Macrophage CD5L is a target for cancer immunotherapy

BACKGROUND

Reprogramming of immunosuppressive tumor-associated macrophages (TAMs) presents an attractive therapeutic strategy in cancer. The aim of this study was to explore the role of macrophage CD5L protein in TAM activity and assess its potential as a therapeutic target.

METHODS

Monoclonal antibodies (mAbs) against recombinant CD5L were raised by subcutaneous immunization of BALB/c mice. Peripheral blood monocytes were isolated from healthy donors and stimulated with IFN/LPS, IL4, IL10, and conditioned medium (CM) from different cancer cell lines in the presence of anti-CD5L mAb or controls. Subsequently, phenotypic markers, including CD5L, were quantified by flow cytometry, IF and RT-qPCR. Macrophage CD5L protein expression was studied in 55 human papillary lung adenocarcinoma (PAC) samples by IHC and IF. Anti-CD5L mAb and isotype control were administered intraperitoneally into a syngeneic Lewis Lung Carcinoma mouse model and tumor growth was measured. Tumor microenvironment (TME) changes were determined by flow cytometry, IHC, IF, Luminex, RNAseq and RT-qPCR.

FINDINGS

Cancer cell lines CM induced an immunosuppressive phenotype (increase in CD163, CD206, MERTK, VEGF and CD5L) in cultured macrophages. Accordingly, high TAM expression of CD5L in PAC was associated with poor patient outcome (Log-rank (Mantel-Cox) test p = 0.02). We raised a new anti-CD5L mAb that blocked the immunosuppressive phenotype of macrophages in vitro. Its administration in vivo inhibited tumor progression of lung cancer by altering the intratumoral myeloid cell population profile and CD4⁺ T-cell exhaustion phenotype, thereby significantly modifying the TME and increasing the inflammatory milieu.

INTERPRETATION

CD5L protein plays a key function in modulating the activity of macrophages and their interactions within the TME, which supports its role as a therapeutic target in cancer immunotherapy.

FUNDING

For a full list of funding bodies, please see the Acknowledgements.

Co-targeting CDK2 and CDK4/6 overcomes resistance to aromatase and CDK4/6 inhibitors in ER+ breast cancer

Resistance to aromatase inhibitor (AI) treatment and combined CDK4/6 inhibitor (CDK4/6i) and endocrine therapy (ET) are crucial clinical challenges in treating estrogen receptor-positive (ER+) breast cancer. Understanding the resistance mechanisms and identifying reliable predictive biomarkers and novel treatment combinations to overcome resistance are urgently needed. Herein, we show that upregulation of CDK6, p-CDK2, and/or cyclin E1 is associated with adaptation and resistance to AI-monotherapy and combined CDK4/6i and ET in ER+ advanced breast cancer. Importantly, co-targeting CDK2 and CDK4/6 with ET synergistically impairs cellular growth, induces cell cycle arrest and apoptosis, and delays progression in AI-resistant and combined CDK4/6i and fulvestrant-resistant cell models and in an AI-resistant autocrine breast tumor in a postmenopausal xenograft model. Analysis of CDK6, p-CDK2, and/or cyclin E1 expression as a combined biomarker in metastatic lesions of ER+ advanced breast cancer patients treated with AI-monotherapy or combined CDK4/6i and ET revealed a correlation between high biomarker expression and shorter progression-free survival (PFS), and the biomarker combination was an independent prognostic factor in both patients cohorts. Our study supports the clinical development of therapeutic strategies co-targeting ER, CDK4/6 and CDK2 following progression on AI-monotherapy or combined CDK4/6i and ET to improve survival of patients exhibiting high tumor levels of CDK6, p-CDK2, and/or cyclin E1.

Co-targeting CDK4/6 and AKT with endocrine therapy prevents progression in CDK4/6 inhibitor and endocrine therapy-resistant breast cancer

CDK4/6 inhibitors (CDK4/6i) combined with endocrine therapy have shown impressive efficacy in estrogen receptor-positive advanced breast cancer. However, most patients will eventually experience disease progression on this combination, underscoring the need for effective subsequent treatments or better initial therapies. Here, we show that triple inhibition with fulvestrant, CDK4/6i and AKT inhibitor (AKTi) durably impairs growth of breast cancer cells, prevents progression and reduces metastasis of tumor xenografts resistant to CDK4/6i-fulvestrant combination or fulvestrant alone. Importantly, switching from combined fulvestrant and CDK4/6i upon resistance to dual combination with AKTi and fulvestrant does not prevent tumor progression. Furthermore, triple combination with AKTi significantly inhibits growth of patient-derived xenografts resistant to combined CDK4/6i and fulvestrant. Finally, high phospho-AKT levels in metastasis of breast cancer patients treated with a combination of CDK4/6i and endocrine therapy correlates with shorter progression-free survival. Our findings support the clinical development of ER, CDK4/6 and AKT co-targeting strategies following progression on CDK4/6i and endocrine therapy combination, and in tumors exhibiting high phospho-AKT levels, which are associated with worse clinical outcome.

Non-covalent Encapsulation of siRNA with Cell-Penetrating Peptides

SiRNAs may act as selective and potent therapeutics, but poor deliverability in vivo is a limitation. Among the recently proposed vectors, cell-penetrating peptides (CPPs), also referred as protein transduction domains (PTDs), allow siRNA stabilization and increased cellular uptake. This chapter aims to guide scientists in the preparation and characterization of CPP-siRNA complexes, particularly the evaluation of novel CPPs variants for siRNA encapsulation and delivery. Herein, we present a collection of methods to determine CPP-siRNA interaction, encapsulation, stability, conformation, transfection, and silencing efficiency.

Simple FRET Electrophoresis Method for Precise and Dynamic Evaluation of Serum siRNA Stability

Small interfering RNAs (siRNAs) are potent therapeutic molecules, but despite recent progress, their administration in vivo remains challenging due to their low stability in the bloodstream. Thus, techniques for investigating the stability of siRNA are fundamental for the development of efficient siRNA delivery systems. We designed a simple FRET electrophoresis method to dynamically evaluate serum siRNA stability in parallel with its interaction with the serum components. Each strand of the siRNA was labeled with the fluorophore carboxyfluorescein (FAM) at the 5'-end and the quencher carboxytetramethylrhodamine (TAMRA) at the 3'-end. After incubation in serum, molecular stability was proportional to the FRET efficiency that could be quantified in-gel by ImageJ analysis. Compared to the usual gel-shift and other plate-based FRET assays, this method is more sensitive and allows investigation of the stability of serum siRNA and siRNA-based nanoparticles, as well as the extrapolation of degradation kinetics in parallel with interaction analysis.

One-step FPLC-size-exclusion chromatography procedure for purification of rDMBT1 6 kb with increased biological activity

Deleted in Malignant Brain Tumor 1 (DMBT1, alias SAG or gp340) is a pattern recognition receptor involved in immune defense, cell polarization, differentiation and regeneration. To investigate the role of the protein in physiological and pathological processes, the protein has often been isolated from saliva or produced in vitro and purified by a multistep affinity purification procedure using bacteria, followed by FPLC. Here, we compared a simple, one-step FPLC-SEC protocol for purification of recombinant DMBT1 6 kb, with that of the standard bacteria affinity purification-based protocol. Our data suggest that our FPLC-SEC protocol yields DMBT1 in a more native conformation.

Human DMBT1-Derived Cell-Penetrating Peptides for Intracellular siRNA Delivery

Small interfering RNA (siRNA) is a promising molecule for gene therapy, but its therapeutic administration remains problematic. Among the recently proposed vectors, cell-penetrating peptides show great promise in in vivo trials for siRNA delivery. Human protein DMBT1 (deleted in malignant brain tumor 1) is a pattern recognition molecule that interacts with polyanions and recognizes and aggregates bacteria. Taking advantage of these properties, we investigated whether specific synthetic DMBT1-derived peptides could be used to formulate nanoparticles for siRNA administration. Using an electrophoretic mobility shift assay and UV spectra, we identified two DMBT1 peptides that could encapsulate the siRNA with a self- and co-assembly mechanism. The complexes were stable for at least 2 hr in the presence of either fetal bovine serum (FBS) or RNase A, with peptide-dependent time span protection. ζ-potential, circular dichroism, dynamic light scattering, and transmission electron microscopy revealed negatively charged nanoparticles with an average diameter of 10–800 nm, depending on the reaction conditions, and a spherical or rice-shaped morphology, depending on the peptide and β-helix conformation. We successfully transfected human MCF7 cells with fluorescein isothiocyanate (FITC)-DMBT1-peptide-Cy3-siRNA complexes. Finally, DMBT1 peptides encapsulating an siRNA targeting a fluorescent reporter gene showed efficient gene silencing in MCF7-recombinant cells. These results lay the foundation for a new research line to exploit DMBT1-peptide nanocomplexes for therapeutic siRNA delivery.