Project Details
Projekt
Characterization of RAS-dependent effector signaling pathways in multiple myeloma
Subject Area
Hematology, Oncology
Term
from 2009 to 2018
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 100308792
Scientific background: Oncogenic RAS signaling is considered to be a hallmark of multiple myeloma (MM) pathogenesis, marking the transition from the MGUS precursor stage to MM and increasingly occurring in progressed disease stages. Because RAS currently remains an undruggable therapeutic target, we aim to elucidate oncogenic RAS-dependent survival mechanisms in MM cells in order to identify and characterize RAS effector candidates as potential therapeutic targets.Results from the first funding period: Using specific shRNA-expression constructs, we could demonstrate for the first time that MM cells strongly depend on oncogenic RAS. Further signaling analysis revealed that mutated RAS does mediate its oncogenic effect not necessarily via classic and so-called RAS-dependent pathways such as Raf/MAPK and PI3K/Akt. However, although not primarily activated by oncogenic RAS, both Raf/MAPK and PI3K/Akt are constitutively activated in subgroups of MM patients and were shown to contribute to malignant tumor growth in preclinical MM models. This suggests that PI3K/Akt and Raf/MAPK are activated at least in parts by mechanisms other than mutated RAS. In addition, we have evidence that Raf mediates its effect not mandatorily via the classic MEK/MAPK module. Based on results from our whole-exome sequencing program (Z3), we assume that upstream mutations of receptor tyrosine kinases (RTKs) are the major underlying genetic cause of constitutive PI3K/Akt and Raf activation in MM. Furthermore, from shRNA-mediated knockdown experiments in MM cell lines we have tentative evidence that the Ral pathway might mediate the oncogenic effect of RAS in a subgroup of MM. Overall, these observations suggest that RTKs, RAS, Raf and PI3K, although differentially activated by various mutations, co-operate in maintaining malignant growth and thus constitute a central oncogenic signaling network in MM. In order to effectively block this network we have started to evaluate combinations of inhibitors in a systematic manner. In the first combinatorial approach we concomitantly blocked MEK/MAPK and PI3K/Akt in a large primary MM sample set, and could identify sensitive and insensitive subgroups.Planned experiments for the second funding period: Based on our previous work, this project has two main underlying hypotheses. The first hypothesis is that the Raf/MAPK and the PI3K/Akt pathway might be activated by upstream mechanisms other than mutated RAS. The second hypothesis is that mutated RAS mediates its oncogenic effect at least in parts via pathways other than Raf/MAPK or PI3K/Akt. The first goal is therefore to identify the upstream mechanisms that lead to deregulation of Raf and PI3K with a particular focus on the analysis of mutations in RTKs and other candidates identified during the previous funding period. The second aim is to analyze the mechanisms downstream of Raf and PI3K in order to identify potential salvage mechanisms and interactions with other oncogenic pathways. The third aim is to test our hypothesis that yet unidentified Ral-effector proteins play a critical pro-survival role in MM in a RAS-dependent fashion. Finally, sparked by our promising results with the above-mentioned combination treatment, we will aim to develop pharmacological treatment approaches to target critical nodes of the RTK/RAS/Raf/PI3K network in vivo. For this, we will systematically test various combinatorial approaches in different MM mouse models.
DFG Programme
Clinical Research Units
