Cancer cells and their associated tumors have long been considered to exhibit unregulated proliferation or growth. However, a substantial body of evidence indicates that tumor growth is subject to both positive and negative regulatory controls. Here, we describe a novel property of tumor growth regulation that is neither species nor tumor-type specific. This property, functionally a type of feedback control, is triggered by the encapsulation of neoplastic cells in a growth-restricting hydrogel composed of an agarose matrix with a second coating of agarose to form 6- to 8-mm diameter macrobeads. In a mouse cell model of renal adenocarcinoma (RENCA cells), this process resulted in selection for a stem cell–like subpopulation which together with at least one other cell subpopulation drove colony formation in the macrobeads. Cells in these colonies produced diffusible substances that markedly inhibited in vitro and in vivo proliferation of epithelial-derived tumor cells outside the macrobeads. RENCA cells in monolayer culture that were exposed to RENCA macrobead-conditioned media exhibited cell-cycle accumulation in S phase due to activation of a G2/M checkpoint. At least 10 proteins with known tumor suppression functions were identified by analysis of RENCA macrobead-conditioned media, the properties of which offer opportunities to further dissect the molecular basis for tumor growth control. More generally, macrobead culture may permit the isolation of cancer stem cells and other cells of the stem cell niche, perhaps providing strategies to define more effective biologically based clinical approaches to treat neoplastic disease. Cancer Res; 71(3); 725–35. 2011 AACR. cancerres.aacrjournals.org
Cellular and genetic diversity in the progression of in situ human breast carcinomas to an invasive phenotype by So Yeon Park and 4 co-authors, including Kornelia Polyak, J Clin Invest 2010(Jan 25) [Epub ahead of print][FriendFeed entry][Connotea bookmark][Full text is publicly accessible (via Gratis OA)]. PubMed Abstract:
Intratumor genetic heterogeneity is a key mechanism underlying tumor progression and therapeutic resistance. The prevailing model for explaining intratumor diversity, the clonal evolution model, has recently been challenged by proponents of the cancer stem cell hypothesis. To investigate this issue, we performed combined analyses of markers associated with cellular differentiation states and genotypic alterations in human breast carcinomas and evaluated diversity with ecological and evolutionary methods. Our analyses showed a high degree of genetic heterogeneity both within and between distinct tumor cell populations that were defined based on markers of cellular phenotypes including stem cell-like characteristics. In several tumors, stem cell-like and more-differentiated cancer cell populations were genetically distinct, leading us to question the validity of a simple differentiation hierarchy-based cancer stem cell model. The degree of diversity correlated with clinically relevant breast tumor subtypes and in some tumors was markedly different between the in situ and invasive cell populations. We also found that diversity measures were associated with clinical variables. Our findings highlight the importance of genetic diversity in intratumor heterogeneity and the value of analyzing tumors as distinct populations of cancer cells to more effectively plan treatments.
The final sentence of the Discussion section of the full text:
In summary, in this study we have demonstrated the power of analyzing tumors as ecosystems and suggest that quantitative measures of intratumor diversity might be clinically useful biomarkers predicting prognosis and response to treatment.
Another recent article from the same group: Heterogeneity for Stem Cell–Related Markers According to Tumor Subtype and Histologic Stage in Breast Cancer by So Yeon Park and 5 co-authors, including Kornelia Polyak, Clin Cancer Res 2010; 16(3): 876–87 [Epub 2010(Jan 26)][FriendFeed entry][Connotea bookmark][PubMed Citation].
From the Conclusions section of the abstract:
Our findings suggest that in breast cancer, the frequency of tumor cells positive for stem cell-like and more differentiated cell markers varies according to tumor subtype and histologic stage.
Neoplastic transformation of intestinal SC Check it out – Colon-Rectal Cancer What are the symptoms of breast cancer Patent application: cancer stem cell vaccine technology Review about retroviral-induced leukemogenesis and the CSC hypothesis
We have used in vitro and mouse xenograft models to examine the interaction between breast cancer stem cells (CSC) and bone marrow–derived mesenchymal stem cells (MSC). We show that both of these cell populations are organized in a cellular hierarchy in which primitive aldehyde dehydrogenase expressing mesenchymal cells regulate breast CSCs through cytokine loops involving IL6 and CXCL7. In NOD/SCID mice, labeled MSCs introduced into the tibia traffic to sites of growing breast tumor xenografts where they accelerated tumor growth by increasing the breast CSC population. With immunochemistry, we identified MSC–CSC niches in these tumor xenografts as well as in frozen sections from primary human breast cancers. Bone marrow–derived MSCs may accelerate human breast tumor growth by generating cytokine networks that regulate the CSC population. Cancer Res; 71(2); 614–24. 2011 AACR. cancerres.aacrjournals.org
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