Iron chelators target both proliferating and quiescent cancer cells

Poorly vascularized areas of solid tumors contain quiescent cell populations that are resistant to cell cycle-active cancer drugs. The compound VLX600 was recently identified to target quiescent tumor cells and to inhibit mitochondrial respiration. We here performed gene expression analysis in order to characterize the cellular response to VLX600. The compound-specific signature of VLX600 revealed a striking similarity to signatures generated by compounds known to chelate iron. Validation experiments including addition of ferrous and ferric iron in excess, EXAFS measurements, and structure activity relationship analyses showed that VLX600 chelates iron and supported the hypothesis that the biological effects of this compound is due to iron chelation. Compounds that chelate iron possess anti-cancer activity, an effect largely attributed to inhibition of ribonucleotide reductase in proliferating cells. Here we show that iron chelators decrease mitochondrial energy production, an effect poorly tolerated by metabolically stressed tumor cells. These pleiotropic features make iron chelators an attractive option for the treatment of solid tumors containing heterogeneous populations of proliferating and quiescent cells.

Mouse Models of Pediatric Supratentorial High-grade Glioma Reveal How Cell-of-Origin Influences Tumor Development and Phenotype

High-grade glioma (HGG) is a group of primary malignant brain tumors with dismal prognosis. Whereas adult HGG has been studied extensively, childhood HGG, a relatively rare disease, is less well-characterized. Here, we present two novel platelet-derived growth factor (PDGF)-driven mouse models of pediatric supratentorial HGG. Tumors developed from two different cells of origin reminiscent of neural stem cells (NSC) or oligodendrocyte precursor cells (OPC). Cross-species transcriptomics showed that both models are closely related to human pediatric HGG as compared with adult HGG. Furthermore, an NSC-like cell-of-origin enhanced tumor incidence, malignancy, and the ability of mouse glioma cells (GC) to be cultured under stem cell conditions as compared with an OPC-like cell. Functional analyses of cultured GC from these tumors showed that cells of NSC-like origin were more tumorigenic, had a higher rate of self-renewal and proliferation, and were more sensitive to a panel of cancer drugs compared with GC of a more differentiated origin. These two mouse models relevant to human pediatric supratentorial HGG propose an important role of the cell-of-origin for clinicopathologic features of this disease. Cancer Res; 77(3); 802-12. ©2016 AACR.

Large-Scale Gene Expression Profiling Platform for Identification of Context-Dependent Drug Responses in Multicellular Tumor Spheroids

Cancer cell lines grown as two-dimensional (2D) cultures have been an essential model for studying cancer biology and anticancer drug discovery. However, 2D cancer cell cultures have major limitations, as they do not closely mimic the heterogeneity and tissue context of in vivo tumors. Developing three-dimensional (3D) cell cultures, such as multicellular tumor spheroids, has the potential to address some of these limitations. Here, we combined a high-throughput gene expression profiling method with a tumor spheroid-based drug-screening assay to identify context-dependent treatment responses. As a proof of concept, we examined drug responses of quiescent cancer cells to oxidative phosphorylation (OXPHOS) inhibitors. Use of multicellular tumor spheroids led to discovery that the mevalonate pathway is upregulated in quiescent cells during OXPHOS inhibition, and that OXPHOS inhibitors and mevalonate pathway inhibitors were synergistically toxic to quiescent spheroids. This work illustrates how 3D cellular models yield functional and mechanistic insights not accessible via 2D cultures.

Induction of mitochondrial dysfunction as a strategy for targeting tumour cells in metabolically compromised microenvironments

Abnormal vascularization of solid tumours results in the development of microenvironments deprived of oxygen and nutrients that harbour slowly growing and metabolically stressed cells. Such cells display enhanced resistance to standard chemotherapeutic agents and repopulate tumours after therapy. Here we identify the small molecule VLX600 as a drug that is preferentially active against quiescent cells in colon cancer 3-D microtissues. The anticancer activity is associated with reduced mitochondrial respiration, leading to bioenergetic catastrophe and tumour cell death. VLX600 shows enhanced cytotoxic activity under conditions of nutrient starvation. Importantly, VLX600 displays tumour growth inhibition in vivo. Our findings suggest that tumour cells in metabolically compromised microenvironments have a limited ability to respond to decreased mitochondrial function, and suggest a strategy for targeting the quiescent populations of tumour cells for improved cancer treatment.

Quiescent sub-populations of cells in tumours are resistant to traditional chemotherapeutics and are responsible for tumour recurrence. Here, Zhang et al. identify a compound that kills quiescent tumour cells in solid tumour tissue by inducing mitochondrial dysfunction.

In vitro discovery of promising anti-cancer drug combinations using iterative maximisation of a therapeutic index

In vitro-based search for promising anti-cancer drug combinations may provide important leads to improved cancer therapies. Currently there are no integrated computational-experimental methods specifically designed to search for combinations, maximizing a predefined therapeutic index (TI) defined in terms of appropriate model systems. Here, such a pipeline is presented allowing the search for optimal combinations among an arbitrary number of drugs while also taking experimental variability into account. The TI optimized is the cytotoxicity difference (in vitro) between a target model and an adverse side effect model. Focusing on colorectal carcinoma (CRC), the pipeline provided several combinations that are effective in six different CRC models with limited cytotoxicity in normal cell models. Herein we describe the identification of the combination (Trichostatin A, Afungin, 17-AAG) and present results from subsequent characterisations, including efficacy in primary cultures of tumour cells from CRC patients. We hypothesize that its effect derives from potentiation of the proteotoxic action of 17-AAG by Trichostatin A and Afungin. The discovered drug combinations against CRC are significant findings themselves and also indicate that the proposed strategy has great potential for suggesting drug combination treatments suitable for other cancer types as well as for other complex diseases.

Abstract 1736: The anticancer activity of the DUB inhibitor b-AP15 is associated with accumulation of proteasome bound ubiquitin and oxidative stress

Background: The ubiquitin proteasome system (UPS) is the major cellular degradation system for damaged or short-lived proteins. Tumor cells are dependent on a functioning UPS, making it an ideal target for the development of anti-cancer therapies. Bortezomib, an inhibitor of the proteolytic activities of the proteasome core particle (20SCP), is approved for treatment of multiple myeloma and mantle cell lymphoma; however several problems have emerged including dose-limiting toxicity and tumor relapse. We previously identified b-AP15 as a novel inhibitor of the proteasome associated deubiquitinases (DUBs) USP14 and UCH37/UCHL5. Treatment with b-AP15 induced cell death in several in vitro and in vivo cancer models. The aim of this study was to investigate how the different modes of UPS inhibition affect the structure of the 26S proteasome and cellular response as well as the potential for proteasome DUB inhibitors as a therapeutic option for cancer. Methods: HCT116 colon carcinoma cells were cultured in McCoy's 5A modified medium/10% fetal calf serum. For protein expression analysis cell extracts were resolved by Tris-Acetate gel and transferred to nitrocellulose membrane for western blotting. Proteasome integrity and cellular distribution of polyubiquitin chains were assessed in cell extracts subjected to density gradient centrifugation, conducted in 4-24% linear glycerol gradients, followed by western blot analysis. Apoptotic response was assessed with M30-CytoDeath ELISA, measuring level of caspase-cleavage of the endogenous cellular substrate keratin-18. Results: We found that inhibitors of proteasome function do not alter proteasome assembly or structure; however treatment induced the accumulation of polyubiquitinated proteins associated with the 26S proteasome. Comparison of 20S CP and 19S DUB inhibition showed that b-AP15 induced more rapid and sustained apoptotic response in comparison to bortezomib. Proteasome inhibition has been previously associated with endoplasmic reticulum and oxidative stress, however our findings show that reactive oxygen species (ROS) are main mediators of b-AP15 induced apoptosis. b-AP15 strongly induces several genes associated with oxidative stress response; hemoxygenase-1 (HMOX1), p38-MAPK, c-JUN and Jun N-terminal kinase (JNK). Additionally, treatment with a pharmacological inhibitor of JNK and several ROS scavengers decreased the levels of apoptosis in response to b-AP15 treatment. Conclusions: Cellular response to b-AP15 mediated proteasome inhibition is distinct from clinically used bortezomib; therefore b-AP15 has a potential clinical use, in particular for treatment of malignancies resistant to other proteasome inhibitors.

Citation Format: Magdalena Mazurkiewicz, Slavica Brnjic, Mårten Fryknäs, Chao Sun, Xiaonan Zhang, Rolf Larsson, Pádraig D'Arcy, Stig Linder. The anticancer activity of the DUB inhibitor b-AP15 is associated with accumulation of proteasome bound ubiquitin and oxidative stress. [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 1736. doi:10.1158/1538-7445.AM2015-1736

Three-Dimensional Cell Culture-Based Screening Identifies the Anthelmintic Drug Nitazoxanide as a Candidate for Treatment of Colorectal Cancer

Because dormant cancer cells in hypoxic and nutrient-deprived regions of solid tumors provide a major obstacle to treatment, compounds targeting those cells might have clinical benefits. Here, we describe a high-throughput drug screening approach, using glucose-deprived multicellular tumor spheroids (MCTS) with inner hypoxia, to identify compounds that specifically target this cell population. We used a concept of drug repositioning-using known molecules for new indications. This is a promising strategy to identify molecules for rapid clinical advancement. By screening 1,600 compounds with documented clinical history, we aimed to identify candidates with unforeseen potential for repositioning as anticancer drugs. Our screen identified five molecules with pronounced MCTS-selective activity: nitazoxanide, niclosamide, closantel, pyrvinium pamoate, and salinomycin. Herein, we show that all five compounds inhibit mitochondrial respiration. This suggests that cancer cells in low glucose concentrations depend on oxidative phosphorylation rather than solely glycolysis. Importantly, continuous exposure to the compounds was required to achieve effective treatment. Nitazoxanide, an FDA-approved antiprotozoal drug with excellent pharmacokinetic and safety profile, is the only molecule among the screening hits that reaches high plasma concentrations persisting for up to a few hours after single oral dose. Nitazoxanide activated the AMPK pathway and downregulated c-Myc, mTOR, and Wnt signaling at clinically achievable concentrations. Nitazoxanide combined with the cytotoxic drug irinotecan showed anticancer activity in vivo. We here report that the FDA-approved anthelmintic drug nitazoxanide could be a potential candidate for advancement into cancer clinical trials.

Drug screen in patient cells suggests quinacrine to be repositioned for treatment of acute myeloid leukemia

To find drugs suitable for repositioning for use against leukemia, samples from patients with chronic lymphocytic, acute myeloid and lymphocytic leukemias as well as peripheral blood mononuclear cells (PBMC) were tested in response to 1266 compounds from the LOPAC¹²⁸⁰ library (Sigma). Twenty-five compounds were defined as hits with activity in all leukemia subgroups (<50% cell survival compared with control) at 10 μM drug concentration. Only one of these compounds, quinacrine, showed low activity in normal PBMCs and was therefore selected for further preclinical evaluation. Mining the NCI-60 and the NextBio databases demonstrated leukemia sensitivity and the ability of quinacrine to reverse myeloid leukemia gene expression. Mechanistic exploration was performed using the NextBio bioinformatic software using gene expression analysis of drug exposed acute myeloid leukemia cultures (HL-60) in the database. Analysis of gene enrichment and drug correlations revealed strong connections to ribosomal biogenesis nucleoli and translation initiation. The highest drug–drug correlation was to ellipticine, a known RNA polymerase I inhibitor. These results were validated by additional gene expression analysis performed in-house. Quinacrine induced early inhibition of protein synthesis supporting these predictions. The results suggest that quinacrine have repositioning potential for treatment of acute myeloid leukemia by targeting of ribosomal biogenesis.

Label free high throughput screening for apoptosis inducing chemicals using time-lapse microscopy signal processing

Label free time-lapse microscopy has opened a new avenue to the study of time evolving events in living cells. When combined with automated image analysis it provides a powerful tool that enables automated large-scale spatiotemporal quantification at the cell population level. Very few attempts, however, have been reported regarding the design of image analysis algorithms dedicated to the detection of apoptotic cells in such time-lapse microscopy images. In particular, none of the reported attempts is based on sufficiently fast signal processing algorithms to enable large-scale detection of apoptosis within hours/days without access to high-end computers. Here we show that it is indeed possible to successfully detect chemically induced apoptosis by applying a two-dimensional linear matched filter tailored to the detection of objects with the typical features of an apoptotic cell in phase-contrast images. First a set of recorded computational detections of apoptosis was validated by comparison with apoptosis specific caspase activity readouts obtained via a fluorescence based assay. Then a large screen encompassing 2,866 drug like compounds was performed using the human colorectal carcinoma cell line HCT116. In addition to many well known inducers (positive controls) the screening resulted in the detection of two compounds here reported for the first time to induce apoptosis.

Detection of cell aggregation and altered cell viability by automated label-free video microscopy: a promising alternative to endpoint viability assays in high-throughput screening

Automated phase-contrast video microscopy now makes it feasible to monitor a high-throughput (HT) screening experiment in a 384-well microtiter plate format by collecting one time-lapse video per well. Being a very cost-effective and label-free monitoring method, its potential as an alternative to cell viability assays was evaluated. Three simple morphology feature extraction and comparison algorithms were developed and implemented for analysis of differentially time-evolving morphologies (DTEMs) monitored in phase-contrast microscopy videos. The most promising layout, pixel histogram hierarchy comparison (PHHC), was able to detect several compounds that did not induce any significant change in cell viability, but made the cell population appear as spheroidal cell aggregates. According to recent reports, all these compounds seem to be involved in inhibition of platelet-derived growth factor receptor (PDGFR) signaling. Thus, automated quantification of DTEM (AQDTEM) holds strong promise as an alternative or complement to viability assays in HT in vitro screening of chemical compounds.

Induction of tumor cell apoptosis by a proteasome deubiquitinase inhibitor is associated with oxidative stress

AIMS

b-AP15 is a recently described inhibitor of the USP14/UCHL5 deubiquitinases (DUBs) of the 19S proteasome. Exposure to b-AP15 results in blocking of proteasome function and accumulation of polyubiquitinated protein substrates in cells. This novel mechanism of proteasome inhibition may potentially be exploited for cancer therapy, in particular for treatment of malignancies resistant to currently used proteasome inhibitors. The aim of the present study was to characterize the cellular response to b-AP15-mediated proteasome DUB inhibition.

RESULTS

We report that b-AP15 elicits a similar, but yet distinct, cellular response as the clinically used proteasome inhibitor bortezomib. b-AP15 induces a rapid apoptotic response, associated with enhanced induction of oxidative stress and rapid activation of Jun-N-terminal kinase 1/2 (JNK)/activating protein-1 signaling. Scavenging of reactive oxygen species and pharmacological inhibition of JNK reduced b-AP15-induced apoptosis. We further report that endoplasmic reticulum (ER) stress is induced by b-AP15 and is involved in apoptosis induction. In contrast to bortezomib, ER stress is associated with induction of α-subunit of eukaryotic initiation factor 2 phosphorylation.

INNOVATION

The findings establish that different modes of proteasome inhibition result in distinct cellular responses, a finding of potential therapeutic importance.

CONCLUSION

Our data show that enhanced oxidative stress and ER stress are major determinants of the strong apoptotic response elicited by the 19S DUB inhibitor b-AP15.

Elevation of proteasomal substrate levels sensitizes cells to apoptosis induced by inhibition of proteasomal deubiquitinases

Inhibitors of the catalytic activity of the 20S proteasome are cytotoxic to tumor cells and are currently in clinical use for treatment of multiple myeloma, whilst the deubiquitinase activity associated with the 19S regulatory subunit of the proteasome is also a valid target for anti-cancer drugs. The mechanisms underlying the therapeutic efficacy of these drugs and their selective toxicity towards cancer cells are not known. Here, we show that increasing the cellular levels of proteasome substrates using an inhibitor of Sec61-mediated protein translocation significantly increases the extent of apoptosis that is induced by inhibition of proteasomal deubiquitinase activity in both cancer derived and non-transformed cell lines. Our results suggest that increased generation of misfolded proteasome substrates may contribute to the mechanism(s) underlying the increased sensitivity of tumor cells to inhibitors of the ubiquitin-proteasome system.

Abstract 3781: A spheroid-based screen identifies mitochondrial targeting as a promising strategy for cancer treatment and drug repositioning

In the search for novel anticancer agents, the established principle is to harness differences between normal and tumor tissue. Thus, most of current chemotherapeutic agents target fast-proliferating cancerous cells. However, over the years such treatment strategies have proven less effective than initially expected. One of the main reasons for this is that conditions present in solid tumors, such as hypoxia, low glucose availability and high concentrations of metabolites, promote quiescent, highly resistant cell phenotypes.

In our research, we aimed to target and exploit these tumor-specific conditions. To mimic the harsh conditions in a tumor, we used multicellular tumor spheroids (MCTS), which are known to simulate tumor microenvironment in vitro. We developed a novel method to easily form MCTS in 384-well format. There is only one spheroid per well formed and all are comparable in terms of size and shape. For the MCTS formation, we used colon carcinoma cell line, HCT116, with constitutive expression of green fluorescent protein (GFP). Then, we performed spheroid-based high-throughput drug screening using 1600 clinically active compounds. As a surrogate marker for cell viability, we measured mean spheroid GFP fluorescence intensity complemented with a standard resazurin-based assay. Active hits were tested in dose-response experiments in both spheroid and monolayer setup. We identified 12 compounds, which showed preferential activity against the MCTS model. We tested them in spheroid-based clonogenic assay and identified five compounds, which after 72 hrs treatment resulted in no clonogenicity at concentrations equal to monolayer-based IC50-values.

Interestingly, all of these compounds have been previously reported to impair mitochondrial function. Three of them have been also reported as uncouplers of oxidative phosphorylation. We tested the influence of all five compounds on oxygen consumption rate. All, except one compound, caused irreversible shutdown of mitochondrial function. For further experiments, we decided to choose nitazoxanide - a clinically used anti-parasitic agent with excellent pharmacokinetics, bioavailability and safety profile. We show that treatment with nitazoxanide, at concentrations well below what is reached clinically, results in down regulation of c-myc, mTOR and Wnt signaling. Preliminary in vivo experiments show encouraging results. We conclude that MCTS-based screening identifies mitochondria as a potential target for cancer treatment and the anthelmintic drug nitazoxanide as a promising candidate.

Citation Format: Wojciech Senkowski, Xiaonan Zhang, Maria Hägg Olofsson, Stig Linder, Rolf Larsson, Mårten Fryknäs. A spheroid-based screen identifies mitochondrial targeting as a promising strategy for cancer treatment and drug repositioning. [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 3781. doi:10.1158/1538-7445.AM2014-3781

Cell crowding induces interferon regulatory factor 9, which confers resistance to chemotherapeutic drugs

The mechanism of multicellular drug resistance, defined as the reduced efficacy of chemotherapeutic drugs in solid tumors is incompletely understood. Here we report that colon carcinoma cells cultured as 3D microtissues (spheroids) display dramatic increases in the expression of a subset of type I interferon-(IFN)-stimulated genes (ISGs). A similar gene signature was associated previously with resistance to radiation and chemotherapy, prompting us to examine the underlying biological mechanisms. Analysis of spheroids formed by different tumor cell lines and studies using knock-down of gene expression showed that cell crowding leads to the induction of IFN regulatory factor-9 (IRF9) which together with STAT2 and independently of IFNs, is necessary for ISG upregulation. Increased expression of IRF9 alone was sufficient to induce the ISG subset in monolayer cells and to confer increased resistance to clinically used cytotoxic drugs. Our data reveal a novel mechanism of regulation of a subset of ISGs, leading to drug resistance in solid tumors.

The 19S Deubiquitinase inhibitor b-AP15 is enriched in cells and elicits rapid commitment to cell death

b-AP15 [(3E,5E)-3,5-bis[(4-nitrophenyl)methylidene]-1-(prop-2-enoyl)piperidin-4-one] is a small molecule inhibitor of the ubiquitin specific peptidase (USP) 14/ubiquitin carboxyl-terminal hydrolase (UCH) L5 deubiquitinases of the 19S proteasome that shows antitumor activity in a number of tumor models, including multiple myeloma. b-AP15 contains an α,β-unsaturated carbonyl unit that is likely to react with intracellular nucleophiles such as cysteine thiolates by Michael addition. We found that binding of b-AP15 to USP14 is partially reversible, and that inhibition of proteasome function is reversible in cells. Despite reversible binding, tumor cells are rapidly committed to apoptosis/cell death after exposure to b-AP15. We show that b-AP15 is rapidly taken up from the medium and enriched in cells. Enrichment provides an explanation of the stronger potency of the compound in cellular assays compared with in vitro biochemical assays. Cellular uptake was impaired by 30-minute pretreatment of cells with low concentrations of N-ethylmaleimide (10 µM), suggesting that enrichment was thiol dependent. We report that in addition to inhibition of deubiquitinases, b-AP15 inhibits the selenoprotein thioredoxin reductase (TrxR). Whereas proteasome inhibition was closely associated with cell death induction, inhibition of TrxR was not. TrxR inhibition is, however, likely to contribute to triggering of oxidative stress observed with b-AP15. Furthermore, we present structure-activity, in vivo pharmacokinetic, and hepatocyte metabolism data for b-AP15. We conclude that the strong enrichment of b-AP15 in cells and a rapid commitment to apoptosis/cell death are factors that likely contribute to the strong antitumor activity of this compound.

Identification of an inhibitor of the ubiquitin–proteasome system that induces accumulation of polyubiquitinated proteins in the absence of blocking of proteasome function

The ubiquitin–proteasome system (UPS) represents one of the most promising therapeutic targets in oncology to emerge in recent years.

AKN-028 induces cell cycle arrest, downregulation of Myc associated genes and dose dependent reduction of tyrosine kinase activity in acute myeloid leukemia

AKN-028 is a novel tyrosine kinase inhibitor with preclinical activity in acute myeloid leukemia (AML), presently undergoing investigation in a phase I/II study. It is a potent inhibitor of the FMS-like kinase 3 (FLT3) but shows in vitro activity in a wide range of AML samples. In the present study, we have characterized the effects of AKN-028 on AML cells in more detail. AKN-028 induced a dose-dependent G0/1 arrest in AML cell line MV4-11. Treatment with AKN-028 caused significantly altered gene expression in all AML cell types tested (430 downregulated, 280 upregulated transcripts). Subsequent gene set enrichment analysis revealed enrichment of genes associated with the proto-oncogene and cell cycle regulator c-Myc among the downregulated genes in both AKN-028 and midostaurin treated cells. Kinase activity profiling in AML cell lines and primary AML samples showed that tyrosine kinase activity, but not serine/threonine kinase activity, was inhibited by AKN-028 in a dose dependent manner in all samples tested, reaching approximately the same level of kinase activity. Cells sensitive to AKN-028 showed a higher overall tyrosine kinase activity than more resistant ones, whereas serine/threonine kinase activity was similar for all primary AML samples. In summary, AKN-028 induces cell cycle arrest in AML cells, downregulates Myc-associated genes and affect several signaling pathways. AML cells with high global tyrosine kinase activity seem to be more sensitive to the cytotoxic effect of AKN-028 in vitro.

Abstract A108: Induction of mitochondrial dysfunction as a strategy for targeting tumor cells in hypoxic microenvironment

A fundamental problem in cancer drug discovery is to identify compounds that eliminate dormant malignant cells responsible for tumor relapse. Abnormal vascularization of solid tumors leads to the generation of tissue microenvironments that are chronically starved of oxygen and nutrients. Cells residing in such environments are slowly growing or quiescent and display altered phenotypic characteristics when compared to cells located in more vascularized regions. Such non-dividing cells are often resistant to mainstay standard chemotherapies that rely on DNA replication and cell division to elicit their anti-tumor effect. The altered phenotype of quiescent cells enables them to survive chemotherapeutic regimes and reseed nascent tumors following secession of chemotherapy. Indeed resistance to agents such as doxorubicin, cisplatin and vinblastine has been correlated with poor vasculature, tumor relapse and poor patient survival. Thus there is a need to alter the scope of cancer drug discovery and focus more on screening for agents that can exploit the altered phenotype of quiescent metabolically stressed cells to eliminate tumors.

Cell-based screening for novel anticancer drugs is typically performed using monolayer cultures of tumor cells, however such monolayer cultures do not represent the characteristics of 3-D solid tumors, frequently leading to the failure of subsequent in vivo models. The multicellular tumor spheroid model is of intermediate complexity between in vivo tumors and in vitro monolayer cultures and is more suitable for drug screening and evaluation. Spheroids are known to be more resistant to drug effects compared to monolayer cultures. Resistance is due not only to pharmacokinetic obstacles limiting drug penetrance to inner layers, but also to multi-cellular interactions leading to altered expression of genes and proteins regulating drug response. An additional benefit of growing cells three- dimensionally is the opportunity to explore the core regions’ potential vulnerability related to hypoxia and nutrient defiency and to reflect the heterogeneous milieu in tumor microregions relative to the supply. Poorly vascularized and perfused tumor microareas in many aggressive cancers have limited access not only to oxygen but also to glucose. Core regions are also associated with acidic pHsince these tumor cells change their metabolism towards increased glycolysis, resulting in increased lactic acid production.

We here employed spheroid cultures of HCT116 colon cancer cells to screen a diverse chemical library with the aim to find compounds with cytotoxic activity in core, hypoxic, regions. The screen identified a compound (VLX600) demonstrating anti-cancer activity with a large therapeutic window both in vitro and in vivo. Here we characterized the mechanism of action and potential of VLX600 as anti-cancer therapy.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A108.

Citation Format: Xiaonan Zhang, Mårten Fryknäs, Emma Hernlund, Walid Fayad, Angelo De Milito, Maria Hägg Olofsson, Stig Linder. Induction of mitochondrial dysfunction as a strategy for targeting tumor cells in hypoxic microenvironment. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A108.

Repositioning of the anthelmintic drug mebendazole for the treatment for colon cancer

Purpose

In the present study, we screened a compound library containing 1,600 clinically used compounds with the aim to identify compounds, which potentially could be repositioned for colon cancer therapy.

Methods

Two established colon cancer cell lines were tested using the fluorometric microculture cytotoxicity assay (FMCA). For compound comparison connectivity map (CMAP) analysis, NCI 60 data mining and protein kinase binding measurements were performed.

Results

Sixty-eight compounds were defined as hits with activity in both of these cell lines (<40 % cell survival compared with control) at 10 μM drug concentration. Analysis of chemical similarity of the hit compounds revealed several distinct clusters, among them the antiparasitic benzimidazole group. Two of these compounds, mebendazole (MBZ) and albendazole (ABZ) are registered for human use. Data from the NCI 60 cell line panel revealed only modest correlation between MBZ and ABZ, indicating differences in mechanism of action. This was further supported when gene expression signatures were compared in the CMAP database; ABZ ranked very low when MBZ was used as the query signature. Furthermore, MBZ, but not ABZ, was found to significantly interact with several protein kinases including BCR–ABL and BRAF. Analysis of the diagnosis-specific activity of MBZ showed activity in 80 % of the colon cancer cell lines in the NCI 60 panel. Three additional colon cancer cell lines and three cell models with non-malignant phenotypes were subsequently tested, confirming selective colon cancer activity of MBZ.

Conclusion

MBZ seemingly has repositioning potential for colorectal cancer therapy.

The novel alkylating prodrug melflufen (J1) inhibits angiogenesis in vitro and in vivo

Aminopeptidase N (APN) has been reported to have a functional role in tumor angiogenesis and repeatedly reported to be over-expressed in human tumors. The melphalan-derived prodrug melphalan-flufenamide (melflufen, previously designated J1) can be activated by APN. This suggests that this alkylating prodrug may exert anti-angiogenic properties, which will possibly contribute to the anti-tumoral activity in vivo. This work presents a series of experiments designed to investigate this effect of melflufen. In a cytotoxicity assay we show that bovine endothelial cells were more than 200 times more sensitive to melflufen than to melphalan, in HUVEC cells the difference was more than 30-fold and accompanied by aminopetidase-mediated accumulation of intracellular melphalan. In the chicken embryo chorioallantoic membrane (CAM) assay it is indicated that both melflufen and melphalan inhibit vessel ingrowth. Two commercially available assays with human endothelial cells co-cultured with fibroblasts (TCS Cellworks AngioKit, and Essen GFP-AngioKit) also illustrate the superior anti-angiogenic effect of melflufen compared to melphalan. Finally, in a commercially available in vivo assay in mice (Cultrex DIVAA angio-reactor assay) melflufen displayed an anti-angiogenic effect, comparable to bevacizumab. In conclusion, this study demonstrates through all methods used, that melphalan-flufenamide besides being an alkylating agent also reveals anti-angiogenic effects in different preclinical models in vitro and in vivo.

Screening for phenotype selective activity in multidrug resistant cells identifies a novel tubulin active agent insensitive to common forms of cancer drug resistance

BACKGROUND

Drug resistance is a common cause of treatment failure in cancer patients and encompasses a multitude of different mechanisms. The aim of the present study was to identify drugs effective on multidrug resistant cells.

METHODS

The RPMI 8226 myeloma cell line and its multidrug resistant subline 8226/Dox40 was screened for cytotoxicity in response to 3,000 chemically diverse compounds using a fluorometric cytotoxicity assay (FMCA). Follow-up profiling was subsequently performed using various cellular and biochemical assays.

RESULTS

One compound, designated VLX40, demonstrated a higher activity against 8226/Dox40 cells compared to its parental counterpart. VLX40 induced delayed cell death with apoptotic features. Mechanistic exploration was performed using gene expression analysis of drug exposed tumor cells to generate a drug-specific signature. Strong connections to tubulin inhibitors and microtubule cytoskeleton were retrieved. The mechanistic hypothesis of VLX40 acting as a tubulin inhibitor was confirmed by direct measurements of interaction with tubulin polymerization using a biochemical assay and supported by demonstration of G2/M cell cycle arrest. When tested against a broad panel of primary cultures of patient tumor cells (PCPTC) representing different forms of leukemia and solid tumors, VLX40 displayed high activity against both myeloid and lymphoid leukemias in contrast to the reference compound vincristine to which myeloid blast cells are often insensitive. Significant in vivo activity was confirmed in myeloid U-937 cells implanted subcutaneously in mice using the hollow fiber model.

CONCLUSIONS

The results indicate that VLX40 may be a useful prototype for development of novel tubulin active agents that are insensitive to common mechanisms of cancer drug resistance.