Microenvironmental stromal cells abrogate NF-κB inhibitor-induced apoptosis in chronic lymphocytic leukemia.

Nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) is known to play an important role in the pathogenesis of chronic lymphocytic leukemia (CLL). Several NF-κB inhibitors were shown to successfully induce apoptosis of CLL cells in vitro Since the microenvironment is known to be crucial for the survival of CLL cells, herein, we tested whether NF-κB inhibition may still induce apoptosis in these leukemic cells in the presence of protective stromal interaction. We used the specific NF-κB inhibitor dehydroxymethylepoxyquinomicin (DHMEQ). Microenvironmental support was mimicked by co-culturing CLL cells with bone marrow-derived stromal cell lines (HS-5 and M2-10B4). NF-κB inhibition by DHMEQ in CLL cells could be confirmed in both the monoculture and co-culture setting. In line with previous reports, NF-κB inhibition induced apoptosis in the monoculture setting by activating the intrinsic apoptotic pathway resulting in poly (ADP-ribose) polymerase (PARP)-cleavage; however, it was unable to induce apoptosis in leukemic cells co-cultured with stromal cells. Similarly, small interfering ribonucleic acid (siRNA)-mediated RELA downregulation induced apoptosis of CLL cells cultured alone, but not in the presence of supportive stromal cells. B-cell activating factor (BAFF) was identified as a microenvironmental messenger potentially protecting the leukemic cells from NF-κB inhibition-induced apoptosis. Finally, we show improved sensitivity of stroma-supported CLL cells to NF-κB inhibition when combining the NF-κB inhibitor with the SYK inhibitor R406 or the Bruton's tyrosine kinase (BTK) inhibitor ibrutinib, agents known to inhibit the stroma-leukemia crosstalk. We conclude that NF-κB inhibitors are not promising as monotherapies in CLL, but may represent attractive therapeutic partners for ibrutinib and R406.

BCR and chemokine responses upon anti-IgM and anti-IgD stimulation in chronic lymphocytic leukaemia.

Dysregulation of B cell receptor (BCR) signalling is a hallmark of chronic lymphocytic leukaemia (CLL) pathology, and targeting BCR pathway kinases has brought great therapeutic advances. Activation of the BCR in lymphoid organs has been associated with CLL cell proliferation and survival, leading to progressive disease. While these responses are mediated predominantly by IgM, the role of IgD is less clear. Seeking to uncover downstream consequences of individual and combined stimulation of the two BCR isotypes, we found an amplification of IgD expression and IgD-mediated calcium signalling by previous stimulation of IgM in CLL. Furthermore, no heterologous downmodulation of the isotypes, as observed in healthy donors, was present. Only marginal downregulation of the expression of various chemokine receptors by α-IgM and α-IgD stimulation was found as compared to normal B cells. Consistently, calcium responses of CLL cells to different chemokines were only weakly affected by preceding BCR activation. In contrast, migration towards the two homeostatic chemokines CXCL12 and CCL21 was differentially regulated by IgM and IgD. While IgM activation reduced migration of CLL cells towards CXCL12, but not CCL21, IgD activation predominantly impacted on CCL21 but not CXCL12-mediated chemotaxis. This indicates that the preference for one chemokine over the other may depend on the functional presence of the two isotypes in CLL. Inhibitors against the kinases Syk, Lyn, and Btk antagonised both BCR- and chemokine-induced calcium signals.

A feeder-free differentiation system identifies autonomously proliferating B cell precursors in human bone marrow.

The peripheral B cell compartment is maintained by homeostatic proliferation and through replenishment by bone marrow precursors. Because hematopoietic stem cells cycle at a slow rate, replenishment must involve replication of precursor B cells. To study proliferation of early human B cell progenitors, we established a feeder cell-free in vitro system allowing the development of B cells from CD34(+) hematopoietic stem cells up to the stage of immature IgM(+) B cells. We found that pro-B and pre-B cells generated in vitro can proliferate autonomously and persist up to 7 wk in culture in the absence of signals induced by exogenously added cytokines. Nevertheless, addition of IL-7 enhanced pre-B cell expansion and inhibited maturation into IgM(+) B cells. The B cell precursor subsets replicating in vitro were highly similar to the bone marrow B cell precursors cycling in vivo. The autonomous proliferation of B cell precursor subsets in vitro and their long-term persistence implies that proliferation during pro-B and pre-B cell stages plays an important role in the homeostasis of the peripheral B cell compartment. Our in vitro culture can be used to study defects in B cell development or in reconstitution of the B cell pool after depletion and chemotherapy.

Insulin-like growth factor-1 receptor (IGF1R) as a novel target in chronic lymphocytic leukemia.

The receptor tyrosine kinase (RTK) insulin-like growth factor-1 receptor (IGF1R) is implicated in various tumor entities including chronic lymphocytic leukemia (CLL), but its functional significance in this disease remains poorly characterized. Here, we show that the IGF1R protein is overexpressed in various CLL subsets, suggesting a contribution to CLL pathology. Indeed, we show that IGF1R knockdown in primary human CLL cells compromised their viability. Likewise, IGF1R inhibition with 3 structurally distinct compounds induced apoptosis, even in the presence of protective stroma components. Furthermore, IGF1R inhibition effectively limited CLL development in Eµ-TCL1 transgenic mice and of primary human CLL xenografts. In agreement with its prosurvival function, IGF1R inhibition affected the phosphorylation and/or expression of multiple signaling proteins. The multikinase inhibitor sorafenib yielded similar effects on these signaling elements as IGF1R inhibitors. Indeed, IGF1R appears to be a direct sorafenib target because sorafenib decreased IGF1R expression and phosphorylation, counteracted insulin-like growth factor-1 (IGF-1) binding to CLL cells, and lowered the in vitro kinase activity of recombinant, purified IGF1R. Thus, we demonstrate that blockade of IGF1R-mediated signaling represents a novel mechanism of action for sorafenib in CLL. Importantly, IGF1R inhibitors compromise CLL viability in their microenvironment context, implicating this RTK as a promising therapeutic target.

Sphingosine-1-phosphate receptors control B-cell migration through signaling components associated with primary immunodeficiencies, chronic lymphocytic leukemia, and multiple sclerosis.

BACKGROUND: Five different G protein-coupled sphingosine-1-phosphate (S1P) receptors (S1P1-S1P5) regulate a variety of physiologic and pathophysiologic processes, including lymphocyte circulation, multiple sclerosis (MS), and cancer. Although B-lymphocyte circulation plays an important role in these processes and is essential for normal immune responses, little is known about S1P receptors in human B cells. OBJECTIVE: To explore their function and signaling, we studied B-cell lines and primary B cells from control subjects, patients with leukemia, patients with S1P receptor inhibitor-treated MS, and patients with primary immunodeficiencies. METHODS: S1P receptor expression was analyzed by using multicolor immunofluorescence microscopy and quantitative PCR. Transwell assays were used to study cell migration. S1P receptor internalization was visualized by means of time-lapse imaging with fluorescent S1P receptor fusion proteins expressed by using lentiviral gene transfer. B-lymphocyte subsets were characterized by means of flow cytometry and immunofluorescence microscopy. RESULTS: Showing that different B-cell populations express different combinations of S1P receptors, we found that S1P1 promotes migration, whereas S1P4 modulates and S1P2 inhibits S1P1 signals. Expression of CD69 in activated B lymphocytes and B cells from patients with chronic lymphocytic leukemia inhibited S1P-induced migration. Studying B-cell lines, normal B lymphocytes, and B cells from patients with primary immunodeficiencies, we identified Bruton tyrosine kinase, ß-arrestin 2, LPS-responsive beige-like anchor protein, dedicator of cytokinesis 8, and Wiskott-Aldrich syndrome protein as critical signaling components downstream of S1P1. CONCLUSION: Thus S1P receptor signaling regulates human B-cell circulation and might be a factor contributing to the pathology of MS, chronic lymphocytic leukemia, and primary immunodeficiencies.

Toxin-induced RhoA activity mediates CCL1-triggered signal transducers and activators of transcription protein signaling.

RhoA is reportedly involved in signal transducers and activators of transcription (STAT)-dependent transcription. However, the pathway connecting the GTPase and STAT signaling has not been characterized. Here, we made use of bacterial toxins, which directly activate Rho GTPases to analyze this pathway. Cytotoxic necrotizing factors (CNFs) are produced by pathogenic Escherichia coli strains and by Yersinia pseudotuberculosis. They activate small GTPases of the Rho family by deamidation of a glutamine, which is crucial for GTP hydrolysis. We show that RhoA activation leads to phosphorylation and activation of STAT3 and identify signal proteins involved in this pathway. RhoA-dependent STAT3 stimulation requires ROCK and Jun kinase activation as well as AP1-induced protein synthesis. The secretion of one or more factors activates the JAK-STAT pathway in an auto/paracrine manner. We identify CCL1/I-309 as an essential cytokine, which is produced and secreted upon RhoA activation and which is able to activate STAT3-dependent signaling pathways.

Spleen tyrosine kinase inhibition prevents chemokine- and integrin-mediated stromal protective effects in chronic lymphocytic leukemia.

The microenvironment provides essential growth and survival signals to chronic lymphocytic leukemia (CLL) cells and contributes to their resistance to cytotoxic agents. Pharmacologic inhibition of spleen tyrosine kinase (SYK), a key mediator of B-cell receptor (BCR) signaling, induces apoptosis in primary CLL cells and prevents stroma contact-mediated cell survival. This report demonstrates a role of SYK in molecularly defined pathways that mediate the CLL-microenvironmental crosstalk independent from the BCR. Chemokine and integrin stimulation induced SYK phosphorylation, SYK-dependent Akt phosphorylation, and F-actin formation in primary CLL cells. Inhibition of SYK by 2 pharmacologic inhibitors and siRNA-knockdown abrogated downstream SYK signaling and morphologic changes induced by these stimuli. CLL cell migration toward CXCL12, the major homing attractor, and CLL cell adhesion to VCAM-1, a major integrin ligand expressed on stromal cells, were markedly reduced by SYK inhibition. In combination with fludarabine, the SYK inhibitor R406 abrogated stroma-mediated drug resistance by preventing up-regulation of the antiapoptotic factor Mcl-1 in CLL cells. SYK blockade in CLL is a promising therapeutic principle not only for its inhibition of the BCR signaling pathway, but also by inhibiting protective stroma signals in a manner entirely independent of BCR signaling.

Retraction notice to "Enhanced AC133-specific CAR T cell therapy induces durable remissions in mice with metastatic small cell lung cancer" [Canc. Lett. 520 (2021) 385-399].

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. Following the publication of the above article, the Editor was notified that an error occurred in which all images were published with incorrect versions. The Editor has taken the decision that the manuscript is no longer acceptable in its current form, nor with a corrigendum, as the extensive changes to the figures and publication would lead to ambiguity for our readers. We have therefore made the decision to retract this manuscript from Cancer Letters with the possibility of resubmission and republication of the manuscript in its corrected form after peer review.

Enhanced AC133-specific CAR T cell therapy induces durable remissions in mice with metastatic small cell lung cancer.

Metastatic small cell lung cancer (SCLC) is not curable. While SCLC is initially sensitive to chemotherapy, remissions are short-lived. The relapse is induced by chemotherapy-selected tumor stem cells, which express the AC133 epitope of the CD133 stem cell marker. We studied the effectiveness of AC133-specific CAR T cells post-chemotherapy using human primary SCLC and an orthotopic xenograft mouse model. AC133-specific CAR T cells migrated to SCLC tumor lesions, reduced the tumor burden, and prolonged survival in a humanized orthotopic SCLC model, but were not able to entirely eliminate tumors. We identified CD73 and PD-L1 as immune-escape mechanisms and combined PD-1-inhibition and CD73-inhibition with CAR T cell treatment. This triple-immunotherapy induced cures in 25% of the mice, without signs of graft-versus-host disease or bone marrow failure. AC133+ cancer stem cells and PD-L1+CD73+ myeloid cells were detectable in primary human SCLC tissues, suggesting that patients may benefit from the triple-immunotherapy. We conclude that the combination of AC133-specific CAR T cells, anti-PD-1-antibody and CD73-inhibitor specifically eliminates chemo-resistant tumor stem cells, overcomes SCLC-mediated T cell inhibition, and might induce long-term complete remission in an otherwise incurable disease.

RETRACTED: Enhanced AC133-specific CAR T cell therapy induces durable remissions in mice with metastatic small cell lung cancer.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal). This article has been retracted at the request of the Editor-in-Chief. Following the publication of the above article, the Editor was notified that an error occurred in which all images were published with incorrect versions. The Editor has taken the decision that the manuscript is no longer acceptable in its current form, nor with a corrigendum, as the extensive changes to the figures and publication would lead to ambiguity for our readers. We have therefore made the decision to retract this manuscript from Cancer Letters with the possibility of resubmission and republication of the manuscript in its corrected form after peer review.

CCL19 is a specific ligand of the constitutively recycling atypical human chemokine receptor CRAM-B.

The human chemokine receptor CRAM (chemokine receptor on activated macrophages), encoded by the gene CCRL2, is a new candidate for the atypical chemokine receptor family that includes the receptors DARC, D6 and chemocentryx chemokine receptor (CCX-CKR). CRAM is maturation-stage-dependently expressed on human B lymphocytes and its surface expression is up-regulated upon short-term CCL5 exposure. Here, we demonstrate that the homeostatic chemokine CCL19 is a specific ligand for CRAM. In radioactive labelling studies CCL19 bound to CRAM-expressing cells with an affinity similar to the described binding of its other receptor CCR7. In contrast to the known CCL19/CCR7 ligand/receptor pair, CRAM stimulation by CCL19 did not result in typical chemokine-receptor-dependent cellular activation like calcium mobilization or migration. Instead, we demonstrate that CRAM is constitutively recycling via clathrin-coated pits and able to internalize CCL19 as well as anti-CRAM antibodies. As this absence of classical chemokine receptor responses and the recycling and internalization features are characteristic for non-classical chemokine receptors, we suggest that CRAM is the newest member of this group. As CCL19 is known to be critically involved in lymphocyte and dendritic cell trafficking, CCL19-binding competition by CRAM might be involved in modulating these processes.

Role of the atypical chemoattractant receptor CRAM in regulating CCL19 induced CCR7 responses in B-cell chronic lymphocytic leukemia.

BACKGROUND: The non-signalling chemokine receptors, including receptors DARC, D6 and CCX-CKR, have recently been shown to be involved in chemokine clearance and activity regulation. The human chemokine receptor CRAM (also known as HCR or CCRL2) is the most recently identified member of this atypical group. CRAM is expressed on B cells in a maturation-stage dependent manner and absent on T cells. We have recently shown that it competitively binds CCL19. CCL19 and its signalling receptor CCR7 are critical components involved in cell recruitment to secondary lymphoid organs and in maturation. B cell Chronic Lymphocytic Leukemia (B-CLL) is a low-grade lymphoma characterized by proliferative centres (or pseudofollicles). Proliferative centres develop due to abnormal cellular localisation and they are involved in the development of malignant cells. CCR7 is highly expressed on B cells from CLL patients and mediates migration towards its ligands CCL19 and CCL21, while CRAM expression and potential interferences with CCR7 are yet to be characterized. RESULTS: In this study, we show that B cells from patients with B-CLL present highly variable degrees of CRAM expression in contrast to more consistently high levels of CCR7. We investigated the hypothesis that, similar to the atypical receptor DARC, CRAM can modulate chemokine availability and/or efficacy, resulting in the regulation of cellular activation. We found that a high level of CRAM expression was detrimental to efficient chemotaxis with CCL19. MAP-kinase phosphorylation and intracellular calcium release induced by CCL19 were also altered by CRAM expression. In addition, we demonstrate that CRAM-induced regulation of CCL19 signalling is maintained over time. CONCLUSIONS: We postulate that CRAM is a factor involved in the fine tuning/control of CCR7/CCL19 mediated responses. This regulation could be critical to the pivotal role of CCL19 induced formation of proliferation centres supporting the T/B cells encounter as well as disease progression in B-CLL.

The microenvironment differentially impairs passive and active immunotherapy in chronic lymphocytic leukaemia - CXCR4 antagonists as potential adjuvants for monoclonal antibodies.

Direct contact with stromal cells protects chronic lymphocytic leukaemia (CLL) B cells from chemotherapy-induced apoptosis in vitro. Blockade of CXCR4 signalling antagonizes stroma-mediated interactions and restores CLL chemosensitivity. In vivo, administration of CXCR4 antagonists effectively mobilizes haematopoietic progenitor cells. Therefore, combinations of CXCR4 blockade and cytoreductive treatment with selective activity on CLL cells may avoid potential haematotoxicity. Hence, we tested CXCR4 antagonists in the context of passive and active immunotherapeutic approaches. We evaluated how efficiently rituximab, alemtuzumab and cytotoxic T cells killed CLL cells cocultured with stromal cells in the presence and absence of a CXCR4 antagonist. Stromal cell contact attenuated rituximab- and alemtuzumab-induced complement-dependent cytotoxicity of CLL cells. Addition of CXCR4 antagonists abrogated the protective effect of stroma. In contrast, stromal cells did not impair antibody-dependent cell-mediated cytotoxicity and cytotoxicity induced by activated T cells. Destruction of microtubules in CLL target cells restored the protective effect of stroma coculture for CLL cells during Natural Killer cell attack by preventing mitochondrial relocalization towards the immunological synapse. Our data identify the combination of CXCR4 antagonists with passive - but not active - immunotherapy as a promising potential treatment concept in CLL.

The role of chemokines in B cell chronic lymphocytic leukaemia: pathophysiological aspects and clinical impact.

Chemokines are centrally involved in leukocyte migration, homing and haematopoiesis. Besides these physiological aspects, their role in pathological processes especially with respect to solid tumour and haematological neoplasias is well established. In this context, the focus was set here on disclosing their contribution in B cell chronic lymphocytic leukaemia (B-CLL), which is regarded as the most characteristic low-grade lymphoma. Up to now, it has been demonstrated that several chemokines are involved in migration of B-CLL cells to lymph nodes, secondary lymphoid organs and bone marrow. Moreover, some chemokines are known to have an anti-apoptotic effect and thus contribute to the survival of B-CLL cells. By interfering with both of these aspects, new therapeutic targets for this yet incurable disease may be developed. Furthermore, a correlation can be drawn between the concentration of some chemokines in patients' serum, the expression of their respective receptors on B-CLL cells and well-established predictive clinical parameters. Consequently, further systematic investigation of the chemokine network may lead to the identification of new diagnostic and prognostic markers. This review focuses on the impact of chemokines and their receptors on B-CLL pathophysiology and points out potential implications for both treatment and diagnosis.

Human B cells express the orphan chemokine receptor CRAM-A/B in a maturation-stage-dependent and CCL5-modulated manner.

Chemokines orchestrate the organization of leucocyte recruitment during inflammation and homeostasis. Despite growing knowledge of chemokine receptors, some orphan chemokine receptors are still not characterized. The gene CCRL2 encodes such a receptor that exists in two splice variants, CRAM-A and CRAM-B. Here, we report that CRAM is expressed by human peripheral blood and bone marrow B cells, and by different B-cell lines dependent on the B-cell maturation stage. Intriguingly, CRAM surface expression on the pre-B-cell lines Nalm6 and G2 is specifically upregulated in response to the inflammatory chemokine CCL5 (RANTES), a chemokine that is well known to play an important role in modulating immune responses. Although Nalm6 cells do not express any of the known CCL5 binding receptors, extracellular signal-regulated kinases 1 and 2 (ERK1/2) are phosphorylated upon CCL5 stimulation, suggesting a direct effect of CCL5 through the CRAM receptor. However, no calcium mobilization or migratory responses upon CCL5 stimulation are induced in B-cell lines or in transfected cells. Also, ERK1/2 phosphorylation cannot be inhibited by pertussis toxin, suggesting that CRAM does not couple to Gi proteins. Our results describe the expression of a novel, non-classical chemokine receptor on B cells that is potentially involved in immunomodulatory functions together with CCL5.

Proteasome inhibitor bortezomib enhances the effect of standard chemotherapy in small cell lung cancer.

Small cell lung cancer (SCLC) is an aggressive cancer showing a very poor prognosis because of metastasis formation at an early stage and acquisition of chemoresistance. One key driver of chemoresistance is the transcription factor Forkhead box protein M1 (FOXM1) that regulates cell cycle proliferation, maintenance of genomic stability, DNA damage response, and cell differentiation in numerous tumor entities. In this study we investigated the role of FOXM1 in SCLC progression and analyzed the effect of FOXM1 inhibition using two proteasome inhibitors, bortezomib and siomycin A. FOXM1 was strongly expressed in patient-derived SCLC samples (n=123) and its nuclear localization was associated with the proliferation marker Ki-67. Both proteasome inhibitors successfully inhibited FOXM1 expression leading to a significantly reduced proliferation and a decreased mitotic rate along with cell cycle arrest and apoptosis induction. These effects were further enhanced by addition of bortezomib to standard chemotherapy. Treatment of mice bearing chemoresistant SCLC xenografts with bortezomib reduced the mean bioluminescence signal of tumors by 54%. Similarly, treatment with cisplatin as a standard chemotherapy reduced the mean bioluminescence signal of tumors by 58%. However, in combination with standard chemotherapy bortezomib further reduced the mean bioluminescence signal by 93% (p=0.0258). In conclusion, we demonstrate the effect of bortezomib in inhibiting FOXM1 expression and thus in sensitizing resistant SCLC cells to standard chemotherapy. Thus, addition of bortezomib to standard chemotherapy might potently improve SCLC therapy, particularly in an extensive cancer stage.

KSHV-GPCR and CXCR2 transforming capacity and angiogenic responses are mediated through a JAK2-STAT3-dependent pathway.

The Kaposi's sarcoma herpesvirus encodes a G-protein-coupled chemokine receptor termed KSHV-GPCR. Expression of this constitutively active GPCR leads to cell transformation and vascular overgrowth characteristic of Kaposi's sarcoma. Previously, we have shown that CXCR2, the closest human homolog, is similarly able to transform cells if continuously stimulated or constitutively activated by amino-acid exchange D138V of the DRY sequence. Here, we demonstrate that STAT3 activation is a prerequisite for transformation in KSHV-GPCR and CXCR2 transfected NIH 3T3 cells. In KSHV-GPCR and D138V transfected cells, STAT-3 is constitutively phosphorylated on Tyr705. In CXCR2 transfected NIH 3T3 cells and human microvascular endothelial cells (HMEC), which express the CXCR2 constitutively, STAT3 is phosphorylated upon stimulation with IL-8 (CXCL8). Focus formation in NIH 3T3 cells transfected with the KSHV-GPCR, CXCR2, or the D138V mutant, was blocked by the specific JAK2 inhibitor AG490. Typical functions of the CXCR2 including actin stress fiber formation, haptotaxis, and the angiogenic response in HMEC shown by tube formation in Matrigel were blocked by AG490. These data suggest that the transforming capacity and migratory responses that are involved in tumor development, metastasis, and angiogenesis in KSHV or CXCR2-expressing cells is at least partially mediated through a JAK2-STAT3 dependent pathway.

CXCR4 chemokine receptor and integrin signaling co-operate in mediating adhesion and chemoresistance in small cell lung cancer (SCLC) cells.

Small cell lung cancer (SCLC) is an aggressive, rapidly metastazising neoplasm with a high propensity for marrow involvement. SCLC cells express high levels of functional CXCR4 receptors for the chemokine stromal-cell-derived factor-1 (SDF-1/CXCL12). Adhesion of SCLC cells to extracellular matrix or accessory cells within the tumor microenvironment confers resistance to chemotherapy via integrin signaling and thus may be responsible for residual disease and relapses commonly seen in SCLC. We examined the signaling mechanisms that regulate CXCL12-induced adhesion of SCLC cells to fibronectin, collagen, and stromal cells and the effects on SCLC cell chemoresistance. We found that CXCL12-induced integrin activation which resulted in an increased adhesion of SCLC cells to fibronectin and collagen. This was mediated by alpha2, alpha4, alpha5, and beta1 integrins along with CXCR4 activation, which could be inhibited by CXCR4 antagonists. Stromal cells protected SCLC cells from chemotherapy-induced apoptosis, and this protection could also be antagonized by CXCR4 inhibitors. We conclude that activation of integrins and CXCR4 chemokine receptors co-operate in mediating adhesion and survival signals from the tumor microenvironment to SCLC cells. Therefore, CXCR4 antagonists in combination with cytotoxic drugs should be explored in SCLC to overcome CXCL12-mediated adhesion and survival signals in the tumor microenvironment.

An orthotopic mouse model of small cell lung cancer reflects the clinical course in patients.

Small cell lung cancer (SCLC) is a highly aggressive subtype of lung cancer with very poor prognosis due to early metastatic spread and development of chemoresistance. In the last 30 years the study of SCLC has been constrained by a lack of primary human tumor specimen thus highlighting the need of a suitable mouse model. In this article we present the establishment of an orthotopic xenograft mouse model which accurately reproduced the clinical course of SCLC. Orthotopic implantation enabled engraftment of primary lung tumors in all injected mice. Furthermore, immunodeficiency of mice allowed formation of spontaneous metastases in characteristic organs. Bioluminescence Imaging, Magnetic Resonance Imaging and Positron emission tomography were applied to monitor engraftment, metabolism and the exact growth of tumors over time. In order to mimic the extensive disease stage, mice were injected with aggressive human chemoresistant cells leading to development of chemoresistant tumors and early metastatic spread. As a proof of concept treatment of tumor-bearing mice with conventional chemotherapeutics reduced tumor volumes, but a complete regression of tumors was not achieved. By mimicking the extensive disease stage our mouse model can facilitate the study of mechanisms contributing to chemoresistance and metastasis formation, as well as drug screening and evaluation of new treatment strategies for SCLC patients.

CXCR4 antagonists suppress small cell lung cancer progression.

Small cell lung cancer (SCLC) is an aggressive tumor with poor prognosis due to early metastatic spread and development of chemoresistance. Playing a key role in tumor-stroma interactions the CXCL12-CXCR4 axis may be involved in both processes and thus represent a promising therapeutic target in SCLC treatment. In this study we investigated the effect of CXCR4 inhibition on metastasis formation and chemoresistance using an orthotopic xenograft mouse model. This model demonstrates regional spread and spontaneous distant metastases closely reflecting the clinical situation in extensive SCLC. Tumor engraftment, growth, metabolism, and metastatic spread were monitored using different imaging techniques: Magnetic Resonance Imaging (MRI), Bioluminescence Imaging (BLI) and Positron Emission Tomography (PET). Treatment of mice bearing chemoresistant primary tumors with the specific CXCR4 inhibitor AMD3100 reduced the growth of the primary tumor by 61% (P<0.05) and additionally suppressed metastasis formation by 43%. In comparison to CXCR4 inhibition as a monotherapy, standard chemotherapy composed of cisplatin and etoposide reduced the growth of the primary tumor by 71% (P<0.01) but completely failed to suppress metastasis formation. Combination of chemotherapy and the CXCR4 inhibitor integrated the highest of both effects. The growth of the primary tumor was reduced to a similar extent as with chemotherapy alone and metastasis formation was reduced to a similar extent as with CXCR4 inhibitor alone. In conclusion, we demonstrate in this orthotopic mouse model that the addition of a CXCR4 inhibitor to chemotherapy significantly reduces metastasis formation. Thus, it might improve the overall therapy response and consequently the outcome of SCLC patients.