Lucie Laplane

Une nouvelle théorie du cancer s’est récemment imposée dans la communauté scientifique. Selon cette dernière, les cancers se développeraient à partir d’une sous-population bien particulière de cellules cancéreuses, appelées « cellules souches cancéreuses » (CSC). Les partisans de la théorie des CSC soutiennent que les rechutes seraient causées par ces cellules, plus aptes à échapper aux thérapies classiques. En conséquence, ils soutiennent que l’élimination de toutes les CSC, dans un cancer donné, est nécessaire et suffisante pour guérir le patient. Dans cette thèse, je propose d’examiner cette stratégie thérapeutique de ciblage des CSC et je montre que sa capacité à guérir les cancers dépend de la façon dont on envisage la nature de la propriété souche. En effet, les cellules souches cancéreuses sont définies par la possession de la propriété souche, c’est-à-dire par leur capacité à s’auto-renouveler et à se différencier. Cependant, cette propriété elle-même reste obscure quant à sa nature. S’agit-il d’une propriété catégorique ou d’une disposition ? Une cellule non-souche (cancéreuse ou non) peut-elle acquérir la propriété souche et sous quelle condition ? En me basant sur une analyse de la littérature scientifique, je montre que quatre conceptions distinctes de la nature de la propriété souche sont aujourd’hui possibles et que, si la théorie des CSC est vraie, déterminer la nature exacte de la propriété souche est capital pour le traitement des cancers.

Whether mitigation of myeloproliferation improves prognosis of CMML independently of bone marrow response is unknown. Flow-defined classical monocytes (cMo) and immature granulocytes (iGRAN) have not yet been studied as biomarkers of response. We inspected the prognostic value of WBC, circulating monocytes, cMo and iGRANs in the 120 DACOTA (NCT02214407) patients randomized to decitabine (n = 63) or hydroxyurea (n = 57) evaluated after 3 cycles with BM aspiration and complete blood count. Across arms, 59% and 56% patients had monocytes > 1 × 10⁹/L or WBC > 10 × 10⁹/L at the 3- and 6-cycle evaluation respectively. After 6 cycles, persistence of monocytes > 1 × 10⁹/L or WBC > 10 × 10⁹/L increased the hazard of death (HR = 5.38, p = 0.0003) irrespective of treatment, baseline CPSS and persistence of BM blast excess. After 3 cycles, both higher absolute cMo and iGRAN counts independently predicted poorer OS, without significant interaction with treatment arm. Median OS from landmark was 35.1 months in the 28% patients with cMo ≤ 0.94 ×10⁹/L AND iGRAN ≤ 0.40 ×10⁹/L versus 15.3 months in others (p = 0.013). Biomarkers integrating blood counts and flow cytometry may predict CMML prognosis irrespective of treatment.

The clonal evolution model provides a framework for understanding the evolution of cancer cells. According to this model, cancer cells accumulate genetic mutations over time, and these mutations are passed down to their descendants, leading to genetic diversity within the tumor. Some of these mutations confer selective advantages, causing certain lineages of cancer cells (clones) to dominate and expand. However, this model is rooted in certain conceptual assumptions, which we propose to revisit by considering the potential involvement of retrotransposons in cancer initiation and progression. In recent years, it has become evident that transposable elements, particularly retrotransposons, play a significant role in driving cancer transformation and progression. We first review how current knowledge about retrotransposon activity aligns with the clonal evolution model by highlighting its ability to modulate cancer cell fitness. We then take a forward‐looking perspective to explore additional ways retrotransposons may also influence clonal dynamics beyond the current model.

Summary: Clonal memory, a cellular property inherited across at least two divisions, has emerged as a key driver of cell heterogeneity. To uncover its roles in human haematopoiesis, we developed high-resolution ex vivo tools that track both division and fate commitment of individual primary human haematopoietic stem and progenitor cells (HSPCs). We show that human HSPCs display a clonal memory of division, as cells descending from the same ancestor cell divide synchronously over multiple generations. In parallel, HSPCs inherit a clonal memory of fate commitment, independently of lineage identity. Both forms of clonal memory persist over at least two divisions, across different HSPC commitment stages and cell culture conditions. In contrast, malignant haematopoiesis exhibits lower synchronicity, revealing a disruption of clonal memory in leukemic cells. Epigenetic remodelling using a bromodomain inhibitor partially restores the clonal memory in division in leukemic HSPCs, highlighting the plasticity of this trait and its potential for therapeutic modulation. Our findings position clonal memory as a key regulator of human haematopoietic stem cell behaviour. Demonstrating that clonal memory can be modulated opens new avenues for tuning cell heterogeneity in healthy and pathological tissues.

Cancers are hard to treat, and this is largely because cancer cells evolve and diversify through space and time, in patients. The study of clonal evolution relies on the study of cancer cell lineages, and the cutting of these lineages into clones, each clone representing cancer cells with distinctive properties relevant to cancer development and treatment. This notion of clone implies a (set of) simplification(s) that misrepresents the reality. The simplification has been useful and productive, but I argue that maintaining a critical awareness of what is done through this simplification can also be useful and productive. I distinguish three types of simplifications and show that each can offer a panel of therapeutic alternatives that may complement our arsenal of strategies in the battle against clones. The clinical challenge of better treating cancer partly relies on better defining (delineating) clones, but also partly on the more fundamental way we conceive clones. With or without changing the definition, changes in the way we conceive of clones induce changes in the way we treat clones.

Chronic myelomonocytic leukemia (CMML) is a severe myeloid malignancy affecting the elderly, for which therapeutic options are limited. DNA hypomethylating agents (HMAs) provide transient responses, failing to eradicate the malignant clone. Hematopoietic stem cell (HSC) aging involves heterochromatin reorganization, evidenced by alterations in histone marks H3K9me2 and H3K9me3. These repressive marks together with DNA methylation are essential for suppressing transposable elements (TEs). In solid cancers, the antitumor efficacy of HMAs involves the derepression of TEs, mimicking a state of viral infection. In this study, we demonstrate a significant disorganization of heterochromatin in CMML HSCs and progenitors (HSPCs) characterized by an increase in the repressive mark H3K9me2, mainly at the level of TEs, and a repression of immune and age-associated transcripts. Combining HMAs with G9A/GLP H3K9me2 methyltransferase inhibitors reactivates these pathways, selectively targeting mutated cells while preserving wild-type HSCs, thus offering new therapeutic avenues for this severe myeloid malignancy.

The clonal evolution model of cancer was developed in the 1950s–1970s and became central to cancer biology in the twenty-first century, largely through studies of cancer genetics. Although it has proven its worth, its structure has been challenged by observations of phenotypic plasticity, non-genetic forms of inheritance, non-genetic determinants of clone fitness and non-tree-like transmission of genes. There is even confusion about the definition of a clone, which we aim to resolve. The performance and value of the clonal evolution model depends on the empirical extent to which evolutionary processes are involved in cancer, and on its theoretical ability to account for those evolutionary processes. Here, we identify limits in the theoretical performance of the clonal evolution model and provide solutions to overcome those limits. Although we do not claim that clonal evolution can explain everything about cancer, we show how many of the complexities that have been identified in the dynamics of cancer can be integrated into the model to improve our current understanding of cancer.

Background: Restorative regeneration, the capacity to reform a lost body part following amputation or injury, is an important and still poorly understood process in animals. Annelids, or segmented worms, show amazing regenerative capabilities, and as such are a crucial group to investigate. Elucidating the molecular mechanisms that underpin regeneration in this major group remains a key goal. Among annelids, the nereididae Platynereis dumerilii (re)emerged recently as a front-line regeneration model. Following amputation of its posterior part, Platynereis worms can regenerate both differentiated tissues of their terminal part as well as a growth zone that contains putative stem cells. While this regeneration process follows specific and reproducible stages that have been well characterized, the transcriptomic landscape of these stages remains to be uncovered. Results: We generated a high quality de novo Reference transcriptome for the annelid Platynereis dumerilii . To do so, we produced and analyzed three RNA-sequencing datasets, encompassing five stages of posterior regeneration, along with blastema stages and non-amputated tissues as controls. We included these regeneration RNA-seq datasets, as well as embryonic and tissue-specific datasets from the literature to produce a Reference transcriptome. We used this Reference transcriptome to perform in depth analyzes of RNA-seq data during the course of regeneration to reveal the important dynamics of the gene expression, process with thousands of genes differentially expressed between stages, as well as unique and specific genes expression at each regeneration stage. The study of these genes highlighted the importance of the nervous system at both early and late stages of regeneration, as well as the enrichment of RNA-binding proteins (RBPs) during almost the entire regeneration process. Conclusions: In this study, we provided a high-quality de novo Reference transcriptome for the annelid Platynereis that is useful for investigating various developmental processes, including regeneration. Our extensive stage-specific transcriptional analysis during the course of posterior regeneration shed light upon major molecular mechanisms and pathways, and will foster many specific studies in the future.

Cancers rely on multiple, heterogeneous processes at different scales, pertaining to many biomedical fields. Therefore, understanding cancer is necessarily an interdisciplinary task that requires placing specialised experimental and clinical research into a broader conceptual, theoretical, and methodological framework. Without such a framework, oncology will collect piecemeal results, with scant dialogue between the different scientific communities studying cancer. We argue that one important way forward in service of a more successful dialogue is through greater integration of applied sciences (experimental and clinical) with conceptual and theoretical approaches, informed by philosophical methods. By way of illustration, we explore six central themes: (i) the role of mutations in cancer; (ii) the clonal evolution of cancer cells; (iii) the relationship between cancer and multicellularity; (iv) the tumour microenvironment; (v) the immune system; and (vi) stem cells. In each case, we examine open questions in the scientific literature through a philosophical methodology and show the benefit of such a synergy for the scientific and medical understanding of cancer.