Galectins are a family of carbohydrate-binding proteins with an affinity for beta-galactosides. Galectin-1 (Gal-1) is differentially expressed by various normal and pathological tissues and appears to be functionally polyvalent, with a wide range of biological activity. The intracellular and extracellular activity of Gal-1 has been described. Evidence points to Gal-1 and its ligands as one of the master regulators of such immune responses as T-cell homeostasis and survival, T-cell immune disorders, inflammation and allergies as well as host-pathogen interactions. Gal-1 expression or overexpression in tumors and/or the tissue surrounding them must be considered as a sign of the malignant tumor progression that is often related to the long-range dissemination of tumoral cells (metastasis), to their dissemination into the surrounding normal tissue, and to tumor immune-escape. Gal-1 in its oxidized form plays a number of important roles in the regeneration of the central nervous system after injury. The targeted overexpression (or delivery) of Gal-1 should be considered as a method of choice for the treatment of some kinds of inflammation-related diseases, neurodegenerative pathologies and muscular dystrophies. In contrast, the targeted inhibition of Gal-1 expression is what should be developed for therapeutic applications against cancer progression. Gal-1 is thus a promising molecular target for the development of new and original therapeutic tools.

A number of signaling pathways can be constitutively activated in migrating glioma cells, thus rendering these cells resistant to cytotoxic insults. However, these pathways are not all constitutively activated at the same time in any one glioma. Particular inhibitors should therefore only be chosen if the target is present in the tumor tissue, but this is only possible if individual patients are submitted to the molecular profiling of their tumors before undergoing any treatment to combat their migratory glioma cells. Specific antimigratory compounds should be added to conventional radio- and/or chemotherapy.

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Twenty-two lycorine-related compounds were investigated for in vitro anti-tumor activity using four cancer cell lines displaying different levels of resistance to pro-apoptotic stimuli and two cancer cell lines sensitive to pro-apoptotic stimuli. Lycorine and six of its congeners exhibited potency in the single-digit micromolar range, while no compound appeared more active than lycorine. Lycorine also displayed the highest potential (in vitro) therapeutic ratio, being at least 15 times more active against cancer than normal cells. Our studies also showed that lycorine exerts its in vitro anti-tumor activity through cytostatic rather than cytotoxic effects. Furthermore, lycorine provided significant therapeutic benefit in mice bearing brain grafts of the B16F10 melanoma model at non-toxic doses. Thus, the results of the current study make lycorine an excellent lead for the generation of compounds able to combat cancers, which are naturally resistant to pro-apoptotic stimuli, such as glioblastoma, melanoma, non-small-cell-lung cancers, metastatic cancers, among others.

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Tumor angiogenesis is a key event in cancer progression. Here, we report that tumors can stimulate tumor angiogenesis by secretion of galectin-1. Tumor growth and tumor angiogenesis of different tumor models are hampered in galectin-1-null (gal-1 −/− ) mice. However, tumor angiogenesis is less affected when tumor cells express and secrete high levels of galectin-1. Furthermore, tumor endothelial cells in gal-1 −/− mice take up galectin-1 that is secreted by tumor cells. Uptake of galectin-1 by cultured endothelial cells specifically promotes H-Ras signaling to the Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (Erk) kinase (Mek)/Erk cascade and stimulates endothelial cell proliferation and migration. Moreover, the activation can be blocked by galectin-1 inhibition as evidenced by hampered membrane translocation of H-Ras.GTP and impaired Raf/Mek/Erk phosphorylation after treatment with the galectin-1-targeting angiogenesis inhibitor anginex. Altogether, these data identify galectin-1 as a proangiogenic factor. These findings have direct implications for current efforts on galectin-1-targeted cancer therapies. Cancer Res; 70(15); 6216-24. ©2010 AACR.

After completing this course, the reader will be able to:1. Describe the pathways involved in the natural resistance of cancer cells to cytotoxic insults including radio-/chemotherapy.2. Explain autophagic cell death as a potent alternative tumor-suppressing mechanism.3. Identify the common targets in apoptosis and autophagy resistance pathways and the surrogate markers that could be used in clinical practice for proautophagic therapy.4. Discuss the rationale for incorporating endoplasmic reticulum stress inhibitors as adjuvant chemotherapies against apoptosis-resistant cancers.Access and take the CME test online and receive 1 AMA PRA Category 1 Credit ™ at CME.TheOncologist.com CME CME ABSTRACTThe therapeutic goal of cancer treatment has been to trigger tumor-selective cell death. Although cell death can be achieved not only by apoptosis (type I programmed cell death) but also by necrosis, mitotic catastrophe, and autophagy, drugs inducing apoptosis remain the main chemotherapeutic agents in medical oncology. However, cancer cells in their relentless drive to survive, hijack cell processes, resulting in apoptosis resistance, which underlies not only tumorigenesis but also the inherent resistance of certain cancers to radiotherapy and chemotherapy. Unlike apoptosis, which is a caspase-dependent process characterized by nuclear condensation and fragmentation, autophagic cell death is a caspase-independent process characterized by the accumulation of autophagic vacuoles in the cytoplasm accompanied by extensive degradation of the Golgi apparatus, the polyribosomes, and the endoplasmic reticulum, which precedes the destruction of the nucleus. Another apoptosis target generating great excitement is X-linked inhibitor of apoptosis (XIAP) [3], which binds to three key caspases, preventing them from activating and killing cancer cells. However, like Bcl-2 inhibitors, XIAP inhibitors must block a protein-protein interaction. Smac, an endogenous protein that is released from mitochondria, binds with XIAP and inactivates it, triggering apoptosis [11]. This discovery raised the possibility of Smac mimetics to treat cancer [11]. Most companies are designing drugs targeting one of the two XIAP-caspase binding domains in order to mimic Smac's full caspase activation function and ensure that apoptosis takes place. Small-molecule XIAP inhibitors are in preclinical evaluation. All three approaches, Bcl-2 inhibitors, TRAIL modulators, and Smac mimetics, have thus yet to be clinically validated. NATURAL RESISTANCE OF CANCER CELLS TO APOPTOSISResistance to apoptosis is considered to be a characteristic of many diverse cancer cells [3]. Defects in apoptosis underlie not only tumorigenesis but also resistance to cancer treatments [3]. Furthermore, the inherent resistance of cancer cells to radiotherapy and chemotherapy is contributed to by changes at genomic, transcriptional, and post-transcriptional levels of proteins and protein kinases and their transcriptional factor effectors [3] (Fig. 1). The phosphatase and tensin homologue de...

Narciclasine (1) is a plant growth regulator that has been previously demonstrated to be proapoptotic to cancer cells at high concentrations (> or = 1 microM). Data generated in the present study show that narciclasine displays potent antitumor effects in apoptosis-resistant as well as in apoptosis-sensitive cancer cells by impairing the organization of the actin cytoskeleton in cancer cells at concentrations that are not cytotoxic (IC(50) values of 30-90 nM). The current study further revealed that any chemical modification to the narciclasine backbone generally led to compounds of variable stability, weaker activity, or even the complete loss of antiproliferative effects in vitro. However, one hemisynthetic derivative of narciclasine, compound 7k, demonstrated by both the intravenous and oral routes higher in vivo antitumor activity in human orthotopic glioma models in mice when compared to narciclasine at nontoxic doses. Narciclasine and compound 7k may therefore be of potential use to combat brain tumors.