A Proteomic Investigation to Discover Candidate Proteins Involved in Novel Mechanisms of 5-Fluorouracil Resistance in Colorectal Cancer

One of the main obstacles to therapeutic success in colorectal cancer (CRC) is the development of acquired resistance to treatment with drugs such as 5-fluorouracil (5-FU). Whilst some resistance mechanisms are well known, it is clear from the stasis in therapy success rate that much is still unknown. Here, a proteomics approach is taken towards identification of candidate proteins using 5-FU-resistant sublines of human CRC cell lines generated in house. Using a multiplexed stable isotope labelling with amino acids in cell culture (SILAC) strategy, 5-FU-resistant and equivalently passaged sensitive cell lines were compared to parent cell lines by growing in Heavy medium with 2D liquid chromatography and Orbitrap Fusion™ Tribrid™ Mass Spectrometry analysis. Among 3003 commonly quantified proteins, six (CD44, APP, NAGLU, CORO7, AGR2, PLSCR1) were found up-regulated, and six (VPS45, RBMS2, RIOK1, RAP1GDS1, POLR3D, CD55) down-regulated. A total of 11 of the 12 proteins have a known association with drug resistance mechanisms or role in CRC oncogenesis. Validation through immunodetection techniques confirmed high expression of CD44 and CD63, two known drug resistance mediators with elevated proteomics expression results. The information revealed by the sensitivity of this method warrants it as an important tool for elaborating the complexity of acquired drug resistance in CRC.

Synthesis and Biological Evaluation of Cyclobutane-Based β3 Integrin Antagonists: A Novel Approach to Targeting Integrins for Cancer Therapy

The Arg-Gly-Asp (RGD)-binding family of integrin receptors, and notably the β3 subfamily, are key to multiple physiological processes involved in tissue development, cancer proliferation, and metastatic dissemination. While there is compelling preclinical evidence that both αvβ3 and αIIbβ3 are important anticancer targets, most integrin antagonists developed to target the β3 integrins are highly selective for αvβ3 or αIIbβ3. We report the design, synthesis, and biological evaluation of a new structural class of ligand-mimetic β3 integrin antagonist. These new antagonists combine a high activity against αvβ3 with a moderate affinity for αIIbβ3, providing the first evidence for a new approach to integrin targeting in cancer.

Anticancer water-soluble organoruthenium complexes: synthesis and preclinical evaluation

The synthesis, characterisation, and evaluation of the in vitro cytotoxicity of five maleonitriledithiolate‐based ruthenium metal complexes bearing various phosphine ligands towards two ovarian cancer cell lines (A2780 and A2780cisR), one non‐small‐cell lung cancer cell line (H460) and one normal prostate cell line (PNT2) are presented herein. These 18‐electron complexes were designed with four water‐soluble phosphine ligands to increase the water‐solubility character of the corresponding electron‐deficient ruthenium complex which showed great in vitro promises, and triphenylphosphine for comparison. The complexes with triphenylphosphine‐3,3′,3′′‐trisulfonic acid and triphenylphosphine present similar cytotoxicity compared to the 16‐electron precursor, with equal cytotoxicity to both A2780 and A2780cisR. Hints at the mechanism of action suggest an apoptotic pathway based on reactive oxygen species (ROS) production. No toxicity was observed in preliminary in vivo pilot studies for these two complexes in subcutaneous A2780 and A2780cisR xenograft models, with some evidence of tumour growth delay.

Controlled Bioactive Delivery Using Degradable Electroactive Polymers

Biomaterials capable of precisely controlling the delivery of agrochemicals/biologics/drugs/fragrances have significant markets in the agriscience/healthcare industries. Here, we report the development of degradable electroactive polymers and their application for the controlled delivery of a clinically relevant drug (the anti-inflammatory dexamethasone phosphate, DMP). Electroactive copolymers composed of blocks of polycaprolactone (PCL) and naturally occurring electroactive pyrrole oligomers (e.g., bilirubin, biliverdin, and hemin) were prepared and solution-processed to produce films (optionally doped with DMP). A combination of in silico/in vitro/in vivo studies demonstrated the cytocompatibility of the polymers. The release of DMP in response to the application of an electrical stimulus was observed to be enhanced by ca. 10–30% relative to the passive release from nonstimulated samples in vitro. Such stimuli-responsive biomaterials have the potential for integration devices capable of delivering a variety of molecules for technical/medical applications.

Semi-Synthetic Analogues of Cryptolepine as a Potential Source of Sustainable Drugs for the Treatment of Malaria, Human African Trypanosomiasis, and Cancer

The prospect of eradicating malaria continues to be challenging in the face of increasing parasite resistance to antimalarial drugs so that novel antimalarials active against asexual, sexual, and liver-stage malaria parasites are urgently needed. In addition, new antimalarials need to be affordable and available to those most in need and, bearing in mind climate change, should ideally be sustainable. The West African climbing shrub Cryptolepis sanguinolenta is used traditionally for the treatment of malaria; its principal alkaloid, cryptolepine (1), has been shown to have antimalarial properties, and the synthetic analogue 2,7-dibromocryptolepine (2) is of interest as a lead toward new antimalarial agents. Cryptolepine (1) was isolated using a two-step Soxhlet extraction of C. sanguinolenta roots, followed by crystallization (yield 0.8% calculated as a base with respect to the dried roots). Semi-synthetic 7-bromo- (3), 7, 9-dibromo- (4), 7-iodo- (5), and 7, 9-dibromocryptolepine (6) were obtained in excellent yields by reaction of 1 with N-bromo- or N-iodosuccinimide in trifluoroacetic acid as a solvent. All compounds were active against Plasmodia in vitro, but 6 showed the most selective profile with respect to Hep G2 cells: P. falciparum (chloroquine-resistant strain K1), IC₅₀ = 0.25 µM, SI = 113; late stage, gametocytes, IC₅₀ = 2.2 µM, SI = 13; liver stage, P. berghei sporozoites IC₅₀ = 6.13 µM, SI = 4.6. Compounds 3-6 were also active against the emerging zoonotic species P. knowlesi with 5 being the most potent (IC₅₀ = 0.11 µM). In addition, 3-6 potently inhibited T. brucei in vitro at nM concentrations and good selectivity with 6 again being the most selective (IC₅₀ = 59 nM, SI = 478). These compounds were also cytotoxic to wild-type ovarian cancer cells as well as adriamycin-resistant and, except for 5, cisplatin-resistant ovarian cancer cells. In an acute oral toxicity test in mice, 3-6 did not exhibit toxic effects at doses of up to 100 mg/kg/dose × 3 consecutive days. This study demonstrates that C. sanguinolenta may be utilized as a sustainable source of novel compounds that may lead to the development of novel agents for the treatment of malaria, African trypanosomiasis, and cancer.

Cytochrome P450 isoforms 1A1, 1B1 AND 2W1 as targets for therapeutic intervention in head and neck cancer

Epidemiological studies have shown that head and neck cancer (HNC) is a complex multistage process that in part involves exposure to a combination of carcinogens and the capacity of certain drug-metabolising enzymes including cytochrome P450 (CYP) to detoxify or activate such carcinogens. In this study, CYP1A1, CYP1B1 and CYP2W1 expression in HNC was correlated with potential as target for duocarmycin prodrug activation and selective therapy. In the HNC cell lines, elevated expression was shown at the gene level for CYP1A1 and CYP1B1 whereas CYP2W1 was hardly detected. However, CYP2W1 was expressed in FaDu and Detroit-562 xenografts and in a cohort of human HNC samples. Functional activity was measured in Fadu and Detroit-562 cells using P450-Glo™ assay. Antiproliferative results of duocarmycin prodrugs ICT2700 and ICT2706 revealed FaDu and Detroit-562 as the most sensitive HNC cell lines. Administration of ICT2700 in vivo using a single dose of ICT2700 (150 mg/kg) showed preferential inhibition of small tumour growth (mean size of 60 mm³) in mice bearing FaDu xenografts. Significantly, our findings suggest a potential targeted therapeutic approach to manage HNCs by exploiting intratumoural CYP expression for metabolic activation of duocarmycin-based prodrugs such as ICT2700.

Abstract 1331: Synthesis and evaluation of FPR1 inhibitors as a novel treatment for cancers

The formyl peptide receptor-1 (FPR1) is a member of 7TM GPCRs. It was first identified in phagocytic leukocytes and has been found to play a role in innate immune response to bacterial infection. Recently FPR1 has been shown to be overexpressed in many malignant cancers and particularly in glioblastoma. Our more recent investigation has shown that increased expression of FPR1 in cancer is most notably prominent in the periphery of the necrotic foci. We have hypothesised that FPR1 activation by molecules released from the hypoxic/necrotic core of tumours (including Annexin-A1 and short chain-N-formylated peptides such as fMLF) leads to increased proliferation, invasion, resistance, and angiogenesis. Therefore, antagonism of FPR1 should prevent these key drivers of malignancy in cancer. Here we present the synthesis and biological evaluation of a series of pyrazole compounds that potently inhibit FPR1. In addition, we provide a computational rationale for their relative potency based on docking of the molecules inside a homology model of FPR1. We will also show the efficacy of our lead compound, ICT12035 (IC50 =30nM in calcium mobilisation assay) in a number 2D and 3D proliferation and invasion assays in vitro, and in an in vivo animal model where it arrests tumour growth. Furthermore, we demonstrate the significance of FPR1 in tumour resistance by showing that ICT12035 increases the efficacy of cytotoxic agents TMZ and BCNU, as well as radiation in vitro. ICT12035 significantly abrogates the effects fMLF induced resistance to TMZ and BCNU in in U87 cell lines. A similar effect is also observed in a cell viability assay where in the addition of ICT12035 significantly increased cell death following radiation. Our findings suggest that inhibiting FPR1 in combination with chemotherapy and radiotherapy could be a new treatment strategy against cancers.

Citation Format: Amin Aghamohammadi, Di Lu, Anwar Salem, Patricia A. Cooper, Steven D. Shnyder, Victoria Vinader, Kamyar Afarinkia. Synthesis and evaluation of FPR1 inhibitors as a novel treatment for cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1331.

Abstract 2872: Methods of assessment of polysialyltransferase inhibitors for treatment of tumor cell dissemination

Polysialic acid (polySia) decorates the surface of NCAM (neuronal cell adhesion molecule) on neuroendocrine tumors, notably neuroblastoma and small cell lung cancer, and is strongly associated with poor prognosis and aggressive disease in patients in the clinic [1]. PolySia modulates tumor cell-cell and cell-matrix adhesion, migration, invasion and metastasis. SiRNA knockdown of polysialyltransferase (polyST) ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumors, abrogates tumor cell migration and invasion. PolyST is a selective and largely unexplored therapeutic target for neuroblastoma dissemination [1]. While assays are available to assess polyST enzyme activity, there is no methodology available specifically optimized for identification of novel polyST inhibitors. We describe the development of cell-free and cell-based assays that enable assessment of polysialyltransferase inhibition.

Development of the HPLC-fluorescence-based enzyme assay includes a comprehensive optimization of assay conditions, including evaluation of metal ion composition, enzyme concentration, substrate and acceptor concentration, temperature, pH and tolerance to DMSO, followed by validation using known polyST inhibitors. Thorough analysis of each of the assay components provided a set of optimized conditions. Under these optimized conditions, the experimentally observed Ki value for CMP, a competitive polyST inhibitor, was strongly correlated with the predicted Ki value, based on the classical Cheng-Prusoff equation [average fold error (AFE) = 1.043]. These results indicate that this assay can provide medium-throughput analysis for enzyme inhibitors with high accuracy. We additionally report optimized HPLC-based and ELISA-based methodologies for assessment of polyST inhibition in neuroblastoma cells, using endoneuraminidase N as control, and assessment of ICT3176 (a polysialylation inhibitor) as a test agent.

In conclusion, in vitro cell-free and cell-based assays for accurate measurement of polysialyltransferase (polyST) inhibition are described, specifically designed for routine identification of potential polyST inhibitors, generation of kinetics data and assessment of mode of inhibition, and assessment of effects on cellular polysialylation. Given the considerable and growing interest in the polySTs as important anti-metastatic targets in cancer drug discovery, these are vital tools to enable preclinical identification and evaluation of novel polyST inhibitors for neuroblastoma therapy.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939.

Citation Format: Xiaoxiao Guo, Jodie R. Malcolm, Anjana Patel, Marrwa M. Ali, Goreti Ribeiro Morais, Steven D. Shnyder, Paul M. Loadman, Laurence H. Patterson, Robert A. Falconer. Methods of assessment of polysialyltransferase inhibitors for treatment of tumor cell dissemination [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2872.

An assay for quantitative analysis of polysialic acid expression in cancer cells

Polysialic acid (polySia) is a linear polysaccharide comprised of N-acetylneuraminic acid residues and its over-expression in cancer cells has been correlated with poor clinical prognosis. An assay has been developed for quantitative analysis of cellular polySia expression. This was achieved by extracting and purifying released polySia from glycoproteins by mild acid hydrolysis and optimised organic extraction. The polySia was further hydrolysed into Sia monomers, followed by fluorescent labelling and quantitative analysis. The assay was qualified utilising endoneuraminidase-NF to remove polySia from the surface of C6-ST8SiaII cancer cells (EC₅₀ = 2.13 ng/mL). The result was comparable to that obtained in a polySia-specific cellular ELISA assay. Furthermore, the assay proved suitable for evaluation of changes in polySia expression following treatment with a small molecule inhibitor of polysialylation. Given the importance of polySia in multiple disease states, notably cancer, this is a potentially vital tool with applications in the fields of drug discovery and glycobiology.

Recent Advances in the Chemistry and Pharmacology of Cryptolepine

Cryptolepine, the principal constituent of the West African climbing shrub Cryptolepis sanguinolenta, continues to be of interest as a lead to new therapeutic agents, especially for the treatment of protozoal infections and cancer. This contribution reviews the research published in the last decade, highlighting new synthesis routes to cryptolepine and to analogs of this alkaloid, as well as their pharmacology. Studies relating to the use of C. sanguinolenta as an herbal medicine for the treatment of malaria are discussed, as well as the development of analogs of cryptolepine as leads to new agents for the treatment of malaria, trypanosomiasis, and cancer with an emphasis on the pharmacological mechanisms involved. Other potential therapeutic applications include antimicrobial, antidiabetic, and anti-inflammatory activities; the pharmacokinetics and toxicity of cryptolepine are also reviewed.

Abstract 4847: Optimizing the combination of the CDK4/6 inhibitor palbociclib and paclitaxel using cell cycle analysis

Background: Palbociclib is a CDK4/6 inhibitor approved for the treatment of ER+ HER2- advanced/metastatic breast cancer (MBC). We explored the hypothesis that palbociclib can enhance the efficacy of cytotoxics by synchronising the cell cycle prior to treatment with a cytotoxic, namely paclitaxel. This may be of particular importance in retinoblastoma protein (Rb) expressing triple negative (TN) BC, where hormone therapy is not an option, and increasing the efficacy of cytotoxics could be of great benefit.

Methods: We studied 4 BC cell lines of different molecular subtypes: MDA-MB-175 (ER+, HER2 -, Rb+), MDA-MB-361 (ER+, HER2+, Rb+), HCC-38 (TN, Rb+) and MDA-MB-468 (TN, Rb- as negative control). Cells were exposed to 100 nM palbociclib for up to 72h, followed by washout for up to 72h, with cell cycling monitored throughout by flow cytometry using propidium iodide (PI) staining to establish optimal timings for combining palbociclib with paclitaxel. Cytotoxic activity of the combination was quantified by cell counting and clonogenic assays.

Results: MDA-MB-361, MDA-MB-175 and HCC38 cells exposed to 100 nM palbociclib are arrested in G0/1 by 24h with up to 2%, 3.9% and 5.2% respectively, continuing into S-phase. MDA-MB-468 is unaffected, with the percentage of cells in S-phase similar to controls after treatment with up to 10 μM palbociclib. After palbociclib withdrawal, cells begin to re-enter the cell cycle before 12h. The highest level of synchronization occurs in MDA-MB-361 with up to 47% of cells in S-phase by 16h. By 24h there is a peak in the number of cells in G2/M, after which they return to a normal unsynchronised cycling pattern (4.9-13.2% cells in S-phase). Precise timing of re-entry into the cell cycle after palbociclib withdrawal varies between cell lines and, as this is important for combination with cytotoxics, warrants further investigation. Treating with higher concentrations of palbociclib slows re-entry of cells into S-phase and reduces synchronization. Combination with paclitaxel 16h after palbociclib withdrawal reduces the IC50 of paclitaxel by up to 72% compared to paclitaxel alone in MDA-MB-361 cells. Mice bearing MDA-MB-361 xenografts are being treated using the optimized schedule determined in vitro and tumors are to be dissociated into single cells for cell cycle analysis by flow cytometry, allowing the comparison of the efficacy of paclitaxel +/- palbociclib in vivo. In addition, tissues will be assayed for palbociclib pharmacokinetics. Results of ongoing in vivo studies results will be presented.

Conclusion: Short-term exposure to low dose palbociclib can synchronize Rb expressing cells in S-phase in vitro and, when combined optimally, increases the efficacy of paclitaxel in these cell lines, as indicated by a reduction in IC50. This is being investigated in in vivo studies, the results of which may help to inform future clinical trial design.

Citation Format: Jade A. Spencer, Amanda D. Race, Patricia A. Cooper, Steven D. Shnyder, Paul M. Loadman, Christopher J. Twelves. Optimizing the combination of the CDK4/6 inhibitor palbociclib and paclitaxel using cell cycle analysis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4847.

An efficient assay for identification and quantitative evaluation of potential polysialyltransferase inhibitors

The polysialyltransferases (polySTs) catalyse the polymerisation of polysialic acid, which plays an important role in tumour metastasis. While assays are available to assess polyST enzyme activity, there is no methodology available specifically optimised for identification and quantitative evaluation of potential polyST inhibitors. The development of an HPLC-fluorescence-based enzyme assay described within includes a comprehensive investigation of assay conditions, including evaluation of metal ion composition, enzyme, substrate and acceptor concentrations, temperature, pH, and tolerance to DMSO, followed by validation using known polyST inhibitors. Thorough analysis of each of the assay components provided a set of optimised conditions. Under these optimised conditions, the experimentally observed K_i value for CMP, a competitive polyST inhibitor, was strongly correlated with the predicted K_i value, based on the classical Cheng-Prusoff equation [average fold error (AFE) = 1.043]. These results indicate that this assay can provide medium-throughput analysis for enzyme inhibitors with high accuracy, through determining the corresponding IC₅₀ values with substrate concentration at the K_M, without the need to perform extensive kinetic studies for each compound. In conclusion, an in vitro cell-free assay for accurate assessment of polyST inhibition is described. The utility of the assay for routine identification of potential polyST inhibitors is demonstrated, allowing quantitative measurement of inhibition to be achieved, and exemplified through assessment of full competitive inhibition. Given the considerable and growing interest in the polySTs as important anti-metastatic targets in cancer drug discovery, this is a vital tool to enable preclinical identification and evaluation of novel polyST inhibitors.

Preclinical Anticancer Activity of an Electron-Deficient Organoruthenium(II) Complex

Ruthenium compounds have been shown to be promising alternatives to platinum(II) drugs. However, their clinical success depends on achieving mechanisms of action that overcome Pt-resistance mechanisms. Electron-deficient organoruthenium complexes are an understudied class of compounds that exhibit unusual reactivity in solution and might offer novel anticancer mechanisms of action. Here, we evaluate the in vitro and in vivo anticancer properties of the electron-deficient organoruthenium complex [(p-cymene)Ru(maleonitriledithiolate)]. This compound is found to be highly cytotoxic: 5 to 60 times more potent than cisplatin towards ovarian (A2780 and A2780cisR), colon (HCT116 p53+/+ and HCT116 p53-/-), and non-small cell lung H460 cancer cell lines. It shows no cross-resistance and is equally cytotoxic to both A2780 and A2780cisR cell lines. Furthermore, unlike cisplatin, the remarkable in vitro antiproliferative activity of this compound appears to be p53-independent. In vivo evaluation in the hollow-fibre assay across a panel of cancer cell types and subcutaneous H460 non-small cell lung cancer xenograft model hints at the activity of the complex. Although the impressive in vitro data are not fully corroborated by the in vivo follow-up, this work is the first preclinical study of electron-deficient half-sandwich complexes and highlights their promise as anticancer drug candidates.

Abstract 241: An efficient cell-based assay for quantification of cellular polysialic acid in neuroblastoma

Introduction Polysialic acid (polySia) decorates the surface of NCAM (neuronal cell adhesion molecule) on neuroendocrine tumors, notably neuroblastoma and small cell lung cancer, and is strongly associated with poor prognosis and aggressive disease in patients in the clinic [1]. PolySia modulates tumor cell-cell and cell-matrix adhesion, migration, invasion and metastasis. SiRNA knockdown of polysialyltransferase (polyST) ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumors, abrogates tumor cell migration and invasion. PolyST is a selective and largely unexplored therapeutic target for neuroblastoma dissemination [1].

Methods and Results We describe the development of a cell-based assay that quantifies the formation of polySia on the cell surface of neuroblastoma cells. This is a sensitive assay that detects the polySia that is released after pH adjustment, organic precipitation and acid hydrolysis. PolySia was first separated from cell lysate by mild acid hydrolysis and acetone precipitation. It was then purified by ethanol precipitation. We further analysed the role of lactonisation of polySia during organic precipitation. The purified polySia is further hydrolysed into sialic acid monomers, followed by DMB labelling and RPLC-fluorescence analysis. This method was validated by analysis of polySia in C6-ST8SiaII cells, following treatment with Endo-NF in a various concentrations. This method proved to be useful to assess polySia changes after treatment of cells with novel polyST inhibitors. The effect of lactonisation of polySia during organic precipitation was also investigated. It was found that lactonised polySia was mainly soluble in 90% acetone/90% ethanol, while natural polySia (non-lactonised) can be precipitated by ethanol in the presence salts. Based on the different solubility of polySia, a cost-efficient assay was designed to purify polySia released from cells with a low level of non-polySia-derived sialic acid contamination before further acid hydrolysis. With this method we quantified the different levels of cell-surface polySia-derived sialic acid between polySia-positive and polySia-negative cell lines. Furthermore, we successfully validated this method by Endo-NF treatment in C6-ST8SiaII cells: the EC50 of Endo-NF digestion of polySia in C6-ST8SiaII cells was approximately 5.4 pM. The assay has been successfully utilised to evaluate novel polyST inhibitors in vitro. [1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939; [2] Al-Saraireh YMJ et al., PLoS ONE, 2013, 8:e73366.

Citation Format: Xiaoxiao Guo, Francis Mprah Barnieh, Jodie Malcolm, Amanda D Race, Goreti Ribeiro Morais, Steven D Shnyder, Paul M Loadman, Laurence H Patterson, Robert A. Falconer. An efficient cell-based assay for quantification of cellular polysialic acid in neuroblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 241.

Abstract 350: Investigating the mechanisms of cellular uptake and metabolism of ICT2588, an MT-MMP-activated prodrug

ICT2588 is a non-toxic MT1-MMP-activated peptide prodrug of the potent vascular disrupting agent (VDA) azademethylcolchicine [1]. ICT2588 produces significant tumor-selective delivery (≥10-fold) of the toxic and potent azademethylcolchicine, as compared to the administration of azademethylcolchicine alone, in murine models of human colorectal, breast, lung and prostate cancers. In addition, ICT2588 exhibited reduced potential for toxicity, and cardiotoxicity in particular (a phenomenon associated with most VDAs) as a result of its metabolic stability in plasma and normal tissues [2]. ICT2588 is progressing towards clinical evaluation in the UK in 2019. In this study we aim to further investigate the cellular uptake and metabolism of ICT2588 and related compounds in MT1-MMP positive (HT1080) and MT1-MMP negative (MCF-7) cells in vitro. ICT2588 and related compounds were synthesized in-house and purified by preparative HPLC in excellent yield and purity. Activation of ICT2588 by recombinant MT1-MMP and its preferential metabolism in MT1-MMP positive tumor xenograft homogenates has been shown previously [1]. We are currently studying the mechanism of cellular uptake and metabolism of these peptide prodrugs by incubating these compounds in HT1080 and MCF-7 cell cultures. Cellular concentrations of ICT2588 and all metabolites identified were determined using RP-HPLC, mass spectrometry and immunofluorescent microscopy. We describe the first data on the cellular mechanism of uptake and metabolism of ICT2588 and related peptide prodrugs in cancer cells. Our findings have important implications in the future design of effective peptide-based tumor-targeted prodrugs. Reference: [1] Atkinson, J.M et al “Development of a tumor-targeted vascular disrupting agent activated by Membrane-type Matrix Metalloproteinases (MT-MMPs).” Cancer Research, 2010, 70, 6902-12. [2] Gill, J.H et al “Tumor-targeted prodrug ICT2588 demonstrates therapeutic activity against solid tumors and reduced potential for cardiovascular toxicity”. Mol Pharm. 2014,11:1294-300.

Citation Format: Francis Mprah Barnieh, Amanda D. Race, Steven D. Shnyder, Paul M. Loadman, Robert A. Falconer. Investigating the mechanisms of cellular uptake and metabolism of ICT2588, an MT-MMP-activated prodrug [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 350.

Tumor growth suppression using a combination of taxol-based therapy and GSK3 inhibition in non-small cell lung cancer

Glycogen synthase kinase-3 (GSK3) is over-expressed and hyperactivated in non-small cell lung carcinoma (NSCLC) and plays a role in ensuring the correct alignment of chromosomes on the metaphase plate during mitosis through regulation of microtubule stability. This makes the enzyme an attractive target for cancer therapy. We examined the effects of a selective cell-permeant GSK3 inhibitor (CHIR99021), used alone or in combination with paclitaxel, using an in vitro cell growth assay, a quantitative chromosome alignment assay, and a tumor xenograft model. CHIR99021 inhibits the growth of human H1975 and H1299 NSCLC cell lines in a synergistic manner with paclitaxel. CHIR99021 and paclitaxel promoted a synergistic defect in chromosomal alignment when compared to each compound administered as monotherapy. Furthermore, we corroborated our in vitro findings in a mouse tumor xenograft model. Our results demonstrate that a GSK3 inhibitor and paclitaxel act synergistically to inhibit the growth of NSCLC cells in vitro and in vivo via a mechanism that may involve converging modes of action on microtubule spindle stability and thus chromosomal alignment during metaphase. Our findings provide novel support for the use of the GSK3 inhibitor, CHIR99021, alongside taxol-based chemotherapy in the treatment of human lung cancer.

Evaluation of Alangium lamarckii Bark for Antiplasmodial and Cytotoxic Constituents and Isolation of a Novel Tubulosine Analogue

Alangium lamarkii is traditionally used in India for the treatment of malaria. Partial activity guided-fractionation of the basic chloroform fraction of the methanolic extract of the bark led to the isolation of a novel tubulosine analogue, 10-demethyl-9'- N-methyltubulosine (1), for which the trivial name tubulosatine is suggested. In addition, the known A. lamarkii constituents, tubulosine (2), cephaeline and emetine were isolated as potent antiplasmodial and cytotoxic constituents, but 1 was up to 1000-fold less potent than the former alkaloids against both malaria parasites and human cancer cell lines. The compounds were active against both chloroquine-sensitive and chloroquine-resistant malaria parasites, but no selective toxicity was observed towards malaria parasites compared with cancer cells with any of the alkaloids. Further work to explore the basis for the relatively weak biological activities of 1 would be worthwhile. Betulinic acid, stigmasterol and its 3- O-glucoside were isolated from the neutral chloroform fraction of the methanolic extract.

Hypoxia modulates CCR7 expression in head and neck cancers

BACKGROUND

The chemokine receptor CCR7 is expressed on lymphocytes and dendritic cells and is responsible for trafficking of these cells in and out of secondary lymphoid organs. It has recently been shown that CCR7 expression is elevated in a number of cancers, including head and neck cancers, and that its expression correlates to lymph node (LN) metastasis. However, little is known about the factors that can induce CCR7 expression in head and neck cancers.

METHOD

We compared the protein expression and functional responses of CCR7 under normoxia and hypoxia in head and neck cancer cell lines OSC-19, FaDu, SCC-4, A-253 and Detroit-562 cultured as monolayers, spheroids, and grown in vivo as xenografts in balb/c mice. In addition, we analysed the correlation between hypoxia marker HIF-1α and CCR7 expression in a tissue microarray comprising 80 clinical samples with various stages and grades of malignant tumour and normal tissue.

RESULTS

Under hypoxia, the expression of CCR7 is elevated in both in vitro and in vivo models. Furthermore, in malignant tissue, a correlation is observed between hypoxia marker HIF-1α and CCR7 across all clinical stages. This correlation is also strong in early histological grade of tumours.

CONCLUSION

Hypoxia plays a role in the regulation of the expression of CCR7 and it may contribute to the development of a metastatic phenotype in head and neck cancers through this axis.

RGD-Binding Integrins in Head and Neck Cancers

Alterations in integrin expression and function promote tumour growth, invasion, metastasis and neoangiogenesis. Head and neck cancers are highly vascular tumours with a tendency to metastasise. They express a wide range of integrin receptors. Expression of the αv and β1 subunits has been explored relatively extensively and linked to tumour progression and metastasis. Individual receptors αvβ3 and αvβ5 have proved popular targets for diagnostic and therapeutic agents but lesser studied receptors, such as αvβ6, αvβ8, and β1 subfamily members, also show promise. This review presents the current knowledge of integrin expression and function in squamous cell carcinoma of the head and neck (HNSCC), with a particular focus on the arginine-glycine-aspartate (RGD)-binding integrins, in order to highlight the potential of integrins as targets for personalised tumour-specific identification and therapy.

Agarose Spot as a Comparative Method for in situ Analysis of Simultaneous Chemotactic Responses to Multiple Chemokines

We describe a novel protocol to quantitatively and simultaneously compare the chemotactic responses of cells towards different chemokines. In this protocol, droplets of agarose gel containing different chemokines are applied onto the surface of a Petri dish, and then immersed under culture medium in which cells are suspended. As chemokine molecules diffuse away from the spot, a transient chemoattractant gradient is established across the spots. Cells expressing the corresponding cognate chemokine receptors migrate against this gradient by crawling under the agarose spots towards their centre. We show that this migration is chemokine-specific; meaning that only cells that express the cognate chemokine cell surface receptor, migrate under the spot containing its corresponding chemokine ligand. Furthermore, we show that migration under the agarose spot can be modulated by selective small molecule antagonists present in the cell culture medium.

Tubulin-binding dibenz[c,e]oxepines: Part 2. Structural variation and biological evaluation as tumour vasculature disrupting agents

5,7-Dihydro-3,9,10,11-tetramethoxybenz[c,e]oxepin-4-ol 1, prepared from a dibenzyl ether precursor via Pd-catalysed intramolecular direct arylation, possesses broad-spectrum in vitro cytotoxicity towards various tumour cell lines, and induces vascular shutdown, necrosis and growth delay in tumour xenografts in mice at sub-toxic doses. The biological properties of 1 and related compounds can be attributed to their ability to inhibit microtubule assembly at the micromolar level, by binding reversibly to the same site of the tubulin αβ-heterodimer as colchicine 2 and the allocolchinol, N-acetylcolchinol 4.

The use of thermographic imaging to evaluate therapeutic response in human tumour xenograft models

Non-invasive methods to monitor tumour growth are an important goal in cancer drug development. Thermographic imaging systems offer potential in this area, since a change in temperature is known to be induced due to changes within the tumour microenvironment. This study demonstrates that this imaging modality can be applied to a broad range of tumour xenografts and also, for the first time, the methodology's suitability to assess anti-cancer agent efficacy. Mice bearing subcutaneously implanted H460 lung cancer xenografts were treated with a novel vascular disrupting agent, ICT-2552, and the cytotoxin doxorubicin. The effects on tumour temperature were assessed using thermographic imaging over the first 6 hours post-administration and subsequently a further 7 days. For ICT-2552 a significant initial temperature drop was observed, whilst for both agents a significant temperature drop was seen compared to controls over the longer time period. Thus thermographic imaging can detect functional differences (manifesting as temperature reductions) in the tumour response to these anti-cancer agents compared to controls. Importantly, these effects can be detected in the first few hours following treatment and therefore the tumour is observable non-invasively. As discussed, this technique will have considerable 3Rs benefits in terms of reduction and refinement of animal use.

PIK3CA dependence and sensitivity to therapeutic targeting in urothelial carcinoma

Background

Many urothelial carcinomas (UC) contain activating PIK3CA mutations. In telomerase-immortalized normal urothelial cells (TERT-NHUC), ectopic expression of mutant PIK3CA induces PI3K pathway activation, cell proliferation and cell migration. However, it is not clear whether advanced UC tumors are PIK3CA-dependent and whether PI3K pathway inhibition is a good therapeutic option in such cases.

Methods

We used retrovirus-mediated delivery of shRNA to knock down mutant PIK3CA in UC cell lines and assessed effects on pathway activation, cell proliferation, migration and tumorigenicity. The effect of the class I PI3K inhibitor GDC-0941 was assessed in a panel of UC cell lines with a range of known molecular alterations in the PI3K pathway.

Results

Specific knockdown of PIK3CA inhibited proliferation, migration, anchorage-independent growth and in vivo tumor growth of cells with PIK3CA mutations. Sensitivity to GDC-0941 was dependent on hotspot PIK3CA mutation status. Cells with rare PIK3CA mutations and co-occurring TSC1 or PTEN mutations were less sensitive. Furthermore, downstream PI3K pathway alterations in TSC1 or PTEN or co-occurring AKT1 and RAS gene mutations were associated with GDC-0941 resistance.

Conclusions

Mutant PIK3CA is a potent oncogenic driver in many UC cell lines and may represent a valuable therapeutic target in advanced bladder cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2570-0) contains supplementary material, which is available to authorized users.

Abstract 3105: Probing cytochrome P450 activity with benzofuran-based duocarmycins in a panel of head and neck cancer cell lines and CYP1A1, 1B1 and CYP2W1 transfected cell lines

Background:

The cytochrome P450 (CYP) isoforms CYP1A1, 1B1 and 2W1 are highly expressed in tumour tissue and surrounding stroma compared to nearby normal tissue, which

provides an opportunity for development of selective cancer therapeutics as previously reported by us.1-2 However, no reagent is available to interrogate CYP2W1 and hence the purpose of this study was to evaluate a series of novel benzofuran-based duocarmycins as chemical probes to study the functional activity of CYP2W1.

Materials and methods:

Standard materials and methods can be found in the references below. Briefly, these include route to synthesis of duocarmycin bioprecursors, use of recombinant CYP bactosomes with LC/MS for metabolite identification, and cell culture MTT proliferation assay. CYP expression was measured by RT-PCR and western blot.

Results:

A panel of head and neck cancer (HNC) cell lines (SCC4, FaDu, Detroit-562, A-253, OSC19, UT-SCC5, UT-SCC10, UT-SCC14) were analysed for the expression of CYP1A1, CYP1B1 and CYP2W1. Significant expression (5-10 fold) was shown at the gene level while protein expression experiments are currently underway and will be reported at the meeting. Furthermore, CYP2W1 functional activity was probed with a novel series of benzofuran-based duocarmycin analogues. The compounds were incubated with recombinant CYP bactosomes or HEK2932W1-transfected cells and their oxidative metabolism was studied using LCMS. CYP2W1 was shown to metabolise one chemical probe, ICT2726, to a unique metabolite not observed for any other CYP isoform. The compounds were investigated for antiproliferative activity in a panel of cell lines (CHO, CHO1A1, RT112, HEK293, HEK2932W1, Cal27, Cal271B1, Cal33, Cal331B1). Obtained IC50 values > 1 μM, which for these ultrapotent (picomolar) duocarmycins, indicated no CYP-bioactivation, consistent with no active duocarmycin metabolite identified from the LCMS studies.

Conclusion:

Our findings support the use of non-toxic ICT2726 as a chemical tool that can be employed in vitro to probe CYP2W1 functional activity.

[1] Sheldrake et al.

Re-engineering of the duocarmycin structural architecture enables bioprecursor

development targeting CYP1A1 and CYP2W1 for biological activity. J Med Chem.

2013, 56, 6273-7.

[2] Travica et al. Colon cancer-specific

cytochrome P450 2W1 converts duocarmycin analogues into potent tumor

cytotoxins. Clin Cancer Res. 2013, 19, 2952-61.

Citation Format: Daniela Presa, Paul M. Loadman, Giuliano Nigro, Helen M. Sheldrake, Mark Sutherland, Steven D. Shnyder, Valerie Le Morvan, Jacques Robert, Magnus Ingelman-Sundberg, Laurence H. Patterson, Klaus Pors. Probing cytochrome P450 activity with benzofuran-based duocarmycins in a panel of head and neck cancer cell lines and CYP1A1, 1B1 and CYP2W1 transfected cell lines. [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 3105.

Abstract 1270: Polysialyltransferase ST8SiaII as a target for neuroblastoma dissemination

Polysialic acid (polySia) is expressed on the surface of NCAM (neuronal cell adhesion molecule) on neuroendocrine tumours, notably neuroblastoma and small cell lung cancer, where it modulates cell-cell and cell-matrix adhesion, migration, invasion and metastasis. PolySia expression is strongly associated with poor prognosis and aggressive disease in neuroblastoma patients in the clinic[1]. SiRNA knockdown of polysialyltransferase (polyST) ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumours, abrogates tumour cell migration and invasion. Besides brain regions with persistent neuronal plasticity, polySia is essentially absent from the body post-embryogenesis. PolyST is thus a selective and largely unexplored therapeutic target for neuroblastoma dissemination [1].

We have established a highly sensitive HPLC-based polyST inhibition assay, amenable to high-throughput screening. We report our efforts to further optimise this cell-free assay, and include details of our novel methodology to quantify cell-surface polySia expression. Having demonstrated in vitro that inhibition of polyST by a small molecule leads to a reduction in tumour cell migration [2], we designed and synthesised ST8SiaII inhibitors. Using isogenic cell lines (C6-STX: polySia+/polyST+ and C6-WT: polySia-/polyST-) and naturally polySia expressing human neuroblastoma cells (SH-SY5Y, IMR-32) these compounds were evaluated for their ability to reduce polySia expression, to modulate tumour cell migration and invasion in vitro. We have identified novel agents which significantly reduce polySia expression, tumour cell migration and invasion. These effects were only found in cell lines expressing ST8SiaII and polySia. Specificity of agents for polySTs over other members of the sialyltransferase (ST) family (i.e. α-2,3-ST and α-2,6-ST) was subsequently investigated using lectin differential labelling probes. Agents did not inhibit sialyltransferase activity.

We have investigated effects of agents on key intracellular signalling pathways. We demonstrated the effects of polyST inhibition on the dynamics of FAK and on ERK1/2, AKT, CREB and VEGFR-3 signalling. Furthemore, we have explored the behaviour of polySia-expressing cells under hypoxic conditions. Our data suggest that polySia is associated with a resistant phenotype, with C6-STX polySia-expressing cells demonstrating a survival advantage and additionally maintaining their migratory capacity under hypoxia (compared to WT cells, where migration is dramatically reduced).

In summary, we have demonstrated that polyST inhibition dramatically decreases cell-surface polysialylation, migration and invasion in vitro, under both normoxic and hypoxic conditions. This work paves the way for development of a novel therapeutic for the treatment of neuroblastoma.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939; [2] Al-Saraireh YMJ et al., PLoS ONE, 2013, 8:e73366.

Citation Format: Sara M. Elkashef, Rida F. Saeed, Goreti Ribeiro Morais, Xiaoxiao Guo, Marcella Sini, Virginie F. Viprey, Mark Sutherland, Paul M. Loadman, Laurence H. Patterson, Steven D. Shnyder, Robert A. Falconer. Polysialyltransferase ST8SiaII as a target for neuroblastoma dissemination. [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 1270.

Abstract 4541: Tumor-selective bioactivation of duocarmycin bioprecursors by cytochrome P450 enzymes provides an opportunity to treat drug-resistant breast cancer cells

Background

The cytochrome P450 (CYP) enzymes are responsible for the oxidation of a diverse range of xenobiotic and endogenous compounds. The high expression of CYP1A1, 1B1 and 2W1 in tumour tissue and surrounding stroma compared to nearby normal tissue provides an opportunity for development of selective cancer therapeutics. The ultrapotent duocarmycins are ideal candidates for bioprecursor development and we have demonstrated that these can be re-engineered into derivatives selectively activated by CYP1A1, 1B1 (unpublished) and 2W1 in vitro and in vivo.1-3

Materials and methods

Standard material and methods can be found in the references below. Briefly, these include synthetic chemistry necessary for synthesis of duocarmycin bioprecursors, use of recombinant CYP bactosomes for metabolite identification using LC/MS and cell culture experiments using the MTT assay.

Results

In the present study, we have focussed on the potential of eradicating both sensitive and drug-resistant breast cancer cells (MCF-7, MDA-MB-468 and MDA-MB-231). We have evaluated a library of novel compounds in vitro and shown 3-modified CPI bioprecursors to be bioactivated to potent (<10 nM) metabolites capable of damaging DNA as shown using H2A.X phosphorylation as a marker of DNA damage. LCMS confirmed the presence of hydroxylated seco-duocarmycins and structure-activity relationship studies revealed that subtle changes to the substitution pattern of the DNA recognition motif resulted in changes to the CYP bioactivation and chemosensitivity. The duocarmycin bioprecursors were intolerant by functionalization at position 7, to some extent position 6 while position 5 was needed for potent bioactivation and anticancer activity.

Conclusion Modifications to the structure of the seco-duocarmycins influences the extent of their CYP-mediated activation and indicates their potential for breast cancer chemotherapy. [1] Sheldrake et al. Re-engineering of the duocarmycin structural architecture enables bioprecursor development targeting CYP1A1 and CYP2W1 for biological activity. J Med Chem. 2013, 56, 6273-7.

[2] Travica et al. Colon cancer-specific cytochrome P450 2W1 converts duocarmycin analogues into potent tumor cytotoxins. Clin Cancer Res. 2013, 19, 2952-61.

[3] Pors et al. Modification of the duocarmycin pharmacophore enables CYP1A1 targeting for biological activity. Chem Commun. 2011, 47, 12062-4.

Citation Format: Steven D. Shnyder, Paul M. Loadman, Mark Sutherland, Helen M. Sheldrake, Mark Searcey, Laurence H. Patterson, Klaus Pors. Tumor-selective bioactivation of duocarmycin bioprecursors by cytochrome P450 enzymes provides an opportunity to treat drug-resistant breast cancer cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4541. doi:10.1158/1538-7445.AM2015-4541

Abstract 5431: Polysialyltransferase ST8SiaII: A novel target for the treatment of neuroblastoma

Polysialic acid (polySia) is a carbohydrate polymer expressed on the surface of NCAM (neuronal cell adhesion molecule) in many cancer cells where it modulates cell-cell and cell-matrix adhesion, migration, invasion and metastasis. PolySia expression is strongly associated with poor clinical prognosis and correlates with aggressive/invasive disease in neuroblastoma and many other tumours principally of neuroendocrine origin [1]. SiRNA knockdown of polysialyltransferase ST8SiaII, the enzyme primarily responsible for polySia synthesis in tumours, has been shown to abolish tumour cell migration [2]. Besides brain regions with persistent neuronal plasticity, polySia is essentially absent from the body post-embryogenesis. ST8SiaII inhibition thus presents a novel, selective and largely unexplored therapeutic opportunity to reduce neuroblastoma dissemination [1].

Progress towards development of ST8SiaII inhibitors has been limited by lack of an efficient technique for quantitative assessment of enzyme activity. We have validated a highly sensitive HPLC-based inhibition assay, amenable to high-throughput screening [3]. Having demonstrated that inhibition of ST8SiaII by small molecules leads to a reduction in tumour cell migration and invasion, we have designed and synthesised ST8SiaII inhibitors. Using isogenic cell lines (C6-STX: polySia+/ST8SiaII+ and C6-WT: polySia-/ST8SiaII-) and naturally polySia expressing human neuroblastoma cells (SH-SY5Y, IMR-32) these compounds were evaluated for their ability to reduce polySia expression and to modulate cell migration in vitro. We have identified CMP-sialic acid precursors, including ICT-3176, which reduced polySia expression (as determined by flow cytometry and HPLC analysis) and tumour cell migration by up to 70%. These effects were only found in cell lines expressing ST8SiaII and polySia. Specificity of agents for polySTs over other sialyltransferases (α-2,3 and α-2,6) was subsequently investigated using lectin differential labelling probes. Agents did not inhibit sialyltransferase activity, as evidenced by lack of effect on α-2,3 and α-2,6-sialic acid expression.

Furthermore, we have investigated effects of polyST inhibition by ICT3176 on key intracellular signalling pathways. ICT3176 has been shown to disturb the dynamics of focal adhesion kinase and modulate ERK1/2 and AKT signalling. We have also investigated the effects of ICT3176 on chemosensitivity of neuroblastoma cells to various molecularly targeted chemotherapeutics.

In summary, we have identified ST8SiaII inhibitors which dramatically decrease cell migration and invasion in vitro through modulation of polySia assembly. This work paves the way for development of a novel therapeutic for the treatment of neuroblastoma.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939; [2] Schreiber et al., Gastroenterology, 2008, 134, 1555-1566; [3] Al-Saraireh YMJ et al., PLoS ONE, 2013, 8:e73366.

Citation Format: Sara M. Elkashef, Virginie Viprey, Rida F. Saeed, Bradley R. Springett, Mark Sutherland, Paul M. Loadman, Laurence H. Patterson, Steven D. Shnyder, Robert A. Falconer. Polysialyltransferase ST8SiaII: A novel target for the treatment of neuroblastoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5431. doi:10.1158/1538-7445.AM2015-5431

Probing cytochrome P450-mediated activation with a truncated azinomycin analogue

Selective cytochrome P450 bioactivation of truncated azinomycin.

Non-invasive molecular imaging for preclinical cancer therapeutic development

Molecular and non-invasive imaging are rapidly emerging fields in preclinical cancer drug discovery. This is driven by the need to develop more efficacious and safer treatments, the advent of molecular-targeted therapeutics, and the requirements to reduce and refine current preclinical in vivo models. Such bioimaging strategies include MRI, PET, single positron emission computed tomography, ultrasound, and optical approaches such as bioluminescence and fluorescence imaging. These molecular imaging modalities have several advantages over traditional screening methods, not least the ability to quantitatively monitor pharmacodynamic changes at the cellular and molecular level in living animals non-invasively in real time. This review aims to provide an overview of non-invasive molecular imaging techniques, highlighting the strengths, limitations and versatility of these approaches in preclinical cancer drug discovery and development.

Abstract 1774: Polysialyltransferase ST8SiaII: a new target for the treatment of metastatic tumors

Polysialic acid (polySia) is a carbohydrate polymer expressed on the surface of NCAM (neuronal cell adhesion molecule) in many cancer cells where it modulates cell-cell and cell-matrix adhesion, migration, invasion and metastasis. PolySia-NCAM expression is strongly associated with poor clinical prognosis and correlates with aggressive/invasive disease in small cell lung cancer, pancreatic cancer, neuroblastoma and many other tumors principally of neuroendocrine origin [1]. SiRNA knockdown of polysialyltransferase ST8SiaII (STX), the enzyme primarily responsible for polySia synthesis in tumors, has been shown to abolish tumor cell migration [2]. Besides brain regions with persistent neuronal plasticity, polySia is essentially absent from the adult body. STX inhibition thus presents a novel, selective, highly attractive and largely unexplored therapeutic opportunity to reduce dissemination of polySia-expressing tumors [1]. Using cytidine monophosphate (CMP) as a tool compound, we have validated a highly sensitive HPLC-based inhibition assay, and demonstrated competitive inhibition of STX, leading to a reduction in polySia expression [3]. Having demonstrated for the first time that inhibition of STX by a small molecule leads to a reduction in tumor cell migration and invasion, we have designed and synthesised inhibitors of STX and the polysialylation process. The potency of these compounds has been increased by chemical modification, resulting in greater lipophilicity. Using an isogenic cell line system (rat glioma cells C6-STX: polySia+/STX+ and C6-WT: polySia-/STX- [4]) and naturally polySia expressing human neuroblastoma cells (SH-SY5Y, IMR-32) these compounds were evaluated for their ability to reduce polySia expression and to modulate cell migration in vitro. We have identified CMP-sialic acid precursors, including compounds ICT-3172 and ICT-3176, which reduced polySia expression and tumor cell migration by up to 70%. These effects were only found in cell lines expressing STX and polySia. In summary, we have identified a number of key modifications to polySia biosynthetic precursors which dramatically decrease cell migration in cells over-expressing STX through modulation of polySia assembly. The potential of the polySia biosynthesis pathway, and in particular STX, as attractive therapeutic targets in metastatic tumors is discussed.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939

[2] Schreiber et al.,Gastroenterology, 2008, 134, 1555-1566

[3] Al-Saraireh YMJ et al., PLoS ONE, 2013, 8:e7336

[4] Suzuki, M. et al., Glycobiology, 2005, 15, 887-894.

Citation Format: Virginie Viprey, Bradley R. Springett, Yousef Al-Saraireh, Matthew Northrop, Mark Sutherland, Rida Saeed, Paul M. Loadman, Laurence H. Patterson, Steven D. Shnyder, Robert A. Falconer. Polysialyltransferase ST8SiaII: a new target for the treatment of metastatic tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1774. doi:10.1158/1538-7445.AM2014-1774

Abstract 5391: MT-MMP cleavage profiling using rapid endopeptidase profiling library (REPLi)

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that are associated with the metastatic process. Relative to non-diseased tissue, the increased expression and activity of Membrane-type matrix metalloproteinases (MT-MMPs) such as MMP-15 within the prostate tumour microenvironment can be exploited in order to selectively activate highly toxic chemotherapeutics. The main advantage to such a targeted drug delivery system is a significant reduction of systemic toxicity, resulting in a highly efficacious and successful treatment for prostate cancer.

We have screened 3375 peptides with a variety of residue combinations using Rapid Endopeptidase Profiling Library (REPLi). A ‘small but smart’ design, the REPLi library template: MCA-Gly-Gly-Gly-Xaa-Xaa-Xaa-Gly-Gly-DPA-Lys-Lys contains a donor (MCA) and quenching acceptor (DPA) FRET pair. No fluorescence indicates the molecules within the pools are intact, however, upon cleavage, the tri-variable cores can be assessed via auto fluorescence of the MCA molecule.

By analysing the 512 distinct substrate pools we have identified combinations of Phe/Tyr and Asn/Gln residues as having a greater MMP-15 cleavage bias over MMP-14, with the opposite being true for variable cores with Ile/Leu and Lys/Arg combinations. Since most known substrates show little (if any) MMP selectivity this is a novel finding, and as such, provides us with insights that are essential for designing prodrugs targeted to specific MMPs.

Through detailed metabolic studies, this information is being utilised in a bid to maximise the successful development of novel MMP-15 targeted paclitaxel conjugated prostate cancer prodrugs.

Citation Format: Andrew Mitchell, Javier Giménez-Warren, Steven D. Shnyder, Jason H. Gill, Robert A. Falconer, Paul M. Loadman. MT-MMP cleavage profiling using rapid endopeptidase profiling library (REPLi). [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5391. doi:10.1158/1538-7445.AM2014-5391

Abstract 1779: CYP2W1 as a novel therapeutic target in colon cancer

Colorectal cancer is the third most frequently diagnosed malignancy in both men and women and a leading cause of cancer-related deaths in the Western world. Advances in neoadjuvant/adjuvant chemotherapy (including 5-fluorouracil, irinotecan, and oxaliplatin) as well as radiation therapy have improved the clinical outcome, however, the overall impact of these amended treatment regiments has been relatively modest, leaving metastasised or recurrent disease largely incurable by conventional approaches and requiring the development of better therapeutics. Targeted chemotherapy aimed towards more effective advanced colon cancer treatment could be achieved by the use of agents that are systemically inactive but selectively converted to potent cytotoxins locoregionally. We have shown cytochrome P450 2W1 (CYP2W1) to be overexpressed in colorectal cancer, and recently shown this enzyme to be a druggable target in a proof-of-concept study using CYP2W1-transfected colon cancer cells [selected references below]. At this meeting we will present an update on our progress on re-engineering the duocarmycin family of compounds for CYP2W1-targeting. New findings reveal that subtle changes in the duocarmycin pharmacophore can lead to dramatic changes (> 100-fold) in the anti-cancer activity. This drop in anticancer activity of small molecules such as ICT2726 means these can be used as biomarker to detect CYP2W1 functional activity, which can be used alongside immunological methods to characterise malignant colorectal tissue. Similarly, interrogation of R and S-enantiomers of duocarmycin bioprecursors also reveal significant differential anticancer activity in vitro. Studies are currently underway to understand if this differential activity is also observed in CYP2W1-expressing colon cancer xenografts and the results will be presented at the AACR meeting. Our findings reveal the opportunities in targeting CYP2W1 as a novel therapeutic approach in colon cancer chemotherapy.

[1] Travica S. et al. Colon cancer-specific cytochrome P450 2W1 converts duocarmycin analogues into potent tumor cytotoxins. Clin. Cancer Res. 2013, 19(11), 2952-61.

[2] Sheldrake et al. Re-engineering of the Duocarmycin Structural Architecture Enables Bioprecursor Development Targeting CYP1A1 and CYP2W1 for Biological Activity. J Med Chem. 2013, 56 (15), 6273-7.

[3] Stenstedt, K. et al. Cytochrome P450 2W1 polymorphism: functional aspects and relation to risk for colorectal cancer. Pharmacogenomics. 2013, 14(13), 1615-1622.

[4] Sutherland M. et al. Anti-tumor Activity of a Duocarmycin Analogue Rationalised to be Metabolically Activated By Cytochrome P450 1A1 in Human Bladder Cancer. Mol Cancer Ther. 2013, 12 (1), 27-37.

[5] Pors K. et al. Modification of the duocarmycin pharmacophore enables CYP1A1 targeting for biological activity. Chem. Commun., 2011, 47, 12062-4.

[6] Stenstedt K et al. The expression of CYP2W1: a prognostic marker in colon cancer. Anticancer Res. 2012, 32, 3869-74.

Citation Format: Klaus Pors, Paul M. Loadman, Sandra Travica, Steven D. Shnyder, Mark Sutherland, Helen Sheldrake, Mark Searcey, Inger Johansson, Souren Mkrtchian, Magnus Ingelman-Sundberg, Laurence H. Patterson. CYP2W1 as a novel therapeutic target in colon cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1779. doi:10.1158/1538-7445.AM2014-1779

Tumor-targeted prodrug ICT2588 demonstrates therapeutic activity against solid tumors and reduced potential for cardiovascular toxicity

Development of therapeutic strategies for tumor-selective delivery of therapeutics through exploitation of the proteolytic tumor phenotype has significant scope for improvement of cancer treatment. ICT2588 is a peptide-conjugated prodrug of the vascular disrupting agent (VDA) azademethylcolchicine developed to be selectively hydrolyzed by matrix metalloproteinase-14 (MMP-14) within the tumor. In this report, we extend our previous proof-of-concept studies and demonstrate the therapeutic potential of this agent against models of human colorectal, lung, breast, and prostate cancer. In all tumor types, ICT2588 was superior to azademethylcolchicine and was greater or comparable to standard clinically used agents for the respective tumor type. Prodrug activation in clinical human lung tumor homogenates relative to stability in human plasma and liver was observed, supporting clinical translation potential. A major limiting factor to the clinical value of VDAs is their inherent cardiovascular toxicity. No increase in plasma von Willebrand factor (vWF) levels, an indicator of systemic vascular dysfunction and acute cardiovascular toxicity, was detected with ICT2588, thereby supporting the tumor-selective activation and reduced potential of ICT2588 to cause cardiovascular toxicity. Our findings reinforce the improved therapeutic index and tumor-selective approach offered by ICT2588 and this nanotherapeutic approach.

Pharmacological inhibition of polysialyltransferase ST8SiaII modulates tumour cell migration

Polysialic acid (polySia), an α-2,8-glycosidically linked polymer of sialic acid, is a developmentally regulated post-translational modification predominantly found on NCAM (neuronal cell adhesion molecule). Whilst high levels are expressed during development, peripheral adult organs do not express polySia-NCAM. However, tumours of neural crest-origin re-express polySia-NCAM: its occurrence correlates with aggressive and invasive disease and poor clinical prognosis in different cancer types, notably including small cell lung cancer (SCLC), pancreatic cancer and neuroblastoma. In neuronal development, polySia-NCAM biosynthesis is catalysed by two polysialyltransferases, ST8SiaII and ST8SiaIV, but it is ST8SiaII that is the prominent enzyme in tumours. The aim of this study was to determine the effect of ST8SiaII inhibition by a small molecule on tumour cell migration, utilising cytidine monophosphate (CMP) as a tool compound. Using immunoblotting we showed that CMP reduced ST8iaII-mediated polysialylation of NCAM. Utilizing a novel HPLC-based assay to quantify polysialylation of a fluorescent acceptor (DMB-DP3), we demonstrated that CMP is a competitive inhibitor of ST8SiaII (K i = 10 µM). Importantly, we have shown that CMP causes a concentration-dependent reduction in tumour cell-surface polySia expression, with an absence of toxicity. When ST8SiaII-expressing tumour cells (SH-SY5Y and C6-STX) were evaluated in 2D cell migration assays, ST8SiaII inhibition led to significant reductions in migration, while CMP had no effect on cells not expressing ST8SiaII (DLD-1 and C6-WT). The study demonstrates for the first time that a polysialyltransferase inhibitor can modulate migration in ST8SiaII-expressing tumour cells. We conclude that ST8SiaII can be considered a druggable target with the potential for interfering with a critical mechanism in tumour cell dissemination in metastatic cancers.

Potentiation of the activity of cisplatin in a human colon tumour xenograft model by auristatin PYE, a structural modification of dolastatin 10

Dolastatin 10, a marine natural product peptide, is now known to act as a vascular disrupting agent (VDA). These VDA properties were not known when other aspects of its promising pre-clinical profile led to initial unsuccessful clinical trials. Auristatin PYE, a synthetic analogue of dolastatin 10, has demonstrated improved activity in preliminary in vivo studies. However, as with other VDAs, tumour eradication was incomplete due to the maintenance of functional vasculature supporting the viable tumour at the periphery of the tumour xenograft, meaning that once the VDA effect subsides, the tumour regrows. One possible strategy for removing this peripheral tumour involves combining VDA therapy with another anticancer drug with a different mechanism of action. Here, we evaluated the effect of combining auristatin PYE with cisplatin in an HCT-116 human colon adenocarcinoma xenograft model. The effects on the growth of subcutaneously implanted HCT-116 xenografts in mice following intraperitoneal administration of a single dose of 4 mgkg-1 cisplatin and intravenous administration of 1 mgkg-1 auristatin PYE were evaluated compared to the effect of each agent administered alone. The effects on the functional tumour vasculature were also assessed. Statistically significant potentiation (p<0.01) was noted with a 465% growth delay for the combination group compared to the control, and 142 and 310% growth delays for the cisplatin and auristatin PYE groups, respectively. Shut down of tumour vasculature in the combination group was similar to that observed with auristatin PYE on its own. Auristatin PYE demonstrated synergistic antitumour effects when combined with cisplatin, suggesting that a combination chemotherapy regimen would be the most effective strategy when applying this new anticancer drug.

Polysialyltransferase: a new target in metastatic cancer

Polysialic acid (polySia) is a carbohydrate polymer critical for neuronal cell migration and axon pathfinding in embryonic development. Besides brain regions requiring persistent neuronal plasticity, polySia is essentially absent from the adult body. However, polySia is aberrantly re-expressed on many tumours, where it decorates the surface of NCAM (neuronal cell adhesion molecule) and modulates cell adhesion, migration and invasion. PolySia-NCAM expression is strongly associated with poor clinical prognosis and correlates with aggressive and invasive disease in many cancers, including lung cancer, neuroblastoma and gliomas. The synthesis of polySia is mediated by two polysialyltransferases (polySTs), ST8SiaIV (PST) and particularly ST8SiaII (STX) in cancer cells. The demonstration that polyST knock-down negates events associated with tumour cell dissemination indicates that PST and STX are validated targets. Selective inhibition of polySTs therefore presents a therapeutic opportunity to inhibit tumour invasion and metastasis.

Abstract 4410: Inhibition of cell surface polysialic acid biosynthesis modulates tumor cell migration

Polysialic acid (polySia) is a linear alpha-2,8-linked carbohydrate homopolymer of up to 100 sialic acid residues. It is characteristically re-expressed on the surface of NCAM (neuronal cell adhesion molecule) in many cancer cells where it modulates tumour dissemination. PolySia-NCAM expression is strongly associated with poor clinical prognosis and correlates with aggressive/invasive disease in small cell lung cancer, pancreatic cancer, neuroblastoma and many other tumours principally of neural crest origin [1]. SiRNA knockdown of polysialyltransferases (polySTs) ST8SiaII and ST8SiaIV, the enzymes responsible for polysialylation of neural cell adhesion molecule (NCAM), has been shown to abolish cell migration in tumour cells [2]. Besides brain regions with persistent neuronal plasticity, polySia is essentially absent from the adult body. Its exclusive synthesis by two polySTs, ST8SiaIV and particularly ST8SiaII, present a novel, selective, highly attractive but largely unexplored therapeutic opportunity [1].

We have embarked on a programme of design and synthesis of novel polyST inhibitors, and have established a screening cascade to determine enzyme inhibition and effects on polySia-expressing cells in vitro. Using endoneuraminidase, an enzyme that specifically cleaves polySia chains from NCAM, we can assess the rate and extent to which polySia growth is inhibited in the presence of agent in cellular systems. In addition, an in vitro scratch assay was established to evaluate modulation of cell migration using a transfected isogenic cell line system (C6-STX: polySia +, ST8SiaII + / C6-WT: polySia -, ST8SiaII - [3]) and neuroblastoma cell lines known to express polySia-NCAM, ST8SiaIV and ST8SiaII (SHSY-5Y and IMR-32).

We have identified compounds, including ICT-3067, ICT-3128 and ICT-3147, which lead to a significant reduction in cell surface polySia-NCAM and that modulate tumour cell migration in in vitro. We have also identified a number of key modifications to CMP-sialic acid precursor molecules which dramatically decrease cell migration in ST8SiaII-expressing cells, through modulation of polySia assembly. It is also noteworthy that the potency of these compounds has been increased with simple chemical modifications, resulting in greater lipophilicity.

In summary, a number of efficient modulators of polySia assembly and their efficacy in reducing cell migration is described. This points to the potential of the polySia biosynthesis pathway, and in particular the polySTs, as attractive therapeutic targets in metastatic tumours.

[1] Falconer, R.A. et al., Curr. Cancer Drug Targets, 2012, 12, 925-939; [2] Schreiber et al., Gastroenterology, 2008, 134, 1555-1566; [3] Suzuki, M. et al., Glycobiology, 2005, 15, 887-894.

Citation Format: Bradley R. Springett, Yousef M.J. Al-Saraireh, Virginie Viprey, Mark Sutherland, Melanie Begouin, Matthew Northrop, Rida Saeed, Paul M. Loadman, Laurence H. Patterson, Steven D. Shnyder, Robert A. Falconer. Inhibition of cell surface polysialic acid biosynthesis modulates tumor cell migration. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4410. doi:10.1158/1538-7445.AM2013-4410

The microtubule depolymerizing agent CYT997 causes extensive ablation of tumor vasculature in vivo

The orally active microtubule-disrupting agent (S)-1-ethyl-3-(2-methoxy-4-(5-methyl-4-((1-(pyridin-3-yl)butyl)amino)pyrimidin-2-yl)phenyl)urea (CYT997), reported previously by us (Bioorg Med Chem Lett 19:4639-4642, 2009; Mol Cancer Ther 8:3036-3045, 2009), is potently cytotoxic to a variety of cancer cell lines in vitro and shows antitumor activity in vivo. In addition to its cytotoxic activity, CYT997 possesses antivascular effects on tumor vasculature. To further characterize the vascular disrupting activity of CYT997 in terms of dose and temporal effects, we studied the activity of the compound on endothelial cells in vitro and on tumor blood flow in vivo by using a variety of techniques. In vitro, CYT997 is shown to potently inhibit the proliferation of vascular endothelial growth factor-stimulated human umbilical vein endothelial cells (IC(50) 3.7 ± 1.8 nM) and cause significant morphological changes at 100 nM, including membrane blebbing. Using the method of corrosion casting visualized with scanning electron microscopy, a single dose of CYT997 (7.5 mg/kg i.p.) in a metastatic cancer model was shown to cause destruction of tumor microvasculature in metastatic lesions. Furthermore, repeat dosing of CYT997 at 10 mg/kg and above (intraperitoneally, b.i.d.) was shown to effectively inhibit development of liver metastases. The time and dose dependence of the antivascular effects were studied in a DLD-1 colon adenocarcinoma xenograft model using the fluorescent dye Hoechst 33342. CYT997 demonstrated rapid and dose-dependent vascular shutdown, which persists for more than 24 h after a single oral dose. Together, the data demonstrate that CYT997 possesses potent antivascular activity and support continuing development of this promising compound.

Adenovirus-mediated hypoxia-targeted gene therapy using HSV thymidine kinase and bacterial nitroreductase prodrug-activating genes in vitro and in vivo

Hypoxia is an important factor in tumor growth. It is associated with resistance to conventional anticancer treatments. Gene therapy targeting hypoxic tumor cells therefore has the potential to enhance the efficacy of treatment of solid tumors. Transfection of a panel of tumor cell lines with plasmid constructs containing hypoxia-responsive promoter elements from the genes, vascular endothelial growth factor (VEGF) and erythropoietin, linked to the minimal cytomegalovirus (mCMV) or minimal interleukin-2 (mIL-2) promoters showed optimum hypoxia-inducible luciferase reporter gene expression with five repeats of VEGF hypoxic-response element linked to the mCMV promoter. Adenoviral vectors using this hypoxia-inducible promoter to drive therapeutic transgenes produced hypoxia-specific cell kill of HT1080 and HCT116 cells in the presence of prodrug with both herpes simplex virus thymidine kinase/ganciclovir and nitroreductase (NTR)/CB1954 prodrug-activating systems. Significant cytotoxic effects were also observed in patient-derived human ovarian cancer cells. The NTR/CB1954 system provided more readily controllable transgene expression and so was used for in vivo experiments of human HCT116 xenografts in nude mice. Subjects treated intratumorally with Ad-VEGFmCMV-NTR and intraperitoneal injection of CB1954 demonstrated a statistically significant reduction in tumor growth. Immunohistochemistry of treated xenografts showed a good correlation between transgene expression and hypoxic areas. Further investigation of these hypoxia-inducible adenoviral vectors, alone or in combination with existing modalities of cancer therapy, may aid in the future development of successful Gene-Directed Enzyme Prodrug Therapy systems, which are much needed for targeting solid tumors.

Small molecule FGF receptor inhibitors block FGFR-dependent urothelial carcinoma growth in vitro and in vivo

BACKGROUND

Activating mutations of FGFR3 are frequently identified in superficial urothelial carcinoma (UC) and increased expression of FGFR1 and FGFR3 are common in both superficial and invasive UC.

METHODS

The effects of inhibition of receptor activity by three small molecule inhibitors (PD173074, TKI-258 and SU5402) were investigated in a panel of bladder tumour cell lines with known FGFR expression levels and FGFR3 mutation status.

RESULTS

All inhibitors prevented activation of FGFR3, and inhibited downstream MAPK pathway signalling. Response was related to FGFR3 and/or FGFR1 expression levels. Cell lines with the highest levels of FGFR expression showed the greatest response and little or no effect was measured in normal human urothelial cells or in UC cell lines with activating RAS gene mutations. In sensitive cell lines, the drugs induced cell cycle arrest and/or apoptosis. IC(50) values for PD173074 and TKI-258 were in the nanomolar concentration range compared with micromolar concentrations for SU5402. PD173074 showed the greatest effects in vitro and in vivo significantly delayed the growth of subcutaneous bladder tumour xenografts.

CONCLUSION

These results indicate that inhibition of FGFR1 and wild-type or mutant FGFR3 may represent a useful therapeutic approach in patients with both non-muscle invasive and muscle invasive UC.

Organometallic osmium arene complexes with potent cancer cell cytotoxicity

Iodido osmium(II) complexes [Os(η(6)-arene)(XY)I](+) (XY = p-hydroxy or p-dimethylaminophenylazopyridine, arene = p-cymene or biphenyl) are potently cytotoxic at nanomolar concentrations toward a panel of human cancer cell lines; e.g., IC(50) = 140 nM for [Os(η(6)-bip)(azpy-NMe(2))I](+) toward A2780 ovarian cancer cells. They exhibit low toxicity and negligible deleterious effects in a colon cancer xenograft model, giving rise to the possibility of a broad therapeutic window. The most active complexes are stable and inert toward aquation. Their cytotoxic activity appears to involve redox mechanisms.

Development of a novel tumor-targeted vascular disrupting agent activated by membrane-type matrix metalloproteinases

Vascular disrupting agents (VDA) offer a strategy to starve solid tumors of nutrients and oxygen concomitant with tumor shrinkage. Several VDAs have progressed into early clinical trials, but their therapeutic value seems to be compromised by systemic toxicity. In this report, we describe the design and characterization of a novel VDA, ICT2588, that is nontoxic until activated specifically in the tumor by membrane-type 1 matrix metalloproteinase (MT1-MMP). HT1080 cancer cells expressing MT1-MMP were selectively chemosensitive to ICT2588, whereas MCF7 cells that did not express MT1-MMP were nonresponsive. Preferential hydrolysis of ICT2588 to its active metabolite (ICT2552) was observed in tumor homogenates of HT1080 relative to MCF7 homogenates, mouse plasma, and liver homogenate. ICT2588 activation was inhibited by the MMP inhibitor ilomastat. In HT1080 tumor-bearing mice, ICT2588 administration resulted in the formation of the active metabolite, diminution of tumor vasculature, and hemorrhagic necrosis of the tumor. The antitumor activity of ICT2588 was superior to its active metabolite, exhibiting reduced toxicity, improved therapeutic index, enhanced pharmacodynamic effect, and greater efficacy. Coadministration of ICT2588 with doxorubicin resulted in a significant antitumor response (22.6 d growth delay), which was superior to the administration of ICT2588 or doxorubicin as a single agent, including complete tumor regressions. Our findings support the clinical development of ICT2588, which achieves selective VDA targeting based on MT-MMP activation in the tumor microenvironment.

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.

Abstract A16: Antitumor activity of CYT997: A phase II vascular disrupting agent administered orally in combination with cisplatin in a colon adenocarcinoma xenograft model

CYT997 is an orally bioavailable small molecule vascular-disrupting agent (VDA) that is currently being investigated in Phase II clinical studies. In vitro efficacy studies have demonstrated that CYT997 exhibits potent antiproliferative activity against the DLD-1 cell line (IC50 21 nM), with a similar potency to doxorubicin, paclitaxel and vincristine (IC50 8 – 53 nM). The antitumor and vascular targeting activity of CYT997 has been demonstrated in the current series of studies following alternate dosing regimens (single dose vs metronomic sub-maximal daily dose) and in combination with a standard chemotherapeutic agent, cisplatin.

Female Balb/C immunodeficient nude mice were implanted subcutaneously with DLD-1 human colon adenocarcinoma fragments and efficacy was assessed via tumor caliper measurements, in addition to histological assessment of tumor vascular shutdown (Hoechst 33342 staining) and necrotic area (haematoxylin and eosin staining). Animals were administered CYT997 (dihydrochloride salt) by oral gavage and efficacy was expressed relative to vehicle control.

Administration of CYT997 resulted in a time and concentration dependent shutdown of tumor vasculature. Following a single CYT997 administration (40 mg/kg), vascular shutdown was extensive and rapid (ca 95% ablation compared with vehicle control at 1h post-dose; p&lt;0.01). Significant vascular shutdown was maintained in tumors 4 days post treatment (ca 67% shutdown; p&lt;0.05) and subsequent histological examination demonstrated increased necrosis (ca 280% increase; p&lt;0.05) of the tumor in mice treated with CYT997 compared with vehicle control. A single oral dose at 10 mg/kg (ca 1/5th the maximum tolerated dose), resulted in statistically-significant shutdown of tumor vasculature in this model (61 – 94% shutdown at 1 h post-dose compared to vehicle control; p&lt;0.05).

Daily oral administration of CYT997 (10 mg/kg/day) resulted in sustained shutdown of tumor vasculature over 10 days of treatment (57% shutdown compared to vehicle control; p&lt;0.05), which was associated with a significant increase (ca 44% increase; p&lt;0.05) in the necrotic area of the tumor relative to control. The efficacy of the metronomic CYT997 dosing schedule was assessed in combination with weekly administration of cisplatin (6 mg/kg i.p.). Despite some toxicity associated with the second cycle of cisplatin administration, the greatest tumor growth delay was observed in the combination group (2.7 days), relative to cisplatin (1.9 days) or CYT997 (1.8 days) alone.

These findings demonstrate that CYT997 exhibits rapid and long lasting antivascular effects following a single oral dose or following sub-maximal metronomic dosing. There is clear potential for increased anti-tumor efficacy when CYT997 is dosed in combination with other common anticancer therapies.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A16.