Editorial [Hot Topic: Reprogramming of Normal and Cancer Stem Cells (Guest Editor: Pier Mario Biava)]

Over the last decade there has been an exponential rise in our understanding of the biochemical mechanisms controlling cell proliferation and differentiation. While the four transcription factors Oct4, Sox2, Klf4 and cMyc have shown to be sufficient to induce pluripotency in fibroblasts, there has in addition been much research into the mechanisms and pathways of cell differentiation and the specific properties of stem cells, namely their plasticity and capacity for trans-differentiation. These studies have allowed progress at very fundamental level, with the prospect of further progress - until recent years quite unimaginable - in the field of reparative, regenerative and transplant medicine. In fact, from the present time, the genetic engineering production of regulatory factors identified through such research, has allowed the production of new tissues and a new category of cell therapy products, in which the main biological action is carried out by cells or tissues, albeit in the presence of organic or inorganic matrices or coatings. Examples of this type of product are anti-tumor vaccines, in vitro cultivated skin, products made of structural and cellular elements for the reconstruction of bones, cartilages, teeth, etc. From the best, most analytical and detailed characterization of stem cells, then, it has become clear that some tumor cell behaviors - that have a crucial role in determining their malignity - can be attributed to the presence of cells with characteristics similar to those of stem cells. The field of cancer research is consequently also witnessing a surge in studies designed to identify the metabolic pathways common to tumor and stem cells. This will in turn cast light on which micro-environment factors can direct these pathways towards differentiation and induce cancerous cells to behave less aggressively. From this point of view, over recent years there has been a lively return to studies that were very significant in the 70's and 80's, on the role of the embryonic micro-environment in conditioning tumor cell behavior towards normal phenotypes. This research is now underway, and will in all probability lead to important results over the next few years. Against this background, this special issue on “Reprogramming of normal and cancer stem cells” focuses on research in terms of conditioning the fate of normal and tumor stem cells with a view to new prospects for therapies. The issue therefore begins with articles covering the possibility of reprogramming normal stem cells, including through use of biomaterials, and goes on to consider what characteristics of tumor stem cells can allow them to be identified and studied. This is followed by a series of further articles illustrating the role of the micro-environment in conditioning the fate of a tumor cell. A number of metabolic pathways characterizing and common to both stem and tumor cells are examined, in order to gain a better understanding of the possibilities of conditioning the fate of both cell types; in addition, the role played by infectious and inflammatory diseases in the genesis of tumor diseases is also considered. Today, in fact, we know that inflammatory processes can support rather than hinder tumor growth, and also that pro-inflammatory cytokines can promote tumor proliferation, inhibiting the cell pathways that are able to block the neoplastic growth. The special issue goes on with a series of articles taking a close look at the specific role played by the micro-environment in conditioning the destiny of the tumor stem cells present in some tumors, for example breast and retinoblastoma tumor, and the role played by the use of normal stem cells in treating disorders such as hematological diseases. One article also considers the risks run by some reprogramming techniques: for example, creating embryo cells via parthenogenesis can give rise to tumors. The issue continues with various articles illustrating in close detail the role of the embryonic micro-environment in conditioning the destiny of tumor cells. In this context, one review takes a look at general aspects, while others consider aspects that can help clarify the mechanisms underlying the capacity of factors of this type of microenvironment to reprogram a tumor cell. One mathematical model sets out from a description of the state of cell differentiation, making use of existing data from studies of tumor growth slowing, linked to the use of such factors, with the goal of shedding light on aspects such as fitness, dosage, and administration time for the differentiation factors on improvement in tumor inhibitory response. Other articles illustrate a number of clinical cases of full regression of hepatocellular carcinomas in intermediate-advanced stages observed following administration of stem cell differentiation factors, and describe the molecular mechanisms that might explain these inhibitory responses on the tumor growth. It should be noted that the randomized and controlled clinical studies launched to date using stem cell differentiation factors are limited to patients with intermediate-advanced stage of hepatocellular carcinomas where other therapies were no longer possible. These factors are at present used only for hepatocellular carcinomas, since it has been demonstrated that substances capable of slowing one tumor’s growth may be inefficacious for another type. Finally, it is important to note that research into the possibility of reprogramming normal and tumor stem cells requires a complex approach to the issue. In fact, the problem requires the study of networks of substances and genes involved in the reprogramming phase, demanding skills in a variety of different areas of research, not simply of medical/biological, but also mathematical/ computational and modeling, in view of the complexity and non-linearity of the processes being studied. A paradigm shift is underway, and the future will witness our engagement in increasing numbers of scientific studies requiring cross-disciplinary skills.

The new paradigm and the new ideas were well understood many years ago by Professor John Klavins, who has been for a long time President of the International Academy of Tumor Marker Oncology. Professor Klavins has always sustained my studies on reprogramming cancer cells, though the possibility of controlling tumor growth by using reprogramming factors was not considered realistic at the time I began studying it.

I wish to dedicate this work to my friend John Klavins.

ACKNOWLEDGEMENTS

Many thanks to Roberta Zorovini and Silvia Cefalo from Smile Tech srl, via Valdirivo 19 Trieste, Italy ([email protected]), for their accurate and thorough work as organizing and editing secretariat.