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Projekt Druckansicht

Integrative Analyse der molekularen und zellulären Mechanismen bei Therapieversagen und Entstehung von Tumorrezidiven bei Kopf-Halstumoren nach operativer Tumorresektion

Fachliche Zuordnung Hals-Nasen-Ohrenheilkunde, Phoniatrie und Audiologie
Zellbiologie
Förderung Förderung von 2013 bis 2017
Projektkennung Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 232863538
 
Erstellungsjahr 2017

Zusammenfassung der Projektergebnisse

Advances in surgery and radiochemotherapy have substantially improved the management of head and neck squamous cell cancer (HNSCC). However, local tumor recurrence and distant metastasis remain major obstacles in curative treatment of HNSCC. We postulated that local tumor recurrences evolve from few invasive and relapse tumor initiating cells (R-TIC) after surgery that resist adjuvant radiochemotherapy, forming avascular microscopic tumors until they gain the ability to modulate niches and switch into an angiogenic macroscopic disease. Therefore, the main focus of joined initiative was to develop sophisticated experimental platforms to generate and characterize R-TICs in genetically modified cell culture models and via surgical resection of orthotopically growing tumors, and to clonally trace their evolution into recurrent macroscopic tumors. Applying these novel and unique tools, we identified several key regulators of genetic networks and signaling cascades which regulate characteristic traits of R-TICs, such as tumor cell motility, epithelial-to-mesenchymal transition and treatment resistance. Our data provide compelling experimental evidence that some of these key regulators are under the control of epigenetic events. Epigenetic regulation by means of DNA methylation enables a high degree of tumor cell plasticity, which is a prerequisite for the development, maintenance and clonal expansion of R-TICs. In addition, we identified loss of a functional circuit including key nodes in RA signaling as an important step in R-TIC formation. It will be a major challenge for future preclinical studies as well as clinical trials to address the attractive question, whether specific targeting of the epigenome by DNA methyltransferase inhibitors or restoration of RA signaling can prevent the formation and/or clonal expansion of R-TICs as a new strategy for more efficient and less toxic treatment of HNSCC patients. In addition, we report here the first successful implementation of a genome-wide CRISPR/Cas9 based screen for engineering R-TICs in an orthotopic HNSCC model. This was an important prerequisite for simulating tumor heterogeneity and studying the impact of the in-vivo “niches” in tumor evolution under controlled conditions. The clonal diversity was engineered by a pool of cells, each containing an additional CRISPR/Cas9 mediated loss-of gene function on the top of their tumorigenic genomic background. Intriguingly, recurrent tumors were highly clonal underscoring the high selection pressures induced by in-vivo niches. Moreover, the clonal composition markedly differed between the recurrent tumors vs. tumor metastases in lymph nodes and lungs, with later demonstrating lower clonal selection indicating an early dissemination and parallel evolution of distant metastases in HNSCC. Together, our data support the hypothesis that not invasiveness per se is sufficient to form R-TIC, gain of additional traits increasing the fitness of tumor cells to adapt to conditions dictated by tumor niches is critical for formation to tumor recurrence. Only a rare but highly plastic R-TIC population is capable to execute this process. We propose to validate the functional impact of 15 candidate R-TIC associated genes and their corresponding pathways that potential govern the formation of recurrent tumors. We further aim to determine the sensitivity of genetically engineered R-TIC to radio-chemotherapy, and decipher the involvement of critical pathways which were enriched by engineered R-TIC.

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