Tumour Microenvironment: Cancer “Little Helpers”

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Although distinct cancers differ in a panoply of factors, the process of cancer evolution has common steps. The formation of tumour-derived blood vessels is the same regardless of cancer type, as well as the components surrounding them. Interestingly, tumours can benefit, a lot, from the healthy cells present in their little universe. But how?

Cancer is the term used to refer to a pool of diseases that display a common trait: the excessive division of abnormal cells1.

Healthy cells divide only upon previous stimuli and when it is needed. After a number of divisions, different cell mechanisms make sure that the cell is still able to divide without any error or loss of information2. When the cell can no longer properly divide, it enters a state of senescence3 or goes through a process called apoptosis4.

Box1 | Senescence and Apoptosis

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However, the abnormal cells that give rise to the different types of cancer, do not follow this procedure. These cells divide when it is not demanded by the organism1, in an uncontrollable way, accumulating errors2 and forming masses of cells beyond the tissue boundaries, with the ability to invade the surrounding tissues and metastasize5.

Box2 | Tumour Microenvironment, Extracellular Matrix and Metastasis

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Yet, cancer does not simply rely on selfish, undisciplined and unstable cells11. It is supported by a Tumour Microenvironment (TME)7, composed of a multitude of non-malignant cells8, Extracellular Matrix (ECM)9 and soluble molecules. TME allows tumour growth6,10 and is responsible for the attribution of a major part of the cancer-associated hallmarks8,11 (see Figure 1).

CancerHallmarks.png
Figure 1 | The Hallmarks of Cancer was a paper published by Douglas Hanahan and Robert Weinberg that establishes biological capabilities acquired through the development of human tumours. As stated, tumour microenvironment is an important part of the acquaintance of some of these capacities, including induction of angiogenesis. (Adapted from Douglas Hanahan and Robert A. Weinberg “Hallmarks of Cancer: The Next Generation”, 2011) 11

When cancer cells divide, the tumour grows in volume, limiting the access of nutrients and oxygen to the internal part of the mass. Thus, internal cells cannot access enough oxygen or none at all (state of hypoxia)12. Hypoxia is, therefore, a common characteristic of growing tumours, to which cancer cells respond by promoting angiogenesis13, a crucial process for tumour progression, i.e. growth, invasion and metastasis. Angiogenesis is the formation of new blood vessels, from the already existing ones, towards the tumour10. It grants the flow of oxygen and nutrients while creating a road for tumour metastasis14.

To enhance the formation of new blood vessels, different growth factors (promoters) are liberated from various cells. These molecules are perceived at the surface of the already existing blood vessels and act as a stimulus, promoting the division of the endothelial cells that cover the vessels to form new ones8. The most common “promoter” in the angiogenic process is Vascular Endothelial Growth Factor (VEGF), although other growth factors might conduct the same function15,16.

In contrast, when endothelial cells are not supposed to divide, the molecules that are released from other cells are perceived, by receptors at the endothelial membrane, as inhibitors of angiogenesis16.

Hereby, to “switch on” angiogenesis, the balance between inhibitors and promoters of this process has to decline toward the promoters (see figure 2)17.

SwitchAngiogenesis.png
Figure 2 | The balance hypothesis for the angiogenic switch: The regulation of the formation of new blood vessels is dependent on molecules that can be either promoters or inhibitors of this process. When the promoters outnumber the inhibitors, angiogenesis occurs and new blood vessels are formed. On the other hand, when inhibitors are more numerous than promoter molecules, angiogenesis does not occur and there is no formation of new blood vessels. (Adapted from Douglas Hanahan and Judah Folkman “Patterns and Emerging Mechanisms of the Angiogenic Switch during Tumorigenesis”, 1996) 17

After successfully “switching on” angiogenesis, Endothelial Cells (EC) separate from stabilizing cells (mostly pericytes and smooth muscle cells) or scaffolds and the degradation of the ECM ensues. ECs invade their surroundings and migrate heading for the tumour, giving rise to tube formation and reorganization across the basement membrane17. These steps result in newly formed vessels, to whom Smooth Muscle Cells (SMC) and pericytes are recruited and attach in order to stabilize the new structures. Once stable, this leads to molecular cross-talk that foster survival signalling and VEGF production to maintain the stimuli6,8.

Throughout the process described above, it is possible to find the engagement of various cell types and components that belong to the tumour microenvironment.

ECM acts as a storage of angiogenesis inhibitors and promoters. The liberation of these factors occurs through the degradation of ECM by proteases (e.g. MMPs), that can be released by tumour or stromal18,19 cells. These factors can promote endothelial survival, proliferation, migration and tube formation6,14.

Box3 | Basement Membrane and Stromal Cells

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Tumour cells can recruit progenitor endothelial cells. This type of cells can overexpress VEGF receptors becoming active participants in the angiogenic process16.

Fibroblasts (another cell type present in the tumour microenvironment) synthesize ECM components, can regulate the angiogenic “switch” and contribute to the behaviour of ECs by secreting proteases and growth factors6,10. The actions of fibroblasts in the TME are mostly determined by a paracrine regulation20 that arises from the tumour itself, through the secretion of interleukins, interferons and growth factors21.

Inflammatory components and immune cells are able to produce cytokines and chemokines that can act as mitogens22 for endothelial, epithelial and mesenchymal cells, therefore inducing the proliferation, survival and migration of other TME cell types, new vessels driver cells and tumour cells. In the TME, and working in behalf of tumour progression, we can find myeloid-derived suppressor cells, T lymphocytes, B cells, natural killer cells, plasma cells, monocytes, macrophages, neutrophils and eosinophils. Platelets create a pro-angiogenic environment releasing PDGF (Platelet-Derived Growth Factor) upon interacting with tumour cells23.

Box4 | Paracrine Regulation and Mitogens

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As seen (Figure 3), the tumour milieu is complex and dynamic in cell composition and cell communication. Even though different types of tumours can use different strategies to “switch on” angiogenesis17, every tactic involves TME components and they always play an important role.

angiogenisis3
Figure 3 | Schematic Illustration of the contributing components of the TME to Tumour-Derived Angiogenesis (Image kindly created by João Morais)

Without TME collaboration and angiogenesis, most solid tumours could not grow beyond a few millimetres, due to lack of nutrients and oxygen, neither invade nor metastasize; Therefore they would not be threatening to human life6,8,14.

Regarding this statement, many efforts have been done in order to therapeutically target the angiogenic process and the involved parties21,24,25.

Despite no one had called “Eureka” for this, it seems the way to go in order to find an innovative therapy that can handle cancer progression, regardless of tumour type.

References
  1. What Is Cancer? – National Cancer Institute. Available at: https://www.cancer.gov/about-cancer/understanding/what-is-cancer. (Accessed: 12th July 2018)
  2. Browner, W. S. et al. The genetics of human longevity. Am. J. Med. 117, 851–860 (2004).
  3. Campisi, J. & D’Adda Di Fagagna, F. Cellular senescence: When bad things happen to good cells. Nat. Rev. Mol. Cell Biol. 8, 729–740 (2007).
  4. Renehan, A. G., Booth, C. & Potten, C. S. What is apoptosis, and why is it important? BMJ 322, 1536–8 (2001).
  5. Definition of metastasize – NCI Dictionary of Cancer Terms – National Cancer Institute. Available at: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/metastasize. (Accessed: 12th July 2018)
  6. Webby, R. J. & Sandbulte, M. R. Table of contents 1. 4912–4924 (2008).
  7. Definition of tumor microenvironment – NCI Dictionary of Cancer Terms – National Cancer Institute. Available at: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/tumor-microenvironment. (Accessed: 12th July 2018)
  8. Mittal, K., Ebos, J. & Rini, B. Angiogenesis and the tumor microenvironment: Vascular endothelial growth factor and beyond. Semin. Oncol. 41, 235–251 (2014).
  9. Frantz, C., Stewart, K. M. & Weaver, V. M. The extracellular matrix at a glance. J. Cell Sci. 123, 4195–200 (2010).
  10. Watnick, R. S. The Role of the Tumor Microenvironment in Regulating Angiogenesis The Role of the Tumor Microenvironment in Regulating Angiogenesis. 1–21 (2012). doi:10.1101/cshperspect.a006676
  11. Hanahan, D. & Weinberg, R. A. Hallmarks of Cancer: The Next Generation. Cell 144, 646–674 (2011).
  12. Samuel, J. & Franklin, C. in Common Surgical Diseases 391–394 (Springer New York, 2008). doi:10.1007/978-0-387-75246-4_97
  13. Chouaib, S., Umansky, V. & Kieda, C. The role of hypoxia in shaping the recruitment of proangiogenic and immunosuppressive cells in the tumor microenvironment. Contemp. Oncol. (Poznan, Poland) 22, 7–13 (2018).
  14. Nogués, L., Benito-Martin, A., Hergueta-Redondo, M. & Peinado, H. The influence of tumour-derived extracellular vesicles on local and distal metastatic dissemination. Mol. Aspects Med. 60, 15–26 (2018).
  15. Itatani, Y., Kawada, K., Yamamoto, T. & Sakai, Y. Resistance to anti-angiogenic therapy in cancer-alterations to anti-VEGF pathway. Int. J. Mol. Sci. 19, 1–18 (2018).
  16. Hida, K., Maishi, N., Annan, D. & Hida, Y. Contribution of Tumor Endothelial Cells in Cancer Progression. Int. J. Mol. Sci. 19, 1272 (2018).
  17. Hanahan, D. & Folkman, J. Patterns and emerging mechanisms of the angiogenic switch during tumorigenesis. Cell 86, 353–364 (1996).
  18. Definition of stromal cell – NCI Dictionary of Cancer Terms – National Cancer Institute. Available at: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/stromal-cell. (Accessed: 12th July 2018)
  19. Wiseman, B. S. Stromal Effects on Mammary Gland Development and Breast Cancer. Science (80-. ). 296, 1046–1049 (2002).
  20. Paracrine regulation | definition of paracrine regulation by Medical dictionary. Available at: https://medical-dictionary.thefreedictionary.com/paracrine+regulation. (Accessed: 12th July 2018)
  21. Sundararajan, V., Sarkar, F. H. & Ramasamy, T. S. The versatile role of exosomes in cancer progression: diagnostic and therapeutic implications. Cell. Oncol. 41, 223–252 (2018).
  22. Mitogens | definition of Mitogens by Medical dictionary. Available at: https://medical-dictionary.thefreedictionary.com/Mitogens. (Accessed: 12th July 2018)
  23. Albini, A., Bruno, A., Noonan, D. M. & Mortara, L. Contribution to tumor angiogenesis from innate immune cells within the tumor microenvironment: Implications for immunotherapy. Front. Immunol. 9, (2018).
  24. Podar, K., Fan, F., Schimming, A. & Jaeger, D. Targeting the tumor microenvironment: Focus on angiogenesis. J. Oncol. 2012, (2012).
  25. Hameed, S., Bhattarai, P. & Dai, Z. Nanotherapeutic approaches targeting angiogenesis and immune dysfunction in tumor microenvironment. Sci. China Life Sci. 61, 380–391 (2018).

How Painful is life for a Human Embryo?

Embryo pain

While abortion policies are discussed throughout the world, science provides some insights into this controversial debate. Even before the dilemma of personhood, there is another question that is often overlooked when regarding abortion: Does a human embryo feel pain?

Current developments in abortion policies around the world demand answers from science1. Aside from the problem of “personhood”2,3, a major point in this discussion is fetal pain4. In the context of abortion, fetal pain is a keystone ethical argument: there is the duty to do all that can be done to relieve all the pain and suffering which can be alleviated5. Within this opportunity to study fetal pain, other problems are also backlit such as the use of anesthesia in fetal surgery6, and possible impacts of pain and anesthesia in the developing fetus7.

Box 1 | Difference between an embryo and a fetus.

Embryo: “Discrete entity that has arisen from either the first mitotic division when fertilization of a human oocyte by a human sperm is complete, (…) and has not yet reached 8 weeks of development since the first mitotic division10.

Fetus: “The fetal stage is from the beginning of the 9th week after fertilization and continues until birth, at this time the developing human is referred to as fetus11,12.

Before we approach this question, there are some concepts about pain that should be clarified. Primarily, what is pain? How do we feel it? Pain is defined as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage”8. There are two components of pain: (1) physiologic reaction towards a noxious stimulus, nociception or stress response, and (2) an emotional negative perception. Respectively, in order for pain to occur, there are two requisites: (1) a neuroanatomical apparatus that allow pain perception at a cortical level and (2) awareness9. Within this limited paradigm we now have the semantic tools to accurately tackle this biological dilemma.10,11,12 (Figure 1)

components of pain

Figure 1 |Components of Pain: Pain is an emotional negative perception that arises from a physiologic reaction towards a “painful” stimulus. Because an emotional negative perception can only happen if there is awareness to perceive it; and a physiologic reaction can only happen if there is the neuroanatomical apparatus (nerves) to do so, without either of those requisites, pain can not occur.

In the light of embryo definition in Box 1, and considering pain perception requisites stated above, the answer to the original question “How painful is life for a human embryo” is simply that: life is not in any way painful to an embryo during its 8 weeks of development. It lacks both requisites. In adult, the neuronal pathways and structures required for pain perception (represented in red in figure 1) are: the peripheric receptors, afferent nerves that connect to the spinal cord, the spinothalamic tract and the somatosensitive cortex13. During development, sensory fibers are only abundant by 20 weeks; a functional spinal reflex is just present by 19 weeks; connections to the thalamus emerge by 20 weeks; and connections to subplate neurons are present by 17 weeks with intensive differentiation by 25 weeks. Mature thalamocortical projections are not present until 29 to 30 weeks14(Figure 2). Therefore, there is, theoretically, no physiological way an 8-week embryo could feel pain. However, when we turn the spotlight to fetus the situation is not so clear. There is in fact, a time window for when the physiological requisites for pain might emerge. To assess fetal pain, withdrawal reflexes and hormonal stress responses are not valid markers as they may be elicited by non-painful stimuli. Fetal pain assessment must follow an imaging approach relying in techniques such as electroencephalography15. Early imaging research suggests that no functional pain perception exists before the third trimester15,16.

neuroanatomic
Figure 2| The neuroanatomical apparatus of pain. These are required fore a physiological reaction to noxious stimuli and, therefore, for pain arise. Developmental fetal stages that lack any of this anatomical features are theoretically incapable of feeling pain. Afferent nerves are abundant by ~20 weeks of development; Mature thalamocortical projections by ~30 weeks.

In 2010, the Royal College of Obstetricians and Gynaecologists (RCOG) published a game-breaking paper supporting the physiological view that the lack of cortical connections before 24 weeks implies the inexistence of pain until then. The novelty, though, is that pain in further stages in fetus development is also improbable as the fetus is sedated by the chemical environment of the womb17. No awareness no pain. In the following year, Martin Platt heavily criticized the latter view as the lack of fetal awareness appointed by RCOG is mainly supported by comparative evidence. He also refers to the existence of extensive literature, on fetal sleep and wakefulness, motility, memory, hearing, and fetal behaviour18. The controversy was installed and persist to this day.

We’ve reached a point where progress in which effective fetal pain assessment is crucial and, given the hedonic nature of pain, this can only be achieved by imaging techniques19. Pain neuroimaging techniques are already revolutionizing the way we conceptualize moral itself, hinting to be a decisive factor in the future discussion of abortion, both in fetal pain and personhood aspects3,20. As the world attitude towards abortion seems to stabilize in a 10-20-week limit acceptable consensus21,22, fetal aspects of pain acquire new proportions regarding fetal surgery and anaesthetics7. With scarce empirically evidenced impact on the fetus development6, anesthesia should still be preventively used during fetal surgery regardless of pain existence23.

Embryo pain2

Wrapping up, considering fetal pain physiologically impossible before 20th week and controversially possible from then on, it is important to refer to a final research case. A case of fetal pain response with bradycardia during surgery, led authors to consider that the fetus was not adequately anesthetized and strengthen the hypothesis that fetus under the second trimester of pregnancy may indeed feel pain: Even if the sensory cortex itself is not fully developed, other structures in the developing brain may act as surrogates for it (How cool!). Neurons of the subplate zone are particularly susceptible to preterm injuries, and this zone is active in the second-trimester human fetus. Consequently, fetus may still be able to process the information from nociceptive stimuli and model the developing nervous system in response to pain23.

            As the study in fetal pain proceeds, this last possibility is indeed a crude reminder that our understanding in science is never the full picture but a proportion that we can illuminate with the flashlight of our current knowledge.

References and Acknowledgements

References:

  1. Porter, L. Abortion, infanticide and moral context. J. Med. Ethics 39, 350–352 (2013).
  2. Will, J. F. Beyond abortion: why the personhood movement implicates reproductive choice. Am. J. Law Med. 39, 573–616 (2013).
  3. Wrigley, A. Limitations on personhood arguments for abortion and ‘after-birth abortion’. J. Med. Ethics 39, e15–e18 (2013).
  4. Brugger, E. C. The problem of fetal pain and abortion: toward an ethical consensus for appropriate behavior. Kennedy Inst. Ethics J. 22, 263–87 (2012).
  5. Edwards, R. B. Pain and the ethics of pain management. Soc. Sci. Med. 18, 515–23 (1984).
  6. Bellieni, C. V. et al. Use of fetal analgesia during prenatal surgery. J. Matern. Neonatal Med. 26, 90–95 (2013).
  7. Seo, H. & Yi, J.-W. Beyond the neonate: how do anesthetics affect the fetal brain? Korean J. Anesthesiol. 70, 589 (2017).
  8. IASP Taxonomy – IASP. Available at: https://www.iasp-pain.org/Taxonomy#Pain. (Accessed: 5th January 2018)
  9. Garland, E. L. Pain processing in the human nervous system: a selective review of nociceptive and biobehavioral pathways. Prim. Care 39, 561–71 (2012).
  10. Findlay, J. K. et al. Human embryo: a biological definition. Hum. Reprod. 22, 905–911 (2007).
  11. N. Jayne Klossner. Introductory Maternity Nursing. (2006).
  12. B. Scott. The Anthropology of the Fetus: Biology, Culture, and Society – Google Livros. (2017).
  13. Gonçalves, N., Rebelo, S. & Tavares, I. [Fetal pain – neurobiological causes and consequences]. Acta Med. Port. 23, 419–26
  14. Lowery, C. L. et al. Neurodevelopmental Changes of Fetal Pain. Semin. Perinatol. 31, 275–282 (2007).
  15. Lee, S. J., Ralston, H. J. P., Drey, E. A., Partridge, J. C. & Rosen, M. A. Fetal Pain. JAMA 294, 947 (2005).
  16. Bellieni, C. V. & Buonocore, G. Is fetal pain a real evidence? J. Matern. Neonatal Med. 25, 1203–1208 (2012).
  17. Royal College of Obstetricians and Gynaecologists. Fetal Awareness – Review of Research and Recommendations for Practice. Rcog.Org.Uk (2010).
  18. Platt, M. W. Fetal awareness and fetal pain: The Emperor’s new clothes. Arch. Dis. Child. Fetal Neonatal Ed. 96, F236–F237 (2011).
  19. Bellieni, C. V. Pain Assessment in Human Fetus and Infants. AAPS J. 14, 456–461 (2012).
  20. Pustilnik, A. C. Pain as a fact and heuristic: how pain neuroimaging illuminates moral dimensions of law. Cornell Law Rev. 97, 801–48 (2012).
  21. Berer, M. Abortion Law and Policy Around the World: In Search of Decriminalization. Health Hum. Rights 19, 13–27 (2017).
  22. The World’s Abortion Laws. Available at: http://worldabortionlaws.com/. (Accessed: 7th January 2018)
  23. Mayorga-Buiza, M. J., Marquez-Rivas, J. & Gomez-Gonzalez, E. Can fetus feel pain in the second trimester? Lessons learned from a sentinel event. Child’s Nerv. Syst. (2017). doi:10.1007/s00381-017-3677-6

Acknowledgements

Credits to Anthony Bossard, alvarobueno, C.S. Lee, Eugene Khvan, FLPLF Ivan Colic, snide, among others from the Noun Project (https://thenounproject.com/) where most of the icons used to create the illustrations were taken.

Together we fire, together we wire!

Donald Hebb
Donald Hebb

In 1949, neuroscientist Donald Hebb published “The Organization of Behaviour” in which he postulated what was soon to be summarized as “Cells that fire together wire together”.  This primordial, yet crucial, work by Hebb is an early reminder that biological processes are the background of all human character: We are a community of cells that communicate with each other.

This community is poetically reminiscent of our own society: They cooperate so they can prosper; They specialize and perform different functions; They are heavily influenced by their environment; They all share the same “moral” code which guides their behavior. Occasionally, foreigners with different moralities enter their society. Some are selfish and bad intended and the society tracks them and fights them. Others are well intended and are welcomed into the society despite being inherently different. Sometimes members of the community lose their moral code and start to live for their own interest, despite the society.

In the end, the aim of this cellular community is the same as ours: to pass their values onto their offspring, to the next generation. Some of these societies succeed, others do not.

Understanding these societies is understanding the Human being, and understanding the human being is understanding society.

firewireeee
The Hebian theory

One of the enthusiastic corollaries of this humble, reductionist point of view, came from the Hebbian theory itself: plasticity. We are free. We are not stuck with an immutable brain. We are not stuck with an inflexible mind. We are not predetermined to stick with a certain self-identity or personality.

With this blog, We would like bring the latest gossip of the lives of cells. Because the life of cells is, itself, our life. We aim to bring arcticles supported only by peer-reviewed bibliography that is captivating, elucidative and accessible.

Let’s fire together, so we can wire together!