Preclinical Evaluation of Zn(II) Self-Assemblies with Selective Cytotoxic Activity Against Cancer Cells In Vitro and In Ovo

Dipodal pyridylthiazole amine ligands L1 and L2 both form different metallo-supramolecular self-assemblies with Zn2+ and Cu2+ and these are shown to be toxic and selective towards cancer cell lines in vitro. Furthermore, potency and selectivity are highly dependent upon the metal ions, ligand system and bound anion, with significant changes in chemosensitivity and selectivity dependent upon which species are employed. Importantly, significant anti-tumor activity was observed in ovo at doses that are non-toxic.

Infrared and Raman Diagnostic Modeling of Phosphate Adsorption on Ceria Nanoparticles

Cerium dioxide (CeO2; ceria) nanoparticles (CeNPs) are promising nanozymes that show a variety of biological activity. Effective nanozymes need to retain their activity in the face of surface speciation in biological environments, and characterizing surface speciation is therefore critical to understanding and controlling the therapeutic capabilities of CeNPs. In particular, adsorbed phosphates can impact the enzymatic activity exploited to convert phosphate prodrugs into therapeutics in vivo and also define the early stages of the phosphate-scavenging processes that lead to the transformation of active CeO2 into inactive CePO4. In this work, we utilize ab initio lattice-dynamics calculations to study the interaction of phosphates with the three major surfaces of ceria and to predict the infrared (IR) and Raman spectral signatures of adsorbed phosphate species. We find that phosphates adsorb strongly to CeO2 surfaces in a range of stable binding configurations, of which 5-fold coordinated P species in a trigonal bipyramidal coordination may represent a stable intermediate in the early stages of phosphate scavenging. We find that the phosphate species show characteristic spectral fingerprints between 500 and 1500 cm-1, whereas the bare CeO2 surfaces show no active modes above 600 cm-1, and the 5-fold coordinated P species in particular show potential diagnostic P-O stretching modes between 650 and 700 cm-1 in both IR and Raman spectra. This comprehensive exploration of different binding modes for phosphates on CeO2 and the set of reference spectra provides an important step toward the experimental characterization of phosphate speciation and, ultimately, control of its impact on the performance of ceria nanozymes.

Cross-species oncogenomics offers insight into human muscle-invasive bladder cancer

BACKGROUND

In humans, muscle-invasive bladder cancer (MIBC) is highly aggressive and associated with a poor prognosis. With a high mutation load and large number of altered genes, strategies to delineate key driver events are necessary. Dogs and cats develop urothelial carcinoma (UC) with histological and clinical similarities to human MIBC. Cattle that graze on bracken fern also develop UC, associated with exposure to the carcinogen ptaquiloside. These species may represent relevant animal models of spontaneous and carcinogen-induced UC that can provide insight into human MIBC.

RESULTS

Whole-exome sequencing of domestic canine (n = 87) and feline (n = 23) UC, and comparative analysis with human MIBC reveals a lower mutation rate in animal cases and the absence of APOBEC mutational signatures. A convergence of driver genes (ARID1A, KDM6A, TP53, FAT1, and NRAS) is discovered, along with common focally amplified and deleted genes involved in regulation of the cell cycle and chromatin remodelling. We identify mismatch repair deficiency in a subset of canine and feline UCs with biallelic inactivation of MSH2. Bovine UC (n = 8) is distinctly different; we identify novel mutational signatures which are recapitulated in vitro in human urinary bladder UC cells treated with bracken fern extracts or purified ptaquiloside.

CONCLUSION

Canine and feline urinary bladder UC represent relevant models of MIBC in humans, and cross-species analysis can identify evolutionarily conserved driver genes. We characterize mutational signatures in bovine UC associated with bracken fern and ptaquiloside exposure, a human-linked cancer exposure. Our work demonstrates the relevance of cross-species comparative analysis in understanding both human and animal UC.

Cytotoxicity of Ruthenium(II) Arene Complexes Containing Functionalized Ferrocenyl β-Diketonate Ligands

The synthesis and characterization of 24 ruthenium(II) arene complexes of the type [(p-cym)RuCl(Fc-acac)] (where p-cym = p-cymene and Fc-acac = functionalized ferrocenyl β-diketonate ligands) are reported, including single-crystal X-ray diffraction for 21 new complexes. Chemosensitivity studies have been conducted against human pancreatic carcinoma (MIA PaCa-2), human colorectal adenocarcinoma p53-wildtype (HCT116 p53+/+) and normal human retinal epithelial cell lines (APRE-19). The most active complex, which contains a 2-furan-substituted ligand (4), is 5x more cytotoxic than the analogs 3-furan complex (5) against MIA PaCa-2. Several complexes were screened under hypoxic conditions and at shorter-time incubations, and their ability to damage DNA was determined by the comet assay. Compounds were also screened for their potential to inhibit the growth of both bacterial and fungal strains.

Investigation of the cytotoxicity induced by didocosahexaenoin, an omega 3 derivative, in human prostate carcinoma cell lines

The aim of the present study was to investigate the cytotoxicity induced by an omega-3 derivative, didocosahexaenoin (Dido) on human prostate carcinoma cells and to compare the cytotoxicity to that of docosahexaenoic acid (DHA). Different carcinoma- and non-carcinoma cells were exposed to various concentrations of omega-3 compounds at varying exposure times and the cytotoxicity was measured by MTT assay. The mechanism of Dido-induced apoptosis was investigated in prostate carcinoma cells. Dido induced stronger cytotoxicity than DHA in human prostate carcinoma cells in a dose- and time-dependent manner. Dido was also more selective and potent in inducing cytotoxicity in prostate carcinoma cells than other carcinoma cell lines tested. Pre-treatment with Dido increased the level of reactive oxygen species (ROS) in prostate carcinoma cells. Pre-treatment with various antioxidants reduced the cytotoxicity induced by Dido. Pre-treatment with Dido ≥30 ​μM also induced apoptosis which was suggested to involve an externalisation of phosphatidyl serine, a significant increase in the mitochondrial membrane potential (p ​< ​0.01) and the level of activated caspase 3/7 (p ​< ​0.05) in prostate carcinoma cells. This study is the first to show that Dido induced cytotoxicity with high selectivity and higher potency than DHA in human prostate carcinoma cells. The mechanism of action is likely to involve an increase in the level of ROS, loss in the mitochondrial membrane potential as well as externalisation of phosphatidyl serine and increase in the caspase 3/7 activity. Dido may have potential to be used for the adjuvant therapy or combination therapy with conventional chemotherapeutic drugs.

The Warburg effect as a therapeutic target for bladder cancers and intratumoral heterogeneity in associated molecular targets

Bladder cancer is the 10th most common cancer worldwide. For muscle-invasive bladder cancer (MIBC), treatment includes radical cystectomy, radiotherapy, and chemotherapy; however, the outcome is generally poor. For non-muscle-invasive bladder cancer (NMIBC), tumor recurrence is common. There is an urgent need for more effective and less harmful therapeutic approaches. Here, bladder cancer cell metabolic reprogramming to rely on aerobic glycolysis (the Warburg effect) and expression of associated molecular therapeutic targets by bladder cancer cells of different stages and grades, and in freshly resected clinical tissue, is investigated. Importantly, analyses indicate that the Warburg effect is a feature of both NMIBCs and MIBCs. In two in vitro inducible epithelial-mesenchymal transition (EMT) bladder cancer models, EMT stimulation correlated with increased lactate production, the end product of aerobic glycolysis. Protein levels of lactate dehydrogenase A (LDH-A), which promotes pyruvate enzymatic reduction to lactate, were higher in most bladder cancer cell lines (compared with LDH-B, which catalyzes the reverse reaction), but the levels did not closely correlate with aerobic glycolysis rates. Although LDH-A is expressed in normal urothelial cells, LDH-A knockdown by RNAi selectively induced urothelial cancer cell apoptotic death, whereas normal cells were unaffected-identifying LDH-A as a cancer-selective therapeutic target for bladder cancers. LDH-A and other potential therapeutic targets (MCT4 and GLUT1) were expressed in patient clinical specimens; however, positive staining varied in different areas of sections and with distance from a blood vessel. This intratumoral heterogeneity has important therapeutic implications and indicates the possibility of tumor cell metabolic coupling.

An Efficient Method for the Isolation of Toxins from Pteridium aquilinum and Evaluation of Ptaquiloside Against Cancer and Non-cancer Cells

The common fern, bracken (Pteridium aquilinum), is well known for its toxic effects on livestock due principally to the carcinogenic constituent ptaquiloside ( 1: ), although other toxins are present including the cyanogenic glycoside, prunasin ( 2: ). Here, we report an improved and relatively "green" process for the isolation of 1: and 2: from fresh bracken fronds and the evaluation of 1: for cytotoxicity against several cancer cell lines. The results indicate that 1: displays selective toxicity against cancer cells relative to noncancer retinal epithelial cells, and the improved method for the isolation of 1: is expected to facilitate further exploration of its pharmacological properties.

Self-assembly of an anion receptor with metal-dependent kinase inhibition and potent in vitro anti-cancer properties

One topical area of supramolecular chemistry is the binding of anionic species but despite the importance of anions in diverse cellular processes and for cancer development, anion receptors or 'binders' have received little attention as potential anti-cancer therapeutics. Here we report self-assembling trimetallic cryptands (e.g. [L₂(Metal)₃]⁶⁺ where Metal = Cu²⁺, Zn²⁺ or Mn²⁺) which can encapsulate a range of anions and which show metal-dependent differences in chemical and biological reactivities. In cell studies, both [L₂Cu₃]⁶⁺ and [L₂Zn₃]⁶⁺ complexes are highly toxic to a range of human cancer cell lines and they show significant metal-dependent selective activity towards cancer cells compared to healthy, non-cancerous cells (by up to 2000-fold). The addition of different anions to the complexes (e.g. PO₄³-, SO₄²- or PhOPO₃²-) further alters activity and selectivity allowing the activity to be modulated via a self-assembly process. The activity is attributed to the ability to either bind or hydrolyse phosphate esters and mechanistic studies show differential and selective inhibition of multiple kinases by both [L₂Cu₃]⁶⁺ and [L₂Zn₃]⁶⁺ complexes but via different mechanisms.

Bis(bipyridine)ruthenium(II) Ferrocenyl β-Diketonate Complexes: Exhibiting Nanomolar Potency against Human Cancer Cell Lines

The synthesis and characterization of new bis(bipyridine)ruthenium(II) ferrocenyl β-diketonate complexes, [(bpy)2 Ru(Fc-acac)][PF6 ] (bpy=2,2'-bipyridine; Fc-acac=functionalized ferrocenyl β-diketonate ligand) are reported. Alongside clinical platinum drugs, these bimetallic ruthenium-iron complexes have been screened for their cytotoxicity against MIA PaCa-2 (human pancreatic carcinoma), HCT116 p53+/+ (human colon carcinoma, p53-wild type) and ARPE-19 (human retinal pigment epithelial) cell lines. With the exception of one complex, the library exhibit nanomolar potency against cancerous cell lines, and their relative potencies are up to 40x, 400x and 72x more cytotoxic than cisplatin, carboplatin and oxaliplatin, respectively. Under hypoxic conditions, the complexes remain cytotoxic (sub-micromolar range), highlighting their potential in targeting hypoxic tumor regions. The Comet assay was used to determine their ability to damage DNA, and results show dose dependent damage which correlates well with the cytotoxicity results. Their potential to treat bacterial and fungal strains has been determined, and highlight complexes have selective growth inhibition of up to 87-100 % against Staphylococcus aureus and Candida albicans.

Triazole-based, optically-pure metallosupramolecules; highly potent and selective anticancer compounds

Functionalised triazole aldehydes are used in the highly selective self-assembly of water-compatible, optically pure, low symmetry Fe(ii)- and Zn(ii)-based metallohelices. Sub-micromolar antiproliferative activity is observed against various cancerous cell lines, accompanied by excellent selectivity versus non-cancerous cells and potential for synergistic combinatorial therapy with cisplatin.

Glycoconjugated Metallohelices have Improved Nuclear Delivery and Suppress Tumour Growth In Vivo

Monosaccharides are added to the hydrophilic face of a self-assembled asymmetric FeII metallohelix, using CuAAC chemistry. The sixteen resulting architectures are water-stable and optically pure, and exhibit improved antiproliferative selectivity against colon cancer cells (HCT116 p53+/+ ) with respect to the non-cancerous ARPE-19 cell line. While the most selective compound is a glucose-appended enantiomer, its cellular entry is not mainly glucose transporter-mediated. Glucose conjugation nevertheless increases nuclear delivery ca 2.5-fold, and a non-destructive interaction with DNA is indicated. Addition of the glucose units affects the binding orientation of the metallohelix to naked DNA, but does not substantially alter the overall affinity. In a mouse model, the glucose conjugated compound was far better tolerated, and tumour growth delays for the parent compound (2.6 d) were improved to 4.3 d; performance as good as cisplatin but with the advantage of no weight loss in the subjects.

Revisiting Bromohexitols as a Novel Class of Microenvironment-Activated Prodrugs for Cancer Therapy

Bromohexitols represent a potent class of DNA-alkylating carbohydrate chemotherapeutics that has been largely ignored over the last decades due to safety concerns. The limited structure-activity relationship data available reveals significant changes in cytotoxicity with even subtle changes in stereochemistry. However, no attempts have been made to improve the therapeutic window by rational drug design or by using a prodrug approach to exploit differences between tumour physiology and healthy tissue, such as acidic extracellular pH and hypoxia. Herein, we report the photochemical synthesis of highly substituted endoperoxides as key precursors for dibromohexitol derivatives and investigate their use as microenvironment-activated prodrugs for targeting cancer cells. One endoperoxide was identified to have a marked increased activity under hypoxic and low pH conditions, indicating that endoperoxides may serve as microenvironment-activated prodrugs.

Discovery of selective, antimetastatic and anti-cancer stem cell metallohelices via post-assembly modification

A remarkable array of mechanistic and pharmacological behaviours is discovered via click derivatisation of asymmetric, optically pure helicate-like compounds.

Helicates and related metallofoldamers, synthesised by dynamic self-assembly, represent an area of chemical space inaccessible by traditional organic synthesis, and yet with potential for discovery of new classes of drug. Here we report that water-soluble, optically pure Fe(ii)- and even Zn(ii)-based triplex metallohelices are an excellent platform for post-assembly click reactions. By these means, the in vitro anticancer activity and most importantly the selectivity of a triplex metallohelix Fe(ii) system are dramatically improved. For one compound, a remarkable array of mechanistic and pharmacological behaviours is discovered: inhibition of Na⁺/K⁺ ATPase with potency comparable to the drug ouabain, antimetastatic properties (including inhibition of cell migration, re-adhesion and invasion), cancer stem cell targeting, and finally colonosphere inhibition competitive with the drug salinomycin.

Inactivation of apaziquone by haematuria: implications for the design of phase III clinical trials against non-muscle invasive bladder cancer

Purpose

Despite positive responses in phase II clinical trials, the bioreductive prodrug apaziquone failed to achieve statistically significant activity in non-muscle invasive bladder cancer in phase III trials. Apaziquone was administered shortly after transurethral resection and here we test the hypothesis that haematuria inactivates apaziquone.

Methods

HPLC analysis was used to determine the ability of human whole blood to metabolise apaziquone ex vivo. An in vitro model of haematuria was developed and the response of RT112 and EJ138 cells following a 1-h exposure to apaziquone was determined in the presence of urine plus or minus whole blood or lysed whole blood.

Results

HPLC analysis demonstrated that apaziquone is metabolised by human whole blood with a half-life of 78.6 ± 23.0 min. As a model for haematuria, incubation of cells in media containing up to 75% buffered (pH 7.4) urine and 25% whole blood was not toxic to cells for a 1-h exposure period. Whole blood (5% v/v) significantly (p < 0.01) reduced the potency of apaziquone in this experimental model. Lysed whole blood also significantly (p < 0.05) reduced cell growth, although higher concentrations were required to achieve an effect (15% v/v).

Conclusions

The results of this study demonstrate that haematuria can reduce the potency of apaziquone in this experimental model. These findings impact upon the design of further phase III clinical trials and strongly suggest that apaziquone should not be administered immediately after transurethral resection of non-muscle invasive bladder cancer when haematuria is common.

Ruthenium-Containing Linear Helicates and Mesocates with Tuneable p53-Selective Cytotoxicity in Colorectal Cancer Cells

The ligands L¹ and L² both form separable dinuclear double-stranded helicate and mesocate complexes with Ru^II . In contrast to clinically approved platinates, the helicate isomer of [Ru₂ (L¹ )₂ ]⁴⁺ was preferentially cytotoxic to isogenic cells (HCT116 p53^-/- ), which lack the critical tumour suppressor gene. The mesocate isomer shows the reverse selectivity, with the achiral isomer being preferentially cytotoxic towards HCT116 p53^+/+ . Other structurally similar Ru^II -containing dinuclear complexes showed very little cytotoxic activity. This study demonstrates that alterations in ligand or isomer can have profound effects on cytotoxicity towards cancer cells of different p53 status and suggests that selectivity can be "tuned" to either genotype. In the search for compounds that can target difficult-to-treat tumours that lack the p53 tumour suppressor gene, [Ru₂ (L¹ )₂ ]⁴⁺ is a promising compound for further development.

Abstract 2139: Evaluation of a novel hypoxia-activated prodrug strategy in colorectal cancer cells

Introduction: Current chemotherapeutic drugs are often ineffective against cancer cells that reside within the tumor microenvironment due to contributing factors such as hypoxia (low O2 tension) and acidic extracellular pH (pHe). Hypoxia is known to drive the aggressive cancer phenotype in many solid tumors, making it a key component of drug development. The use of hypoxia-activated prodrugs (HAPs) has been extensively studied over 40 years but to date no HAP has been approved for use in humans, largely because of poor activity and toxicity profiles. The design of prodrugs that are activated by both hypoxia and acidic pHe may provide a greater degree of selectivity and activity than HAPs alone, and this study was designed to evaluate a series of novel bromosugar-based HAPs under hypoxic and acidic pHe conditions.

Method: A library of 13 HAPs was evaluated against HCT116 colorectal cancer cells and ARPE-19 human retinal epithelial noncancerous cell line. Cytotoxicity was determined under (i) aerobic condition (21% oxygen) at pHe 7.4 or mild acidic conditions (pHe 6.5) and (ii) hypoxic condition (0.1% oxygen) at pHe 7.4 or mild acidic conditions (pHe 6.5). ARPE-19 cells were only tested under aerobic conditions and pHe 7.4 to reflect normal physiologic conditions. Compounds were tested at different concentrations ranging from 0.1-100µM from which an IC50 value was determined. Cell survival was measured after a 96-hour continuous drug exposure using the MTT assay.

Results: Among the compounds screened, DS10 demonstrated the most enhanced potency against HCT116 cells under hypoxic conditions with an IC50 value of 28.18 ± 7.01 µM as compared to an IC50 value of 66.39 ± 8.10 µM under normoxic conditions at pHe 7.4. Potency was further increased when DS10 was evaluated under a combination of hypoxic and acidic pHe conditions with an IC50 value of 16.30 µM ± 4.11. ARPE-19 cells showed an IC50 value of 42.95 µM ± 5.03 under aerobic conditions.

Discussion: The results of this study demonstrated that bromosugar derivatives may have the potential to selectively target hypoxic cancer cells in an acidic extracellular environment. Specifically, DS10 exhibited potential HAP properties with the ability to target cells that reside within the hypoxic and acidic microenvironment of tumors. Selectivity to tumor cells as opposed to noncancer cells was observed under these conditions, suggesting that DS10 is a promising compound to take forward for further evaluation.

Citation Format: Omar Hussain, Henrik Johansson, Simon J. Allison, Daniel S. Pedersen, Roger M. Phillips. Evaluation of a novel hypoxia-activated prodrug strategy in colorectal cancer cells [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 2139.

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.

Efficacy, pharmacokinetic and pharmacodynamic evaluation of apaziquone in the treatment of non-muscle invasive bladder cancer

INTRODUCTION

Apaziquone (also known as EO9 and Qapzola^TM) is a prodrug that is activated to DNA damaging species by oxidoreductases (particularly NQO1) and has the ability to kill aerobic and/or hypoxic cancer cells. Areas covered: Whilst its poor pharmacokinetic properties contributed to its failure in phase II clinical trials when administered intravenously, these properties were ideal for loco-regional therapies. Apaziquone demonstrated good anti-cancer activity against non-muscle invasive bladder cancer (NMIBC) when administered intravesically to marker lesions and was well tolerated with no systemic side effects. However, phase III clinical trials did not reach statistical significance for the primary endpoint of 2-year recurrence in apaziquone over placebo although improvements were observed. Post-hoc analysis of the combined study data did indicate a significant benefit for patients treated with apaziquone, especially when the instillation of apaziquone was given 30 min or more after surgery. A further phase III study is ongoing to test the hypotheses generated in the unsuccessful phase III studies conducted to date. Expert opinion: Because of its specific pharmacological properties, Apaziquone is excellently suited for local therapy such as NMIBC. Future studies should include proper biomarkers.

Abstract 970: Probing the expression and function of aldehyde dehydrogenases in prostate cancer using ALDH-affinic compounds and siRNA

The human aldehyde dehydrogenases (ALDHs) play a major role in detoxifying highly reactive aldehydes into carboxylic acids. Deregulation of ALDHs have implications in a number of cancers including prostate cancer. They play an important role as a cancer stem cell (CSC) marker due to high activity found in CSCs while high expression is also known to lead to resistance to drugs including docetaxel. Although the exact role of ALDHs is not fully understood, emerging information indicates several isoforms including ALDH1A3 and ALDH7A1 play a key role in cancer. To further elucidate the role of ALDHs in prostate cancer, we here report on the perturbation of ALDH expression and function using chemical probes and siRNA.

Primary prostate epithelial cells cultured from patient tissue were used for this study. Cancer samples were obtained from radical prostatectomies and benign samples from transurethral resection of the prostate.

qPCR analysis showed ALDH1A3 to be more highly expressed than ALDH7A1 in the primary prostate epithelial cultures in 18 patient samples. Expression of ALDH1A3 was 3-fold higher in the cancer samples compared to the benign samples. The RNA data correlates with protein expression in 6 patient samples by immunofluorescence. qPCR analysis also showed that knockdown of ALDH7A1 resulted in an increase in the expression of ALDH1A3 suggesting a compensatory mechanism. Trypan blue exclusion assay showed that knockdown of ALDH1A3, ALDH7A1 or a combination of both resulted in a reduction in cell numbers. Flow cytometry was used to study cell differentiation upon knockdown of ALDH1A3, ALDH7A1 or both. In all 7 samples studied there was a reduction in CD49b expression indicating cell differentiation. ALDH7A1 knockdown showed a higher level of cell differentiation in all cases. The colony forming ability of primary cells was also investigated post-transfection of siRNAs against ALDH1A3, ALDH7A1 or both using the colony formation assay which resulted in a lower number of colonies in all 7 samples tested. The effect was more pronounced in benign prostatic hyperplasia (BPH) than in malignant cancer samples and patient variability was observed. ALDH-affinic probe compounds (DEAB and three derivatives, Ali-9, Ali-14 & Ali-18) were tested against 5 patient samples to investigate if they have an effect on cell viability. All four compounds showed reduction in cell viability at the highest concentration while Ali-14 and Ali-18 showed a synergistic effect in combination treatment with docetaxel.

In conclusion, knockdown of ALDH1A3 and ALDH7A1 reduce cell number, induce cells to differentiate and reduce their colony forming ability. Novel ALDH-affinic probe compounds reduced cell viability alone and in combination with docetaxel, therefore these compounds may be of value both as single treatments and to provide a strategy to enhance taxane-based therapy such as docetaxel.

Citation Format: Maria Sadiq, Ali I. Ibrahim, Fiona Frame, Simon J. Allison, Mark Sutherland, Roger M. Phillips, Norman J. Maitland, Klaus Pors. Probing the expression and function of aldehyde dehydrogenases in prostate cancer using ALDH-affinic compounds and siRNA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 970. doi:10.1158/1538-7445.AM2017-970

Increasing anti-cancer activity with longer tether lengths of group 9 Cp* complexes

Here in, we report the cytotoxicity of both rhodium and iridium functionalised Cp* analogues of the [Cp*MCl2]2 dimers. The functionalised dimers contain a hydroxy tethered arm of differing carbon length. These show promising IC50 values when tested against HT-29, A2780 and cisplatin-resistant A2780cis human cancer cell lines, with the cytotoxicity improving proportionally with an increase in carbon tether length of the Cp* ring. The most promising results are seen for the 14-carbon Cp* tethered rhodium () and iridium () complexes, which show up to a 24-fold increase in IC50 compared to the unfunctionalised [Cp*MCl2]2 dimer. All complexes were potent inhibitors of purified thioredoxin reductase suggesting that disruption of cellular anti-oxidant function is one potential mechanism of action.

Development and characterization of a microfluidic model of the tumour microenvironment

The physical microenvironment of tumours is characterized by heterotypic cell interactions and physiological gradients of nutrients, waste products and oxygen. This tumour microenvironment has a major impact on the biology of cancer cells and their response to chemotherapeutic agents. Despite this, most in vitro cancer research still relies primarily on cells grown in 2D and in isolation in nutrient- and oxygen-rich conditions. Here, a microfluidic device is presented that is easy to use and enables modelling and study of the tumour microenvironment in real-time. The versatility of this microfluidic platform allows for different aspects of the microenvironment to be monitored and dissected. This is exemplified here by real-time profiling of oxygen and glucose concentrations inside the device as well as effects on cell proliferation and growth, ROS generation and apoptosis. Heterotypic cell interactions were also studied. The device provides a live 'window' into the microenvironment and could be used to study cancer cells for which it is difficult to generate tumour spheroids. Another major application of the device is the study of effects of the microenvironment on cellular drug responses. Some data is presented for this indicating the device's potential to enable more physiological in vitro drug screening.

Abstract 4093: The impact of the prostate cancer microenvironment on the expression and regulation of aldehyde dehydrogenases

Introduction:

Aldehyde dehydrogenase (ALDH) enzymes are involved in the detoxification of specific endogenous and exogenous aldehyde substrates. High ALDH activity is used to identify stem cells and has also been associated with poor prognosis in cancer. In prostate cancer (PCa) high ALDH activity has been associated with elevated clonogenicity, migratory behaviour, tumor progression and metastasis. Despite these observations there exists a poor understanding of the role of selected ALDH isoforms in PCa. In an attempt to understand if the tumor microenvironment impacts on ALDH function, we investigated their expression under hypoxia.

Methods:

Gene and protein expression analysis of ALDH isoforms -1A1, -1A2, -1A3, -1B1, -2, -3A1 and -7A1 in normal prostate cell line PNT2C2, and a panel of PCa cell lines with different stages of cancer was carried out by quantitative PCR and western blot under normoxic and hypoxic conditions at 24 and 48 hours. Gene expression of the ALDHs in primary prostate cultures was assessed following retinoic acid treatment. siRNA knockdown technology was used to study functional roles of selected ALDH isoforms.

Results:

Gene expression of ALDH1A3 was increased in Bob cells at 24h under hypoxia, at 48h this was less apparent but the expression of most ALDHs in Bob cells including ALDH1A2, -2, -3A1 and -7A1 was reduced at 48h. In SerBob cells, the gene expression of ALDH1A1 and -1B1 was reduced at both time points, whereas the expression of ALDH1A2, -2, and -7A1 was increased under hypoxia. At protein level, the expression of ALDH1A3 appeared low under hypoxia at both time points in SerBob cells while the expression of ALDH3A1 also appeared low after 24h exposure to hypoxia. In DU145 cells, there was an increase in ALDH1A1, -1A2, 1A3, -2, and -3A1 gene expression under hypoxia at 48h. In LNCAP cells, the gene expression of ALDH2 was increased at 48h under hypoxia whereas the expression of ALDH7A1 was reduced at 48h. The protein expression of ALDH7A1 was higher in PC3 cells under hypoxia at 24h. A significant increase was observed in ALDH1A3 and ALDH3A1 expression in response to retinoic acid. ALDH1A3 knockdown showed a significant reduction of cell viability in PC3 cells. Other investigations underway that will be reported at the conference are focused on how prostate cancer stem-like cells expressing ALDHs are responding to hypoxia.

Conclusion:

Our data suggests that the expression of certain ALDHs is affected by hypoxia and ALDH1A3 potentially is involved in cell survival in PCa. Future work will investigate if any of these isoforms can be used as biomarkers to distinguish indolent from malignant PCa.

Citation Format: Maria Sadiq, Simon J. Allison, Fiona Frame, Mark Sutherland, Roger M. Phillips, Norman J. Maitland, Klaus Pors. The impact of the prostate cancer microenvironment on the expression and regulation of aldehyde dehydrogenases. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4093.

Targeting the hypoxic fraction of tumours using hypoxia-activated prodrugs

The presence of a microenvironment within most tumours containing regions of low oxygen tension or hypoxia has profound biological and therapeutic implications. Tumour hypoxia is known to promote the development of an aggressive phenotype, resistance to both chemotherapy and radiotherapy and is strongly associated with poor clinical outcome. Paradoxically, it is recognised as a high-priority target and one of the therapeutic strategies designed to eradicate hypoxic cells in tumours is a group of compounds known collectively as hypoxia-activated prodrugs (HAPs) or bioreductive drugs. These drugs are inactive prodrugs that require enzymatic activation (typically by 1 or 2 electron oxidoreductases) to generate cytotoxic species with selectivity for hypoxic cells being determined by (1) the ability of oxygen to either reverse or inhibit the activation process and (2) the presence of elevated expression of oxidoreductases in tumours. The concepts underpinning HAP development were established over 40 years ago and have been refined over the years to produce a new generation of HAPs that are under preclinical and clinical development. The purpose of this article is to describe current progress in the development of HAPs focusing on the mechanisms of action, preclinical properties and clinical progress of leading examples.

Synthesis and anticancer activity of silver(I)-N-heterocyclic carbene complexes derived from the natural xanthine products caffeine, theophylline and theobromine

A new library of silver(I)-N-heterocyclic carbene complexes prepared from the natural products caffeine, theophylline and theobromine is reported. The complexes have been fully characterised using a combination of NMR spectroscopy, mass spectrometry, elemental analysis and X-ray diffraction analysis. Furthermore, the hydrophobicity of the complexes has been measured. The silver(I)-N-heterocyclic carbenes have been evaluated for their antiproliferative properties against a range of cancer cell lines of different histological types, and compared to cisplatin. The data shows different profiles of response when compared to cisplatin in the same panel of cells, indicating a different mechanism of action. Furthermore, it appears that the steric effect of the ligand and the hydrophobicity of the complex both play a role in the chemosensitivity of these compounds, with greater steric bulk and greater hydrophilicity delivering higher cytotoxicity.

Anticancer metallohelices: nanomolar potency and high selectivity

New optically pure helicate-like architectures are extremely active against cancer cell lines, with IC₅₀ values as low as 40 nM, but nearly three orders of magnitude less active against healthy cells. There is also low toxicity to microbes and amoeba.

A range of new helicate-like architectures have been prepared via highly diastereoselective self-assembly using readily accessible starting materials. Six pairs of enantiomers [Fe₂L₃]Cl₄·nH₂O (L = various bidentate ditopic ligands NN–NN) show very good water solubility and stability. Their activity against a range of cancer cell lines in vitro is structure-dependent and gives IC₅₀ values as low as 40 nM. In an isogenic pair of HCT116 colorectal cancer cells, preferential activity was observed against cell lines that lack functional p53. Selectivity is also excellent, and against healthy human retinal pigment epithelial (ARPE19) and lung fibroblast (WI38) cells IC₅₀ values are nearly three orders of magnitude higher. Cisplatin is unselective in the same tests. The compounds also appear to have low general toxicity in a number of models: there is little if any antimicrobial activity against methicillin-resistant Staphylococcus aureus and Escherichia coli; Acanthamoeba polyphaga is unaffected at 25 μg mL^–1 (12.5 μM); Manduca sexta larvae showed clear evidence of systemic distribution of the drug, and rather than any observation of adverse effects they exhibited a significant mean weight gain vs. controls. Investigation of the mode of action revealed no significant interaction of the molecules with DNA, and stimulation of substantial cell death by apoptosis.

Hypoxia-Sensitive Metal β-Ketoiminato Complexes Showing Induced Single-Strand DNA Breaks and Cancer Cell Death by Apoptosis

A series of ruthenium and iridium complexes have been synthesized and characterized with 20 novel crystal structures discussed. The library of β-ketoiminato complexes has been shown to be active against MCF-7 (human breast carcinoma), HT-29 (human colon carcinoma), A2780 (human ovarian carcinoma), and A2780cis (cisplatin-resistant human ovarian carcinoma) cell lines, with selected complexes' being more than three times as active as cisplatin against the A2780cis cell line. Selected complexes were also tested against the noncancerous ARPE-19 (retinal pigment epithelial cells) cell line, in order to evaluate the complexes selectivity for cancer cells. Complexes have also been shown to be highly active under hypoxic conditions, with the activities of some complexes increasing with a decrease in O2 concentration. The enzyme thioredoxin reductase is overexpressed in cancer cells, and complexes reported herein have the advantage of inhibiting this enzyme, with IC50 values measured in the nanomolar range. The anticancer activity of these complexes was further investigated to determine whether activity is due to effects on cellular growth or cell survival. The complexes were found to induce significant levels of cancer cell death by apoptosis with levels induced correlating closely with activity in chemosensitivity studies. As a possible cause of cell death, the ability of the complexes to induce damage to cellular DNA was also assessed. The complexes failed to induce double-strand DNA breaks or DNA cross-linking but induced significant levels of single-strand DNA breaks, indicating a mechanism of action different from that of cisplatin.

Evaluation of novel imidazotetrazine analogues designed to overcome temozolomide resistance and glioblastoma regrowth

The cellular responses to two new temozolomide (TMZ) analogues, DP68 and DP86, acting against glioblastoma multiforme (GBM) cell lines and primary culture models are reported. Dose-response analysis of cultured GBM cells revealed that DP68 is more potent than DP86 and TMZ and that DP68 was effective even in cell lines resistant to TMZ. On the basis of a serial neurosphere assay, DP68 inhibits repopulation of these cultures at low concentrations. The efficacy of these compounds was independent of MGMT and MMR functions. DP68-induced interstrand DNA cross-links were demonstrated with H2O2-treated cells. Furthermore, DP68 induced a distinct cell-cycle arrest with accumulation of cells in S phase that is not observed for TMZ. Consistent with this biologic response, DP68 induces a strong DNA damage response, including phosphorylation of ATM, Chk1 and Chk2 kinases, KAP1, and histone variant H2AX. Suppression of FANCD2 expression or ATR expression/kinase activity enhanced antiglioblastoma effects of DP68. Initial pharmacokinetic analysis revealed rapid elimination of these drugs from serum. Collectively, these data demonstrate that DP68 is a novel and potent antiglioblastoma compound that circumvents TMZ resistance, likely as a result of its independence from MGMT and mismatch repair and its capacity to cross-link strands of DNA.

Hypoxia modulates the activity of a series of clinically approved tyrosine kinase inhibitors

BACKGROUND AND PURPOSE

Hypoxia in tumours is known to cause resistance to conventional chemotherapeutic drugs. In contrast, little is known about the effects of hypoxia on targeted anti-cancer drugs. This study evaluated the effect of hypoxia on a series of clinically approved tyrosine kinase inhibitors (TKIs).

EXPERIMENTAL APPROACH

The effect of hypoxia (0.1% oxygen) on the activity of conventional cytotoxic drugs (5-fluorouracil, doxorubicin and vinblastine), the hypoxia-activated prodrug tirapazamine and 9 TKIs was determined in a panel of cell lines. Where hypoxia had a marked effect on chemosensitivity, Western blot analysis was conducted to determine the effect of hypoxia on target expression and the effect of TKIs on cell signalling response under aerobic and hypoxic conditions.

KEY RESULTS

Three patterns of chemosensitivity were observed: resistance under hypoxia, equitoxic activity against hypoxic and aerobic cells, and preferential cytotoxicity to hypoxic cells. Significant hypoxia selectivity (independent of HIF1) was observed in the case of dasatinib and this correlated with the ability of dasatinib to inhibit phosphorylation of Src at tyrosine 530. Sorafenib was significantly less effective under hypoxic conditions but resistance did not correlate with hypoxia-induced changes in Raf/MEK/ERK signalling.

CONCLUSIONS AND IMPLICATIONS

Hypoxia influences the activity of TKIs but in contrast to conventional cytotoxic drugs, preferential activity against hypoxic cells can occur. The search for hypoxia-targeted therapies has been long and fruitless and this study suggests that some clinically approved TKIs could preferentially target the hypoxic fraction of some tumour types.

Asymmetric triplex metallohelices with high and selective activity against cancer cells

Small cationic amphiphilic α-helical peptides are emerging as agents for the treatment of cancer and infection, but they are costly and display unfavourable pharmacokinetics. Helical coordination complexes may offer a three-dimensional scaffold for the synthesis of mimetic architectures. However, the high symmetry and modest functionality of current systems offer little scope to tailor the structure to interact with specific biomolecular targets, or to create libraries for phenotypic screens. Here, we report the highly stereoselective asymmetric self-assembly of very stable, functionalized metallohelices. Their anti-parallel head-to-head-to-tail 'triplex' strand arrangement creates an amphipathic functional topology akin to that of the active sub-units of, for example, host-defence peptides and p53. The metallohelices display high, structure-dependent toxicity to the human colon carcinoma cell-line HCT116 p53(++), causing dramatic changes in the cell cycle without DNA damage. They have lower toxicity to human breast adenocarcinoma cells (MDA-MB-468) and, most remarkably, they show no significant toxicity to the bacteria methicillin-resistant Staphylococcus aureus and Escherichia coli.

Mechanistic and cytotoxicity studies of group IV β-diketonate complexes

Group IV metal complexes have previously shown promise as novel anticancer agents. Here, we discuss the mechanistic and cytotoxic nature of a series of group IV β-diketonate coordination complexes. Clear evidence that the ligands are exchangeable on the metal centre and that the β-diketonate ligands can act as potential drug delivery vehicles of the group IV metal ions was obtained. When evaluated for the cytotoxicity against human colon adenocarcinoma (HT-29) and human breast adenocarcinoma (MCF-7) cell lines, a general trend of decreasing potency down the group IV metals was observed. The most promising results obtained were for the hafnium complexes, with the tris diphenyl β-diketonate hafnium complex exhibiting IC50 values of 4.9 ± 0.9 μM and 3.2 ± 0.3 μM against HT-29 and MCF-7, respectively, which are comparable with the activity of cisplatin against the same cell lines. This tri β-diketonate hafnium complex is the first to show potent in vitro cytotoxic activity. The results reported show that ligand design has a significant effect on the cytotoxic potential of the complexes, and that these group IV complexes warrant further evaluation as novel metal-containing anticancer agents.

Mathematical and computational models of drug transport in tumours

The ability to predict how far a drug will penetrate into the tumour microenvironment within its pharmacokinetic (PK) lifespan would provide valuable information about therapeutic response. As the PK profile is directly related to the route and schedule of drug administration, an in silico tool that can predict the drug administration schedule that results in optimal drug delivery to tumours would streamline clinical trial design. This paper investigates the application of mathematical and computational modelling techniques to help improve our understanding of the fundamental mechanisms underlying drug delivery, and compares the performance of a simple model with more complex approaches. Three models of drug transport are developed, all based on the same drug binding model and parametrized by bespoke in vitro experiments. Their predictions, compared for a 'tumour cord' geometry, are qualitatively and quantitatively similar. We assess the effect of varying the PK profile of the supplied drug, and the binding affinity of the drug to tumour cells, on the concentration of drug reaching cells and the accumulated exposure of cells to drug at arbitrary distances from a supplying blood vessel. This is a contribution towards developing a useful drug transport modelling tool for informing strategies for the treatment of tumour cells which are 'pharmacokinetically resistant' to chemotherapeutic strategies.