Functional Investigation of Mutations in Multiple Myeloma

High expression of the receptor tyrosine kinase (RTK) insulin-like growth factor-1 receptor () and RTK mutations are associated with high-risk/worse prognosis in multiple myeloma (MM). Combining the pIGF1R/pINSR inhibitor linsitinib with the proteasome inhibitor (PI) bortezomib seemed promising in a clinical trial, but IGF1R expression was not associated with therapy response. Because the oncogenic impact of mutations is so far unknown, we investigated the functional impact of mutations on survival signaling, viability/proliferation and survival response to therapy. We transfected four human myeloma cell lines (HMCLs) with , and (Sleeping Beauty), generated CRISPR-Cas9 knockouts in the HMCLs U-266 (IGF1R) and L-363 (IGF1R) and tested the anti-MM activity of linsitinib alone and in combination with the second-generation PI carfilzomib in seven HMCLs. knockout entailed reduced proliferation. Upon IGF1R overexpression, survival signaling was moderately increased in all HCMLs and slightly affected by in one HMCL, whereby the viability remained unaffected. Expression of IGF1R reduced pIGF1R-Y1135, especially under serum reduction, but did not impact downstream signaling. Linsitinib and carfilzomib showed enhanced anti-myeloma activity in six out of seven HMCL irrespective of the mutation status. In conclusion, mutations can impact IGF1R activation and/or downstream signaling, and a combination of linsitinib with carfilzomib might be a suitable therapeutic approach for MM patients potentially responsive to IGF1R blockade.