‘One Renegade Cell’, written by Robert A. Weinberg, describes the steps involved in cancer development – a complex journey involving multiple events and factors. Following my review of the book (found here), to provide more information on the book’s contents, here you will find a chapter-by-chapter summary – giving you a whistle-stop ‘Oncology 101’ overview. Chapter 1 Chapter 1 lays the foundation for the basic understanding of the organisation and make-up of the human body. It sets the scene that we develop from one cell, which duplicates to produce exact replicas, all with the same ‘blueprint’ to follow – to carry out all the functions of the human body. As Weinberg explains, there is not ‘a single overseeing master builder’ but instead control over the make-up of the human body is exercised by each individual cell. In cancer development, at some point, either during embryonic development or in our lifetime, one cell becomes a ‘renegade cell’, in that it has its own growth agenda. Over a long period of time, descendants of this renegade cell increase in number to form a tumour that, like the founding cell, has only one program in mind: more growth. To understand the development of cancer, it is important to understand the blueprint of normal cells…which comes in the form of DNA, and the ‘information packets’ formed from DNA known as genes. Long stretches of DNA is organised into structures called chromosomes, found within the nucleus of a cell. DNA is made up of a string of chemical bases, which come in ‘four chemical flavours’: A, C, G and T. These bases can be strung together in any order, offering total flexibility in the information contained in DNA. Certain punctuation markers, written in this four-letter code, denote the end of the gene. DNA is arranged as a double helix, carrying 2 copies of the genetic information, facing each other. The structure of the double DNA helix is maintained by bases binding to each other: the ‘A’ appearing on one strand always faces a ‘T’ on the opposite strand, and a ‘C’ will always face a ‘G’. During cell replication, the DNA strands of the double helix separate, and each strand serves as a copy for the new complementary sequence. Today, it is estimated that humans have between 20,000 and 25,000 genes – each person has two copies of each gene, one inherited from each parent. The relevance of DNA and genes in cancer development soon becomes apparent as the book progresses. Chapter 2 Whereas Chapter 1 looked at inside the body, Chapter 2 focuses on the impact of the outside world on the origin of cancer. The chapter takes us on an epidemiological journey through time, through which a multitude of carcinogens, i.e., any agent with the capacity to cause cancer, are identified and catalogued. The earliest of these catalogues came in 18th century, whereby scrotal cancers were linked to men who had worked as chimney sweeps in their youth and nasal cancers linked to gentlemen who used snuff. By the early 1950’s, it was also noticed that people who smoked cigarettes were at greater risk of lung cancer. The chapter also describes how the risk of developing different types of cancers varies by country, relating to lifestyle, diet, and/or the environment. These discoveries begged the question: How precisely could environmental factors affect the behaviour of cells/tissue within the body? To start answering this question, the chapter goes on to introduce the concept of genetic mutations, whereby the function of a gene is altered through changes in its DNA sequence, that ultimately leads to increase cell growth – this was first documented in fruit flies exposed to X-rays. To this end, carcinogens (cancer-causing agents) can also be described as mutagens (mutation-causing agents). The chapter continues to explain that mutational damage on genes carried in sperm or eggs (i.e., ‘germ cells’ in testes or ovaries) can be transmitted to offspring (known as germline mutations), whereas mutations in genes in cells arising elsewhere in the body (the ‘soma’) could not (known as somatic mutations). Weinberg explains, ‘Mutagens create cancer through their ability to enter cells and damage genes’ The next big question following the discovery of carcinogens and the premise genetic mutations, was which specific genes, when mutated, lead to cancer development? Chapter 3 Chapter 3 familiarises the reader with the term onco-genes, building from the term oncology and described by Weinberg as ‘a small set of genes operating inside a cancer cell capable of causing the cell and its descendants to grow without limits’. Two main theories existed for the origin of oncogenes: The ‘chemical’ theory, whereby cancer-causing agents alter genes indigenous to the cancer cell and the ‘viral’ theory, whereby viruses introduce foreign viral genes to its host’s cell through infection. Evidence was present for both of these theories; it was clear that some viruses had the ability to cause cancer, but it was also clear that most kinds of human cancers do not behave like contagious diseases with a growing catalogue of chemical carcinogens. The discovery that cancer-causing viruses were found to have incorporated a cellular gene, from their host, into their viral genome, and had subverted this normal cellular gene to one that has the potential to cause cancer, bridged the gap between the ‘viral’ and ‘chemical’ oncogene theories. The normal versions of these genes, found in the animal host, were called proto-oncogenes, to indicate that they had the potential to become oncogenes. The proto-oncogenes (i.e., the normal cellular versions) took on the name of the virus in which their cancer-causing counterpart had been discovered, e.g., src (found in Rous sarcoma virus), myc (Myelocytomatosis avian virus), and ras (Rat sarcoma virus) among others. The obvious next question is how do proto-oncogenes become oncogenes? Chapter 4 begins to address this key question… Chapter 4 The development of gene cloning technology, in 1982, allowed for isolation and comparison of oncogenes. Comparison of the ras oncogene in human bladder cancer cells to its normal proto-oncogene counterpart (in normal cells) resulted in a stunning discovery: the two gene versions, each 5,000 DNA bases long, were found to be identical except for 1 base; a single G present in the normal version of the gene had been replaced with a T in the gene carried in the bladder cancer cells. This is termed a single point mutation and turned out to be the most subtle of the changes required — each proto-oncogene is converted to oncogene through its own distinct mutational mechanisms. Chapter 5 At the start of Chapter 5, Weinberg recaps on the story told so far: A mutagenic chemical strikes a proto-oncogene, converting it to an oncogene, resulting in unconstrained proliferation where copies of the oncogene are made and passed on to descendant cells…billions of descendent renegade cells accumulate to form a life-threatening tumour. However, this view was thought to be too simplistic… New thoughts arose that cancer was a multi-step process involving a succession of mutations, until a tipping point is reached that results in runaway growth. Key evidence came from epidemiologists who measured rates of cancers in various populations at different ages and the finding that the incidence of most adult cancers increases steeply with age. The school of thought was that cancer development requires multiple events, each with a low probability, therefore the chance of all events happening increases as life span increases. The human body erects obstacles to prevent cancer development and only when all obstacles are surmounted, i.e., when multiple events have occurred, will cancer develop. The true test of this hypothesis came in 1983. Oncogenes were inserted into ‘normal’ cells, not the immortalised cell lines typically used in experiments. The finding was that fully normal cells could not be transformed by the introduction of a single oncogene. The conclusion was that cancer involved a succession of at least 2, but possibly more changes in the cell, which could be brought about by carcinogens. Chapter 6 Chapter 6 highlights that not all carcinogens are mutagens. Agents that cause cell division (i.e., not gene mutations per se) can also be cancer-causing e.g., alcohol, hepatitis B virus (HBV), and oestrogen. By driving cells to grow, some agents can force the cancer process forward – the increased cell growth increases the likelihood of mistakes (mutations) being made during the multiple rounds of DNA replication and the likelihood of a cell to acquire oncogenes. Although the thinking was that cancer was a multi-step process, large number of mutant oncogenes in the same human tumour cell could not be found. By the mid-1980s, mutant genes that very different from oncogenes were found, which came to be called tumour suppressor genes, introduced in Chapter 7. Chapter 7 Weinberg gives a car analogy to help put the different types of genes into context: Proto-oncogenes are the accelerator pedal in a car, the mutant oncogene version is the accelerator pedal is stuck to the floor, and tumour suppressor genes are the car brakes counteracting the effects of oncogenes. As normal cells turn into cancer cells they lose or inactive the brakes. Evidence of tumour suppressor genes came through cell fusion experiments, where a normal cell was fused with a cancer cell. The expectation was that cancer cell would be the dominating force resulting in a hybrid cell that exhibited characteristics of the cancer cell. But opposite was true; the hybrids lacked the ability to seed tumours, the normal cell’s growth genes were dominant, and the cancer-causing genes were recessive… It would take years before tumour suppressor genes were isolated by gene cloning, but evidence that they existed was there. The discovery of tumour suppressor genes also offered some explanation into the heritability of cancers. The mutant versions of tumour suppressor genes in the sperm or egg, which are transmitted from parent to offspring, result in greater susceptibility to cancer. Importantly, only when both copies of the tumour suppressor gene are mutated will the ‘braking’ function be lost – as Weinberg states “half a brake lining is as good as whole one in slowing down cancer growth”. Chapter 8 Chapter 8 links sporadic and genetic/inherited cancers, using colon cancer as an example. The incidence of colon cancer has increased – driven by people living longer (i.e., increasing the chance of the succession of mutations needed for cancer cells to break away from normal controlled cell growth) and changes to our diet (i.e., intake of foods/drinks that contain carcinogens). There is a high turnover of cells in the gut, but despite this high turnover, the architecture of the gut lining is maintained. However, for some, abnormal structures appear, which vary in their level of ‘abnormality’ – from an excess of normal cells (hyperplasia), to clumps of abnormal cells taking on some of the attributes of cancer cells (dysplasia), to larges masses of dysplastic cells (adenomas or polyps), to more extreme changes with obvious malignant growth (neoplasia), which are considered as carcinomas. The different levels of abnormality hint at the series of steps required for cancer development. Investigations into the genetic makeup of colon cells at each of these different stages of abnormality lead to the following discoveries: The Apc tumour suppressor gene was found to be mutated in colon polyps An additional ras oncogenic mutation was detected in more advanced polyps Loss of tumour suppressor gene DCC was detected in cells on the brink to becoming malignant Additional loss of p53 was found in colon cancer carcinomas The findings corroborated that cancer development is a complex multistep process, involving both tumour suppressor genes and at least one oncogene. The presence of these genes in the mutated form in the germ line (sperm or egg) generates a congenital predisposition to cancer. The same genes when mutated by random processes in the cells of a target organ, yield the unpredictable tumours that represent >90% of cancer burden in human population. Chapter 9 To add further complexity to process of cancer development, Chapter 9 outlines genes, other than oncogenes and tumour suppressor genes, that also play a major part in cancer creation… DNA replication is prone to error and an ever-vigilant repair apparatus continuously fights off genetic chaos. Scrutiny of the machinery used by the cell to copy its DNA molecules and repair any damage has identified other key players, underscored by the finding that several kinds of familial cancers are driven by inherited defects in DNA repair. In the book, Weinberg states ‘evidence suggests that two genes implicated in familial breast and ovarian cancers – BRCA1 and BRCA2 – specify proteins that are also involved in maintaining the integrity of the cell’s DNA’. There is now a wealth of evidence documenting the increased risk of developing ovarian and breast cancer if a person carries a mutated BRCA1 or BRCA2 gene. Indeed, since publishing of One Renegade Cell, drugs have been developed to exploit these mutations, such as poly(ADP)-ribose polymerase (PARP) inhibitors. The PARP enzyme and BRCA1/2 normally function to repair daily DNA damage. Mutations in BRCA1 and/or BRCA2 result in higher dependency on the cell on PARP for DNA repair. Inhibition of PARP in BRCA-mutated tumour cells results in DNA damaged that cannot be repaired, to a level that ultimately results in tumour cell death. Chapter 10 Chapter 10 serves as an introduction to signal transduction in cells, that is how cells receive and send messages. Essentially, normal cells rely on messages to grow. These messages are relayed in the form of growth factors – proteins that may be released from one site in the body and travel through the blood to an appropriate target cell, where it is detected by receptors that span from the exterior to the interior of the cell to transmit a signal into the cell. The signal is passed from one protein to the next (known as signal transduction) in a signal cascade that may ultimately result in proliferation. A good example of a signal transducer (i.e., passing along the growth signal within the cell) is the normal ras proto-oncogene, which sits near cell periphery on inner surface of cell membrane awaiting prompting for a nearby growth factor. If the appropriate growth factor binds to the receptor, the ras protein becomes activated and activates a downstream partner, the raf proto-oncogene…the signal is ultimately passed into nucleus of the cell where the message is processed to move the cell from dormancy to active growth. Importantly for this story, cancer cells, are much less dependent on external growth signals, seeming to respond to their own internal growth signals. Chapter 11 Chapter 11 describes the different ways in which cancer cells can be liberated from their dependence on growth factors, whereby the cell is tricked into believing it has encountered a growth factor. This trickery can be achieved through a variety of different mechanisms… Oncoproteins encouraging cells to make their own growth factors Mutation of growth factor receptors resulting in a structure that continuously fire growth-stimulating signals (in the absence of growth factors) Overexpression (increased number) of growth factor receptors on the cell surface Inability of signal transducing proteins to turn themselves ‘off’ e.g., ras oncoprotein remains in an active state, flooding the cell with growth signals Overexpression of growth signal transducers e.g., oncogenic myc In addition to proteins that transmit growth signals, there are proteins that inhibit the transduction and act as brakes to cell growth, called tumour suppressor proteins (e.g., TGF-ß). The two kinds of proteins counterbalance each other allowing for finely tuned cell growth decisions – although in cancer cells, the balance is tipped towards cell growth. Chapter 12 The barrier to unlimited proliferation is often termed cell mortality – the focus of Chapter 12. Cell mortality is defined by cells having a limited number of rounds of doubling before they stop growing and is a barrier that must be breached by the developing tumour cell population…but how do cancer cells become immortal? The answer came after the discovery of telomeres, distinctive structures found at the ends of our chromosomes, consisting of the same short DNA sequence repeated over and over again (in humans the telomere sequence is TTAGGG). In 2009, the Nobel prize in Physiology or Medicine was awarded to three scientists who discovered that telomeres, built by the enzyme telomerase, act as protective caps for chromosomes, preventing their degradation. As cells undergo repeated rounds of cell division, the telomeres shorten as bases are lost. Once the telomere becomes too short the cell enters a state of senescence or cell death. In most cancer cells, telomere length is maintained by telomerase, i.e., telomere length and telomerase activity are crucial for cancer initiation and cancer cell survival to overcome cell mortality. Although drugs targeting telomerase are an attractive target, the development of telomerase inhibitors has been challenging and thus far there are no clinically approved strategies exploiting this target. Chapter 13 Chapter 13 introduces the process of apoptosis (programmed cell death) and how describes way in which cancer cells can evades this fate. Weinberg’s describes apoptosis as ‘not a pretty sight’. First, the nucleus shrinks, the outer membrane then herniates at many points, chromosomal DNA is chewed into pieces, and finally the cell explodes into fragments that are gobbled up by neighbours. There are many cues for apoptosis e.g., a cell infected by a virus will activate the apoptotic program – sacrificing itself to deprive the virus of a suitable host, immune cells that fail to produce necessary antibodies will under apoptosis, as do defective cells that have sustained irreparable DNA damage. Weinberg comments that “A cell en route to becoming cancerous must carefully negotiate the minefield of apoptosis” One way in which cells can escape apoptosis is by activating the Bcl-2 oncogene – the Bcl-2 protein serves to inhibit apoptosis. Cancer cells can help ensure their long-term survival through activating Bcl-2 oncogene. Since the writing of Renegade Cell, venetoclax, a selective Bcl-2 inhibitor, has become a key treatment for haematological malignancies. Another key guardian of apoptosis, a ‘central controller’ is the p53 tumour suppressor gene. The p53 protein serves as an ‘arbiter between life and death’. The role of p53 is most apparent in response to DNA damage. Levels of p53 inside the cell builds up within minutes after DNA damaged is sensed. Once at a high enough level, the p53 protein acts as an emergency brake, rapidly shutting down the cell’s progress through the cell cycle (discussed in more detail in the subsequent chapter). During this pause in cell cycle progression, the cell’s DNA repair apparatus can find and repair the DNA damage. Once fixed, p53 backs off and cell can begin to grow once more. For cancer cells, inactivating the p53 gene has obvious benefits…and from the therapeutic point of view, anti-cancer treatments activating p53 is beneficial. Chemotherapy and X-rays create enough DNA damage to activate p53 and induce cancer cell death. Indeed, p53 inactivation is detected in many cancer types and is typically a marker of poor prognosis – these cells are more resistant to undergoing cell death. Chapter 14 Although mentioned in Chapter 13, the cell cycle is the key focus of Chapter 14, which is controlled by what is called the cell cycle clock – ‘Sooner or later all signals received and processed by proto-oncogenes and tumour suppressor genes converge on the cell cycle clock’. The cell cycle can be divided into phases: The S phase, where DNA is copied (this takes approximately 6-8 hours), the G2 phase, where the cell prepares for division (~3-4h), and the M phase, the ‘complex choreography of cell division’ known as mitosis (~1h). After division, the newly formed ‘daughter cells’ prepare for next round of DNA copying, this is the G1 phase (~10-12h). Alternatively, cells may exit G1 phase and enter a quiescent, non-growing state, known as G0. The machinery of the clock, that controls the cell cycle, is assembled from 2 key proteins: cyclins and cyclin-dependent kinases (CDKs). CDKs are the core components but are guided by their partners, cyclins. Weinberg describes CDKs and their cyclins are the “unthinking gears” of the clock. It is the controllers of these gears that control the cell clock – such as genes such as p15, p16 and p21 (induced by p53), which act as brakes of the cell cycle. Very simply, activation of CDKs, by activating kinases, promotes cell cycle progression and conversely, inhibitors of CDKs can block cell progression. In cancer cells, the cell cycle clock is disrupted e.g., mutations that disrupt cell cycle control and compromise the ability of cells to exit the cell cycle. Targeting the cell cycle machinery has therefore been an attractive therapeutic target in cancer. Since the writing of One Renegade Cell, CDK4/6 inhibitors (such as abemaciclib, palbociclib and ribociclib) have become a mainstay of treatment in breast cancer. Chapter 15 The penultimate chapter, Chapter 15, describes the how “the body places numerous obstacles in the path of cells intent on forming tumours”. These obstacles appear in many guises. Many researchers believed that the immune system plays a role in erecting a line of defence against developing tumours. This notion has been endorsed by the explosion of immunotherapies that have since appeared on the market as effective cancer treatments. These immunotherapies act by exploiting the body’s own immune system to target cancer cells. Another barrier to tumour growth relates to the requirement of the tumour mass for nutrients and oxygen – once the tumour reaches a critical mass, it can no longer receive adequate flow of nutrients and oxygen. Cells within the clump will start to ‘starve’ and anoxic cells (i.e., deficient in oxygen) will often die as a result of p53-mediated apoptosis. However, tumours have developed a solution…they develop their own blood circulation system, releasing ‘angiogenic’ factors that encourage the construction of new blood vessels (angiogenesis) to restore oxygen and nutrient supply. Targeting tumour vasculature is therefore also therapeutic target…the cancer drug, bevacizumab, approved across multiple cancer types, targets vascular endothelial growth factor (VEGF) – a protein that stimulates the formation of new blood vessels. Chapter 15 also introduces the concept of metastasis. Of the patients that succumb to cancer, fewer than 10% die from tumours at the primary site (where the tumour first started to grow), in most cases it is the consequence of metastases – colonies of cancer cells that have left the original site and settled elsewhere. The process of metastasis is very complex, but to settle and invade a new site, the tumour cells needs to destroy nearby tissue (involving enzymes called proteases). Blood vessels or the lymphatic system can be used as routes for tumour cells seeking out a secondary site. There are specific high frequency sites for particular primary tumours e.g., liver metastases in the case of colon cancer, lung metastases for breast cancer. Our understanding of metastasis has progressed substantially since publication of One Renegade Cell, however there is still lots to understand. Chapter 16 The final chapter, Chapter 16, focuses on how we can use the knowledge of cancer development, described throughout the book, to develop treatments and cures for cancer. There has been a huge amount of progress that has been made in cancer drug development since publication of the book – if written today, this would no longer be the shortest chapter the book. The identification of specific oncogenes, tumour suppressor genes, the increased understanding of the stages and processes involved in cancer development and uncovering the cell cycle clock at the heart of the cell division, has led to the identification of new targets for cancer treatments and subsequent approvals that have dramatically impacted how patients are managed. The chapter also touches on how ‘Conquering cancer by preventing it’. Screening programs (such as for colon cancer), BRCA1/2 mutation testing (to understand risk of breast and ovarian cancer), changing to lifestyle such as stopping smoking and changes, can all play a role in reducing the risk of cancer development or allowing for early detection for early treatment. As mentioned in my book review, great progress has been made in cancer drug development since publication of the book, and if written today more time would likely be dedicated to this final chapter! By Gemma McConnell Apply Now!