P10.05.B Platelet-derived growth factor signalling pathways in patient-derived glioblastoma cells

Background

Platelet-derived growth factor (PDGF) signalling is essential in the development and maintenance of the neurovasculature. Of particular importance is PDGFRβ signalling for the recruitment and maintenance of the mural cell type pericytes, which occupy an important position in coordinating blood-brain barrier functions. The PDGF pathway is also implicated in glioblastoma, where overexpression of PDGFRα is a signature of the proneural subtype of the highly malignant and invasive tumour. The expression and signalling of both PDGFRα and β by tumour cells have been implicated in tumorigenesis and progression. Therefore, we sought to study PDGF receptor signalling in primary human-derived glioblastoma tumour cells to gain a better understanding of the signalling mechanisms driven by these receptors.

Material and Methods

Primary human epilepsy pericytes and glioblastoma tumour cells were isolated from surgical resections obtained from consenting patients at Auckland City Hospital. PDGF signalling pathways were investigated through treatment with exogenous PDGF ligands. Pathway activation was quantified using immunocytochemistry, human cytokine XL Proteome Profiler and cytometric bead arrays.

Results

PDGF-BB and PDGF-DD treatment led to the activation of PDGFRβ in pericyte cultures, which mediated the activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/Akt cascades, ultimately increasing pericyte proliferation and cytokine secretion. PDGF-AA treatment resulted in transient MAPK activation, but was not followed by increased proliferation in pericytes. In contrast, although PDGF-AA, -BB and -DD induced PDGFRα internalisation (and PDGF-BB and -DD induced PDGFRβ internalisation) in GBM tumour cells, this did not result in MAPK or PI3K/Akt activation or cell proliferation.

Conclusion

Despite PDGF receptor expression, the GBM tumour cells, in contrast to pericytes, surprisingly displayed a lack of responses to ligand stimulation through either PDGFRα or PDGFRβ. This warrants further investigation into the signalling mechanisms behind tumour cells to better understand tumour biology.

P12.07.B Getting to the core of microglia versus bone marrow-derived macrophages in glioblastoma

Background

Microglia and bone marrow-derived macrophages (BMDMs) are two ontogenetically distinct myeloid populations present within glioblastoma that can comprise 30-50% of the tumour mass. Historically, these cell types have been conflated and studied as a single population of ‘tumour-associated macrophages’. Recent advances in single-cell omics have allowed population delineation, suggesting microglia and BMDMs may play different roles within the tumour and subsequently differentially affect tumour progression. Despite building evidence for the unique functions of these cells within glioblastoma, the inherent heterogeneity of the tumour landscape has complicated such studies. Indeed, macrophages exist as phenotypically and functionally diverse populations that are polarised in a context-dependent manner. Hence, to understand the differences between microglia and BMDMs within glioblastoma, both ontogeny and spatial location must be considered.

Material and Methods

To elucidate the functional roles of microglia and BMDMs across the tumour landscape, a publicly available RNAseq dataset was utilised to classify myeloid cells into four populations based on spatial location and ontogeny. These were tumour core BMDMs and microglia, or tumour periphery BMDMs and microglia. Differential gene analysis was then performed to identify significant differentially expressed genes (DEGs) between classified myeloid populations. Tumour core DEGs were then compared against the Ivy Glioblastoma Atlas to define their expression across anatomical tumour regions. Finally, myeloid DEGs were validated at the protein level on human glioblastoma tissue through immunohistochemistry.

Results

Microglia and BMDMs showed different spatial distributions across the tumour landscape and displayed distinct functional expression profiles. Microglia held a more chemotactic and pro-inflammatory profile, whereas BMDMs held a more pro-tumoural profile. However, a comparison of microglia between the tumour core and periphery revealed that tumour microglia upregulate many pro-tumoural genes, including multiple genes that have previously been defined as ‘BMDM-enriched’. Moreover, we found myeloid DEGs identified within the tumour core cluster to distinct spatial tumour regions such as the vascular or hypoxic niche. Immunohistochemical staining reflected these spatial expression profiles, identifying a distinct population of phagocytic macrophages within the hypoxic niche.

Conclusion

Although microglia and BMDMs represent two ontogenetically distinct myeloid populations within glioblastoma, both cell types can adopt similar functional expression profiles within the tumour core, particularly within tumour niches. This indicates that myeloid cell function is strongly influenced by the tumour microenvironment, rather than ontogeny alone.

P10.04.A The development of a potent, tumour-specific heptamethine cyanine dye-palbociclib conjugate with novel mechanisms of action for the treatment of glioblastoma

Background

Glioblastoma is the most common and aggressive primary brain tumour in adults. The development of anti-cancer agents for brain tumours is challenged by the blood-brain barrier and the resistance conferred by the local tumour microenvironment. Heptamethine cyanine dyes (HMCDs) are a class of near-infrared fluorescence compounds that have recently emerged as promising agents for drug delivery

Material and Methods

We conjugated palbociclib, a cyclin-dependent kinase 4/6 inhibitor to the HMCD, MHI 148 for the treatment of GBM. Patient-derived GBM cell lines were established from surgically resected biopsy GBM tissue.

Results

High-throughput drug screening revealed an almost 100-fold increase in cytotoxicity of the palbociclib-MHI 148 conjugate compared to palbociclib alone. Moreover, the palbociclib-MHI 148 conjugate was synergistic with radiation, but not with temozolomide. Further analysis revealed the palbociclib-MHI 148 conjugate was superior to other cyclin-dependent kinase inhibitors in vitro. The shift of palbociclib from cytostatic to cytotoxic when conjugated to MHI 148 prompted further investigation. We revealed that palbociclib-MHI 148-dependent inhibition of cell-cycle progression resulted in increased DNA damage. This preceded increased transcription of key extrinsic apoptosis genes and caused a time-dependent upregulation of TNFR1 endocytosis-dependent cell death signalling. Notably, inhibition of endocytosis and siRNA knockdown of TNFR1 prevented palbociclib-MHI 148-induced cell death.

Conclusion:

These results highlight a novel mechanism of action of palbociclib when conjugated to MHI-148 that induced autocrine-driven TNFR1-mediated apoptosis. In addition, we highlight the potential application of HMCDs in repurposing tyrosine kinase inhibitors, to overcome the current limitations preventing the expansion of second-line treatment options for GBM.

P10.03 Immunological differences between patient-matched normal-derived and GBM-derived pericytes

BACKGROUND

Glioblastoma Multiforme (GBM) is the most aggressive, fatal, yet most common form of brain malignancy in adults. Despite advances in immune-based treatments for other modes of cancer, GBM remains a challenge due to its ability to dampen immune responses via mechanisms not yet fully understood. With a median survival time of only 15 months following diagnosis, there is a strong push to find new targets for therapy. The microenvironment comprises a mixture of malignant tumour cells, stroma, blood vessels and infiltrating inflammatory cells. Despite advances in understanding the contribution of these cells in establishing an anti-inflammatory microenvironment, the contribution of pericytes, an important neurovascular mural cell that forms the blood-brain barrier, has been inadequately studied. Therefore, we investigated the differences in immune profile between patient-matched non-neoplastic brain- and GBM-derived pericytes under basal and induced conditions.

MATERIAL AND METHODS

Primary patient-matched non-neoplastic brain and GBM tumour derived pericytes were isolated from specimens excised from consenting patients undergoing GBM surgical resection at Auckland City Hospital. Pericytes were treated with inflammatory cytokines including IL-1β, IFN-γ, TNFα and TGFβ for up to 24 hours. Inflammatory profile changes were probed for using fluorescent immunocytochemistry, qRT-PCR and spectral flow cytometry. Media was also collected for secretome analysis via cytometric bead array.

RESULTS

GBM pericytes show decreased expression of CX3CL1, both basally and following IL-1β treatment, via qRT-PCR and CBA. In contrast, increased gene expression and secretion of IL-6 and IL-8 by GBM pericytes were observed. GBM pericytes also basally express CD90 and anti-inflammatory molecule PD-L1 compared to their normal counterparts. In terms of activated pathways, basal SMAD2/3 activation is increased in GBM pericytes, while also showing greater activation following treatment with IL-1β, IFN-γ but not TNFα. C/EBPδ is activated and translocated following inflammatory stimulation; however, shows localised expression within the cytoplasm only observed in GBM pericytes.

CONCLUSION

This immunological screen of GBM pericytes highlights them as key players in the establishment of the tumour microenvironment. With data suggesting the activation of pathways such as the SMAD2/3 pathway in an unconventional manner, it suggests the potential for pericytes to manipulate pathways towards a more immunosuppressive outcome. Further immune characterisation of such cells is required to fully understand how they might contribute to the immunosuppressive nature of GBM.

Use of tissue plasminogen activator in the treatment of shunt blockage secondary to intraventricular haemorrhage

A 51-year-old woman with a history of idiopathic aqueduct stenosis, treated initially with insertion of a ventriculo peritoneal shunt, presented to our institution with shunt dysfunction. She had previously undergone multiple shunt revisions for shunt infection, shunt blockage and low-pressure symptoms, most recently with conversion to a ventriculo atrial (VA) shunt. Her VA shunt was again revised, with replacement of the ventricular catheter, however surgery was complicated by a large intraventricular haemorrhage (IVH) requiring placement of an external ventricular drain (EVD). Prior to eventual removal of her EVD it was determined that the VA shunt had blocked as a result of the IVH. Subsequently alteplase, a recombinant tissue plasminogen activator (tPA), was administered into the shunt reservoir, resulting in successful return of shunt function, therefore avoiding the need for further shunt revision. This is the first description of the use of tPA to unblock a shunt obstructed by blood.

[Urolithiasis and its conservative treatment based on analysis of the calculi]

The exact analysis of urinary calculi is the condition for an aimed conservative therapy of urolithiasis. As standardized method of the analysis of urinary calculi the X-ray diffraction was introduced in the GDR. This investigation method allows a qualitative and quantitative analysis of the concrements. The possibilities of the conservative therapy of urolithiasis were explained. To this conservative treatment belong the treatment of a colic, the removal of a calculus, the litholysis and the prophylaxis of recidivations.