SAR of Novel 3-Arylisoquinolinones: meta-Substitution on the Aryl Ring Dramatically Enhances Antiproliferative Activity through Binding to Microtubules

A set of meta-substituted 3-arylisoquinolinones have been identified that show substantial cytotoxicity in breast, liver, lung and colon cancer cell lines; these are up to 700-fold more active than the corresponding para analogues. These compounds were initially proposed as inhibitors of N-ribosyl dihydronicotinamide (NRH): quinone oxidoreductase 2 (NQO2) but were found to be inactive against the enzyme. Instead, COMPARE analysis suggested that 6-fluoro-3-(meta-fluorophenyl)isoquinolin-1(2H)-one (4) could mimic colchicine and interact with microtubules, a recognized target for cancer therapy. Subsequent docking, molecular dynamics simulations, and free energy analysis further suggested that compound 4 bound well into the colchicine-binding pocket of tubulin. Indeed, 4 suppressed tubulin polymerization, caused G₂/M cell cycle arrest, and induced apoptosis. Also, 4 inhibited the formation of endothelial cell capillary-like tubes and further disrupted the structure of preestablished tubes; the effects were not observed with para analogue 5. In accordance with this, the computed free energy of binding of 5 to tubulin was lower in magnitude than that for 4 and appeared to arise in part from the inability of the para substituent to occupy a tubulin subpocket, which is possible in the meta orientation. In conclusion, the antiproliferative potential of the novel 3-arylisoquinolinones is markedly influenced by a subtle change in the structure (meta versus para). The meta-substituted isoquinolinone 4 is a microtubule-destabilizing agent with potential tumor-selectivity and antiangiogenic and vascular disrupting features.

Hypoxia and hyperglycaemia determine why some endometrial tumours fail to respond to metformin

BACKGROUND

High expression of Ki67, a proliferation marker, is associated with reduced endometrial cancer-specific survival. Pre-surgical metformin reduces tumour Ki-67 expression in some women with endometrial cancer. Metformin's anti-cancer activity may relate to effects on cellular energy metabolism. Since tumour hypoxia and glucose availability are major cellular redox determinants, we evaluated their role in endometrial cancer response to metformin.

METHODS

Endometrial cancer biopsies from women treated with pre-surgical metformin were tested for the hypoxia markers, HIF-1α and CA-9. Endometrial cancer cell lines were treated with metformin in variable glucose concentrations in normoxia or hypoxia and cell viability, mitochondrial biogenesis, function and energy metabolism were assessed.

RESULTS

In women treated with metformin (n = 28), Ki-67 response was lower in hypoxic tumours. Metformin showed minimal cytostatic effects towards Ishikawa and HEC1A cells in conventional medium (25 mM glucose). In low glucose (5.5 mM), a dose-dependent cytostatic effect was observed in normoxia but attenuated in hypoxia. Tumours treated with metformin showed increased mitochondrial mass (n = 25), while in cultured cells metformin decreased mitochondrial function. Metformin targets mitochondrial respiration, however, in hypoxic, high glucose conditions, there was a switch to glycolytic metabolism and decreased metformin response.

CONCLUSIONS

Understanding the metabolic adaptations of endometrial tumours may identify patients likely to derive clinical benefit from metformin.

Binding and Internalization in Receptor-Targeted Carriers: The Complex Role of CD44 in the Uptake of Hyaluronic Acid-Based Nanoparticles (siRNA Delivery)

CD44 is an endocytic hyaluronic acid (HA) receptor, and is overexpressed in many carcinomas. This has encouraged the use of HA to design CD44-targeting carriers. This paper is about dissecting the mechanistic role of CD44. Here, HA-decorated nanoparticles are used to deliver siRNA to both tumoral (AsPC-1, PANC-1, HT-29, HCT-116) and non-tumoral (fibroblasts, differently polarized THP-1 macrophages, HUVEC) human cell lines, evaluating the initial binding of the nanoparticles, their internalization rate, and the silencing efficiency (cyclophilin B (PPIB) gene). Tumoral cells internalize faster and experience higher silencing than non-tumoral cells. This is promising as it suggests that, in a tumor, HA nanocarriers may have limited off-target effects. More far-reaching is the inter-relation between the four parameters of the study: CD44 expression, HA binding on cell surfaces, internalization rate, and silencing efficiency. No correlation is found between binding (an early event) and any of the other parameters, whereas silencing correlates both with speed of the internalization process and CD44 expression. This study confirms on one hand that HA-based carriers can perform a targeted action, but on the other it suggests that this may not be due to a selective binding event, but rather to a later recognition leading to selective internalization.

Discovery of potent 4-aminoquinoline hydrazone inhibitors of NRH:quinoneoxidoreductase-2 (NQO2)

(NRH):quinone oxidoreductase 2 (NQO2) is associated with various processes involved in cancer initiation and progression probably via the production of ROS during quinone metabolism. Thus, there is a need to develop inhibitors of NQO2 that are active in vitro and in vivo. As part of a strategy to achieve this we have used the 4-aminoquinoline backbone as a starting point and synthesized 21 novel analogues. The syntheses utilised p-anisidine with Meldrum's acid and trimethyl orthoacetate or trimethyl orthobenzoate to give the 4-hydrazin-quinoline scaffold, which was derivatised with aldehydes or acid chlorides to give hydrazone or hydrazide analogues, respectively. The hydrazones were the most potent inhibitors of NQO2 in cell free systems, some with low nano-molar IC50 values. Structure-activity analysis highlighted the importance of a small substituent at the 2-position of the 4-aminoquinoline ring, to reduce steric hindrance and improve engagement of the scaffold within the NQO2 active site. Cytotoxicity and NQO2-inhibitory activity in vitro was evaluated using ovarian cancer SKOV-3 and TOV-112 cells (expressing high and low levels of NQO2, respectively). Generally, the hydrazones were more toxic than hydrazide analogues and further, toxicity is unrelated to cellular NQO2 activity. Pharmacological inhibition of NQO2 in cells was measured using the toxicity of CB1954 as a surrogate end-point. Both the hydrazone and hydrazide derivatives are functionally active as inhibitors of NQO2 in the cells, but at different inhibitory potency levels. In particular, 4-((2-(6-methoxy-2-methylquinolin-4-yl)hydrazono)methyl)phenol has the greatest potency of any compound yet evaluated (53 nM), which is 50-fold lower than its toxicity IC50. This compound and some of its analogues could serve as useful pharmacological probes to determine the functional role of NQO2 in cancer development and response to therapy.

Evaluating the Efficiency of Hyaluronic Acid for Tumor Targeting via CD44

The development of delivery systems capable of tumor targeting represents a promising strategy to overcome issues related to nonspecific effects of conventional anticancer therapies. Currently, one of the most investigated agents for cancer targeting is hyaluronic acid (HA), since its receptor, CD44, is overexpressed in many cancers. However, most of the studies on CD44/HA interaction have been so far performed in cell-free or genetically modified systems, thus leaving some uncertainty regarding which cell-related factors influence HA binding and internalization (collectively called "uptake") into CD44-expressing cells. To address this, the expression of CD44 (both standard and variants, designated CD44s and CD44v, respectively) was evaluated in human dermal fibroblasts (HDFs) and a large panel of cancer cell lines, including breast, prostate, head and neck, pancreatic, ovarian, colorectal, thyroid, and endometrial cancers. Results showed that CD44 isoform profiles and expression levels vary across the cancer cell lines and HDF and are not consistent within the cell origin. Using composite information of CD44 expression, HA binding, and internalization, we found that the expression of CD44v can negatively influence the uptake of HA, and, instead, when cells primarily expressed CD44s, a positive correlation was observed between expression and uptake. In other words, CD44shigh cells bound and internalized more HA compared to CD44slow cells. Moreover, CD44shigh HDFs were less efficient in uptaking HA compared to CD44shigh cancer cells. The experiments described here are the first step toward understanding the interplay between CD44 expression, its functionality, and the underlying mechanism(s) for HA uptake. The results show that factors other than the amount of CD44 receptor can play a role in the interaction with HA, and this represents an important advance with respect to the design of HA-based carriers and the selection of tumors to treat according to their CD44 expression profile.

Statin-induced metabolic reprogramming in head and neck cancer: a biomarker for targeting monocarboxylate transporters

Prognosis of HPV negative head and neck squamous cell carcinoma (HNSCC) patients remains poor despite surgical and medical advances and inadequacy of predictive and prognostic biomarkers in this type of cancer highlights one of the challenges to successful therapy. Statins, widely used for the treatment of hyperlipidaemia, have been shown to possess anti-tumour effects which were partly attributed to their ability to interfere with metabolic pathways essential in the survival of cancer cells. Here, we have investigated the effect of statins on the metabolic modulation of HNSCC cancers with a vision to predict a personalised anticancer therapy. Although, treatment of tumour-bearing mice with simvastatin did not affect tumour growth, pre-treatment for 2 weeks prior to tumour injection, inhibited tumour growth resulting in strongly increased survival. This was associated with increased expression of the monocarboxylate transporter 1 (MCT1) and a significant reduction in tumour lactate content, suggesting a possible reliance of these tumours on oxidative phosphorylation for survival. Since MCT1 is responsible for the uptake of mitochondrial fuels into the cells, we reasoned that inhibiting it would be beneficial. Interestingly, combination of simvastatin with AZD3965 (MCT1 inhibitor) led to further tumour growth delay as compared to monotherapies, without signs of toxicity. In clinical biopsies, prediagnostic statin therapy was associated with a significantly higher MCT1 expression and was not of prognostic value following conventional chemo-radiotherapy. These findings provide a rationale to investigate the clinical effectiveness of MCT1 inhibition in patients with HNSCC who have been taking lipophilic statins prior to diagnosis.

Evaluation of analogues of furan-amidines as inhibitors of NQO2

Inhibitors of the enzyme NQO2 (NRH: quinone oxidoreductase 2) are of potential use in cancer chemotherapy and malaria. We have previously reported that non-symmetrical furan amidines are potent inhibitors of NQO2 and here novel analogues are evaluated. The furan ring has been changed to other heterocycles (imidazole, N-methylimidazole, oxazole, thiophene) and the amidine group has been replaced with imidate, reversed amidine, N-arylamide and amidoxime to probe NQO2 activity, improve solubility and decrease basicity of the lead furan amidine. All compounds were fully characterised spectroscopically and the structure of the unexpected product N-hydroxy-4-(5-methyl-4-phenylfuran-2-yl)benzamidine was established by X-ray crystallography. The analogues were evaluated for inhibition of NQO2, which showed lower activity than the lead furan amidine. The observed structure-activity relationship for the furan-amidine series with NQO2 was rationalized by preliminary molecular docking and binding mode analysis. In addition, the oxazole-amidine analogue inhibited the growth of Plasmodium falciparum with an IC50 value of 0.3 μM.

Monocarboxylate Transporter 1 (MCT1) is an independent prognostic biomarker in endometrial cancer

BACKGROUND

Endometrial cancer (EC) is a major health concern due to its rising incidence. Whilst early stage disease is generally cured by surgery, advanced EC has a poor prognosis with limited treatment options. Altered energy metabolism is a hallmark of malignancy. Cancer cells drive tumour growth through aerobic glycolysis and must export lactate to maintain intracellular pH. The aim of this study was to evaluate the expression of the lactate/proton monocarboxylate transporters MCT1 and MCT4 and their chaperone CD147 in EC, with the ultimate aim of directing future drug development.

METHODS

MCT1, MCT4 and CD147 expression was examined using immunohistochemical analysis in 90 endometrial tumours and correlated with clinico-pathological characteristics and survival outcomes.

RESULTS

MCT1 and MCT4 expression was observed in the cytoplasm, the plasma membrane or both locations. CD147 was detected in the plasma membrane and associated with MCT1 (p = 0.003) but not with MCT4 (p = 0.207) expression. High MCT1 expression was associated with reduced overall survival (p = 0.029) and remained statistically significant after adjustment for survival covariates (p = 0.017).

CONCLUSION

Our data suggest that MCT1 expression is an important marker of poor prognosis in EC. MCT1 inhibition may have potential as a treatment for advanced or recurrent EC.

Akt inhibition improves long-term tumour control following radiotherapy by altering the microenvironment

Radiotherapy is an important anti-cancer treatment, but tumour recurrence remains a significant clinical problem. In an effort to improve outcomes further, targeted anti-cancer drugs are being tested in combination with radiotherapy. Here, we have studied the effects of Akt inhibition with AZD5363. AZD5363 administered as an adjuvant after radiotherapy to FaDu and PE/CA PJ34 tumours leads to long-term tumour control, which appears to be secondary to effects on the irradiated tumour microenvironment. AZD5363 reduces the downstream effectors VEGF and HIF-1α, but has no effect on tumour vascularity or oxygenation, or on tumour control, when administered prior to radiotherapy. In contrast, AZD5363 given after radiotherapy is associated with marked reductions in tumour vascular density, a decrease in the influx of CD11b+ myeloid cells and a failure of tumour regrowth. In addition, AZD5363 is shown to inhibit the proportion of proliferating tumour vascular endothelial cells in vivo, which may contribute to improved tumour control with adjuvant treatment. These new insights provide promise to improve outcomes with the addition of AZD5363 as an adjuvant therapy following radiotherapy.

Expression of NAD(P)H quinone dehydrogenase 1 (NQO1) is increased in the endometrium of women with endometrial cancer and women with polycystic ovary syndrome

OBJECTIVE

Women with a prior history of polycystic ovary syndrome (PCOS) have an increased risk of endometrial cancer (EC).

AIM

To investigate whether the endometrium of women with PCOS possesses gene expression changes similar to those found in EC.

DESIGN AND METHODS

Patients with EC, PCOS and control women unaffected by either PCOS or EC were recruited into a cross-sectional study at the Nottingham University Hospital, UK. For RNA sequencing, representative individual endometrial biopsies were obtained from women with EC, PCOS and a woman unaffected by PCOS or EC. Expression of a subset of differentially expressed genes identified by RNA sequencing, including NAD(P)H quinone dehydrogenase 1 (NQO1), was validated by quantitative reverse transcriptase PCR validation (n = 76) and in the cancer genome atlas UCEC (uterine corpus endometrioid carcinoma) RNA sequencing data set (n = 381). The expression of NQO1 was validated by immunohistochemistry in EC samples from a separate cohort (n = 91) comprised of consecutive patients who underwent hysterectomy at St Mary's Hospital, Manchester, between 2011 and 2013. A further 6 postmenopausal women with histologically normal endometrium who underwent hysterectomy for genital prolapse were also included. Informed consent and local ethics approval were obtained for the study.

RESULTS

We show for the first that NQO1 expression is significantly increased in the endometrium of women with PCOS and EC. Immunohistochemistry confirms significantly increased NQO1 protein expression in EC relative to nonmalignant endometrial tissue (P < .0001).

CONCLUSIONS

The results obtained here support a previously unrecognized molecular link between PCOS and EC involving NQO1.

Preclinical anti-cancer activity and multiple mechanisms of action of a cationic silver complex bearing N-heterocyclic carbene ligands

Organometallic complexes offer the prospect of targeting multiple pathways that are important in cancer biology. Here, the preclinical activity and mechanism(s) of action of a silver-bis(N-heterocyclic carbine) complex (Ag8) were evaluated. Ag8 induced DNA damage via several mechanisms including topoisomerase I/II and thioredoxin reductase inhibition and induction of reactive oxygen species. DNA damage induction was consistent with cytotoxicity observed against proliferating cells and Ag8 induced cell death by apoptosis. Ag8 also inhibited DNA repair enzyme PARP1, showed preferential activity against cisplatin resistant A2780 cells and potentiated the activity of temozolomide. Ag8 was substantially less active against non-proliferating non-cancer cells and selectively inhibited glycolysis in cancer cells. Ag8 also induced significant anti-tumour effects against cells implanted intraperitoneally in hollow fibres but lacked activity against hollow fibres implanted subcutaneously. Thus, Ag8 targets multiple pathways of importance in cancer biology, is less active against non-cancer cells and shows activity in vivo in a loco-regional setting.

Chitosan/Hyaluronic Acid Nanoparticles: Rational Design Revisited for RNA Delivery

Chitosan/hyaluronic acid (HA) nanoparticles can be used to deliver an RNA/DNA cargo to cells overexpressing HA receptors such as CD44. For these systems, unequivocal links have not been established yet between chitosan macromolecular (molecular weight; degree of deacetylation, i.e., charge density) and nanoparticle variables (complexation strength, i.e., stability; nucleic acid protection; internalization rate) on one hand, and transfection efficiency on the other hand. Here, we have focused on the role of avidity on transfection efficiency in the CD44-expressing HCT-116 as a cellular model; we have employed two differently sized payloads (a large luciferase-encoding mRNA and a much smaller anti-Luc siRNA), and a small library of chitosans (variable molecular weight and degree of deactylation). The RNA avidity for chitosan showed-as expected-an inverse relationship: higher avidity-higher polyplex stability-lower transfection efficiency. The avidity of chitosan for RNA appears to lead to opposite effects: higher avidity-higher polyplex stability but also higher transfection efficiency. Surprisingly, the best transfecting particles were those with the lowest propensity for RNA release, although this might be a misleading relationship: for example, the same macromolecular parameters that increase avidity can also boost chitosan's endosomolytic activity, with a strong enhancement in transfection. The performance of these nonviral vectors appears therefore difficult to predict simply on the basis of carrier- or payload-related variables, and a more holistic consideration of the journey of the nanoparticle, from cell uptake to cytosolic bioavailability of payload, is needed. It is also noteworthy that the nanoparticles used in this study showed optimal performance under slightly acidic conditions (pH 6.4), which is promising for applications in a tumoral extracellular environment. It is also worth pointing out that under these conditions we have for the first time successfully delivered mRNA with chitosan/HA nanoparticles.

The CD44-Mediated Uptake of Hyaluronic Acid-Based Carriers in Macrophages

CD44 is a potentially rewarding target in cancer therapy, although its mechanisms of ligand binding and internalization are still poorly understood. In this study, we have established quantitative relationships between CD44 expression in differently polarized macrophages (M0, M1, and M2-polarized THP-1 human macrophages) and the uptake of hyaluronic acid (HA)-based materials, which are potentially usable for CD44 targeting. We have validated a robust method for macrophage polarization, which sequentially uses differentiating and polarizing factors, and allows to show that CD44 expression depends on polarization (M1 > M0 ≥ M2). It is noteworthy that THP-1 M2 expressed CD44v6, suggesting their suitability as a model of tumor-associated macrophages. In the uptake of HA, both as a soluble polymer and in the form of (siRNA-loaded) nanoparticles, CD44 expression correlated positively with binding, but negatively with internalization. Counterintuitively, it appears that a higher presence of CD44 (in M1) allows a more efficient capture of HA materials, but a lower expression (in M2) is conducive to better internalization. Although possibly cell-specific, this unexpected relationship indicates that the common paradigm "higher CD44 expression = better targetability" is too simplistic; mechanistic details of both receptor presentation and association still need to be elucidated for a predictable targeting behavior.

Clinical development of new drug-radiotherapy combinations

In countries with the best cancer outcomes, approximately 60% of patients receive radiotherapy as part of their treatment, which is one of the most cost-effective cancer treatments. Notably, around 40% of cancer cures include the use of radiotherapy, either as a single modality or combined with other treatments. Radiotherapy can provide enormous benefit to patients with cancer. In the past decade, significant technical advances, such as image-guided radiotherapy, intensity-modulated radiotherapy, stereotactic radiotherapy, and proton therapy enable higher doses of radiotherapy to be delivered to the tumour with significantly lower doses to normal surrounding tissues. However, apart from the combination of traditional cytotoxic chemotherapy with radiotherapy, little progress has been made in identifying and defining optimal targeted therapy and radiotherapy combinations to improve the efficacy of cancer treatment. The National Cancer Research Institute Clinical and Translational Radiotherapy Research Working Group (CTRad) formed a Joint Working Group with representatives from academia, industry, patient groups and regulatory bodies to address this lack of progress and to publish recommendations for future clinical research. Herein, we highlight the Working Group's consensus recommendations to increase the number of novel drugs being successfully registered in combination with radiotherapy to improve clinical outcomes for patients with cancer.

Intravenous administration of the selective toll-like receptor 7 agonist DSR-29133 leads to anti-tumor efficacy in murine solid tumor models which can be potentiated by combination with fractionated radiotherapy

Strategies to augment anti-cancer immune responses have recently demonstrated therapeutic utility. To date clinical success has been achieved through targeting co-inhibitory checkpoints such as CTLA-4, PD-1, and PD-L1. However, approaches that target co-activatory pathways are also being actively being developed. Here we report that the novel TLR7-selective agonist DSR-29133 is well tolerated in mice and leads to acute immune activation. Administration of DSR-29133 leads to the induction of IFNα/γ, IP-10, TNFα, IL-1Ra and IL-12p70, and to a reduction in tumor burden in syngeneic models of renal cancer (Renca), metastatic osteosarcoma (LM8) and colorectal cancer (CT26). Moreover, we show that the efficacy of DSR-29133 was significantly improved when administered in combination with low-dose fractionated radiotherapy (RT). Effective combination therapy required weekly administration of DSR-29133 commencing on day 1 of a fractionated RT treatment cycle, whereas no enhancement of radiation response was observed when DSR-29133 was administered at the end of the fractionated RT cycle. Combined therapy resulted in curative responses in a high proportion of mice bearing established CT26 tumors which was dependent on the activity of CD8+ T-cells but independent of CD4+ T-cells and NK/NKT cells. Moreover, long-term surviving mice originally treated with DSR-29133 and RT were protected by a tumor-specific memory immune response which could prevent tumor growth upon rechallenge. These results demonstrate that DSR-29133 is a potent selective TLR7 agonist that when administered intravenously can induce anti-tumor immune responses that can be further enhanced through combination with low-dose fractionated RT.

Non-symmetrical furan-amidines as novel leads for the treatment of cancer and malaria

NRH:quinone oxidoreductase 2 enzyme (NQO2) is a potential therapeutic target in cancer and neurodegenerative diseases, with roles in either chemoprevention or chemotherapy. Here we report the design, synthesis and evaluation of non-symmetrical furan-amidines and their analogues as novel selective NQO2 inhibitors with reduced adverse off-target effects, such as binding to DNA. A pathway for the synthesis of the non-symmetrical furan-amidines was established from the corresponding 1,4-diketones. The synthesized non-symmetrical furan-amidines and their analogues showed potent NQO2 inhibition activity with nano-molar IC50 values. The most active compounds were non-symmetrical furan-amidines with meta- and para-nitro substitution on the aromatic ring, with IC50 values of 15 nM. In contrast to the symmetric furan-amidines, which showed potent intercalation in the minor grooves of DNA, the synthesized non-symmetrical furan-amidines showed no affinity towards DNA, as demonstrated by DNA melting temperature experiments. In addition, Plasmodium parasites, which possess their own quinone oxidoreductase PfNDH2, were inhibited by the non-symmetrical furan-amidines, the most active possessing a para-fluoro substituent (IC50 9.6 nM). The high NQO2 inhibition activity and nanomolar antimalarial effect of some of these analogues suggest the lead compounds are worthy of further development and optimization as potential drugs for novel anti-cancer and antimalarial strategies.

Inhibition of monocarboxylate transporter-1 (MCT1) by AZD3965 enhances radiosensitivity by reducing lactate transport

Inhibition of the monocarboxylate transporter MCT1 by AZD3965 results in an increase in glycolysis in human tumor cell lines and xenografts. This is indicated by changes in the levels of specific glycolytic metabolites and in changes in glycolytic enzyme kinetics. These drug-induced metabolic changes translate into an inhibition of tumor growth in vivo. Thus, we combined AZD3965 with fractionated radiation to treat small cell lung cancer (SCLC) xenografts and showed that the combination provided a significantly greater therapeutic effect than the use of either modality alone. These results strongly support the notion of combining MCT1 inhibition with radiotherapy in the treatment of SCLC and other solid tumors.

Acquired resistance to fractionated radiotherapy can be overcome by concurrent PD-L1 blockade

Radiotherapy is a major part in the treatment of most common cancers, but many patients experience local recurrence with metastatic disease. In evaluating response biomarkers, we found that low doses of fractionated radiotherapy led to PD-L1 upregulation on tumor cells in a variety of syngeneic mouse models of cancer. Notably, fractionated radiotherapy delivered in combination with αPD-1 or αPD-L1 mAbs generated efficacious CD8(+) T-cell responses that improved local tumor control, long-term survival, and protection against tumor rechallenge. These favorable outcomes were associated with induction of a tumor antigen-specific memory immune response. Mechanistic investigations showed that IFNγ produced by CD8(+) T cells was responsible for mediating PD-L1 upregulation on tumor cells after delivery of fractionated radiotherapy. Scheduling of anti-PD-L1 mAb was important for therapeutic outcome, with concomitant but not sequential administration with fractionated radiotherapy required to improve survival. Taken together, our results reveal the mechanistic basis for an adaptive response by tumor cells that mediates resistance to fractionated radiotherapy and its treatment failure. With attention to scheduling, combination immunoradiotherapy with radiotherapy and PD-1/PD-L1 signaling blockade may offer an immediate strategy for clinical evaluation to improve treatment outcomes.

A novel systemically administered Toll-like receptor 7 agonist potentiates the effect of ionizing radiation in murine solid tumor models

Although topical TLR7 therapies such as imiquimod have proved successful in the treatment of dermatological malignancy, systemic delivery may be required for optimal immunotherapy of nondermatological tumors. We report that intravenous delivery of the novel small molecule TLR7 agonist, DSR-6434, leads to the induction of type 1 interferon and activation of T and B lymphocytes, NK and NKT cells. Our data demonstrate that systemic administration of DSR-6434 enhances the efficacy of ionizing radiation (IR) and leads to improved survival in mice bearing either CT26 or KHT tumors. Of the CT26 tumor-bearing mice that received combined therapy, 55% experienced complete tumor resolution. Our data reveal that these long-term surviving mice have a significantly greater frequency of tumor antigen specific CD8(+) T cells when compared to age-matched tumor-naïve cells. To evaluate therapeutic effects on spontaneous metastases, we showed that combination of DSR-6434 with local IR of the primary tumor significantly reduced metastatic burden in the lung, when compared to time-matched cohorts treated with IR alone. The data demonstrate that systemic administration of the novel TLR7 agonist DSR-6434 in combination with IR primes an antitumor CD8(+) T-cell response leading to improved survival in syngeneic models of colorectal carcinoma and fibrosarcoma. Importantly, efficacy extends to sites outside of the field of irradiation, reducing metastatic load. Clinical evaluation of systemic TLR7 therapy in combination with IR for the treatment of solid malignancy is warranted.

The two common polymorphic forms of human NRH-quinone oxidoreductase 2 (NQO2) have different biochemical properties

There are two common forms of NRH-quinone oxidoreductase 2 (NQO2) in the human population resulting from SNP rs1143684. One has phenylalanine at position 47 (NQO2-F47) and the other leucine (NQO2-L47). Using recombinant proteins, we show that these variants have similar steady state kinetic parameters, although NQO2-L47 has a slightly lower specificity constant. NQO2-L47 is less stable towards proteolytic digestion and thermal denaturation than NQO2-F47. Both forms are inhibited by resveratrol, but NQO2-F47 shows negative cooperativity with this inhibitor. Thus these data demonstrate, for the first time, clear biochemical differences between the variants which help explain previous biomedical and epidemiological findings.

Emerging opportunities for the combination of molecularly targeted drugs with radiotherapy

Recent drug discovery developments in the field of small molecule targeted agents have led to much interest in combining these with radiotherapy. There are good preclinical data to suggest this approach worthy of investigation and in this review we discuss how this has translated into recent clinical trials. The outcome of clinical trials investigating radiotherapy/targeted drug combinations published in the last 5 years is discussed, as are trials in progress. The perceived future opportunities and challenges in the development of this exciting area are considered.

A synthetic approach to novel carvotacetone and antheminone analogues with anti-tumour activity

A synthetic approach to analogues of the terpenoid natural product antheminone A is described which employs (-)-quinic acid as starting material. A key conjugate addition step proved to be unpredictable regarding its stereochemical outcome however the route allowed access to two diastereoisomeric series of compounds. The results of biological assay of the toxicity of the target compounds towards non-small-cell lung cancer cell line A549 are reported.

Inhibition of carbonic anhydrase activity modifies the toxicity of doxorubicin and melphalan in tumour cells in vitro

Carbonic anhydrase IX (CA IX) is a hypoxia-regulated enzyme, overexpressed in many types of human cancer. CA IX is involved in pH homeostasis, contributing to extracellular acidification and tumourigenesis. Acidification of the extracellular milieu can impact upon cellular uptake of chemotherapeutic drugs by favouring weak acids (e.g. melphalan), but limiting access of weak bases (e.g. doxorubicin). We investigated whether alterations of CA IX activity affected anti-cancer drug uptake and toxicity. CA inhibitor acetazolamide (AZM) enhanced doxorubicin toxicity but reduced melphalan toxicity in cell lines that highly expressed CA IX under anoxic conditions (HT29 and MDA435 CA9/18). The toxicity changes reflected modification of passive drug uptake. AZM did not alter toxicity or uptake in cells with low CA IX activity (HCT116 and MDA435 EV1). AZM lowered intracellular pH in HT29 and MDA435 CA9/18 cells under anoxic conditions. CA IX activity has chemomodulatory properties and is an attractive target for anti-cancer therapy.

In silico screening reveals structurally diverse, nanomolar inhibitors of NQO2 that are functionally active in cells and can modulate NF-κB signaling

The National Cancer Institute chemical database has been screened using in silico docking to identify novel nanomolar inhibitors of NRH:quinone oxidoreductase 2 (NQO2). The inhibitors identified from the screen exhibit a diverse range of scaffolds and the structure of one of the inhibitors, NSC13000 cocrystalized with NQO2, has been solved. This has been used to aid the generation of a structure-activity relationship between the computationally derived binding affinity and experimentally measured enzyme inhibitory potency. Many of the compounds are functionally active as inhibitors of NQO2 in cells at nontoxic concentrations. To show this, advantage was taken of the NQO2-mediated toxicity of the chemotherapeutic drug CB1954. The toxicity of this drug is substantially reduced when the function of NQO2 is inhibited, and many of the compounds achieve this in cells at nanomolar concentrations. The NQO2 inhibitors also attenuated TNFα-mediated, NF-кB-driven transcriptional activity. The link between NQO2 and the regulation of NF-кB was confirmed by using short interfering RNA to NQO2 and by the observation that NRH, the cofactor for NQO2 enzyme activity, could regulate NF-кB activity in an NQO2-dependent manner. NF-кB is a potential therapeutic target and this study reveals an underlying mechanism that may be usable for developing new anticancer drugs.

Inhibition of PARP-1 by olaparib (AZD2281) increases the radiosensitivity of a lung tumor xenograft

PARP-1 is a critical enzyme in the repair of DNA strand breaks. Inhibition of PARP-1 increases the effectiveness of radiation in killing tumor cells. However, although the mechanism(s) are well understood for these radiosensitizing effects in vitro, the underlying mechanism(s) in vivo are less clear. Nicotinamide, a drug structurally related to the first generation PARP-1 inhibitor, 3-aminobenzamide, reduces tumor hypoxia by preventing transient cessations in tumor blood flow, thus improving tumor oxygenation and sensitivity to radiotherapy. Here, we investigate whether olaparib, a potent PARP-1 inhibitor, enhances radiotherapy, not only by inhibiting DNA repair but also by changing tumor vascular hemodynamics in non-small cell lung carcinoma (NSCLC). In irradiated Calu-6 and A549 cells, olaparib enhanced the cytotoxic effects of radiation (sensitizer enhancement ratio at 10% survival = 1.5 and 1.3) and DNA double-strand breaks persisted for at least 24 hours after treatment. Combination treatment of Calu-6 xenografts with olaparib and fractionated radiotherapy caused significant tumor regression (P = 0.007) relative to radiotherapy alone. To determine whether this radiosensitization was solely due to effects on DNA repair, we used a dorsal window chamber model to establish the drug/radiation effects on vessel dynamics. Olaparib alone, when given as single or multiple daily doses, or in combination with fractionated radiotherapy, increased the perfusion of tumor blood vessels. Furthermore, an ex vivo assay in phenylephrine preconstricted arteries confirmed olaparib to have higher vasodilatory properties than nicotinamide. This study suggests that olaparib warrants consideration for further development in combination with radiotherapy in clinical oncology settings such as NSCLC.

Abstract 1713: Mechanisms of resistance to platinum based drugs uncovered by protection caused by substituted coumarins

Disruption of p53 can have a profound effect on cellular sensitivity to Platinum-based drugs. Inhibition of NQO1 by dicoumarol and other substituted coumarins can target p53 for degradation. Thus, we tested the ability of NQO1 inhibitors to protect HCT116 cells (containing wild type p53) against the cytotoxic effects of cisplatin. All the NQO1 inhibitors protect cells against the damaging effects of cisplatin (see the table for representative data for one of the inhibitors, AS3). Protection was also seen in a second cell line with wild type p53 (RT112 bladder carcinoma cells). To confirm p53 dependence, experiments were carried out using cells with mutant (MDA231) or null (HCT116 -/-) p53. Surprisingly, the coumarin-based agents also protected these cells against cisplatin-induced damage. In addition, these observations were not dependent on NQO1, since MDA231 cells, with negligible NQO1, and cells overexpressing NQO1 (MDA321-DTD) were similarly protected. Protection is also observed for oxaliplatin but, interestingly, there is no protection against etoposide toxicity.

Cell cycle analysis of HCT116 cells treated with cisplatin show that, 24 hours after treatment, cells are blocked in G2. When cells are given the dicoumarol analogues at the same time as the cisplatin, no cell cycle delay is observed. Further, analysis of apoptosis mediators shows that treatment with AS3 inhibits oxaliplatin induction of Bak and reduces caspase-3 activity. Understanding the mechanism by which treatment with the dicoumarol analogues can cause resistance to cisplatin could reveal new methods for potentially overcoming resistance to platinum-based drugs in the clinic.

Abstract 4123: Monocarboxylate transporter 4 expression is a prognostic factor for radiotherapy outcome in squamous cell carcinoma of the head and neck

Background: Hypoxia contributes significantly to tumor progression and resistance to radiotherapy, decreasing local tumor control and lowering the rates of disease-free and overall survival. Hypoxic tumor cells utilize the glycolytic pathway for survival, producing vast quantities of lactate. Monocarboxylate Transporters (MCTs) 1 and 4 are key transporters of lactate, enabling sustained high glycolytic rates and maintenance of intra-cellular pH.

Aim: To carry out the first study evaluating tumor MCT1 and 4 expression as potential biomarkers of prognosis in patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy, and to determine the impact of MCT expression on radiation resistance.

Methods: 125 histologically confirmed SCC pre-treatment diagnostic oropharyngeal cancer biopsies (tonsil or posterior third of the tongue) were collected retrospectively from diagnostic archives. The biopsies were analyzed immunohistochemically to evaluate MCT1 and 4 membrane expression. MCT expression was assessed in a double blind manner using a semi-quantitative scoring system. Scores were analyzed for possible correlations with clinicopathological data relating to outcome 5 years post diagnosis, where all patients had received radiotherapy to the primary site. FaDu HNSCC cells expressing doxycycline inducible shRNA targeting MCT4 were used to evaluate radiosensitivity of wild-type and MCT4-knockdown cells.

Results: A univariate analysis comparing high (top 25% of scores) vs low MCT expression (lower 75%) showed that MCT4, but not MCT1, is a significant adverse prognostic factor for radiotherapy outcome. High MCT4 expression correlates with poor loco-regional control (p = 0.017), reduced cancer-specific survival (p = 0.02) and reduced overall survival (p = 0.055). In a multivariate analysis high MCT4 expression retained prognostic significance for poor loco-regional control (p = 0.007). Confirmation of MCT4 as a novel target for increasing hypoxic radiosensitivity was carried out by clonogenic assay in FaDu wild-type and shMCT4 cell lines, MCT4-knockdown cells showed a marked increase in hypoxic radiosensitivity compared to wild-type cells.

Conclusions: The increase in significance from overall survival to loco-regional control is consistent with a hypoxia-regulated marker of radiotherapy resistance. The functional role of MCT4 as a lactate transporter in hypoxia may be of key underlying biological importance to this finding, maintaining intracellular pH in a hypoxic microenvironment. These findings suggest that inhibition of MCT4 may modify hypoxic tumor regions and sensitize tumor cells to radiation treatment.

Therefore, MCT4 should be explored further as a novel target and biomarker for prognosis and prediction of benefit from hypoxia-modifying therapy in patients undergoing radiotherapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4123. doi:10.1158/1538-7445.AM2011-4123

Abstract 5088: Exploring ATM deficiency as a potential therapeutic target for the PARP inhibitor olaparib in head and neck squamous cell carcinoma

Background: Ataxia telangiectasia mutated (ATM) gene, localized in chromosome 11q22-23 is a key player in the signaling response to double strand breaks (DSBs). Impaired DSB repair due to ATM deficiency in tumor cells may lead to a wider application of the ‘‘synthetic lethality’’ approach seen with PARP inhibitors in BRCA-deficient tumors. Targeting DNA repair mechanisms with specific small molecule inhibitors will in principle sensitize tumor cells to DNA-damaging agents such as radiation. Radiation therapy remains the most common treatment of choice for head and neck cancers; however, there is still a large scope for improvement. Loss of distal 11q chromosome and subsequent ATM deficiency has been reported in primary head and neck tumors. Therefore, there are two aims to this work. First, we will establish the potential of targeting this cellular deficiency with the potent poly (ADP-ribose) polymerase (PARP) inhibitor olaparib; second, we will determine the prognostic significance of ATM deficiency in patients with head and neck squamous cell carcinoma (HNSCC) undergoing radiotherapy.

Methods: A panel of 10 HNSCC cell lines was screened for sensitivity to radiation in combination with olaparib by clonogenic survival assay in normoxic and anoxic conditions. The effect of olaparib as a single agent was also assessed in a PE/CA PJ34 (ATM deficient) xenograft model. A panel of 155 HNSCC biopsies taken prior to treatment with radiotherapy and where 5 year outcome data was available were used for ATM expression analysis by immunohistochemistry (IHC) and fluorescent in situ hybridization (FISH).

Results: Olaparib enhanced the effect of ionizing radiation (IR) in all HNSCC cell lines. In vitro, the increase in sensitivity to 2Gy after olaparib treatment ranged between 1.5- and 8.4-fold in normoxia and between 1.2- and 3.9-fold in anoxia. In vivo, administration of olaparib (50mg/kg p.o) as a single agent in PE/CA PJ34 xenografts daily for 5 days caused a substantial increase in tumor growth delay compared to vehicle alone. The IHC and FISH studies of the 155 HNSCC biopsies showed a variable level of ATM deficiency and the prognostic significance (if any) of these observations are being established.

Conclusion: We demonstrate that olaparib is a promising candidate as a single agent in tumors with ATM deficiency, and given the radiosensitizing effects in vitro and in vivo it warrants consideration for combining with radiation for the treatment of HNSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5088. doi:10.1158/1538-7445.AM2011-5088

Guidelines for the welfare and use of animals in cancer research

Animal experiments remain essential to understand the fundamental mechanisms underpinning malignancy and to discover improved methods to prevent, diagnose and treat cancer. Excellent standards of animal care are fully consistent with the conduct of high quality cancer research. Here we provide updated guidelines on the welfare and use of animals in cancer research. All experiments should incorporate the 3Rs: replacement, reduction and refinement. Focusing on animal welfare, we present recommendations on all aspects of cancer research, including: study design, statistics and pilot studies; choice of tumour models (e.g., genetically engineered, orthotopic and metastatic); therapy (including drugs and radiation); imaging (covering techniques, anaesthesia and restraint); humane endpoints (including tumour burden and site); and publication of best practice.

Abstract SY34-03: Hypoxia-metabolic targets for drug development: Identification of targets and their validation

The low oxygen status of solid tumours relative to normal tissues has been known for over 50 years. However, methods targeting or exploiting the presence of hypoxia in tumours, for therapeutic benefit, have generally met with little success. Initially, these methods included the use of hypoxic cell radiosensitizers and bioreductive drugs. In the light of current knowledge the reason for “failure” was not necessarily a flaw in the hypotheses being tested, but rather an inability to identify those patients most likely to respond to the modifying treatment. It is now known that tumours vary in their level and extent of hypoxia, with those tumours showing the least hypoxia (highest oxygen tension) being the most responsiveness to therapy. The discovery of the hypoxia-dependent transcription factor, HIF-1, and identification of its downstream gene targets revealed new avenues for targeting tumours. Expression of HIF-1, CAIX, and GLUT-1 have been used as molecular markers of hypoxia and there has been some success in their use as prognostic markers. Further, there has been recent development of a hypoxia metagene signature (Cancer Res. 2007, 67, 3441-9) that has shown prognostic significance in multiple cancers. Despite this progress in identifying molecular markers of hypoxia there has only been one well defined example of using this information for developing novel therapeutic targets; this is the identification and validation of lysyl oxidase (Nature 2006, 440, 1222-6).

Associated with hypoxia is an abnormal metabolic phenotype often characterized by high levels of lactate in human tumours. Monocarboxylate transporter-4 (mct-4) functions to transport lactate out of the cell preventing intra-cellular accumulation of lactate and therefore enabling sustained high glycolytic rates and maintenance of intra-cellular pH. We have demonstrated that mct-4 is a hypoxia/HIF-dependent gene and we evaluated its potential as a novel therapeutic target. Firstly, we evaluated whether expression of mct-4 protein in a panel of 155 oropharangeal tumours correlated with outcome of treatment with radiotherapy. Using a univariate analysis to assess high mct-4 expression (top 25% of scores) vs low mct-4 expression (lower 75%) we showed that mct-4 is a significant adverse prognostic factor in this series of biopsies. High mct-4 expression correlated with poor loco-regional control (p = 0.017), reduced cancer-specific survival (p = 0.02) and reduced overall survival (p = 0.055). In a multivariate analysis high mct-4 expression retained prognostic significance for poor loco-regional control (p = 0.007). We have therefore identified mct-4 as a potential target in head and neck cancer and we have gone on to validate its therapeutic significance by carrying out various gene knock-down studies in vitro and in vivo. Using siRNA to mct-4 we have shown that cells lacking mct-4 are substantially more radioresponsive under hypoxic conditions. Hence, not only is mct-4 expression an indicator of adverse outcome but it is also a target for the development of potential therapeutics (particularly when combined with radiotherapy).

Citation Format: Ian J. Stratford. Hypoxia-metabolic targets for drug development: Identification of targets and their validation [abstract]. In: Proceedings of the AACR 101st Annual Meeting 2010; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr SY34-03

Abstract 5635: Analysis of monocarboxylate transporter 4 as a biomarker shows prognostic significance as an indicator of radiotherapy in squamous cell carcinoma of the head and neck

BACKGROUND: Hypoxia is known to contribute significantly to tumor progression and resistance to radiotherapy, decreasing local tumor control and lowering the rates of disease free and overall survival. Research to target hypoxia in the clinic has produced varying results; hence the discovery of hypoxia markers has become more significant. Monocarboxylate Transporter 4 (MCT4) is a hypoxia-regulated transporter of lactate out of the cell, preventing its intra-cellular accumulation, enabling sustained high glycolytic rates and maintenance of intra-cellular pH.

AIM: To evaluate MCT4 immunohistochemically as a potential biomarker for prognosis of patients with head and neck squamous cell carcinoma (SCC) of tonsil or tongue undergoing radiotherapy, and to determine the impact of MCT4 expression on radiotherapy resistance.

METHODS: 155 histologically confirmed SCC pre-treatment diagnostic biopsies, originating from the tonsil or posterior third of the tongue, were collected retrospectively from a diagnostic archive. The biopsies were analyzed immunohistochemically to evaluate MCT4 membrane expression. MCT4 expression was assessed in a double blind study using a semi-quantitative scoring system. Scores were analyzed for possible correlations with clinicopathological data relating to outcome 5 years post diagnosis, where all patients had received radiotherapy to the primary site. siRNA against MCT4 was used in SCC cell lines to evaluate radiosensitivity of wild-type and MCT4-knockdown cells by colony forming assays.

RESULTS: A univariate analysis to assess high MCT4 expression (top 25% of scores) vs low MCT4 expression (lower 75%) showed that MCT4 is a significant adverse prognostic factor in the series of biopsies. High MCT4 expression correlates with poor loco-regional control (p = 0.017), reduced cancer-specific survival (p = 0.02) and reduced overall survival (p = 0.055). In a multivariate analysis high MCT4 expression retained prognostic significance for poor loco-regional control (p = 0.007). This was confirmed by clonogenic assay in FaDu and PE/CA-PJ-34 cell lines, MCT4-knockdown cells showed a marked increase in radiosensitivity compared to wild-type cells.

CONCLUSIONS: MCT4 is a significant biomarker for prognosis and treatment outcome following radiotherapy in SCC of tonsil and tongue. The increase in significance from overall survival to loco-regional control is consistent with a hypoxia-regulated marker of radiotherapy resistance. The functional role of MCT4 as a lactate transporter in hypoxia may be of key underlying biological importance to this finding, maintaining intracellular pH in an hypoxic microenvironment. This suggests that drug inhibition of MCT4 may potentially sensitize tumor cells to radiation treatment.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5635.

Abstract 3713: Inhibition of NQO2 by imidozoacridinones, including C1311 (Symadex, NSC645809): Implications for their mechanism of action

INTRODUCTION: Imidazoacridinones (IAs) have well documented anti-tumour activity in vitro and in vivo. They are thought to act as intercalating agents and inhibitors of topoisomerase II. More recently C1311 and other IAs have been shown to act as inhibitors of receptor tyrosine kinases such as FLT3 (J Clin Oncol 2008. Vol 26(15S) 2576). We have recently demonstrated that a structurally related series of triazoloacridinones can act as potent inhibitors of the oxidoreductases NQO1 and NQO2 (Bioorg Med Chem, 2009. In Press). Consequently, we conducted a computational substructure screen of the NCI chemical database to identify compounds with an IA scaffold. Here we describe these compounds, as novel inhibitors of NQO2, with low nanomolar potency. Moreover, some of these agents are up to 50-fold more efficient than the standard inhibitor, resveratrol.

EXPERIMENTAL: Compounds were evaluated spectrophotometrically for their ability to inhibit human NQO2 using NRH and DCPIP as co-substrates. Inhibitory potency (IC50) was related to computational binding affinity in order to derive potential structure/activity relationships. Toxicity was assessed in HCT116 cells (measured as the concentration required to reduce proliferation by 50%) using the MTT assay. The capacity of the compounds to interact with DNA was measured by changes in DNA melting temperature. Intercalative properties were confirmed by ethidium bromide displacement in SDS-PAGE gel electrophoresis

RESULTS: Seventeen compounds were evaluated for inhibitory potency which ranged from 6 to 1000nM. IC50 values were correlated with computationally derived binding affinities with a correlation coefficient of 0.93. However, the 200 fold difference in NQO2 inhibitory potency was not associated with any major change in toxicity which ranged from 460 to 3000nM. All compounds (at 10μM) were able to increase the melting temperature of calf thymus DNA in low salt solution. Changes in Tm ranged from 4.5 to 9oC and correlated well with ethidium bromide displacement. Though, as previously reported for IAs (Biochem Pharma, 2002. Vol 63, 1653), no obvious relationship could be determined between toxicity and Tm or the ability to displace ethidium bromide from DNA.

CONCLUSION: We have identified IAs as novel inhibitors of NQO2, with some in the series being the most potent inhibitors yet reported. Therefore, these agents could have applications in processes, such as inflammation, where NQO2 may be important. Furthermore, one of the IAs in the series is C1311 (IC50 = 148nM), an agent currently in clinical trial. It has been reported that tyrosine kinase inhibitors, such as imatinib, can also interact with NQO2 (BMC Struct Biol, 2009. Vol 9(7) 1472) and this may compromise drug action. Hence, when reviewing the activity of C1311, the cellular content of NQO2 should be considered since drug/enzyme interactions could influence overall activity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3713.

In vivo activation of the hypoxia-targeted cytotoxin AQ4N in human tumor xenografts

AQ4N (banoxantrone) is a prodrug that, under hypoxic conditions, is enzymatically converted to a cytotoxic DNA-binding agent, AQ4. Incorporation of AQ4N into conventional chemoradiation protocols therefore targets both oxygenated and hypoxic regions of tumors, and potentially will increase the effectiveness of therapy. This current pharmacodynamic and efficacy study was designed to quantify tumor exposure to AQ4 following treatment with AQ4N, and to relate exposure to outcome of treatment. A single dose of 60 mg/kg AQ4N enhanced the response of RT112 (bladder) and Calu-6 (lung) xenografts to treatment with cisplatin and radiation therapy. AQ4N was also given to separate cohorts of tumor-bearing mice 24 hours before tumor excision for subsequent analysis of metabolite levels. AQ4 was detected by high performance liquid chromatography/mass spectrometry in all treated samples of RT112 and Calu-6 tumors at mean concentrations of 0.23 and 1.07 microg/g, respectively. These concentrations are comparable with those shown to be cytotoxic in vitro. AQ4-related nuclear fluorescence was observed in all treated tumors by confocal microscopy, which correlated with the high performance liquid chromatography/mass spectrometry data. The presence of the hypoxic marker Glut-1 was shown by immunohistochemistry in both Calu-6 tumors and RT112 tumors, and colocalization of AQ4 fluorescence and Glut-1 staining strongly suggested that AQ4N was activated in these putatively hypoxic areas. This is the first demonstration that AQ4N will increase the efficacy of chemoradiotherapy in preclinical models; the intratumoral levels of AQ4 found in this study are comparable with tumor AQ4 levels found in a recent phase I clinical study, which suggests that these levels could be potentially therapeutic.

Glucocorticoid receptor over-expression promotes human small cell lung cancer apoptosis in vivo and thereby slows tumor growth

Small cell lung cancer (SCLC) is an aggressive tumor, associated with ectopic ACTH syndrome. We have shown that SCLC cells are glucocorticoid receptor (GR) deficient, and that restoration of GR expression confers glucocorticoid sensitivity and induces apoptosis in vitro. To determine the effects of GR expression in vivo, we characterized a mouse SCLC xenograft model that secretes ACTH precursor peptides, and so drives high circulating corticosterone concentrations (analogous to the ectopic ACTH syndrome). Infection of SCLC xenografts with GR-expressing adenovirus significantly slowed tumor growth compared with control virus infection. Time to fourfold initial tumor volume increased from a median of 9 days to 16 days (P=0.05; n=7 per group). Post-mortem analysis of GR-expressing tumors revealed a threefold increase in apoptotic (TUNEL positive) cells (P<0.01). Infection with the GR-expressing adenovirus caused a significant reduction in Bcl-2 and Bcl-xL transcripts. Furthermore, in both the GR-expressing adenovirus-infected cells and tumors, a significant number of uninfected cells underwent apoptosis, supporting a bystander cell killing effect. Therefore, GR expression is pro-apoptotic for human SCLCs in vivo, as well as in vitro, suggesting that loss of GR confers a survival advantage to SCLCs.

Design, synthesis and enzymatic evaluation of 6-bridged imidazolyluracil derivatives as inhibitors of human thymidine phosphorylase

A series of novel imidazolyluracil conjugates were rationally designed and synthesised to probe the active site constraints of the angiogenic enzyme, thymidine phosphorylase (TP, E.C. 2.4.2.4). The lead compound in the series, 15d, showed good binding in the active site of human TP with an inhibition in the low μM range. The absence of a methylene bridge between the uracil and the imidazolyl sub-units (series 16) decreased potency (up to 3-fold). Modelling suggested that active site residues Arg202, Ser217 and His116 are important for inhibitor binding.

Site and strain-specific variation in gut microbiota profiles and metabolism in experimental mice

Background

The gastrointestinal tract microbiota (GTM) of mammals is a complex microbial consortium, the composition and activities of which influences mucosal development, immunity, nutrition and drug metabolism. It remains unclear whether the composition of the dominant GTM is conserved within animals of the same strain and whether stable GTMs are selected for by host-specific factors or dictated by environmental variables.

Methodology/Principal Findings

The GTM composition of six highly inbred, genetically distinct strains of mouse (C3H, C57, GFEC, CD1, CBA nu/nu and SCID) was profiled using eubacterial –specific PCR-DGGE and quantitative PCR of feces. Animals exhibited strain-specific fecal eubacterial profiles that were highly stable (c. >95% concordance over 26 months for C57). Analyses of mice that had been relocated before and after maturity indicated marked, reproducible changes in fecal consortia and that occurred only in young animals. Implantation of a female BDF1 mouse with genetically distinct (C57 and Agoutie) embryos produced highly similar GTM profiles (c. 95% concordance) between mother and offspring, regardless of offspring strain, which was also reflected in urinary metabolite profiles. Marked institution-specific GTM profiles were apparent in C3H mice raised in two different research institutions.

Conclusion/Significance

Strain-specific data were suggestive of genetic determination of the composition and activities of intestinal symbiotic consortia. However, relocation studies and uterine implantation demonstrated the dominance of environmental influences on the GTM. This was manifested in large variations between isogenic adult mice reared in different research institutions.

The mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 inhibitor AZD6244 (ARRY-142886) enhances the radiation responsiveness of lung and colorectal tumor xenografts

PURPOSE

Novel molecularly targeted agents, given in combination with radiotherapy, have the potential to increase tumor response rates and the survival of patients with lung cancer. AZD6244 is a potent and selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2), a critical enzyme within the MAPK/extracellular signal-regulated kinase (ERK) signaling pathway that regulates the proliferation and survival of tumor cells.

EXPERIMENTAL DESIGN

This study examined the potential benefit of combining AZD6244 with fractionated radiotherapy using human lung and colon carcinoma xenograft models.

RESULTS

AZD6244 reduced ERK phosphorylation in Calu-6 lung cancer cells in vitro. Administration of AZD6244 for 10 days (25 mg/kg twice daily p.o.) inhibited the tumor growth of Calu-6 xenografts, with regrowth occurring on cessation of drug treatment. When fractionated tumor-localized radiotherapy (5 x 2 Gy) was combined with AZD6244 treatment, the tumor growth delay was enhanced significantly when compared with either modality alone, and this effect was also seen in a colon tumor model. We examined the effect of inhibiting MEK1/2 on the molecular responses to hypoxia, a potential interaction that could contribute to radioresponsiveness. AZD6244 reduced hypoxia-inducible factor-specific transactivation in vivo, shown using Calu-6 dual clone cells that stably express a Firefly luciferase gene under the control of a hypoxia-driven promoter. Furthermore, hypoxia-inducible factor-1 alpha, GLUT-1, and vascular endothelial growth factor levels were reduced by AZD6244, and there was a significant decrease in vascular perfusion in the tumors given combination treatment when compared with the other treatment groups.

CONCLUSIONS

These data provide support for the clinical development of AZD6244 in combination with radiotherapy and indicate a potential role for AZD6244 in inhibiting the tumor hypoxia response.

Contribution of HIF-1 and drug penetrance to oxaliplatin resistance in hypoxic colorectal cancer cells

BACKGROUND

Hypoxia is as an indicator of poor treatment outcome. Consistently, hypoxic HCT116 colorectal cancer cells are resistant to oxaliplatin, although the mechanistic basis is unclear. This study sought to investigate the relative contribution of HIF-1 (hypoxia-inducible factor-1)-mediated gene expression and drug penetrance to oxaliplatin resistance using three-dimensional spheroids.

METHODS

Hypoxia-inducible factor-1alpha function was suppressed by the stable expression of a dominant-negative form in HCT116 cells (DN). Cells were drug exposed as monolayer or multicellular spheroid cultures. Cells residing at differing oxygenation status were isolated from Hoechst 33342-treated spheroids using flow cytometry. Sub-populations were subjected to clonogenic survival assays and to Inductively-Coupled Plasma Mass Spectroscopy to determine oxaliplatin uptake.

RESULTS

In spheroids, a sensitivity gradient (hypoxic<aerobic) was revealed by survival assays and this correlated with levels of platinum-bound DNA. The resistance of hypoxic sub-populations exceeded relative changes in adduct levels, implicating factors other than drug penetrance in cell response. Dominant-negative monolayer cells showed no resistance to oxaliplatin in hypoxia and spheroids; the relative resistance of hypoxic compared with aerobic sub-populations was reduced compared with those from controls.

CONCLUSION

Overall, data show that drug penetration, DNA damage levels and HIF-1-dependent processes, all contribute to the resistance of hypoxic cells to oxaliplatin.

Effects of cytokine-induced macrophages on the response of tumor cells to banoxantrone (AQ4N)

Tumor-associated macrophages (TAMs) are found in many solid tumors and have often been shown to accumulate in the hypoxic regions surrounding areas of necrosis. TAMs are the major site of expression of nitric oxide synthase (NOS), a heme-containing homodimeric enzyme consisting of oxygenase and reductase domains. The latter has a high degree of sequence homology to cytochrome P450 reductase and a functional consequence of this is the ability of NOS, under hypoxic conditions, to activate the bioreductive drugs tirapazamine and RSU1069. Banoxantrone (AQ4N) is a bioreductive prodrug activated in hypoxia by an oxygen-dependent two-electron reductive process to yield the topoisomerase II inhibitor AQ4. A feature of this process is that the final product could potentially show bystander cell killing. Thus, in this study, we investigated the ability of inducible NOS (iNOS)-expressing TAMs to activate AQ4N and elicit toxicity in cocultured human tumor cells. Murine macrophages were induced to overexpress iNOS by treatment with a combination of cytokines, mixed with HT1080 and HCT116 human tumor cells, and the toxicity of AQ4N was determined under aerobic or hypoxic conditions. The aerobic toxicity of AQ4N toward tumor cells was not affected through coculturing with macrophages. However, under hypoxic conditions, the induction of iNOS activity in the macrophages was associated with an increase in AQ4N metabolism and a substantial increase in tumor cell toxicity, which was dependent on the proportion of macrophages in the culture. This study is the first demonstration of TAM-mediated prodrug activation to result in bystander killing of human tumor cells.