Irreversible inhibition of cytosolic thioredoxin reductase 1 as a mechanistic basis for anticancer therapy

Cancer cells adapt to their inherently increased oxidative stress through activation of the glutathione (GSH) and thioredoxin (TXN) systems. Inhibition of both of these systems effectively kills cancer cells, but such broad inhibition of antioxidant activity also kills normal cells, which is highly unwanted in a clinical setting. We therefore evaluated targeting of the TXN pathway alone and, more specifically, selective inhibition of the cytosolic selenocysteine-containing enzyme TXN reductase 1 (TXNRD1). TXNRD1 inhibitors were discovered in a large screening effort and displayed increased specificity compared to pan-TXNRD inhibitors, such as auranofin, that also inhibit the mitochondrial enzyme TXNRD2 and additional targets. For our lead compounds, TXNRD1 inhibition correlated with cancer cell cytotoxicity, and inhibitor-triggered conversion of TXNRD1 from an antioxidant to a pro-oxidant enzyme correlated with corresponding increases in cellular production of H2O2 In mice, the most specific TXNRD1 inhibitor, here described as TXNRD1 inhibitor 1 (TRi-1), impaired growth and viability of human tumor xenografts and syngeneic mouse tumors while having little mitochondrial toxicity and being better tolerated than auranofin. These results display the therapeutic anticancer potential of irreversibly targeting cytosolic TXNRD1 using small molecules and present potent and selective TXNRD1 inhibitors. Given the pronounced up-regulation of TXNRD1 in several metastatic malignancies, it seems worthwhile to further explore the potential benefit of specific irreversible TXNRD1 inhibitors for anticancer therapy.

MYC is downregulated by a mitochondrial checkpoint mechanism

The MYC proto-oncogene serves as a rheostat coupling mitogenic signaling with the activation of genes regulating growth, metabolism and mitochondrial biogenesis. Here we describe a novel link between mitochondria and MYC levels. Perturbation of mitochondrial function using a number of conventional and novel inhibitors resulted in the decreased expression of MYC mRNA. This decrease in MYC mRNA occurred concomitantly with an increase in the levels of tumor-suppressive miRNAs such as members of the let-7 family and miR-34a-5p. Knockdown of let-7 family or miR-34a-5p could partially restore MYC levels following mitochondria damage. We also identified let-7-dependent downregulation of the MYC mRNA chaperone, CRD-BP (coding region determinant-binding protein) as an additional control following mitochondria damage. Our data demonstrates the existence of a homeostasis mechanism whereby mitochondrial function controls MYC expression.

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.

Preclinical PET imaging of EGFR levels: pairing a targeting with a non-targeting Sel-tagged Affibody-based tracer to estimate the specific uptake

Background

Though overexpression of epidermal growth factor receptor (EGFR) in several forms of cancer is considered to be an important prognostic biomarker related to poor prognosis, clear correlations between biomarker assays and patient management have been difficult to establish. Here, we utilize a targeting directly followed by a non-targeting tracer-based positron emission tomography (PET) method to examine some of the aspects of determining specific EGFR binding in tumors.

Methods

The EGFR-binding Affibody molecule Z_EGFR:2377 and its size-matched non-binding control Z_Taq:3638 were recombinantly fused with a C-terminal selenocysteine-containing Sel-tag (Z_EGFR:2377-ST and Z_Taq:3638-ST). The proteins were site-specifically labeled with DyLight488 for flow cytometry and ex vivo tissue analyses or with ¹¹C for in vivo PET studies. Kinetic scans with the ¹¹C-labeled proteins were performed in healthy mice and in mice bearing xenografts from human FaDu (squamous cell carcinoma) and A431 (epidermoid carcinoma) cell lines. Changes in tracer uptake in A431 xenografts over time were also monitored, followed by ex vivo proximity ligation assays (PLA) of EGFR expressions.

Results

Flow cytometry and ex vivo tissue analyses confirmed EGFR targeting by Z_EGFR:2377-ST-DyLight488. [Methyl-¹¹C]-labeled Z_EGFR:2377-ST-CH₃ and Z_Taq:3638-ST-CH₃ showed similar distributions in vivo, except for notably higher concentrations of the former in particularly the liver and the blood. [Methyl-¹¹C]-Z_EGFR:2377-ST-CH₃ successfully visualized FaDu and A431 xenografts with moderate and high EGFR expression levels, respectively. However, in FaDu tumors, the non-specific uptake was large and sometimes equally large, illustrating the importance of proper controls. In the A431 group observed longitudinally, non-specific uptake remained at same level over the observation period. Specific uptake increased with tumor size, but changes varied widely over time in individual tumors. Total (membranous and cytoplasmic) EGFR in excised sections increased with tumor growth. There was no positive correlation between total EGFR and specific tracer uptake, which, since Z_EGFR:2377 binds extracellularly and is slowly internalized, indicates a discordance between available membranous and total EGFR expression levels.

Conclusions

Same-day in vivo dual tracer imaging enabled by the Sel-tag technology and ¹¹C-labeling provides a method to non-invasively monitor membrane-localized EGFR as well as factors affecting non-specific uptake of the PET ligand.

Electronic supplementary material

The online version of this article (doi:10.1186/s13550-016-0213-8) contains supplementary material, which is available to authorized users.

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.

Abstract 4557A: Development of the proteasome deubiquitinase inhibitor VLX1570 for treatment of multiple myeloma

Inhibitors of the proteasome-ubiquitin system have been found to be effective in the clinical management of multiple myeloma. We here describe the compound VLX1570, an optimized lead of the 19S deubiquitinase inhibitor b- AP15. VLX1570 was shown to inhibit the enzymatic activities of both USP14 and UCHL5 in vitro, and was shown to induce accumulation of high molecular weight polyubiquitinated proteins in multiple myeloma cells. The compound showed limited inhibitory activity of a panel of kinases. VLX1570 induces apoptosis and cell death of multiple myeloma cell lines at submicromolar concentrations. Importantly, a multiple myeloma cell line selected for bortezomib resistance was found to be sensitive to VLX1570. VLX1570 was found to be able to overcome apoptosis resistance by these cells. Induction of the phosphorylation of stress-activated kinases (JNK and p38) and inhibition of ERK phosphorylation was observed in multiple myeloma cells. We finally showed that VLX1570 confers antineoplastic activity in two different myeloma xenograft models and conclude that VLX1570 is a candidate agent for treatment of multiple myeloma.

Citation Format: Xin Wang, Chitralehka Mohanty, Padraig D'Arcy, Maria Hägg Olofsson, Felicitas Bossler, Asher Chanan-Khan, Stig Linder. Development of the proteasome deubiquitinase inhibitor VLX1570 for treatment of multiple myeloma. [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 4557A. doi:10.1158/1538-7445.AM2015-4557A

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.

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

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.

Inhibition of proteasome deubiquitinating activity as a new cancer therapy

Ubiquitin-tagged substrates are degraded by the 26S proteasome, which is a multisubunit complex comprising a proteolytic 20S core particle capped by 19S regulatory particles. The approval of bortezomib for the treatment of multiple myeloma validated the 20S core particle as an anticancer drug target. Here we describe the small molecule b-AP15 as a previously unidentified class of proteasome inhibitor that abrogates the deubiquitinating activity of the 19S regulatory particle. b-AP15 inhibited the activity of two 19S regulatory-particle-associated deubiquitinases, ubiquitin C-terminal hydrolase 5 (UCHL5) and ubiquitin-specific peptidase 14 (USP14), resulting in accumulation of polyubiquitin. b-AP15 induced tumor cell apoptosis that was insensitive to TP53 status and overexpression of the apoptosis inhibitor BCL2. We show that treatment with b-AP15 inhibited tumor progression in four different in vivo solid tumor models and inhibited organ infiltration in an acute myeloid leukemia model. Our results show that the deubiquitinating activity of the 19S regulatory particle is a new anticancer drug target.

Identification of agents that induce apoptosis of multicellular tumour spheroids: enrichment for mitotic inhibitors with hydrophobic properties

Cell-based anticancer drug screening generally utilizes rapidly proliferating tumour cells grown as monolayer cultures. Hit compounds from such screens are not necessarily effective on hypoxic and slowly proliferating cells in 3-D tumour tissue. The aim of this study was to examine the potential usefulness of 3-D cultured tumour cells for anticancer drug screening. We used colon carcinoma multicellular spheroids containing hypoxic and quiescent cells in core areas for this purpose. Three libraries (∼11 000 compounds) were screened using antiproliferative activity and/or apoptosis as end-points. Screening of monolayer and spheroid cultures was found to identify different sets of hit compounds. Spheroid screening enriched for hydrophobic compounds: median XLogP values of 4.3 and 4.4 were observed for the hits in two independent screening campaigns. Mechanistic analysis revealed that the majority of spheroid screening hits were microtubuli inhibitors. One of these inhibitors was examined in detail and found to be effective against non-dividing cells in the hypoxic centres of spheroids. Spheroid screening represents a conceptually new strategy for anticancer drug discovery. Our findings have implications for drug library design and hit selection in projects aimed to develop drugs for the treatment of solid tumours.

Utilization of cytokeratin-based biomarkers for pharmacodynamic studies

Cytokeratin (CK)18 is a useful serum biomarker for the determination of cell death of epithelial-derived tumors (carcinomas). ELISAs are available for caspase-cleaved CK18 (M30) released from apoptotic cells, or total CK18 (M65) released by cells undergoing cell death by any cause. These assays have been demonstrated to have prognostic or predictive utility in various types of carcinomas. Encouraging data have been reported by different investigators with regard to the potential use of CK18 as a serum efficacy biomarker for monitoring therapy efficiency in carcinoma patients. The ratio of caspase-cleaved to total CK18 can be determined conveniently in serum or plasma using commercially available ELISA kits (M30-Apoptosense and M65 ELISA, Peviva AB, Bromma, Sweden). M30:M65 ratios potentially provide information as to whether tumor cells undergo apoptosis or necrosis. However, as discussed in this review, M30:M65 ratios should be interpreted with caution and, preferably, only be applied to samples that contain significant levels of CK18. We conclude that M30 and M65 biomarkers provide both quantitative and qualitative information on carcinoma cell death.

Screening of natural products for therapeutic activity against solid tumors

Most of the currently used cancer therapeutics are natural products. These agents were generally discovered based on their toxicity to tumour cells using various bioassays. Although the exact mechanisms of action of the most commonly used cancer therapeutics such as anthracyclins, podophyllotoxins and camptothecin are incompletely understood, it is becoming increasingly clear that these agents often show complex modes of action at the cellular level, interacting with numerous targets. Such complex modes of action may be the very reason for clinical efficacy. For discovering new cytotoxic anticancer drugs sophisticated screening methods were used. The principles of such screening projects conducted, using collections of purified natural products or extracts from plants have been described. By performing simple but robust prescreening tests such as the brine shrimp assay, bioactive extracts can be identified. Extracts (65) prepared from a collection of Egyptian plants were identified that showed cytotoxity on HepG2 cells. Interestingly, 22 (33%) of these raw extracts, induced > 2-fold induction of caspase-cleavage activity in a colon carcinoma cell line, consistent with induction of apoptosis. Only a fraction of the diversity of the biosphere has been tested for biological activity and novel cancer therapeutics remains to be discovered.

Chemical biology suggests a role for calcium signaling in mediating sustained JNK activation during apoptosis

Calcium (Ca(2+)) is used as a signaling molecule to regulate many cellular processes. Calcium signaling generally involves transient elevations of the concentration of free Ca(2+) in the cytosol. More pronounced and sustained elevations of intracellular Ca(2+) concentrations are observed during apoptosis (programmed cell death). These Ca(2+) elevations have been shown to lead to the activation of proteases (calpains) and to changes in protein phosphorylation. Recent evidence, using chemical biology, has raised the possibility that calcium signaling is involved in sustained JNK activation during late phases of apoptosis. For at least some stimuli, calcium release leads to activation of calmodulin kinase II (CaMKII), apoptosis signaling kinase 1 (ASK1) and JNK. Calcium signaling may help to orchestrate the apoptotic response during the execution phase.

Restriction of cisplatin induction of acute apoptosis to a subpopulation of cells in a three-dimensional carcinoma culture model

Cisplatin is a clinically important chemotherapeutical agent used to treat epithelial malignancies. High concentrations (20-100 microM) of cisplatin have been used in numerous studies to induce apoptosis of carcinoma cells grown in monolayer culture over 24-48 hr. These conditions may not be relevant to 3-D tumor tissue in vivo and the importance of apoptosis for tumor response is controversial. We here studied the effects of cisplatin on a 3-D colon carcinoma in vitro model (multicellular spheroids). Cisplatin at a dose of 40 microM induced active caspase-3 preferentially in the peripheral 30 microm cell layer of spheroids, mainly during late stages (72-96 hr). The p53 response to cisplatin was also largely confined to peripheral cell layers. Despite the use of a high cisplatin concentration, a significant fraction of the cells in the spheroids survived treatment. A high proportion of surviving cells stained positive for beta-galactosidase, a marker of premature senescence. Cells growth-arrested by cisplatin treatment showed a higher spontaneous cell death rate than untreated proliferating cells. We propose that acute apoptosis is of minor significance for the overall response of carcinoma cells to cisplatin treatment.

Charting calcium-regulated apoptosis pathways using chemical biology: role of calmodulin kinase II

BACKGROUND

Intracellular free calcium ([Ca2+]i) is a key element in apoptotic signaling and a number of calcium-dependent apoptosis pathways have been described. We here used a chemical biology strategy to elucidate the relative importance of such different pathways.

RESULTS

A set of 40 agents ("bioprobes") that induce apoptosis was first identified by screening of a chemical library. Using p53, AP-1, NFAT and NF-kappaB reporter cell lines, these bioprobes were verified to induce different patterns of signaling. Experiments using the calcium chelator BAPTA-AM showed that Ca2+ was involved in induction of apoptosis by the majority of the bioprobes and that Ca2+ was in general required several hours into the apoptosis process. Further studies showed that the calmodulin pathway was an important mediator of the apoptotic response. Inhibition of calmodulin kinase II (CaMKII) resulted in more effective inhibition of apoptosis compared to inhibition of calpain, calcineurin/PP2B or DAP kinase. We used one of the bioprobes, the plant alkaloid helenalin, to study the role of CaMKII in apoptosis. Helenalin induced CaMKII, ASK1 and Jun-N-terminal kinase (JNK) activity, and inhibition of these kinases inhibited apoptosis.

CONCLUSION

Our study shows that calcium signaling is generally not an early event during the apoptosis process and suggests that a CaMKII/ASK1 signaling mechanism is important for sustained JNK activation and apoptosis by some types of stimuli.

Cytokeratin-18 is a useful serum biomarker for early determination of response of breast carcinomas to chemotherapy

PURPOSE

With a widening arsenal of cancer therapies available, it is important to develop therapy-specific predictive markers and methods to rapidly assess treatment efficacy. We here evaluated the use of cytokeratin-18 (CK18) as a serum biomarker for monitoring chemotherapy-induced cell death in breast cancer.

EXPERIMENTAL DESIGN

Different molecular forms of CK18 (caspase cleaved and total) were assessed by specific ELISA assays. Drug-induced release of CK18 was examined from breast carcinoma cells and tissue. CK18 protein composition was examined in serum. CK18 levels were determined in serum from 61 breast cancer patients during docetaxel or cyclophosphamide/epirubicin/5-fluorouracil (CEF) therapy.

RESULTS

Caspase-cleaved CK18 molecules were released from monolayer cultures and tumor organ cultures to the extracellular compartment. CK18 was present in complexes with other cytokeratins in serum. Such CK18 protein complexes are remarkably stable, leading to favorable performance of CK18 biomarker assays for clinical investigations. Docetaxel induced increased levels of caspase-cleaved CK18 in serum from breast cancer patients, indicating apoptosis. CEF therapy led to increases predominantly in uncleaved CK18, indicating induction of necrotic cell death in many tumors. The increase in total CK18 at 24 h of the first treatment cycle correlated to the clinical response to CEF therapy (P < 0.0001).

CONCLUSIONS

Induction of necrotic cell death may explain the clinical efficacy of anthracycline-based therapy for breast carcinomas with defective apoptosis pathways. We suggest that CK18 biomarkers are useful for early prediction of the response to CEF therapy in breast cancer and may be useful biomarkers for clinical trials.