Genevieve M. Boland

Adult mesenchymal stem cells and cell-based tissue engineering

The identification of multipotential mesenchymal stem cells (MSCs) derived from adult human tissues, including bone marrow stroma and a number of connective tissues, has provided exciting prospects for cell-based tissue engineering and regeneration. This review focuses on the biology of MSCs, including their differentiation potentials in vitro and in vivo, and the application of MSCs in tissue engineering. Our current understanding of MSCs lags behind that of other stem cell types, such as hematopoietic stem cells. Future research should aim to define the cellular and molecular fingerprints of MSCs and elucidate their endogenous role(s) in normal and abnormal tissue functions.

Wnt 3a promotes proliferation and suppresses osteogenic differentiation of adult human mesenchymal stem cells

Multipotential adult mesenchymal stem cells (MSCs) are able to differentiate along several known lineages, and lineage commitment is tightly regulated through specific cellular mediators and interactions. Recent observations of a low/high bone‐mass phenotype in patients expressing a loss‐/gain‐of‐function mutation in LRP5, a coreceptor of the Wnt family of signaling molecules, suggest the importance of Wnt signaling in bone formation, possibly involving MSCs. To analyze the role of Wnt signaling in mesenchymal osteogenesis, we have profiled the expression of WNTs and their receptors, FRIZZLEDs (FZDs), and several secreted Wnt inhibitors, such as SFRPs, and examined the effect of Wnt 3a, as a representative canonical Wnt member, during MSC osteogenesis in vitro. WNT11, FZD6, SFRP2, and SFRP3 are upregulated during MSC osteogenesis, while WNT9A and FZD7 are downregulated. MSCs also respond to exogenous Wnt 3a, based on increased β‐catenin nuclearization and activation of a Wnt‐responsive promoter, and the magnitude of this response depends on the MSC differentiation state. Wnt 3a exposure inhibits MSC osteogenic differentiation, with decreased matrix mineralization and reduced alkaline phosphatase mRNA and activity. Wnt 3a treatment of fully osteogenically differentiated MSCs also suppresses osteoblastic marker gene expression. The Wnt 3a effect is accompanied by increased cell number, resulting from both increased proliferation and decreased apoptosis, particularly during expansion of undifferentiated MSCs. The osteo‐suppressive effects of Wnt 3a are fully reversible, i.e., treatment prior to osteogenic induction does not compromise subsequent MSC osteogenesis. The results also showed that sFRP3 treatment attenuates some of the observed Wnt 3a effects on MSCs, and that inhibition of canonical Wnt signaling using a dominant negative TCF1 enhances MSC osteogenesis. Interestingly, expression of Wnt 5a, a non‐canonical Wnt member, appeared to promote osteogenesis. Taken together, these findings suggest that canonical Wnt signaling functions in maintaining an undifferentiated, proliferating progenitor MSC population, whereas non‐canonical Wnts facilitate osteogenic differentiation. Release from canonical Wnt regulation is a prerequisite for MSC differentiation. Thus, loss‐/gain‐of‐function mutations of LRP5 would perturb Wnt signaling and depress/promote bone formation by affecting the progenitor cell pool. Elucidating Wnt regulation of MSC differentiation is important for their potential application in tissue regeneration. Published 2004 Wiley‐Liss, Inc.

Cross‐talk between Wnt signaling pathways in human mesenchymal stem cells leads to functional antagonism during osteogenic differentiation

Wnt signaling is involved in developmental processes and in adult stem cell homeostasis. This study analyzes the role(s) of key Wnt signaling mediators in the maintenance and osteogenesis of mesenchymal stem cells (MSCs). We focus specifically on the involvement of low‐density lipoprotein‐related protein 5 (LRP5), T‐cell factor 1 (TCF1), and Frizzled (Fz) receptors, in the presence or absence of exogenous, prototypical canonical (Wnt3a), and non‐canonical (Wnt5a) Wnts. In undifferentiated MSCs, LRP5 and TCF1 mediate canonical Wnt signal transduction, leading to increased proliferation, enhanced synergistically by Wnt3a. However, LRP5 overexpression inhibits osteogenic differentiation, further suppressed by Wnt3a. Wnt5a does not affect cell proliferation but enhances osteogenesis of MSCs. Interestingly, Wnt5a inhibits Wnt3a effects on MSCs, while Wnt3a suppresses Wnt5a‐mediated enhancement of osteogenesis. Flow cytometry revealed that LRP5 expression elicits differential changes in Fz receptor profiles in undifferentiated versus osteogenic MSCs. Taken together, these results suggest that Wnt signaling crosstalk and functional antagonism with the LRP5 co‐receptor are key signaling regulators of MSC maintenance and differentiation. J. Cell. Biochem. 101:1109–1124, 2007.

Wnt signaling during BMP-2 stimulation of mesenchymal chondrogenesis.

Members of both the Wnt and bone morphogenetic protein (BMP) families of signaling molecules have been implicated in the regulation of cartilage development. A key component of the Wnt signaling pathway is the cytosolic protein, β‐catenin. We have recently shown that the chondrogenic activity of BMP‐2 in vitro involves the action of the cell–cell adhesion protein, N‐cadherin, which functionally complexes with β‐catenin. The aim of this study is to test the hypothesis that Wnts may be involved in BMP‐2 induced chondrogenesis, using an in vitro model of high‐density micromass cultures of the murine multipotent mesenchymal cell line, C3H10T1/2. Expression of a number of Wnt members was detected in these cultures, including Wnt‐3A and Wnt‐7A, whose levels were up‐ and downregulated, respectively, by BMP‐2. To assess the functional involvement of Wnt signaling in BMP‐2 induced chondrogenesis, cultures were treated with lithium chloride, a Wnt‐7A mimetic that acts by inhibiting the serine/threonine phosphorylation activity of glycogen synthase kinase‐3β (GSK‐3β). Lithium treatment significantly inhibited BMP‐2 stimulation of chondrogenesis as well as GSK‐3β enzymatic activity, and decreased the levels of N‐cadherin protein and mRNA. Furthermore, lithium decreased BMP‐2 upregulation of total and nuclear levels of LEF‐1 and β‐catenin as well as their interaction during later chondrogenesis; similarly, the interaction of β‐catenin with N‐cadherin was also decreased. Interestingly, lithium treatment did not affect the ability of BMP‐2 to decrease ubiquitination of β‐catenin, although it did reduce the interaction of β‐catenin with GSK‐3β during late chondrogenesis (days 9–13). We suggest that the chondro‐inhibitory effect of lithium on BMP‐2 induced chondrogenesis indicates antagonism between lithium‐like Wnts and BMP‐2 during mesenchymal condensation. J. Cell. Biochem. 84: 816–831, 2002.

Association between adherence to National Comprehensive Cancer Network treatment guidelines and improved survival in patients with colon cancer

The objective of the current study was to examine the impact of adherence to guidelines on stage‐specific survival outcomes in patients with stage III and high‐risk stage II colon cancer. The National Comprehensive Cancer Network (NCCN) has established working, expert consensus, and evidence‐based guidelines for organ‐specific cancer care, including care of patients with colon cancer.

Activation of PI3K signaling in Merkel cell carcinoma

Purpose: Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor, often metastatic at presentation, for which current chemotherapeutic regimens are largely ineffective. As its pathogenesis is still unknown, we hypothesized that deregulation of signaling pathways commonly activated in cancer may contribute to MCC tumorigenesis and may provide insights into targeted therapy approaches for this malignancy. Experimental Design: We retrospectively profiled 60 primary MCC samples using a SNaPshot-based tumor genotyping assay to screen for common mutations in 13 cancer genes. Results: We identified mutations in 9 (15%) MCC primary tumors, including mutations in TP53 (3 of 60) and activating mutations in the PIK3CA gene (6 of 60). Sanger sequencing of the primary MCC tumors detected one additional PIK3CA mutation (R19K) that had not been previously described in cancer. Merkel cell polyoma virus (MCPyV) was detected in 38 (66%) MCC cases and patients with MCPyV-positive cancers showed a trend toward better survival. With one exception, the presence of MCPyV and activating mutations in PIK3CA appeared mutually exclusive. We observed that signaling through the PI3K/pAKT pathway was active in one MCPyV-positive and in all MCPyV-negative MCC cell lines, as evidenced by AKT phosphorylation. Importantly, the presence of a PIK3CA-activating mutation was associated with sensitivity to treatment with ZST474, a specific phosphoinositide 3-kinase (PI3K) inhibitor, and to NVP-BEZ235, a dual PI3K/mTOR inhibitor, targeted agents under active clinical development. Conclusions: PI3K pathway activation may drive tumorigenesis in a subset of MCC and screening these tumors for PIK3CA mutations could help identify patients who may respond to treatment with PI3K pathway inhibitors. Clin Cancer Res; 18(5); 1227–36. ©2012 AACR.

Co-clinical assessment identifies patterns of BRAF inhibitor resistance in melanoma

Multiple mechanisms have been described that confer BRAF inhibitor resistance to melanomas, yet the basis of this resistance remains undefined in a sizable portion of patient samples. Here, we characterized samples from a set of patients with melanoma that included individuals at baseline diagnosis, on BRAF inhibitor treatment, and with resistant tumors at both the protein and RNA levels. Using RNA and DNA sequencing, we identified known resistance-conferring mutations in 50% (6 of 12) of the resistant samples. In parallel, targeted proteomic analysis by protein array categorized the resistant samples into 3 stable groups, 2 of which were characterized by reactivation of MAPK signaling to different levels and 1 that was MAPK independent. The molecular relevance of these classifications identified in patients was supported by both mutation data and the similarity of resistance patterns that emerged during a co-clinical trial in a genetically engineered mouse (GEM) model of melanoma that recapitulates the development of BRAF inhibitor resistance. Additionally, we defined candidate biomarkers in pre- and early-treatment patient samples that have potential for predicting clinical responses. On the basis of these observations, we suggest that BRAF inhibitor-resistant melanomas can be actionably classified using protein expression patterns, even without identification of the underlying genetic alteration.

Resistance to checkpoint blockade therapy through inactivation of antigen presentation

Treatment with immune checkpoint blockade (CPB) therapies often leads to prolonged responses in patients with metastatic melanoma, but the common mechanisms of primary and acquired resistance to these agents remain incompletely characterized and have yet to be validated in large cohorts. By analyzing longitudinal tumor biopsies from 17 metastatic melanoma patients treated with CPB therapies, we observed point mutations, deletions or loss of heterozygosity (LOH) in beta-2-microglobulin (B2M), an essential component of MHC class I antigen presentation, in 29.4% of patients with progressing disease. In two independent cohorts of melanoma patients treated with anti-CTLA4 and anti-PD1, respectively, we find that B2M LOH is enriched threefold in non-responders (~30%) compared to responders (~10%) and associated with poorer overall survival. Loss of both copies of B2M is found only in non-responders. B2M loss is likely a common mechanism of resistance to therapies targeting CTLA4 or PD1.Resistance to immune-checkpoint blockade often occurs in treated patients. Here, the authors demonstrate that B2M loss is a mechanism of primary and acquired resistance to therapies targeting CTLA4 or PD-1 in melanoma patients.

Sentinel lymph node biopsy in melanoma.

The technique of lymphatic mapping and sentinel lymph node (SLN) biopsy for melanoma has emerged during the last 2 decades as a minimally invasive approach to evaluate regional lymph node basins in patients with intermediate- and high-risk primary cutaneous melanoma and has changed our approach to the clinically negative lymph node basin in melanoma during the same period. This review focuses on preoperative assessment and operative strategies, pathologic evaluation of the SLN, issues related to regional lymph node basin control, and current clinical practice guidelines. Predictors of SLN status, the prognostic significance of the SLN, and areas of controversy are also discussed.

Ex Vivo Profiling of PD-1 Blockade Using Organotypic Tumor Spheroids

Ex vivo systems that incorporate features of the tumor microenvironment and model the dynamic response to immune checkpoint blockade (ICB) may facilitate efforts in precision immuno-oncology and the development of effective combination therapies. Here, we demonstrate the ability to interrogate ex vivo response to ICB using murine- and patient-derived organotypic tumor spheroids (MDOTS/PDOTS). MDOTS/PDOTS isolated from mouse and human tumors retain autologous lymphoid and myeloid cell populations and respond to ICB in short-term three-dimensional microfluidic culture. Response and resistance to ICB was recapitulated using MDOTS derived from established immunocompetent mouse tumor models. MDOTS profiling demonstrated that TBK1/IKKε inhibition enhanced response to PD-1 blockade, which effectively predicted tumor response in vivo Systematic profiling of secreted cytokines in PDOTS captured key features associated with response and resistance to PD-1 blockade. Thus, MDOTS/PDOTS profiling represents a novel platform to evaluate ICB using established murine models as well as clinically relevant patient specimens.Significance: Resistance to PD-1 blockade remains a challenge for many patients, and biomarkers to guide treatment are lacking. Here, we demonstrate feasibility of ex vivo profiling of PD-1 blockade to interrogate the tumor immune microenvironment, develop therapeutic combinations, and facilitate precision immuno-oncology efforts. Cancer Discov; 8(2); 196-215. ©2017 AACR.See related commentary by Balko and Sosman, p. 143See related article by Deng et al., p. 216This article is highlighted in the In This Issue feature, p. 127.