Iron Oxide Nanoparticles: Selectively Targeting Melanoma Cells In Vitro by Inducing DNA Damage via H2AX Phosphorylation and Hindering Proliferation through ERK Dephosphorylation

This study investigates the distinctive characteristics of iron oxide magnetic nanoparticles (mNPs) and their potential application in cancer therapy, focusing on melanoma. Three types of mNPs, pre-validated for safety, underwent molecular analysis to uncover the activated signaling pathways in melanoma cells. Using the Western blot technique, the study revealed that mNPs induce cytotoxicity, hinder proliferation through ERK1/2 dephosphorylation, and prompt proapoptotic effects, including DNA damage by inducing H2AX phosphorylation. Additionally, in vitro magnetic hyperthermia notably enhanced cellular damage in melanoma cells. Moreover, the quantification of intracellular iron levels through Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis unveils the precise dosage required to induce cellular damage effectively. These compelling findings not only shed light on the therapeutic potential of mNPs in melanoma treatment but also open exciting avenues for future research, heralding a new era in the development of targeted and effective cancer therapies. Indeed, by discerning the effective dose, our approach becomes instrumental in optimizing the therapeutic utilization of iron oxide magnetic nanoparticles, enabling the induction of precisely targeted and controlled cellular responses.

Inhibition of MMPs supports amoeboid angiogenesis hampering VEGF-targeted therapies via MLC and ERK 1/2 signaling

BACKGROUND

In the past decades studies on anti-tumoral drugs inhibiting matrix metalloproteinase (MMPs) were disappointing. Recently, we demonstrated that mature endothelial cells (ECs) and endothelial colony forming cells (ECFCs) can switch between invasion modes to cope with challenging environments, performing the "amoeboid angiogenesis" in the absence of proteases activity.

METHODS

We first set out to investigate by ELISA if the inhibitors of the main protease family involved in angiogenesis were differently expressed during breast cancer progression. We used Marimastat, a broad-spectrum MMP inhibitor, as a means of inducing amoeboid characteristics and studied VEGF role in amoeboid angiogenesis. Thus, we performed invasion and capillary morphogenesis assay, morphological, cell signaling and in vivo mouse studies.

RESULTS

Our data showed that TIMP1, TIMP2, alpha2-antiplasmin, PAI-1 and cystatin increase in breast cancer serum of patients with primary cancer and lymph node positive compared to healthy women. In vitro results revealed that the most high-powered protease inhibitors able to induce amoeboid invasion of ECFCs were TIMP1, 2 and 3. Surprisingly, Marimastat promotes ECFC invasion and tubular formation in vitro and in vivo, inducing amoeboid characteristics. We observed that the combination of Marimastat plus VEGF doesn't boost neither cell invasion nor vessel formation capacity. Moreover, inhibition of VEGF activity with Bevacizumab in the presence of Marimastat confirmed that amoeboid angiogenesis is independent from the stimulus of the main vascular growth factor, VEGF.

CONCLUSIONS

We underline the importance to consider the amoeboid mechanism of endothelial and cancer cell invasion, probably responsible for the failure of synthetic metalloproteinase inhibitors as cancer therapy and tumor resistance to VEGF-targeted therapies, to set-up new drugs to be used in cancer therapy.

Olive phenols preserve lamin B1 expression reducing cGAS/STING/NFκB-mediated SASP in ionizing radiation-induced senescence

Senescence occurs upon critical telomere shortening, or following DNA damage, oncogenic activation, hypoxia and oxidative stress, overall referred to stress-induced premature senescence (SIPS). In response to DNA damage, senescent cells release cytoplasmic chromatin fragments (CCFs), and express an altered secretome, the senescence-associated secretory phenotype (SASP), which contributes to generate a pro-inflammatory and pro-tumoral extracellular milieu. Polyphenols have gained significant attention owing to their anti-inflammatory and anti-tumour activities. Here, we studied the effect of oleuropein aglycone (OLE) and hydroxytyrosol (HT) on DNA damage, CCF appearance and SASP in a model of irradiation-induced senescence. Neonatal human dermal fibroblasts (NHDFs) were γ-irradiated and incubated with OLE, 5 µM and HT, 1 µM. Cell growth and senescence-associated (SA)-β-Gal-staining were used as senescence markers. DNA damage was evaluated by Comet assay, lamin B1 expression, release of CCFs, cyclic GMP-AMP Synthase (cGAS) activation. IL-6, IL-8, MCP-1 and RANTES were measured by ELISA assay. Our results showed that OLE and HT exerted a protective effect on 8 Gy irradiation-induced senescence, preserving lamin B1 expression and reducing cGAS/STING/NFκB-mediated SASP. The ability of OLE and HT to mitigate DNA damage, senescence status and the related SASP in normal cells can be exploited to improve the efficacy and safety of cancer radiotherapy.

CRISPR/Cas9 uPAR Gene Knockout Results in Tumor Growth Inhibition, EGFR Downregulation and Induction of Stemness Markers in Melanoma and Colon Carcinoma Cell Lines

uPAR is a globular protein, tethered to the cell membrane by a GPI-anchor involved in several cancer-related properties and its overexpression commonly correlates with poor prognosis and metastasis. We investigated the consequences of uPAR irreversible loss in human melanoma and colon cancer cell lines, knocking out its expression by CRISPR/Cas9. We analyzed through flow cytometry, western blotting and qPCR, the modulation of the most known cancer stem cells-associated genes and the EGFR while we observed the proliferation rate exploiting 2D and 3D cellular models. We also generated uPAR “rescue” expression cell lines as well as we promoted the expression of only its 3’UTR to demonstrate the involvement of uPAR mRNA in tumor progression. Knocking out PLAUR, uPAR-encoding gene, we observed an inhibited growth ratio unexpectedly coupled with a significant percentage of cells acquiring a stem-like phenotype. In vivo experiments demonstrated that uPAR loss completely abrogates tumorigenesis despite the gained stem-like profile. Nonetheless, we proved that the reintroduction of the 3’UTR of PLAUR gene was sufficient to restore the wild-type status validating the hypothesis that such a region may act as a “molecular sponge”. In particular miR146a, by binding PLAUR 3’ UTR region might be responsible for uPAR-dependent inhibition of EGFR expression.

Enhanced Antitumoral Activity and Photoacoustic Imaging Properties of AuNP-Enriched Endothelial Colony Forming Cells on Melanoma

Near infrared (NIR)-resonant gold nanoparticles (AuNPs) hold great promise in cancer diagnostics and treatment. However, translating the theranostic potential of AuNPs into clinical applications still remains a challenge due to the difficulty to improve the efficiency and specificity of tumor delivery in vivo as well as the clearance from liver and spleen to avoid off target toxicity. In this study, endothelial colony forming cells (ECFCs) are exploited as vehicles to deliver AuNPs to tumors. It is first demonstrated that ECFCs display a great capability to intake AuNPs without losing viability, and exert antitumor activity per se. Using a human melanoma xenograft mouse model, it is next demonstrated that AuNP-loaded ECFCs retain their capacity to migrate to tumor sites in vivo 1 day after injection and stay in the tumor mass for more than 1 week. In addition, it is demonstrated that ECFC-loaded AuNPs are efficiently cleared by the liver over time and do not elicit any sign of damage to healthy tissue.

Tipifarnib as a Precision Therapy for HRAS-Mutant Head and Neck Squamous Cell Carcinomas

Tipifarnib is a potent and highly selective inhibitor of farnesyltransferase (FTase). FTase catalyzes the posttranslational attachment of farnesyl groups to signaling proteins that are required for localization to cell membranes. Although all RAS isoforms are FTase substrates, only HRAS is exclusively dependent upon farnesylation, raising the possibility that HRAS-mutant tumors might be susceptible to tipifarnib-mediated inhibition of FTase. Here, we report the characterization of tipifarnib activity in a wide panel of HRAS-mutant and wild-type head and neck squamous cell carcinoma (HNSCC) xenograft models. Tipifarnib treatment displaced both mutant and wild-type HRAS from membranes but only inhibited proliferation, survival, and spheroid formation of HRAS-mutant cells. In vivo, tipifarnib treatment induced tumor stasis or regression in all six HRAS-mutant xenografts tested but displayed no activity in six HRAS wild-type patient-derived xenograft (PDX) models. Mechanistically, drug treatment resulted in the reduction of MAPK pathway signaling, inhibition of proliferation, induction of apoptosis, and robust abrogation of neovascularization, apparently via effects on both tumor cells and endothelial cells. Bioinformatics and quantitative image analysis further revealed that FTase inhibition induces progressive squamous cell differentiation in tipifarnib-treated HNSCC PDXs. These preclinical findings support that HRAS represents a druggable oncogene in HNSCC through FTase inhibition by tipifarnib, thereby identifying a precision therapeutic option for HNSCCs harboring HRAS mutations.

Th17 lymphocyte-dependent degradation of joint cartilage by synovial fibroblasts in a humanized mouse model of arthritis and reversal by secukinumab

How T-helper (Th) lymphocyte subpopulations identified in synovial fluid from patients with juvenile idiopathic arthritis (JIA) (Th17, classic Th1, or nonclassic Th1) drive joint damage is of great interest for the possible use of biological drugs that inhibit the specific cytokines. Our objective was to clarify the role of such Th subpopulations in the pathogenesis of articular cartilage destruction by synovial fibroblasts (SFbs), and the effect of Th17 blockage in an animal model. SFbs were isolated from healthy subjects and patients with JIA, and peripheral blood Th lymphocytes subsets were obtained from healthy subjects. Fragments of human cartilage from healthy subjects in a collagen matrix containing JIA or normal SFbs grafted underskin in SCID mice were used to measure cartilage degradation under the effects of Th supernatants. JIA SFbs overexpress MMP9 and MMP2 and Th17 induce both MMPs in normal SFbs, while nonclassic Th1 upregulate urokinase plasminogen activator (uPA) activity. In vitro invasive phenotype of normal SFbs is stimulated with conditioned medium of Th17 and nonclassic-Th1. In the in vivo "inverse wrap" model, normal SFbs stimulated with supernatants of Th17-lymphocytes and nonclassic Th1 produced a cartilage invasion and degradation similar to JIA SFbs. Secukinumab inhibits the cartilage damage triggered by factors produced by Th17.

Cell-Mediated Release of Nanoparticles as a Preferential Option for Future Treatment of Melanoma

Targeted and immune therapies have unquestionably improved the prognosis of melanoma patients. However the treatment of this neoplasm still requires approaches with a higher therapeutic index, in order to reduce shortcomings related to toxic effects and aspecific targeting. This means developing therapeutic tools derived with high affinity molecules for tumor components differentially expressed in melanoma cells with respect to their normal counterpart. Nanomedicine has sought to address this problem owing to the high modulability of nanoparticles. This approach exploits not only the enhanced permeability and retention effect typical of the tumor microenvironment (passive targeting), but also the use of specific "molecular antennas" that recognize some tumor-overexpressed molecules (active targeting). This line of research has given rise to the so-called "smart nanoparticles," some of which have already passed the preclinical phase and are under clinical trials in melanoma patients. To further improve nanoparticles partition within tumors, for some years now a line of thought is exploiting the molecular systems that regulate the innate tumor-homing activity of platelets, granulocytes, monocytes/macrophages, stem cells, endothelial-colony-forming cells, and red blood cells loaded with nanoparticles. This new vision springs from the results obtained with some of these cells in regenerative medicine, an approach called "cell therapy." This review takes into consideration the advantages of cell therapy as the only one capable of overcoming the limits of targeting imposed by the increased interstitial pressure of tumors.

Chronic Resveratrol Treatment Reduces the Pro-angiogenic Effect of Human Fibroblast "Senescent-Associated Secretory Phenotype" on Endothelial Colony-Forming Cells: The Role of IL8

Senescent cells are characterized by an increased secretion of inflammatory and growth factors, known as the "senescence-associated secretory phenotype" (SASP), producing a pro-tumoral and pro-angiogenic microenvironment. This work proposes chronic resveratrol treatment (5 µM for 5 weeks, termed R5) of senescent MRC5 fibroblasts as a mean to mimic and target the angiogenic trait of stromal fibroblast SASP. Senescent fibroblast conditioned medium (CM sen) was effective in enhancing the angiogenic properties of endothelial colony-forming cells (ECFCs), that is, invasive activity and capillary morphogenesis capability in vitro, that were significantly reduced when conditioned media were collected after resveratrol pretreatment (CM senR5). The attenuation of ECFC angiogenic phenotype induced by CM senR5 was accompanied by reduced protein levels of epidermal growth factor and urokinase plasminogen activator receptors (EGFR, uPAR), and by a related decreased activation of receptor-tyrosine-kinase signaling pathways. IL8 levels were found reduced in CM senR5 compared to CM sen, with the associated reduction of IL8-CXCR2 binding in ECFCs. IL8-subtraction mitigated the pro-angiogenic features of CM sen and the associated intracellular signaling in ECFCs, indicating a prominent role of IL8 in the pro-angiogenic effects of CM sen. IL8 modulation is an important mechanism underlying the antiangiogenic activity of resveratrol on MRC5 SASP.

uPAR Knockout Results in a Deep Glycolytic and OXPHOS Reprogramming in Melanoma and Colon Carcinoma Cell Lines

Urokinase Plasminogen Activator (uPA) Receptor (uPAR) is a well-known GPI-anchored three-domain membrane protein with pro-tumor roles largely shown in all the malignant tumors where it is over-expressed. Here we have exploited the Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 gene knock out approach to investigate its role in the oxidative metabolism in human melanoma and colon cancer as the consequences of its irreversible loss. Knocking out PLAUR, a uPAR-encoding gene, in A375p, A375M6 and HCT116, which are two human melanoma and a colon carcinoma, respectively, we have observed an increased number of mitochondria in the two melanoma cell lines, while we evidenced an immature biogenesis of mitochondria in the colon carcinoma culture. Such biological diversity is, however, reflected in a significant enhancement of the mitochondrial spare respiratory capacity, fueled by an increased expression of GLS2, and in a decreased glycolysis paired with an increased secretion of lactate by all uPAR KO cells. We speculated that this discrepancy might be explained by an impaired ratio between LDHA and LDHB.

EGFR/uPAR interaction as druggable target to overcome vemurafenib acquired resistance in melanoma cells

Background

BRAF inhibitor (BRAF-I) therapy for melanoma patients harboring the V600E mutation is initially highly effective, but almost all patients relapse within a few months. Understanding the molecular mechanisms behind BRAF-I responsiveness and acquired resistance is therefore an important issue. Here we assessed the role of urokinase type plasminogen activator receptor (uPAR) as a potentially valuable biomarker in the acquisition of BRAF-I resistance in V600E mutant melanoma cells.

Methods

We examined uPAR and EGFR levels by real time PCR and western blot analysis. uPAR loss of function was realized by knocking down uPAR by RNAi or using M25, a peptide that uncouples uPAR-integrin interaction. We investigated uPAR-β1integrin-EGFR association by co-immunoprecipitation and confocal immuno-fluorescence analysis. Acquired resistance to BRAF-I was generated by chronic exposure of cells to vemurafenib.

Findings

We proved that uPAR knockdown in combination with vemurafenib inhibits melanoma cell proliferation to greater extent than either treatment alone causing a decrease in AKT and ERK1/2 phosphorylation. Conversely, we demonstrated that uPAR enforced over-expression results in reduced sensitivity to BRAF inhibition. Moreover, by targeting uPAR and EGFR interaction with an integrin antagonist peptide we restored vemurafenib responsiveness in melanoma resistant cells. Furthermore, we found significant detectable uPAR and EGFR levels in tumor biopsies of 4 relapsed patients.

Interpretation

We disclosed an unpredicted mechanism of reduced sensitiveness to BRAF inhibition, driven by elevated levels of uPAR and identified a potential therapeutic strategy to overcome acquired resistance.

Funds

Associazione Italiana Ricerca sul Cancro (AIRC); Ente Cassa di Risparmio di Firenze.

Delivery systems of CRISPR/Cas9-based cancer gene therapy

CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) is today one of the most reliable method for gene-editing, supporting previous gene therapies technologies such as TALEN, Meganucleases and ZFNs. There is a growing up number of manuscripts reporting several successful gene-edited cancer cell lines, but the real challenge is to translate this technique to the clinical practice. While treatments for diseases based on a single gene mutation is closer, being possible to target and repair the mutant allele in a selective way generating specific guide RNAs (gRNAs), many steps need to be done to apply CRISPR to face cancer. In this review, we want to give a general overview to the recent advancements in the delivery systems of the CRISPR/Cas9 machinery in cancer therapy.

Mature and progenitor endothelial cells perform angiogenesis also under protease inhibition: the amoeboid angiogenesis

Background

Controlling vascular growth is a challenging aim for the inhibition of tumor growth and metastasis. The amoeboid and mesenchymal types of invasiveness are two modes of migration interchangeable in cancer cells: the Rac-dependent mesenchymal migration requires the activity of proteases; the Rho-ROCK-dependent amoeboid motility is protease-independent and has never been described in endothelial cells.

Methods

A cocktail of physiologic inhibitors (Ph-C) of serine-proteases, metallo-proteases and cysteine-proteases, mimicking the physiological environment that cells encounter during their migration within the angiogenesis sites was used to induce amoeboid style migration of Endothelial colony forming cells (ECFCs) and mature endothelial cells (ECs). To evaluate the mesenchymal-ameboid transition RhoA and Rac1 activation assays were performed along with immunofluorescence analysis of proteins involved in cytoskeleton organization. Cell invasion was studied in Boyden chambers and Matrigel plug assay for the in vivo angiogenesis.

Results

In the present study we showed in both ECFCs and ECs, a decrease of activated Rac1 and an increase of activated RhoA upon shifting of cells to the amoeboid conditions. In presence of Ph-C inhibitors both cell lines acquired a round morphology and Matrigel invasion was greatly enhanced with respect to that observed in the absence of protease inhibition. We also observed that the urokinase-plasminogen-activator (uPAR) receptor silencing and uPAR-integrin uncoupling with the M25 peptide abolished both mesenchymal and amoeboid angiogenesis of ECFCs and ECs in vitro and in vivo, indicating a role of the uPAR-integrin-actin axis in the regulation of amoeboid angiogenesis. Furthermore, under amoeboid conditions endothelial cells seem to be indifferent to VEGF stimulation, which induces an amoeboid signaling pattern also in mesenchymal conditions.

Conclusion

Here we first provide a data set disclosing that endothelial cells can move and differentiate into vascular structures in vitro and in vivo also in the absence of proteases activity, performing a new type of neovascularization: the “amoeboid angiogenesis”. uPAR is indispensable for ECs and ECFCs to perform an efficient amoeboid angiogenesis. Therefore, uPAR silencing or the block of its integrin-interaction, together with standard treatment against VEGF, could be a possible solution for angiogenesis inhibition.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0742-2) contains supplementary material, which is available to authorized users.

Endothelial Progenitor Cells as Shuttle of Anticancer Agents

Cell therapies are treatments in which stem or progenitor cells are stimulated to differentiate into specialized cells able to home to and repair damaged tissues. After their discovery, endothelial progenitor cells (EPCs) stimulated worldwide interest as possible vehicles to perform autologous cell therapy of tumors. Taking into account the tumor-homing properties of EPCs, two different approaches to control cancer progression have been pursued by combining cell-based therapy with gene therapy or with nanomedicine. The first approach is based on the possibility of engineering EPCs to express different transgenes, and the second is based on the capacity of EPCs to take up nanomaterials. Here we review the most important progress covering the following issues: the characterization of bona fide endothelial progenitor cells, their role in tumor vascularization and metastasis, and preclinical data about their use in cell-based tumor therapy, considering antiangiogenic, suicide, immune-stimulating, and oncolytic virus gene therapy. The mixed approach of EPC cell therapy and nanomedicine is discussed in terms of plasmonic-dependent thermoablation and molecular imaging.

Tumor-tropic endothelial colony forming cells (ECFCs) loaded with near-infrared sensitive Au nanoparticles: A "cellular stove" approach to the photoablation of melanoma

In the photothermal treatments (PTs) of tumor, the localization of a high number of near-infrared (NIR) absorbing gold nanoparticles in the tumor mass is still a challenging issue. Here, we propose a promising strategy to deliver therapeutic chitosan-coated gold nanoparticles to tumor cells as hidden cargo of Endothelial Colony Forming Cells (ECFCs) endowed with an innate tumor-tropism. Remarkably, ECFC gold enrichement doesn't affect cell viability and preserves the endothelial lineage characteristics such as capillary morphogenesis and cell migration. We demonstrate that heavily Au-doped ECFCs are able to efficiently warm up the tumor environment, and kill the cancer cells via hyperthermic heating both in vitro as well as in vivo. Thus, we show an excellent thermotransductive property of gold enriched ECFCs and their capability to kill melanoma cells at moderate NIR light intensities.

Chronic Resveratrol Treatment Inhibits MRC5 Fibroblast SASP-Related Protumoral Effects on Melanoma Cells

Cellular senescence is related to organismal aging and is observed after DNA damaging cancer therapies, that induce tumor-suppressive modifications, but it is characterized by a strong increase in secreted factors, termed the "senescence-associated secretory phenotype" (SASP). Particularly, SASP from stroma senescent fibroblasts creates a cancer-favoring microenvironment, providing targets for anti-cancer interventions. In the present article, chronic treatment (5 weeks) with 5 µM resveratrol has been used to modulate senescence-related protumoral features of MRC5 fibroblasts, reducing SASP-related interleukins IL1α, IL1β, IL6, and IL8; transforming-growth-factor-β (TGFβ); matrix metallo-proteinases MMP3 and MMP2; urokinase plasminogen activator (uPA); receptor proteins uPAR, IL6R, insulin growth factor receptor-1 (IGF-1R), TGFβ-R2, and CXCR4. The cellular nuclear-factor-kB (NF-kB) protein level was also reduced, confirming its role in the induction of SASP. Resveratrol pretreated MRC5 fibroblasts were resistant to activation by TGFβ. Resveratrol treatment of senescent MRC5 induced the production of conditioned media (CM) which counteracted the protumoral effect of senescent CM on A375 and A375-M6 melanoma cell proliferation and invasiveness, and reduced the expression of epithelial-to-mesenchymal transition markers related to malignant features. This experimental approach proposes a treatment that targets the senescent stromal cell phenotype to induce an anti-tumor hosting microenvironment, which is suitable for both preventive and therapeutic purposes.

u-PAR expression in cancer associated fibroblast: new acquisitions in multiple myeloma progression

Background

Multiple Myeloma (MM) is a B-cell malignancy in which clonal plasma cells progressively expand within the bone marrow (BM) as effect of complex interactions with extracellular matrix and a number of microenvironmental cells. Among these, cancer-associated fibroblasts (CAF) mediate crucial reciprocal signals with MM cells and are associated to aggressive disease and poor prognosis. A large body of evidence emphasizes the role of the urokinase plasminogen activator (u-PA) and its receptor u-PAR in potentiating the invasion capacity of tumor plasma cells, but little is known about their role in the biology of MM CAF. In this study, we investigated the u-PA/u-PAR axis in MM-associated fibroblasts and explore additional mechanisms of tumor/stroma interplay in MM progression.

Methods

CAF were purified from total BM stromal fraction of 64 patients including monoclonal gammopathy of undetermined significance, asymptomatic and symptomatic MM, as well as MM in post-treatment remission. Flow cytometry, Real Time PCR and immunofluorescence were performed to investigate the u-PA/u-PAR system in relation to the level of activation of CAF at different stages of the disease. Moreover, proliferation and invasion assays coupled with silencing experiments were used to prove, at functional level, the function of u-PAR in CAF.

Results

We found higher activation level, along with increased expression of pro-invasive molecules, including u-PA, u-PAR and metalloproteinases, in CAF from patients with symptomatic MM compared to the others stages of the disease. Consistently, CAF from active MM as well as U266 cell line under the influence of medium conditioned by active MM CAF, display higher proliferative rate and invasion potential, which were significantly restrained by u-PAR gene expression inhibition.

Conclusions

Our data suggest that the stimulation of u-PA/u-PAR system contributes to the activated phenotype and function of CAF during MM progression, providing a biological rationale for future targeted therapies against MM.

Abstract 5063: The receptor for urokinase-plasminogen activator controls plasticity of cancer cell movement in mesenchymal and amoeboid migration style

Introduction. The receptor for the urokinase plasminogen activator (uPAR) is up-regulated in malignant tumors. Historically the function of uPAR in cancer cell invasion is strictly related to its property to promote uPA-dependent proteolysis of extracellular matrix and to open a path to malignant cells. These features are typical of mesenchymal motility.

Materials and methods. To evaluate the mesenchymal ameboid transition we performed RhoA and Rac1 activation assay, immunofluorescence analysis of protein involved in cytoskeleton organization, and collagen degradation assay. For a clear visualization of collagen fiber breakdown in the process of proteolytic migration we used reconstruction by time-lapse video microscopy. Cell invasion was studied in Boyden chambers using filters coated with Matrigel. uPAR gene expression was inhibited using a 18-mer phosphorothioate aODN, and as a negative control we used a degenerated oligodeoxynucleotide, which is a mixture of all possible combinations of bases that compose the aODN.

Results and discussion. Here we show that the full-length form of uPAR is required when prostate and melanoma cancer cells convert their migration style from the “path generating” mesenchymal to the “path finding” amoeboid one, thus conferring a plasticity to tumor cell invasiveness across three-dimensional matrices. Indeed, in response to a protease inhibitors-rich milieu, prostate and melanoma cells activated an amoeboid invasion program connoted by retraction of cell protrusions, RhoA-mediated rounding of the cell body, formation of a cortical ring of actin and a reduction of Rac-1 activation. While the mesenchymal movement was reduced upon silencing of uPAR expression, the amoeboid one was almost completely abolished, in parallel with a deregulation of small Rho-GTPases activity. In melanoma and prostate cancer cells we have shown uPAR colocalization with β1/β3 integrins and actin cytoskeleton, as well integrins-actin co-localization under both mesenchymal and amoeboid conditions. Such co-localizations were lost upon treatment of cells with a peptide that inhibits uPAR-integrin interactions. Similarly to uPAR silencing, the peptide reduced mesenchymal invasion and almost abolished the amoeboid one.

Conclusion. These results indicate that full-length uPAR bridges the mesenchymal and amoeboid style of movement by an inward-oriented activity based on its property to promote integrin-actin interactions and the following cytoskeleton assembly.

Citation Format: Anastasia Chillà, Francesca Margheri, Anna Laurenzana, Cristina Luciani, Alessio Biagioni, Gabriella Fibbi, Mario Del Rosso. The receptor for urokinase-plasminogen activator controls plasticity of cancer cell movement in mesenchymal and amoeboid migration style. [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 5063.

Th1-Induced CD106 Expression Mediates Leukocytes Adhesion on Synovial Fibroblasts from Juvenile Idiopathic Arthritis Patients

This study tested the hypothesis that subsets of human T helper cells can orchestrate leukocyte adhesion to synovial fibroblasts (SFbs), thus regulating the retention of leukocytes in the joints of juvenile idiopathic arthritis (JIA) patients. Several cell types, such as monocytes/macrophages, granulocytes, T and B lymphocytes, SFbs and osteoclasts participate in joint tissue damage JIA. Among T cells, an enrichment of classic and non-classic Th1 subsets, has been found in JIA synovial fluid (SF), compared to peripheral blood (PB). Moreover, it has been shown that IL-12 in the SF of inflamed joints mediates the shift of Th17 lymphocytes towards the non-classic Th1 subset. Culture supernatants of Th17, classic and non-classic Th1 clones, have been tested for their ability to stimulate proliferation, and to induce expression of adhesion molecules on SFbs, obtained from healthy donors. Culture supernatants of both classic and non-classic Th1, but not of Th17, clones, were able to induce CD106 (VCAM-1) up-regulation on SFbs. This effect, mediated by tumor necrosis factor (TNF)-α, was crucial for the adhesion of circulating leukocytes on SFbs. Finally, we found that SFbs derived from SF of JIA patients expressed higher levels of CD106 than those from healthy donors, resembling the phenotype of SFbs activated in vitro with Th1-clones supernatants. On the basis of these findings, we conclude that classic and non-classic Th1 cells induce CD106 expression on SFbs through TNF-α, an effect that could play a role in leukocytes retention in inflamed joints.

Abstract 406: Effects of an RGD peptide in osteoclast maturation and behavior as a therapeutic option for metastatic bone disease

Metastatic bone disease is a common feature of many types of cancer and has a severe impact on the quality of life of patients. Hence, specific therapeutic strategies inhibiting tumor induced osteolysis are urgently needed. In this study, we aimed to interfere with integrin adhesion receptors, which are central players of the bone resorption process, including osteoclastogenesis as well as osteoclast/bone matrix interaction. For this purpose, we used a cyclic RGD peptide which blocks integrin áVâ3 and áVâ5-ligand binding. Our results revealed that the RGD peptide blocked osteoclast maturation in a dose-dependent manner. In detail, pre-osteoclasts treated with the RGD peptide exhibited reduced cell spreading, migration and adhesion on RGD-containing matrix proteins, such as osteopontin and fibrinogen, which are ligands of integrin áVâ3. The activation of the most upstream signal transduction molecules of the integrin receptor-initiated pathway, such as FAK and c-Src, were consistently blocked by the RGD peptide. First evidence has suggested that the RGD peptide might interfere with metastatic bone disease in vivo and the evidence presented herein describes the underlying mechanisms of the inhibitory effect of the RGD peptide on áV-integrin expressing pre-osteoclasts by blocking integrin ligand binding and interfering with osteoclast maturation and cell behavior. In conclusion, our findings suggest that using an RGD peptide to interfere with áV-integrins on osteoclasts may represent a novel therapeutic strategy in the treatment of malignant bone disease.

Citation Format: Gerald Prager, Daniela Bianconi, Anastasia Chillà, Alexandra Dorda, Nisha Geetha, Matthias Unseld, Despoina Sykoutri, Marina Poettler, Kurt Redlich, Christoph Zielinski. Effects of an RGD peptide in osteoclast maturation and behavior as a therapeutic option for metastatic bone disease. [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 406. doi:10.1158/1538-7445.AM2015-406

Inhibition of uPAR-TGFβ crosstalk blocks MSC-dependent EMT in melanoma cells

The capacity of cancer cells to undergo epithelial-to-mesenchymal transition (EMT) is now considered a hallmark of tumor progression, and it is known that interactions between cancer cells and mesenchymal stem cells (MSCs) of tumor microenvironment may promote this program. Herein, we demonstrate that MSC-conditioned medium (MSC-CM) is a potent inducer of EMT in melanoma cells. The EMT profile acquired by MSC-CM-exposed melanoma cells is characterized by an enhanced level of mesenchymal markers, including TGFβ/TGFβ-receptors system upregulation, by increased invasiveness and uPAR expression, and in vivo tumor growth. Silencing TGFβ in MSC is found to abrogate ability of MSC to promote EMT characteristics in melanoma cells, together with uPAR expression, and this finding is strengthened using an antagonist peptide of TGFβRIII, the so-called P17. Finally, we demonstrate that the uPAR antisense oligonucleotide (uPAR aODN) may inhibit EMT of melanoma cells either stimulated by exogenous TGFβ or MSC-CM. Thus, uPAR upregulation in melanoma cells exposed to MSC-medium drives TGFβ-mediated EMT. On the whole, TGFβ/uPAR dangerous liaison in cancer cell/MSC interactions may disclose a new strategy to abrogate melanoma progression.

KEY MESSAGE

Mesenchymal stem cell (MSC)-conditioned medium induces EMT-like profile in melanoma. MSC-derived TGFβ promotes uPAR and TGFβ/TGFβ-receptor upregulation in melanoma. TGFβ gene silencing in MSCs downregulates uPAR expression and EMT in melanoma. uPAR downregulation prevents MSC-induced EMT-like profile in melanoma cells. Inhibition of the dangerous TGFβ/uPAR relationship might abrogate melanoma progression.

The receptor for urokinase-plasminogen activator (uPAR) controls plasticity of cancer cell movement in mesenchymal and amoeboid migration style

The receptor for the urokinase plasminogen activator (uPAR) is up-regulated in malignant tumors. Historically the function of uPAR in cancer cell invasion is strictly related to its property to promote uPA-dependent proteolysis of extracellular matrix and to open a path to malignant cells. These features are typical of mesenchymal motility. Here we show that the full-length form of uPAR is required when prostate and melanoma cancer cells convert their migration style from the “path generating” mesenchymal to the “path finding” amoeboid one, thus conferring a plasticity to tumor cell invasiveness across three-dimensional matrices. Indeed, in response to a protease inhibitors-rich milieu, prostate and melanoma cells activated an amoeboid invasion program connoted by retraction of cell protrusions, RhoA-mediated rounding of the cell body, formation of a cortical ring of actin and a reduction of Rac-1 activation. While the mesenchymal movement was reduced upon silencing of uPAR expression, the amoeboid one was almost completely abolished, in parallel with a deregulation of small Rho-GTPases activity. In melanoma and prostate cancer cells we have shown uPAR colocalization with β1/β3 integrins and actin cytoskeleton, as well integrins-actin co-localization under both mesenchymal and amoeboid conditions. Such co-localizations were lost upon treatment of cells with a peptide that inhibits uPAR-integrin interactions. Similarly to uPAR silencing, the peptide reduced mesenchymal invasion and almost abolished the amoeboid one. These results indicate that full-length uPAR bridges the mesenchymal and amoeboid style of movement by an inward-oriented activity based on its property to promote integrin-actin interactions and the following cytoskeleton assembly.

Differential uPAR recruitment in caveolar-lipid rafts by GM1 and GM3 gangliosides regulates endothelial progenitor cells angiogenesis

Gangliosides and the urokinase plasminogen activator receptor (uPAR) tipically partition in specialized membrane microdomains called lipid-rafts. uPAR becomes functionally important in fostering angiogenesis in endothelial progenitor cells (EPCs) upon recruitment in caveolar-lipid rafts. Moreover, cell membrane enrichment with exogenous GM1 ganglioside is pro-angiogenic and opposite to the activity of GM3 ganglioside. On these basis, we first checked the interaction of uPAR with membrane models enriched with GM1 or GM3, relying on the adoption of solid-supported mobile bilayer lipid membranes with raft-like composition formed onto solid hydrophilic surfaces, and evaluated by surface plasmon resonance (SPR) the extent of uPAR recruitment. We estimated the apparent dissociation constants of uPAR-GM1/GM3 complexes. These preliminary observations, indicating that uPAR binds preferentially to GM1-enriched biomimetic membranes, were validated by identifying a pro-angiogenic activity of GM1-enriched EPCs, based on GM1-dependent uPAR recruitment in caveolar rafts. We have observed that addition of GM1 to EPCs culture medium promotes matrigel invasion and capillary morphogenesis, as opposed to the anti-angiogenesis activity of GM3. Moreover, GM1 also stimulates MAPKinases signalling pathways, typically associated with an angiogenesis program. Caveolar-raft isolation and Western blotting of uPAR showed that GM1 promotes caveolar-raft partitioning of uPAR, as opposed to control and GM3-challenged EPCs. By confocal microscopy, we have shown that in EPCs uPAR is present on the surface in at least three compartments, respectively, associated to GM1, GM3 and caveolar rafts. Following GM1 exogenous addition, the GM3 compartment is depleted of uPAR which is recruited within caveolar rafts thereby triggering angiogenesis.

Desmoglein-2-integrin Beta-8 interaction regulates actin assembly in endothelial cells: deregulation in systemic sclerosis

Background

The inability of endothelial cells of patients affected by the diffuse form of Systemic sclerosis (SSc) to perform angiogenesis is a marker of the disease. We previously demonstrated that desmoglein-2 reduction is a major difference between (SSc)-microvascular endothelial cells (MVECs) and normal (N)-MVECs. Here we investigated the role of desmoglein-2 in human N-MVECs and SSc-MVECs angiogenesis.

Methodology/principal findings

Angiogenesis was studied by Matrigel invasion, capillary morphogenesis in vitro and Matrigel plug assay in vivo. Gene profiling was studied by Affymetrix technology and signal transduction by Western blotting. Colocalization was validated by immunoprecipitation and confocal microscopy. SiRNAs were used to validate the roles of specific molecules. We observed that desmoglein-2 co-localizes with integrin-beta8 in N-MVECs. This complex is required to signal through Rac, FAK, SMAD1/5 and MAP-kinases, promoting an angiogenic program. Inhibition of desmoglein-2 by DSG2-siRNA impaired actin stress fibres formation, capillary morphogenesis in vitro and angiogenesis in vivo. Transcriptome profiling after DSG2 inhibition revealed alterations of several genes involved in actin organization. siRNA inhibition of integrin-beta8 and RAC2 also resulted into capillary morphogenesis impairment in N-MVECs, due to reduced expression of the same actin-assembly genes that were down-regulated by DSG2 silencing. SSc-MVECs showed down-regulation of the same genes in DSG2-siRNA treated N-MVECs, suggesting that impairment of desmoglein-2/integrin-beta8 complex contributes to angiogenesis derangement in SSc. Transfection of DSG2 in SSc-MVEC partially restored their angiogenic properties in vitro.

Conclusions/significance

We have shown that impairment of actin assembly as a result of desmoglein-2/integrin-beta8 complex formation is a major factor contributing to angiogenesis deregulation in Systemic sclerosis.

Proteomic identification of VEGF-dependent protein enrichment to membrane caveolar-raft microdomains in endothelial progenitor cells

Endothelial cell caveolar-rafts are considered functional platforms that recruit several pro-angiogenic molecules to realize an efficient angiogenic program. Here we studied the differential caveolar-raft protein composition of endothelial colony-forming cells following stimulation with VEGF, which localizes in caveolae on interaction with its type-2 receptor. Endothelial colony-forming cells are a cell population identified in human umbilical blood that show all the properties of an endothelial progenitor cell and a high proliferative rate. Two-dimensional gel electrophoresis analysis was coupled with mass spectrometry to identify candidate proteins. The twenty-eight differentially expressed protein spots were grouped according to their function using Gene Ontology classification. In particular, functional categories relative to cell death inhibition and hydrogen peroxide metabolic processes resulted enriched. In these categories, Peroxiredoxin-2 and 6, that control hydrogen peroxide metabolic processes, are the main enriched molecules together with the anti-apoptotic 78 kDa glucose regulated protein. Some of the proteins we identified had never before identified as caveolar-raft components. Other identified proteins include calpain small subunit-1, known to mediates angiogenic response to VEGF, gelsolin, which regulates stress fiber assembly, and annexin A3, an angiogenic mediator that induces VEGF production. We validated the functional activity of the above proteins, showing that the siRNA silencing of these resulted in the inhibition of capillary morphogenesis. Overall, our data show that VEGF stimulation triggers the caveolar-raft recruitment of proteins that warrant a physiological amount of reactive oxygen species to maintain a proper angiogenic function of endothelial colony-forming cells and preserve the integrity of the actin cytoskeleton.

Systemic sclerosis endothelial cells recruit and activate dermal fibroblasts by induction of a connective tissue growth factor (CCN2)/transforming growth factor β-dependent mesenchymal-to-mesenchymal transition

OBJECTIVE

Clinical evidence suggests that the vascular abnormalities of systemic sclerosis (SSc) precede the onset of fibrosis, but molecular cues accounting for a possible vascular connection of SSc fibrosis have been elusive, although they have been searched for intensively. Since we had previously shown that connective tissue growth factor (CCN2), endowed with fibroblast-oriented activities, was overexpressed by endothelial cells (ECs) from SSc patients, we undertook this study to investigate its role and mechanisms in fibroblast activation.

METHODS

Normal fibroblasts were challenged with conditioned medium of normal microvascular ECs (MVECs) and MVECs obtained from SSc patients with the diffuse form of the disease. Fibroblast invasion was studied using the Boyden chamber Matrigel assay. Fibroblast activation was evaluated by Western blotting and immunofluorescence of α-smooth muscle actin (α-SMA), vimentin, and type I collagen. Matrix metalloproteinase (MMP) production was evaluated by zymography and reverse transcription-polymerase chain reaction. Signal transduction and activation of the small GTPases RhoA and Rac1 were studied by Western blotting. Inhibition of SSc MVEC conditioned medium-dependent fibroblast activation was obtained by anti-CCN2 antibodies and the transforming growth factor β (TGFβ) antagonist peptide p17.

RESULTS

SSc MVEC CCN2 stimulated fibroblast activation and invasion. Such activities depended on CCN2-induced overexpression of TGFβ and its type I, II, and III receptors combined with overproduction of MMP-2 and MMP-9 gelatinases. All of these effects were reversed by the TGFβ antagonist peptide p17. Motility increase required Rac1 activation and RhoA inhibition and was inhibited by an MMP inhibitor. These features connoted a mesenchymal style of cell invasion. Since fibroblast activation also fostered overexpression of α-SMA, vimentin, and type I collagen, the CCN2-dependent increase in fibroblast activities recapitulated the characteristics of a mesenchymal-to-mesenchymal transition.

CONCLUSION

SSc MVECs recruit and activate dermal fibroblasts by induction of a CCN2/TGFβ-dependent mesenchymal-to-mesenchymal transition.

GDF5 regulates TGFß-dependent angiogenesis in breast carcinoma MCF-7 cells: in vitro and in vivo control by anti-TGFß peptides

BACKGROUND

TGFß overproduction in cancer cells is one of the main characteristics of late tumor progression being implicated in metastasis, tumor growth, angiogenesis and immune response. We investigated the therapeutic efficacy of anti-TGFß peptides in the control of angiogenesis elicited by conditional over-expression of TGFß.

METHODS

We have inserted in human MCF7 mammary-cancer cells a mutated TGFß gene in a tetracycline-repressible vector to obtain conditional expression of mature TGFß upon transient transfection, evaluated the signaling pathways involved in TGFß-dependent endothelial cells activation and the efficacy of anti-TGFß peptides in the control of MCF7-TGFß-dependent angiogenesis.

RESULTS

TGFß over-expression induced in MCF7 several markers of the epithelial-to-mesenchymal transition. Conditioned-medium of TGFß-transfected MCF7 stimulated angiogenesis in vivo and in vitro by subsequent activation of SMAD2/3 and SMAD1/5 signaling in endothelial cells, as well as SMAD4 nuclear translocation, resulting in over-expression of the pro-angiogenic growth and differentiation factor-5 (GDF5). Inhibition or silencing of GDF5 in TGFß-stimulated EC resulted in impairment of GDF5 expression and of TGFß-dependent urokinase-plasminogen activator receptor (uPAR) overproduction, leading to angiogenesis impairment. Two different TGFß antagonist peptides inhibited all the angiogenesis-related properties elicited in EC by exogenous and conditionally-expressed TGFß in vivo and in vitro, including SMAD1/5 phosphorylation, SMAD4 nuclear translocation, GDF5 and uPAR overexpression. Antagonist peptides and anti-GDF5 antibodies efficiently inhibited in vitro and in vivo angiogenesis.

CONCLUSIONS

TGFß produced by breast cancer cells induces in endothelial cells expression of GDF5, which in turn stimulates angiogenesis both in vitro and in vivo. Angiogenesis activation is rapid and the involved mechanism is totally opposed to the old and controversial dogma about the AKL5/ALK1 balance. The GDF-dependent pro-angiogenic effects of TGFß are controlled by anti-TGFß peptides and anti-GDF5 antibodies, providing a basis to develop targeted clinical studies.

The urokinase receptor system, a key regulator at the intersection between inflammation, immunity, and coagulation

The urokinase plasminogen activator (uPA) and its receptor (uPAR) provide a cell surface integrated multimolecular complex that exerts pleiotropic functions influencing the development of inflammatory, immune, coagulation and fibrinolytic responses. Here we review the evidences indicating a role of the uPA/uPAR system in the regulation of the innate immune system in the inflammation process, of the adaptive immune response, as well as the role of fibrin and fibrin degradation products at the cross-road between coagulation and inflammation. Comparative studies have clearly highlighted the notion that coagulation and immunity are co-regulated and intertwined. The implication is that the vertebrate blood clotting system is evolutionarily by product of the innate immune system, where the blood clotting proteases have diverged from those comprising the complement system. Differences have emerged gradually, as shown by the acquisition of unique protein structures, such as kringle domains and gla (glutammic acid) domains, in order to comply with the increasingly complex vertebrate systems and to defend higher organisms against a range of infections and injuries. Plasminogen activation also controls the formation of complement anaphylotoxins (responsibe for vasodilatation, increase of venular permeability and leukocyte chemotaxis) and of bradykinin (which accounts for vasodilatation, increase of venular permeability and pain) by regulating the plasma contact system. The urokinase plasminogen activator and its cellular receptor, expressed on the surface of human leukocytes, provide a functional unit that, by regulating interaction of leukocytes with extracellular matrix, as well as its degradation, is critical for the migration of leukocytes and for their movement in the damaged tissues.

Reduction of in vitro invasion and in vivo cartilage degradation in a SCID mouse model by loss of function of the fibrinolytic system of rheumatoid arthritis synovial fibroblasts

OBJECTIVE

Urokinase plasminogen activator (uPA), uPA receptor (uPAR), and PA inhibitor 1 (PAI-1) have pivotal roles in the proliferation and invasion of several cell types, including synovial fibroblasts (SFs). The aim of this study was to investigate the possibility of controlling the invasion of rheumatoid arthritis (RA) SFs in vitro and in vivo by inhibiting uPA and uPAR.

METHODS

Normal SFs, SFs from patients with RA, and SFs from patients with psoriatic arthritis (PsA) were used. The levels of uPA, uPAR, and PAI-1 were measured by enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction analysis of messenger RNA. The activity of uPA was studied by zymography. Proliferation was measured by cell counting, and cell invasion was measured with a Boyden chamber assembled with Matrigel-coated porous filters. Human cartilage and RA SF implantation in the SCID mouse model of RA were used to study cartilage invasion in vivo.

RESULTS

RA SFs and PsA SFs overexpressed uPAR and as a result were more active than their normal counterparts in terms of both Matrigel invasion and proliferation. This effect was counteracted by a specific inhibitor of uPA enzymatic activity (WX-340) and by uPAR antisense treatment. The use of both WX-340 and uPAR antisense treatment in vitro showed cooperative effects in RA SFs that were more intense than the effects of either treatment alone. Significant inhibition of cartilage invasion was obtained in vivo with uPAR antisense treatment, while uPA inhibition was inefficient, either alone or in combination with antisense treatment.

CONCLUSION

The decrease in uPAR expression in RA SFs reduced invasion of human cartilage in vitro and in the SCID mouse model.

Modulation of the angiogenic phenotype of normal and systemic sclerosis endothelial cells by gain-loss of function of pentraxin 3 and matrix metalloproteinase 12

OBJECTIVE

Studies have shown that in systemic sclerosis (SSc) endothelial cells, overproduction of matrix metalloproteinase 12 (MMP-12) and pentraxin 3 (PTX3) is associated with defective angiogenesis. This study was undertaken to examine whether overexpression of the relevant molecules could inhibit angiogenesis of normal microvascular endothelial cells (MVECs), and whether silencing of these molecules in SSc MVECs could restore the lost angiogenic properties of the cells in vitro and in vivo.

METHODS

Transient transfection of MVECs with human MMP12 and PTX3 was performed by electroporation. Silencing of MMP12 and PTX3 was obtained by treatment with small interfering RNA, and treatment effects were validated by Western blotting with specific antibodies and a fluorimetric assay. In vitro cell migration and capillary morphogenesis were studied on Matrigel substrates. In vivo angiogenesis was studied using a Matrigel sponge assay in mice.

RESULTS

Transfection of MMP12 and PTX3 in normal MVECs resulted in loss of proliferation, invasion, and capillary morphogenesis in vitro, attributed to truncation of the urokinase-type plasminogen activator receptor by MMP12 and to the anti-fibroblast growth factor 2/anti-vascular endothelial growth factor activity of PTX3. These effects were particularly evident in mixed populations of transfected normal MVECs (50% transfected with MMP12 and 50% with PTX3). Silencing of the same molecules in SSc MVECs increased their invasion in Matrigel. Single-gene silencing did not increase the capillary morphogenesis of SSc MVECs, whereas double-gene-silenced cells showed a burst of capillary tube formation. Culture medium of silenced SSc MVECs stimulated angiogenesis in assays of Matrigel sponge invasion in mice.

CONCLUSION

Overexpression of either MMP12 or PTX3 in normal MVECs blunts their angiogenic properties. Loss of function of MMP12 and PTX3 in SSc MVECs restores the ability of the cells to produce capillaries in vitro and induces vascularization in vivo on a Matrigel sponge.

Thymidylate synthase protein expression and activity are related to the cell proliferation rate in human cancer cell lines

AIMS

To ascertain whether the expression and enzyme activity of thymidylate synthase (TS) are related to the rapidity of cell proliferation in human cancer cell lines.

METHODS

Ten asynchronously growing human cancer cell lines of different origin were used, characterised by various doubling times. TS expression was evaluated by western blot analysis using the TS 106 monoclonal antibody. TS activity was determined by the enzyme catalytic assay. The quantitative variation of TS in different phases of the cell cycle was investigated using two parameter flow cytometry for the TS protein and DNA analysis. The number of proliferating cells was evaluated by Ki67 immunostaining.

RESULTS

TS expression and activity were significantly related to each other (r = 0.765; p = 0.01) and to the cell doubling time (r = -0.899; p < 0.001 and r = -0.919; p < 0.001, respectively). Ki67 immunolabelling showed no association between the number of cycling cells and TS protein expression and activity. Two parameter flow cytometry indicated that differences of TS expression in the cell lines were not related to the cell cycle phases or to the proportion of S phase cells.

CONCLUSIONS

These results show that the expression and activity of the TS protein in asynchronously growing cancer cells are significantly related to the cell doubling time; the faster the cell proliferation, the greater the expression and activity of TS. These findings could explain why TS values are of prognostic value per se and why tumours with high TS expression benefit more from chemotherapy.