Discovery of novel small molecule orally bioavailable C-X-C chemokine receptor 4 antagonists that are potent inhibitors of T-tropic (X4) HIV-1 replication

Development and therapeutic perspectives of CXCR4 antagonists for disease therapy

Chemokine receptor 4 (CXCR4) is a subtype receptor protein of the GPCR family with a seven-transmembrane structure widely distributed in human tissues. CXCR4 is involved in diseases (e.g., HIV-1 infection), cancer proliferation and metastasis, inflammation signaling pathways, and leukemia, making it a promising drug target. Clinical trials on CXCR4 antagonists mainly focused on peptides and antibodies, with a few small molecule compounds, such as AMD11070 (2) and MSX-122 (3), showing promise in cancer treatment. This perspective discusses the structure-activity relationship (SAR) of CXCR4 and its role in diseases, mainly focusing on the SAR of CXCR4 antagonists. It also explores the standard structural features and target interactions of CXCR4 binding in different disease categories. Furthermore, it investigates various modification strategies to propose potential improvements in the effectiveness of CXCR4 drugs.

Radiosynthesis and preclinical evaluation of a 68Ga-labeled tetrahydroisoquinoline-based ligand for PET imaging of C-X-C chemokine receptor type 4 in an animal model of glioblastoma

BACKGROUND

This study aimed to develop a novel positron emission tomography (PET) tracer, [68Ga]Ga-TD-01, for CXCR4 imaging. To achieve this goal, the molecular scaffold of TIQ15 was tuned by conjugation with the DOTA chelator to make it suitable for 68Ga radiolabeling.

METHODS

A bifunctional chelator was prepared by conjugating the amine group of TIQ15 with p-NCS-Bz-DOTA, yielding TD-01, with a high yield (68.92%). TD-01 was then radiolabeled with 68Ga using 0.1 M ammonium acetate at 60 °C for 10 min. A 1-h dynamic small animal PET/MRI study of the labeled compound in GL261-luc2 tumor-bearing mice was performed, and brain tumor uptake was assessed. Blocking studies involved pre-administration of TIQ15 (10 mg/kg) 10 min before the PET procedure started.

RESULTS

[68Ga]Ga-TD-01 exhibited a radiochemical yield (RCY) of 36.33 ± 1.50% (EOS), with a radiochemical purity > 99% and a molar activity of 55.79 ± 1.96 GBq/µmol (EOS). The radiotracer showed in vitro stability in PBS and human plasma for over 4 h. Biodistribution studies in healthy animals revealed favorable kinetics for subsequent PET pharmacokinetic modeling with low uptake in the brain and moderate uptake in lungs, intestines and spleen. Elimination could be assigned to a renal-hepatic pathway as showed by high uptake in kidneys, liver, and urinary bladder. Importantly, [68Ga]Ga-TD-01 uptake in glioblastoma (GBM)-bearing mice significantly decreased upon competition with TIQ15, with a baseline tumor-to-background ratios > 2.5 (20 min p.i.), indicating high specificity.

CONCLUSION

The newly developed CXCR4 PET tracer, [68Ga]Ga-TD-01, exhibited a high binding inhibition for CXCR4, excellent in vitro stability, and favorable pharmacokinetics, suggesting that the compound is a promising candidate for full in vivo characterization of CXCR4 expression in GBM, with potential for further development as a tool in cancer diagnosis.

A promising strategy of surface-modified nanoparticles targeting CXCR4 for precision cancer therapy

Nanoparticle (NP) functionalization with specific ligands enhances targeted cancer therapy and imaging by promoting receptor recognition and improving cellular uptake. This review focuses on recent research exploring the interaction between cancer cell-expressed chemokine receptor 4 (CXCR4) and ligand-conjugated NPs, utilising small molecules, peptides, and antibodies. Active NP targeting has shown improved tumour targeting and reduced toxicity, enabling precision therapy and diagnosis. However, challenges persist in the clinical translation of targeted NPs due to issues with biological response, tumour accumulation, and maintaining NP quality at an industrial scale. Biological and intratumoral barriers further hinder efficient NP accumulation in tumours, hampering translatability. To address these challenges, the academic community is refocusing efforts on understanding NP biological fate and establishing robust preclinical models. Future studies should investigate NP-body interactions, develop computational models, and identify optimal preclinical models. Establishing central NP research databases and fostering collaboration across disciplines is crucial to expediting clinical translation. Overcoming these hurdles will unlock the transformative potential of CXCR4-ligand-NP conjugates in revolutionising cancer treatment.

Multiplex Detection of Fluorescent Chemokine Binding to CXC Chemokine Receptors by NanoBRET

NanoLuc-mediated bioluminescence resonance energy transfer (NanoBRET) has gained popularity for its ability to homogenously measure ligand binding to G protein-coupled receptors (GPCRs), including the subfamily of chemokine receptors. These receptors, such as ACKR3, CXCR4, CXCR3, play a crucial role in the regulation of the immune system, are associated with inflammatory diseases and cancer, and are seen as promising drug targets. The aim of this study was to optimize NanoBRET-based ligand binding to NLuc-ACKR3 and NLuc-CXCR4 using different fluorescently labeled chemokine CXCL12 analogs and their use in a multiplex NanoBRET binding assay of two chemokine receptors at the same time. The four fluorescent CXCL12 analogs (CXCL12-AZD488, -AZD546, -AZD594, -AZD647) showed high-affinity saturable binding to both NLuc-ACKR3 and NLuc-CXCR4, with relatively low levels of non-specific binding. Additionally, the binding of all AZDye-labeled CXCL12s to Nluc receptors was inhibited by pharmacologically relevant unlabeled chemokines and small molecules. The NanoBRET binding assay for CXCL10-AZD488 binding to Nluc-CXCR3 was also successfully established and successfully employed for the simultaneous measurement of the binding of unlabeled small molecules to NLuc-CXCR3 and NLuc-CXCR4. In conclusion, multiplexing the NanoBRET-based competition binding assay is a promising tool for testing unlabeled (small) molecules against multiple GPCRs simultaneously.

Hematopoietic stem cell collection for sickle cell disease gene therapy

PURPOSE OF REVIEW

Gene therapy for sickle cell disease (SCD) is advancing rapidly, with two transformative products recently approved by the US Food and Drug Administration and numerous others under study. All current gene therapy protocols require ex vivo modification of autologous hematopoietic stem cells (HSCs). However, several SCD-related problems impair HSC collection, including a stressed and damaged bone marrow, potential cytotoxicity by the major therapeutic drug hydroxyurea, and inability to use granulocyte colony stimulating factor, which can precipitate severe vaso-occlusive events.

RECENT FINDINGS

Peripheral blood mobilization of HSCs using the CXCR4 antagonist plerixafor followed by apheresis collection was recently shown to be safe and effective for most SCD patients and is the current strategy for mobilizing HSCs. However, exceptionally large numbers of HSCs are required to manufacture an adequate cellular product, responses to plerixafor are variable, and most patients require multiple mobilization cycles, increasing the risk for adverse events. For some, gene therapy is prohibited by the failure to obtain adequate numbers of HSCs.

SUMMARY

Here we review the current knowledge on HSC collection from individuals with SCD and potential improvements that may enhance the safety, efficacy, and availability of gene therapy for this disorder.

Using alternative SMILES representations to identify novel functional analogues in chemical similarity vector searches

Chemical similarity searches are a widely used family of in silico methods for identifying pharmaceutical leads. These methods historically relied on structure-based comparisons to compute similarity. Here, we use a chemical language model to create a vector-based chemical search. We extend previous implementations by creating a prompt engineering strategy that utilizes two different chemical string representation algorithms: one for the query and the other for the database. We explore this method by reviewing search results from nine queries with diverse targets. We find that the method identifies molecules with similar patent-derived functionality to the query, as determined by our validated LLM-assisted patent summarization pipeline. Further, many of these functionally similar molecules have different structures and scaffolds from the query, making them unlikely to be found with traditional chemical similarity searches. This method may serve as a new tool for the discovery of novel molecular structural classes that achieve target functionality.

Rethinking the chemokine cascade in brain metastasis: Preventive and therapeutic implications

Brain metastasis (BrM) is one of the major causes of death in cancer patients and is associated with an estimated 10-40 % of total cancer cases. The survival rate of brain metastatic patients has not improved due to intratumor heterogeneity, the survival adaptations of brain homing metastatic cells, and the lack of understanding of underlying molecular mechanisms that limit the availability of effective therapies. The heterogeneous population of immune cells and tumor-initiating cells or cancer stem cells in the tumor microenvironment (TME) release various factors, such as chemokines that upon binding to their cognate receptors enhance tumor growth at primary sites and help tumor cells metastasize to the brain. Furthermore, brain metastatic sites have unique heterogeneous microenvironment that fuels cancer cells in establishing BrM. This review explores the crosstalk of chemokines with the heterogeneous TME during the progression of BrM and recognizes potential therapeutic approaches. We also discuss and summarize different targeted, immunotherapeutic, chemotherapeutic, and combinatorial strategies (with chemo-/immune- or targeted-therapies) to attenuate chemokines mediated BrM.

Design, synthesis, and biological evaluation of tetrahydroquinoline amphiphiles as membrane-targeting antimicrobials against pathogenic bacteria and fungi

The rising prevalence of drug-resistant pathogens is one of the biggest threats to human health. The development of new antibiotics that can overcome drug resistance is in urgent need. Herein, we designed and synthesized a series of amphiphilic tetrahydroquinoline derivatives as small-molecule-based antimicrobial peptidomimetics. Two lead compounds 36 and 52 which contained the tetrahydroquinoline core, hydrophobic alkyl chains (n-nonyl or isoprenyl group), different spacer lengths (n = 4 or 8), and cationic guanidine moiety, showed poor hemolytic activity, low cytotoxicity, and potent broad-spectrum antimicrobial activity against Gram-positive and Gram-negative bacteria, as well as fungi. The further biological evaluation revealed that compounds 36 and 52 can kill bacteria and fungi rapidly via membrane-targeting action and avoid drug resistance development. More importantly, compounds 36 and 52 exhibited similarly potent in vivo antimicrobial activities in a murine corneal infection caused by Staphylococcus aureus ATCC29213 or Pseudomonas aeruginosa ATCC9027, as compared to vancomycin or gatifloxacin. These results suggest that compounds 36 and 52 have great potential as new broad-spectrum antimicrobial agents to combat microbial resistance.

GPCR Inhibition in Treating Lymphoma

G protein-coupled receptors (GPCRs) are important classes of cell surface receptors involved in multiple physiological functions. Aberrant expression, upregulation, and mutation of GPCR signaling pathways are frequent in many types of cancers, promoting hyperproliferation, angiogenesis, and metastasis. Recent studies showed that alterations of GPCRs are involved in different lymphoma types. Herein, we review the synthetic strategies to obtain GPCR inhibitors, focusing on CXCR4 inhibitors which represent most of the GPCR inhibitors available in the market or under preclinical investigations for these diseases.

Synthesis and Evaluation of Novel Tetrahydronaphthyridine CXCR4 Antagonists with Improved Drug-like Profiles

Our first-generation CXCR4 antagonist TIQ15 was rationally modified to improve drug-like properties. Introducing a nitrogen atom into the aromatic portion of the tetrahydroisoquinoline ring led to several heterocyclic variants including the 5,6,7,8-tetrahydro-1,6-naphthyridine series, greatly reducing the inhibition of the CYP 2D6 enzyme. Compound 12a demonstrated the best overall properties after profiling a series of isomeric tetrahydronaphthyridine analogues in a battery of biochemical assays including CXCR4 antagonism, CYP 2D6 inhibition, metabolic stability, and permeability. The butyl amine side chain of 12a was substituted with various lipophilic groups to improve the permeability. These efforts culminated in the discovery of compound 30 as a potent CXCR4 antagonist (IC50 = 24 nM) with diminished CYP 2D6 activity, improved PAMPA permeability (309 nm/s), potent inhibition of human immunodeficiency virus entry (IC50 = 7 nM), a cleaner off-target in vitro safety profile, lower human ether a-go-go-related gene channel activity, and higher oral bioavailability in mice (% FPO = 27) compared to AMD11070 and TIQ15.

Ligand-Based Modeling of CXC Chemokine Receptor 4 and Identification of Inhibitors of Novel Chemotypes as Potential Leads towards New Anti-COVID-19 Treatments

BACKGROUND

Chemokines are involved in several human diseases and in different stages of COVID-19 infection and play critical role in the pathophysiology of the associated acute respiratory disease syndrome, a major complication leading to death among COVID-19 patients. In particular, CXC chemokine receptor 4 (CXCR4) was found to be highly expressed in COVID-19 patients.

METHODS

We herein describe a computational workflow based on combining pharmacophore modeling and QSAR analysis towards the discovery of novel CXCR4 inhibitors. Subsequent virtual screening identified two promising CXCR4 inhibitors from the National Cancer Institute (NCI) list of compounds. The most active hit showed in vitro IC50 value of 24.4 µM.

RESULTS AND CONCLUSION

These results prove the validity of the QSAR model and associated pharmacophore models as means to screen virtual databases towards new CXCR4 inhibitors as leads for the development of new COVID-19 therapies.

Pd(II)-Catalyzed Synthesis of Alicyclic[b]-Fused Pyridines via C(sp2)-H Activation of α,β-Unsaturated N-Acetyl Hydrazones with Vinyl Azides

A new synthetic protocol for alicyclic[b]-fused pyridines with complete regioselectivity from α,β-unsaturated N-acetyl hydrazones and vinyl azides via Pd(II)-catalyzed C-H activation/cyclization/aromatization strategy has been described. A series of five- to eight-membered alicyclic[b]-fused pyridines were prepared in a one-step manner with wide substrate scope and good functional group tolerance.

Amino-Heterocycle Tetrahydroisoquinoline CXCR4 Antagonists with Improved ADME Profiles via Late-Stage Buchwald Couplings

This work surveys a variety of diamino-heterocycles as an isosteric replacement for the piperazine substructure of our previously disclosed piperarinyl-tetrahydroisoquinoline containing CXCR4 antagonists. A late-stage Buchwald coupling route was developed for rapid access to final compounds from commercial building blocks. Among 13 analogs in this study, compound 31 embodying an aza-piperazine linkage was found to have the best overall profile with potent CXCR4 inhibitory activity and favorable in vitro absorption, distribution, metabolism, and excretion (ADME) properties. An analysis of the calculated physiochemical parameters (ROF, cLogD) and the experimental ADME attributes of the analogs lead to the selection of 31 for pharmacokinetic studies in mice. Compared with the clinical compound AMD11070, compound 31 has no CYP450 3A4 or 2D6 inhibition, higher metabolic stability and PAMPA permeability, greatly improved physiochemical parameters, and superior oral bioavailability (%F = 24). A binding rationale for 31 within CXCR4 was elucidated from docking and molecular simulation studies.

A "Two-Birds-One-Stone" Approach toward the Design of Bifunctional Human Immunodeficiency Virus Type 1 Entry Inhibitors Targeting the CCR5 Coreceptor and gp41 N-Terminal Heptad Repeat Region

Previous studies have reported the stepwise nature of human immunodeficiency virus type 1 (HIV-1) entry and the pivotal role of coreceptor CCR5 and the gp41 N-terminal heptad repeat (NHR) region in this event. With this in mind, we herein report a dual-targeted drug compound featuring bifunctional entry inhibitors, consisting of a piperidine-4-carboxamide-based CCR5 antagonist, TAK-220, and a gp41 NHR-targeting fusion-inhibitory peptide, C34. The resultant chimeras were constructed by linking both pharmacophores with a polyethylene glycol spacer. One chimera, CP12TAK, exhibited exceptionally potent antiviral activity, about 40- and 306-fold over that of its parent inhibitors, C34 and TAK-220, respectively. In addition to R5-tropic viruses, CP12TAK also strongly inhibited infection of X4-tropic HIV-1 strains. These data are promising for the further development of CP12TAK as a new anti-HIV-1 drug. Results show that this strategy could be extended to the design of therapies against infection of other enveloped viruses.

HIV-1 Entry and Membrane Fusion Inhibitors

HIV-1 (human immunodeficiency virus type 1) infection begins with the attachment of the virion to a host cell by its envelope glycoprotein (Env), which subsequently induces fusion of viral and cell membranes to allow viral entry. Upon binding to primary receptor CD4 and coreceptor (e.g., chemokine receptor CCR5 or CXCR4), Env undergoes large conformational changes and unleashes its fusogenic potential to drive the membrane fusion. The structural biology of HIV-1 Env and its complexes with the cellular receptors not only has advanced our knowledge of the molecular mechanism of how HIV-1 enters the host cells but also provided a structural basis for the rational design of fusion inhibitors as potential antiviral therapeutics. In this review, we summarize our latest understanding of the HIV-1 membrane fusion process and discuss related therapeutic strategies to block viral entry.

CXCR4 in Waldenström's Macroglobulinema: chances and challenges

It is one of the major aims in cancer research to improve our understanding of the underlying mechanisms which initiate and maintain tumor growth and to translate these findings into novel clinical diagnostic and therapeutic concepts with the ultimate goal to improve patient care. One of the greater success stories in this respect has been Waldenström's Macroglobulinemia (WM), which is an incurable B-cell neoplasm characterized by serum monoclonal immunoglobulin M (IgM) and clonal lymphoplasmacytic cells infiltrating the bone marrow. Recent years have succeeded to describe the molecular landscape of WM in detail, highlighting two recurrently mutated genes, the MYD88 and the CXCR4 genes: MYD88 with an almost constant and recurrent point mutation present in over 90% of patients and CXCR4 with over 40 different mutations in the coding region affecting up to 40% of patients. Intriguingly, both mutations are activating mutations leading in the case of CXCR4 to an indelible activation and perpetual signaling of the chemokine receptor. These data have shed light on the essential role of CXCR4 in this disease and have paved the way to use these findings for predicting treatment response to the Bruton tyrosine kinase (BTK) inhibitor ibrutinib and novel therapeutic approaches in WM, which might be transferable to other related CXCR4 positive diseases. Well known for its central role in cancer progression and distribution, CXCR4 is highlighted in this review with regard to its biology, prognostic and predictive relevance and therapeutic implications in WM.

Biased agonism at chemokine receptors

In the human chemokine system, interactions between the approximately 50 known endogenous chemokine ligands and 20 known chemokine receptors (CKRs) regulate a wide range of cellular functions and biological processes including immune cell activation and homeostasis, development, angiogenesis, and neuromodulation. CKRs are a family of G protein-coupled receptors (GPCR), which represent the most common and versatile class of receptors in the human genome and the targets of approximately one third of all Food and Drug Administration-approved drugs. Chemokines and CKRs bind with significant promiscuity, as most CKRs can be activated by multiple chemokines and most chemokines can activate multiple CKRs. While these ligand-receptor interactions were previously regarded as redundant, it is now appreciated that many chemokine:CKR interactions display biased agonism, the phenomenon in which different ligands binding to the same receptor signal through different pathways with different efficacies, leading to distinct biological effects. Notably, these biased responses can be modulated through changes in ligand, receptor, and or the specific cellular context (system). In this review, we explore the biochemical mechanisms, functional consequences, and therapeutic potential of biased agonism in the chemokine system. An enhanced understanding of biased agonism in the chemokine system may prove transformative in the understanding of the mechanisms and consequences of biased signaling across all GPCR subtypes and aid in the development of biased pharmaceuticals with increased therapeutic efficacy and safer side effect profiles.

The CXCL12/CXCR4/ACKR3 Axis in the Tumor Microenvironment: Signaling, Crosstalk, and Therapeutic Targeting

Elevated expression of the chemokine receptors CXCR4 and ACKR3 and of their cognate ligand CXCL12 is detected in a wide range of tumors and the tumor microenvironment (TME). Yet, the molecular mechanisms by which the CXCL12/CXCR4/ACKR3 axis contributes to the pathogenesis are complex and not fully understood. To dissect the role of this axis in cancer, we discuss its ability to impinge on canonical and less conventional signaling networks in different cancer cell types; its bidirectional crosstalk, notably with receptor tyrosine kinase (RTK) and other factors present in the TME; and the infiltration of immune cells that supporttumor progression. We discuss current and emerging avenues that target the CXCL12/CXCR4/ACKR3 axis. Coordinately targeting both RTKs and CXCR4/ACKR3 and/or CXCL12 is an attractive approach to consider in multitargeted cancer therapies. In addition, inhibiting infiltrating immune cells or reactivating the immune system along with modulating the CXCL12/CXCR4/ACKR3 axis in the TME has therapeutic promise.

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.

Design, synthesis, and evaluation of novel CXCR4 antagonists based on an aminoquinoline template

The chemokine receptor CXCR4 has been explored as a drug target due to its involvement in pathological conditions such as HIV infection and cancer metastasis. Here we report the structure-activity relationship study of novel CXCR4 antagonists based on an aminoquinoline template. This template is devoid of the chiral center in the classical tetrahydroquinoline (THQ) ring moiety and therefore can be easily synthesized. A number of potent CXCR4 antagonists were identified, exemplified by compound 3, which demonstrated excellent binding affinity with CXCR4 receptor (IC₅₀ = 57 nM) and inhibited CXCL12 induced cytosolic calcium increase (IC₅₀ = 0.24 nM). Furthermore, compound 3 potently inhibited CXLC12/CXCR4 mediated cell migration in a transwell invasion assay. The simplified synthetic approach combined with good physicochemical properties (e.g. MW 362, clogP 2.1, PSA 48, pKa 7.0 for compound 3) demonstrate the potential of this aminoquinoline template as a novel scaffold to develop CXCR4 antagonists.

Synthetic Activators of Cell Migration Designed by Constructive Machine Learning

Constructive machine learning aims to create examples from its learned domain which are likely to exhibit similar properties. Here, a recurrent neural network was trained with the chemical structures of known cell-migration modulators. This machine learning model was used to generate new molecules that mimic the training compounds. Two top-scoring designs were synthesized, and tested for functional activity in a phenotypic spheroid cell migration assay. These computationally generated small molecules significantly increased the migration of medulloblastoma cells. The results further corroborate the applicability of constructive machine learning to the de novo design of druglike molecules with desired properties.

Nucleic acid testing and molecular characterization of HIV infections

Significant advances have been made in the molecular assays used for the detection of human immunodeficiency virus (HIV), which are crucial in preventing HIV transmission and monitoring disease progression. Molecular assays for HIV diagnosis have now reached a high degree of specificity, sensitivity and reproducibility, and have less operator involvement to minimize risk of contamination. Furthermore, analyses have been developed for the characterization of host gene polymorphisms and host responses to better identify and monitor HIV-1 infections in the clinic. Currently, molecular technologies including HIV quantitative and qualitative assays are mainly based on the polymerase chain reaction (PCR), transcription-mediated amplification (TMA), nucleic acid sequence-based amplification (NASBA), and branched chain (b) DNA methods and widely used for HIV detection and characterization, such as blood screening, point-of-care testing (POCT), pediatric diagnosis, acute HIV infection (AHI), HIV drug resistance testing, antiretroviral (AR) susceptibility testing, host genome polymorphism testing, and host response analysis. This review summarizes the development and the potential utility of molecular assays used to detect and characterize HIV infections.

Discovery of N-Alkyl Piperazine Side Chain Based CXCR4 Antagonists with Improved Drug-like Properties

A novel series of CXCR4 antagonists with piperidinyl and piperazinyl alkylamine side chains designed as butyl amine replacements are described. Several of these compounds showed similar activity to the parent compound TIQ-15 (5) in a SDF-1 induced calcium flux assay. Preliminary structure-activity relationship investigations led us to identify a series containing N-propyl piperazine side chain analogs exemplified by 16 with improved off-target effects as measured in a muscarinic acetylcholine receptor (mAChR) calcium flux assay and in a limited drug safety panel screen. Further efforts to explore SAR and optimize drug properties led to the identification of the N'-ethyl-N-propyl-piperazine tetrahydroisoquinoline derivative 44 and the N-propyl-piperazine benzimidazole compound 37, which gave the best overall profiles with no mAChR or CYP450 inhibition, good permeability in PAMPA assays, and metabolic stability in human liver microsomes.

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.

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.

Discovery of Tetrahydroisoquinoline-Containing CXCR4 Antagonists with Improved in Vitro ADMET Properties

CXCR4 is a seven-transmembrane receptor expressed by hematopoietic stem cells and progeny, as well as by ≥48 different cancers types. CXCL12, the only chemokine ligand of CXCR4, is secreted within the tumor microenvironment, providing sanctuary for CXCR4⁺ tumor cells from immune surveillance and chemotherapeutic elimination by (1) stimulating prosurvival signaling and (2) recruiting CXCR4⁺ immunosuppressive leukocytes. Additionally, distant CXCL12-rich niches attract and support CXCR4⁺ metastatic growths. Accordingly, CXCR4 antagonists can potentially obstruct CXCR4-mediated prosurvival signaling, recondition the CXCR4⁺ leukocyte infiltrate from immunosuppressive to immunoreactive, and inhibit CXCR4⁺ cancer cell metastasis. Current small molecule CXCR4 antagonists suffer from poor oral bioavailability and off-target liabilities. Herein, we report a series of novel tetrahydroisoquinoline-containing CXCR4 antagonists designed to improve intestinal absorption and off-target profiles. Structure-activity relationships regarding CXCR4 potency, intestinal permeability, metabolic stability, and cytochrome P450 inhibition are presented.

Synthesis and SAR of 1,2,3,4-Tetrahydroisoquinoline-Based CXCR4 Antagonists

CXCR4 is the most common chemokine receptor expressed on the surface of many cancer cell types. In comparison to normal cells, cancer cells overexpress CXCR4, which correlates with cancer cell metastasis, angiogenesis, and tumor growth. CXCR4 antagonists can potentially diminish the viability of cancer cells by interfering with CXCL12-mediated pro-survival signaling and by inhibiting chemotaxis. Herein, we describe a series of CXCR4 antagonists that are derived from (S)-5,6,7,8-tetrahydroquinolin-8-amine that has prevailed in the literature. This series removes the rigidity and chirality of the tetrahydroquinoline providing 2-(aminomethyl)pyridine analogs, which are more readily accessible and exhibit improved liver microsomal stability. The medicinal chemistry strategy and biological properties are described.

Pharmacophore modeling, atom based 3D-QSAR and Molecular docking approaches to screen C-X-C chemokine receptor type 4 antagonists as microbicides for human immunodeficiency virus-1

The C-X-C chemokine receptor type 4 receptor CXCR4 which acts as a co-receptor for human immunodeficiency virus-1, expressed in the later stages of infection is considered as an attractive and new target for drug design. Microbicides acting as co-receptor blockers are highly significant as these drugs block HIV lifecycle at early stage itself. The urgent need for a safe and effective microbicide urges to explore new CXCR4 antagonists which could be developed as microbicides. The pharmacophore based 3D-QSAR models and docking models were developed using PHASE and GLIDE modules of Schrodinger software. Three-dimensional quantitative structure-activity relationships (3D-QSAR) studies and pharmacophore modelling was carried out on a dataset of 114 CXCR4 antagonists with the intention of exploring entry inhibitors with better therapeutic potential. A training set of 43 compounds was used to create 3D-QSAR models and they were validated using a test set of 28 compounds. CXCR4 antagonists with good inhibitory activity could be designed and structurally modified based upon the QSAR model developed with necessary pharmacophore features. The results revealed that the common pharmacophore hypothesis ADHPR.1 was used for 3D-QSAR model development and the most active compound, CXCR4 antagonist no.44 which is a imidazopyridine-tetrahydro-8-quinolinamine derivative interacted with the CXCR4 receptor residue ASP 97 by the formation of a hydrogen bond. Also, the docking studies were carried out for the dataset for analyzing the binding conformation of CXCR4 and 114 antagonists. The results obtained from the 3D-QSAR studies and docking simulation can be used for designing new and potent CXCR4 antagonists. The compound identified from this study can be taken up further for validation by in vitro/in vivo studies.

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.

Improved Synthesis of MDL 73811 - a Potent AdoMetDC Inhibitor and Anti-Trypanosomal Compound

An improved synthesis of MDL 73811 - a potent AdoMetDC (S-adenosylmethionine decarboxylease) inhibitor and anti-trypanosomal compound with in vivo activity has been completed in four steps from commercially available 2',3'-O-isopropylideneadenosine. Utilization of Mitsunobu chemistry was crucial for the reliable and scalable introduction of the 5'-methylamine moiety, which was problematic using traditional activation/displacement chemistry as previously reported. All reactions in this synthesis were run on gram-scale resulting in a five-fold increase in yield over the original synthesis.

Enhancement of the CXCL12/CXCR4 axis due to acquisition of gemcitabine resistance in pancreatic cancer: effect of CXCR4 antagonists

BACKGROUND

The CXCL12-CXCR4 signaling axis in malignant tumor biology has increased in importance, and these peptides are implicated in tumor growth, invasion and metastasis. The aim of our study was to examine the important role of the axis in pancreatic cancer (PaCa) cells' relationship with stromal cells in gemcitabine-resistant (GEM-R) tumors and to confirm the effectiveness of CXCR4 antagonists for the treatment of GEM-R PaCa cells.

METHODS

We established two GEM-R PaCa cell lines using MIA PaCa-2 and AsPC-1 cells. The expression of CXCR4 mRNA in PaCa cells and the expression of CXCL12 mRNA in fibroblasts were examined by reverse transcription polymerase chain reaction (RT-PCR). The expression of CXCR4 protein in PaCa cells was examined by immunosorbent assay (ELISA) and immunocytochemistry. Using Matrigel invasion assays and animal studies, we then examined the effects of two CXCR4 antagonists, AMD11070 and KRH3955, on the invasiveness and tumorigenicity of GEM-R PaCa cells stimulated by CXCL12.

RESULTS

We found that the expression of CXCR4 in GEM-R PaCa cells was significantly enhanced by GEM but not in normal GEM-sensitive (GEM-S) PaCa cells. In RT-PCR and ELISA assays, the production and secretion of CXCL12 from fibroblasts was significantly enhanced by co-culturing with GEM-R PaCa cells treated with GEM. In Matrigel invasion assays, the invasiveness of GEM-R PaCa cells treated with GEM was significantly activated by fibroblast-derived CXCL12 and was significantly inhibited by CXCR4 antagonists, AMD11070 and KRH3955. In vivo, the tumorigenicity of GEM-R PaCa cells was activated by GEM, and it was significantly inhibited by the addition with CXCR4 antagonists.

CONCLUSIONS

Our findings demonstrate that the CXCL12-CXCR4 signaling axis plays an important role in PaCa cells' resistance to GEM. CXCR4 expression was significantly enhanced by the exposure to GEM in GEM-R PaCa cells but not in GEM-S PaCa cells. Furthermore, CXCR4 antagonists can inhibit the growth and invasion of GEM-R PaCa cells. These agents may be useful as second-line chemotherapy for GEM-R PaCa in the future.

Targeting chemokine receptor CXCR4 for treatment of HIV-1 infection, tumor progression, and metastasis

The chemokine receptor CXCR4 is required for the entry of human immunodeficiency virus type 1 (HIV-1) into target cells and for the development and dissemination of various types of cancers, including gastrointestinal, cutaneous, head and neck, pulmonary, gynecological, genitourinary, neurological, and hematological malignancies. The T-cell (T)-tropic HIV-1 strains use CXCR4 as the entry coreceptor; consequently, multiple CXCR4 antagonistic inhibitors have been developed for the treatment of acquired immune deficiency syndrome (AIDS). However, other potential applications of CXCR4 antagonists have become apparent since its discovery in 1996. In fact, increasing evidence demonstrates that epithelial and hematopoietic tumor cells exploit the interaction between CXCR4 and its natural ligand, stromal cellderived factor (SDF)-1α, which normally regulates leukocyte migration. The CXCR4 and/or SDF-1α expression patterns in tumor cells also determine the sites of metastatic spread. In addition, the activation of CXCR4 by SDF-1α promotes invasion and proliferation of tumor cells, enhances tumor-associated neoangiogenesis, and assists in the degradation of the extracellular matrix and basement membrane. As such, the evaluation of CXCR4 and/or SDF-1α expression levels has a significant prognostic value in various types of malignancies. Several therapeutic challenges remain to be overcome before the use of CXCR4 inhibitors can be translated into clinical practice, but promising preclinical data demonstrate that CXCR4 antagonists can mobilize tumor cells from their protective microenvironments, interfere with their metastatic and tumorigenic potentials, and/or make tumor cells more susceptible to chemotherapy.

Impact of a CXCL12/CXCR4 Antagonist in Bleomycin (BLM) Induced Pulmonary Fibrosis and Carbon Tetrachloride (CCl4) Induced Hepatic Fibrosis in Mice

Modulation of chemokine CXCL12 and its receptor CXCR4 has been implicated in attenuation of bleomycin (BLM)-induced pulmonary fibrosis and carbon tetrachloride (CCl4)-induced hepatic injury. In pulmonary fibrosis, published reports suggest that collagen production in the injured lung is derived from fibrocytes recruited from the circulation in response to release of pulmonary CXCL12. Conversely, in hepatic fibrosis, resident hepatic stellate cells (HSC), the key cell type in progression of fibrosis, upregulate CXCR4 expression in response to activation. Further, CXCL12 induces HSC proliferation and subsequent production of collagen I. In the current study, we evaluated AMD070, an orally bioavailable inhibitor of CXCL12/CXCR4 in alleviating BLM-induced pulmonary and CCl4-induced hepatic fibrosis in mice. Similar to other CXCR4 antagonists, treatment with AMD070 significantly increased leukocyte mobilization. However, in these two models of fibrosis, AMD070 had a negligible impact on extracellular matrix deposition. Interestingly, our results indicated that CXCL12/CXCR4 signaling has a role in improving mortality associated with BLM induced pulmonary injury, likely through dampening an early inflammatory response and/or vascular leakage. Together, these findings indicate that the CXCL12-CXCR4 signaling axis is not an effective target for reducing fibrosis.

Discovery of non-peptide small molecular CXCR4 antagonists as anti-HIV agents: Recent advances and future opportunities

CXCR4 plays vital roles in HIV-1 life cycle for it's essential in mediating the interaction of host and virus and completing the entry process in the lifecycle of HIV-1 infection. Compared with some traditional targets, CXCR4 provides a novel and less mutated drug target in the battle against AIDS. Its antagonists have no cross resistance with other antagonists. Great achievements have been made recent years and a number of small molecular CXCR4 antagonists with diversity scaffolds have been discovered. In this review, recent advances in the discovery of CXCR4 antagonists with special attentions on their evolution and structure-activity relationships of representative CXCR4 antagonists are described. Moreover, some classical medicinal chemistry strategies and novel methodologies are also introduced.