Periodic Reporting for period 2 - MADMICS (Metaplasia as an adaptive response to chronic microbial infections)
Reporting period: 2022-07-01 to 2023-12-31
The origin of cancer initiation is still unclear in many cases. Elucidating the basic mechanisms of carcinogenesis would not only give us a better understanding of the evolutionary rules underlying the development of cancer, but inevitably lead to better prevention and treatment strategies.
A considerable proportion of cancers is thought to be due to environmental influences, such as infections. Not surprisingly, therefore, the disease often originates from the epithelial surfaces of the mucosa, which are constantly exposed to microbes and infectious agents with their potential to damage the genome of the host cells. For the majority of cases, cancer development proceeds via multiple consecutive molecular events. Understanding the very initial steps of carcinogenesis that occur, e.g. under the influence of an infection, would be of prime importance.
One of the best studied models of a bacterium driven cancer in humans is the infection of the gastric mucosa by the bacterial pathogen Helicobacter pylori, which is the main risk factor for gastric carcinoma. In a large proportion of chronic H. pylori infections, the gastric mucosa undergoes a transition of the gastric epithelial layer to an intestinal-type epithelium, referred to as gastric intestinal metaplasia (GIM). Most strikingly, this strictly persistent infection, which cannot even be cleared by the host immune system upon vaccination, gets firmly terminated in the course of the metaplastic transition. We refer to this phenomenon as genetic immunity, as an ultimate means of the host to combat this life-long infection of the gastric mucosa. Notably, GIM and the simultaneous eradication of H. pylori are associated with epigenetic and mutational alterations in the genomes of affected epithelial cells. Since GIM also marks the beginning of cancer development we postulate that genetic immunity and cancer development are evolutionarily linked.
A considerable proportion of cancers is thought to be due to environmental influences, such as infections. Not surprisingly, therefore, the disease often originates from the epithelial surfaces of the mucosa, which are constantly exposed to microbes and infectious agents with their potential to damage the genome of the host cells. For the majority of cases, cancer development proceeds via multiple consecutive molecular events. Understanding the very initial steps of carcinogenesis that occur, e.g. under the influence of an infection, would be of prime importance.
One of the best studied models of a bacterium driven cancer in humans is the infection of the gastric mucosa by the bacterial pathogen Helicobacter pylori, which is the main risk factor for gastric carcinoma. In a large proportion of chronic H. pylori infections, the gastric mucosa undergoes a transition of the gastric epithelial layer to an intestinal-type epithelium, referred to as gastric intestinal metaplasia (GIM). Most strikingly, this strictly persistent infection, which cannot even be cleared by the host immune system upon vaccination, gets firmly terminated in the course of the metaplastic transition. We refer to this phenomenon as genetic immunity, as an ultimate means of the host to combat this life-long infection of the gastric mucosa. Notably, GIM and the simultaneous eradication of H. pylori are associated with epigenetic and mutational alterations in the genomes of affected epithelial cells. Since GIM also marks the beginning of cancer development we postulate that genetic immunity and cancer development are evolutionarily linked.
Maintaining health of an organism involves protecting its genome from harmful environmental influences. One such protective mechanism is by the tumor suppressor protein p53, also referred to as the "guardian of the genome". This protein is in the focus of our research as its coding gene TP53 represents one of the most frequently mutated genes in cancer and often stands at the beginning of the mutational cascade of carcinogenesis. Our interest in p53 is twofold; (a) in technical terms: As a highly effective tumor suppressor, p53 can drive cells into apoptosis once they experience double-strand breaks (DSB). DSBs, however, are experimentally generated during CRISPR/Cas9-based mutagenesis. Since adult human stem cells appear to be particularly sensitive to the action of p53, it is difficult to mutate these cells. Moreover, once TP53 mutations are generated, the cells tend to become unstable, which complicates experimental analysis. And (b) in scientific terms: we are interested in our observation that mutant p53 cells exhibit an antibacterial property, which may explain the observed elimination of H. pylori from the gastric mucosa in GIM. The p53 tumor suppressor thus exemplifies the dual function of certain mutational events, collectively referred to ‘adaptive antimicrobial mutations’ (ADAMs) that link the initiation of tumorigenesis and genetic immunity against pathogen infections.
To explore this intricate functional duality of ADAMs in tumor progression and pathogen defense, we have used native human primary cells in the form of so-called organoids. These highly authentic human experimental models constitute an ideal tool for studying the early events of human carcinogenesis. In many respects, organoids are superior to animal models and also to the cell lines used so far, which are mostly derived from tumor tissue, which is the endpoint of our experimental approach and therefore provide an uncertain basis of valid results. The use of organoids, however, will provide us with the anticipated insight in the evolutionary context of, and the link between genetic immunity and premalignancy.
In addition to the characterization of ADAMs, MADMICs also addresses the specific mutational processes that are the cause ADAMs and mutant p53 (mutp53), as well as the competitive features of normal versus mutant cells which ultimately determine the emergence of a cancer lineage in the tissue context.
To explore this intricate functional duality of ADAMs in tumor progression and pathogen defense, we have used native human primary cells in the form of so-called organoids. These highly authentic human experimental models constitute an ideal tool for studying the early events of human carcinogenesis. In many respects, organoids are superior to animal models and also to the cell lines used so far, which are mostly derived from tumor tissue, which is the endpoint of our experimental approach and therefore provide an uncertain basis of valid results. The use of organoids, however, will provide us with the anticipated insight in the evolutionary context of, and the link between genetic immunity and premalignancy.
In addition to the characterization of ADAMs, MADMICs also addresses the specific mutational processes that are the cause ADAMs and mutant p53 (mutp53), as well as the competitive features of normal versus mutant cells which ultimately determine the emergence of a cancer lineage in the tissue context.
The perceived obstacles with the application of CRISPR/Cas9 technology in human primary organoid cells have hampered the analysis of human disease and, in particular, of human carcinogenesis. In the course of our investigations, we realized that adult human stem cells are - for obvious evolutionary reasons - particularly sensitive to the generation of DSBs and therefore incompatible with CRISPR/Cas9-based mutagenesis. Therefore, we have endeavored and succeeded in developing molecular genetic tools for generating specific mutations in human organoids without affecting the stemness of mutant cells. This effort led a considerable breakthrough that will not only fuel our own investigations but will also fertilize experimental studies with human organoids in general. The new technology will help us to analyze the identified ADAMs via genetically modifying host cells and facilitate further genetic manipulation of human organoids.
Additionally, we have investigated tentative commonalities in the development of cancer in a variety of cancers driven by bacterial infections and, thus, addressed infections of the fallopian tubes with Chlamydia as the origin of high-grade serous ovarian cancer as well as the role of colibactin-producing bacteria in the colon as the origin of a fraction of human colon cancers. By doing so, we aim to obtain clues on the general relevance of our hypotheses and initial observations point towards related evolutionary principles.
Additionally, we have investigated tentative commonalities in the development of cancer in a variety of cancers driven by bacterial infections and, thus, addressed infections of the fallopian tubes with Chlamydia as the origin of high-grade serous ovarian cancer as well as the role of colibactin-producing bacteria in the colon as the origin of a fraction of human colon cancers. By doing so, we aim to obtain clues on the general relevance of our hypotheses and initial observations point towards related evolutionary principles.