Patient-derived scaffolds as a model of colorectal cancer

Background

Colorectal cancer is the second most common cause of cancer‐related death worldwide and standardized therapies often fail to treat the more aggressive and progressive types of colorectal cancer. Tumor cell heterogeneity and influence from the surrounding tumor microenvironment (TME) contribute to the complexity of the disease and large variability in clinical outcomes.

Methods

To model the heterogeneous nature of colorectal cancer, we used patient‐derived scaffolds (PDS), which were obtained via decellularization of surgically resected tumor material, as a growth substrate for standardized cell lines.

Results

After confirmation of native cell absence and validation of the structural and compositional integrity of the matrix, 89 colorectal PDS were repopulated with colon cancer cell line HT29. After 3 weeks of PDS culture, HT29 cells varied their gene and protein expression profiles considerably compared to 2D‐grown HT29 cells. Markers associated with proliferation were consistently decreased, while markers associated with pluripotency were increased in PDS‐grown cells compared to their 2D counterparts. When comparing the PDS‐induced changes in HT29 cells with clinically relevant tumor information from individual patients, we observed significant associations between stemness/pluripotency markers and tumor location, and between epithelial‐to‐mesenchymal transition (EMT) markers and cancer mortality. Kaplan–Meier analysis revealed that low PDS‐induced EMT correlated with worse cancer‐specific survival.

Conclusions

The colorectal PDS model can be used as a simplified personalized tool that can potentially reveal important diagnostic and pathophysiological information related to the TME.

Mechanisms of AMPA Receptor Endosomal Sorting

The regulation of synaptic AMPA receptors (AMPARs) is critical for excitatory synaptic transmission, synaptic plasticity and the consequent formation of neural circuits during brain development and their modification during learning and memory processes. The number of synaptic AMPARs is regulated through endocytosis, exocytosis and endosomal sorting that results in recycling back to the plasma membrane or degradation in the lysosome. Hence, endo-lysosomal sorting is vitally important in maintaining AMPAR expression at the synapse, and the dynamic regulation of these trafficking events is a key component of synaptic plasticity. A reduction in synaptic strength such as in long-term depression (LTD) involves AMPAR sorting to lysosomes to reduce synaptic AMPAR number, whereas long-term potentiation (LTP) involves an increase in AMPAR recycling to increase the number of AMPARs at synapses. Here, we review our current understanding of the endosomal trafficking routes taken by AMPARs, and the mechanisms involved in AMPAR endosomal sorting, focussing on the numerous AMPAR associated proteins that have been implicated in this complex process. We also discuss how these events are dysregulated in brain disorders.

Cortactin regulates endo-lysosomal sorting of AMPARs via direct interaction with GluA2 subunit

AMPA receptor (AMPAR) trafficking is a key determinant of synaptic strength and synaptic plasticity. Under basal conditions, constitutive trafficking maintains surface AMPARs by internalization into the endosomal system, where the majority are sorted and targeted for recycling back to the plasma membrane. NMDA receptor (NMDAR)-dependent Long-Term Depression (LTD) is characterised by a reduction in synaptic strength, and involves endosomal sorting of AMPARs away from recycling pathways to lysosomes. The mechanisms that determine whether AMPARs are trafficked to lysosomes or to recycling endosomes, especially in response to NMDAR stimulation, are unclear. Here, we define a role for the actin-regulatory protein cortactin as a mediator of AMPAR endosomal sorting by direct interaction with the GluA2 subunit. Disrupting GluA2-cortactin binding in neurons causes the targeting of GluA2/A3-containing receptors to lysosomes and their consequent degradation, resulting in a loss of surface and synaptic GluA2 under basal conditions and an occlusion of subsequent LTD expression. Furthermore, we show that NMDAR stimulation causes a dissociation of endogenous cortactin from GluA2 via tyrosine phosphorylation of cortactin. These results demonstrate that cortactin maintains GluA2/A3 levels by directing receptors away from lysosomes, and that disrupting GluA2-cortactin interactions to target GluA2/A3 to lysosomes is an essential component of LTD expression.

PICK1 regulates AMPA receptor endocytosis via direct interactions with AP2 α-appendage and dynamin

Clathrin-mediated endocytosis (CME) is used to internalize a diverse range of cargo proteins from the cell surface, often in response to specific signals. In neurons, the rapid endocytosis of GluA2-containing AMPA receptors (AMPARs) in response to NMDA receptor (NMDAR) stimulation causes a reduction in synaptic strength and is the central mechanism for long-term depression, which underlies certain forms of learning. The mechanisms that link NMDAR activation to CME of AMPARs remain elusive. PICK1 is a BAR domain protein required for NMDAR-dependent reductions in surface GluA2; however, the molecular mechanisms involved are unclear. In this study, we show that PICK1 makes direct, NMDAR-dependent interactions with the core endocytic proteins AP2 and dynamin. PICK1-AP2 interactions are required for clustering AMPARs at endocytic zones in dendrites in response to NMDAR stimulation and for consequent AMPAR internalization. We further show that PICK1 stimulates dynamin polymerization. We propose that PICK1 is a cargo-specific endocytic accessory protein required for efficient, activity-dependent AMPAR endocytosis.

The PICK1 Ca2+ sensor modulates N-methyl-d-aspartate (NMDA) receptor-dependent microRNA-mediated translational repression in neurons

MicroRNAs (miRNAs) are important regulators of localized mRNA translation in neuronal dendrites. The presence of RNA-induced silencing complex proteins in these compartments and the dynamic miRNA expression changes that occur in response to neuronal stimulation highlight their importance in synaptic plasticity. Previously, we demonstrated a novel interaction between the major RNA-induced silencing complex component Argounaute-2 (Ago2) and the BAR (bin/amphiphysin/rvs) domain protein PICK1. PICK1 recruits Ago2 to recycling endosomes in dendrites, where it inhibits miRNA-mediated translational repression. Chemical induction of long-term depression via NMDA receptor activation causes the dissociation of Ago2 from PICK1 and a consequent increase in dendritic miRNA-mediated gene silencing. The mechanism that underlies the regulation of PICK1-Ago2 binding is unknown. In this study, we demonstrate that the PICK1-Ago2 interaction is directly sensitive to Ca²⁺ ions so that high [Ca²⁺]_free reduces PICK1 binding to Ago2. Mutating a stretch of C-terminal Ca²⁺-binding residues in PICK1 results in a complete block of NMDA-induced PICK1-Ago2 disassociation in cortical neurons. Furthermore, the same mutant also blocks NMDA-stimulated miRNA-mediated gene silencing. This study defines a novel mechanism whereby elevated [Ca²⁺] induced by NMDA receptor activation modulates Ago2 and miRNA activity via PICK1. Our work suggests a Ca²⁺-dependent process to regulate miRNA activity in neurons in response to the induction of long-term depression.

Abstract P3-10-01: Investigation of HBOC germline mutations in women diagnosed with breast cancer in Trinidad and Tobago

Background: Trinidad and Tobago (T&T) is a southern Caribbean island with a population of approx. 1.3 million. According to WHO/PAHO, T&T has the 2nd highest breast cancer mortality rate in the region, and breast cancer continues to lead in incidence and mortality in cancers among female citizens. Notably, a large proportion of breast cancer cases in T&T appear to occur at a young age; with nearly 36% of breast cancers diagnosed under the age of 50. It is known that a younger age at diagnosis can be associated with Hereditary Breast and Ovarian Cancer syndrome (HBOC), characterized by germline mutations in tumor suppressor genes such as BRCA, PTEN and TP53. Yet, the prevalence of HBOC mutations remains unknown in T&T, as local health services for genetic counseling and testing in T&T currently do not exist. As such, our study aimed to determine the prevalence rate of HBOC mutations among women with breast cancer in T&T who met NCCN criteria for evaluation for HBOC syndrome; thus investigating whether there is a need to include genetic testing and counseling in local oncology management in T&T.

Methods: At the National Radiotherapy Center, the main oncology unit in T&T, female breast cancer patients, who met the NCCN criteria for further genetic counseling/testing, were recruited either through doctor referrals or chart reviews. We conducted interviews inquiring about their personal breast cancer diagnosis, risk factors for breast cancer, as well as any relevant family history. This was followed by the collection of saliva samples using Oragene kits, which were then analyzed by Color Genomics Inc. for 30 genes associated with hereditary cancers; including 19 HBOC associated genes such as BRCA1, BRCA2, TP53 and PTEN. Finalized results were returned to patients by genetic counselors from Color Genomics.

Results: 165 patients who met NCCN guidelines for HBOC counseling/testing were approached, of whom 150 agreed to participate. Due to funding and resource limitations, 60 samples were collected thus far; ages ranged from 19-56. The majority of women met NCCN criteria based on age of personal breast cancer diagnosis (40%), and/or family history of breast and/or ovarian cancer (60%). Preliminary results show that of 49 samples, 10 patients tested positive for deleterious HBOC germline mutations: 7 - BRCA1, 2 - BRCA2 and 1 - PTEN; thus far giving a prevalence rate of 20%.

Discussion: Therefore, our results found a strikingly high HBOC germline mutation prevalence rate of 20% among a cohort of female breast cancer patients meeting NCCN criteria in T&T. As we continue to finalize the incoming data on these patients, we hope to draw associations between their genetic status and their respective tumor markers, family history, and personal medical history. However, these initial results demonstrate the need to include genetic counseling and testing in the local oncology management in T&T, as the identification of HBOC mutations can influence treatment options, as well as help identify family members who are at high risk for cancer predisposition. Ultimately, this integration could help alleviate the country's high incidence and mortality rates with respect to breast cancer, and save the public healthcare system significant financial resources.Background: Trinidad and Tobago (T&T) is a southern Caribbean island with a population of approx. 1.3 million. According to WHO/PAHO, T&T has the 2nd highest breast cancer mortality rate in the region, and breast cancer continues to lead in incidence and mortality in cancers among female citizens. Notably, a large proportion of breast cancer cases in T&T appear to occur at a young age; with nearly 36% of breast cancers diagnosed under the age of 50. It is known that a younger age at diagnosis can be associated with Hereditary Breast and Ovarian Cancer syndrome (HBOC), characterized by germline mutations in tumor suppressor genes such as BRCA, PTEN and TP53. Yet, the prevalence of HBOC mutations remains unknown in T&T, as local health services for genetic counseling and testing in T&T currently do not exist. As such, our study aimed to determine the prevalence rate of HBOC mutations among women with breast cancer in T&T who met NCCN criteria for evaluation for HBOC syndrome; thus investigating whether there is a need to include genetic testing and counseling in local oncology management in T&T.

Methods: At the National Radiotherapy Center, the main oncology unit in T&T, female breast cancer patients, who met the NCCN criteria for further genetic counseling/testing, were recruited either through doctor referrals or chart reviews. We conducted interviews inquiring about their personal breast cancer diagnosis, risk factors for breast cancer, as well as any relevant family history. This was followed by the collection of saliva samples using Oragene kits, which were then analyzed by Color Genomics Inc. for 30 genes associated with hereditary cancers; including 19 HBOC associated genes such as BRCA1, BRCA2, TP53 and PTEN. Finalized results were returned to patients by genetic counselors from Color Genomics.

Results: 165 patients who met NCCN guidelines for HBOC counseling/testing were approached, of whom 150 agreed to participate. Due to funding and resource limitations, 60 samples were collected thus far; ages ranged from 19-56. The majority of women met NCCN criteria based on age of personal breast cancer diagnosis (40%), and/or family history of breast and/or ovarian cancer (60%). Preliminary results show that of 49 samples, 10 patients tested positive for deleterious HBOC germline mutations: 7 - BRCA1, 2 - BRCA2 and 1 - PTEN; thus far giving a prevalence rate of 20%.

Discussion: Therefore, our results found a strikingly high HBOC germline mutation prevalence rate of 20% among a cohort of female breast cancer patients meeting NCCN criteria in T&T. As we continue to finalize the incoming data on these patients, we hope to draw associations between their genetic status and their respective tumor markers, family history, and personal medical history. However, these initial results demonstrate the need to include genetic counseling and testing in the local oncology management in T&T, as the identification of HBOC mutations can influence treatment options, as well as help identify family members who are at high risk for cancer predisposition. Ultimately, this integration could help alleviate the country's high incidence and mortality rates with respect to breast cancer, and save the public healthcare system significant financial resources.

Citation Format: Parkinson GT, Chagpar AB, Hofstatter EW, Nunez-Smith M. Investigation of HBOC germline mutations in women diagnosed with breast cancer in Trinidad and Tobago [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-10-01.