Repurposing of the Iron Chelator Deferasirox to Overcome Venetoclax Resistance in Mantle Cell Lymphoma Via Downregulation of MCL1
Authors: Shapira Saar , Samara Aladin , Gurion Ronit , Gafter-Gvili Anat , Raanani Pia , Granot Galit 
Published: December 2024

Mantle cell lymphoma (MCL) is a difficult to treat B-cell malignancy characterized by cyclin D1 (CD1) overexpression and deregulated AKT, NFκB, MAPK, B-cell receptor and BCL2 pathways. Breakthrough treatments such as BTK inhibitors present clinical benefits in MCL, but resistance inevitably develops and most patients relapse. Prognosis for these relapse/refractory (R/R) patients is very poor, justifying an urgent demand for novel therapies. MCL therapy resistance is associated with evasion of apoptosis frequently involving upregulation of the pro-survival BCL2 protein. The BCL2 inhibitor venetoclax overcomes apoptosis evasion due to BCL2 overexpression however, resistances to venetoclax has also been described. This resistance relies on a switch in apoptosis dependency via overexpression of other anti-apoptotic BCL2 family members, mainly MCL1, compensating for BCL2 inhibition by venetoclax. Several MCL1 inhibitors have entered developmental stages. However, due to cardiotoxicities the FDA placed some of them on clinical hold.

Deferasirox (DFX), a clinically approved iron chelator, exerts anti-tumoral effects in several cancers. We have shown that clinically relevant concentrations of DFX induce apoptosis in MCL cells via CD1 degradation, AKT/GSK3β signaling deregulation and NFκB inhibition. Deregulation of these specific targets is known to interfere with the efficiency of current MCL therapies. Interestingly, MCL1 levels are known to be regulated via NFκB and via the AKT/GSK3β pathway. Taken together, these data alongside DFX's safe profile, suggest that DFX can potentially overcome venetoclax resistance via targeting overexpressed anti-apoptotic BCL2 family members such as MCL1. These data also raise the possibility of a potential synergy when combining venetoclax and DFX.

In this study, our objective was to assess the potential of DFX to overcome resistance in MCL, to assess possible synergism with venetoclax and to investigate the mechanism by which DFX exerts these effects. We generated venetoclax resistant Jeko-1(Jeko-1VR) and Z138 (Z138VR) lines. Initially, we determined which anti-apoptotic BCL2 family member our Jeko-1VR cells utilize to acquire resistance. We revealed a 3.5-fold increase in MCL1 expression in Jeko-1VR cells compared to its expression in Jeko-1 cells. This upregulation may, at least partially, explain Jeko-1VR's resistance to venetoclax. Interestingly, we observed that DFX treatment reduces MCL1 level in these cells to the level seen in the parental venetoclax sensitive Jeko-1 cells. In addition, as we previously observed regarding sensitive Jeko-1 cells, DFX was able to reduce CD1 levels in the resistant Jeko-1VR cells as well. In parallel, we found that clinically relevant concentrations of DFX induce apoptosis in both Jeko-1 and Jeko-1VR cells (48h exposure to 10µM DFX induced &gt;75% annexinV+ cells).

Numerous reports describe a synergistic effect when treating B-cell malignancies with a combination of venetoclax and MCL1 inhibitors. We found DFX to have a synergistic anti-tumoral effect with venetoclax in both Jako-1 and Z138 cells (Bliss, ZIP p&lt;0.001) thus supporting our hypothesis that DFX can act as a surrogate MCL1 inhibitor. Indeed, we found, DFX to significantly reduce MCL1 expression in the Jeko-1 venetoclax-sensitive cells in a dose- and time-dependent manner. This reduction in MCL1 levels was partially rescued by the GSK3β inhibitor LiCl suggesting that DFX reduces MCL1 via the PI3K/AKT/GSK3β pathway. Interestingly, we found that this co-treatment also synergistically enhances CD1 degradation, suggesting an additional mechanism of synergy between DFX and venetoclax.

In conclusion, in this study, we investigated the potential of repurposing the clinically approved drug DFX to combat the issue of MCL resistance. Notably, our results indicate that DFX reduces MCL1 levels in MCL cells. MCL1 overexpression is one of the main causes of venetoclax resistance. Thus, it is an attractive target for overcoming resistance. Several MCL1 inhibitors that have entered developmental stages have been put on hold due to cardiotoxicities. The clinically approved and safe agent, DFX can potentially fill this unmet need and serve as a surrogate for MCL1 inhibitors. To the best of our knowledge, this is the first study to assess the potential of DFX to serve as a therapeutic approach to overcome drug-resistance in MCL.