FTY720 increases CD74 expression and sensitizes mantle cell lymphoma cells to milatuzumab-mediated cell death

Abstract

Mantle cell lymphoma (MCL) is an aggressive B-cell malignancy with a short median survival despite multimodal therapy. FTY720, an immunosuppressive drug approved for the treatment of multiple sclerosis, promotes MCL cell death concurrent with down-modulation of phosphoAkt and cyclin D1 and subsequent cellcycle arrest. However, the mechanism of FTY720-mediated MCL cell death remains to be fully clarified. In the present study, we show features of autophagy blockage by FTY720 treatment, including accumulation of autolysosomes and increased LC3-II and p62 levels. We also show that FTY720-induced cell death is mediated by lysosomal membrane permeabilization with subsequent translocation of lysosomal hydrolases to the cytosol. FTY720-mediated disruption of the autophagiclysosomal pathway led to increased levels of CD74, a potential therapeutic target in MCL that is degraded in the lysosomal compartment. This finding provided rationale for examining combination therapy with FTY720 and milatuzumab, an anti- IntroductionMantle cell lymphoma (MCL) is a B-cell malignancy that comprises 3%-8% of non-Hodgkin lymphoma cases diagnosed each year. 1 Whereas the current treatment approach of using combination chemotherapeutic regimens can lead to complete remission, virtually all MCL patients relapse and outcome remains poor, with a median survival of only 3 years. 2 The aggressive clinical behavior of MCL may be because of the complex pathophysiology of the disease, which includes cell-cycle dysregulation driven by cyclin D1 overexpression, alteration in the DNA-damage response, and constitutive activation of key antiapoptotic pathways such as PI3K/Akt and NF-B. [3][4][5][6] Given the absence of curative therapy and the limited number of options for patients with relapsed/refractory MCL, it will be essential to improve our understanding of the complex biology of this disease so that novel treatment approaches can be developed. FTY720 (fingolimod), is a synthetic analog of sphingosine that was developed as an immunosuppressive agent. 7,8 Based on the results of a recent phase 3 clinical trial, FTY720 has been approved by the US Food and Drug Administration (FDA) to treat relapsed multiple sclerosis. 9 We have recently reported that FTY720 has in vitro and in vivo activity in MCL. 10 FTY720 promotes death of MCL cell lines and primary MCL tumor cells via caspaseindependent radical oxygen species (ROS) generation, downmodulation of phospho-Akt and cyclin D1, with accumulation of cells in G 0 /G 1 and G 2 /M phases of the cell cycle. Whereas these data provided information explaining the antitumor activity of FTY720, the effects of this drug on the pathophysiology of MCL required further characterization.In the present study, we show that FTY720 inhibits autophagic flux and induces MCL cell death through lysosomal membrane permeabilization and subsequent translocation of lysosomal hydrolases in the cytosol. Because the autophagy-lysosomal pathway represents an important regulatory mechanism governing the cellular proteome, we hypo...

FTY720 for cancer therapy (Review)

“…In addition to the induction of autophagy, FTY720 also induced blockage of autophagy. In mantle cell lymphoma cells, FTY720-treated cells showed characteristics of autophagy blockage, including accumulation of autolysosomes and increased LC3-II and p62 levels, which enhanced anticancer efficacy of milatuzumab (27,28). Thus, the effects of FTY720 on autophagy are complex and further studies are required.…”

“…In gastric cancer cells, FTY720 induced apparent decrease of phosphorylation of AKT (473) level, followed by a concentration-dependent reduction of Bcl-2, a concomitant increase of Bax, cleavage caspase-3, -9, PARP, resulting in significant apoptosis in cancer cells (19). Moreover, FTY720 induced p-AKT downmodulation in mantle cell lymphoma, which then caused cell death (23,28). In addition, in prostate cancer (64), neuroblastoma (65) and glioma (10,66) cells, FTY720 also showed anticancer effects by downregulating the phosphorylation of AKT.…”

“…Recently, studies showed that in mantle cell lymphoma (23,28), human hepatoma cells (14), rat glomerular mesangial cells (73) and mouse skin transplantation models (74), FTY720 reduced the protein level of cyclin D1, induced G1 phase cell cycle arrest, eventually inhibited cell proliferation and induced cell death. Meanwhile, recent data have also indicated a role for cyclin D2 and cyclin D3 in the pathogenesis of cancer (75-81); however, no reports have studied the effects of FTY720 on cyclin D2 or cyclin D3 and, thus, remains to be explored.…”

“…In another case, FTY720 induced toxicity in the Raji cell line and primary CLL B cells, which was independent of activation of caspases or PARP processing (24). The mechanisms underlying the caspase-independent cell death are extremely complex, and include the downmodulation of cyclin D1 and phospho-Akt (23), activation of protein phosphatase 2A (PP2A), dephosphorylation of extracellular signal regulated kinase (ERK) 1/2 (24), the generation of reactive oxygen species (ROS) (23,25), and the induction of autophagy (13,(25)(26)(27)(28). However, the precise mechanisms remain unclear and are discussed later.…”

Autophagy in blood cancers: biological role and therapeutic implications

“…27 Finally, the immunosuppressant FTY720 (a synthetic sphingosine analog which is approved for the treatment of multiple sclerosis) also appears to block the autophagic flux and to cause accumulation of autophagolysosomes and increased LC3-II and p62 levels. 28 …”