Deficiency of Glucocerebrosidase Activity beyond Gaucher Disease: PSAP and LIMP-2 Dysfunctions.

Glucocerebrosidase (GCase) is a lysosomal enzyme that catalyzes the breakdown of glucosylceramide in the presence of its activator saposin C (SapC). SapC arises from the proteolytical cleavage of prosaposin (encoded by PSAP gene), which gives rise to four saposins. GCase is targeted to the lysosomes by LIMP-2, encoded by SCARB2 gene. GCase deficiency causes Gaucher Disease (GD), which is mainly due to biallelic pathogenetic variants in the GCase-encoding gene, GBA1. However, impairment of GCase activity can be rarely caused by SapC or LIMP-2 deficiencies. We report a new case of LIMP-2 deficiency and a new case of SapC deficiency (missing all four saposins, PSAP deficiency), and measured common biomarkers of GD and GCase activity. Glucosylsphingosine and chitotriosidase activity in plasma were increased in GCase deficiencies caused by PSAP and GBA1 mutations, whereas SCARB2-linked deficiency showed only Glucosylsphingosine elevation. GCase activity was reduced in fibroblasts and leukocytes: the decrease was sharper in GBA1- and SCARB2-mutant fibroblasts than PSAP-mutant ones; LIMP-2-deficient leukocytes displayed higher residual GCase activity than GBA1-mutant ones. Finally, we demonstrated that GCase mainly undergoes proteasomal degradation in LIMP-2-deficient fibroblasts and lysosomal degradation in PSAP-deficient fibroblasts. Thus, we analyzed the differential biochemical profile of GCase deficiencies due to the ultra-rare PSAP and SCARB2 biallelic pathogenic variants in comparison with the profile observed in GBA1-linked GCase deficiency.

Glucosylsphingosine but not Saposin C, is the target antigen in Gaucher disease-associated gammopathy.

In Gaucher disease type 1 (GD1), genetic deficiency of lysosomal glucocerebrosidase results in the accumulation of glucosylceramide and glucosylsphingosine (GlcSph), that underlie chronic lipid-mediated metabolic inflammation. An important age-related phenotype is high risk of monoclonal gammopathy (MG), including multiple myeloma. We identified GlcSph, a pathological lyso-sphingolipid exclusively elevated in GD, as a mediator of B cell activation and as an antigenic target for GD1-associated MG. Saposin C (SapC), is a lipid-binding protein and activator of lysosomal glucocerebrosidase, which when mutated, cause a rare variant of GD. Sera of GD1 patients with MG of diverse immunoglobulin types were compared to GD patients without gammopathy for reactivity against GlcSph and SapC. We show reactivity of clonal immunoglobulin in GD1 to GlcSph but not to SapC. In two patients with GD1 and gammopathy, GlcSph-reduction therapy with eliglustat resulted in reduction in clonal Ig. Together, our data show that GlcSph but not SapC is the antigenic target in GD1-associated MG and that therapy aimed at reducing the levels of immunogenic lipid resulted in reduction of clonal immunoglobulin in vivo.

Saposin C is a frequent target of paraproteins in Gaucher disease-associated MGUS/multiple myeloma.

Patients with Gaucher disease (GD) have an increased risk of monoclonal gammopathies for which antigenic targets might play a role in their pathogenesis. Here we report the identification of saposin C (sapC) as high-titre (1:1 000 000) target structure of 7/16 GD-associated paraproteins. Anti-sapC immunoglobulin (Ig) showed identity with the paraprotein Ig type and subclass in each patient that showed anti-sapC immunoreactivity. Absorption and depletion studies completely removed the paraprotein from the sera of GD patients. No immunoreactivity against sapC was detected in healthy donors and in other plasma cell dyscrasias, demonstrating that anti-sapC reactivity is highly restricted to GD. Several uncharacterized forms of post-translational modified sapC were detected but their role in the pathogenesis is not clear. We confirm the frequent presence of low-titre (1:250) anti-lysolipid reactivities in the sera of GD patients but we could show that this immunoreactivity is not mediated by the paraprotein and is not restricted to GD patients.

Glio- and neuro-protection by prosaposin is mediated by orphan G-protein coupled receptors GPR37L1 and GPR37.

Discovery of neuroprotective pathways is one of the major priorities for neuroscience. Astrocytes are natural neuroprotectors and it is likely that brain resilience can be enhanced by mobilizing their protective potential. Among G-protein coupled receptors expressed by astrocytes, two highly related receptors, GPR37L1 and GPR37, are of particular interest. Previous studies suggested that these receptors are activated by a peptide Saposin C and its neuroactive fragments (prosaptide TX14(A)), which were demonstrated to be neuroprotective in various animal models by several groups. However, pairing of Saposin C or prosaptides with GPR37L1/GPR37 has been challenged and presently GPR37L1/GPR37 have regained their orphan status. Here, we demonstrate that in their natural habitat, astrocytes, these receptors mediate a range of effects of TX14(A), including protection from oxidative stress. The Saposin C/GPR37L1/GPR37 pathway is also involved in the neuroprotective effect of astrocytes on neurons subjected to oxidative stress. The action of TX14(A) is at least partially mediated by Gi-proteins and the cAMP-PKA axis. On the other hand, when recombinant GPR37L1 or GPR37 are expressed in HEK293 cells, they are not functional and do not respond to TX14(A), which explains unsuccessful attempts to confirm the ligand-receptor pairing. Therefore, this study identifies GPR37L1/GPR37 as the receptors for TX14(A), and, by extension of Saposin C, and paves the way for the development of neuroprotective therapeutics acting via these receptors.

A rare form of Gaucher disease resulting from saposin C deficiency.

Gaucher disease is mainly caused by the deficiency of lysosomal acid ß-glucosidase. Gaucher disease caused by the deficiency of saposin C is rare. Here we report a patient mainly presenting with hepatosplenomegaly, thrombocytopenia and anemia. EEG examination revealed increased theta waves. Gaucher cells identified in his bone marrow and the highly elevated plasma chitotriosidase activity and glucosylsphingosine supported a diagnosis of Gaucher disease. However, the leukocyte ß-glucosidase activity was in a normal range. Sanger sequencing revealed a novel maternal exonic mutation c.1133C>G (p.Pro378Arg) in exon 10 of the PSAP gene, which codes the Sap C domain of PSAP protein. To search for other underlying mutations in this patient, whole genome sequencing was applied and revealed a deletion involving exon 2 to 7 of PSAP gene. The deletion appears as a de novo event on paternal chromosome. We concluded that biallelic mutations of PSAP gene were the cause of this patient's Gaucher disease. Our finding expands the mutation spectrum of Gaucher disease with saposin C deficiency.

Detection of cancer cells using SapC-DOPS nanovesicles.

Unlike normal cells, cancer cells express high levels of phosphatidylserine on the extracellular leaflet of their cell membrane. Exploiting this characteristic, our lab developed a therapeutic agent that consists of the fusogenic protein, saposin C (SapC) which is embedded in dioleoylphosphatidylserine (DOPS) vesicles. These nanovesicles selectively target cancer cells and induce apoptosis. Here we review the data supporting use of SapC-DOPS to locate tumors for surgical resection or for treatment. In addition, there is important evidence suggesting that SapC-DOPS may also prove to be an effective novel cancer therapeutic reagent. Given that SapC-DOPS is easily labeled with lipophilic dyes, it has been combined with the far-red fluorescent dye, CellVue Maroon (CVM), for tumor targeting studies. We also have used contrast agents incorporated in the SapC-DOPS nanovesicles for computed tomography and magnetic resonance imaging, and review that data here. Administered intravenously, the fluorescently labeled SapC-DOPS traversed the blood-brain tumor barrier enabling identification of brain tumors. SapC-DOPS-CVM also detected a variety of other mouse tumors in vivo, rendering them observable by optical imaging using IVIS and multi-angle rotational optical imaging. Dye is detected within 30 min and remains within tumor for at least 7 days, whereas non-tumor tissues were unstained (some dye observed in the liver was transient, likely representing degradation products). Additionally, labeled SapC-DOPS ex vivo delineated tumors in human histological specimens. SapC-DOPS can also be labeled with contrast reagents for computed tomography or magnetic resonance imaging. In conclusion, labeled SapC-DOPS provides a convenient, specific, and nontoxic method for detecting tumors while concurrently offering a therapeutic benefit.

Ambroxol-induced rescue of defective glucocerebrosidase is associated with increased LIMP-2 and saposin C levels in GBA1 mutant Parkinson's disease cells.

Heterozygous mutations in GBA1 gene, encoding for lysosomal enzyme glucocerebrosidase (GCase), are a major risk factor for sporadic Parkinson's disease (PD). Defective GCase has been reported in fibroblasts of GBA1-mutant PD patients and pharmacological chaperone ambroxol has been shown to correct such defect. To further explore this issue, we investigated GCase and elements supporting GCase function and trafficking in fibroblasts from sporadic PD patients--with or without heterozygous GBA1 mutations--and healthy subjects, in basal conditions and following in vitro exposure to ambroxol. We assessed protein levels of GCase, lysosomal integral membrane protein-2 (LIMP-2), which mediates GCase trafficking to lysosomes, GCase endogenous activator saposin (Sap) C and parkin, which is involved in degradation of defective GCase. We also measured activities of GCase and cathepsin D, which cleaves Sap C from precursor prosaposin. GCase activity was reduced in fibroblasts from GBA1-mutant patients and ambroxol corrected this defect. Ambroxol increased cathepsin D activity, GCase and Sap C protein levels in all groups, while LIMP-2 levels were increased only in GBA1-mutant PD fibroblasts. Parkin levels were slightly increased only in the PD group without GBA1 mutations and were not significantly modified by ambroxol. Our study confirms that GCase activity is deficient in fibroblasts of GBA1-mutant PD patients and that ambroxol corrects this defect. The drug increased Sap C and LIMP-2 protein levels, without interfering with parkin. These results confirm that chemical chaperone ambroxol modulates lysosomal markers, further highlighting targets that may be exploited for innovative PD therapeutic strategies.

New insights on glucosylated lipids: metabolism and functions.

Ceramide, cholesterol, and phosphatidic acid are major basic structures for cell membrane lipids. These lipids are modified with glucose to generate glucosylceramide (GlcCer), cholesterylglucoside (ChlGlc), and phosphatidylglucoside (PtdGlc), respectively. Glucosylation dramatically changes the functional properties of lipids. For instance, ceramide acts as a strong tumor suppressor that causes apoptosis and cell cycle arrest, while GlcCer has an opposite effect, downregulating ceramide activities. All glucosylated lipids are enriched in lipid rafts or microdomains and play fundamental roles in a variety of cellular processes. In this review, we discuss the biological functions and metabolism of these three glucosylated lipids.

Prosaposin Reduces α-Synuclein in Cells and Saposin C Dislodges it from Glucosylceramide-enriched Lipid Membranes.

Parkinson's disease (PD) is the second most common progressive neurodegenerative disorder affecting over 1% of the 65 + age population. Saposin C, a lysosomal protein required for the normal activity of glucocerebrosidase (GCase), may serve as a disease modifier in PD. Saposin C is cleaved from its precursor, Prosaposin (PSAP), which is secreted as an uncleaved protein and exerts neuroprotective effects. In this study, we aim to elucidate the neuroprotective roles of PSAP and saposin C in PD by evaluating their effects on α-synuclein accumulation in human neuroblastoma cells. Stable overexpression of PSAP reduced monomeric α-synuclein levels in SH-SY5Y cells, while PSAP knockdown by small interfering RNA led to the opposite effect, and those effects were independent of GCase activity. Autophagy flux was decreased by stable PSAP overexpression. Furthermore, a flow-through assay revealed that recombinant saposin C was able to detach α-synuclein from artificial glucosylceramide-enriched lipid membranes at the lysosomal pH. Taken together, our findings provide further evidence that PSAP and saposin C as key proteins involved in α-synuclein clearance by dislodging it from lipid membranes.

Phenotype Expansion for Atypical Gaucher Disease Due to Homozygous Missense PSAP Variant in a Large Consanguineous Pakistani Family.

Atypical Gaucher disease is caused by variants in the PSAP gene. Saposin C is one of four homologous proteins derived from sequential cleavage of the saposin precursor protein, prosaposin. It is an essential activator for glucocerebrosidase, which is deficient in Gaucher disease. Although atypical Gaucher disease due to deficiency of saposin C is rare, it exhibits vast phenotypic heterogeneity. Here, we report on a Pakistani family that exhibits features of Gaucher disease, i.e., prelingual profound sensorineural hearing impairment, vestibular dysfunction, hepatosplenomegaly, kyphosis, and thrombocytopenia. The family was investigated using exome and Sanger sequencing. A homozygous missense variant c.1076A>C: p.(Glu359Ala) in exon 10 of the PSAP gene was observed in all affected family members. In conclusion, we identified a new likely pathogenic missense variant in PSAP in a large consanguineous Pakistani family with atypical Gaucher disease. Gaucher disease due to a deficiency of saposin C has not been previously reported within the Pakistani population. Genetic screening of patients with the aforementioned phenotypes could ensure adequate follow-up and the prevention of further complications. Our finding expands the genetic and phenotypic spectrum of atypical Gaucher disease due to a saposin C deficiency.

A Type 3 Gaucher-Like Disease Due To Saposin C Deficiency in Two Emirati Families Caused by a Novel Splice Site Variant in the PSAP Gene.

Gaucher disease is caused by glucocerebroside accumulation in different tissues due to beta-glucocerebrosidase enzyme deficiency. Genetic defects in proteins involved in beta-glucocerebrosidase processing and activation may indirectly lead to Gaucher-like phenotypes in affected individuals. Saposin C, derived from the prosaposin precursor, is a crucial activator for beta-glucocerebrosidase, and its deficiency has been linked to Gaucher-like phenotypes in several clinical reports. Here, we report two Emirati families with Gaucher-like disorder due to Saposin C deficiency. Affected patients from both families carry the homozygous state of the novel c.1005 + 1G > A splice site (first to be reported) variant in the PSAP gene. Molecular analysis showed that the underlying variant is predicted to result in the retention of intron 9-10 and the formation of a premature stop codon leading to the complete loss of Saposin C. Clinical examination of the affected patients showed a wide heterogeneity in the patients' age of onset and symptoms ranging from Gaucher-like type 3 phenotype with severe refractory myoclonic epilepsy to Gaucher-like type 1 phenotype with growth retardation and hepatosplenomegaly. Collectively, the available clinical and molecular data confirms the pathogenicity of the reported PSAP splice site variant. The reported clinical cases expand the genetic and clinical spectrum of Saposin C deficiency.

Phosphatidylserine: The Unique Dual-Role Biomarker for Cancer Imaging and Therapy.

Cancer is among the leading causes of death worldwide. In recent years, many cancer-associated biomarkers have been identified that are used for cancer diagnosis, prognosis, screening, and early detection, as well as for predicting and monitoring carcinogenesis and therapeutic effectiveness. Phosphatidylserine (PS) is a negatively charged phospholipid which is predominantly located in the inner leaflet of the cell membrane. In many cancer cells, PS externalizes to the outer cell membrane, a process regulated by calcium-dependent flippases and scramblases. Saposin C coupled with dioleoylphosphatidylserine (SapC-DOPS) nanovesicle (BXQ-350) and bavituximab, (Tarvacin, human-mouse chimeric monoclonal antibodies) are cell surface PS-targeting drugs being tested in clinical trial for treating a variety of cancers. Additionally, a number of other PS-selective agents have been used to trigger cytotoxicity in tumor-associated endothelial cells or cancer cells in pre-clinical studies. Recent studies have demonstrated that upregulation of surface PS exposure by chemodrugs, radiation, and external electric fields can be used as a novel approach to sensitize cancer cells to PS-targeting anticancer drugs. The objectives of this review are to provide an overview of a unique dual-role of PS as a biomarker/target for cancer imaging and therapy, and to discuss PS-based anticancer strategies that are currently under active development.

Rare PSAP Variants and Possible Interaction with GBA in REM Sleep Behavior Disorder.

BACKGROUND: PSAP encodes saposin C, the co-activator of glucocerebrosidase, encoded by GBA. GBA mutations are associated with idiopathic/isolated REM sleep behavior disorder (iRBD), a prodromal stage of synucleinopathy. OBJECTIVE: To examine the role of PSAP mutations in iRBD. METHODS: We fully sequenced PSAP and performed Optimized Sequence Kernel Association Test in 1,113 iRBD patients and 2,324 controls. We identified loss-of-function (LoF) mutations, which are very rare in PSAP, in three iRBD patients and none in controls (uncorrected p = 0.018). RESULTS: Two variants were stop mutations, p.Gln260Ter and p.Glu166Ter, and one was an in-frame deletion, p.332_333del. All three mutations have a deleterious effect on saposin C, based on in silico analysis. In addition, the two carriers of p.Glu166Ter and p.332_333del mutations also carried a GBA variant, p.Arg349Ter and p.Glu326Lys, respectively. The co-occurrence of these extremely rare PSAP LoF mutations in two (0.2%) GBA variant carriers in the iRBD cohort, is unlikely to occur by chance (estimated co-occurrence in the general population based on gnomAD data is 0.00035%). Although none of the three iRBD patients with PSAP LoF mutations have phenoconverted to an overt synucleinopathy at their last follow-up, all manifested initial signs suggestive of motor dysfunction, two were diagnosed with mild cognitive impairment and all showed prodromal clinical markers other than RBD. Their probability of prodromal PD, according to the Movement Disorder Society research criteria, was 98% or more. CONCLUSION: These results suggest a possible role of PSAP variants in iRBD and potential genetic interaction with GBA, which requires additional studies.

Quantitative Studies on the Interaction between Saposin-like Proteins and Synthetic Lipid Membranes.

Members of the saposin-fold protein family and related proteins sharing a similar fold (saposin-like proteins; SAPLIP) are peripheral-membrane binding proteins that perform essential cellular functions. Saposins and SAPLIPs are abundant in both plant and animal kingdoms, and peripherally bind to lipid membranes to play important roles in lipid transfer and hydrolysis, defense mechanisms, surfactant stabilization, and cell proliferation. However, quantitative studies on the interaction between proteins and membranes are challenging due to the different nature of the two components in relation to size, structure, chemical composition, and polarity. Using liposomes and the saposin-fold member saposin C (sapC) as model systems, we describe here a method to apply solution NMR and dynamic light scattering to study the interaction between SAPLIPs and synthetic membranes at the quantitative level. Specifically, we prove with NMR that sapC binds reversibly to the synthetic membrane in a pH-controlled manner and show the dynamic nature of its fusogenic properties with dynamic light scattering. The method can be used to infer the optimal pH for membrane binding and to determine an apparent dissociation constant (KDapp) for protein-liposome interaction. We propose that these experiments can be applied to other proteins sharing the saposin fold.

Engineering of Saposin C Protein Chimeras for Enhanced Cytotoxicity and Optimized Liposome Binding Capability.

Saposin C (sapC) is a lysosomal, peripheral-membrane protein displaying liposome fusogenic capabilities. Proteoliposomes of sapC and phosphatidylserine have been shown to be toxic for cancer cells and are currently on clinical trial to treat glioblastoma. As proof-of-concept, we show two strategies to enhance the applications of sapC proteoliposomes: (1) Engineering chimeras composed of sapC to modulate proteoliposome function; (2) Engineering sapC to modify its lipid binding capabilities. In the chimera design, sapC is linked to a cell death-inducing peptide: the BH3 domain of the Bcl-2 protein PUMA. We show by solution NMR and dynamic light scattering that the chimera is functional at the molecular level by fusing liposomes and by interacting with prosurvival Bcl-xL, which is PUMA's known mechanism to induce cell death. Furthermore, sapC-PUMA proteoliposomes enhance cytotoxicity in glioblastoma cells compared to sapC. Finally, the sapC domain of the chimera has been engineered to optimize liposome binding at pH close to physiological values as protein-lipid interactions are favored at acidic pH in the native protein. Altogether, our results indicate that the properties of sapC proteoliposomes can be modified by engineering the protein surface and by the addition of small peptides as fusion constructs.

Targeting of elevated cell surface phosphatidylserine with saposin C-dioleoylphosphatidylserine nanodrug as individual or combination therapy for pancreatic cancer.

Pancreatic cancer is one of the deadliest of cancers with a five-year survival of roughly 8%. Current therapies are: surgery, radiation and chemotherapy. Surgery is curative only if the cancer is caught very early, which is rare, and the latter two modalities are only marginally effective and have significant side effects. We have developed a nanosome comprised of the lysosomal protein, saposin C (SapC) and the acidic phospholipid, dioleoylphosphatidylserine (DOPS). In the acidic tumor microenvironment, this molecule, SapC-DOPS, targets the phosphatidylserine cancer-biomarker which is predominantly elevated on the surface of cancer cells. Importantly, SapC-DOPS can selectively target pancreatic tumors and metastases. Furthermore, SapC-DOPS has exhibited an impressive safety profile with only a few minor side effects in both preclinical experiments and in phase I clinical trials. With the dismal outcomes for pancreatic cancer there is an urgent need for better treatments and SapC-DOPS is a good candidate for addition to the oncologist's toolbox.

Reuse of Molecules for Glioblastoma Therapy.

Glioblastoma multiforme (GBM) is a highly malignant primary brain tumor. The current standard of care for GBM is the Stupp protocol which includes surgical resection, followed by radiotherapy concomitant with the DNA alkylator temozolomide; however, survival under this treatment regimen is an abysmal 12-18 months. New and emerging treatments include the application of a physical device, non-invasive 'tumor treating fields' (TTFs), including its concomitant use with standard of care; and varied vaccines and immunotherapeutics being trialed. Some of these approaches have extended life by a few months over standard of care, but in some cases are only available for a minority of GBM patients. Extensive activity is also underway to repurpose and reposition therapeutics for GBM, either alone or in combination with the standard of care. In this review, we present select molecules that target different pathways and are at various stages of clinical translation as case studies to illustrate the rationale for their repurposing-repositioning and potential clinical use.

Accumulation of saposin in dystrophic neurites is linked to impaired lysosomal functions in Alzheimer's disease brains.

Neuritic plaques in Alzheimer's disease (AD) brains refer to ß-amyloid (Aß) plaques surrounded by dystrophic neurites (DNs), activated microglia and reactive astrocytes. Most recently, we showed that DNs form sequentially in three layers during plaque growth. Although lysosomal proteins such as LAMP1 are found in DNs, it is not clear how many and how early lysosomal proteins are involved in forming neuritic plaques. To answer this unmet question, we examined APP knock-in (APPNL-G-F), 5xFAD and APP/PS1ΔE9 mouse brains and found that the lysosomal activator proteins saposins (SAPs) and LAMP1 were accumulated to surround Aß plaques at the earliest stage, namely the 1st layer of DNs. Noticeably, lysosomal hydrolases were not detectable in these early DNs, suggesting that DNs at this early stage likely enrich dysfunctional lysosomes. In old AD mouse brains and in the later stage of human AD brains, SAP-C+-DNs and LAMP1+-DNs were gradually reduced in concomitant with the growth of amyloid plaques. Remarkably, the observed LAMP1 immunoreactivity near plaques in aged AD mouse and human brains were actually associated with disease-associated microglia rather than neuronal sources, likely reflecting more severely impaired lysosomal functions in neurons. Western blot analyses showed increased levels of SAP-C in AD mouse brains, and Aß oligomers induced elevated levels of SAP-C in cellular assays. The elevated protein levels of SAP-C in AD mouse brains during plaque growth potentially contributed lysosomal membrane leakage and loss of hydrolases. Together, our study indicates that lysosomal functions are impaired by being entrapped in DNs early during plaque growth, and this may viciously facilitate growth of amyloid plaques.

SapC-DOPS as a Novel Therapeutic and Diagnostic Agent for Glioblastoma Therapy and Detection: Alternative to Old Drugs and Agents.

Glioblastoma multiforme (GBM), the most common type of brain cancer, is extremely aggressive and has a dreadful prognosis. GBM comprises 60% of adult brain tumors and the 5 year survival rate of GBM patients is only 4.3%. Standard-of-care treatment includes maximal surgical removal of the tumor in combination with radiation and temozolomide (TMZ) chemotherapy. TMZ is the "gold-standard" chemotherapy for patients suffering from GBM. However, the median survival is only about 12 to 18 months with this protocol. Consequently, there is a critical need to develop new therapeutic options for treatment of GBM. Nanomaterials have unique properties as multifunctional platforms for brain tumor therapy and diagnosis. As one of the nanomaterials, lipid-based nanocarriers are capable of delivering chemotherapeutics and imaging agents to tumor sites by enhancing the permeability of the compound through the blood-brain barrier, which makes them ideal for GBM therapy and imaging. Nanocarriers also can be used for delivery of radiosensitizers to the tumor to enhance the efficacy of the radiation therapy. Previously, high-atomic-number element-containing particles such as gold nanoparticles and liposomes have been used as radiosensitizers. SapC-DOPS, a protein-based liposomal drug comprising the lipid, dioleoylphosphatidylserine (DOPS), and the protein, saposin C (SapC), has been shown to be effective for treatment of a variety of cancers in small animals, including GBM. SapC-DOPS also has the unique ability to be used as a carrier for delivery of radiotheranostic agents for nuclear imaging and radiotherapeutic purposes. These unique properties make tumor-targeting proteo-liposome nanocarriers novel therapeutic and diagnostic alternatives to traditional chemotherapeutics and imaging agents. This article reviews various treatment modalities including nanolipid-based delivery and therapeutic systems used in preclinical and clinical trial settings for GBM treatment and detection.

Sequencing of the GBA coactivator, Saposin C, in Parkinson disease.

Saposin C (SapC), encoded by PSAP, is required for the activity of glucocerebrosidase, encoded by GBA. Although GBA mutations have been studied thoroughly in Parkinson disease (PD), genetic studies on SapC are still lacking. PSAP was sequenced in 1123 PD patients and 1153 controls, and data from additional 1167 patients and 1685 controls were examined. A total of 6 patients had SapC mutations in the 2 combined cohorts, but no statistically significant association after correction for multiple comparisons was found. Larger studies are necessary to examine the role of very rare SapC variants in PD.