Hyaluronic Acid Present in the Tumor Microenvironment Can Negate the Pro-apototic Effect of a Recombinant Fragment of Human Surfactant Protein D on Breast Cancer Cells

Multivalent, calcium-independent binding of surfactant protein A and D to sulfated glycosaminoglycans of the alveolar epithelial glycocalyx

Lung surfactant collectins, surfactant protein A (SP-A) and D (SP-D), are oligomeric C-type lectins involved in lung immunity. Through their carbohydrate recognition domain, they recognize carbohydrates at pathogen surfaces and initiate lung innate immune response. Here, we propose that they may also be able to bind to other carbohydrates present in typical cell surfaces, such as the alveolar epithelial glycocalyx. To test this hypothesis, we analyzed and quantified the binding affinity of SP-A and SP-D to different sugars and glycosaminoglycans (GAGs) by microscale thermophoresis (MST). In addition, by changing the calcium concentration, we aimed to characterize any consequences on the binding behavior. Our results show that both oligomeric proteins bind with high affinity (in nanomolar range) to GAGs, such as hyaluronan (HA), heparan sulfate (HS) and chondroitin sulfate (CS). Binding to HS and CS was calcium-independent, as it was not affected by changing calcium concentration in the buffer. Quantification of GAGs in bronchoalveolar lavage (BAL) fluid from animals deficient in either SP-A or SP-D showed changes in GAG composition, and electron micrographs showed differences in alveolar glycocalyx ultrastructure in vivo. Taken together, SP-A and SP-D bind to model sulfated glycosaminoglycans of the alveolar epithelial glycocalyx in a multivalent and calcium-independent way. These findings provide a potential mechanism for SP-A and SP-D as an integral part of the alveolar epithelial glycocalyx binding and interconnecting free GAGs, proteoglycans, and other glycans in glycoproteins, which may influence glycocalyx composition and structure.NEW & NOTEWORTHY SP-A and SP-D function has been related to innate immunity of the lung based on their binding to sugar residues at pathogen surfaces. However, their function in the healthy alveolus was considered as limited to interaction with surfactant lipids. Here, we demonstrated that these proteins bind to glycosaminoglycans present at typical cell surfaces like the alveolar epithelial glycocalyx. We propose a model where these proteins play an important role in interconnecting alveolar epithelial glycocalyx components.

Hyaluronic acid: More than a carrier, having an overpowering extracellular and intracellular impact on cancer

Hyaluronic acid (HA), also named hyaluronan, is an omnipresent component of the tissue microenvironment. It is extensively used to formulate targeted drug delivery systems for cancer. Although HA itself has pivotal influences in various cancers, its calibers are somewhat neglected when using it as delivering platform to treat cancer. In the last decade, multiple studies revealed roles of HA in cancer cell proliferation, invasion, apoptosis, and dormancy through pathways like mitogen-activated protein kinase-extracellular signal-regulated kinase (MAPK/ERK), P³⁸, and nuclear factor kappa-light chain-enhancer of activated B cells (NFκB). A more fascinating fact is that the distinct molecular weight (MW) of HA exerts disparate effects on the same type of cancer. Its overwhelming use in cancer therapy and other therapeutic products make collective research on the sundry impact of it on various types of cancer, an essential aspect to be considered in all of these domains. Even the development of new therapies against cancer needed meticulous studies on HA because of its divergence of activity based on MW. This review will provide painstaking insight into the extracellular and intracellular bioactivity of HA, its modified forms, and its MW in cancers, which may improve the management of cancer.

Immunomodulatory Role of Surfactant Protein-D in a Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) Model

Surfactant protein D (SP-D), a pattern recognition molecule, is emerging as a potent anti-tumoural innate immune defense molecule in a range of cancers. Previously, SP-D expression was found to be significantly downregulated at the malignant sites of human prostate adenocarcinoma and associated with an increasing Gleason score and severity. We recently reported selective induction of intrinsic apoptosis by a recombinant fragment of human SP-D (rfhSP-D) in the human Prostate cancer (PCa) biopsy explants and cells with glucose regulated protein of 78 (GRP78) as one of the key interacting partners. The present study evaluated the expression of SP-D in early and advanced stages of PCa using transgenic adenocarcinoma of mouse prostate (TRAMP) model. Both early and late stages of PCa showed significantly decreased SP-D mRNA expression and increased proteolytic degradation of SP-D protein. Systemic and tumoural immunophenotyping of TRAMP model revealed increased serine proteases producing granulocytes and polymorphonuclear myeloid-derived suppressor cells (PMN MDSCs) in the late stage; the serine proteases secreted by these cells could be involved in the degradation of SP-D. Susceptibility of rfhSP-D to elastase-mediated proteolysis provided the rationale to use an elastase-inhibitor to sustain intact rfhSP-D in the tumour microenvironment. The study revealed an immunomodulatory potential of rfhSP-D and elastase inhibitor, sivelestat, to induce macrophage polarization towards M1 with downregulation of PMN MDSCs in ex-vivo cultured TRAMP tumours. Furthermore, rfhSP-D induced immunogenic cell death in murine PCa cells and in TRAMP explants. The findings highlight that SP-D plays an anti-tumourigenic role in PCa by inducing immunogenic cell death and immunomodulation while the prostate tumour milieu adversely impacts SP-D by inhibiting its transcription, and enhancing its proteolytic degradation. Transformation of an immunologically “cold tumour” into a “hot tumour” implicates therapeutic potential of rfhSP-D in PCa.

Engineering hyaluronic acid-based cryogels for CD44-mediated breast tumor reconstruction

Breast cancer is a major health concern worldwide and is the leading cause of cancer-related death among American women. Traditional therapies, such as surgery, chemotherapy, and radiotherapy, are usually ineffective. Furthermore, cancer recurrence following targeted therapy often results from acquired drug resistance. Therefore, more realistic tumor models than monolayer cell culture for drug screening and discovery in an in vitro setting would facilitate the development of new therapeutic strategies. Toward this goal, we first developed a simple, rapid, low-cost, and high-throughput method for generating uniform multi-cellular tumor spheroids (MCTS) with controllable size. Next, biomimetic cryogel scaffolds fabricated from hyaluronic acid (HA) were utilized as a platform to reconstruct breast tumor microtissues with aspects of the complex tumor microenvironment in three dimensions. Finally, we investigated the interactions between the HA-based cryogels and CD44-positive breast tumor cells, individually or as MCTS. We found that incorporating the adhesive RGD peptide in cryogels led to the formation of a monolayer of tumor cells on the polymer walls, whereas MCTS cultured on RGD-free HA cryogels resulted in the growth of large and dense microtumors, more similar to native tumor masses. As a result, the MCTS-laden HA cryogel system induced a highly aggressive and chemotherapy drug-resistant tumor model. RGD-free HA-based cryogels represent an effective starting point for designing tumor models for preclinical research, therapeutic drug screening, and early cancer diagnosis.

Pro-Apoptotic and Immunotherapeutic Effects of Carbon Nanotubes Functionalized with Recombinant Human Surfactant Protein D on Leukemic Cells

Nanoparticles are efficient drug delivery vehicles for targeting specific organs as well as systemic therapy for a range of diseases, including cancer. However, their interaction with the immune system offers an intriguing challenge. Due to the unique physico-chemical properties, carbon nanotubes (CNTs) are considered as nanocarriers of considerable interest in cancer diagnosis and therapy. CNTs, as a promising nanomaterial, are capable of both detecting as well as delivering drugs or small therapeutic molecules to tumour cells. In this study, we coupled a recombinant fragment of human surfactant protein D (rfhSP-D) with carboxymethyl-cellulose (CMC) CNTs (CMC-CNT, 10-20 nm diameter) for augmenting their apoptotic and immunotherapeutic properties using two leukemic cell lines. The cell viability of AML14.3D10 or K562 cancer cell lines was reduced when cultured with CMC-mwCNT-coupled-rfhSP-D (CNT + rfhSP-D) at 24 h. Increased levels of caspase 3, 7 and cleaved caspase 9 in CNT + rfhSP-D treated AML14.3D10 and K562 cells suggested an involvement of an intrinsic pathway of apoptosis. CNT + rfhSP-D treated leukemic cells also showed higher mRNA expression of p53 and cell cycle inhibitors (p21 and p27). This suggested a likely reduction in cdc2-cyclin B1, causing G2/M cell cycle arrest and p53-dependent apoptosis in AML14.3D10 cells, while p53-independent mechanisms appeared to be in operation in K562 cells. We suggest that CNT + rfhSP-D has therapeutic potential in targeting leukemic cells, irrespective of their p53 status, and thus, it is worth setting up pre-clinical trials in animal models.

A Recombinant Fragment of Human Surfactant Protein D Binds Spike Protein and Inhibits Infectivity and Replication of SARS-CoV-2 in Clinical Samples

Coronavirus disease (COVID-19) is an acute infectious disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Human SP-D (surfactant protein D) is known to interact with the spike protein of SARS-CoV, but its immune surveillance against SARS-CoV-2 is not known. The current study aimed to examine the potential of a recombinant fragment of human SP-D (rfhSP-D) as an inhibitor of replication and infection of SARS-CoV-2. The interaction of rfhSP-D with the spike protein of SARS-CoV-2 and human ACE-2 (angiotensin-converting enzyme 2) receptor was predicted via docking analysis. The inhibition of interaction between the spike protein and ACE-2 by rfhSP-D was confirmed using direct and indirect ELISA. The effect of rfhSP-D on replication and infectivity of SARS-CoV-2 from clinical samples was assessed by measuring the expression of RdRp gene of the virus using quantitative PCR. In silico interaction studies indicated that three amino acid residues in the receptor-binding domain of spike protein of SARS-CoV-2 were commonly involved in interacting with rfhSP-D and ACE-2. Studies using clinical samples of SARS-CoV-2–positive cases (asymptomatic, n = 7; symptomatic, n = 8) and negative control samples (n = 15) demonstrated that treatment with 1.67 μM rfhSP-D inhibited viral replication by ∼5.5-fold and was more efficient than remdesivir (100 μM) in Vero cells. An approximately two-fold reduction in viral infectivity was also observed after treatment with 1.67 μM rfhSP-D. These results conclusively demonstrate that the rfhSP-D mediated calcium independent interaction between the receptor-binding domain of the S1 subunit of the SARS-CoV-2 spike protein and human ACE-2, its host cell receptor, and significantly reduced SARS-CoV-2 infection and replication in vitro.

Human Surfactant Protein D Binds Spike Protein and Acts as an Entry Inhibitor of SARS-CoV-2 Pseudotyped Viral Particles

Human SP-D is a potent innate immune molecule whose presence at pulmonary mucosal surfaces allows its role in immune surveillance against pathogens. Higher levels of serum SP-D have been reported in the patients with severe acute respiratory syndrome coronavirus (SARS-CoV). Studies have suggested the ability of human SP-D to recognise spike glycoprotein of SARS-CoV; its interaction with HCoV-229E strain leads to viral inhibition in human bronchial epithelial (16HBE) cells. Previous studies have reported that a recombinant fragment of human SP-D (rfhSP-D) composed of 8 Gly-X-Y repeats, neck and CRD region, can act against a range of viral pathogens including influenza A Virus and Respiratory Syncytial Virus in vitro, in vivo and ex vivo. In this context, this study was aimed at examining the likely protective role of rfhSP-D against SARS-CoV-2 infection. rfhSP-D showed a dose-responsive binding to S1 spike protein of SARS-CoV-2 and its receptor binding domain. Importantly, rfhSP-D inhibited interaction of S1 protein with the HEK293T cells overexpressing human angiotensin converting enzyme 2 (hACE2). The protective role of rfhSP-D against SARS-CoV-2 infection as an entry inhibitor was further validated by the use of pseudotyped lentiviral particles expressing SARS-CoV-2 S1 protein; ~0.5 RLU fold reduction in viral entry was seen following treatment with rfhSP-D (10 µg/ml). These results highlight the therapeutic potential of rfhSP-D in SARS-CoV-2 infection and merit pre-clinical studies in animal models.

Extracellular Matrix: Emerging Roles and Potential Therapeutic Targets for Breast Cancer

Increasing evidence shows that the extracellular matrix (ECM) is an important regulator of breast cancer (BC). The ECM comprises of highly variable and dynamic components. Compared with normal breast tissue under homeostasis, the ECM undergoes many changes in composition and organization during BC progression. Induced ECM proteins, including fibrinogen, fibronectin, hyaluronic acid, and matricellular proteins, have been identified as important components of BC metastatic cells in recent years. These proteins play major roles in BC progression, invasion, and metastasis. Importantly, several specific ECM molecules, receptors, and remodeling enzymes are involved in promoting resistance to therapeutic intervention. Additional analysis of these ECM proteins and their downstream signaling pathways may reveal promising therapeutic targets against BC. These potential drug targets may be combined with new nanoparticle technologies. This review summarizes recent advances in functional nanoparticles that target the ECM to treat BC. Accurate nanomaterials may offer a new approach to BC treatment.