An update on small molecules targeting CXCR4 as starting points for the development of anti-cancer therapeutics

trans-IV restriction: a new configuration for metal bis-cyclam complexes as potent CXCR4 inhibitors

The chemokine receptor CXCR4 is implicated in multiple diseases including inflammatory disorders, cancer growth and metastasis, and HIV/AIDS. CXCR4 targeting has been evaluated in treating cancer metastasis and therapy resistance. Cyclam derivatives, most notably AMD3100 (Plerixafor™), are a common motif in small molecule CXCR4 antagonists. However, AMD3100 has not been shown to be effective in cancer treatment as an individual agent. Configurational restriction and transition metal complex formation increases receptor binding affinity and residence time. In the present study, we have synthesized novel trans-IV locked cyclam-based CXCR4 inhibitors, a previously unexploited configuration, and demonstrated their higher affinity for CXCR4 binding and CXCL12-mediated signaling inhibition compared to AMD3100. These results pave the way for even more potent CXCR4 inhibitors that may provide significant efficacy in cancer therapy.

Structural dynamics of chemokine receptors

Membrane proteins such as G protein-coupled receptors (GPCRs) are involved in awide range of physiological and pathological cellular processes. Binding of extracellular signals to GPCRs, including hormones, neurotransmitters, peptides and proteins, can activate intracellular signaling cascades via G protein interaction. Chemokine receptors are key GPCRs implicated in cancers, immune responses, cell migration and inflammation. Specifically, the CCR5 and CXCR4 chemokine receptors serve as important therapeutic targets against Human Immunodeficiency virus (HIV) entry into human cells. Maraviroc and Vicriviroc, two clinically used HIV entry inhibitors, are antagonists of the CCR5 receptor. These drugs block HIV entry, but ultimately resistance develops, due to emergence of viruses that can utilize the CXCR4 co-receptor. Unfortunately, development of chemokine receptor antagonists as selective drugs of HIV infection has been greatly hindered as their target orthosteric site is conserved among different receptor subtypes. Accordingly, it is important to understand the structural dynamics of these receptors to develop more effective therapeutics. In this chapter, we describe the latest advances in studies of these two key chemokine receptors with respect to their structures, dynamics and function.

Discovery of Bis-Imidazoline Derivatives as New CXCR4 Ligands

The chemokine receptor CXCR4 and its ligand CXCL12 regulate leukocyte trafficking, homeostasis and functions and are potential therapeutic targets in many diseases such as HIV-1 infection and cancers. Here, we identified new CXCR4 ligands in the CERMN chemical library using a FRET-based high-throughput screening assay. These are bis-imidazoline compounds comprising two imidazole rings linked by an alkyl chain. The molecules displace CXCL12 binding with submicromolar potencies, similarly to AMD3100, the only marketed CXCR4 ligand. They also inhibit anti-CXCR4 mAb 12G5 binding, CXCL12-mediated chemotaxis and HIV-1 infection. Further studies with newly synthesized derivatives pointed out to a role of alkyl chain length on the bis-imidazoline properties, with molecules with an even number of carbons equal to 8, 10 or 12 being the most potent. Interestingly, these differ in the functions of CXCR4 that they influence. Site-directed mutagenesis and molecular docking predict that the alkyl chain folds in such a way that the two imidazole groups become lodged in the transmembrane binding cavity of CXCR4. Results also suggest that the alkyl chain length influences how the imidazole rings positions in the cavity. These results may provide a basis for the design of new CXCR4 antagonists targeting specific functions of the receptor.

Development and Evaluation of a Peptide Heterodimeric Tracer Targeting CXCR4 and Integrin αvβ3 for Pancreatic Cancer Imaging

Nowadays, pancreatic cancer is still a formidable disease to diagnose. The CXC chemokine receptor 4 (CXCR4) and integrin αvβ3 play important roles in tumor development, progression, invasion, and metastasis, which are overexpressed in many types of human cancers. In this study, we developed a heterodimeric tracer 68Ga-yG5-RGD targeting both CXCR4 and integrin αvβ3, and evaluated its feasibility and utility in PET imaging of pancreatic cancer. The 68Ga-yG5-RGD could accumulate in CXCR4/integrin αvβ3 positive BxPC3 tumors in a high concentration and was much higher than that of 68Ga-yG5 (p < 0.001) and 68Ga-RGD (p < 0.001). No increased uptake of 68Ga-yG5-RGD was found in MX-1 tumors (CXCR4/integrin αvβ3, negative). In addition, the uptake of 68Ga-yG5-RGD in BxPC3 was significantly blocked by excess amounts of AMD3100 (an FDA-approved CXCR4 antagonist) and/or unlabeled RGD (p < 0.001), confirming its dual-receptor targeting properties. The ex vivo biodistribution and immunohistochemical results were consistent with the in vivo imaging results. The dual-receptor targeting strategy achieved improved tumor-targeting efficiency and prolonged tumor retention in BxPC3 tumors, suggesting 68Ga-yG5-RGD is a promising tracer for the noninvasive detection of tumors that express either CXCR4 or integrin αvβ3 or both, and therefore may have good prospects for clinical translation.

Chemokines and NSCLC: Emerging role in prognosis, heterogeneity, and therapeutics

Lung cancer persists to contribute to one-quarter of cancer-associated deaths. Among the different histologies, non-small cell lung cancer (NSCLC) alone accounts for 85% of the cases. The development of therapies involving immune checkpoint inhibitors and angiogenesis inhibitors has increased patients' survival probability and reduced mortality rates. Developing targeted therapies against essential genetic alterations also translates to better treatment strategies. But the benefits still seem farfetched due to the development of drug resistance and refractory tumors. In this review, we have highlighted the interplay of different tumor microenvironment components, essentially discussing the chemokine families (CC, CXC, C, and CX3C) that regulate the tumor biology in NSCLC and promote tumor growth, metastasis, and associated heterogeneity. The development of therapeutics and prognostic markers is a complex and multipronged approach. However, some essential chemokines can act as critical players for being considered potential prognostic markers and therapeutic targets.

Macrophages Are a Double-Edged Sword: Molecular Crosstalk between Tumor-Associated Macrophages and Cancer Stem Cells

Cancer stem cells (CSCs) are a subset of highly tumorigenic cells in tumors. They have enhanced self-renewal properties, are usually chemo-radioresistant, and can promote tumor recurrence and metastasis. They can recruit macrophages into the tumor microenvironment and differentiate them into tumor-associated macrophages (TAMs). TAMs maintain CSC stemness and construct niches that are favorable for CSC survival. However, how CSCs and TAMs interact is not completely understood. An understanding on these mechanisms can provide additional targeting strategies for eliminating CSCs. In this review, we comprehensively summarize the reported mechanisms of crosstalk between CSCs and TAMs and update the related signaling pathways involved in tumor progression. In addition, we discuss potential therapies targeting CSC–TAM interaction, including targeting macrophage recruitment and polarization by CSCs and inhibiting the TAM-induced promotion of CSC stemness. This review also provides the perspective on the major challenge for developing potential therapeutic strategies to overcome CSC-TAM crosstalk.

A novel immune checkpoint siglec-15 antibody inhibits LUAD by modulating mφ polarization in TME

BACKGROUND

Siglec-15 (S15) is a type-I transmembrane protein and is considered a new candidate of immune checkpoint inhibitor for cancer immunotherapy.

METHODS

In the present study, we first constructed and characterized a chimeric S15-specific monoclonal antibody (S15-4E6A). Then, the antitumor effectiveness and modulatory role of S15-4E6A in macrophages (mφs) were explored in vitro and in vivo. Finally, the underlying mechanism by which S15mAb inhibits LUAD was preliminarily explored.

RESULTS

The results demonstrated the successful construction of S15-4E6A, and S15-4E6A exerted an efficacious tumor-inhibitory effect on LUAD cells and xenografts. S15-4E6A could promote M1-mφ polarization while inhibiting M2-mφ polarization, both in vitro and in vivo.

CONCLUSIONS

S15-based immunotherapy that functions by modulating mφ polarization may be a promising strategy for the treatment of S15-positive LUAD.

Nanomaterials targeting tumor associated macrophages for cancer immunotherapy

Tumor-associated macrophages (TAMs) play an important role in regulating tumor growth, invasion and metastasis, and constitute approximately 50% of tumor mass. TAMs can exist in two different subtypes, M1-polarized phenotype (pro-inflammatory and immunostimulatory) and M2-polarized phenotype (immunosuppressive myeloid cells). M2 macrophages can suppress CD8⁺ T cells to support tumor survival. A number of biological strategies aimed at engineering macrophages to modulate the tumor immune microenvironment remain at the forefront of cancer research. Here, we review the different therapeutic strategies that have been developed based on nanotechnology to modulate macrophage functions, such as inhibition of macrophage recruitment to tumor, depletion of M2-polarized macrophages, reprograming of M2-polarized macrophages to M1-polarized macrophages, and blocking of the CD47-signal-regulatory protein alpha (CD47-SIRPα) pathway. Furthermore, we also discuss how to image TAMs with nanoparticles to unravel novel treatment options and observe their responses to the various therapies. Overall, macrophage-mediated immune modulation based on nanotechnology can be further investigated to be effectively developed as an immunoadjuvant therapy against different cancers.

Predictive and Prognostic Biomarkers for Lung Cancer Bone Metastasis and Their Therapeutic Value

Lung cancer is the leading cause of cancer-related death worldwide. Bone metastasis, which usually accompanies severe skeletal-related events, is the most common site for tumor distant dissemination and detected in more than one-third of patients with advanced lung cancer. Biopsy and imaging play critical roles in the diagnosis of bone metastasis; however, these approaches are characterized by evident limitations. Recently, studies regarding potential biomarkers in the serum, urine, and tumor tissue, were performed to predict the bone metastases and prognosis in patients with lung cancer. In this review, we summarize the findings of recent clinical research studies on biomarkers detected in samples obtained from patients with lung cancer bone metastasis. These markers include the following: (1) bone resorption-associated markers, such as N-terminal telopeptide (NTx)/C-terminal telopeptide (CTx), C-terminal telopeptide of type I collagen (CTx-I), tartrate-resistant acid phosphatase isoform 5b (TRACP-5b), pyridinoline (PYD), and parathyroid hormone related peptide (PTHrP); (2) bone formation-associated markers, including total serum alkaline phosphatase (ALP)/bone specific alkaline phosphatase(BAP), osteopontin (OP), osteocalcin (OS), amino-terminal extension propeptide of type I procollagen/carboxy-terminal extension propeptide of type I procollagen (PICP/PINP); (3) signaling markers, including epidermal growth factor receptor/Kirsten rat sarcoma/anaplastic lymphoma kinase (EGFR/KRAS/ALK), receptor activator of nuclear factor κB ligand/receptor activator of nuclear factor κB/osteoprotegerin (RANKL/RANK/OPG), C-X-C motif chemokine ligand 12/C-X-C motif chemokine receptor 4 (CXCL12/CXCR4), complement component 5a receptor (C5AR); and (4) other potential markers, such as calcium sensing receptor (CASR), bone sialoprotein (BSP), bone morphogenetic protein 2 (BMP2), cytokeratin 19 fragment/carcinoembryonic antigen (CYFRA/CEA), tissue factor, cell-free DNA, long non-coding RNA, and microRNA. The prognostic value of these markers is also investigated. Furthermore, we listed some clinical trials targeting hotspot biomarkers in advanced lung cancer referring for their therapeutic effects.

A narrative review of tumor-associated macrophages in lung cancer: regulation of macrophage polarization and therapeutic implications

Lung cancer is the deadliest malignancy worldwide. An inflammatory microenvironment is a key factor contributing to lung tumor progression. Tumor-Associated Macrophages (TAMs) are prominent components of the cancer immune microenvironment with diverse supportive and inhibitory effects on growth, progression, and metastasis of lung tumors. Two main macrophage phenotypes with different functions have been identified. They include inflammatory or classically activated (M1) and anti-inflammatory or alternatively activated (M2) macrophages. The contrasting functions of TAMs in relation to lung neoplasm progression stem from the presence of TAMs with varying tumor-promoting or anti-tumor activities. This wide spectrum of functions is governed by a network of cytokines and chemokines, cell-cell interactions, and signaling pathways. TAMs are promising therapeutic targets for non-small cell lung cancer (NSCLC) treatment. There are several strategies for TAM targeting and utilizing them for therapeutic purposes including limiting monocyte recruitment and localization through various pathways such as CCL2-CCR2, CSF1-CSF1R, and CXCL12-CXCR4, targeting the activation of TAMs, genetic and epigenetic reprogramming of TAMs to antitumor phenotype, and utilizing TAMs as the carrier for anti-cancer drugs. In this review, we will outline the role of macrophages in the lung cancer initiation and progression, pathways regulating their function in lung cancer microenvironment as well as the role of these immune cells in the development of future therapeutic strategies.

Application of a small molecule inhibitor screen approach to identify CXCR4 downstream signaling pathways that promote a mesenchymal and fulvestrant-resistant phenotype in breast cancer cells

Chemokine receptor 4 (CXCR4) and its ligand stromal-derived factor 1 (SDF-1) have well-characterized functions in cancer metastasis; however, the specific mechanisms through which CXCR4 promotes a metastatic and drug-resistant phenotype remain widely unknown. The aim of the present study was to demonstrate the application of a phenotypic screening approach using a small molecule inhibitor library to identify potential CXCR4-mediated signaling pathways. The present study demonstrated a new application of the Published Kinase Inhibitor Set (PKIS), a library of small molecule inhibitors from diverse chemotype series with varying levels of selectivity, in a phenotypic medium-throughput screen to identify potential mechanisms to pursue. Crystal violet staining and brightfield microscopy were employed to evaluate relative cell survival and changes to cell morphology in the screens. ‘Hits’ or lead active compounds in the first screen were PKIS inhibitors that reversed mesenchymal morphologies in CXCR4-activated breast cancer cells without the COOH-terminal domain (MCF-7-CXCR4-ΔCTD) and in the phenotypically mesenchymal triple-negative breast cancer cells (MDA-MB-231, BT-549 and MDA-MB-157), used as positive controls. In a following screen, the phenotypic and cell viability screen was used with a positive control that was both morphologically mesenchymal and had acquired fulvestrant resistance. Compounds within the same chemotype series were identified that exhibited biological activity in the screens, the ‘active’ inhibitors, were compared with inactive compounds. Relative kinase activity was obtained using published datasets to discover candidate kinase targets responsible for CXCR4 activity. MAP4K4 and MINK reversed both the mesenchymal and drug-resistant phenotypes, NEK9 and DYRK2 only reversed the mesenchymal morphology, and kinases, including ROS, LCK, HCK and LTK, altered the fulvestrant-resistant phenotype. Oligoarray experiments revealed pathways affected in CXCR4-activated cells, and these pathways were compared with the present screening approach to validate our screening tool. The oligoarray approach identified the integrin-mediated, ephrin B-related, RhoA, RAC1 and ErbB signaling pathways to be upregulated in MCF-7-CXCR4-ΔCTD cells, with ephrin B signaling also identified in the PKIS phenotypic screen. The present screening tool may be used to discover potential mechanisms of targeted signaling pathways in solid cancers.

Design, synthesis, and evaluation of pyrrolidine based CXCR4 antagonists with in vivo anti-tumor metastatic activity

The chemokine receptor CXCR4 has been proposed as a drug target based on its important functions in HIV infection, inflammation/autoimmune diseases and cancer metastasis. Herein we report the design, synthesis and evaluation of novel CXCR4 antagonists based on a pyrrolidine scaffold. The structural exploration/optimization identified numerous potent CXCR4 antagonists, represented by compound 46, which displayed potent binding affinity to CXCR4 receptor (IC₅₀ = 79 nM competitively displacing fluorescent 12G5 antibody) and inhibited CXCL12 induced cytosolic calcium flux (IC₅₀ = 0.25 nM). Moreover, in a transwell invasion assay, compound 46 significantly mitigated CXCL12/CXCR4 mediated cell migration. Compound 46 exhibited good physicochemical properties (MW 367, logD_7.4 1.12, pKa 8.2) and excellent in vitro safety profiles (e.g., hERG patch clamp IC₅₀ > 30 μM and minimal CYP isozyme inhibition). Importantly, 46 displayed much improved metabolic stability in human and rat liver microsomes. Lastly, 46 demonstrated marked efficacy in a cancer metastasis model in mice. These results strongly support 46 as a prototypical lead for the development of promising CXCR4 antagonists as clinical candidates.

Design, Synthesis, and Characterization of Novel CXCR4 Antagonists Featuring Cyclic Amines

Chemokine receptor CXCR4 and its natural ligand CXCL12 (also known as stromal cell-derived factor-1, or SDF-1) regulate a broad range of physiological functions. Dysregulation of the CXCL12/CXCR4 axis is involved in numerous pathological conditions such as HIV infection, inflammation and cancer. Herein, we report the design, synthesis, and characterization of novel CXCR4 antagonists based on cyclic amine scaffolds. Compound 24 was identified as a potent CXCR4 receptor antagonist (competitive inhibition of 12G5 binding, IC₅₀ =24 nM; functional inhibition of CXCL12-induced cytosolic calcium increase, IC₅₀ =0.1 nM). In addition, compound 24 potently inhibited cell migration in CXCR4/CXCL12-mediated chemotaxis in a matrigel invasion assay. The absolute configuration of compound 24 was elucidated by X-ray crystallography.

CXCR4 antagonist AMD3100 (plerixafor): From an impurity to a therapeutic agent

AMD3100 (plerixafor), a CXCR4 antagonist, has opened a variety of avenues for potential therapeutic approaches in different refractory diseases. The CXCL12/CXCR4 axis and its signaling pathways are involved in diverse disorders including HIV-1 infection, tumor development, non-Hodgkin lymphoma, multiple myeloma, WHIM Syndrome, and so on. The mechanisms of action of AMD3100 may relate to mobilizing hematopoietic stem cells, blocking infection of X4 HIV-1, increasing circulating neutrophils, lymphocytes and monocytes, reducing myeloid-derived suppressor cells, and enhancing cytotoxic T-cell infiltration in tumors. Here, we first revisit the pharmacological discovery of AMD3100. We then review monotherapy of AMD3100 and combination use of AMD3100 with other agents in various diseases. Among those, we highlight the perspective of AMD3100 as an immunomodulator to regulate immune responses particularly in the tumor microenvironment and synergize with other therapeutics. All the pre-clinical studies support the clinical testing of the monotherapy and combination therapies with AMD3100 and further development for use in humans.

Pathway and mechanism of drug binding to chemokine receptors revealed by accelerated molecular simulations

Background: Chemokine GPCRs play key roles in biology and medicine. Particularly, CXCR4 promotes cancer metastasis and facilitate HIV entry into host cells. Plerixafor (PLX) is a CXCR4 drug, but the pathway and binding site of PLX in CXCR4 remain unknown. Results & methodology: We have performed molecular docking and all-atom simulations using Gaussian accelerated molecular dynamics (GaMD), which are consistent with previous mutation experiments, suggesting that PLX binds to the orthosteric site of CXCR4 as an antagonist. The GaMD simulations further revealed an intermediate allosteric binding site at the extracellular mouth of CXCR4. Conclusion: The newly identified allosteric site can be targeted for novel drug design targeting CXCR4 and other chemokine receptors.

Discovery of novel aminopiperidinyl amide CXCR4 modulators through virtual screening and rational drug design

The C-X-C chemokine receptor type 4 (CXCR4) is a potential therapeutic target for HIV infection, metastatic cancer, and inflammatory autoimmune diseases. In this study, we screened the ZINC chemical database for novel CXCR4 modulators through a series of in silico guided processes. After evaluating the screened compounds for their binding affinities to CXCR4 and inhibitory activities against the chemoattractant CXCL12, we identified a hit compound (ZINC 72372983) showing 100 nM affinity and 69% chemotaxis inhibition at the same concentration (100 nM). To increase the potency of our hit compound, we explored the protein-ligand interactions at an atomic level using molecular dynamics simulation which enabled us to design and synthesize a novel compound (Z7R) with nanomolar affinity (IC₅₀ = 1.25 nM) and improved chemotaxis inhibition (78.5%). Z7R displays promising anti-inflammatory activity (50%) in a mouse edema model by blocking CXCR4-expressed leukocytes, being supported by our immunohistochemistry study.

A benzenesulfonamide derivative as a novel PET radioligand for CXCR4

CXCR4 is involved in various diseases such as inflammation, tumor growth, and cancer metastasis through the interaction with its natural endogenous ligand, chemokine CXCL12. In an effort to develop imaging probes for CXCR4, we developed a novel small molecule CXCR4-targeted PET agent (compound 5) by combining our established benzenesulfonamide scaffold with a labeling component by virtue of click chemistry. 5 shows nanomolar affinity (IC50 = 6.9 nM) against a known CXCR4 antagonist (TN14003) and inhibits more than 65% chemotaxis at 10 nM in vitro assays. Radiofluorinated compound 5 ([18F]5) demonstrates a competitive cellular uptake against CXCL12 in a dose-dependent manner. Further, microPET images of [18F]5 exhibits preferential accumulation of radioactivity in the lesions of λ-carrageenan-induced paw edema, human head and neck cancer orthotopic xenograft, and metastatic lung cancer of each mouse model.

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.

Optimal design, anti-tumour efficacy and tolerability of anti-CXCR4 antibody drug conjugates

Antibody-drug conjugates (ADCs) are promising therapies for haematological cancers. Historically, their therapeutic benefit is due to ADC targeting of lineage-restricted antigens. The C-X-C motif chemokine receptor 4 (CXCR4) is attractive for targeted therapy of haematological cancers, given its expression in multiple tumour types and role in cancer "homing" to bone marrow. However, CXCR4 is also expressed in haematopoietic cells and other normal tissues, raising safety challenges to the development of anti-CXCR4 ADCs for cancer treatment. Here, we designed the first anti-CXCR4 ADC with favourable therapeutic index, effective in xenografts of haematopoietic cancers resistant to standard of care and anti-CXCR4 antibodies. We screened multiple ADC configurations, by varying type of linker-payload, drug-to-antibody ratio (DAR), affinity and Fc format. The optimal ADC bears a non-cleavable linker, auristatin as payload at DAR = 4 and a low affinity antibody with effector-reduced Fc. Contrary to other drugs targeting CXCR4, anti-CXCR4 ADCs effectively eliminated cancer cells as monotherapy, while minimizing leucocytosis. The optimal ADC selectively eliminated CXCR4⁺ cancer cells in solid tumours, but showed limited toxicity to normal CXCR4⁺ tissues, sparing haematopoietic stem cells and progenitors. Our work provides proof-of-concept that through empirical ADC design, it is possible to target proteins with broad normal tissue expression.

CCR5/CXCR4 Dual Antagonism for the Improvement of HIV Infection Therapy

HIV entry in the host cell requires the interaction with the CD4 membrane receptor, and depends on the activation of one or both co-receptors CCR5 and CXCR4. Former selective co-receptor antagonists, acting at early stages of infection, are able to impair the receptor functions, preventing the viral spread toward AIDS. Due to the capability of HIV to develop resistance by switching from CCR5 to CXCR4, dual co-receptor antagonists could represent the next generation of AIDS prophylaxis drugs. We herein present a survey on relevant results published in the last few years on compounds acting simultaneously on both co-receptors, potentially useful as preventing agents or in combination with classical anti-retroviral drugs based therapy.

Developing Nanoceria-Based pH-Dependent Cancer-Directed Drug Delivery System for Retinoblastoma

Development of a single combinatorial nano-platform technology to target cancer cells has been an unprecedented reality in boosting synergistic anti-tumor activities and in reducing off-target effects. We have designed a novel anti-tumor delivery system using a chemotherapy drug and a tumor target molecule covalently linked to cerium oxide nanoparticles (nanoceria). Nanoceria have a unique redox activity in that they possess antioxidant activity at physiological pH but have an intrinsic oxidase activity at acidic pH. Our system is integrated with (1) extracellular pH responsive functionality, (2) tumor cell targetable (CXC chemokine receptor 4, CXCR4 receptor specific) antagonist, (3) reactive oxygen species (ROS) inducible nanoceria, and (4) chemotherapeutic doxorubicin (DOX). These combinatorial nanoparticles (AMD-GCCNPs-DOX) are not only sensitive to the extracellular acidic pH conditions and targeted tumor cells but can also instantaneously induce ROS and release DOX intracellularly to enhance the chemotherapeutic activity in retinoblastoma cells (WERI-Rb-1 and Y79) and in xenograft (Y79/GFP-luc grafted) and genetic p107s (Rb Lox/lox , p107 +/- , p130 -/- ) orthotopic mice models. Together we introduce a lucidly engineered combinatorial nano-construct that offers a viable and simple strategy for delivering a cocktail of therapeutics into tumor cells under acidosis, exhibiting a promising new future for clinical therapeutic opportunities.

Structure-based exploration and pharmacological evaluation of N-substituted piperidin-4-yl-methanamine CXCR4 chemokine receptor antagonists

Using the available structural information of the chemokine receptor CXCR4, we present hit finding and hit exploration studies that make use of virtual fragment screening, design, synthesis and structure-activity relationship (SAR) studies. Fragment 2 was identified as virtual screening hit and used as a starting point for the exploration of 31 N-substituted piperidin-4-yl-methanamine derivatives to investigate and improve the interactions with the CXCR4 binding site. Additionally, subtle structural ligand changes lead to distinct interactions with CXCR4 resulting in a full to partial displacement of CXCL12 binding and competitive and/or non-competitive antagonism. Three-dimensional quantitative structure-activity relationship (3D-QSAR) and binding model studies were used to identify important hydrophobic interactions that determine binding affinity and indicate key ligand-receptor interactions.

CXCR4 Based Therapeutics for Non-Small Cell Lung Cancer (NSCLC)

Lung cancer is the second most common malignancy. Unfortunately, despite advances in multimodality therapeutics for the disease, the overall five-year survival rate among newly diagnosed lung cancer patients remains in the range region of 15%. In addition, although immune checkpoint inhibitors are increasingly being incorporated into lung cancer treatment protocols, the proportion of patients that respond to these agents remains low and the duration of response is often short. Therefore, novel methodologies to enhance the efficacy of immunotherapy in lung cancer are highly desirable. Chemokines are small chemotactic cytokines that interact with their 7 transmembrane G-protein⁻coupled receptors, to guide immune cell trafficking in the body under both physiologic and pathologic conditions. Tumor cells highjack a small repertoire of the chemokine/chemokine receptor system and utilize it in a manner that benefits local tumor growth and distant spread. The chemokine receptor, CXCR4 is expressed in over 30 types of malignant tumors and, through interaction with its ligand CXCL12, was shown exert pleotropic pro-tumorigenic effects. In this review, the pathologic roles that CXCL12/CXCR4 play in lung cancer propagation are presented. Furthermore, the challenges and potential benefits of incorporating drugs that target CXCL12/CXCR4 into immune-based lung cancer therapeutic protocols are discussed.

Development of Mimokines, chemokine N terminus-based CXCR4 inhibitors optimized by phage display and rational design

The chemokine receptor CXCR4 (C-X-C chemokine receptor type 4 also known as fusin or CD184 (cluster of differentiation 184)) is implicated in various biological and pathological processes of the hematopoietic and immune systems. CXCR4 is also one of the major coreceptors for HIV-1 entry into target cells and is overexpressed in many cancers, supporting cell survival, proliferation, and migration. CXCR4 is thus an extremely relevant drug target. Among the different strategies to block CXCR4, chemokine-derived peptide inhibitors hold great therapeutic potential. In this study, we used the N-terminus of vCCL2/vMIPII, a viral CXCR4 antagonist chemokine, as a scaffold motif to engineer and select CXCR4 peptide inhibitors, called Mimokines, which imitate the chemokine-binding mode but display an enhanced receptor affinity, antiviral properties, and receptor selectivity. We first engineered a Mimokine phage displayed library based on the first 21 residues of vCCL2, in which cysteine 11 and 12 were fully randomized and screened it against purified CXCR4 stabilized in liposomes. We identified Mimokines displaying up to 4-fold higher affinity for CXCR4 when compared to the reference peptide and fully protected MT-4 cells against HIV-1 infection. These selected Mimokines were then subjected to dimerization, D-amino acid, and aza-β3-amino acid substitution to further enhance their potency and selectivity. Optimized Mimokines exhibited up to 120-fold enhanced CXCR4 binding (range of 20 nM) and more than 200-fold improved antiviral properties (≤ 1 μM) compared to the parental Mimokines. Interestingly, these optimized Mimokines also showed up to 25-fold weaker affinity for ACKR3/CXCR7 and may therefore serve as lead compounds for further development of more selective CXCR4 peptide inhibitors and probes.

A mouse model for evaluation of efficacy and concomitant toxicity of anti-human CXCR4 therapeutics

The development of therapeutic monoclonal antibodies through mouse immunization often originates drug candidates that are not cross-reactive to the mouse ortholog. In such cases, and particularly in oncology, drug efficacy studies are performed on human tumor xenografts or with "surrogate" anti-mouse ortholog antibodies if targeting tumor host cells. Safety assessment of drug candidate(s) is performed at a later development stage in healthy non-human primates. While the latter remains necessary before a drug advances into human subjects, it precludes evaluation of safety in disease conditions and drug de-risking during early development. Therefore, mouse models that allow concomitant evaluation of drug efficacy and safety are highly desirable. The C-X-C motif chemokine receptor 4 (CXCR4) is an attractive target for tumor-targeted and immuno-oncology therapeutics, with multiple mouse immunization-derived antibodies undergoing clinical trials. Given the pleiotropic role of CXCR4 in cancer biology, we anticipate continuous interest in this target, particularly in the testing of therapeutic combinations for immuno-oncology. Here, we describe the generation and validation of the first mouse knock-in of the whole coding region of human CXCR4. Homozygous human CXCR4 knock-in (hereafter designated as HuCXCR4KI) mice were viable and outwardly healthy, reproduced normally and nursed their young. The expression pattern of human CXCR4 in this model was similar to that of CXCR4 expression in normal human tissues. The human CXCR4 knock-in gene was expressed as a biologically active protein, thereby allowing normal animal development and adequate"homing" of leukocytes to the bone marrow. To further validate our model, we used an in vivo functional assay of leukocyte mobilization from bone marrow to peripheral blood by blocking CXCR4 signaling. Both an anti-human CXCR4 -specific blocking antibody and the small molecule CXCR4 inhibitor AMD3100 induced increased leukocyte counts in peripheral blood, whereas an anti-mouse CXCR4 -specific blocking antibody had no effect. This new mouse model is useful to evaluate efficacy and safety of anti-human CXCR4 -specific drugs as single agents or in combination therapies, particularly in the oncology, immuno-oncology, wound healing and chronic inflammation therapeutic areas.

The Correlation Between Serum Chemokines and Clinical Outcome in Patients with Advanced Biliary Tract Cancer

BACKGROUND

Biliary tract cancers (BTCs) are known to have a dismal prognosis. A number of chemokines play important roles in the progress of BTCs. However, the serum levels of chemokines in BTCs have not yet been explored.

METHODS

The sera of healthy donors (n = 8) and patients with BTCs who were enrolled in second line sunitinib trials (n = 27) were collected. The concentrations of three kinds of chemokines (CXCL5, CXCL8 and CXCL12) were measured using ELISA assay. The median concentrations of chemokines were compared between healthy donors and BTC patients and the role of chemokines as a prognostic biomarker was examined.

RESULTS

BTC patients generally had higher serum levels of CXCL5 and CXCL12 compared to healthy donors. Patients with cholangiocarcinoma showed significantly higher levels of serum CXCL12 than patients with gallbladder cancer. In survival analysis, only CXCL12 level showed a prognostic impact on overall survival (median OS: 6.9 vs. 0.9 months in low CXCL12 vs. high CXCL12, respectively; P = .008). High CXCL5 levels were also correlated with poor survival without statistical insignificance (median OS: 6.2 vs. 2.0 months in low CXCL5 vs. high CXCL5, respectively; P = .070).

CONCLUSIONS

There was a significant difference in OS according to the level of CXCL12, suggesting that serum CXCL12 levels may be a useful surrogate marker for clinical outcome in advanced BTCs.

Design, synthesis, and structure-activity-relationship of a novel series of CXCR4 antagonists

The important roles of the CXCL12/CXCR4 axis in numerous pathogenic pathways involving HIV infection and cancer metastasis make the CXCR4 receptor an attractive target for the development of therapeutic agents. Through scaffold hybridization of a few known CXCR4 antagonists, a series of novel aminopyrimidine derivatives was developed. Compound 3 from this new scaffold demonstrates excellent binding affinity with CXCR4 receptor (IC₅₀ = 54 nM) and inhibits CXCL12 induced cytosolic calcium increase (IC₅₀ = 2.3 nM). Furthermore, compound 3 possesses good physicochemical properties (MW 353, clogP 2.0, PSA 48, pKa 6.7) and exhibits minimal hERG and CYP isozyme (e.g. 3A4, 2D6) inhibition. Collectively, these results strongly support further optimization of this novel scaffold to develop better CXCR4 antagonists.

Substituted tetrahydroisoquinolines: synthesis, characterization, antitumor activity and other biological properties

This work deals with the molecular design, synthesis and biological activity of a series of tetrahydro[1,4]dioxanisoquinolines and dimethoxyisoquinoline analogues. This study describes the synthesis strategy of these potential antitumor compounds, their multi-step synthesis and their optimization. A series of tetrahydroisoquinolines was synthesized and their cytotoxicity evaluated. Some of these tetrahydroisoquinolines showed promising KRas inhibition, antiangiogenesis activity and antiosteoporosis properties. Molecular modeling studies showed that compound 12 bind in the p1 pocket of the KRas protein making interactions with the hydrophobic residues Leu56, Tyr64, Tyr71 and Thr74 and hydrogen bonds with residues Glu37 and Asp38.