Page 279 - Haematologica March 2020

Kinome profiling to target Multiple Myeloma
Lenalidomide and its interest to overcome Melphalan drug resistance. Interestingly, OTSSP167 off-targets’ BUB1 and TTK/MPS139 are also part of our 36 selected kinases, which further highlight the potential of this inhibitor to target MM cells.
Our study represents the first attempt to investigate the therapeutic potential of PLK4, CDC7-DBF4, MPS1, PBK and SRPK1 inhibitors in MM, even though their effect on other cancer cell types has already been established.40-44 All inhibitors did not demonstrate comparable effects, but they all showed MM cell toxicity when used alone. Furthermore, the toxicity of PLK4i was validated on pri- mary MM cells, and synergy in MM apoptosis induction was also identified for PLK4i and CDC7-DBF4i when combined with Melphalan and Lenalidomide.
Remarkably, all the tested inhibitors (CHK1i, MELKi, PLK4i, SRPK1i, CDC7-DBF4i, MPS1/TTKi and PBKi) demonstrated anti myeloma activity by reducing viability and inducing cellular death of MM cells. Interestingly, a significant correlation between the KI and response to PLK4i was identified (Online Supplementary Figure S15). The analysis of the potential mechanisms involved revealed that both cell cycle arrest and apoptosis con- tributed to the observed phenotype. Both intrinsic and extrinsic apoptosis pathways were involved for AZD7762, OTSSP167 and Centrinone B. Interestingly, these three
inhibitors induced p53 pathway in AMO1, although we believe that the effect of these molecules is not exclusively p53 dependent since they similarly demonstrated signifi- cant toxicity in p53 proficient (XG1, OPM2) or p53 defi- cient (XG21, AMO1) MM cell lines. Though, considering AZD7762, this observation is surprising since several stud- ies noted that CHK1 inhibitors were particularly toxic for p53-deficient cells45 probably via the simultaneous abroga- tion of the G2 (CHK1) and G1 (p53) checkpoints, and ini- tiation of mitotic catastrophe.31 However, CHK1 can also suppress death pathways and therefore inhibition of CHK1 can reactivate apoptosis in a p53-independent fash- ion via caspase 2 activation, mitochondrial outer mem- brane permeabilization and cytochrome C release.46 As cytochrome C induction was observed for the three inhibitors tested, this last mechanism could explain the p53-independent effect, which implements considerably its therapeutic interest in MM, where p53 status is highly linked to prognosis.
Here, we demonstrated that low doses of CHK1, MELK, PBK and CDC7-DBF4 inhibitors were able to synergize or even reverse Melphalan resistance. This is very important considering that virtually all MM patients eventually relapse and develop drug resistance. These kinases have all been shown to decrease DNA damage tolerance,47–50 which could explain this observation. Similarly, CHK1, MELK and
Figure 8. Kinome expression profiling to define new therapeutic targets in multiple myeloma. The prognostic impact of the kinome expression was challenged in three independent cohorts of newly-diagnosed multiple myeloma (MM) patients representing 709 patients. 36 clinically relevant genes were selected as potential therapeutic targets, and were used to create a Kinase Index (KI) with a strong prognostic value. Among the 36 selected kinases, we validated seven kinases as new therapeutic targets in MM, as their related inhibitors presented therapeutic interest in MM for personalized treatments.
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