Dr. Silvia von Karstedt

Research Area: Cell Death and Cancer Evolution

Website: Silvia von Karstedt Lab

1. Research Background:

The rates of cell death and mitosis are closely matched in various cancers, laying perfect ground for fast and efficient selection of single clones bearing a growth advantage. Hence, cancer cell populations undergorepeated cycles of clonal selection during carcinogenesis. In many cancers, selection of the fittest is embodied by clonal expansion of heritable traits, such as gain-of-function mutations in proto- oncogenes.The most common oncogenic driver mutation observed in human malignancies is a constitutive activation of the RAS family of small GTPases. RAS mutations occur in the three isoforms (K-, N- and HRAS) and commonly manifest as one of six preferred substitutions at three mutational hotspots (G12, G13 and Q61),allowing for 54 possible oncogenic mutations to form. Despite the broad range of possible variants, most cancers show a clear bias towards mutation in a specific RAS isoform -most notably in KRAS- mutationalhotspot and even specific base substitution (mutational tropism). These differences may, in part, be explained by differences in carcinogen exposure in different organs. However, recent studies also suggest that tissue specific factors may play a role in selecting for one over the other KRAS mutant variant. This raises the question, whether acquisition of a distinct RAS variant may pose a selective advantage during (early) carcinogenesis and what this advantage entails.

2. Research questions addresses by the group:

We are interested in understanding the mechanisms underlying selection-of-the- fittest in carcinogenesis and a possible role of evasion of different forms of cell death. In this context, we aim to deepen our understanding of how KRAS mutation selection bias is shaped in various cancer entities. To tackle this issue, we envisionestablishing novel experimental models to investigate clonal competition between KRAS mutants in vivoand in vitro. Within this exciting field of research, we are placing a particular focus on clarifying mechanisms contributing to selection-of-the- fittest mutant KRAS clone in some of the most aggressive cancers including non- small cell lung cancer (NSCLC) and pancreatic ductal adenocarcinoma (PDAC). Weanticipate that unravelling mechanisms of selection-of-the-fittest in NSCLC and PDAC may contribute toidentifying new target pathways to interfere with (early onset) carcinogenesis and eventually translate into novel therapeutic approaches to treat these patients.

3. Possible projects:

Mutations in KRAS occur in 17% of NSCLC and 57 - 90% of PDAC. In both, NSCLC and PDAC, mutations preferably occur at KRAS amino acid G12. Intriguingly, the predominant mutation that manifests in PDAC is G12D and G12C in NSCLC. Despite possible implications for (early onset) cancer intervention and recent advances in the field of KRAS mutation tropism, this clonal selection bias in KRAS mutated cancers remains incompletely understood. In order to gain a deeper understanding of theunderlying mechanisms, we have recently created a novel genetically engineered mouse model which allows for stochastic, tissue specific expression of common KRAS mutant variants G12C, G12D and G12V alongside a unique color reporter protein each. To our knowledge, this is the first model enabling the study of early- onset competition of mutant KRAS clones. We will intercross this model with mice expressingpancreas specific PDX-Cre and investigate clonal composition of pancreatic cancer precursor lesions. As long-term perspective, this model will be further tested for clonal competition under targeted treatment.

4. Applied Methods and model organisms:

The project described above is based around extensive in vivo work, including weighing, breeding, injecting and sacrificing mice for tissue harvest and subsequent anylysis. Tissues will be analyzed using microscopy and possibly histochemistry and FACS analysis. The project further includes standard wet-lab-work, such asmammalian cell culture, Western blotting and (rt)-PCR.

5. Desirable skills and qualifications:

The successful candidate will have excellent grades and a keen interest in cancer biology. He or she should be positive, curious and resilient. We are looking for an open minded and cooperative person, that is highly motivated and thrives in research projects within an international and competitive environment. Willingness todo mouse work is a prerequisite, and previous experience in in vivo work is desirable. Furthermore,experience in least some of the techniques mentioned above is required.

6. References:

  • Li, S., Balmain, A. & Counter, C.M. A model for RAS mutation patterns in cancers: finding the sweet spot. Nat Rev Cancer 18, 767–777 (2018). https://doi.org/10.1038/s41568-018-0076-6
  • Li, S., MacAlpine, D.M. & Counter, C.M. Capturing the primordial Kras mutation initiating urethane carcinogenesis. Nat Commun 11, 1800 (2020). https://doi.org/10.1038/s41467-020-15660-8
  • Weissman TA, Sanes JR, Lichtman JW, Livet J. Generating and imaging multicolor Brainbow mice. Cold Spring Harb Protoc. 2011 Jul 1;2011(7):763-9. doi: 10.1101/pdb.top114. PMID: 21724826.