Transmissible Cancer Evolution: The Under-Estimated Role of Environmental Factors in the “Perfect Storm” Theory

The widespread vulnerability of Hydra oligactis to tumourigenesis confirms its value as a model for studying the effects of tumoural processes on the ecology and evolution of species

Tumoural processes, ubiquitous phenomena in multicellular organisms, influence evolutionary trajectories of all species. To gain a holistic understanding of their impact on species' biology, suitable laboratory models are required. Such models are characterised by a widespread availability, ease of cultivation, and reproducible tumour induction. It is especially important to explore, through experimental approaches, how tumoural processes alter ecosystem functioning. The cnidarian Hydra oligactis is currently emerging as a promising model due to its development of both transmissible and non-transmissible tumours and the wide breadth of experiments that can be conducted with this species (at the individual, population, mechanistic, and evolutionary levels). However, tumoural hydras are, so far, only documented in Europe, and it is not clear if the phenomenon is local or widespread. In this study we demonstrate that Australian hydras from two independent river networks develop tumours in the laboratory consisting of interstitial stem cells and display phenotypic alterations (supernumerary tentacles) akin to European counterparts. This finding confirms the value of this model for ecological and evolutionary research on host-tumour interactions.

Gamma irradiation green synthesis of (polyacrylamide/chitosan/silver nanoparticles) hydrogel nanocomposites and their using as antifungal against Candida albicans and anti-cancer modulator

Silver nanoparticles-loaded hydrogel nanocomposites are exploited for medicinal and pharmaceutical applications. Hydrogel nanocomposites were prepared from acrylamide (Am), chitosan (CS) and AgNO3 utilizing gamma rays. Diverse variables were applied in preparation of silver nanoparticles-laoded hydrogel nanocomposites of (PAm/CS)-AgNPs such as influence of radiation dose and influnece of CS concentration. Diverse techniques were utilized to characterize hydrogel nanocomposites; Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analysis (TGA), X-ray diffraction (XRD), Transmission electron microscopy (TEM), energy dispersive X-ray (EDX) and scanning electron microscopy (SEM). Results confirmed formation of silver nanoparticles-loaded hydrogel nanocomposites of (PAm/CS)-AgNPs. Antifungal activity of (PAm/CS)-AgNPs hydrogel nanocomposites on viability of C. albicans was esitmated. Results displayed the efficient microbial inhibition activity of treatment against C. albicans compared to control. Furthermore, (PAm/CS)-AgNPs hydrogel nanocomposite against cervical cancer HeLa cell line was investigated. Cytotoxicity of (PAm/CS)-AgNPs hydrogel nanocomposites on prior cancer cell line empolyed to prohibition of cell growth assesssed by MTT test. HeLa cancer cell is treated by (PAm/CS)-AgNPs for 48 h exposed a potential apoptotic activity by noticeable up-regulation of p53 gene expression. Moreover, anticancer activity was investigated by down-regulation of platelet-based growth variable receptor beta (PDGFR-β), Bcl2, Cathepsine, and MMP-2 gene expression. antioxidant activity was investigated and results showed antioxidant activity of (PAm/CS) hydrogel and (PAm/CS)-AgNPs hydrogel nanocomposite are 87.8% and 62.9%, respectively.

Evolution of transmissible cancers: An adaptive, plastic strategy of selfish genetic elements?

A growing number of studies have applied evolutionary and ecological principles to understanding cancer. However, few such studies have examined whether phenotypic plasticity--the ability of a single individual or genome to respond differently to different environmental circumstances--can impact the origin and spread of cancer. Here, we propose the adaptive horizontal transmission hypothesis to explain how flexible decision-making by selfish genetic elements can cause them to spread from the genome of their original host into the genomes of other hosts through the evolution of transmissible cancers. Specifically, we hypothesize that such cancers appear when the likelihood of successful vertical transmission is sufficiently low relative to the likelihood of successful horizontal transmission. We develop an evolutionary optimization model of this hypothesis, highlight empirical findings that support it, and offer suggestions for future research. Generally, phenotypically plastic selfish genetic elements might play an important role in the evolution of transmissible cancers.

De novo evolution of transmissible tumours in hydra

While most cancers are not transmissible, there are rare cases where cancer cells can spread between individuals and even across species, leading to epidemics. Despite their significance, the origins of such cancers remain elusive due to late detection in host populations. Using Hydra oligactis, which exhibits spontaneous tumour development that in some strains became vertically transmitted, this study presents the first experimental observation of the evolution of a transmissible tumour. Specifically, we assessed the initial vertical transmission rate of spontaneous tumours and explored the potential for optimizing this rate through artificial selection. One of the hydra strains, which evolved transmissible tumours over five generations, was characterized by analysis of cell type and bacteriome, and assessment of life-history traits. Our findings indicate that tumour transmission can be immediate for some strains and can be enhanced by selection. The resulting tumours are characterized by overproliferation of large interstitial stem cells and are not associated with a specific bacteriome. Furthermore, despite only five generations of transmission, these tumours induced notable alterations in host life-history traits, hinting at a compensatory response. This work, therefore, makes the first contribution to understanding the conditions of transmissible cancer emergence and their short-term consequences for the host.

In vitro competition between two transmissible cancers and potential implications for their host, the Tasmanian devil

Since the emergence of a transmissible cancer, devil facial tumour disease (DFT1), in the 1980s, wild Tasmanian devil populations have been in decline. In 2016, a second, independently evolved transmissible cancer (DFT2) was discovered raising concerns for survival of the host species. Here, we applied experimental and modelling frameworks to examine competition dynamics between the two transmissible cancers in vitro. Using representative cell lines for DFT1 and DFT2, we have found that in monoculture, DFT2 grows twice as fast as DFT1 but reaches lower maximum cell densities. Using co-cultures, we demonstrate that DFT2 outcompetes DFT1: the number of DFT1 cells decreasing over time, never reaching exponential growth. This phenomenon could not be replicated when cells were grown separated by a semi-permeable membrane, consistent with exertion of mechanical stress on DFT1 cells by DFT2. A logistic model and a Lotka-Volterra competition model were used to interrogate monoculture and co-culture growth curves, respectively, suggesting DFT2 is a better competitor than DFT1, but also showing that competition outcomes might depend on the initial number of cells, at least in the laboratory. We provide theories how the in vitro results could be translated to observations in the wild and propose that these results may indicate that although DFT2 is currently in a smaller geographic area than DFT1, it could have the potential to outcompete DFT1. Furthermore, we provide a framework for improving the parameterization of epidemiological models applied to these cancer lineages, which will inform future disease management.

Tumors alter life-history traits in the freshwater cnidarian, Hydra oligactis

Although tumors can occur during the lifetime of most multicellular organisms and have the potential to influence health, how they alter life-history traits in tumor-bearing individuals remains poorly documented. This question was explored using the freshwater cnidarian Hydra oligactis, a species sometimes affected by vertically transmitted tumors. We found that tumorous polyps have a reduced survival compared to healthy ones. However, they also displayed higher asexual reproductive effort, by producing more often multiple buds than healthy ones. A similar acceleration is observed for the sexual reproduction (estimated through gamete production). Because tumoral cells are not transmitted through this reproductive mode, this finding suggests that hosts may adaptively respond to tumors, compensating the expected fitness losses by increasing their immediate reproductive effort. This study supports the hypothesis that tumorigenesis has the potential to influence the biology, ecology, and evolution of multicellular species, and thus should be considered more by evolutionary ecologists.

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Vertically transmitted tumors influence the life history traits of hydras

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Tumor-bearing hydras have a reduced survival rate

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Tumorous hydras show increased early reproductive effort (asexual and sexual)

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Changes in sexual reproduction pattern can be a compensatory response of the host