Identification of Genetic Vulnerabilities and Synthetic-Lethal Targets in NSD2-High Multiple Myeloma
Authors: Sobh Amin , Kaestner Charlotte , Riva Alberto , Licht Jonathan D. 
Published: November 2019

The histone methyltransferase NSD2 is overexpressed in 15-20% of multiple myeloma (MM) patients due to the t(4;14) chromosomal translocation. NSD2 overexpression drives an oncogenic epigenetic and transcriptional program promoting clonogenicity, proliferation, altered adhesion and chemoresistance in MM cells. Despite strong efforts by academia and industry, there remains no tool compound or drug that inhibits NSD2 enzymatic activity. Therefore we explored the molecular and biochemical consequences of NSD2 overexpression in MM cells and investigated genetic vulnerabilities associated with high NSD2 levels as well as synthetic-lethal drug-gene interactions in t(4;14)-positive MM cells. We utilized the well-studied isogenic pair of human MM cells derived from the t(4;14)-positive KMS-11 cell line, where NSD2 is disrupted by knocking out either the translocated overexpressed allele (TKO; NSD2-low) or the wild-type non-translocated allele (NTKO; NSD2-high). Untargeted metabolomic profiling of TKO and NTKO cells revealed that NSD2 overexpression substantially alters nucleotide metabolism. NSD2-high cells exhibited an increase in purine synthesis and a decrease in pyrimidine synthesis. In addition, a genome-wide loss-of-function CRISPR gene editing screen using the 76,000 guide Brunello library uncovered genes differentially essential between NSD2-high and low MM cells. Intriguingly, one of the genes whose disruption is selectively lethal in NSD2-high cells encodes Adenylate Kinase 2 (AK2), an enzyme involved in purine metabolism, indicating that defective nucleotide metabolism associated with increased NSD2 expression introduces genetic vulnerabilities that can be therapeutically exploited.
We further explored liabilities that can improve therapeutic outcomes in t(4;14) MM. A genome-wide CRISPR screen was performed in KMS-11 MM cells to identify mechanisms of sensitivity and resistance to dexamethasone, a steroid commonly used in MM treatment. As expected, inactivating the gene encoding the glucocorticoid receptor (GR) resulted in remarkable dexamethasone tolerance. We then identified and validated multiple genes/pathways that can alter response of MM cells to dexamethasone when disrupted. For example, inactivation of interleukin 10 (IL10) signaling by disrupting either subunit of the IL10 receptor or components of the downstream JAK/STAT pathway considerably enhances dexamethasone sensitivity. In addition, disruption of many components of heparan sulfate or glycosaminoglycans synthesis pathways, whose targeting has been previously shown to increase sensitivity to conventional MM chemotherapeutic agents, increases susceptibility to dexamethasone. By contrast, genetic perturbations leading to dexamethasone resistance correspond to GR co-chaperones including FKBP4 and PTGES3 and transcriptional coactivators like the nuclear receptor transactivator 1 (NCOA1). Interestingly, disruption of genes encoding proteins implicated in RNA stability and translation such as the N6-methyladenosine (m6A)-containing RNA binding protein YTHDF2 and the PAN2-PAN3 deadenylase complex results in dexamethasone resistance. How these proteins affect the expression of pro or anti-apoptotic genes in response to dexamethasone is under investigation. Our work reveals insight into novel molecular-based treatment options for t(4;14) MM that are independent on direct NSD2 inhibition which remains unsuccessful.

Disclosures
No relevant conflicts of interest to declare.