Schweinfurthins: Lipid Modulators with Promising Anticancer Activity

Clinical relevance of glycosylation in triple negative breast cancer: a review

Glycosylation alterations in TNBC have significant implications for tumor behavior, diagnosis, prognosis, and therapeutic strategies. Dysregulated glycosylation affects cell adhesion, signaling, immune recognition, and response to therapy in TNBC. Different types of glycosylation, including N-linked glycosylation, O-linked glycosylation, glycosphingolipid glycosylation, mucin-type glycosylation, and sialylation, play distinct roles in TNBC. The "barcoding" method based on glycosylation sites of the membrane type mannose receptor (MR) shows promise in accurately distinguishing breast cancer subtypes, including TNBC. Alpha-L-fucosidase 1 (FUCA1) and Monocarboxylate transporter 4 (MCT4) have been identified as potential diagnostic and prognostic markers for TNBC. The glycosylation status of PD-L1 impacts the response to immune checkpoint blockade therapy in TNBC. Inhibiting fucosylation of B7H3 enhances immune responses and improves anti-tumor effects. Targeting glycosylated B7H4 and modulating estrogen metabolism through glycosylation-related mechanisms are potential therapeutic strategies for TNBC. Understanding the role of glycosylation in TNBC provides insights into disease mechanisms, diagnosis, and potential therapeutic targets. Further research in this field may lead to personalized treatment approaches and improved outcomes for TNBC patients.

Structure-Based Design of a Lead Compound Derived from Natural Schweinfurthins with Antitumor Properties That Target Oxysterol-Binding Protein

Schweinfurthins (SWs) are naturally occurring prenylated stilbenes with promising anticancer properties. They act through a novel mechanism of action similar to that of other families of natural compounds. Their known target, oxysterol-binding protein (OSBP), plays a crucial role in controlling the intracellular distribution of cholesterol. We synthesized 15 analogues of SWs and demonstrated for the first time that their cytotoxicity as well as that of natural derivatives correlates with their affinity for OSBP. Through this extensive SAR study, we selected one synthetic analogue obtained in one step from SW-G. Using its fluorescence properties, we showed that this compound recapitulates the effect of natural SW-G in cells and confirmed that it leads to cell death via the same mechanism. Finally, after pilot PK experiments, we provided the first evidence of its in vivo efficacy in combination with temozolomide in a patient-derived glioblastoma xenograft model.

Golgi-Targeting Anticancer Natural Products

The Golgi apparatus plays an important role in maintaining cell homeostasis by serving as a biosynthetic center for glycans, lipids and post-translationally modified proteins and as a sorting center for vesicular transport of proteins to specific destinations. Moreover, it provides a signaling hub that facilitates not only membrane trafficking processes but also cellular response pathways to various types of stresses. Altered signaling at the Golgi apparatus has emerged as a key regulator of tumor growth and survival. Among the small molecules that can specifically perturb or modulate Golgi proteins and organization, natural products with anticancer property have been identified as powerful chemical probes in deciphering Golgi-related pathways and, in particular, recently described Golgi stress response pathways. In this review, we highlight a set of Golgi-targeting natural products that enabled the characterization of the Golgi-mediated signaling events leading to cancer cell death and discuss the potential for selectively exploiting these pathways for the development of novel chemotherapeutic agents.

Schweinfurthin induces ICD without ER stress and caspase activation

Our previous study showed that one of the schweinfurthin compounds, 5’-methoxyschweinfurthin G (MeSG), not only enhances the anti-tumor effect of anti-PD1 antibody in the B16F10 murine melanoma model, but also provokes durable, protective anti-tumor immunity. Here we further investigated the mechanisms by which MeSG treatment induces immunogenic cell death (ICD). MeSG induced significant cell surface calreticulin (CRT) exposure in a time and concentration dependent manner as well as increased phagocytosis of tumor cells by dendritic cells in vitro. Interestingly, this CRT exposure differs from the canonical pathway in several aspects. MeSG does not cause ER stress and does not require PERK to induce CRT exposure. Caspase inhibitors partially rescue cells from MeSG-induced apoptosis, but fail to reduce CRT exposure. MeSG does not cause ERp57 exposure and the absence of ERp57 expression does not reduce CRT exposure. Finally, an intact ER to Golgi transport system is required for this phenomenon. These results lend support to the development of the schweinfurthin family as drugs to enhance clinical response to immunotherapy and highlight the need for additional research on the mechanisms of ICD induction.

Lactoferrin perturbs intracellular trafficking, disrupts cholesterol-rich lipid rafts and inhibits glycolysis of highly metastatic cancer cells harbouring plasmalemmal V-ATPase

The milk-derived bovine lactoferrin (bLf) is an iron-binding glycoprotein with remarkable selective anticancer activity towards highly metastatic cancer cells displaying the proton pump V-ATPase at the plasma membrane. As studies aiming to dissect the bLf mechanisms of action are critical to improve its efficacy and boost its targeted clinical use, herein we sought to further uncover the molecular basis of bLf anticancer activity. We showed that bLf co-localizes with V-ATPase and cholesterol-rich lipid rafts at the plasma membrane of highly metastatic cancer cells. Our data also revealed that bLf perturbs cellular trafficking, induces intracellular accumulation of cholesterol and lipid rafts disruption, downregulates PI3K, and AKT or p-AKT and inhibits glycolysis of cancer cells harbouring V-ATPase at the plasma membrane lipid rafts. Altogether, our results can lay the foundation for future bLf-based targeted anticancer strategies as they unravel a novel cascade of molecular events that explains and further reinforces bLf selectivity for cancer cells displaying plasmalemmal V-ATPase.

Therapeutic Potential of 5'-Methylschweinfurthin G in Merkel Cell Polyomavirus-Positive Merkel Cell Carcinoma

Merkel cell carcinoma (MCC) is a rare but aggressive form of skin cancer predominantly caused by the human Merkel cell polyomavirus (MCPyV). Treatment for MCC includes excision and radiotherapy of local disease, and chemotherapy or immunotherapy for metastatic disease. The schweinfurthin family of natural compounds previously displayed potent and selective growth inhibitory activity against the NCI-60 panel of human-derived cancer cell lines. Here, we investigated the impact of schweinfurthin on human MCC cell lines. Treatment with the schweinfurthin analog, 5'-methylschweinfurth G (MeSG also known as TTI-3114), impaired metabolic activity through induction of an apoptotic pathway. MeSG also selectively inhibited PI3K/AKT and MAPK/ERK pathways in the MCPyV-positive MCC cell line, MS-1. Interestingly, expression of the MCPyV small T (sT) oncogene selectively sensitizes mouse embryonic fibroblasts to MeSG. These results suggest that the schweinfurthin family of compounds display promising potential as a novel therapeutic option for virus-induced MCCs.

Cytotoxic Effects of the Schweinfurthin Analog 5′-Methylschweinfurthin G in Malignant Plasma Cells

<b><i>Introduction:</i></b> Multiple myeloma (MM) is a B plasma cell malignancy currently incurable, and novel therapeutics are needed. Evidences regarding the effect of natural compound schweinfurthins suggest that hematological cancers showed growth inhibitory effects to this family of compounds at single nanomolar concentrations. In this study, we evaluated the cytotoxicity of the schweinfurthin synthetic analog 5′-methylschweinfurthin G (MeSG) in MM cell lines, to better understand the validity of this compound as a therapeutic candidate for further studies in MM. <b><i>Methods:</i></b> MeSG toxicity against MM cell lines RPMI-8226, MM.1S, and H-929 was evaluated. Trypan blue exclusion and MTT assays measured cell viability and mitochondrial activity, respectively. Flow cytometry was performed to detect apoptotic mitochondria. Flow cytometry and Western blotting techniques were used to investigate apoptosis and to examine the cell cycle. Western blotting was used to determine AKT activation upon MeSG treatment. <b><i>Results:</i></b> We provide evidence that in all MM cells analyzed, MeSG exerts diverse cytotoxic effects. MeSG treatment of MM.1S and H-929, but not in RPMI-8226, causes a loss of mitochondria membrane potential. MeSG causes an arrest in G₂/M, especially in RPMI-8226, supported by decreased levels of cyclin-B1 and early increased levels of p21. Finally, there is a diverse response to the MeSG treatment for AKT phosphorylation. MM.1S and H-929 showed a marked decrease in AKT phosphorylation at earlier time points compared to the RPMI-8226 line. <b><i>Conclusions:</i></b> MeSG cytotoxicity has been confirmed in all of 3 cell lines studied. Results suggest an early event of increased reactive oxygen species, and/or involvement of cholesterol homeostasis via decreased AKT activation, both of which are currently under investigation.

Naturally occurring prenylated stilbenoids: food sources, biosynthesis, applications and health benefits

Prenylated stilbenoids are a unique class of natural phenolic compounds consisting of C6-C2-C6 skeleton with prenyl substitution. They are potential nutraceuticals and dietary supplements presented in some edible plants. Prenylated stilbenoids demonstrate promising health benefits, including antioxidant, anti-cancer, anti-inflammatory, anti-microbial activities. This review reports the structure, bioactivity and potential application of prenylated stilbeniods in food industry. Edible sources of these compounds are compiled and summarized. Structure-activity relationship of prenylated stilbenoids are also highlighted. The biosynthesis strategies of prenylated stilbenoids are reviewed. The findings of these compounds as food preservative, nutraceuticals and food additive are discussed. This paper combines the up-to-date information and gives a full image of prenylated stilbenoids.

RNAseq reveals extensive metabolic disruptions in the sensitive SF-295 cell line treated with schweinfurthins

The schweinfurthin family of natural compounds exhibit a unique and potent differential cytotoxicity against a number of cancer cell lines and may reduce tumor growth in vivo. In some cell lines, such as SF-295 glioma cells, schweinfurthins elicit cytotoxicity at nanomolar concentrations. However, other cell lines, like A549 lung cancer cells, are resistant to schweinfurthin treatment up to micromolar concentrations. At this time, the precise mechanism of action and target for these compounds is unknown. Here, we employ RNA sequencing of cells treated with 50 nM schweinfurthin analog TTI-3066 for 6 and 24 h to elucidate potential mechanisms and pathways which may contribute to schweinfurthin sensitivity and resistance. The data was analyzed via an interaction model to observe differential behaviors between sensitive SF-295 and resistant A549 cell lines. We show that metabolic and stress-response pathways were differentially regulated in the sensitive SF-295 cell line as compared with the resistant A549 cell line. In contrast, A549 cell had significant alterations in response genes involved in translation and protein metabolism. Overall, there was a significant interaction effect for translational proteins, RNA metabolism, protein metabolism, and metabolic genes. Members of the Hedgehog pathway were differentially regulated in the resistant A549 cell line at both early and late time points, suggesting a potential mechanism of resistance. Indeed, when cotreated with the Smoothened inhibitor cyclopamine, A549 cells became more sensitive to schweinfurthin treatment. This study therefore identifies a key interplay with the Hedgehog pathway that modulates sensitivity to the schweinfurthin class of compounds.

My 60-Year Love Affair with Natural Products

The author describes his 60-year career in studying the chemistry of natural products, which includes structural, synthetic, and biosynthetic studies of natural products ranging from insect pigments, antibiotics, and fecal mutagens to taxol and other anticancer natural products as well as antimalarial natural products. One of the compounds discussed, napabucasin, is now an anticancer drug in phase III clinical trials.

Molecular and cellular dissection of the oxysterol-binding protein cycle through a fluorescent inhibitor

ORPphilins are bioactive natural products that strongly and selectively inhibit the growth of some cancer cell lines and are proposed to target intracellular lipid-transfer proteins of the oxysterol-binding protein (OSBP) family. These conserved proteins exchange key lipids, such as cholesterol and phosphatidylinositol 4-phosphate (PI(4)P), between organelle membranes. Among ORPphilins, molecules of the schweinfurthin family interfere with intracellular lipid distribution and metabolism, but their functioning at the molecular level is poorly understood. We report here that cell line sensitivity to schweinfurthin G (SWG) is inversely proportional to cellular OSBP levels. By taking advantage of the intrinsic fluorescence of SWG, we followed its fate in cell cultures and show that its incorporation at the trans-Golgi network depends on cellular abundance of OSBP. Using in vitro membrane reconstitution systems and cellular imaging approaches, we also report that SWG inhibits specifically the lipid transfer activity of OSBP. As a consequence, post-Golgi trafficking, membrane cholesterol levels, and PI(4)P turnover were affected. Finally, using intermolecular FRET analysis, we demonstrate that SWG directly binds to the lipid-binding cavity of OSBP. Collectively these results describe SWG as a specific and intrinsically fluorescent pharmacological tool for dissecting OSBP properties at the cellular and molecular levels. Our findings indicate that SWG binds OSBP with nanomolar affinity, that this binding is sensitive to the membrane environment, and that SWG inhibits the OSBP-catalyzed lipid exchange cycle.

The Great Escape: how phosphatidylinositol 4-kinases and PI4P promote vesicle exit from the Golgi (and drive cancer)

Phosphatidylinositol 4-phosphate (PI4P) is a membrane glycerophospholipid and a major regulator of the characteristic appearance of the Golgi complex as well as its vesicular trafficking, signalling and metabolic functions. Phosphatidylinositol 4-kinases, and in particular the PI4KIIIβ isoform, act in concert with PI4P to recruit macromolecular complexes to initiate the biogenesis of trafficking vesicles for several Golgi exit routes. Dysregulation of Golgi PI4P metabolism and the PI4P protein interactome features in many cancers and is often associated with tumour progression and a poor prognosis. Increased expression of PI4P-binding proteins, such as GOLPH3 or PITPNC1, induces a malignant secretory phenotype and the release of proteins that can remodel the extracellular matrix, promote angiogenesis and enhance cell motility. Aberrant Golgi PI4P metabolism can also result in the impaired post-translational modification of proteins required for focal adhesion formation and cell–matrix interactions, thereby potentiating the development of aggressive metastatic and invasive tumours. Altered expression of the Golgi-targeted PI 4-kinases, PI4KIIIβ, PI4KIIα and PI4KIIβ, or the PI4P phosphate Sac1, can also modulate oncogenic signalling through effects on TGN-endosomal trafficking. A Golgi trafficking role for a PIP 5-kinase has been recently described, which indicates that PI4P is not the only functionally important phosphoinositide at this subcellular location. This review charts new developments in our understanding of phosphatidylinositol 4-kinase function at the Golgi and how PI4P-dependent trafficking can be deregulated in malignant disease.