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S.L. Lim et al.
stark contrast, their sensitivity to MZ1, which uses VHL E3 ligase, remained unchanged after either forced expres- sion or silencing CRBN. Taken together, data suggest that ARV 825 may be most potent when this PROTAC is given to patients whose MM cells express CRBN. The sensitivi- ty of MM patients to ARV 825 increased as the CRBN expression increased. In contrast, MZ1 could be a promis- ing therapeutic drug for lenalidomide/pomalidomide- resistant MM. Our ARV 825 data are consistent with a recent study which demonstrated that pomalidomide competed with ARV 825 for binding to CRBN.13 The authors further showed that ARV 825 relied on an intact proteasome pathway with proteasome inhibitors (carfil- zomib or bortezomib) antagonizing the effects of ARV 825.13 This is consistent with our findings.
Based on high throughput screening of small-molecule inhibitors, we identified novel compounds that have syn- ergistic activity with ARV 825 against MM cell lines (KMS11 and KMS28BM), including those against either dual PI3K/mTOR, VEGFR, PDGFRα/b, and FLT3 and IGF- 1R. Previous studies showed the inhibition of PI3K and BET blocked reactivation of PI3K signaling in diverse can- cer models.19 Interestingly, a previous study reported that co-treatment of ARV 825 with ruxolitinib synergistically inhibited growth of secondary acute myeloid leukemia.9 We also observed synergism of this combination against KMS28BM MM cells, but not KMS11 MM cells (Online Supplementary Figure S2B).
RNA sequencing and gene set enrichment analysis demonstrated that MYC expression is significantly down- regulated after treatment with ARV 825 (8 h). MYC is an attractive target in MM due to its role in disease progres- sion. In addition, CCR1 and LGR5 were down-regulated. CCR1 has been reported to play a central role in patho- genesis of MM as well as MM-induced osteolytic bone disease,20 whereas LGR5 has been identified as a marker of early stem cells in the intestine.21
In summary, our studies showed that MM cells are sen- sitive to ARV 825 and a combination of ARV 825 with synergistic small molecule inhibitors may be therapeuti- cally effective for patients. During the final preparation of our manuscript, another manuscript was published report- ing ARV 825 in MM.13 Taken together, these two studies nicely compliment each other and provide the foundation for further pre-clinical studies of both ARV 825 and MZ1 for the treatment of MM.
Acknowledgments
We thank Aaron Eshman and Melmed family for their invalu- able support for this myeloma project. We also express gratitude to Morgan Stanley Inc.
Funding
This work was also supported by a grant from the Leukemia and Lymphoma Society.
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