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

Targeted therapies are regarded as promising approaches to increase 5-year survival rate of head and neck squamous cell carcinoma (HNSCC) patients. For the selection of carcinoma-specific peptides membrane proteome of HNO97 tumor cells fractionated by the ProteomeLab PF2D system and corresponding HNO97 cells were deployed for an alternating biopanning using a sunflower trypsin inhibitor1-based phage display (SFTI8Ph) library. Stability, binding properties and affinity of novel candidates were assessed using radio-HPLC, binding experiments and surface plasmon resonance assay (SPR), respectively. Subsequently, the affinity of the peptide was verified by using peptide histochemistry, using flow cytometry, and by positron emissions tomography (PET/CT). We identified a novel ITGαβ binding peptide (SFITGv6) containing the amino acid sequence FRGDLMQL. SFITGv6 provides stability over a period of 24 hours and demonstrates high affinity ( = 14.8 nmol/L) for ITGαβ In HNO97 cells, a maximal uptake and internalization of up to 37.3% and 37.5%, respectively, was measured. Small-animal PET imaging and biodistribution studies of HNO97 xenografted Balb/c nu/nu mice showed tumor-specific accumulation of Ga- andLu-labeled DOTA-SFITGv6, respectively, 30 to 60 minutes after injection. Moreover, peptide histochemistry revealed a strong and homogenous binding of biotin-labeled SFITGv6 to HNSCC tumors and breast- and lung cancer-derived brain metastases. Finally, first PET/CT scans of HNSCC and NSCLC patients displayed SFITGv6 accumulation specifically in tumors, but not in inflammatory lesions. Thus, SFITGv6 represents a novel powerful tracer for imaging and possibly for endoradiotherapy of ITGαβ-positive carcinoma. .

αβ integrin is overexpressed by several carcinomas and thus considered a target for diagnostic imaging and anticancer therapies. Recently, we presented the αβ integrin-binding peptide SFITGv6 as a novel potential tracer for imaging and targeted therapy of αβ integrin-positive carcinomas. Here, we analyzed the affinity and specificity of 5 native αβ integrin-specific binders in comparison to SFITGv6. Sunflower trypsin inhibitor 1 (SFTI1)-based peptides containing arginine-glycine-aspartic acid (RGD) motif-spanning octamers of fibronectin (SFFN1), tenascin C (SFTNC), vitronectin (SFVTN), and latency-associated peptides (LAP) 1 (SFLAP1) and 3 (SFLAP3) were synthesized, and their binding potential to αβ integrin-expressing head and neck squamous cell carcinoma (HNSCC) cell lines was evaluated. Subsequently, stability, affinity, and specificity were assessed in vitro using radio-high-pressure liquid chromatography, surface plasmon resonance assay, and binding experiments including competition, kinetics, internalization, and efflux. αβ integrin binding specificity was further evaluated by peptide histochemistry. Finally, in vivo binding properties were assessed using small-animal PET imaging and biodistribution experiments in HNSCC-bearing mice, andGa-DOTA-SFLAP3 was applied for diagnostic PET/CT of an HNSCC patient. When the newly designed peptides were compared, significant binding (>20%) to several HNSCC cell lines (HNO97, HNO399, and HNO223) and a fast internalization of up to 60% and 70% were observed for SFLAP3 (GRGDLGRL) and SFITGv6 (FRGDLMQL). In contrast, the other peptides displayed binding that was moderate (SFLAP1, 4.1%-12.1%) to marginal (SFFN1, SFTNC, and SFVTN, <1%) and were therefore excluded from further analysis. Notably, SFLAP3 exhibited improved affinity for αβ integrin (mean half-maximal inhibitory concentration, 3.5 nM; dissociation constant, 7.4). Moreover, small-animal PET imaging and biodistribution studies of HNSCC xenograft mice revealed an increased tumor-specific accumulation 30-60 min after injection of Ga-labeled orLu-labeled DOTA-SFLAP3. Peptide staining further demonstrated binding specificity for SFLAP3 to HNSCC tumor cells. Finally, PET/CT scanning of an HNSCC patient showed specific SFLAP3 accumulation in the primary tumor lesion (SUV, 5.1) and in corresponding lymph node metastases (SUV, 4.1). SFLAP3 represents a promising tracer for prognostic assessment, diagnostic imaging, and possibly targeted therapy of αβ integrin-expressing tumors.