Induction of Apoptosis in Intestinal Toxicity to a Histone Deacetylase Inhibitor in a Phase I Study with Pelvic Radiotherapy

Purpose

When integrating molecularly targeted compounds in radiotherapy, synergistic effects of the systemic agent and radiation may extend the limits of patient tolerance, increasing the demand for understanding the pathophysiological mechanisms of treatment toxicity. In this Pelvic Radiation and Vorinostat (PRAVO) study, we investigated mechanisms of adverse effects in response to the histone deacetylase (HDAC) inhibitor vorinostat (suberoylanilide hydroxamic acid, SAHA) when administered as a potential radiosensitiser.

Materials and Methods

This phase I study for advanced gastrointestinal carcinoma was conducted in sequential patient cohorts exposed to escalating doses of vorinostat combined with standard-fractionated palliative radiotherapy to pelvic target volumes. Gene expression microarray analysis of the study patient peripheral blood mononuclear cells (PBMC) was followed by functional validation in cultured cell lines and mice treated with SAHA.

Results

PBMC transcriptional responses to vorinostat, including induction of apoptosis, were confined to the patient cohort reporting dose-limiting intestinal toxicities. At relevant SAHA concentrations, apoptotic features (annexin V staining and caspase 3/7 activation, but not poly-(ADP-ribose)-polymerase cleavage) were observed in cultured intestinal epithelial cells. Moreover, SAHA-treated mice displayed significant weight loss.

Conclusion

The PRAVO study design implemented a strategy to explore treatment toxicity caused by an HDAC inhibitor when combined with radiotherapy and enabled the identification of apoptosis as a potential mechanism responsible for the dose-limiting effects of vorinostat. To the best of our knowledge, this is the first report deciphering mechanisms of normal tissue adverse effects in response to an HDAC inhibitor within a combined-modality treatment regimen.

Enrichment of nuclear S100A4 during G2/M in colorectal cancer cells: possible association with cyclin B1 and centrosomes

S100A4 promotes metastasis in several types of cancer, but the involved molecular mechanisms are still incompletely described. The protein is associated with a wide variety of biological functions and it locates to different subcellular compartments, including nuclei, cytoplasm and extracellular space. Nuclear expression of S100A4 has been associated with more advanced disease stage as well as poor outcome in colorectal cancer (CRC). The present study was initiated to investigate the nuclear function of S100A4 and thereby unravel potential biological mechanisms linking nuclear expression to a more aggressive phenotype. CRC cell lines show heterogeneity in nuclear S100A4 expression and preliminary experiments revealed cells in G2/M to have increased nuclear accumulation compared to G1 and S cells, respectively. Synchronization experiments validated nuclear S100A4 expression to be most prominent in the G2/M phase, but manipulating nuclear levels of S100A4 using lentiviral modified cells failed to induce changes in cell cycle distribution and proliferation. Proximity ligation assay did, however, demonstrate proximity between S100A4 and cyclin B1 in vitro, while confocal microscopy showed S100A4 to localize to areas corresponding to centrosomes in mitotic cells prior to chromosome segregation. This might indicate a novel and uncharacterized function of the metastasis-associated protein in CRC cells.

Abstract 2004: S100A4 in colorectal cancer - biological function of nuclear localization

S100A4 is a Ca2+-binding protein promoting metastasis in several types of tumors. The protein possesses a wide variety of biological functions, and locates to different subcellular compartments including the nucleus, cytoplasm and extracellular space. Even though S100A4 is mainly localized in the latter two compartments, we have previosusly shown that the protein is localized to the nucleus in more aggressive forms of colorectal cancer (CRC) and that nuclear S100A4 has prognostic impact. This may suggest a function of nuclear S100A4 in the regulation of tumor progression and metastasis formation.

The CRC cell line SW620 shows heterogeneity in nuclear S100A4 expression and in preliminary experiments we sorted cells into three distinct phases of the cell cycle using Fluorescent-activated cell sorting (FACS). When comparing the phases, the G2/M cells showed increased accumulation of nuclear S100A4 compared to cells in the G1 and S phase, respectively. Further validation was done using treatment with the cell cycle inhibitors nocodazole or thymidine, followed by subsequent release of cells. Protein expression of S100A4 at selected time points after release did also show accumulation in the nucleus around the G2/M transition making this subcellular translocation interesting for further investigation. Cancer cells are known to have a dysfunctional cell division apparatus and these results made it tempting to speculate whether S100A4 may be involved in cell cycle regulation. To further study the functional importance of the nuclear expression two different approaches were followed.

First, CRC cells exclusively expressing S100A4 in the nucleus were made and used to identify downstream targets of nuclear S100A4. At the moment potential targets are being validated.

Furthermore, we searched for factors known to be associated with the G2/M phase. Of great interest, the Proximity Ligation Assay (PLA) demonstrated that S100A4 and Cyclin B1, an important regulator of the G2/M transition, are within the same protein complex, and we are currently in the process of further characterizing this interaction.

With clinical data linking nuclear expression of S100A4 with aggressive CRC, elucidation of the biological processes involved might unravel novel therapeutic possibilities.

Citation Format: Eivind V. Egeland, Kjetil Boye, Kjersti Flatmark, Solveig J. Pettersen, Tove Oyjord, Gunhild M. Maelandsmo. S100A4 in colorectal cancer - biological function of nuclear localization. [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 2004. doi:10.1158/1538-7445.AM2014-2004

Abstract B16: Extracellular S100A4 as an inducer of a cytokine network that mediates tumor-stroma crosstalk: Potential implications for metastases

Among soluble factors that appear to be of high importance for metastasis progression are chemokines from the S100 family. One such factor is S100A4, a small calcium binding protein linked to metastasis and poor prognosis in several cancer types. The protein is expressed in and secreted from not only tumor cells, but also various stroma cells, suggesting that S100A4 might be an important factor in the tumor microenvironment. Recently we have revealed that in vivo S100A4-positive stroma cells are tightly associated with the metastatic nodules in the brain and lungs, suggesting the role of S100A4 in facilitating metastatic growth in these microenvironments. How S100A4 executes its metastasis-promoting functions is however not fully elucidated. Here we hypothesize that the extracellular S100A4 can trigger a cytokine network that mediates the tumor-stroma crosstalk and thereby facilitates metastases progression in malignant melanoma. We have shown that extracellular S100A4 stimulates melanoma cells to secrete various cytokines and growth factors, including IL-8, IL-6, CXCL2, sICAM-1 and VEGF, molecules playing a role in cancer progression and angiogenesis in particular. Since cytokines can act in a paracrine manner, they can mediate interactions between tumor cells and stroma cells. Thus, we have shown that conditioned medium from melanoma cells treated with extracellular S100A4 modulates the angiogenic functions of endothelial cells making them more migratory and more proned to make vascular-like networks in vitro. Among factors induced by S100A4 were also pro-inflammatory cytokines associated with macrophage recruitment and/or activation. Currently we are investigating whether the S100A4-triggered cytokines modulate the properties of macrophages making them support tumor cells. Altogether, our results indicate a potential role of S100A4 in stimulating tumor-stoma crosstalk which might mimic the formation of a metastatic niche-like milieu facilitating metastases.

Citation Format: Ingrid J. Bettum, Kotryna Vasiliauskaite, Solveig J. Pettersen, Gunhild M. Malandsmo, Lina Prasmickaite. Extracellular S100A4 as an inducer of a cytokine network that mediates tumor-stroma crosstalk: Potential implications for metastases. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Invasion and Metastasis; Jan 20-23, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;73(3 Suppl):Abstract nr B16.

Nuclear legumain activity in colorectal cancer

The cysteine protease legumain is involved in several biological and pathological processes, and the protease has been found over-expressed and associated with an invasive and metastatic phenotype in a number of solid tumors. Consequently, legumain has been proposed as a prognostic marker for certain cancers, and a potential therapeutic target. Nevertheless, details on how legumain advances malignant progression along with regulation of its proteolytic activity are unclear. In the present work, legumain expression was examined in colorectal cancer cell lines. Substantial differences in amounts of pro- and active legumain forms, along with distinct intracellular distribution patterns, were observed in HCT116 and SW620 cells and corresponding subcutaneous xenografts. Legumain is thought to be located and processed towards its active form primarily in the endo-lysosomes; however, the subcellular distribution remains largely unexplored. By analyzing subcellular fractions, a proteolytically active form of legumain was found in the nucleus of both cell lines, in addition to the canonical endo-lysosomal residency. In situ analyses of legumain expression and activity confirmed the endo-lysosomal and nuclear localizations in cultured cells and, importantly, also in sections from xenografts and biopsies from colorectal cancer patients. In the HCT116 and SW620 cell lines nuclear legumain was found to make up approximately 13% and 17% of the total legumain, respectively. In similarity with previous studies on nuclear variants of related cysteine proteases, legumain was shown to process histone H3.1. The discovery of nuclear localized legumain launches an entirely novel arena of legumain biology and functions in cancer.

Intra- and extracellular regulation of activity and processing of legumain by cystatin E/M

Legumain, an asparaginyl endopeptidase, is up-regulated in tumour and tumour-associated cells, and is linked to the processing of cathepsin B, L, and proMMP-2. Although legumain is mainly localized to the endosomal/lysosomal compartments, legumain has been reported to be localized extracellularly in the tumour microenvironment and associated with extracellular matrix and cell surfaces. The most potent endogenous inhibitor of legumain is cystatin E/M, which is a secreted protein synthesised with an export signal. Therefore, we investigated the cellular interplay between legumain and cystatin E/M. As a cell model, HEK293 cells were transfected with legumain cDNA, cystatin E/M cDNA, or both, and over-expressing monoclonal cell lines were selected (termed M38L, M4C, and M3CL, respectively). Secretion of prolegumain from M38L cells was inhibited by treatment with brefeldin A, whereas bafilomycin A1 enhanced the secretion. Cellular processing of prolegumain to the 46 and 36 kDa enzymatically active forms was reduced by treatment with either substance alone. M38L cells showed increased, but M4C cells decreased, cathepsin L processing suggesting a crucial involvement of legumain activity. Furthermore, we observed internalization of cystatin E/M and subsequently decreased intracellular legumain activity. Also, prolegumain was shown to internalize followed by increased intracellular legumain processing and activation. In addition, in M4C cells incomplete processing of the internalized prolegumain was observed, as well as nuclear localized cystatin E/M. Furthermore, auto-activation of secreted prolegumain was inhibited by cystatin E/M, which for the first time shows a regulatory role of cystatin E/M in controlling both intra- and extracellular legumain activity.

PEPTIDOGLYCAN OF STAPHYLOCCUS AUREUS INDUCES ENHANCED LEVELS OF MATRIX METALLOPROTEINASE-9 IN HUMAN BLOOD ORIGINATING FROM NEUTROPHILS

Enhanced plasma levels of matrix metalloproteinase 9 (MMP-9) detected in patients with severe sepsis are thought to contribute to the development of organ dysfunction in endotoxemia. We have recently reported that peptidoglycan, the major wall component of gram-positive bacteria, increases MMP-9 levels in lung and liver and organ injury in the rat. Thus far, it is unclear whether MMP-9 is part of the septic response to peptidoglycan in human blood. The aim of the present study was to examine the regulation of MMP-9 by peptidoglycan in human leukocytes. The addition of peptidoglycan to whole human blood caused enhanced levels of MMP-9 after 1 h of incubation (306 vs. 75 ng/mL, P < or = 0.05) and onward, as measured by enzyme-linked immunoabsorbant assay. In neutrophil cultures, MMP-9 values increased significantly after 30 min of incubation with peptidoglycan (242 vs. 121 ng/mL, P < or = 0.05), whereas muramyl dipeptide had no effect. In contrast, adherent monocytes released insignificant amounts of MMP-9. To examine whether the released MMP-9 resulted from de novo synthesis, intracellular and secreted MMP-9 was measured during stimulation of neutrophils. The total MMP-9 values (the sum of intracellular and secreted MMP-9) before and after stimulation were mainly unaltered. The enhanced MMP-9 levels induced by peptidoglycan was attenuated by inhibitors of p38 mitogen-activated protein kinases (MAPK), (SB202190, 25 microM) and ERK1/2 (PD98059, 25 microM) and inhibitors of Src Tyrosine kinase (PP2, 5 microM) and PI3-K (LY294002, 25 microM).