Leyre Larzabal

Residual dormant cancer stem-cell foci are responsible for tumor relapse after antiangiogenic metronomic therapy in hepatocellular carcinoma xenografts

Hepatocellular carcinoma (HCC) is the fifth most common solid tumor and the third leading cause of cancer-related deaths. Currently available chemotherapeutic options are not curative due in part to tumor resistance to conventional therapies. We generated orthotopic HCC mouse models in immunodeficient NOD/SCID/IL2rγ null mice by injection of human alpha-feto protein (hAFP)- and/or luciferase-expressing HCC cell lines and primary cells from patients, where tumor growth and spread can be accurately monitored in a non-invasive way. In this model, low-dose metronomic administration of cyclophosphamide (LDM-CTX) caused complete regression of the tumor mass. A significant increase in survival (P<0.0001), reduced aberrant angiogenesis and hyperproliferation, and decrease in the number of circulating tumor cells were found in LDM-CTX-treated animals, in comparison with untreated mice. Co-administration of LDM-CTX with anti-VEGF therapy further improved the therapeutic efficacy. However, the presence of residual circulating hAFP levels suggested that some tumor cells were still present in livers of treated mice. Immunohistochemistry revealed that those cells had a hAFP+/CD13+/PCNA− phenotype, suggesting that they were dormant cancer stem cells (CSC). Indeed, discontinuation of therapy resulted in tumor regrowth. Moreover, in-vitro LDM-CTX treatment reduced hepatosphere formation in both number and size, and the resulting spheres were enriched in CD13+ cells indicating that these cells were particularly resistant to therapy. Co-treatment of the CD13-targeting drug, bestatin, with LDM-CTX leads to slower tumor growth and a decreased tumor volume. Therefore, combining a CD13 inhibitor, which targets the CSC-like population, with LDM-CTX chemotherapy may be used to eradicate minimal residual disease and improve the treatment of liver cancer.

PDGFR Signaling Blockade in Marrow Stroma Impairs Lung Cancer Bone Metastasis

Bone microenvironment and cell-cell interactions are crucial for the initiation and development of metastasis. By means of a pharmacologic approach, using the multitargeted tyrosine kinase inhibitor sunitinib, we tested the relevance of the platelet-derived growth factor receptor (PDGFR) axis in the bone marrow (BM) stromal compartment for the initiation and development of lung cancer metastasis to bone. PDGFRβ was found to be the main tyrosine kinase target of sunitinib expressed in BM stromal ST-2 and MC3T3-E1 preosteoblastic cells. In contrast, no expression of sunitinib-targeted receptors was found in A549M1 and low levels in H460M5 lung cancer metastatic cells. Incubation of ST-2 and human BM endothelial cells with sunitinib led to potent cell growth inhibition and induction of apoptosis in a dose-dependent manner. Similarly, sunitinib induced a robust proapoptotic effect in vivo on BM stromal PDGFRβ(+) cells and produced extensive disruption of tissue architecture and vessel leakage in the BM cavity. Pretreatment of ST-2 cells with sunitinib also hindered heterotypic adhesion to lung cancer cell lines. These effects were correlated with changes in cell-cell and cell-matrix molecules in both stromal and tumor cells. Pretreatment of mice with sunitinib before intracardiac inoculation of A549M1 or H460M5 cells caused marked inhibition of tumor cells homing to bone, whereas no effect was found when tumor cells were pretreated before inoculation. Treatment with sunitinib dramatically increased overall survival and prevented tumor colonization but not bone lesions, whereas combination with zoledronic acid resulted in marked reduction of osteolytic lesions and osseous tumor burden. Thus, disruption of the PDGFR axis in the BM stroma alters heterotypic tumor-stromal and tumor-matrix interactions, thereby preventing efficient engagement required for bone homing and osseous colonization. These results support the notion that concomitant targeting of the tumor and stromal compartment is a more effective approach for blocking bone metastasis.

Differential effects of drugs targeting cancer stem cell (CSC) and non-CSC populations on lung primary tumors and metastasis.

Cancer stem cells (CSCs) are thought to be responsible for tumor initiation and recurrence after chemotherapy. Targeting CSCs and non-CSCs with specific compounds may be an effective approach to reduce lung cancer growth and metastasis. The aim of this study was to investigate the effect of salinomycin, a selective inhibitor of CSCs, with or without combination with paclitaxel, in a metastatic model. To evaluate the effect of these drugs in metastasis and tumor microenvironment we took advantage of the immunocompetent and highly metastatic LLC mouse model. Aldefluor assays were used to analyze the ALDH+/− populations in murine LLC and human H460 and H1299 lung cancer cells. Salinomycin reduced the proportion of ALDH+ CSCs in LLC cells, whereas paclitaxel increased such population. The same effect was observed for the H460 and H1299 cell lines. Salinomycin reduced the tumorsphere formation capacity of LLC by more than 7-fold, but paclitaxel showed no effect. In in vivo experiments, paclitaxel reduced primary tumor volume but increased the number of metastatic nodules (p<0.05), whereas salinomycin had no effect on primary tumors but reduced lung metastasis (p<0.05). Combination of both drugs did not improve the effect of single therapies. ALDH1A1, SOX2, CXCR4 and SDF-1 mRNA levels were higher in metastatic lesions than in primary tumors, and were significantly elevated in both locations by paclitaxel treatment. On the contrary, such levels were reduced (or in some cases did not change) when mice were administered with salinomycin. The number of F4/80+ and CD11b+ cells was also reduced upon administration of both drugs, but particularly in metastasis. These results show that salinomycin targets ALDH+ lung CSCs, which has important therapeutic effects in vivo by reducing metastatic lesions. In contrast, paclitaxel (although reducing primary tumor growth) promotes the selection of ALDH+ cells that likely modify the lung microenvironment to foster metastasis.

VEGF121b and VEGF165b are weakly angiogenic isoforms of VEGF-A

BackgroundDifferent isoforms of VEGF-A (mainly VEGF121, VEGF165 and VEGF189) have been shown to display particular angiogenic properties in the generation of a functional tumor vasculature. Recently, a novel class of VEGF-A isoforms, designated as VEGFxxxb, generated through alternative splicing, have been described. Previous studies have suggested that these isoforms may inhibit angiogenesis. In the present work we have produced recombinant VEGF121/165b proteins in the yeast Pichia pastoris and constructed vectors to overexpress these isoforms and assess their angiogenic potential.ResultsRecombinant VEGF121/165b proteins generated either in yeasts or mammalian cells activated VEGFR2 and its downstream effector ERK1/2, although to a lesser extent than VEGF165. Furthermore, treatment of endothelial cells with VEGF121/165b increased cell proliferation compared to untreated cells, although such stimulation was lower than that induced by VEGF165. Moreover, in vivo angiogenesis assays confirmed angiogenesis stimulation by VEGF121/165b isoforms. A549 and PC-3 cells overexpressing VEGF121b or VEGF165b (or carrying the PCDNA3.1 empty vector, as control) and xenotransplanted into nude mice showed increased tumor volume and angiogenesis compared to controls. To assess whether the VEGFxxxb isoforms are differentially expressed in tumors compared to healthy tissues, immunohistochemical analysis was conducted on a breast cancer tissue microarray. A significant increase (p < 0.05) in both VEGFxxxb and total VEGF-A protein expression in infiltrating ductal carcinomas compared to normal breasts was observed. A positive significant correlation (r = 0.404, p = 0.033) between VEGFxxxb and total VEGF-A was found.ConclusionsOur results demonstrate that VEGF121/165b are not anti-angiogenic, but weakly angiogenic isoforms of VEGF-A. In addition, VEGFxxxb isoforms are up-regulated in breast cancer in comparison with non malignant breast tissues. These results are to be taken into account when considering a possible use of VEGF121/165b-based therapies in patients.

TMPRSS4 regulates levels of integrin α5 in NSCLC through miR-205 activity to promote metastasis.

Background:TMPRSS4 is a membrane-anchored protease involved in cell migration and invasion in different cancer types including lung cancer. TMPRSS4 expression is increased in NSCLC and its inhibition through shRNA reduces lung metastasis. However, molecular mechanisms leading to the protumorigenic regulation of TMPRSS4 in lung cancer are unknown.Methods:miR-205 was identified as an overexpressed gene upon TMPRSS4 downregulation through microarray analysis. Cell migration and invasion assays and in vivo lung primary tumour and metastasis models were used for functional analysis of miR-205 overexpression in H2170 and H441 cell lines. Luciferase assays were used to identify a new miR-205 direct target in NSCLC.Results:miR-205 overexpression promoted an epithelial phenotype with increased E-cadherin and reduced fibronectin. Furthermore, miR-205 expression caused a G0/G1 cell cycle arrest and inhibition of cell growth, migration, attachment to fibronectin, primary tumour growth and metastasis formation in vivo. Integrin α5 (a proinvasive protein) was identified as a new miR-205 direct target in NSCLC. Integrin α5 downregulation in lung cancer cells resulted in complete abrogation of cell migration, a decreased capacity to adhere to fibronectin and reduced in vivo tumour growth, compared with control cells. TMPRSS4 silencing resulted in a concomitant reduction of integrin α5 levels.Conclusion:We have demonstrated for the first time a new molecular pathway that connects TMPRSS4 and integrin α5 through miR-205 to regulate cancer cell invasion and metastasis. Our results will help designing new therapeutic strategies to inhibit this novel pathway in NSCLC.

Tumor--stromal interactions in lung cancer: novel candidate targets for therapeutic intervention

Introduction: Lung cancer is the leading cause of cancer deaths worldwide. Although standard treatment regimens have produced promising results with neoadjuvant and adjuvant strategies, outcomes for patients with lung cancer are still considered disappointing. Recent data provide evidence that the tumor-stromal environment is a leading player in carcinogenesis, not just a supporting tumor compartment. Areas covered: This article reviews the current understanding of the lung cancer microenvironment and the complex bidirectional interplay between the tumor and lung microenvironment in non-small cell lung cancer (NSCLC). In particular, this review emphasizes the role of fibroblasts, mesenchymal stem cells and myeloid cells as well as mediators and molecular pathways regulated by these cells within the tumor microenvironment (TME) that contribute to lung tumor initiation, progression and metastasis. In addition, this review also summarizes the therapeutic strategies currently being applied in preclinical and clinical trials. Expert opinion: Considering the recent advances in understanding lung tumor stroma, lung cancer progression could be effectively hampered by combining cytotoxic strategies with therapies that target the TME. However, more preclinical and clinical research is needed to prove the efficacy of this strategy for treating NSCLC.

Inactivation of encapsulated cells and their therapeutic effects by means of TGL triple-fusion reporter/biosafety gene.

The immobilization of cells within alginate-poly-l-lysine-alginate (APA) microcapsules has been demonstrated to be an effective technology design for long term delivery of therapeutic products. Despite promising advances, biosafety aspects still remain to be improved. Here, we describe a complete characterization of the strategy based on TGL triple-fusion reporter gene--which codifies for Herpes Simplex virus type 1 thymidine-kinase (HSV1-TK), green fluorescent protein (GFP) and Firefly Luciferase--(SFG(NES)TGL) to inactivate encapsulated cells and their therapeutic effects. Myoblasts genetically engineered to secrete erythropoietin (EPO) were retroviraly transduced with the SFG(NES)TGL plasmid to further characterize their ganciclovir (GCV)-mediated inactivation process. GCV sensitivity of encapsulated cells was 100-fold lower when compared to cells plated onto 2D surfaces. However, the number of cells per capsule and EPO secretion decayed to less than 15% at the same time that proliferation was arrested after 14 days of GCV treatment in vitro. In vivo, ten days of GCV treatment was enough to restore the increased hematocrit levels of mice implanted with encapsulated TGL-expressing and EPO-secreting cells. Altogether, these results show that TGL triple-fusion reporter gene may be a good starting point in the search of a suitable biosafety strategy to inactivate encapsulated cells and control their therapeutic effects.

Sphere-derived tumor cells exhibit impaired metastasis by a host-mediated quiescent phenotype

The spread of lung cancer cells to distant sites represents a common event associated with poor prognosis. A fraction of tumor cells named cancer stem cells (CSCs) have the ability to overcome therapeutic stress and remain quiescent. However, whether these CSCs have also the capacity to initiate and sustain metastasis remains unclear. Here, we used tumor sphere cultures (TSC) isolated from mouse and human lung cancer models to enrich for CSCs, and assessed their metastatic potential as compared to non-CSCs. As expected, TSC overexpressed a variety of stem cell markers and displayed chemoresistance. The CSC phenotype of TSC was confirmed by their higher growth ability in soft agar and tumorigenic potential in vivo, despite their reduced in vitro cell growth kinetics. Surprisingly, the appearance of spontaneous lung metastases was strongly delayed in mice injected with TSC as compared to non-TSC cells. Similarly, this finding was confirmed in several other models of metastasis, an effect associated with a retarded colonization activity. Interestingly, such delay correlated with a quiescent phenotype whose underlined mechanisms included an increase in p27 protein and lower phospho-ERK1/2 levels. Thus, these data suggest that cells enriched for CSC properties display an impaired metastatic activity, a finding with potential clinical implications.

Abstract 2304: Stem features associated with EMT are driven by TGFβ1 in liver-metastatic cells

The liver is a major target organ for metastasis. Development of metastases requires an early release of tumour-initiating-cells from the primary tumour and adhesion of metastatic-cells into a permissive niche. We hypothesized that Epithelial-Mesenchymal Transition (EMT) underlies not only the early events, but also the promotion of the most advanced stages of a successful dissemination process to the liver. It is believed that TGFβ1 might allow tumour-initiating-cells to acquire cancer stem cell properties via EMT as a mechanism that modulates the microenvironment contributing to primary and also metastatic tumor progression. However, the mechanism of EMT induction by TGFβ1 and its involvement in liver metastases remain largely unknown. Aiming to recapitulate the hepatic metastases, we established a murine model of highly metastatic colon carcinoma cells in the context of TGFβ1-signaling. To this end, luciferase-expressing cells (MC-38luc) were pre-treated with TGFβ1 (100 pM, 48 h), before intrasplenic injection of 106 cells in C57BL/6J mice. Larger primary tumours were consistently observed and liver metastasis was achieved more rapidly after injection of MC-38luc+TGFβ1 cells, than after injection of untreated MC-38luc cells. Histological examination of liver micrometastasis also revealed slightly increased staining of Ki67, α-SMA and F4/80 markers in MC-38luc+TGFβ1 tumours. Splenic co-injection of these liver-metastatic-stem cells with non transformed hepatocytes (AML-12 cells) accelerated the incidence of liver metastasis, indicating the supportive role of the normal hepatic parenchyma. Intraperitoneal injection with a novel TGFβ1-inhibitory peptide P17 (obtained from a peptide library binding to TGFβ1) resulted in reduced liver metastasis and decrease of both CECs and CEPs. We isolated liver-metastatic cells that showed higher cellular proliferation as compared to the parental counterparts. These cells posses increased tumorogenicity in vivo, a complete lack of E-cadherin expression, and increased TGFβ1/EMT signalling properties that all relate to stem cell features. Our results provide an insight into the molecular events leading to TGFβ1-mediated malignant progression and indicate that targeting TGFβ1/EMT might represent an optimal therapeutic strategy by impairing tumor growth, stemness and further liver metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2304.

Abstract 289: VEGFR/PDGFR blockade impairs tumor-stroma interactions through multiple mechanisms that inhibit bone metastatic homing

Bone microenvironment and tumor-stromal interactions are critical for the initiation and development of metastasis. The aim of this study was to delineate the role of VEGFR/PDGFR axes in bone metastatic homing and colonization using a multi-tyrosine kinase inhibitor (SU11248). SU blocks 7 different receptors, including VEGFRs and PDGFRs, resulting in the blockade of many biological functions. Here we show that SU blocks lung cancer metastasis to the bone through different mechanisms. Incubation of bone metastatic lung A549M1 cells with SU in vitro had no effect on cell proliferation whereas a potent effect on bone marrow (BM) stromal ST2 cells, and BM-derived endothelial cells (BMEC) was seen. The inhibitory effects of SU over ST2 cells were mediated through PDGFRbeta, which was highly expressed by ST2 cells. Direct heterotypic adhesion of tumor cells to a ST2 monolayer was significantly decreased by SU, whereas no effects were found in BMEC or HUVEC monolayers. SU markedly impaired invasion in vitro. Furthermore, SU inhibited the adhesion of A549M1 cells to collagen I. To evaluate these effects in an in vivo model of bone homing, we pretreated mice with SU two days before intracardiac (i.c.) inoculation of luciferase expressing A549M1 cells. Dramatic inhibition of bioluminescence was observed in SU treated mice 4 days post-inoculation. Quantification of A549M1 colony forming units after BM flushing revealed identical results suggesting an effect of SU in bone homing. To test SU effects in bone metastasis colonization, we used SU alone or in combination with the zoledronic acid (ZA) daily, starting from 6 days after i.c. of A549 M1 cells. As expected, ZA treatment slightly increased survival, whereas SU or combination led to a double lifespan. Bioluminescence imaging showed a moderate decrease in skeletal tumor burden in single ZA and SU treated mice, whereas marked reduction in osteolytic lesions assessed by X-Ray imaging and microCT scans was only evident in ZA treated mice. However, combination abrogated tumor burden and severely prevented the development of osteolytic lesions as compared to SU treated mice, which correlated with the number of TRAP positive cells at tumor-bone interphase. Treatment of tumor-free mice with SU revealed a potent proapoptotic effect on BM stromal PDGFRbeta+ compartment, as seen by extensive active Caspase-3 immunoreactiviy 24h after treatment. This effect over stroma leads to severe haemorrhage after 4 days of treatment, indicating a severe disruption of the BM microenvironment by SU. These data suggest that disruption of VEGFR/PDGFR axes alters heterotypic tumor-stromal cell and tumor-matrix interactions during bone homing preventing osseous colonization. We suggest that SU in combination with ZA could be suitable for the treatment of osteolytic bone metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 289.