Differences in mutational processes and intra-tumour heterogeneity between organs: The local selective filter hypothesis

Mapping Spatiotemporal Heterogeneity in Tumor Profiles by Integrating High-Throughput Imaging and Omics Analysis

Intratumoral heterogeneity associates with more aggressive disease progression and worse patient outcomes. Understanding the reasons enabling the emergence of such heterogeneity remains incomplete, which restricts our ability to manage it from a therapeutic perspective. Technological advancements such as high-throughput molecular imaging, single-cell omics, and spatial transcriptomics allow recording of patterns of spatiotemporal heterogeneity in a longitudinal manner, thus offering insights into the multiscale dynamics of its evolution. Here, we review the latest technological trends and biological insights from molecular diagnostics as well as spatial transcriptomics, both of which have witnessed burgeoning growth in the recent past in terms of mapping heterogeneity within tumor cell types as well as the stromal constitution. We also discuss ongoing challenges, indicating possible ways to integrate insights across these methods to have a systems-level spatiotemporal map of heterogeneity in each tumor and a more systematic investigation of the implications of heterogeneity for patient outcomes.

Transmissible cancer and longitudinal telomere dynamics in Tasmanian devils (Sarcophilus harrisii)

A plethora of intrinsic and environmental factors have been shown to influence the length of telomeres, the protector of chromosome ends. Despite the growing interest in infection-telomere interactions, there is very limited knowledge on how transmissible cancers influence telomere maintenance. An emblematic example of transmissible cancer occurs in the Tasmanian devil (Sarcophilus harrisii), whose populations have been dramatically reduced by infectious cancer cells. To investigate associations between telomere dynamics and the transmissible cancer, we used longitudinal data from a Tasmanian devil population that has been exposed to the disease for over 15 years. We detected substantial temporal variation in individual telomere length (TL), and a positive significant association between TL and age, as well as a marginally significant trend for devils with devil facial tumour disease (DFTD) having longer telomeres. A proportional hazard analysis yielded no significant effect of TL on the development of DFTD. Like previous studies, we show the complexity that TL dynamics may exhibit across the lifetime of organisms. Our work highlights the importance of long-term longitudinal sampling for understanding the effects of wildlife diseases on TL.

From developmental to atavistic bet-hedging: How cancer cells pervert the exploitation of random single-cell phenotypic fluctuations

Stochastic gene expression plays a leading developmental role through its contribution to cell differentiation. It is also proposed to promote phenotypic diversification in malignant cells. However, it remains unclear if these two forms of cellular bet-hedging are identical or rather display distinct features. Here we argue that bet-hedging phenomena in cancer cells are more similar to those occurring in unicellular organisms than to those of normal metazoan cells. We further propose that the atavistic bet-hedging strategies in cancer originate from a hijacking of the normal developmental bet-hedging of metazoans. Finally, we discuss the constraints that may shape the atavistic bet-hedging strategies of cancer cells.

Application of Single-Cell Multi-Omics in Dissecting Cancer Cell Plasticity and Tumor Heterogeneity

Tumor heterogeneity, a hallmark of cancer, impairs the efficacy of cancer therapy and drives tumor progression. Exploring inter- and intra-tumoral heterogeneity not only provides insights into tumor development and progression, but also guides the design of personalized therapies. Previously, high-throughput sequencing techniques have been used to investigate the heterogeneity of tumor ecosystems. However, they could not provide a high-resolution landscape of cellular components in tumor ecosystem. Recently, advance in single-cell technologies has provided an unprecedented resolution to uncover the intra-tumoral heterogeneity by profiling the transcriptomes, genomes, proteomes and epigenomes of the cellular components and also their spatial distribution, which greatly accelerated the process of basic and translational cancer research. Importantly, it has been demonstrated that some cancer cells are able to transit between different states in order to adapt to the changing tumor microenvironment, which led to increased cellular plasticity and tumor heterogeneity. Understanding the molecular mechanisms driving cancer cell plasticity is critical for developing precision therapies. In this review, we summarize the recent progress in dissecting the cancer cell plasticity and tumor heterogeneity by use of single-cell multi-omics techniques.

Genetic diversity through social heterosis can increase virulence in RNA viral infections and cancer progression

In viral infections and cancer tumours, negative health outcomes often correlate with increasing genetic diversity. Possible evolutionary processes for such relationships include mutant lineages escaping host control or diversity, per se, creating too many immune system targets. Another possibility is social heterosis where mutations and replicative errors create clonal lineages varying in intrinsic capability for successful dispersal; improved environmental buffering; resource extraction or effective defence against immune systems. Rather than these capabilities existing in one genome, social heterosis proposes complementary synergies occur across lineages in close proximity. Diverse groups overcome host defences as interacting 'social genomes' with group genetic tool kits exceeding limited individual plasticity. To assess the possibility of social heterosis in viral infections and cancer progression, we conducted extensive literature searches for examples consistent with general and specific predictions from the social heterosis hypothesis. Numerous studies found supportive patterns in cancers across multiple tissues and in several families of RNA viruses. In viruses, social heterosis mechanisms probably result from long coevolutionary histories of competition between pathogen and host. Conversely, in cancers, social heterosis is a by-product of recent mutations. Investigating how social genomes arise and function in viral quasi-species swarms and cancer tumours may lead to new therapeutic approaches.

A modern look at the molecular-biological mechanisms of breast tumours in dogs

High morbidity and increase in the number of registrations of breast tumours in dogs, their wide application as biological models, discussion of numerous questions of oncogenesis, and the lack of a uniform/unified methodological approach to the study of molecular and biological mechanisms of treatment of cancer determine the relevance of the problem of cancer both in humans and in our domestic companions. The analysis of publications allowed us to establish the following patterns of carcinogenesis. The peculiarities of the biological behaviour of breast tumours depend on their pathomorphological structure. Genetic predisposition to breast cancer is characteristic only in the single breed aspect. Environmental factors are of critical relevance to carcinogenesis : chemical pollutants initiate oncogenesis indirectly – by altering the expression of several receptors, impaired endocrine balance and direct mutagenic effects. Reproductive status plays a key role in the initiation and progression of breast tumours by reducing the expression of estrogen, progesterone and prolactin receptor genes. The inflammatory response that accompanies the neoplasia process is characterized by increased production of cytokines, cyclooxygenase-2, interleukins (IL-1, IL-6, IL-8), vascular endothelial growth receptors, and impaired hemostatic status (oxidative stress), which promotes progression of disease. In breast cancer in dogs, genomic instability leads to genomic aberrations, and subsequently, mutations that support the proliferation, survival and dissemination of neoplastic cells. The initiation and progression of mammary gland tumours is provided by cancer stem cells by disrupting the regulation of precursor cell self-renewal, which also predispose to resistance to chemotherapeutic agents, radiation, and hormonal cancer therapy. The analysis of the publications revealed the major markers of carcinogenesis that could potentially be used as biological targets for the design of modern diagnostic strategies and high-performance therapeutic protocols.

The evolution of resistance and tolerance as cancer defences

Although there is a plethora of cancer associated-factors that can ultimately culminate in death (cachexia, organ impairment, metastases, opportunistic infections, etc.), the focal element of every terminal malignancy is the failure of our natural defences to control unlimited cell proliferation. The reasons why our defences apparently lack efficiency is a complex question, potentially indicating that, under Darwinian terms, solutions other than preventing cancer progression are also important contributors. In analogy with host-parasite systems, we propose to call this latter option ‘tolerance’ to cancer. Here, we argue that the ubiquity of oncogenic processes among metazoans is at least partially attributable to both the limitations of resistance mechanisms and to the evolution of tolerance to cancer. Deciphering the ecological contexts of alternative responses to the cancer burden is not a semantic question, but rather a focal point in understanding the evolutionary ecology of host-tumour relationships, the evolution of our defences, as well as why and when certain cancers are likely to be detrimental for survival.