Speaker: Mariano Barbacid, PhD. Molecular Oncology Program, Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain
Organizers: IRB Barcelona
Date: Friday 11 May 2018, 12.00h
Place: Aula Fèlix Serratosa, Parc Científic de Barcelona, Spain
Host: Dr. Eduard Batlle, IRB Barcelona
KRAS oncogenes are responsible for the development of at least one fourth of all human tumors including lung and pancreatic adenocarcinomas, two tumors types with some of the worse prognosis. Unfortunately, development of suitable therapies to treat these tumors has remained elusive for the last thirty years and patients are still treated with old chemotherapy drugs. To address this important health issue, we decided to use genetically engineered mouse tumor models that closely recapitulate the natural history of these tumor types in order to deconstruct, by genetic means, oncogenic K-Ras signaling with the ultimate goal to identify molecular targets whose inhibition will result in therapeutic activity against advanced lung and pancreatic tumors. First, we have designed a new generation of mouse tumor models in which we can separate, both temporally and spatially, tumor induction from target inhibition. These new mouse tumor models make use of the yeast frt-FLp(o) recombinase system to induce cancer-driving mutations by inducing genomic recombination within their endogenous KRas and Trp53 cancer genes in either lung neumocytes or in their pancreatic acinar cells. In addition, these mice carry a transgene that encodes the bacterial CreERT2 inducible recombinase driven by the human Ubiquitin promoter which allows its expression in most, if not all, adult cells and tissues. Finally, these strains are used to introduce conditional knock-out or knock-in alleles of those molecular targets whose therapeutic potential we want to validate. Exposure of mice already bearing advanced tumors (as determined by imaging techniques) to a tamoxifen-containing diet results in the activation of inducible CreERT2 recombinase which allows us to systemically ablate expression of the target (knock-out alleles) or express an inactive isoform (knock-in alleles). This strategy makes it possible not only to evaluate the therapeutic consequences of ablating/inactivating selected targets, but equally important to determine the potentially toxic effects derived from its systemic elimination or inactivation.
We have used this sophisticated experimental strategy to interrogate the therapeutic as well as potentially toxic consequences of ablating or inactivating each of the members of the MAPKinase cascade, including the Raf, Mek and Erk kinases, as well as key effectors of the PI3Kca. pathway including the PI3K p110alpha and mTOR. We have also evaluated additional upstream and downstream signaling elements, such as the EGF Receptor and the Cyclin-dependent kinases (Cdks) responsible for driving the cell cycle. This systematic approach has revealed that most of the K-Ras signaling effectors are not suitable therapeutic targets due to either lack of therapeutic activity, such as Cdk2, Cdk6 A-Raf or B-Raf, or to the induction of unacceptable toxicities such as the Mek1/2 and Erk1/2 kinases, PI3k p110alpha and Cdk1. Therefore, only c-Raf, EGFR and Cdk4 turned to be suitable therapeutic targets, based not only on their anti-tumor properties, but also on the well tolerated toxicities observed upon their systemic ablation/inactivation. We are now combining these targets to define more efficacious therapeutic strategies that could be eventually translated to the clinic.