Growth of cancer stem cell driven tumors: Staged invasion, linear determinacy, and the tumor invasion paradox

Cancer Stem Cell–Directed Therapies: Recent Data From the Laboratory and Clinic

Decision letter: Differentiated glioma cell-derived fibromodulin activates integrin-dependent Notch signaling in endothelial cells to promote tumor angiogenesis and growth

Editor's evaluation: Differentiated glioma cell-derived fibromodulin activates integrin-dependent Notch signaling in endothelial cells to promote tumor angiogenesis and growth

Tumor Angiogenesis: A New Source of Pericytes

BackgroundRecent reports indicate that a subgroup of tumor cells named cancer stem cells (CSCs) or tumor initiating cells (TICs) are responsible for tumor initiation, growth and drug resistance. This subgroup of tumor cells has self-renewal capacity and could differentiate into heterogeneous tumor cell populations through asymmetric proliferation. The idea of CSC provides informative insights into tumor initiation, metastasis and treatment. However, the underlying mechanisms of CSCs regulating tumor behaviors are unclear due to the complex cancer system. To study the functions of CSCs in the complex tumor system, a few mathematical modeling studies have been proposed. Whereas, the effect of microenvironment (mE) factors, the behaviors of CSCs, progenitor tumor cells (PCs) and differentiated tumor cells (TCs), and the impact of CSC fraction and signaling heterogeneity, are not adequately explored yet.MethodsIn this study, a novel 3D multi-scale mathematical modeling is proposed to investigate the behaviors of CSCsin tumor progressions. The model integrates CSCs, PCs, and TCs together with a few essential mE factors. With this model, we simulated and investigated the tumor development and drug response under different CSC content and heterogeneity.ResultsThe simulation results shown that the fraction of CSCs plays a critical role in driving the tumor progression and drug resistance. It is also showed that the pure chemo-drug treatment was not a successful treatment, as it resulted in a significant increase of the CSC fraction. It further shown that the self-renew heterogeneity of the initial CSC population is a cause of the heterogeneity of the derived tumors in terms of the CSC fraction and response to drug treatments.ConclusionsThe proposed 3D multi-scale model provides a new tool for investigating the behaviors of CSC in CSC-initiated tumors, which enables scientists to investigate and generate testable hypotheses about CSCs in tumor development and drug response under different microenvironments and drug perturbations.

Covering the Cover

See related article in EMBO Molecular Medicine http://dx.doi.org/10.1002/emmm.201201516

Many tumors are hierarchically organized, with a minor population of cancer stem cells (CSCs)/tumor-initiating cells at the apex of the hierarchy. These CSCs are highly enriched for the ability to drive tumor initiation, metastasis, and disease recurrence after therapy. Thus, a better understanding of the CSC population will be critical to the design of more effective anticancer therapeutics. To address this challenge, we have generated a lentiviral-based cancer stem cell sensor that reports with high temporal resolution on the cancer stem cell phenotype as a dynamic state. Expression of a destabilized fluorescent protein is driven by activation of an artificial enhancer element (SORE6) that responds to the master stem cell transcription factors Oct4 and Sox2 or their paralogs. We have extensively validated this reporter as marking cells with the expected characteristics of cancer stem cells, including the ability to self-renew, initiate, and sustain tumorigenesis and metastasis and exhibit chemoresistance (Tang et al., Stem Cell Reports 4:155-159). Intravital videomicroscopy and ex vivo imaging of orthotopically-implanted MDAMB231 breast tumors carrying the SORE6 stem cell sensor revealed that 60% of the CSCs in the primary tumor are found in association with macrophages. Macrophage depletion with clodronate liposomes in vivo reduced the number of CSCs in the tumor, indicating a role for macrophages in supporting or expanding the CSC population. Importantly, intravital imaging showed instances in which contact with intratumoral macrophages appeared to cause an induction of the stem phenotype in non-stem tumor cells and that this induction is concentrated at TMEM intravasation doorways where macrophages are enriched. Modeling this phenomenon in heterotypic cocultures in vitro, we showed that coculture of tumor cells with M2-like macrophages but not endothelial cells could increase the proportion of CSCs. This increase was contact dependent and involved Notch signaling. Single cell fate-mapping experiments in the coculture model revealed that the macrophages caused a >4x increase in the rate of direct conversion of non-stem to stem cells, without affecting CSC proliferation. The induced CSCs were capable of initiating tumorsphere formation in vitro, thus confirming their functionality. In summary, this novel imaging approach allowed us to make the important finding that macrophage contact can induce phenotypic plasticity in more differentiated tumor cells, thereby allowing them to acquire a stem phenotype during intravasation and dissemination. These results suggest that targeting the interaction between macrophages and tumor cells may be a new strategy to reduce the cancer stem cell population both locally and systemically. Citation Format: Bingwu Tang, Ved Sharma, Yarong Wang, Yuval Raviv, David Entenberg, Maja Oktay, John Condeelis, Lalage Wakefield. A fluorescent cancer stem cell sensor reveals dynamic induction of a stem phenotype in non-stem tumor cells on contact with macrophages in vitro and in vivo [abstract]. In: Proceedings of the AACR Special Conference on the Evolving Landscape of Cancer Modeling; 2020 Mar 2-5; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2020;80(11 Suppl):Abstract nr B10.

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that orchestrates cell signaling through integrins and growth factor receptors. FAK has been implicated in multiple steps of carcinogenesis including tumor initiation, growth and metastasis. Amplification and overexpression of FAK have been observed in multiple aggressive human cancers including breast and ovarian. VS-4718 is a potent and selective FAK kinase inhibitor that was previously shown by us to exhibit preferential inhibitory activities on breast cancer stem cells. We have further extended our investigation of the role of FAK on cancer stem cells to other solid tumors and report here that pharmacological attenuation of FAK activity by VS-4718 or RNAi-mediated depletion of FAK exhibits preferential inhibitory effects on cancer stem cells. To determine if FAK plays a role in the biology of cancer stem cells, we depleted FAK expression in breast, ovarian and mesothelioma cancer cell lines by RNAi. Our results indicated that shRNA-mediated knock-down of FAK inhibits tumorsphere formation in vitro. In parallel, VS-4718 was evaluated in a multitude of cancer stem cell assays both in vitro and in vivo. Pre-treatment of SUM159 cells with VS-4718 in matrigel reduced the percentage of ALDEFLUOR+ cancer stem cells and side population (SP). Similar effects were observed in ovarian cancer cell lines OVCAR-8 and OVCAR-5 where VS-4718 inhibited cancer stem cells as measured by multiple CSC assays. In an analogous fashion, VS-4718 also reduced the proportion of the ALDEFLUOR+ cells in H2052 human mesothelioma cells. In direct contrast, standard-of-care agents paclitaxel, carboplatin or pemetrexed increased the percentage of cancer stem cells, suggesting these agents do not effectively target cancer stem cells. Importantly combination of VS-4718 with standard-of-care agents attenuated chemotherapy-induced increases in the percentage of cancer stem cells in vitro in all three cancer models. The in vivo effect of VS-4718 on cancer stem cells was evaluated in SUM159 and MDA-MB-231 human triple negative breast cancer xenograft models. Following systemic administration, VS-4718 significantly reduced the proportion of cancer stem cells in tumors as evidenced by decreases in the percentage of ALDEFLUOR+ cells and tumorsphere-forming efficiency relative to vehicle-treated tumors and significantly abrogated tumor-initiating capabilities of cancer cells in a limiting dilution re-implantation assay. In summary, our results indicate the importance of FAK in the self-renewal of cancer stem cells in vitro and in vivo, and support the clinical development of FAK inhibitors to target cancer stem cells for the treatment of multiple cancers. Citation Format: Vihren Kolev, Quentin Wright, Christian Vidal, Irina Shapiro, Mahesh Pavdal, Mitchell Keegan, Qunli Xu, Jonathan Pachter. Pharmacological and genetic inhibition of FAK attenuates cancer stem cell function in vitro and in vivo. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 236. doi:10.1158/1538-7445.AM2013-236

Despite promising, and sometimes dramatic, efficacy of targeted therapies, primary and acquired resistance to targeted therapies limits their broad and long-term use in the clinic. Therefore, the ability to rationally design anticipatory or combination therapies as early in the treatment process as possible could significantly improve the utility of targeted therapies and cancer outcome. Here, we report that one can predict a priori the types of mutations that will occur in SHH pathway inhibitor treated medulloblastomas based on different cancer stem cell (CSC) phenotypes in each tumor. CSCs are a subset of cancer cells that are more resistant to cytotoxic therapies (chemo and radiation) than bulk tumor cells, and are responsible for tumor recurrence. Previously, we reported that cell-of-origin is a major driver of CSC phenotypes. In particular, we showed that CSCs retain epigenetic memory of their cells-of-origin and the mitogenic pathways that drive CSC proliferation and survival are reflective of their cells-of-origin. We also demonstrated that CSCs and bulk tumor cells do not necessarily depend on the same mitogenic/survival signaling pathways. An important implication of this finding is that targeted therapies selected based on bulk tumor analyses may not be effective in ablating CSCs in some tumors. Furthermore, the selective pressure imposed on CSCs in individual patient tumors by a targeted therapy will vary greatly, depending on whether the selected drug targets a critical pathway in CSCs and not just bulk tumor cells. Another clinically significant implication is that based on the resident CSC phenotype, we may able to predict whether individual SHH tumors will or will not acquire treatment-induced mutations in the SHH pathway upon SHH pathway inhibitors (SMOi) treatment. To test this hypothesis, we treated allografts of spontaneous Ptch;p53 mouse medulloblastomas arising from different cells-of-origins with SMOi's (LDE225 and GDC0449). While all tumors responded to SMOi's initially, most acquired resistance over time. We took an integrated genomics approach to identify molecular mechanisms of therapy resistance in these SMOi-resistant tumors. We report that acquired mutations in SHH pathway genes occurred only in tumors that contained CSCs that depended on the SHH pathway. In tumors where only the bulk tumor cells, but not CSCs, depended on SHH signaling, no acquired mutations in SHH pathway genes were detected. In sum, we report that CSCs drive mechanisms of therapy resistance and also provide the first proof-of-principle evidence that it is possible to predict the types of mutations that will occur in therapy-resistant tumors in advance of treatment, which can be exploited to design anticipatory therapies in the future. Citation Format: Joshy George, Yaohui Chen, Keiko Yamamoto, Scott Adamson, Jeff Chuang, Kyuson Yun. Cancer stem cell phenotypes determine mechanisms of resistance to targeted therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 165.

e17527 Background: Resistance to chemotherapy is a complex problem in the treatment of patients with ovarian cancer (OC), and this phenomenon is associated, among other things, with the presence of cancer stem cells (CSCs). The purpose of the study was to determine the amount of CSCs in tumors of OC patients with different responses to chemotherapy they receive. Methods: Samples of ovarian tumors were obtained from 100 patients (aged 29-79 years) with advanced ovarian cancer stage IIIC-IV with/without ascites. All patients recruited in 2016-2020 received standard combination treatment with surgery and platinum-containing polychemotherapy (Pt CT). Based on the results of neoadjuvant Pt CT, patients were divided into groups: patients with stabilization or progression–group 1 “without effect”; patients with complete/partial regression–group 2 with positive effect. All patients gave their informed consent for the study. Cell suspension obtained from the tumor fragments was processed using monoclonal antibodies labeled with various fluorochromes: CD45-APC-Cy7, CD44-FITС, CD133–РЕ according to the manufacturer's instructions (BD, USA). The percentage of CSCs was determined using the FACS Canto II flow cytometer (BD, USA). The amount of cells with CSC markers (CD44+, CD133+, CD44+CD133+) was calculated as a percentage from the total amount of CD45--cells. Statistics: STATISTICA 13 (StatSoftInc., USA). Results were presented as Me (LQ; UQ). The significance of differences was assessed using the Mann-Whitney test (the differences were considered significant at p<0.05). Results: The amount of CD45- _cells, as well as CD45-CD44+ cells, in OC tumors did not differ between patients of groups 1 and 2: 79.0 (72.1; 85.9) vs. 82.8 (76.7; 89.0), and 6.2 (3.3; 9.1) vs. 6.6 (3.5; 9.8), respectively. The percentage of cancer cells with the CD45-CD133+ phenotype in group 2 was significantly lower than in group 1: by 52% (p≤0.05), 3.2 (2.4; 3.9) vs. 6.7 (3.8; 9.6), respectively. The amount of CD45-CD44+CD133- CSCs in tumors in group 1 was lower than in group 2: by 82% (p≤0.05), 0.6 (0.3; 0.7) vs. 3.3 (1.8; 4.7), respectively. Conclusions: The results demonstrated certain differences in the distribution of CSCs in tumors of OC patients with different sensitivity to chemotherapy, which may be one of the factors determining the treatment outcomes.

BackgroundRecently, a small population of cancer stem cells in adult and pediatric brain tumors has been identified. Some evidence has suggested that CD133 is a marker for a subset of leukemia and glioblastoma cancer stem cells. Especially, CD133 positive cells isolated from human glioblastoma may initiate tumors and represent novel targets for therapeutics. The gene expression and the drug resistance property of CD133 positive cancer stem cells, however, are still unknown.ResultsIn this study, by FACS analysis we determined the percentage of CD133 positive cells in three primary cultured cell lines established from glioblastoma patients 10.2%, 69.7% and 27.5%, respectively. We also determined the average mRNA levels of markers associated with neural precursors. For example, CD90, CD44, CXCR4, Nestin, Msi1 and MELK mRNA on CD133 positive cells increased to 15.6, 5.7, 337.8, 21.4, 84 and 1351 times, respectively, compared to autologous CD133 negative cells derived from cell line No. 66. Additionally, CD133 positive cells express higher levels of BCRP1 and MGMT mRNA, as well as higher mRNA levels of genes that inhibit apoptosis. Furthermore, CD133 positive cells were significantly resistant to chemotherapeutic agents including temozolomide, carboplatin, paclitaxel (Taxol) and etoposide (VP16) compared to autologous CD133 negative cells. Finally, CD133 expression was significantly higher in recurrent GBM tissue obtained from five patients as compared to their respective newly diagnosed tumors.ConclusionOur study for the first time provided evidence that CD133 positive cancer stem cells display strong capability on tumor's resistance to chemotherapy. This resistance is probably contributed by the CD133 positive cell with higher expression of on BCRP1 and MGMT, as well as the anti-apoptosis protein and inhibitors of apoptosis protein families. Future treatment should target this small population of CD133 positive cancer stem cells in tumors to improve the survival of brain tumor patients.

Cancer stem cells: A promising concept and therapeutic challenge

Targeting the Untargetable: Oncolytic Virotherapy for the Cancer Stem Cell

Cancer cells and cancer stem cells (CSCs) are the major players of cancer malignancy and metastasis, but they are extremely difficult to access. Inspired by the vital role of macrophages and microvesicle-mediated cell–cell communication in tumors, we herein designed M2 macrophage microvesicle-inspired nanovehicle of cabazitaxel (M-CFN) to promote accessibility to cancer cells and CSCs in tumors. In the 4T1 tumor model, M-CFN flexibly permeated the tumor mass, accessed cancer cells and CD90-positive cells, and significantly promoted their entry into CSC fractions in tumors. Moreover, M-CFN treatment profoundly eliminated aldehyde dehydrogenase (ALDH)-expressing CSCs in 4T1 and MCF-7 tumors, produced notable depression of tumor growth and caused 93.86% suppression of lung metastasis in 4T1 models. Therefore, the M2 macrophage microvesicle-inspired nanovehicle provides an encouraging strategy to penetrate the tumor tissues and access these insult cells in tumors for effective cancer therapy.Graphical