Functional expression of CXCR4 (CD184) on small-cell lung cancer cells mediates migration, integrin activation, and adhesion to stromal cells

Design of a New 99mTc-radiolabeled Cyclo-peptide as Promising Molecular Imaging Agent of CXCR4 Receptor: Molecular Docking, Synthesis, Radiolabeling, and Biological Evaluation

INTRODUCTION

C-X-C Chemokine receptor type 4 (CXCR4) is often overexpressed or overactivated in different types and stages of cancer disease. Therefore, it is considered a promising target for imaging and early detection of primary tumors and metastasis. In the present research, a new cyclo-peptide radiolabelled with 99mTc, 99mTc-Cyclo [D-Phe-D-Tyr-Lys (HYNIC)- D-Arg-2-Nal-Gly-Lys(iPr)], was designed based on the parental LY251029 peptide, as a potential in vivo imaging agent of CXCR4-expressing tumors.

METHODS

The radioligand was successfully prepared using the method of Fmoc solid-phase peptide synthesis and was evaluated in biological assessment. Molecular docking findings revealed high affinity (binding energy of -9.7 kcal/mol) and effective interaction of Cyclo [D-Phe- D-Tyr-Lys (HYNIC)-D-Arg-2-Nal-Gly-Lys(iPr)] in the binding pocket of CXCR4 receptor (PDB code: 3OE0) as well.

RESULT

The synthesized peptide and its purity were assessed by both reversed-phase high-performance liquid chromatography (RP-HPLC) and mass spectroscopy. High stability (95%, n = 3) in human serum and favorable affinity (Kd = 28.70 ± 13.56 nM and Bmax = 1.896 ± 0.123 fmol/mg protein) in the B16-F10 cell line resulted. Biodistribution evaluation findings and planar image interpretation of mice both showed high affinity and selectivity of the radiotracer to the CXCR4 receptors.

CONCLUSION

Therefore, the findings indicate this designed radioligand could be used as a potential SPECT imaging agent in highly proliferated CXCR4 receptor tumors.

Chemokine Receptor CXCR4 Radioligand Targeted Therapy Using 177Lutetium-pentixather for Pulmonary Neuroendocrine Cancers

Intermediate to high-grade lung neuroendocrine tumors (NETs; i.e., atypical carcinoid tumors) and neuroendocrine carcinomas (NECs) are currently difficult to cure. These tumors were found to express the CXCR4 G-protein coupled receptor that can be targeted with radioligands. PCR and flow cytometric analysis of lung NET and NEC cell lines using an anti-CXCR4 antibody demonstrated that all cell lines tested expressed CXCR4. PET/CT imaging with 68Galium-pentixafor in mouse xenografts of NETs and NECs verified tumor targeting that was blocked by a CXCR4 agonist. Clonogenic survival analysis demonstrated a more than additive enhancement of killing when 1 μM auranofin (a thioredoxin reductase inhibitor) was used as a radiosensitizer in combination with 177Lu-pentixather (10 μCi). DMS273 small cell lung cancer xenografts in female nude mice treated with 25 μCi/g 177Lu-pentixather induced inhibition of tumor growth and resulted in an increase in overall survival without causing unacceptable normal tissue toxicities. Immunohistochemical staining of 95 retrospective human samples (containing 90 small cell lung carcinomas) demonstrated 84% CXCR4 positivity. In a multivariable analysis of this cohort that included age, gender, stage, primary site, SSTR2 status, and CXCR4 status, Cox regression models determined that only distant metastasis at presentation (P < 0.01) and a CXCR4 H-score >30 (P = 0.04) were significantly associated with reduced survival. Prospective clinical testing of patient tumors identified CXCR4-positivity in 76% of 21 NECs, 67% of 15 lung NETs (including 8 of 10 atypical carcinoids), and 0% of 25 non-lung NETs (including 5 NETS G3s). These data support the hypothesis that CXCR4-targeted theranostics can be utilized effectively for select NETs and NECs.

Immune checkpoint inhibitors in bone metastasis: Clinical challenges, toxicities, and mechanisms

Immune checkpoint inhibitors (ICIs) have revolutionized the field of anti-cancer therapy over the last decade; they provide durable clinical responses against tumors by inhibiting immune checkpoint proteins that canonically regulate the T cell-mediated immune response. Despite their success in many primary tumors and soft tissue metastases, ICIs function poorly in patients with bone metastases, and these patients do not have the same survival benefit as patients with the same primary tumor type (e.g., non-small cell lung cancer [NSCLC], urothelial, renal cell carcinoma [RCC], etc.) that has not metastasized to the bone. Additionally, immune-related adverse events including rheumatologic and musculoskeletal toxicities, bone loss, and increased fracture risk develop after treatment with ICIs. There are few preclinical studies that investigate the interplay of the immune system in bone metastases; however, the current literature suggests a role for CD8+ T cells and myeloid cell subsets in bone homeostasis. As such, this review focuses on findings from the clinical and pre-clinical studies that have investigated immune checkpoint blockade in the bone metastatic setting and highlights the need for more comprehensive investigations into the relationship between immune cell subsets, ICIs, and the bone-tumor microenvironment.

The importance of CXCR4 expression in tumor stroma as a potential biomarker in pancreatic cancer

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is one of the main causes of cancer mortality in the world. A characteristic feature of this cancer is that a large part of the tumor volume is composed of a stroma with different cells and factors. Among these, we can highlight the cytokines, which perform their function through binding to their receptors. Given the impact of the CXCR4 receptor in the interactions between tumor cells and their microenvironment and its involvement in important signaling pathways in cancer, it is proposed as a very promising prognostic biomarker and as a goal for new targeted therapies. Numerous studies analyze the expression of CXCR4 but we suggest focusing on the expression of CXCR4 in the stroma.

METHODS

Expression of CXCR4 in specimens from 33 patients with PDAC was evaluated by immunohistochemistry techniques and matched with clinicopathological parameters, overall and disease-free survival rates.

RESULTS

The percentage of stroma was lower in non-tumor tissue (32.4 ± 5.2) than in tumor pancreatic tissue (67.4 ± 4.8), P-value = 0.001. The level of CXCR4 expression in stromal cells was diminished in non-tumor tissue (8.7 ± 4.6) and higher in tumor pancreatic tissue (23.5 ± 6.1), P-value = 0.022. No significant differences were identified in total cell count and inflammatory cells between non-tumor tissue and pancreatic tumor tissue. No association was observed between CXCR4 expression and any of the clinical or pathological data, overall and disease-free survival rates. Analyzing exclusively the stroma of tumor samples, the CXCR4 expression was associated with tumor differentiation, P-value = 0.05.

CONCLUSIONS

In this study, we reflect the importance of CXCR4 expression in the stroma of patients diagnosed with PDAC. Our results revealed a high CXCR4 expression in the tumor stroma, which is related to a poor tumor differentiation. On the contrary, we could not find an association between CXCR4 expression and survival and the rest of the clinicopathological variables. Focusing the study on the CXCR4 expression in the tumor stroma could generate more robust results. Therefore, we consider it key to develop more studies to enlighten the role of this receptor in PDAC and its implication as a possible biomarker.

Oncogenic Proteomics Approaches for Translational Research and HIV-Associated Malignancy Mechanisms

Recent advances in the field of proteomics have allowed extensive insights into the molecular regulations of the cell proteome. Specifically, this allows researchers to dissect a multitude of signaling arrays while targeting for the discovery of novel protein signatures. These approaches based on data mining are becoming increasingly powerful for identifying both potential disease mechanisms as well as indicators for disease progression and overall survival predictive and prognostic molecular markers for cancer. Furthermore, mass spectrometry (MS) integrations satisfy the ongoing demand for in-depth biomarker validation. For the purpose of this review, we will highlight the current developments based on MS sensitivity, to place quantitative proteomics into clinical settings and provide a perspective to integrate proteomics data for future applications in cancer precision medicine. We will also discuss malignancies associated with oncogenic viruses such as Acquire Immunodeficiency Syndrome (AIDS) and suggest novel mechanisms behind this phenomenon. Human Immunodeficiency Virus type-1 (HIV-1) proteins are known to be oncogenic per se, to induce oxidative and endoplasmic reticulum stresses, and to be released from the infected or expressing cells. HIV-1 proteins can act alone or in collaboration with other known oncoproteins, which cause the bulk of malignancies in people living with HIV-1 on ART.

[68Ga]Ga-Pentixafor PET/CT imaging for in vivo CXCR4 receptor mapping in different lung cancer histologic sub-types: correlation with quantitative receptors' density by immunochemistry techniques

PURPOSE

In vivo CXCR4 receptor quantification in different lung cancer (LC) sub-types using [⁶⁸Ga]Ga-Pentixafor PET/CT and to study correlation with quantitative CXCR4 receptors' tissue density by immunochemistry analyses.

METHODS

[⁶⁸Ga]Ga-Pentixafor PET/CT imaging was performed prospectively in 94 (77 M: 17F, mean age 60.1 ± 10.1 years) LC patients. CXCR4 receptors' expression on lung mass in all the patients was estimated by immunohistochemistry (IHC) and fluorescence-activated cell sorting (FACS) analyses. SUV_max on PET, intensity score on IHC, and mean fluorescence index (MFI) on FACS analyses were measured.

RESULTS

A total of 75/94 (79.8%) cases had non-small cell lung cancer (NSCLC), 14 (14.9%) had small cell lung cancer (SCLC), and 5 (5.3%) had lung neuroendocrine neoplasm (NEN). All LC types showed increased CXCR4 expression on PET (SUV_max) and FACS (MFI). However, both these parameters (mean SUV_max = 10.3 ± 5.0; mean MFI = 349.0 ± 99.0) were significantly (p = 0.005) higher in SCLC as compared to those in NSCLC and lung NEN. The mean SUV_max in adenocarcinoma (n = 16) was 8.0 ± 1.9 which was significantly (p = 0.003) higher than in squamous cell carcinoma (n = 54; 6.2 ± 2.1) and in not-otherwise specified (NOS) sub-types (n = 5; 5.8 ± 1.5) of NSCLC. A significant correlation (r = 0.697; p = 001) was seen between SUV_max and MFI values in squamous cell NSCLC as well as in NSCLC adenocarcinoma (r = 0.538, p = 0.031) which supports the specific in vivo uptake of [⁶⁸Ga]Ga-Pentixafor by CXCR4 receptors. However, this correlation was not significant in SCLC (r = 0.435, p = 0.121) and NEN (r = 0.747, p = 0.147) which may be due to the small sample size. [⁶⁸Ga]Ga-Pentixafor PET/CT provided good sensitivity (85.7%) and specificity (78.1%) for differentiating SCLC from NSCLC (ROC cutoff SUV_max = 7.2). This technique presented similar sensitivity (87.5%) and specificity (71.4%) (ROC cutoff SUV_max = 6.7) for differentiating adenocarcinoma and squamous cell variants of NSCLC.

CONCLUSION

The high sensitivity and specificity of [⁶⁸Ga]Ga-Pentixafor PET/CT for in vivo targeting of CXCR4 receptors in lung cancer can thus be used effectively for the response assessment and development of CXCR4-based radioligand therapies in LC.

MicroRNA-1 attenuates the growth and metastasis of small cell lung cancer through CXCR4/FOXM1/RRM2 axis

BACKGROUND

Small cell lung cancer (SCLC) is an aggressive lung cancer subtype that is associated with high recurrence and poor prognosis. Due to lack of potential drug targets, SCLC patients have few therapeutic options. MicroRNAs (miRNAs) provide an interesting repertoire of therapeutic molecules; however, the identification of miRNAs regulating SCLC growth and metastasis and their precise regulatory mechanisms are not well understood.

METHODS

To identify novel miRNAs regulating SCLC, we performed miRNA-sequencing from donor/patient serum samples and analyzed the bulk RNA-sequencing data from the tumors of SCLC patients. Further, we developed a nanotechnology-based, highly sensitive method to detect microRNA-1 (miR-1, identified miRNA) in patient serum samples and SCLC cell lines. To assess the therapeutic potential of miR-1, we developed various in vitro models, including miR-1 sponge (miR-1Zip) and DOX-On-miR-1 (Tet-ON) inducible stable overexpression systems. Mouse models derived from intracardiac injection of SCLC cells (miR-1Zip and DOX-On-miR-1) were established to delineate the role of miR-1 in SCLC metastasis. In situ hybridization and immunohistochemistry were used to analyze the expression of miR-1 and target proteins (mouse and human tumor specimens), respectively. Dual-luciferase assay was used to validate the target of miR-1, and chromatin immunoprecipitation assay was used to investigate the protein-gene interactions.

RESULTS

A consistent downregulation of miR-1 was observed in tumor tissues and serum samples of SCLC patients compared to their matched normal controls, and these results were recapitulated in SCLC cell lines. Gain of function studies of miR-1 in SCLC cell lines showed decreased cell growth and oncogenic signaling, whereas loss of function studies of miR-1 rescued this effect. Intracardiac injection of gain of function of miR-1 SCLC cell lines in the mouse models showed a decrease in distant organ metastasis, whereas loss of function of miR-1 potentiated growth and metastasis. Mechanistic studies revealed that CXCR4 is a direct target of miR-1 in SCLC. Using unbiased transcriptomic analysis, we identified CXCR4/FOXM1/RRM2 as a unique axis that regulates SCLC growth and metastasis. Our results further showed that FOXM1 directly binds to the RRM2 promoter and regulates its activity in SCLC.

CONCLUSIONS

Our findings revealed that miR-1 is a critical regulator for decreasing SCLC growth and metastasis. It targets the CXCR4/FOXM1/RRM2 axis and has a high potential for the development of novel SCLC therapies. MicroRNA-1 (miR-1) downregulation in the tumor tissues and serum samples of SCLC patients is an important hallmark of tumor growth and metastasis. The introduction of miR-1 in SCLC cell lines decreases cell growth and metastasis. Mechanistically, miR-1 directly targets CXCR4, which further prevents FOXM1 binding to the RRM2 promoter and decreases SCLC growth and metastasis.

The role of CXCL12 axis in pancreatic cancer: New biomarkers and potential targets

Introduction

Chemokines are small, secreted peptides involved in the mediation of the immune cell recruitment. Chemokines have been implicated in several diseases including autoimmune diseases, viral infections and also played a critical role in the genesis and development of several malignant tumors. CXCL12 is a homeostatic CXC chemokine involved in the process of proliferation, and tumor spread. Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive tumors, that is still lacking effective therapies and with a dramatically poor prognosis.

Method

We conducted a scientific literature search on Pubmed and Google Scholar including retrospective, prospective studies and reviews focused on the current research elucidating the emerging role of CXCL12 and its receptors CXCR4 - CXCR7 in the pathogenesis of pancreatic cancer.

Results

Considering the mechanism of immunomodulation of the CXCL12-CXCR4-CXCR7 axis, as well as the potential interaction with the microenvironment in the PDAC, several combined therapeutic approaches have been studied and developed, to overcome the "cold" immunological setting of PDAC, like combining CXCL12 axis inhibitors with anti PD-1/PDL1 drugs.

Conclusion

Understanding the role of this chemokine's axis in disease initiation and progression may provide the basis for developing new potential biomarkers as well as therapeutic targets for related pancreatic cancers.

Aberrant regulation of CXCR4 in cancer via deviant microRNA-targeted interactions

CXCR4 is involved in many facets of cancer, including being a major player in establishing metastasis. This is in part due to the deregulation of CXCR4, which can be attributed to many genetic and epigenetic mechanisms, including aberrant microRNA-CXCR4 interaction. MicroRNAs (miRNAs) are a type of small non-coding RNA that primarily targets the 3' UTR of mRNA transcripts, which in turn suppresses mRNA and subsequent protein expression. In this review, we reported and characterized the many aberrant miRNA-CXCR4 interactions that occur throughout human cancers. In particular, we reported known target sequences located on the 3' UTR of CXCR4 transcripts that tumour suppressor miRNAs bind and therefore regulate expression by. From these aberrant interactions, we also documented affected downstream genes/pathways and whether a particular tumour suppressor miRNA was reported as a prognostic marker in its respected cancer type. In addition, a limited number of cancer-causing miRNAs coined 'oncomirs' were reported and described in relation to CXCR4 regulation. Moreover, the mechanisms underlying both tumour suppressor and oncomir deregulations concerning CXCR4 expression were also explored. Furthermore, the miR-146a-CXCR4 axis was delineated in oncoviral infected endothelial cells in the context of virus-causing cancers. Lastly, miRNA-driven therapies and CXCR4 antagonist drugs were discussed as potential future treatment options in reported cancers pertaining to deregulated miRNA-CXCR4 interactions.

Emerging role of chemokines in small cell lung cancer: Road signs for metastasis, heterogeneity, and immune response

Small cell lung cancer (SCLC) is a recalcitrant, relatively immune-cold, and deadly subtype of lung cancer. SCLC has been viewed as a single or homogenous disease that includes deletion or inactivation of the two major tumor suppressor genes (TP53 and RB1) as a key hallmark. However, recent sightings suggest the complexity of SCLC tumors that comprises highly dynamic multiple subtypes contributing to high intratumor heterogeneity. Furthermore, the absence of targeted therapies, the understudied tumor immune microenvironment (TIME), and subtype plasticity are also responsible for therapy resistance. Secretory chemokines play a crucial role in immunomodulation by trafficking immune cells to the tumors. Chemokines and cytokines modulate the anti-tumor immune response and wield a pro-/anti-tumorigenic effect on SCLC cells after binding to cognate receptors. In this review, we summarize and highlight recent findings that establish the role of chemokines in SCLC growth and metastasis, and sophisticated intratumor heterogeneity. We also discuss the chemokine networks that are putative targets or modulators for augmenting the anti-tumor immune responses in targeted or chemo-/immuno-therapeutic strategies, and how these combinations may be utilized to conquer SCLC.

Small molecule inhibitors targeting the cancers

Compared with traditional therapies, targeted therapy has merits in selectivity, efficacy, and tolerability. Small molecule inhibitors are one of the primary targeted therapies for cancer. Due to their advantages in a wide range of targets, convenient medication, and the ability to penetrate into the central nervous system, many efforts have been devoted to developing more small molecule inhibitors. To date, 88 small molecule inhibitors have been approved by the United States Food and Drug Administration to treat cancers. Despite remarkable progress, small molecule inhibitors in cancer treatment still face many obstacles, such as low response rate, short duration of response, toxicity, biomarkers, and resistance. To better promote the development of small molecule inhibitors targeting cancers, we comprehensively reviewed small molecule inhibitors involved in all the approved agents and pivotal drug candidates in clinical trials arranged by the signaling pathways and the classification of small molecule inhibitors. We discussed lessons learned from the development of these agents, the proper strategies to overcome resistance arising from different mechanisms, and combination therapies concerned with small molecule inhibitors. Through our review, we hoped to provide insights and perspectives for the research and development of small molecule inhibitors in cancer treatment.

Emerging Biomarkers and the Changing Landscape of Small Cell Lung Cancer

Simple Summary

Small cell lung cancer (SCLC) is an aggressive cancer representing 15% of all lung cancers. Unlike other types of lung cancer, treatments for SCLC have changed very little in the past 20 years and therefore, the survival rate remains low. This is due, in part, to the lack of understanding of the biological basis of this disease and the previous idea that all SCLCs are the same. Multiple recent studies have identified that SCLCs have varying biological activity and can be divided into four different groups. The advantage of this is that each of these four groups responds differently to new treatments, which hopefully will dramatically improve survival. Additionally, the aim of these new treatments is to specifically target these biological differences in SCLC so normal/non cancer cells are unaffected, leading to decreased side effects and a better quality of life. There is still a lot unknown about SCLC, but these new findings offer a glimmer of hope for patients in the future.

Abstract

Small cell lung cancer (SCLC) is a high-grade neuroendocrine malignancy with an aggressive behavior and dismal prognosis. 5-year overall survival remains a disappointing 7%. Genomically, SCLCs are homogeneous compared to non-small cell lung cancers and are characterized almost always by functional inactivation of RB1 and TP53 with no actionable mutations. Additionally, SCLCs histologically appear uniform. Thus, SCLCs are currently managed as a single disease with platinum-based chemotherapy remaining the cornerstone of treatment. Recent studies have identified expression of dominant transcriptional signatures which may permit classification of SCLCs into four biologically distinct subtypes, namely, SCLC-A, SCLC-N, SCLC-P, and SCLC-I. These groups are readily detectable by immunohistochemistry and also have potential predictive utility for emerging therapies, including PARPi, immune checkpoint inhibitors, and DLL3 targeted therapies. In contrast with their histology, studies have identified that SCLCs display both inter- and intra-tumoral heterogeneity. Identification of subpopulations of cells with high expression of PLCG2 has been linked with risk of metastasis. SCLCs also display subtype switching under therapy pressure which may contribute furthermore to metastatic ability and chemoresistance. In this review, we summarize the recent developments in the understanding of the biology of SCLCs, and discuss the potential diagnostic, prognostic, and treatment opportunities the four proposed subtypes may present for the future. We also discuss the emerging evidence of tumor heterogeneity and plasticity in SCLCs which have been implicated in metastasis and acquired therapeutic resistance seen in these aggressive tumors.

CXCR4-targeted theranostics in oncology

A growing body of literature reports on the upregulation of C-X-C motif chemokine receptor 4 (CXCR4) in a variety of cancer entities, rendering this receptor as suitable target for molecular imaging and endoradiotherapy in a theranostic setting. For instance, the CXCR4-targeting positron emission tomography (PET) agent [⁶⁸ Ga]PentixaFor has been proven useful for a comprehensive assessment of the current status quo of solid tumors, including adrenocortical carcinoma or small-cell lung cancer. In addition, [⁶⁸ Ga]PentixaFor has also provided an excellent readout for hematological malignancies, such as multiple myeloma, marginal zone lymphoma, or mantle cell lymphoma. PET-based quantification of the CXCR4 capacities in vivo allows for selecting candidates that would be suitable for treatment using the theranostic equivalent [¹⁷⁷Lu]/[⁹⁰Y]PentixaTher. This CXCR4-directed theranostic concept has been used as a conditioning regimen prior to hematopoietic stem cell transplantation and to achieve sufficient anti-lymphoma/-tumor activity in particular for malignant tissues that are highly sensitive to radiation, such as the hematological system. Increasing the safety margin, pretherapeutic dosimetry is routinely performed to determine the optimal activity to enhance therapeutic efficacy and to reduce off-target adverse events. The present review will provide an overview of current applications for CXCR4-directed molecular imaging and will introduce the CXCR4-targeted theranostic concept for advanced hematological malignancies.

Epigenetic Regulation of CXCR4 Signaling in Cancer Pathogenesis and Progression

Signaling involving chemokine receptor CXCR4 and its ligand SDF-1/CXL12 has been investigated for many years for its possible role in cancer progression and pathogenesis. Evidence emerging from clinical studies in recent years has further established diagnostic as well as prognostic importance of CXCR4 signaling. CXCR4 and SDF-1 are routinely reported to be elevated in tumors, distant metastases, which correlates with poor survival of patients. These findings have kindled interest in the mechanisms that regulate CXCR4/SDF-1 expression. Of note, there is a particular interest in the epigenetic regulation of CXCR4 signaling that may be responsible for upregulated CXCR4 in primary as well as metastatic cancers. This review first lists the clinical evidence supporting CXCR4 signaling as putative cancer diagnostic and/or prognostic biomarker, followed by a discussion on reported epigenetic mechanisms that affect CXCR4 expression. These mechanisms include regulation by non-coding RNAs, such as, microRNAs, long non-coding RNAs and circular RNAs. Additionally, we also discuss the regulation of CXCR4 expression through methylation and acetylation. Better understanding and appreciation of epigenetic regulation of CXCR4 signaling can invariably lead to identification of novel therapeutic targets as well as therapies to regulate this oncogenic signaling.

An Evaluation of CXCR4 Targeting with PAMAM Dendrimer Conjugates for Oncologic Applications

The chemokine receptor 4 (CXCR4) is a promising diagnostic and therapeutic target for the management of various cancers. CXCR4 has been utilized in immunotherapy, targeted drug delivery, and endoradiotherapy. Poly(amidoamine) [PAMAM] dendrimers are well-defined polymers with unique properties that have been used in the fabrication of nanomaterials for several biomedical applications. Here, we describe the formulation and pharmacokinetics of generation-5 CXCR4-targeted PAMAM (G5-X4) dendrimers. G5-X4 demonstrated an IC50 of 0.95 nM to CXCR4 against CXCL12-Red in CHO-SNAP-CXCR4 cells. Single-photon computed tomography/computed tomography imaging and biodistribution studies of 111In-labeled G5-X4 showed enhanced uptake in subcutaneous U87 glioblastoma tumors stably expressing CXCR4 with 8.2 ± 2.1, 8.4 ± 0.5, 11.5 ± 0.9, 10.4 ± 2.6, and 8.8 ± 0.5% injected dose per gram of tissue at 1, 3, 24, 48, and 120 h after injection, respectively. Specific accumulation of [111In]G5-X4 in CXCR4-positive tumors was inhibited by the peptidomimetic CXCR4 inhibitor, POL3026. Our results demonstrate that while CXCR4 targeting is beneficial for tumor accumulation at early time points, differences in tumor uptake are diminished over time as passive accumulation takes place. This study further confirms the applicability of PAMAM dendrimers for imaging and therapeutic applications. It also emphasizes careful consideration of image acquisition and/or treatment times when designing dendritic nanoplatforms for tumor targeting.

Polyfunctionality of the CXCR4/CXCL12 axis in health and disease: Implications for therapeutic interventions in cancer and immune-mediated diseases

Historically the chemokine receptor CXCR4 and its canonical ligand CXCL12 are associated with the bone marrow niche and hematopoiesis. However, CXCL12 exhibits broad tissue expression including brain, thymus, heart, lung, liver, kidney, spleen, and bone marrow. CXCR4 can be considered as a node which is integrating and transducing inputs from a range of ligand-receptor interactions into a responsive and divergent network of intracellular signaling pathways that impact multiple cellular processes such as proliferation, migration, and stress resistance. Dysregulation of the CXCR4/CXCL12 axis and consequent fundamental cellular processes, are associated with a panoply of disease. This review frames the polyfunctionality of the receptor at a molecular, physiological, and pathophysiological levels. Transitioning our perspective of this axis from a single gene/protein:single function model to a polyfunctional signaling cascade highlights the potential for finer therapeutic intervention and cautions against a reductionist approach.

Prognostic Significance of CXCR4 in Colorectal Cancer: An Updated Meta-Analysis and Critical Appraisal

Simple Summary

C-X-C chemokine receptor type 4 (CXCR4), a G-protein-coupled receptor, has been demonstrated to stimulate proliferation and invasiveness of many different tumors, including colorectal cancer. Through in vitro evidence, overexpression of CXCR4 has been identified as a negative prognostic factor in colorectal cancer. The identification of prognostic biomarkers can improve the prediction of disease evolution and disease characterization, and guide treatment efforts. This systematic review with a meta-analysis was conducted to pool hazard ratios from prognostic studies on CXCR4, provide an updated estimate of prognostic power of CXCR4, and analyze modalities of evaluating and reporting CXCR4 expression.

Abstract

Background: This study was conducted to provide an updated estimate of the prognostic power of C-X-C chemokine receptor type 4 (CXCR4) in colorectal cancer (CRC), and analyze modalities of evaluating and reporting its expression. Methods: A systematic review with meta-analysis was performed and described according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. Studies were identified through PubMed and Google Scholar. The pooled hazard ratios (HRs) for overall survival (OS) or progression-free survival (PFS) with 95% confidence interval (CI) were estimated with the random-effect model. Results: Sixteen studies were selected covering a period from 2005 to 2020. An immunohistochemical evaluation of CXCR4 was performed in all studies. Only in three studies assessment of mRNA through RT–PCR was correlated with prognosis; in the remaining studies, the authors identified prognostic categories based on immunohistochemical expression. In pooled analyses, significant associations were found between positive or high or strong expression of CXCR4 and T stage ≥3 (P = 0.0001), and positive or high or strong expression of CXCR4 and left side primary tumor localization (P = 0.0186). The pooled HR for OS was 2.09 (95% CI: 1.30–2.88) in favor of high CXCR4 expression; for PFS, it was 1.42 (95% CI: 1.13–1.71) in favor of high CXCR4 expression. Conclusion: High CXCR4 expression is clearly associated with increased risk of death and progression in CRC. However, strong methodologic heterogeneity in CXCR4 assessment hinders direct translation into clinical practice; thus, a consensus to streamline detection and scoring of CXCR4 expression in CRC is indicated.

Small-cell lung cancer

Small-cell lung cancer (SCLC) represents about 15% of all lung cancers and is marked by an exceptionally high proliferative rate, strong predilection for early metastasis and poor prognosis. SCLC is strongly associated with exposure to tobacco carcinogens. Most patients have metastatic disease at diagnosis, with only one-third having earlier-stage disease that is amenable to potentially curative multimodality therapy. Genomic profiling of SCLC reveals extensive chromosomal rearrangements and a high mutation burden, almost always including functional inactivation of the tumour suppressor genes TP53 and RB1. Analyses of both human SCLC and murine models have defined subtypes of disease based on the relative expression of dominant transcriptional regulators and have also revealed substantial intratumoural heterogeneity. Aspects of this heterogeneity have been implicated in tumour evolution, metastasis and acquired therapeutic resistance. Although clinical progress in SCLC treatment has been notoriously slow, a better understanding of the biology of disease has uncovered novel vulnerabilities that might be amenable to targeted therapeutic approaches. The recent introduction of immune checkpoint blockade into the treatment of patients with SCLC is offering new hope, with a small subset of patients deriving prolonged benefit. Strategies to direct targeted therapies to those patients who are most likely to respond and to extend the durable benefit of effective antitumour immunity to a greater fraction of patients are urgently needed and are now being actively explored.

Mechanisms of small cell lung cancer metastasis

Metastasis is a major cause of morbidity and mortality in cancer patients. However, the molecular and cellular mechanisms underlying the ability of cancer cells to metastasize remain relatively poorly understood. Among all solid tumors, small cell lung cancer (SCLC) has remarkable metastatic proclivity, with a majority of patients diagnosed with metastatic disease. Our understanding of SCLC metastasis has been hampered for many years by the paucity of material from primary tumors and metastases, as well as the lack of faithful pre-clinical models. Here, we review recent advances that are helping circumvent these limitations. These advances include methods that employ circulating tumor cells from the blood of SCLC patients and the development of diverse genetically engineered mouse models of metastatic SCLC. New insights into the cellular mechanisms of SCLC metastasis include observations of cell fate changes associated with increased metastatic ability. Ongoing studies on cell migration and organ tropism promise to expand our understanding of SCLC metastasis. Ultimately, a better molecular understanding of metastatic phenotypes may be translated into new therapeutic options to limit metastatic spread and treat metastatic SCLC.

Anti-HIV-1 Activity of pepRF1, a Proteolysis-Resistant CXCR4 Antagonist Derived from Dengue Virus Capsid Protein

There is an urgent need for the development of new anti-HIV drugs that can complement existing medicines to be used against resistant strains. Here, we report the anti-HIV-1 peptide pepRF1, a human serum-resistant peptide derived from the Dengue virus capsid protein. In vitro, pepRF1 shows a 50% inhibitory concentration of 1.5 nM with a potential therapeutic window higher than 53 000. This peptide is specific for CXCR4-tropic strains, preventing viral entry into target cells by binding to the viral coreceptor CXCR4, acting as an antagonist of this receptor. pepRF1 is more effective than T20, the only peptide-based HIV-1 entry inhibitor approved, and excels in inhibiting a HIV-1 strain resistant to T20. Potentially, pepRF1 can be used alone or in combination with other anti-HIV drugs. Furthermore, one can also envisage its use as a novel therapeutic strategy for other CXCR4-related diseases.

The Roles of Stroma-Derived Chemokine in Different Stages of Cancer Metastases

The intricate interplay between malignant cells and host cellular and non-cellular components play crucial role in different stages of tumor development, progression, and metastases. Tumor and stromal cells communicate to each other through receptors such as integrins and secretion of signaling molecules like growth factors, cytokines, chemokines and inflammatory mediators. Chemokines mediated signaling pathways have emerged as major mechanisms underlying multifaceted roles played by host cells during tumor progression. In response to tumor stimuli, host cells-derived chemokines further activates signaling cascades that support the ability of tumor cells to invade surrounding basement membrane and extra-cellular matrix. The host-derived chemokines act on endothelial cells to increase their permeability and facilitate tumor cells intravasation and extravasation. The tumor cells-host neutrophils interaction within the vasculature initiates chemokines driven recruitment of inflammatory cells that protects circulatory tumor cells from immune attack. Chemokines secreted by tumor cells and stromal immune and non-immune cells within the tumor microenvironment enter the circulation and are responsible for formation of a "pre-metastatic niche" like a "soil" in distant organs whereby circulating tumor cells "seed' and colonize, leading to formation of metastatic foci. Given the importance of host derived chemokines in cancer progression and metastases several drugs like Mogamulizumab, Plerixafor, Repertaxin among others are part of ongoing clinical trial which target chemokines and their receptors against cancer pathogenesis. In this review, we focus on recent advances in understanding the complexity of chemokines network in tumor microenvironment, with an emphasis on chemokines secreted from host cells. We especially summarize the role of host-derived chemokines in different stages of metastases, including invasion, dissemination, migration into the vasculature, and seeding into the pre-metastatic niche. We finally provide a brief description of prospective drugs that target chemokines in different clinical trials against cancer.

Automated Synthesis of Fluorine-18 Labeled CXCR4 Ligand via the Conjugation with Nicotinic Acid N-Hydroxysuccinimide Ester (6-[18F]SFPy)

The C-X-C motif chemokine receptor 4 (CXCR4) is a seven-transmembrane G protein-coupled receptor that is overexpressed in numerous diseases, particularly in various cancers and is a powerful chemokine, attracting cells to the bone marrow niche. Therefore, CXCR4 is an attractive target for imaging and therapeutic purposes. The goal of this study is to develop an efficient, reproducible, and straightforward method to prepare a fluorine-18 labeled CXCR4 ligand. 6-[18F]Fluoronicotinic acid-2,3,5,6-tetrafluorophenyl ester (6-[18F]FPy-TFP) and nicotinic acid N-hydroxysuccinimide ester (6-[18F]SFPy) have been prepared using 'fluorination on the Sep-Pak' method. Conjugation of 6-[18F]SFPy or 6-[18F]FPy-TFP with the alpha-amino group at the N terminus of the protected T140 precursor followed by deprotection, yielded the final product 6-[18F]FPy-T140. The overall radiochemical yields were 6-17% (n = 15, decay-corrected) in a 90-min radiolabeling time with a radiochemical purity >99%. 6-[18F]FPy-T140 exhibited high specific binding and nanomolar affinity for CXCR4 in vitro, indicating that the biological activity of the peptide was preserved. For the first time, [18F]SFPy has been prepared using 'fluorination on the Sep-Pak' method that allows rapid automated synthesis of 6-[18F]FPy-T140. In addition to increased synthetic efficiency, this construct binds with CXCR4 in high affinity and may have potential as an in vivo positron emission tomography (PET) imaging agent. This radiosynthesis method should encourage wider use of this PET agent to quantify CXCR4 in both research and clinical settings.

CXCR4 in Tumor Epithelial Cells Mediates Desmoplastic Reaction in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) features abundant stromal cells with an excessive extracellular matrix (ECM), termed the desmoplastic reaction. CXCR4 is a cytokine receptor for stromal cell-derived factor-1 (CXCL12) expressed in PDAC, but its roles in PDAC and the characteristic desmoplastic reaction remain unclear. Here, we generated a mouse model of PDAC with conditional knockout of Cxcr4 (KPC-Cxcr4-KO) by crossing Cxcr4 flox mice with Pdx1-Cre;KrasLSL-G12D/+;Trp53LSL-R172H/+ (KPC-Cxcr4-WT) mice to assess the development of pancreatic intraepithelial neoplasia (PanIN) and pancreatic cancers. Tumor cell characteristics of those two types were analyzed in vitro. In addition, CXCR4 expression in human pancreatic cancer specimens was evaluated by IHC staining. In KPC-Cxcr4-KO mice, the number and pathologic grade of PanIN lesions were reduced, but the frequency of pancreatic cancers did not differ from that in KPC-Cxcr4-WT mice. The pancreatic tumor phenotype in KPC-Cxcr4-KO mice was significantly larger and undifferentiated, characterized by abundant vimentin-expressing cancer cells, significantly fewer fibroblasts, and markedly less deposition of ECM. In vitro, KPC-Cxcr4-KO tumor cells exhibited higher proliferative and migratory activity than KPC-Cxcr4-WT tumor cells. Myofibroblasts induced invasion activity in KPC-Cxcr4-WT tumor cells, showing an epithelial-mesenchymal interaction, whereas KPC-Cxcr4-KO tumor cells were unaffected by myofibroblasts, suggesting their unique nature. In human pancreatic cancer, undifferentiated carcinoma did not express CXCR4 and exhibited histologic and IHC features similar to those in KPC-Cxcr4-KO mice. In summary, the CXCL12/CXCR4 axis may play an important role in the desmoplastic reaction in PDAC, and loss of CXCR4 induces phenotype changes in undifferentiated carcinoma without a desmoplastic reaction. SIGNIFICANCE: The current study uncovers CXCR4 as a key regulator of desmoplastic reaction in PDAC and opens the way for new therapeutic approaches to overcome the chemoresistance in patients with PDAC.

Radiation-induced alterations in immunogenicity of a murine pancreatic ductal adenocarcinoma cell line

Pancreatic ductal adenocarcinoma (PDA) is highlighted by resistance to radiotherapy with the possible exception of hypofractionated irradiation. As single photon doses were reported to increase immunogenicity, we investigated dose-dependent irradiation effects on clonogenic survival, expression of immunologically relevant cell surface molecules and susceptibility to cytotoxic T cell (CTL) mediated killing using a murine PDA cell line. Clonogenicity decreased in a dose-responsive manner showing enhanced radioresistance at single photon doses below 5 Gy. Cell cycle analysis revealed a predominant G2/M arrest, being most pronounced 12 h after irradiation. Polyploidy increased in a dose- and time-dependent manner reaching a maximum frequency 60 h following irradiation with 10 Gy. Irradiation increased surface expression of MHC class I molecules and of immunological checkpoint molecules PDL-1 and CD73, especially at doses ≥ 5 Gy, but not of MHC class II molecules and CXCR4 receptors. Cytotoxicity assays revealed increased CTL lysis of PDA cells at doses ≥ 5 Gy. For the PDA cell line investigated, our data show for the first time that single photon doses ≥ 5 Gy effectively inhibit colony formation and induce a G2/M cell cycle arrest. Furthermore, expression levels of immunomodulatory cell surface molecules became altered possibly enhancing the susceptibility of tumour cells to CTL lysis.

Axon-like protrusions promote small cell lung cancer migration and metastasis

Metastasis is the main cause of death in cancer patients but remains a poorly understood process. Small cell lung cancer (SCLC) is one of the most lethal and most metastatic cancer types. SCLC cells normally express neuroendocrine and neuronal gene programs but accumulating evidence indicates that these cancer cells become relatively more neuronal and less neuroendocrine as they gain the ability to metastasize. Here we show that mouse and human SCLC cells in culture and in vivo can grow cellular protrusions that resemble axons. The formation of these protrusions is controlled by multiple neuronal factors implicated in axonogenesis, axon guidance, and neuroblast migration. Disruption of these axon-like protrusions impairs cell migration in culture and inhibits metastatic ability in vivo. The co-option of developmental neuronal programs is a novel molecular and cellular mechanism that contributes to the high metastatic ability of SCLC.

CXCL12/CXCR4 signal transduction in diseases and its molecular approaches in targeted-therapy

Chemokines are small molecules called "chemotactic cytokines" and regulate many processes like leukocyte trafficking, homing of immune cells, maturation, cytoskeletal rearrangement, physiology, migration during development, and host immune responses. These proteins bind to their corresponding 7-membrane G-protein-coupled receptors. Chemokines and their receptors are anti-inflammatory factors in autoimmune conditions, so consider as potential targets for neutralization in such diseases. They also express by cancer cells and function as angiogenic factors, and/or survival/growth factors that enhance tumor angiogenesis and development. Among chemokines, the CXCL12/CXCR4 axis has significantly been studied in numerous cancers and autoimmune diseases. CXCL12 is a homeostatic chemokine, which is acts as an anti-inflammatory chemokine during autoimmune inflammatory responses. In cancer cells, CXCL12 acts as an angiogenic, proliferative agent and regulates tumor cell apoptosis as well. CXCR4 has a role in leukocyte chemotaxis in inflammatory situations in numerous autoimmune diseases, as well as the high levels of CXCR4, observed in different types of human cancers. These findings suggest CXCL12/CXCR4 as a potential therapeutic target for therapy of autoimmune diseases and open a new approach to targeted-therapy of cancers by neutralizing CXCL12 and CXCR4. In this paper, we reviewed the current understanding of the role of the CXCL12/CXCR4 axis in disease pathology and cancer biology, and discuss its therapeutic implications in cancer and diseases.

TCF12 promotes the tumorigenesis and metastasis of hepatocellular carcinoma via upregulation of CXCR4 expression

TCF12, which is known to be involved in the regulation of cell growth and differentiation, has been reported to function as an oncogene or a tumor suppressor gene in the progression of various malignant tumors. However, its function and molecular mechanism in hepatocellular carcinoma (HCC) remain unclear.

Methods: Stable ectopic TCF12 expression or knockdown in HCC cell lines was established by lentiviral infection. Then, MTT, colony formation, migration, invasion and HUVECs tube formation assays as well as an orthotopic xenograft model were used to investigate the biologic function of TCF12 in HCC cells in vitro and in vivo. Subsequently, RNA-Seq analysis was utilized to explore the target genes regulated by TCF12. RT-qPCR, western blotting, a dual-luciferase reporter assay, Ch-IP, CHIP-Seq and functional rescue experiments were used to confirm the target gene regulated by TCF12. Finally, RT-qPCR, western blot and immunohistochemical (IHC) staining were performed to detect the expression level of TCF12 and to analyze the correlation of TCF12 with downstream genes as well as the clinical significance of TCF12 in human primary HCC.

Results: Our functional studies revealed that stable overexpression of TCF12 in human HCC cells enhanced cell proliferation, migration and invasion in vitro and in vivo, whereas knockdown of TCF12 showed opposing effects. Mechanistically, CXCR4 was a downstream target of TCF12, and TCF12 directly bound to the CXCR4 promoter to regulate its expression. Moreover, CXCR4, with its ligand CXCL12, played a critical role in tumor progression induced by TCF12 via activation of the MAPK/ERK and PI3K/AKT signaling pathways. Clinically, IHC analysis revealed that TCF12 was significantly associated with poor survival of HCC patients and that TCF12 expression was closely correlated with CXCR4 expression in primary HCC tissues.

Conclusion: Our findings are the first to indicate that TCF12 could promote the tumorigenesis and progression of HCC mainly by upregulating CXCR4 expression and is a prognostic indicator for patients with HCC.

High affinity CXCR4 inhibitors generated by linking low affinity peptides

G-protein coupled receptors (GPCRs) are implicated in many diseases and attractive targets for drug discovery. Peptide fragments derived from protein ligands of GPCRs are commonly used as probes of GPCR function and as leads for drug development. However, these peptide fragments lack the structural integrity of their parent full-length protein ligands and often show low receptor affinity, which limits their research and therapeutic values. It remains a challenge to efficiently generate high affinity peptide inhibitors of GPCRs. We have investigated a combinational approach involving the synthetic covalent linkage of two low affinity peptide fragments to determine if the strategy can yield high affinity GPCR inhibitors. We examined this design approach using the chemokine receptor CXCR4 as a model of GPCR system. Here, we provide a proof of concept demonstration by designing and synthesizing two peptides, AR5 and AR6, that combine a peptide fragment derived from two viral ligands of CXCR4, vMIP-II and HIV-1 envelope glycoprotein gp120. AR5 and AR6 display nanomolar binding affinity, in contrast to the weak micromolar CXCR4 binding of each peptide fragment alone, and inhibit HIV-1 entry via CXCR4. Further studies were carried out for the representative peptide AR6 using western blotting and site-directed mutagenesis in conjunction with molecular dynamic simulation and binding free energy calculation to determine how the peptide interacts with CXCR4 and inhibits its downstream signaling. These results demonstrate that this combinational approach is effective for generating nanomolar active inhibitors of CXCR4 and may be applicable to other GPCRs.

Targeting CXCL12/CXCR4 Axis in Tumor Immunotherapy

Chemokines, which have chemotactic abilities, are comprised of a family of small cytokines with 8-10 kilodaltons. Chemokines work in immune cells by trafficking and regulating cell proliferation, migration, activation, differentiation, and homing. CXCR-4 is an alpha-chemokine receptor specific for stromal-derived-factor-1 (SDF-1, also known as CXCL12), which has been found to be expressed in more than 23 different types of cancers. Recently, the SDF-1/CXCR-4 signaling pathway has emerged as a potential therapeutic target for human tumor because of its critical role in tumor initiation and progression by activating multiple signaling pathways, such as ERK1/2, ras, p38 MAPK, PLC/ MAPK, and SAPK/ JNK, as well as regulating cancer stem cells. CXCL12/CXCR4 antagonists have been produced, which have shown encouraging results in anti-cancer activity. Here, we provide a brief overview of the CXCL12/CXCR4 axis as a molecular target for cancer treatment. We also review the potential utility of targeting CXCL12/CXCR4 axis in combination of immunotherapy and/or chemotherapy based on up-to-date literature and ongoing research progress.

Are there any theranostic biomarkers in small cell lung carcinoma?

Small cell lung cancer (SCLC), an aggressive lung tumour with a poor prognosis, has a high load of somatic mutations, mainly induced by tobacco carcinogens given the strong association with smoking. Advances in genomic, epigenetic and proteomic profiling have significantly improved our understanding of the molecular and cellular biology of SCLC. Given the high mutational burden of SCLC the immune microenvironment is another exciting area under investigation even if it seems to be quite distinct from that of other solid tumours. In this review we will outline the current progress in molecular etiology of SCLC mentioning some key markers considered promising theranostic biomarkers.

Intertumoral Heterogeneity in SCLC Is Influenced by the Cell Type of Origin

The extent to which early events shape tumor evolution is largely uncharacterized, even though a better understanding of these early events may help identify key vulnerabilities in advanced tumors. Here, using genetically defined mouse models of small cell lung cancer (SCLC), we uncovered distinct metastatic programs attributable to the cell type of origin. In one model, tumors gain metastatic ability through amplification of the transcription factor NFIB and a widespread increase in chromatin accessibility, whereas in the other model, tumors become metastatic in the absence of NFIB-driven chromatin alterations. Gene-expression and chromatin accessibility analyses identify distinct mechanisms as well as markers predictive of metastatic progression in both groups. Underlying the difference between the two programs was the cell type of origin of the tumors, with NFIB-independent metastases arising from mature neuroendocrine cells. Our findings underscore the importance of the identity of cell type of origin in influencing tumor evolution and metastatic mechanisms.Significance: We show that SCLC can arise from different cell types of origin, which profoundly influences the eventual genetic and epigenetic changes that enable metastatic progression. Understanding intertumoral heterogeneity in SCLC, and across cancer types, may illuminate mechanisms of tumor progression and uncover how the cell type of origin affects tumor evolution. Cancer Discov; 8(10); 1316-31. ©2018 AACR. See related commentary by Pozo et al., p. 1216 This article is highlighted in the In This Issue feature, p. 1195.

[Stromal cell-derived factor-1 inducing metastasis squamous cell carcinoma of head and neck induced via integrin ανβ3-CXC chemokine receptor 4/7 biological axis]

OBJECTIVE

To observe the influence of LM609/AMD3100/CCX754 on chemotactic capability, cytoskeleton, and expression of integrin ανβ3 protein of squamous cell carcinoma of head and neck (SCCHN) cell line PCI-13 induced by stromal cell-derived factor-1 (SDF-1) in vitro.

METHODS

Migration assays, flow cytometry and immunofluorescence were used to observe the effects of SDF-1, LM609, AMD3100 and CCX754 on the migration, cytoskeleton and the expression of integrin ανβ3 protein in PCI-13 cell lines.

RESULTS

SDF-1 favored PCI-13 cell migration, pseudopod formation, and activities of integrin ανβ3 phosphorylation. LM609, AMD3100, and CCX754 blocked all these effects.

CONCLUSIONS

SDF-1 can induce metastatic SCCHN by integrin ανβ3-CXC chemokine receptor (CXCR) 4/CXCR7 axi. LM609, AMD3100, and CCX754 and can reduce the regulation of SDF-1 on SCCHN activity.

Reversibly Stabilized Polycation Nanoparticles for Combination Treatment of Early- and Late-Stage Metastatic Breast Cancer

Metastatic breast cancer is a major cause of cancer-related female mortality worldwide. The signal transducer and activator of transcription 3 (STAT3) and the chemokine receptor CXCR4 are involved in the metastatic spread of breast cancer. The goal of this study was to develop nanomedicine treatment based on combined inhibition of STAT3 and CXCR4. We synthesized a library of CXCR4-inhibiting polymers with a combination of beneficial features that included PEGylation, fluorination, and bioreducibility to achieve systemic delivery of siRNA to silence STAT3 expression in the tumors. An in vivo structure-activity relationship study in an experimental lung metastasis model revealed superior antimetastatic activity of bioreducible fluorinated polyplexes when compared with nonreducible controls despite similar CXCR4 antagonism and the ability to inhibit in vitro cancer cell invasion. When compared with nonreducible and nonfluorinated polyplexes, improved siRNA delivery was observed with the bioreducible fluorinated polyplexes. The improvement was ascribed to a combination of enhanced physical stability, decreased serum destabilization, and improved intracellular trafficking. Pharmacokinetic analysis showed that fluorination decreased the rate of renal clearance of the polyplexes and contributed to enhanced accumulation in the tumors. Therapeutic efficacy of the polyplexes with STAT3 siRNA was assessed in early stage breast cancer and late-stage metastatic breast cancer with primary tumor resection. Strong inhibition of the primary tumor growth and pronounced antimetastatic effects were observed in both models of metastatic breast cancer. Mechanistic studies revealed multifaceted mechanism of action of the combined STAT3 and CXCR4 inhibition by the developed polyplexes relying both on local and systemic effects.

Modeling small cell lung cancer (SCLC) biology through deterministic and stochastic mathematical models

Mathematical cancer models are immensely powerful tools that are based in part on the fractal nature of biological structures, such as the geometry of the lung. Cancers of the lung provide an opportune model to develop and apply algorithms that capture changes and disease phenotypes. We reviewed mathematical models that have been developed for biological sciences and applied them in the context of small cell lung cancer (SCLC) growth, mutational heterogeneity, and mechanisms of metastasis. The ultimate goal is to develop the stochastic and deterministic nature of this disease, to link this comprehensive set of tools back to its fractalness and to provide a platform for accurate biomarker development. These techniques may be particularly useful in the context of drug development research, such as combination with existing omics approaches. The integration of these tools will be important to further understand the biology of SCLC and ultimately develop novel therapeutics.

Bioinformatic analyses reveal the key pathways and genes in the CXCR4 mediated mesenchymal subtype of glioblastoma

Glioblastoma multiforme (GBM) is one of the most lethal types of tumour, despite severe treatment methods. The Cancer Genome Atlas has categorised GBMs into proneural, neural, classical and mesenchymal subtypes; the mesenchymal subgroup has the worst prognosis. CXCR4 has been reported as selectively overexpressed in the mesenchymal subtype and positively associated with MES markers. However, to the best of our knowledge the underlying mechanisms regarding how CXCR4 may regulate mesenchymal GBM are still unknown. The present study aimed to investigate the critical pathways mediated by CXCR4 in mesenchymal GBM using bioinformatic analyses. The results suggested that CXCR4 is a predictor of poor prognosis and may serve as a biomarker of the mesenchymal subtype in patients with GBM. In addition, CXCR4 mediated the mitogen‑activated protein kinase signaling pathway, which was identified specifically in patients with mesenchymal GBM. CXCR4 associated genes or pathways may be a 'basket trial' option for the management of melanoma, prostate cancer and mesenchymal GBM.

Ligand-activated PPARγ downregulates CXCR4 gene expression through a novel identified PPAR response element and inhibits breast cancer progression

Stromal Derived Factor-1α (SDF-1α) and its cognate receptor CXCR4 play a key role in mediating breast cancer cell invasion and metastasis. Therefore, drugs able to inhibit CXCR4 activation may add critical tools to reduce tumor progression, especially in the most aggressive form of the breast cancer disease. Peroxisome Proliferator-Activated Receptor (PPAR) γ, a member of the nuclear receptor superfamily, has been found to downregulate CXCR4 gene expression in different cancer cells, however the molecular mechanism underlying this effect is not fully understood. Here, we identified a novel PPARγ-mediated mechanism that negatively regulates CXCR4 expression in both epithelial and stromal breast cancer cells. We found that ligand-activated PPARγ downregulated CXCR4 transcriptional activity through the recruitment of the silencing mediator of retinoid and thyroid hormone receptor (SMRT) corepressor onto a newly identified PPAR response element (PPRE) within the CXCR4 promoter in breast cancer cell lines. As a consequence, the PPARγ agonist rosiglitazone (BRL) significantly inhibited cell migration and invasion and this effect was PPARγ-mediated, since it was reversed in the presence of the PPARγ antagonist GW9662. According to the ability of cancer-associated fibroblasts (CAFs), the most abundant component of breast cancer stroma, to secrete high levels of SDF-1α, BRL reduced migratory promoting activities induced by conditioned media (CM) derived from CAFs and affected CXCR4 downstream signaling pathways activated by CAF-CM. In addition, CAFs exposed to BRL showed a decreased expression of CXCR4, a reduced motility and invasion along with a phenotype characterized by an altered morphology. Collectively, our findings provide novel insights into the role of PPARγ in inhibiting breast cancer progression and further highlight the utility of PPARγ ligands for future therapies aimed at targeting both cancer and surrounding stromal cells in breast cancer patients.

The chemical diversity and structure-based evolution of non-peptide CXCR4 antagonists with diverse therapeutic potential

The CXC chemokine receptor 4 (CXCR4) is a highly reserved G-protein coupled 7-transmembrane (TM) chemokine receptor which consists of 352 amino acids. CXCR4 has only one endogenous chemokine ligand of CXCL12, besides several other natural nonchemokine ligands such as extracellular ubiquitin and noncognate ligand of MIF. CXCR4 strongly binds to CXCL12 and the resulting CXCLl2/CXCR4 axis is the molecular basis of their various biological functions, which include: (1) mediating immune and inflammatory response; (2) regulation of hematopoietic stem cell migration and homing; (3) an essential co-receptor for HIV entry into host cells; (4) participation in the process of embryonic development; (5) malignant tumor invasion and metastasis; (6) myocardial infarction, ischemic stroke and acute kidney injury. Correspondingly, CXCR4 antagonists find potential therapeutic applications in HIV infection, as well as hematopoietic stem cell migration, inflammation, immune-related diseases, tumor and ischemic diseases. Recently, great achievements have been made and a number of non-peptide CXCR4 antagonists with diversity scaffolds have been discovered. In this review, the discovery of small molecule CXCR4 antagonists focused on the structures, activities, evolution and development of representative CXCR4 antagonists is comprehensively described. The central role of CXCR4 in diverse cellular signaling pathways and its involvement in several diseases progressions are discussed as well.

Mechanistic Exploration of Cancer Stem Cell Marker Voltage-Dependent Calcium Channel α2δ1 Subunit-mediated Chemotherapy Resistance in Small-Cell Lung Cancer

Purpose: Chemoresistance in small-cell lung cancer (SCLC) is reportedly attributed to the existence of resistant cancer stem cells (CSC). Studies involving CSC-specific markers and related mechanisms in SCLC remain limited. This study explored the role of the voltage-dependent calcium channel α2δ1 subunit as a CSC marker in chemoresistance of SCLC, and explored the potential mechanisms of α2δ1-mediated chemoresistance and strategies of overcoming the resistance.Experimental Design: α2δ1-positive cells were identified and isolated from SCLC cell lines and patient-derived xenograft (PDX) models, and CSC-like properties were subsequently verified. Transcriptome sequencing and Western blotting were carried out to identify pathways involved in α2δ1-mediated chemoresistance in SCLC. In addition, possible interventions to overcome α2δ1-mediated chemoresistance were examined.Results: Different proportions of α2δ1⁺ cells were identified in SCLC cell lines and PDX models. α2δ1⁺ cells exhibited CSC-like properties (self-renewal, tumorigenic, differentiation potential, and high expression of genes related to CSCs and drug resistance). Chemotherapy induced the enrichment of α2δ1⁺ cells instead of CD133⁺ cells in PDXs, and an increased proportion of α2δ1⁺ cells corresponded to increased chemoresistance. Activation and overexpression of ERK in the α2δ1-positive H1048 cell line was identified at the protein level. mAb 1B50-1 was observed to improve the efficacy of chemotherapy and delay relapse as maintenance therapy in PDX models.Conclusions: SCLC cells expressing α2δ1 demonstrated CSC-like properties, and may contribute to chemoresistance. ERK may play a key role in α2δ1-mediated chemoresistance. mAb 1B50-1 may serve as a potential anti-SCLC drug. Clin Cancer Res; 24(9); 2148-58. ©2018 AACR.

When Immune Cells Turn Bad-Tumor-Associated Microglia/Macrophages in Glioma

As a substantial part of the brain tumor microenvironment (TME), glioma-associated microglia/macrophages (GAMs) have an emerging role in tumor progression and in controlling anti-tumor immune responses. We review challenges and improvements of cell models and highlight the contribution of this highly plastic cell population to an immunosuppressive TME, besides their well-known functional role regarding glioma cell invasion and angiogenesis. Finally, we summarize first therapeutic interventions to target GAMs and their effect on the immunobiology of gliomas, focusing on their interaction with T cells.

Carcinoma associated fibroblasts (CAFs) promote breast cancer motility by suppressing mammalian Diaphanous-related formin-2 (mDia2)

The tumor microenvironment (TME) promotes tumor cell invasion and metastasis. An important step in the shift to a pro-cancerous microenvironment is the transformation of normal stromal fibroblasts to carcinoma-associated fibroblasts (CAFs). CAFs are present in a majority of solid tumors and can directly promote tumor cell motility via cytokine, chemokine and growth factor secretion into the TME. The exact effects that the TME has upon cytoskeletal regulation in motile tumor cells remain enigmatic. The conserved formin family of cytoskeleton regulating proteins plays an essential role in the assembly and/or bundling of unbranched actin filaments. Mammalian Diaphanous-related formin 2 (mDia2/DIAPH3/Drf3/Dia) assembles a dynamic F-actin cytoskeleton that underlies tumor cell migration and invasion. We therefore sought to understand whether CAF-derived chemokines impact breast tumor cell motility through modification of the formin-assembled F-actin cytoskeleton. In MDA-MB-231 cells, conditioned media (CM) from WS19T CAFs, a human breast tumor-adjacent CAF line, significantly and robustly increased wound closure and invasion relative to normal human mammary fibroblast (HMF)-CM. WS19T-CM also promoted proteasome-mediated mDia2 degradation in MDA-MB-231 cells relative to control HMF-CM and WS21T CAF-CM, a breast CAF cell line that failed to promote robust MDA-MB-231 migration. Cytokine array analysis of CM identified up-regulated secreted factors in WS19T relative to control WS21T CM. We identified CXCL12 as a CM factor influencing loss of mDia2 protein while increasing MDA-MB-231 cell migration. Our data suggest a mechanism whereby CAFs promote tumor cell migration and invasion through CXCL12 secretion to regulate the mDia2-directed cytoskeleton in breast tumor cells.

The good and bad faces of the CXCR4 chemokine receptor

Chemokines are chemotactic cytokines that promote cell migration and activation under homeostatic and inflammatory conditions. Chemokines bind to seven transmembrane-spanning receptors that are coupled to heterotrimeric guanine nucleotide-binding (G) proteins, which are the responsible for intracellularly transmitting the activating signals for cell migration. Hematopoiesis, vascular development, lymphoid organ morphogenesis, cardiogenesis and neural differentiation are amongst the processes involving chemokine function. In addition, immune cell trafficking from bone marrow to blood circulation, and from blood and lymph to lymphoid and inflamed tissues, is tightly regulated by chemokines both under physiological conditions and also in autoimmune diseases. Furthermore, chemokine binding to their receptors stimulate trafficking to and positioning of cancer cells into target tissues and organs during tumour dissemination. The CXCL12 chemokine (also known as stromal-cell derived factor-1α, SDF-1α) plays key roles in hematopoiesis and lymphoid tissue architecture, in cardiogenesis, vascular formation and neurogenesis, as well as in the trafficking of solid and hematological cancer cell types. CXCL12 binds to the CXCR4 receptor, a multi-facetted molecule which tightly mirrors CXCL12 functions in homeostasis and disease. This review addresses the important roles of the CXCR4-CXCL12 axis in homeostasis, specially focusing in hematopoiesis, as well as it provides a picture of CXCR4 as mediator of cancer cell spreading, and a view of the available CXCR4 antagonists in different cancer types.

Targeting the CXCR4/CXCL12 axis with the peptide antagonist E5 to inhibit breast tumor progression

Emerging evidence has demonstrated that stromal cell-derived factor 1 (SDF-1) and its cognate receptor CXCR4 have critical roles in tumorigenesis, angiogenesis and metastasis. In this study, we demonstrated the significant inhibitory effects of a novel chemically synthetic peptide (E5) on the CXCR4/CXCL12 axis in breast cancer both in vitro and in vivo. E5 was capable of specifically binding to the murine breast cancer cell line 4T1, remarkably inhibiting CXCL12- or stromal cell (MS-5)-induced migration, and adhesion and sensitizing 4T1 cells to multiple chemotherapeutic drugs. Furthermore, E5 combined with either paclitaxel or cyclophosphamide significantly inhibited tumor growth in a breast cancer model. Mechanistic studies implied that E5 can inhibit the expression of CXCR4 to block the CXCL12-mediated recruitment of endothelial progenitor cells and repress CXCR4 downstream of the Akt and Erk signaling pathway, which are involved in tumor angiogenesis and progression. Further pharmacokinetic evaluation suggested that E5 has an acceptable stability, with a half-life of 10 h in healthy mice. In conclusion, E5 demonstrates a promising anti-tumor effect and could be a potential chemotherapeutic sensitizer to improve current clinical breast cancer therapies.

CXCL13 is androgen-responsive and involved in androgen induced prostate cancer cell migration and invasion

Androgen receptor (AR) is a key transcription factor playing a critical role in prostate cancer (PCa) initiation and progression. However, the molecular mechanisms of AR action in prostate cancer are not very clear. CXCL13, known as B cell attracting chemokine1 (BCA-1), is a member of CXC chemokine family and relevant to cancer metastasis. This study shows that CXCL13 is an androgen-responsive gene and involved in AR-induced PCa cell migration and invasion. In clinical specimens, expression of CXCL13 in PCa tissues is markedly higher than that in adjacent normal tissues. In cultures, expression of CXCL13 is up-regulated by androgen-AR axis at both mRNA and protein levels. Furthermore, Chip-Seq assay identifies canonical androgen responsive elements (ARE) at CXCL13 enhancer and dual-luciferase reporter assays reveals that the ARE is highly responsive to androgen while mutations of the ARE abolish the reporter activity. Additional chromatin immunoprecipitation (ChIP) assays also identify that the ARE presents androgen responsiveness. In addition, CXCL13 promotes G2/M phase transition by increasing Cyclin B1 levels in PCa cells. Functional studies demonstrate that reducing endogenous CXCL13 expression in LNCaP cells largely weakens androgen-AR axis induced cell migration and invasion. Taken together, our study implicates for the first time that CXCL13 is an AR target gene and involved in AR-mediated cell migration and invasion in primary PCa.

Harnessing CXCR4 antagonists in stem cell mobilization, HIV infection, ischemic diseases, and oncology

CXCR4 antagonists (e.g., Plerixafor^TM ) have been successfully validated as stem cell mobilizers for peripheral blood stem cell transplantation. Applications of the CXCR4 antagonists have heralded the era of cell-based therapy and opened a potential therapeutic horizon for many unmet medical needs such as kidney injury, ischemic stroke, cancer, and myocardial infarction. In this review, we first introduce the central role of CXCR4 in diverse cellular signaling pathways and discuss its involvement in several disease progressions. We then highlight the molecular design and optimization strategies for targeting CXCR4 from a large number of case studies, concluding that polyamines are the preferred CXCR4-binding ligands compared to other structural options, presumably by mimicking the highly positively charged natural ligand CXCL12. These results could be further justified with computer-aided docking into the CXCR4 crystal structure wherein both major and minor subpockets of the binding cavity are considered functionally important. Finally, from the clinical point of view, CXCR4 antagonists could mobilize hematopoietic stem/progenitor cells with long-term repopulating capacity to the peripheral blood, promising to replace surgically obtained bone marrow cells as a preferred source for stem cell transplantation.

Emerging roles of the CXCL12/CXCR4 axis in pancreatic cancer progression and therapy

Chemokine networks regulate a variety of cellular, physiological, and immune processes. These normal functions can become appropriated by cancer cells to facilitate a more hospitable niche for aberrant cells by enhancing growth, proliferation, and metastasis. This is especially true in pancreatic cancer, where chemokine signaling is a vital component in the development of the supportive tumor microenvironment and the signaling between the cancer cells and surrounding stromal cells. Although expression patterns vary among cancer types, the chemokine receptor CXCR4 has been implicated in nearly every major malignancy and plays a prominent role in pancreatic cancer development and progression. This receptor, in conjunction with its primary chemokine ligand CXCL12, promotes pancreatic cancer development, invasion, and metastasis through the management of the tumor microenvironment via complex crosstalk with other pathways. Thus, CXCR4 likely contributes to the poor prognoses observed in patients afflicted with this malignancy. Recent exploration of combination therapies with CXCR4 antagonists have demonstrated improved outcomes, and abolishing the contribution of this pathway may prove crucial to effectively treat pancreatic cancer at both the primary tumor and metastases.

Galectin-1-driven upregulation of SDF-1 in pancreatic stellate cells promotes pancreatic cancer metastasis

Galectin-1, mainly expressed in activated pancreatic stellate cells (PSCs), is involved in many important cancer-related processes. However, very little is known how Galectin-1 modulates PSCs and subsequently impacts pancreatic cancer cells (PCCs). Our chemokine antibody array and in vitro studies demonstrates that Galectin-1 induces secretion of stromal cell-derived factor-1(SDF-1) in PSCs by activating NF-κB signaling. The secreted SDF-1 increases migration and invasion of PCCs. Knockdown of Galectin-1 and inhibitor-mediated blockade of SDF-1 as well as its ligand CXCR4 and NF-κB verifies the findings. In vivo experiment by knockdown of Galectin-1 in PSCs further demonstrates the conclusion. Collectively, the present studies demonstrate that Galectin-1-driven production of SDF-1 in PSCs through activation of NF-κB promotes metastasis in PDAC, offering a potential target in the treatment of pancreatic cancer.

Prognostic and predictive value of circulating tumor cells and CXCR4 expression as biomarkers for a CXCR4 peptide antagonist in combination with carboplatin-etoposide in small cell lung cancer: exploratory analysis of a phase II study

Background Circulating tumor cells (CTCs) and chemokine (C-X-C motif) receptor 4 (CXCR4) expression in CTCs and tumor tissue were evaluated as prognostic or predictive markers of CXCR4 peptide antagonist LY2510924 plus carboplatin-etoposide (CE) versus CE in extensive-stage disease small cell lung cancer (ED-SCLC). Methods This exploratory analysis of a phase II study evaluated CXCR4 expression in baseline tumor tissue and peripheral blood CTCs and in post-treatment CTCs. Optimum cutoff values were determined for CTC counts and CXCR4 expression in tumors and CTCs as predictors of survival outcome. Kaplan-Meier estimates and hazard ratios were used to determine biomarker prognostic and predictive values. Results There was weak positive correlation at baseline between CXCR4 expression in tumor tissue and CTCs. Optimum cutoff values were H-score ≥ 210 for CXCR4⁺ tumor, ≥7% CTCs with CXCR4 expression (CXCR4⁺ CTCs), and ≥6 CTCs/7.5 mL blood. Baseline H-score for CXCR4⁺ tumor was not prognostic of progression-free survival (PFS) or overall survival (OS). Baseline CXCR4⁺ CTCs ≥7% was prognostic of shorter PFS. CTCs ≥6 at baseline and cycle 2, day 1 were prognostic of shorter PFS and OS. None of the biomarkers at their respective optimum cutoffs was predictive of treatment response of LY2510924 plus CE versus CE. Conclusions In patients with ED-SCLC, baseline CXCR4 expression in tumor tissue was not prognostic of survival or predictive of LY2510924 treatment response. Baseline CXCR4⁺ CTCs ≥7% was prognostic of shorter PFS. CTC count ≥6 at baseline and after 1 cycle of treatment were prognostic of shorter PFS and OS.