Targeting hedgehog in cancer stem cells: how a paradigm shift can improve treatment response

The role of hypoxia and exploitation of the hypoxic environment in hematologic malignancies

Tumor hypoxia is a well-described phenomenon during the progression of solid tumors affecting cell signaling pathways and cell metabolism; however, its role in hematologic malignancies has not been given the same attention in the literature. Therefore, this review focuses on the comparative differences between solid and hematologic malignancies with emphasis on the role of hypoxia during tumorigenesis and progression. In addition, contribution of the bone marrow and angiogenic environment are also discussed. Insight is provided into the role of hypoxia in metastatic spread, stemness, and drug resistance in hematologic conditions. Finally, emerging therapeutic strategies such as small-molecule prodrugs and hypoxia-inducible factor (HIF) targeting approaches are outlined to combat hypoxic cells and/or adaptive mechanisms in the treatment of hematologic malignancies.

Regulation of apoptosis pathways in cancer stem cells

Cancer stem cell are considered to represent a population within the bulk tumor that share many similarities to normal stem cells as far as their capacities to self-renew, differentiate, proliferate and to reconstitute the entire tumor upon serial transplantation are concerned. Since cancer stem cells have been shown to be critical for maintaining tumor growth and have been implicated in treatment resistance and tumor progression, they constitute relevant targets for therapeutic intervention. Indeed, it has been postulated that eradication of cancer stem cells will be pivotal in order to achieve long-term relapse-free survival. However, one of the hallmarks of cancer stem cells is their high resistance to undergo cell death including apoptosis in response to environmental cues or cytotoxic stimuli. Since activation of apoptosis programs in tumor cells underlies the antitumor activity of most currently used cancer therapeutics, it will be critical to develop strategies to overcome the intrinsic resistance to apoptosis of cancer stem cells. Thus, a better understanding of the molecular mechanisms that are responsible for the ability of cancer stem cells to evade apoptosis will likely open new avenues to target this critical pool of cells within the tumor in order to develop more efficient treatment options for patients suffering from cancer.

Outcome and toxicity associated with a dose-intensified, maintenance-free CHOP-based chemotherapy protocol in canine lymphoma: 130 cases

A dose-intensified/dose-dense chemotherapy protocol for canine lymphoma was designed and implemented at the Veterinary Hospital of the University of Pennsylvania. In this study, we describe the clinical characteristics, prognostic factors, efficacy and toxicity in 130 dogs treated with this protocol. The majority of the dogs had advanced stage disease (63.1% stage V) and sub-stage b (58.5%). The median time to progression (TTP) and lymphoma-specific survival were 219 and 323 days, respectively. These results are similar to previous less dose-intense protocols. Sub-stage was a significant negative prognostic factor for survival. The incidence of toxicity was high; 53.9 and 45% of the dogs needed dose reductions and treatment delays, respectively. Dogs that required dose reductions and treatment delays had significantly longer TTP and lymphoma-specific survival times. These results suggest that dose density is important, but likely relative, and needs to be adjusted according to the individual patient's toxicity for optimal outcome.

Cancer stem cell epigenetics and chemoresistance

Cancer stem cells (CSCs) are thought to sustain cancer progression, metastasis and recurrence after therapy. There is in vitro and in vivo evidence supporting the idea that CSCs are highly chemoresistant. Epigenetic gene regulation is crucial for both stem cell biology and chemoresistance. In this review, we summarize current data on epigenetic mechanisms of chemoresistance in cancer stem cells. We propose a model integrating classical CSC pathways (Wnt, Hedgehog and Notch), epigenetic effectors (Polycomb) and drug resistance genes (ABCG2, CD44). Moreover, we analyze the potential of epigenetic drugs to reverse CSC chemoresistance. In the future, CSC epigenomic profiling could help to dissect specific chemoresistance pathways, and have a significant clinical impact for patient stratification and rational design of therapeutic regimens.

Cancer stem cells, hypoxia and metastasis

The successful growth of a metastasis, by definition, requires the presence of at least 1 cancer stem cell. Metastasis is a complex process, and an important contributor to this process is the influence of the tissue microenvironment, both cell-cell and cell-matrix interactions and the pathophysiologic conditions in tumors, such as hypoxia. A number of studies have suggested that normal stem cells may reside in "niches," where cell-cell and cell-matrix interactions can provide critical signals to support and maintain the undifferentiated phenotype of the stem cells. In this article, the evidence that these niches may be hypoxic is described, and the potential role that hypoxia may play in maintaining the stem cell phenotype in cancers is discussed. Recent work has suggested that there may be a linkage between the stem cell phenotype and that induced by the process of epithelial-mesenchymal transition (EMT). EMT plays an important role in cell movement and organ formation during embryogenesis, and it is currently hypothesized to be a major mechanism by which epithelial cancers may generate cells that can form metastases. Recent evidence suggests that the expression of certain genes involved in EMT is influenced by low oxygen levels, again suggesting a linkage between stem cells and hypoxia. Whether this supposition is correct remains an open question that will only be answered by further experimentation, but the potential role of hypoxia is critical because of its widespread existence in tumors and its known role in resistance to both radiation and drug treatment.

Chemoresistant colorectal cancer cells, the cancer stem cell phenotype, and increased sensitivity to insulin-like growth factor-I receptor inhibition

5-Fluorouracil (5FU) and oxaliplatin are standard therapy for metastatic colorectal cancer (CRC), but the development of chemoresistance is inevitable. Because cancer stem cells (CSC) are hypothesized to be chemoresistant, we investigated CSC properties in newly developed chemoresistant CRC cell lines and sought to identify targets for therapy. The human CRC cell line HT29 was exposed to increasing doses of 5FU (HT29/5FU-R) or oxaliplatin (HT29/OxR) to achieve resistance at clinically relevant doses. Western blotting and flow cytometry were done to determine molecular alterations. The insulin-like growth factor-I receptor (IGF-IR) monoclonal antibody (mAb) AVE-1642 was used to inhibit signaling in vitro and in vivo using murine xenograft models. HT29/5FU-R and HT29/OxR showed 16- to 30-fold enrichment of CD133(+) cells and 2-fold enrichment of CD44(+) cells (putative CRC CSC markers). Resistant cells were enriched 5- to 22-fold for double-positive (CD133(+)/CD44(+)) cells. Consistent with the CSC phenotype, resistant cells exhibited a decrease in cellular proliferation in vitro (47-59%; P < 0.05). Phosphorylated and total IGF-IR levels were increased in resistant cell lines. HT29/5FU-R and HT29/OxR cells were approximately 5-fold more responsive to IGF-IR inhibition relative to parental cells (P < 0.01) in vitro. Tumors derived from HT29/OxR cells showed significantly greater growth inhibition in response to an IGF-IR mAb than did parental cells (P < 0.05). Chemoresistant CRC cells are enriched for CSC markers and the CSC phenotype. Chemotherapy-induced IGF-IR activation provided for enhanced sensitivity to IGF-IR-targeted therapy. Identification of CSC targets presents a novel therapeutic approach in this disease.

Chemoresistant colorectal cancer cells, the cancer stem cell phenotype, and increased sensitivity to insulin-like growth factor-I receptor inhibition

5-Fluorouracil (5FU) and oxaliplatin are standard therapy for metastatic colorectal cancer (CRC), but the development of chemoresistance is inevitable. Because cancer stem cells (CSC) are hypothesized to be chemoresistant, we investigated CSC properties in newly developed chemoresistant CRC cell lines and sought to identify targets for therapy. The human CRC cell line HT29 was exposed to increasing doses of 5FU (HT29/5FU-R) or oxaliplatin (HT29/OxR) to achieve resistance at clinically relevant doses. Western blotting and flow cytometry were done to determine molecular alterations. The insulin-like growth factor-I receptor (IGF-IR) monoclonal antibody (mAb) AVE-1642 was used to inhibit signaling in vitro and in vivo using murine xenograft models. HT29/5FU-R and HT29/OxR showed 16- to 30-fold enrichment of CD133(+) cells and 2-fold enrichment of CD44(+) cells (putative CRC CSC markers). Resistant cells were enriched 5- to 22-fold for double-positive (CD133(+)/CD44(+)) cells. Consistent with the CSC phenotype, resistant cells exhibited a decrease in cellular proliferation in vitro (47-59%; P < 0.05). Phosphorylated and total IGF-IR levels were increased in resistant cell lines. HT29/5FU-R and HT29/OxR cells were approximately 5-fold more responsive to IGF-IR inhibition relative to parental cells (P < 0.01) in vitro. Tumors derived from HT29/OxR cells showed significantly greater growth inhibition in response to an IGF-IR mAb than did parental cells (P < 0.05). Chemoresistant CRC cells are enriched for CSC markers and the CSC phenotype. Chemotherapy-induced IGF-IR activation provided for enhanced sensitivity to IGF-IR-targeted therapy. Identification of CSC targets presents a novel therapeutic approach in this disease.