Adaptation to microenvironmental stress in glioblastoma. Mechanistic studies and potential targets.

Although the overall mortality in cancer is steadily decreasing, major groups of patients still respond poorly to available treatments. The key clinical challenge addressed in the present thesis work relates to the inherent adaptive capacity of glioblastoma (GBM) tumors, resulting in treatment resistance and dismal prognosis. GBM represents the most common and lethal primary CNS tumor in adults. Tumor hypoxia and associated metabolic acidosis are main traits of GBM, and the adaptive responses include aberrant, intracellular lipid accumulation in lipid droplets (LDs), which associate with GBM and other aggressive cancers.Papers I and II show that scavenging of extracellular vesicles (EVs) may contribute to stress adaptation by transforming tumor cells into the LD+ phenotype. On a mechanistic level, hypoxia-induced EV uptake depended on heparan sulfate proteoglycan (HSPG) endocytosis, preferentially via the lipid raft pathway. In Paper II, we studied glioma cell adaptation to chronic acidosis, which triggered a robust induction of chondroitin sulfate (CS) in in vitro models and patient samples. As a functional consequence, lipid particle scavenging was decreased. Hence, CS induction together with LD loading may be a targetable protective mechanism to avoid lipotoxicity. In Paper III, we investigate whether necrosis, a histological hallmark of GBM, is a scavengeable nutrient source for glioma cells. Preliminary results show efficient transfer of protein, DNA and lipids via cell debris. Robust induction of LDs following debris scavenging may dampen the response to irradiation. LD+ cells were hypersensitive to drugs inhibiting LD biosynthesis or utilization, which deserves further exploration.In Paper IV, we developed a methodology for tumor surfaceome mapping (TS-MAP) from intact tumor specimens. Importantly, the TS-MAP method allows to specifically identify the internalizing activity of a given target, an essential feature for cytotoxic drug delivery using antibody-based therapies.Altogether, this thesis work contributes to mechanistic understanding of stress adaptation in GBM and presents new avenues for target identification strategies

Pro-metastatic functions of lipoproteins and extracellular vesicles in the acidic tumor microenvironment

Although the overall mortality in cancer is steadily decreasing, major groups of patients still respond poorly to available treatments. The key clinical challenge discussed here relates to the inherent capacity of cancer cells to metabolically adapt to hypoxic and acidic stress, resulting in treatment resistance and a pro-metastatic behavior. Hence, a detailed understanding of stress adaptive responses is critical for the design of more rational therapeutic strategies for cancer. We will focus on the emerging role of extracellular vesicles (EVs) and lipoprotein particles in cancer cell metabolic stress adaptation and how these pathways may constitute potential Achilles’ heels of the cancer cell machinery and alternative treatment targets of metastasis. In this context, common extracellular lipid uptake mechanisms, involving specific cell-surface receptors and endocytic pathways, may operate during remodeling of acidic atherosclerotic plaques as well as the tumor microenvironment. The role of endocytosis in regulating the cellular response to hypoxic and acidic stress through spatial coordination of receptor proteins may be exploited for therapeutic purposes. As a consequence, molecular mechanisms of endocytosis have attracted increasing attention as potential targets for tumor specific delivery of therapeutic substances, such as antibody–drug conjugates. The identification of internalizing surface proteins specific to the acidic tumor niche remains an unmet need of high clinical relevance. Among the currently explored, acidosis-related, internalizing target proteins, we will focus on the cell-surface proteoglycan carbonic anhydrase 9

Proteoglycans : a common portal for SARS-CoV-2 and extracellular vesicle uptake

As structural components of the glycocalyx, heparan sulfate proteoglycans (HSPGs) are involved in multiple pathophysiological processes at the apex of cell signaling cascades, and as endocytosis receptors for particle structures, such as lipoproteins, extracellular vesicles, and enveloped viruses, including SARS-CoV-2. Given their diversity and complex biogenesis regulation, HSPGs remain understudied. Here we compile some of the latest studies focusing on HSPGs as internalizing receptors of extracellular vesicles ("endogenous virus") and SARS-CoV-2 lipid-enclosed particles and highlight similarities in their biophysical and structural characteristics. Specifically, the similarities in their biogenesis, size, and lipid composition may explain a common dependence on HSPGs for efficient cell-surface attachment and uptake. We further discuss the relative complexity of extracellular vesicle composition and the viral mechanisms that evolve towards increased infectivity that complicate therapeutic strategies addressing blockade of their uptake

Functional role of extracellular vesicles and lipoproteins in the tumour microenvironment

Cancer can be regarded as an invasive organ that exhibits unique plasticity provided by coordinated, cancer cell-stromal cell communication in the tumour microenvironment. Typical stress factors in the tumour niche, such as hypoxia and acidosis, are major drivers and modulators of these events. Recent findings reveal an important role of extracellular vesicles and lipoproteins in cancer cell adaption to exogenous stress. Adaptive mechanisms include stimulation of angiogenesis and increased metastasis. Here, we will discuss the similarities and distinct features of these endogenous nanoparticles and their roles as signalosomes and nutrient sources in cancer. We will focus on the accumulating evidence for a central role of cell-surface heparan sulphate proteoglycans in the uptake of extracellular vesicles and lipoproteins. This article is part of the discussion meeting issue ‘Extracellular vesicles and the tumour microenvironment’

Landscape of surfaceome and endocytome in human glioma is divergent and depends on cellular spatial organization

Therapeutic strategies directed at the tumor surfaceome (TS), including checkpoint inhibitor blocking antibodies, antibody drug conjugates (ADCs), and chimeric antigen receptor T (CAR-T) cells, provide a new armament to fight cancer. However, a remaining bottleneck is the lack of strategies to comprehensively interrogate patient tumors for potential TS targets. Here, we have developed a platform (tumor surfaceome mapping [TS-MAP]) integrated with a newly curated TS classifier (SURFME) that allows profiling of primary 3D cultures and intact patient glioma tumors with preserved tissue architecture. Moreover, TS-MAP specifically identifies proteins capable of endocytosis as tractable targets for ADCs and other modalities requiring toxic payload internalization. In high-grade gliomas that remain among the most aggressive forms of cancer, we show that cellular spatial organization (2D vs. 3D) fundamentally transforms the surfaceome and endocytome (e.g., integrins, proteoglycans, semaphorins, and cancer stem cell markers) with general implications for target screening approaches, as exemplified by an ADC targeting EGFR. The TS-MAP platform was further applied to profile the surfaceome and endocytome landscape in a cohort of freshly resected gliomas. We found a highly diverse TS repertoire between patient tumors, not directly associated with grade and histology, which highlights the need for individualized approaches. Our data provide additional layers of understanding fundamental to the future development of immunotherapy strategies, as well as procedures for proteomics-based target identification and selection. The TS-MAP platform should be widely applicable in efforts aiming at a better understanding of how to harness the TS for personalized immunotherapy