Targeted sequencing of refractory myeloma reveals a high incidence of mutations in CRBN and Ras pathway genes

Abstract

• The incidence of mutations within the MAPK pathway, the CRBN pathway, and TP53 is significantly increased in drug-refractory MM.• Mutations in CRBN might contribute to IMiD resistance in drug-refractory MM.In this study, targeted sequencing to screen 50 multidrug refractory multiple myeloma (rMM) patients was performed by using the Multiple Myeloma Mutation Panel. Patients were pretreated with both immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs), and 88%, 78%, and 68% were refractory to an IMiD, a PI, or both, respectively. The majority of patients had progressive (82%) or refractory (78%) disease immediately before sampling, with 43% being IMiD refractory and 46% being PI refractory in the most recent line of therapy. Compared with newly diagnosed MM, an increased prevalence of mutations in the Ras pathway genes KRAS, NRAS, and/or BRAF (72%), as well as TP53 (26%), CRBN (12%), and CRBN pathway genes (10%) was observed. Longitudinal analyses performed in 3 patients with CRBN mutations at time of IMiD resistance confirmed that these mutations were undetectable at earlier, IMiD-sensitive time points. Furthermore, the functional introduction of these mutations in MM cells conferred lenalidomide resistance in vitro. These data indicate a differential genetic landscape in rMM associated with drug response. (Blood. 2016;128(9):1226-1233

CRISPR Genome-Wide Screening Identifies Dependence on the Proteasome Subunit PSMC6 for Bortezomib Sensitivity in Multiple Myeloma

“…We did however analyze the 895 patients sequenced as part of the MMRF CoMMpass trial and found only one mutation in PSMC6 , however a significant number of patients with other 19S subunits mutations (3.7%) are noted. Most of these patients are newly diagnosed and we hypothesize that mutations would be enriched in resistant/refractory cases to PIs, in line with our recent findings in patients that have relapsed after treatment with IMiDs (19). Thus, CRBN, the gene targeted by IMiDs, was found mutated in only 0.2% of newly diagnosed MM (https://research.themmrf.org/rp/mycommpass), but in 12% of patients refractory to IMiDs therapies with mutations in the CRBN pathway in at least 22% of the same patients and probably higher since structural variations were not analyzed (19).…”

“…PSBM5 mutations have been identified frequently in MM cell line but are not found in newly diagnosed patients (17, 18) while XBP-1 mutations have also been seen but are also found in less than 1% of newly diagnosed MM cases. Indeed the mutation prevalence of these genes combined is only 2% in supposedly PI refractory patients (19). XBP1 knock down experiments have shown correlation with BTZ resistance (14, 20).…”

Novel genomic findings in multiple myeloma identified through routine diagnostic sequencing

“…Cereblon (encoded by CRBN ) is important in mediating the anti-myeloma activity of the IMiD class of therapeutics, and therefore the pattern of mutations seen in CRBN is truncation or deleterious missense mutation in critical functional domains 12. The missense mutation we detected (Pro382Arg) has not been previously described in myeloma but is in the IMiD-binding domain next to a previously described missense mutation 13. No mutations in other genes associated with IMiD resistance ( IKZF1 , IKZF3 or IRF4 ) were identified.…”

Utilizing next-generation sequencing in the management of multiple myeloma

“…• Some preliminary attempts aimed at introducing NGS-based technologies during routine diagnostic workup for MM have been made [68,69,70,71], and certainly will continue to be implemented.…”