The Immunomodulatory Drugs, through Loss of Ikaros and Aiolos, Derepress CD38 and Functionally Synergise with Daratumumab

The transcription factors Ikaros (IKZF1) and Aiolos (IKZF3) have recently been found to be targeted for destruction by the immunomodulatory drugs (IMiDs). However, the role of Ikaros and Aiolos and why their loss leads to multiple myeloma (MM) cell death remains unclear. We have used CRISPR-Cas9 genome editing to delete IKZF1 and IKZF3 in human MM cell lines to gain further insight into their downstream gene regulatory networks.

Consistent with the action of the IMiDs, loss of either of these genes resulted in both a G1/S cell cycle arrest and induction of apoptosis. This was not dependent on the subsequent reduction of the IRF4-MYC "axis", as neither IRF4 or MYC were consistently downregulated across all cell lines examined (despite cell death occurring) and overexpression of either factor failed to rescue for Ikaros loss. This led us to further investigate the transcriptional changes resulting from deletion of Ikaros, Aiolos or treatment with the IMiD lenalidomide using RNA-sequencing.

Supporting their central role in the action of the IMiDs, significant overlap was seen on loss of Ikaros, Aiolos, or lenalidomide treatment; with loss of Ikaros/Aiolos accounting for approximately 75% of differential gene expression following lenalidomide.

Importantly both Ikaros and Aiolos were found to repress the expression of interferon stimulated genes (ISGs) and their loss led to the activation of an interferon-like response, possibly contributing to cell death. In keeping with this, treatment with lenalidomide and low dose IFNb resulted in synergistic cell death. Furthermore, CD38 appeared to be both an ISG and repressed target of Ikaros/Aiolos through their interaction with the nucleosome remodelling and deacetylase complex, and its expression is increased at both mRNA and protein level on their loss. Given recent clinical studies have shown improved outcomes with combination treatment with lenalidomide and the anti-CD38 monoclonal antibody daratumumab, we wondered whether this represented a MM cell intrinsic mechanism explaining this synergy. Consistent with this hypothesis, loss of Ikaros, or treatment with lenalidomide or IFNb led to increased daratumumab induced NK cell mediated antibody-dependent cellular cytotoxicity.

These results give further insight into the mechanism of action of the IMiDs, and provide mechanistic rationale for combination with anti-CD38 monoclonal antibodies.