Tumor heterogeneity poses a formidable challenge in our understanding of tumor biology and therapy efficacy. Complex clonal patterns, patient-to-patient variations and microenvironmental differences all underpin tumor heterogeneity and render the study of this disease extremely difficult. Moreover, it has become increasingly clear that intra-tumor heterogeneity is a direct result of a hierarchical organization that is highly reminiscent to normal tissue organization with a minor fraction of tumor initiating cells (TICs) at the apex. TICs form the root of the tumor, are instructed by the microenvironment and can very efficiently give rise to tumor phenocopies upon injection in mice. Importantly, recent evidence in colorectal cancer (CRC) by our team members has shown that this TIC population displays a further heterogeneity that is dictating therapy efficacy. These findings indicate that a subset of quiescent cells can be identified that, upon re-activation, can regenerate the complete tumor. More importantly, these cells are extremely therapy resistant and effectively colonize distant metastatic sites.
This proposal therefore builds on the hypothesis that TIC heterogeneity is a major culprit in CRC progression and resistance to therapy and that targeting quiescent TICs is of crucial importance for therapy success. To increase our understanding of the (epi-)genetic wiring of these quiescent TICs, to validate and circumvent their role in therapy success and to define their relation to patient outcome the program has three main aims that together will have a major impact on CRC treatment.
Aim1: Identification of unique markers, pathways and resistance mechanisms that define TIC heterogeneity.
Within this part we will use our unique models and specialties to isolate different TIC populations and perform deep-sequencing, epigenetic and RPPA protein analysis to determine the wiring of different TICs. In addition, we will use our in house developed protocols to screen for therapy resistance and to identify novel combinatorial therapies.
Aim2: Identification of genetic heterogeneity within TICs and validation of markers and therapies to target quiescent TICs. Using genetic tracing and label retention techniques, the identified markers and pathways will be validated in a large and unique panel of CRC PDX models. In addition, the combination therapies will be studied in xenotrials and the genetic variation that underlies escape will be analyzed.
Aim3: Linking of quiescent TICs to patient outcome and analyzing novel therapeutic approaches.
Data derived from aim1/2 will be validated in retrospective patient sets as well as in ongoing clinical phase I/II trials that study novel targeted agents in CRC. Combined these studies are expected to provide validated tools to identify and target quiescent TICs, which through the unique link to clinical trials will provide a rapid translation of our findings to clinical practice.