Identification of Drivers of SKY92 High-Risk Multiple Myeloma

Introduction:

High-risk multiple myeloma (HR-MM) continues to result in inferior progression free survival (PFS) and overall survival (OS) despite unprecedented advances in therapy in recent years. The SKY92 gene signature can accurately identify patients with an OS of less than 2-years from diagnosis and is increasingly being utilised in the clinic. However, HR-MM treatment is not yet risk-adapted and deeper knowledge of drivers and targets in this distinct group are needed to enable progress. We aimed to investigate potential drivers and novel therapeutic targets of SKY92 HR-MM.

Methods:

Publicly available patient data from SKY92 risk-classified patients from the HOVON-87/NMSG-18 trials (GSE87900, n=180) and CoMMpass (n=768) (Kuiper R et al. doi: 10.1182/bloodadvances.2020002838.) were analysed for gene expression, chromosomal structural variants (CSVs) and survival. On identification of driver genes, KMS-18 cells were transfected with siRNAs. 80 compounds (MedChem Express™) targeting the cell cycle/mitosis were screened at 1 µM, with standard-of-care bortezomib used as a positive control. The CellTox™ Green assay was used to determine cytotoxicity.

Results:

Gene set enrichment analysis revealed the SKY92 gene signature is enriched for processes relating to cell cycle and mitosis, with chromosome segregation being the top-most enriched process. Accordingly, SKY92 HR patients display an increased frequency of CSVs (37 vs 27, p<0.001), indicative of genomic instability. Further analysis of the chromosome segregation pathway revealed NUF2, NCAPG and ZWINT as highly expressed SKY92 genes in HR-MM patients. This was confirmed in both GSE87900 and CoMMpass datasets (p<0.0001). Moreover, high expression of each gene, independently, was associated with inferior overall survival and increased presence of CSVs. Therefore, we proposed that these could be potential therapeutic targets for HR-MM.

NUF2 is located on chromosome 1q23.3. Analysis of common genetic abnormalities described in the CoMMpass dataset revealed high expression of NUF2 is associated with high-risk abnormality gain(1q) (p<0.01). Moreover, in our own patient dataset (ongoing MM-PIRE study, n=76), we also observed higher prevalence of gain(1q) in SKY92 HR patients (54% vs 31%). NUF2 was highly expressed in a panel of MM cell lines, with highest expression shown in KMS-18 (p=0.0197). NUF2 siRNA knockdown was performed in KMS-18 cells. Given the association with NUF2 and mitotic regulation, 48 hours following transfection, cells were treated with small molecule inhibitors against various components of mitotic/cell cycle regulation to identify if NUF2 may regulate drug sensitivity. Dehydrocorydaline, an alkaloid targeting mitosis, was identified as a potential therapy, with cells with high expression of NUF2 showing enhanced cytotoxicity at 1µM concentration (p=0.0455). Dehydrocoryladine is reported to regulate autophagy and PARP. Accordingly, we observed increased PARP expression in SKY92 HR patients (p<0.001).

Conclusion:

We have identified dysregulation of mitosis and chromosomal instability as a driver of SKY92 HR-MM. Our data indicates that high NUF2 expression, associated with gain(1q), is a driver of HR pathogenesis. Importantly, we show that this may be therapeutically exploited through the use of dehydrocoryldaline. Therefore, we propose targeting NUF2 as a novel risk-adapted, molecularly targeted therapeutic strategy for HR-MM.

Glavey:ReNAgade: Consultancy; Janssen: Honoraria, Research Funding, Speakers Bureau; Pfizer: Honoraria, Research Funding; Amgen: Honoraria, Research Funding, Speakers Bureau; Skyline Dx: Research Funding.