The role of Cereblon binding protein in immunomodulatory therapy of Multiple Myeloma.

• Applicant: Professor Dr. Martin Kortüm
• Subject Area: Hematology, Oncology ; Human Genetics
• Term: from 2012 to 2015
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 224778962

Immunomodulative drugs (IMiDs, thalidomide (THAL), lenalidomide (LEN), pomalidomide (POM)) are well established as the backbone of most treatment regimen in the therapy of the malignant plasma cell dyscrasia multiple myeloma (MM). We and other groups demonstrated that a protein, called cereblon (CRBN) is required for anti-MM activity of IMiDs. Low CRBN expression was found to correlate with IMiD drug resistance in MM cell lines and primary MM cells. Clinical correlative studies have observed a positive association between CRBN and response to THAL maintenance and upfront LEN and dexamethasone therapy. Our recent study further indicated that CRBN expression is highly predictive of response and survival outcomes following POM therapy. Furthermore, expression of cereblon protein assessed by immunohistochemical staining in myeloma cells is associated with superior response of THAL- and LEN-based treatment. By binding to CRBN, LEN potentiates the ubiquitination and proteolysis of 2 specific proteins, IKZF1 and IKZF3. IKZF1 and IKZF3 are important transcription factors for B cell differentiation. Knockdown of IKZF1 and IKZF3 in myeloma cells induced myeloma cell cytotoxicity and downregulation of IRF4. A single amino acid substitution of IKZF3 conferred resistance to LEN-induced degradation and rescued LEN induced inhibition of cell growth, suggesting repression of these transcription factors is a likely mechanism for LEN activity in this disease. We were first to publish a CRBN point mutation in an IMiD refractory MM patient. To further elaborate on this we established the first next gen sequencing based MM specific targeted sequencing panel to investigate the most commonly mutated, or drug resistance related genes in MM, including all genes of the cereblon pathway (DNA needed 10ng, time from library to analysis 2 days). We have sequenced >250 MM samples using this gene panel so far: We identified the lack of FAM46C mutations in untreated high risk myeloma and successfully tracked clonal evolution over time in 25 MM patients. Based on the results obtained so far we are working on an updated version of the panel that includes the up to date known targetable and drug resistance associated genes, as well allowing for detection of clinically relevant copy number abnormalities. Mutations in drug resistance genes in untreated MM have been shown to be rather low, however no data are available for drug resistant MM patients yet. We have the unique chance to obtain those data by investigating 50 well-annotated MM samples of 50 drug refractory MM patients. We hypothesize to find an increased incidence of mutations in drug resistance associated genes, including the cereblon pathway. Finally we will have established a translational genetest that provides clinically relevant information to enable the treating physician to more comprehensively judge treatment decisions and perform more precisely individualized treatment concepts.

• DFG Programme: Research Fellowships
• International Connection: USA
• Host: Professor Dr. A.Keith Stewart