Sustained tumour eradication after induced caspase-3 activation and synchronous tumour apoptosis requires an intact host immune response

Effective anticancer treatments often result in the induction of large amounts of tumour cell death. In vivo, such dying tumour cells are a potential source of antigens for T-cell stimulation. Although apoptosis is generally considered nonimmunogenic, recent evidence suggests that some anticancer therapies that induce apoptosis can elicit antitumour immune responses. Here, a doxycycline-inducible, constitutively active caspase-3 (‘death switch'') was constructed in a murine tumour model to explore the impact of the host immune response to rapid, synchronous and substantial tumour cell apoptosis. In vitro, up to 80% of tumour cells underwent apoptotic cell death within 24 h and death was accompanied by the release of potential ‘danger signal'' molecules HMGB1 and HSP90. In vivo, death switch induction provoked rapid, pronounced tumour regression in immune-competent and immune-deficient mice, but sustained tumour eradication was observed only in immune-competent mice. Moreover, the majority of mice that were tumour free after death switch induction were protected from further tumour rechallenge. In addition, long-term remission after induction of the death switch was completely abrogated following depletion of CD8 T cells. These data suggest that sustained tumour eradication after substantial tumour apoptosis requires an antitumour host immune response that prevents tumour relapse. In many patients, cancer therapies produce encouraging initial responses that are only short lived. These results provide new insights that may have important implications for further development of strategies that result in long-term tumour clearance after initially effective anticancer treatment.     

The Functional Repertoire of Survivin's Tails

Survivin is a multitasking protein that can inhibit cell death and that is essential for mitosis. Due to these prosurvival activities and the correlation of its expression with tumor resistance to conventional cancer treatments, survivin has received much attention as a potential oncotherapeutic target. Nevertheless, many questions regarding its exact role at the molecular level remain to be elucidated. In this study we ask whether the extreme C- and NH₂ termini of survivin are required for it to carry out its cytoprotective and mitotic duties. When assayed for their ability to act as a cytoprotectant, both survivin_1–120 and survivin_11–142 were able to protect cells against TRAIL-mediated apoptosis, but when challenged with irradiation cells expressing survivin_11–142 had no survival advantage. During mitosis, however, removing the NH₂ terminal 10 amino acids (survivin_11–142) had no apparent effect but truncating 22 amino acids from the C-terminus (survivin_1–120) prevented survivin from transferring to the midzone microtubules during anaphase. Collectively the data herein presented suggest that the C-terminus is required for cell division, and that the NH₂ terminus is dispensable for apoptosis and mitosis but required for protection from irradiation.     

p53 restoration kills primitive leukemia cells in vivo and increases survival of leukemic mice

Loss of p53 function is a common feature of human cancers and it is required for differentiated tumor cell maintenance; however, it is not known whether sustained inactivation of the p53 pathway is needed for cancer stem cell persistence. Chronic myeloid leukemia (CML) is caused by a chromosome translocation that generates the BCRABL oncogene encoding a constitutively active protein tyrosine kinase. The disease originates in a hematopoietic stem cell and is maintained by leukemic stem cells (LSCs). Treatment with specific tyrosine kinase inhibitors does not eliminate LSCs because they do not depend on the oncogene for survival. We have combined a switchable p53 knock-in mouse model, p53^KI/KI, with the well-characterized Sca1-BCRABLp210 CML transgenic model, to show that transient restoration of p53 slows disease progression and significantly extends the survival of leukemic animals, being the mechanism responsible for this effect, apoptotic death of primitive leukemia cells. In agreement with these in vivo findings, in vitro assays show that restoring p53 reduces hematopoietic colony formation by cells of leukemic animals. These results suggest that reestablishing p53 function may be a therapeutic strategy for the eradication of leukemic stem cells and to prevent disease progression.     

Insights into ALS pathomechanisms: from flies to humans

Amyotrophic Lateral Sclerosis (ALS) is a devastating neurodegenerative disease causing the death of motor neurons with consequent muscle atrophy and paralysis. Several neurodegenerative diseases have been modeled in Drosophila and genetic studies on this model organism led to the elucidation of crucial aspects of disease mechanisms. ALS, however, has lagged somewhat behind possibly because of the lack of a suitable genetic model. We were the first to develop a fly model for ALS and over the last few years, we have implemented and used this model for a large scale, unbiased modifier screen. We also report an extensive bioinformatic analysis of the genetic modifiers and we show that most of them are associated in a network of interacting genes controlling known as well as novel cellular processes involved in ALS pathogenesis. A similar analysis for the human homologues of the Drosophila modifiers and the validation of a subset of them in human tissues confirm and expand the significance of the data for the human disease. Finally, we analyze a possible application of the model in the process of therapeutic discovery in ALS and we discuss the importance of novel “non-obvious” models for the disease.     

Interplay between apoptotic and autophagy pathways after exposure to cerium dioxide nanoparticles in human monocytes

Engineered nanomaterials, defined as having at least one dimension smaller than 100 nm, have revolutionized many technology sectors ranging from therapeutics and diagnostics to environmental monitoring and remediation. This has resulted in a rapid increase in their manufacture over the past few years, accompanied by an increased human exposure potential. However, understanding of the interactions of nanomaterials with biological systems is still rudimentary. We have described that an environmentally and medically relevant nano metal (cerium dioxide) can affect primary human monocyte viability and interact with programmed cell death pathways leading to apoptosis and autophagic cell death. Cerium dioxide nanoparticles (CeO₂ NPs)-induced autophagy acts as a prodeath mechanism and leads to increased cytotoxicity of human monocytes. A better understanding of the implication and biological significance of CeO₂ NPs-induced autophagy and apoptosis will help us understand the risks associated with its uses and develop safer nanomedicine.     

Involvement of autophagy in the response of tumor cells to PtdIns3K inhibitors

The phosphoinositide 3-kinase (PI3K) pathway plays a crucial role in cell proliferation and survival and is frequently activated by genetic and epigenetic alterations in human cancer. An arsenal of pharmacological inhibitors of key signaling enzymes in this pathway, including class I_A PI3K isoforms, has been developed in the past decade and several compounds have entered clinical testing in cancer patients. The PIK3CA/p110α isoform is the most studied enzyme of the family and a validated cancer target. The induction of autophagy by PI3K pathway inhibitors has been documented in various cancers, although a clear picture about the significance of this phenomenon is still missing, especially in the in vivo situation. A better understanding of the contribution of autophagy to the action of PI3K inhibitors on tumors cells is important, since it may limit or enhance the action of these compounds, depending on the cellular context.