDu ATM KO = 5.5, FaDu WT = 1.2). The same phenotype was observed in A549 ATM KO versus WT cell lines. In vivo, continuous dosing of AZD7648 (75 mg/kg bid) in combination with olaparib (100 mg/kg qd) inhibited the growth of FaDu WT tumours by ~60%. However, in the FaDu ATM KO tumours complete regressions were seen after 70 days of dosing and no re-growth was detected up to 220 days later. Additionally, in PDX models of breast, lung, ovarian and head and neck cancer this combination showed tumour growth inhibition (50-100%) in 13 models and regression in 5 models, only one of these five models being ATM pathway deficient. These data confirm that DNA-PK inhibition using AZD7648 enhances the efficacy of olaparib in vitro and in vivo, providing a clear rationale for its clinical investigation.

Citation Format: Antonio Ramos-Montoya, Jacqueline H. Fok, Neil James, Valeria Follia, Mercedes Vazquez-Chantada, Paul Wijnhoven, Lenka Oplustil O’Connor, Ankur Karmokar, Anna Staniszewska, Emma Dean, Simon J. Hollingsworth, Barry Davies, Elaine B. Cadogan. AZD7648, a potent and selective inhibitor of DNA-PK, potentiates activity of the PARP inhibitor olaparib resulting in sustained anti-tumour activity in xenograft and PDX models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3506.

Abstract 3512: AZD7648, a potent and selective inhibitor of DNA-PK, potentiates the activity of ionising radiation and doxorubicin in vitro and causes tumour regression in xenograft models

DNA-dependent kinase (DNA-PK) is a nuclear serine/threonine protein kinase complex that is a key component of the non-homologous end joining (NHEJ) process. DNA-PK plays an important role in the cellular response to DNA damage through the detection and repair of DNA double strand breaks (DSB). Cancer therapies such as ionising radiation (IR) or topoisomerase II inhibitors (doxorubicin) generate DSB which can be repaired by homologous recombination (HR) or non-homologous end-joining (NHEJ). It can therefore be hypothesised a DNA-PK inhibitor would potentiate the activity of these agents. We have developed a highly potent and selective inhibitor of DNA-PK, AZD7648, which inhibits IR-induced DNA-PK S2056 auto phosphoryalation with an IC50 = 92 nM in A549 non-small cell lung cancer (NSCLC) cells. AZD7648 is a potent radiosensitiser where treatment in combination with IR led to a concentration-dependent reduction of the colony survival capacity of A549 and H1299 NSCLC cells (DEF37 at 100 nM = 1.7 and 2.5, respectively). In A549 cells, AZD7648 (≥1 µM) in combination with 2Gy IR for 48 hours led to a significant accumulation of cells arrested in the G2/M of the cell cycle, a 4-fold increase in micronuclei formation, and 3-fold induction of γH2AX, pATM S1981 and 53BP1 foci formation compared with IR alone. AZD7648 was also found to combine synergistically with doxorubicin in a panel of ovarian and triple negative breast cancer (TNBC) cell lines in cell growth inhibition assays when applying the Loewe additivity model (synergy scores 4 - 35). In vivo the combination of AZD7648 with IR (5x 2Gy) induced tumour regression in H1299 and A549 NSCLC xenografts in a dose-dependent manner (84 and 11% regression respectively), while monotherapy treatment only achieved tumour growth inhibition. In these two models the increased activation by IR of three primary DNA-PK pharmacodynamic markers, pDNAPK (S2056), pRPA32 (S4/8) and γH2AX, was inhibited by AZD7648 treatment (70-90% inhibition 2 h after IR + AZD7648). Similarly, liposomal doxorubicin (2.5 mg/kg weekly) in combination with AZD7648 (37.5 mg/kg bid) induced tumour regressions in the BT474c ER+ breast cancer xenograft model and in a TNBC PDX model (63% and 33% regression respectively), while monotherapy treatments only achieved tumour growth inhibition. These data confirm that DNA-PK inhibition with AZD7648 enhances the efficacy of a range of DSB inducing agents in vitro and in vivo, providing a clear rationale for its clinical investigation.

Citation Format: Jacqueline H. Fok, Antonio Ramos-Montoya, Neil James, Mercedes Vazquez-Chantada, Valeria Follia, Ankur Karmokar, Anna Staniszewska, Lenka Oplustil O’Connor, Emma Dean, Simon J. Hollingsworth, Barry R. Davies, Elaine B. Cadogan. AZD7648, a potent and selective inhibitor of DNA-PK, potentiates the activity of ionising radiation and doxorubicin in vitro and causes tumour regression in xenograft models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3512.

Sensitivity of Colorectal Cancer to Arginine Deprivation Therapy is Shaped by Differential Expression of Urea Cycle Enzymes

Tumors deficient in the urea cycle enzymes argininosuccinate synthase-1 (ASS1) and ornithine transcarbamylase (OTC) are unable to synthesize arginine and can be targeted using arginine-deprivation therapy. Here, we show that colorectal cancers (CRCs) display negligible expression of OTC and, in subset of cases, ASS1 proteins. CRC cells fail to grow in arginine-free medium and dietary arginine deprivation slows growth of cancer cells implanted into immunocompromised mice. Moreover, we report that clinically-formulated arginine-degrading enzymes are effective anticancer drugs in CRC. Pegylated arginine deiminase (ADI-PEG20), which degrades arginine to citrulline and ammonia, affects growth of ASS1-negative cells, whereas recombinant human arginase-1 (rhArg1peg5000), which degrades arginine into urea and ornithine, is effective against a broad spectrum of OTC-negative CRC cell lines. This reflects the inability of CRC cells to recycle citrulline and ornithine into the urea cycle. Finally, we show that arginase antagonizes chemotherapeutic drugs oxaliplatin and 5-fluorouracil (5-FU), whereas ADI-PEG20 synergizes with oxaliplatin in ASS1-negative cell lines and appears to interact with 5-fluorouracil independently of ASS1 status. Overall, we conclude that CRC is amenable to arginine-deprivation therapy, but we warrant caution when combining arginine deprivation with standard chemotherapy.

Abstract LB-169: Asbestos and anthelmintics: Repurposing drugs to prevent mesothelioma in high-risk populations

The purpose of this study is to address the rising mortality rates in mesothelioma by using repurposed drugs in a chemoprevention setting.

An initial screen of 100 repurposed agents at clinically relevant concentrations was conducted across three mesothelioma cell lines using AlamarBlue assays. Having identified the top three individual and combinatorial treatments, analysis of cell-cycle and apoptosis response to these drugs was used to corroborate the findings of the initial screen. As a more representative disease model a mouse PDX was developed from a human biphasic mesothelioma, and furthermore, primary tissue obtained, both of which we have used for explant experiments to assess the efficacy of the top treatments in a more realistic and translational model. As BAP-1 mutations are highly frequent in both acquired and spontaneous mesotheliomas, a CRISPR generated knock-out cell-line will model early-stage disease, and MET-5A mesothelial cells to assess normal cell response.

The three top agents, comprising zinc acetate, niclosamide, and colchicine, have proven consistently efficacious in reducing mesothelioma cell-line viability by up to 72.59% individually and 93.55% in combination. Congruent results are provided by annexin V-FITC and FACS experiments which indicate treatments induce cell cycle alterations and apoptosis. Furthermore, FACS analysis of PDX explants also shows increased apoptosis of up to 27.0% in response to 24-hour treatment of two combined drugs. Importantly, the PDX still retains original histopathological features of the human tumour, making it an important foundation for further ex vivo and ultimately in vivo study.

Initial results are promising and indicate that several repurposed agents significantly reduce survival and increase death of mesothelioma both in vitro and ex vivo. Mesothelioma, being predominantly caused by long-term asbestos exposure, has been under-researched due to an overreliance on the disuse of asbestos. As such, there is no effectual treatment and average survival remain static at under one year. However, following initial asbestos exposure, a 50-year latency precedes diagnosis, which offers an opportune window for a prevention strategy. Using the CRISPR-BAP-1-knockout cell-line to model early-stage disease, we hope to translate the top candidate into a primary prevention setting. However given the increasing frequency of late stage mesothelioma diagnoses, there is also a tangible need for secondary and tertiary prevention. Repurposed drugs, which offer long term safety and side effect profiles, as well as requiring less temporal and financial investment, allow expedited translation of any potential top candidate into clinic. Through further mechanistic analyses in in vitro and ex vivo cancer models, we hope to identify a single agent or combination that could significantly impede mesothelioma progression and ultimately reduce mortality.

Citation Format: Bethan G. Rogoyski, Ankur Karmokar, Sameena Khan, Hong Cai, Farhat L. Khanim, Sara Busacca, Lynne Howells, Dean A. Fennell, Anne L. Thomas, Karen Brown. Asbestos and anthelmintics: Repurposing drugs to prevent mesothelioma in high-risk populations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-169.

Abstract 258: Targeting Nanog in 3D explant models for the evaluation of cancer prevention agents

Background: The transcription factor Nanog is crucial for the self-renewal of cancer stem-like cells (CSCs). Nanog expression in colorectal cancer (CRC) tissue correlates with lymph node metastasis and poor prognosis. Since Nanog is not expressed in most tissues, including normal adult stem-cells, it represents a therapeutic target specific to cancer cells. Curcumin inhibits proliferation and expansion of CSCs derived from CRC and adenomas. In NOD/SCID mice bearing xenografts from patient-derived CRC CSCs, curcumin significantly inhibited tumour growth and improved survival. In addition, curcumin binds directly to Nanog recombinant protein (quantified using microscale thermophoresis). We have developed 3D in-vitro primary human explant models to further characterise the effects of curcumin on Nanog. In this work the hypothesis is tested that Nanog may be an early marker of response for CRC prevention agents.

Methods: Patient-derived CRC and adenoma tissue was cubed (2x2x2mm) and treated for 24 hours with curcumin. Following treatment, explant tissues were processed for analysis by immunohistochemistry (IHC) (n=6) and flow cytometry (n=17). The effect of curcumin on CSCs (defined by expression of aldehyde dehydrogenase (ALDH) or Nanog) and differentiation (via Mucin 2 expression) was analysed using IHC. Additionally, cells expressing Nanog (Nanog+) or Nanog plus proliferation marker Ki67 (Nanog+Ki67+) were assessed using flow cytometry.

Results: A range of adenoma (n=5) and Dukes stage A-C CRC (n=18) samples were studied. Following exposure to curcumin, a 30% reduction was observed in Nanog+ and Nanog+Ki67+ cells. Nanog+ cell number was decreased in a curcumin concentration-dependent fashion in 6 samples and concentration-independently in a further 8. No response was observed in 3 samples. A reduction in Nanog and ALDH with concurrent increase in differentiation was observed via IHC in one sample.

Conclusion: Our data suggest Nanog is targeted by curcumin in adenoma and CRC tissues. Nanog may serve as a biomarker in clinical trials to identify individuals most amenable to treatment with curcumin alone or in combination treatment. Crucially, this will help select those who are likely to benefit from curcumin as a cancer prevention agent. Ultimately, this concept may be applicable to the evaluation of novel CRC prevention agents.

Citation Format: Sam Khan, Ankur Karmokar, Zahirah Sidat, Nalini Foreman, David Moore, Jennifer Higgins, Emma Parrott, Despoina Theofanous, Dominic Hobbs, Lynne Howells, Anne Thomas, Karen Brown. Targeting Nanog in 3D explant models for the evaluation of cancer prevention agents [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 258.

Cancer chemoprevention: Evidence of a nonlinear dose response for the protective effects of resveratrol in humans and mice

Resveratrol is widely promoted as a potential cancer chemopreventive agent, but a lack of information on the optimal dose prohibits rationally designed trials to assess efficacy. To challenge the assumption that "more is better," we compared the pharmacokinetics and activity of a dietary dose with an intake 200 times higher. The dose-response relationship for concentrations generated and the metabolite profile of [(14)C]-resveratrol in colorectal tissue of cancer patients helped us to define clinically achievable levels. In Apc(Min) mice (a model of colorectal carcinogenesis) that received a high-fat diet, the low resveratrol dose suppressed intestinal adenoma development more potently than did the higher dose. Efficacy correlated with activation of adenosine monophosphate-activated protein kinase (AMPK) and increased expression of the senescence marker p21. Nonlinear dose responses were observed for AMPK and mechanistic target of rapamycin (mTOR) signaling in mouse adenoma cells, culminating in autophagy and senescence. In human colorectal tissues exposed to low dietary concentrations of resveratrol ex vivo, we measured enhanced AMPK phosphorylation and autophagy. The expression of the cytoprotective NAD(P)H dehydrogenase, quinone 1 (NQO1) enzyme was also increased in tissues from cancer patients participating in our [(14)C]-resveratrol trial. These findings warrant a revision of developmental strategies for diet-derived agents designed to achieve cancer chemoprevention.

Targeting cancer stem-like cells using dietary-derived agents - Where are we now?

Diet has been linked to an overwhelming proportion of cancers. Current chemotherapy and targeted therapies are limited by toxicity and the development of resistance against these treatments results in cancer recurrence or progression. In vitro evidence indicates that a number of dietary-derived agents have activity against a highly tumorigenic, chemoradiotherapy resistant population of cells within a tumour. This population is associated with cancer recurrence and is therefore clinically significant. Targeting this subpopulation, termed cancer stem-like cells with dietary-derived agents provides a potentially low toxicity strategy to enhance current treatment regimens. In addition, dietary-derived compounds also provide a novel approach to cancer prevention strategies. This review focusses on selected diet-derived agents that have been shown to specifically target cancer stem-like cells using in vivo models, or in clinical trials. Furthermore, the potential limitations of these studies are discussed, and areas of research that need to be addressed to allow successful translation of dietary-derived agents to the clinical arena are highlighted.

In vivo relevant mixed urolithins and ellagic acid inhibit phenotypic and molecular colon cancer stem cell features: A new potentiality for ellagitannin metabolites against cancer

Colon cancer stem cells (CSCs) offer a novel paradigm for colorectal cancer (CRC) treatment and dietary polyphenols may contribute to battle these cells. Specifically, polyphenol-derived colon metabolites have the potential to interact with and affect colon CSCs. We herein report the effects against colon CSCs of two mixtures of ellagitannin (ET) metabolites, ellagic acid (EA) and the gut microbiota-derived urolithins (Uro) at concentrations detected in the human colon tissues following the intake of ET-containing products (pomegranate, walnuts). These mixtures reduce phenotypic and molecular features in two models of colon CSCs: Caco-2 cells and primary tumour cells from a patient with CRC. The mixture containing mostly Uro-A (85% Uro-A, 10% Uro-C, 5% EA) was most effective at inhibiting the number and size of colonospheres and aldehyde dehydrogenase activity (ALDH, a marker of chemoresistance) whereas the mixture containing less Uro-A but IsoUro-A and Uro-B (30% Uro-A, 50% IsoUro-A, 10% Uro-B, 5% Uro-C, 5% EA) had some effects on the number and size of colonospheres but not on ALDH. These data support a role for polyphenols metabolites in the control of colon cancer chemoresistance and relapse and encourage the research on the effects of polyphenols against CSCs.

Curcumin inhibits cancer stem cell phenotypes in ex vivo models of colorectal liver metastases, and is clinically safe and tolerable in combination with FOLFOX chemotherapy

In vitro and pre-clinical studies have suggested that addition of the diet-derived agent curcumin may provide a suitable adjunct to enhance efficacy of chemotherapy in models of colorectal cancer. However, the majority of evidence for this currently derives from established cell lines. Here, we utilised patient-derived colorectal liver metastases (CRLM) to assess whether curcumin may provide added benefit over 5-fluorouracil (5-FU) and oxaliplatin (FOLFOX) in cancer stem cell (CSC) models. Combination of curcumin with FOLFOX chemotherapy was then assessed clinically in a phase I dose escalation study. Curcumin alone and in combination significantly reduced spheroid number in CRLM CSC models, and decreased the number of cells with high aldehyde dehydrogenase activity (ALDH(high)/CD133(-)). Addition of curcumin to oxaliplatin/5-FU enhanced anti-proliferative and pro-apoptotic effects in a proportion of patient-derived explants, whilst reducing expression of stem cell-associated markers ALDH and CD133. The phase I dose escalation study revealed curcumin to be a safe and tolerable adjunct to FOLFOX chemotherapy in patients with CRLM (n = 12) at doses up to 2 grams daily. Curcumin may provide added benefit in subsets of patients when administered with FOLFOX, and is a well-tolerated chemotherapy adjunct.

Characterization and propagation of tumor initiating cells derived from colorectal liver metastases: trials, tribulations and a cautionary note

Tumor initiating cells (TIC) are increasingly being put forward as a potential target for intervention within colorectal cancer. Whilst characterisation and outgrowth of these cells has been extensively undertaken in primary colorectal cancers, few data are available describing characteristics within the metastatic setting. Tissue was obtained from patients undergoing surgical resection for colorectal liver metastases, and processed into single cell suspension for assessment. Tumor initiating cells from liver metastases were characterised using combinations of EPCAM, Aldehyde dehydrogenase activity, CD133 and CD26. CD133 expression was significantly lower in patients who had received chemotherapy, but this was accounted for by a decrease observed in the male patient cohort only. ALDH^high populations were rare (0.4 and 0.3% for EPCAM⁺/ALDH^high/CD133^- and EPCAM⁺/ALDH^high/CD133⁺ populations respectively) and below the limits of detection in 28% of samples. Spheroid outgrowth of metastatic tumor cells across all samples could not be readily achieved using standard spheroid-formation techniques, thus requiring further method validation to reliably propagate cells from the majority of tissues. Spheroid formation was not enhanced using additional growth factors or fibroblast co-culture, but once cells were passaged through NOD-SCID mice, spheroid formation was observed in 82% samples, accompanied by a significant increase in CD26. Order of spheroid forming ability was ALDH^high>CD133>CD26. Samples sorted by these markers each had the ability to reform ALDH^high, CD133 and CD26 positive populations to a similar extent, suggestive of a high degree of plasticity for each population. Ex vivo TIC models are increasingly being utilised to assess efficacy of therapeutic interventions. It is therefore essential that such investigations use well-characterised models that are able to sustain TIC populations across a large patient cohort in order that the inherent heterogeneity observed in cancer populations is maintained.

Sulfate metabolites provide an intracellular pool for resveratrol generation and induce autophagy with senescence

The phytochemical resveratrol has been shown to exert numerous health benefits in preclinical studies, but its rapid metabolism and resulting poor bioavailability may limit translation of these effects to humans. Resveratrol metabolites might contribute to in vivo activity through regeneration of the parent compound. We present quantitation of sulfate and glucuronide conjugates of resveratrol in human plasma and tissue after repeated ingestion of resveratrol by volunteers and cancer patients, respectively. Subsequent pharmacokinetic characterization of a mixture of resveratrol-3-O-sulfate and resveratrol-4'-O-sulfate in mice showed that these metabolites are absorbed orally but have low bioavailabilities of ~14 and 3%, respectively. Sulfate hydrolysis in vivo liberated free resveratrol, which accounted for ~2% of the total resveratrol species present in mouse plasma. Monosulfate metabolites were also converted to the parent in human colorectal cells. The extent of cellular uptake was dependent on specific membrane transporters and dictated antiproliferative activity. Sulfate metabolites induced autophagy and senescence in human cancer cells; these effects were abrogated by inclusion of a sulfatase inhibitor, which reduced intracellular resveratrol. Together, our findings suggest that resveratrol is delivered to target tissues in a stable sulfate-conjugated form and that the parent compound is gradually regenerated in selected cells and may give rise to the beneficial effects in vivo. At doses considered to be safe in humans, resveratrol generated via this route may be of greater importance than the unmetabolized form.

The role of cancer stem cells in the anti-carcinogenicity of curcumin

Many cancers contain cell subpopulations that display characteristics of stem cells. These cells are characterised by their ability to self-renew, form differentiated progeny and develop resistance to chemotherapeutic strategies. Cancer stem cells may utilise many of the same signalling pathways as normal stem cells including Wnt, Notch and Hedgehog. The dietary agent curcumin exerts a plethora of anti-carcinogenic effects both in vitro and in vivo, and can also inhibit many of the signalling pathways associated with stem cell biology. Emerging evidence suggests that curcumin can exert its anti-carcinogenic activity via targeting cancer stem cells through the disruption of stem cell signalling pathways. In this review we summarise the ability of curcumin to interfere with signalling pathways Wnt, Hedgehog, Notch, Signal Transducers and Activator (STAT) and interleukin-8, and report curcumin-induced changes in function and properties of cancer stem cells. We present evidence that the effects of curcumin on cancer stem cells mediate, or contribute to, its anti-carcinogenic activity.

Dietary intake of rosmarinic acid by Apc(Min) mice, a model of colorectal carcinogenesis: levels of parent agent in the target tissue and effect on adenoma development

SCOPE

Rosmarinic acid (RA), a constituent of culinary herbs is considered to possess cancer chemopreventive properties. It has been shown to inhibit the development of cancer in preclinical models but data are conflicting and whether it can protect against gastrointestinal malignancies in vivo has not been examined. This study aimed to investigate the effect of RA on the development of intestinal adenomas in the Apc(Min) mouse model of colorectal carcinogenesis, and to correlate efficacy with levels of RA achieved in the plasma and gastrointestinal tract.

METHODS AND RESULTS

RA inhibited the growth of APC10.1 cells derived from Apc(Min) mouse adenomas, with an IC₅₀ of 43 μM. Consumption of dietary RA (0.3%) by Apc(Min) mice for 8 weeks post weaning decreased adenoma burden by ∼35%, but the difference from controls was not significant. Although RA significantly decreased the frequency of large adenomas, the number of small ones increased. Using a novel validated HPLC assay, average levels of RA in the plasma and intestinal mucosa of these mice were found to be 1.1 μM and 38 nmol/g, respectively.

CONCLUSION

Chronic consumption of RA furnished quantifiable levels of parent compound in the plasma and intestinal tract of Apc(Min) mice and may slow adenoma development.

Curcumin: the potential for efficacy in gastrointestinal diseases

Curcumin is a naturally occurring phytochemical and an extract of turmeric. Extensive in vitro and in vivo data have paved the way for curcumin to become the subject of clinical trials. Curcumin modulates key signalling pathways important in cellular processes. Numerous mechanisms of action have been elucidated. The potential for clinical efficacy is apparent from benign and malignant disease models. Curcumin has potent anti-inflammatory and anti-neoplastic properties used alone and in combination with standard therapies. Early-phase trials have ascertained pharmacological properties and consistently demonstrate it to be safe and well tolerated. However, bioavailability is limited and efficacious doses have not yet been determined. Evidence of efficacy has been derived from animal models or small clinical trials. There is only finite data supporting the use of curcumin in phase III trials with specific diseases (e.g. ulcerative colitis). However, for the vast majority of conditions additional early-phase studies are required to justify larger trials determining efficacy.