Targeting IGF1R/Insr Pathway with Approved ALK-Inhibitors Overcomes Proteasome Inhibitor Resistance in Multiple Myeloma

Background:

The treatment of multiple myeloma (MM) has advanced rapidly with the discovery of proteasome inhibitors (PIs) bortezomib (BTZ) and carfilzomib (CFZ). PIs disrupt the equilibrium between production and disposal of excess and/or misfolded proteins in MM cells, leading to apoptosis. However, despite this success, essentially all patients with MM eventually develop resistance to PIs. Therefore, identifying strategies to overcome PIs resistance is clinically important.

ALK inhibitors exhibit anti-MM activity ex vivo. Previously, the ALK inhibitor ceritinib has been shown to inhibit IGF1R/InsR signaling. Signaling through the IGF1/IGF1R axis contributes to acquired resistance to BTZ, and PI activity is reduced in the presence of IGF1, suggesting that IGF1R inhibitors may enhance the cytotoxic effect of PIs. To date, IGF1R/InsR inhibitors have not been successful as single agents in clinical trials and no formally approved drugs are available. Importantly, the drug repurposing approach offers a promising strategy for drug development, particularly for MM. Therefore, we aimed to identify i) whether ALK inhibitors are cytotoxic in MM by targeting the IGF1R/InsR pathway, and ii) whether they can be combined with PIs to overcome PI resistance in vitro and in vivo.

Methods:

A set of PI-naïve and PI-resistant cells was used in this study. The cytotoxicity of drugs was determined by CCK8 assay in cell lines and by CellTiter-Glo assay in primary cells. Genome-wide CRISPR/Cas9-based loss-of-function screening using the Brunello library was performed in the AMO-1 cell line to identify the mechanism of action of ceritinib. Kinase inhibitor selectivity data were retrieved from ChEMBL, v30. Western blotting was performed to assess the levels of total and phosphorylated proteins. RNA sequencing was used to determine the number of transcripts in PI-sensitive and PI-resistant cells, and RNA-seq data from patients included in the CoMMpass study were analyzed. Unbiased LC-MS/MS was performed to determine the effects of ceritinib and carfilzomib on intracellular metabolites. An in vivo mouse model based on orthotopic injection of AMO-BTZ cells into the femur of NSG mice was used to determine the effect of the drug combination in vivo.

Results:

Initially, seven ALK inhibitors were tested in PI-naïve and PI-adapted MM cell lines. Based on IC ₅₀ values, the most effective ALK inhibitors to induce cytotoxicity in MM were ceritinib > brigatinib > entrectinib. The combination of ceritinib, brigatinib, and entrectinib showed synergistic cytotoxicity with PI BTZ and CFZ and overcame PI-resistance in four different sets of PI-adapted cells. The strongest synergistic cytotoxicity was observed between ceritinib and CFZ in CFZ-adapted cells. CRISPR/Cas9-screening identified genes involved in the negative regulation of mTORC signaling (DDIT4, NPRL2/3, TSC1/2) and transcription factor FOXO1 as the major resistance candidates to ceritinib. Subsequently, ceritinib treatment significantly inhibited mTORC signaling and impaired purine-pyrimidine and amino acid production pathways, suggesting a metabolic and proliferation shut-down and amino acid starvation due to targeting of the upstream receptor tyrosine kinases (RTK), which are essential for cell viability and thus not identified by CRISPR screening. Further search in the ChemBL database identified InsR and IGF1R, as RTK that was potently inhibited by ceritinib. PI-naïve and PI-resistant cell lines as well as MM patients were negative for ALK, but positive for InsR and IGF1R expression. Accordingly, co-treatment of PI-resistant cells with a combination of InsR/IGF1R inhibitors and CFZ induced strong synergistic cytotoxicity, resembling the synergistic cytotoxicity observed for ceritinib and CFZ, whereas InsR/IGF1R inhibitors did not show any synergistic cytotoxicity with ceritinib, suggesting targeting the same pathway. Importantly, the combination of ceritinib and CFZ was superior to CFZ in an orthotopic mouse model bearing PI-resistant MM cells and showed strong synergistic cytotoxicity in primary cells from MM patients progressing under or after PI-containing therapy.

Conclusion:

Ceritinib, an FDA-approved drug, overcomes PI resistance in MM by targeting InsR/IGF1R signaling, which is essential for PI resistance in MM. Therefore, ceritinib represents a promising, potential option for the treatment of PI-resistant MM.