Drugs that Kill Cancer Stem-like Cells

The hallmarks of cancer include processes like self-sufficiency for growth signals, insensitivity to growth-inhibitory (anti-growth) signals, evasion of programmed cell death (apoptosis), unlimited replicative potential, sustained angiogenesis, and tissue invasion and metastasis (Hanahan & Weinberg, 2000). Recent research dictates that these definitions, while valid, ought to be enriched. That is, we should also consider tumours as a heterogeneous ‘collection of cancer cells’ with a hierarchy. This ‘hierarchical hypothesis’ tells us that tumours contain a minute (sometimes very small) sub-set of cells with distinct properties from the bulk of the tumour mass (D’Amour & Gage, 2002; Visvader & Lindeman, 2008; Visvader, 2009). These cells feature certain characteristics inherent to stem cells, including the capacity of self-renewal, asymmetric division and differentiation. They have also a very high propensity to form tumours. Therefore these cells are referred to as cancer stem cells (CSC) or cancer stem-like cells or, better, tumour-initiating cells (TICs). The terminology, while not too important, may be misleading though, since the term ‘cancer stem cells’ implies that we are dealing with true stem cells, which is not possible to reconcile with at this stage, perhaps even more so, since the origin of CSCs is not exactly known.Griffith Health, School of Medical ScienceFull Tex

Mitochondrially targeted vitamin E succinate efficiently kills breast tumour-initiating cells in a complex II-dependent manner

Background: Accumulating evidence suggests that breast cancer involves tumour-initiating cells (TICs), which play a role in initiation, metastasis, therapeutic resistance and relapse of the disease. Emerging drugs that target TICs are becoming a focus of contemporary research. Mitocans, a group of compounds that induce apoptosis of cancer cells by destabilising their mitochondria, are showing their potential in killing TICs. In this project, we investigated mitochondrially targeted vitamin E succinate (MitoVES), a recently developed mitocan, for its in vitro and in vivo efficacy against TICs.Methods: The mammosphere model of breast TICs was established by culturing murine NeuTL and human MCF7 cells as spheres. This model was verified by stem cell marker expression, tumour initiation capacity and chemotherapeutic resistance. Cell susceptibility to MitoVES was assessed and the cell death pathway investigated. In vivo efficacy was studied by grafting NeuTL TICs to form syngeneic tumours.Results: Mammospheres derived from NeuTL and MCF7 breast cancer cells were enriched in the level of stemness, and the sphere cells featured altered mitochondrial function. Sphere cultures were resistant to several established anti-cancer agents while they were susceptible to MitoVES. Killing of mammospheres was suppressed when the mitochondrial complex II, the molecular target of MitoVES, was knocked down. Importantly, MitoVES inhibited progression of syngeneic HER2(high) tumours derived from breast TICs by inducing apoptosis in tumour cells.Conclusions: These results demonstrate that using mammospheres, a plausible model for studying TICs, drugs that target mitochondria efficiently kill breast tumour-initiating cells

Characterisation of mesothelioma-initiating cells and their susceptibility to anti-cancer agents

Malignant mesothelioma (MM) is an aggressive type of tumour causing high mortality. One reason for this paradigm may be the existence of a subpopulation of tumour-initiating cells (TICs) that endow MM with drug resistance and recurrence. The objective of this study was to identify and characterise a TIC subpopulation in MM cells, using spheroid cultures, mesospheres, as a model of MM TICs. Mesospheres, typified by the stemness markers CD24, ABCG2 and OCT4, initiated tumours in immunodeficient mice more efficiently than adherent cells. CD24 knock-down cells lost the sphere-forming capacity and featured lower tumorigenicity. Upon serial transplantation, mesospheres were gradually more efficiently tumrigenic with increased level of stem cell markers. We also show that mesospheres feature mitochondrial and metabolic properties similar to those of normal and cancer stem cells. Finally, we show that mesothelioma-initiating cells are highly susceptible to mitochondrially targeted vitamin E succinate. This study documents that mesospheres can be used as a plausible model of mesothelioma-initiating cells and that they can be utilised in the search for efficient agents against MM

Suppression of tumor growth in vivo by the mitocan alpha-tocopheryl succinate requires respiratory complex II.

PurposeVitamin E analogues are potent novel anticancer drugs. The purpose of this study was to elucidate the cellular target by which these agents, represented by alpha-tocopoheryl succinate (alpha-TOS), suppress tumors in vivo, with the focus on the mitochondrial complex II (CII).Experimental designChinese hamster lung fibroblasts with functional, dysfunctional, and reconstituted CII were transformed using H-Ras. The cells were then used to form xenografts in immunocompromized mice, and response of the cells and the tumors to alpha-TOS was studied.ResultsThe CII-functional and CII-reconstituted cells, unlike their CII-dysfunctional counterparts, responded to alpha-TOS by reactive oxygen species generation and apoptosis execution. Tumors derived from these cell lines reciprocated their responses to alpha-TOS. Thus, growth of CII-functional and CII-reconstituted tumors was strongly suppressed by the agent, and this was accompanied by high level of apoptosis induction in the tumor cells. On the other hand, alpha-TOS did not inhibit the CII-dysfunctional tumors.ConclusionsWe document in this report a novel paradigm, according to which the mitochondrial CII, which rarely mutates in human neoplasias, is a plausible target for anticancer drugs from the group of vitamin E analogues, providing support for their testing in clinical trials

Suppression of tumor growth in vivo by the mitocan alpha-tocopheryl succinate requires respiratory complex II.

PurposeVitamin E analogues are potent novel anticancer drugs. The purpose of this study was to elucidate the cellular target by which these agents, represented by alpha-tocopoheryl succinate (alpha-TOS), suppress tumors in vivo, with the focus on the mitochondrial complex II (CII).Experimental designChinese hamster lung fibroblasts with functional, dysfunctional, and reconstituted CII were transformed using H-Ras. The cells were then used to form xenografts in immunocompromized mice, and response of the cells and the tumors to alpha-TOS was studied.ResultsThe CII-functional and CII-reconstituted cells, unlike their CII-dysfunctional counterparts, responded to alpha-TOS by reactive oxygen species generation and apoptosis execution. Tumors derived from these cell lines reciprocated their responses to alpha-TOS. Thus, growth of CII-functional and CII-reconstituted tumors was strongly suppressed by the agent, and this was accompanied by high level of apoptosis induction in the tumor cells. On the other hand, alpha-TOS did not inhibit the CII-dysfunctional tumors.ConclusionsWe document in this report a novel paradigm, according to which the mitochondrial CII, which rarely mutates in human neoplasias, is a plausible target for anticancer drugs from the group of vitamin E analogues, providing support for their testing in clinical trials

Modeling SHH-driven medulloblastoma with patient iPS cell-derived neural stem cells

Medulloblastoma is the most common malignant brain tumor in children. Here we describe a medulloblastoma model using In-duced pluripotent stem (iPS) cell-derived human neuroepithelial stem (NES) cells generated from a Gorlin syndrome patient carry-ing a germline mutation in the sonic hedgehog (SHH) receptor PTCH1. We found that Gorlin NES cells formed tumors in mouse cerebellum mimicking human medulloblastoma. Retransplantation of tumor-isolated NES (tNES) cells resulted in accelerated tumor formation, cells with reduced growth factor dependency, en-hanced neurosphere formation in vitro, and increased sensitivity to Vismodegib. Using our model, we identified LGALS1 to be a GLI target gene that is up-regulated in both Gorlin tNES cells and SHH-subgroup of medulloblastoma patients. Taken together, we dem-onstrate that NES cells derived from Gorlin patients can be used as a resource to model medulloblastoma initiation and progression and to identify putative targets