Targeting Sphingosine Kinase Induces Apoptosis and Tumor Regression for KSHV-Associated Primary Effusion Lymphoma

Abstract

Sphingosine kinase (SphK) is overexpressed by a variety of cancers, and its phosphorylation of sphingosine results in accumulation of sphingosine-1-phosphate (S1P) and activation of anti-apoptotic signal transduction. Existing data indicate a role for S1P in viral pathogenesis, but roles for SphK and S1P in virus-associated cancer progression have not been defined. Rare pathologic variants of diffuse large B-cell lymphoma arise preferentially in the setting of HIV infection, including primary effusion lymphoma (PEL), a highly mortal tumor etiologically linked to the Kaposi’s sarcoma-associated herpesvirus (KSHV). We have found that ABC294640, a novel clinical-grade small molecule selectively targeting SphK (SphK2 >> SphK1), induces dose-dependent caspase cleavage and apoptosis for KSHV+ patient-derived PEL cells, in part though inhibition of constitutive signal transduction associated with PEL cell proliferation and survival. These results were validated with induction of PEL cell apoptosis using SphK2-specific siRNA, as well as confirmation of drug-induced SphK inhibition in PEL cells with dose-dependent accumulation of pro-apoptotic ceramides and reduction of intracellular S1P. Furthermore, we demonstrate that systemic administration of ABC294640 induces tumor regression in an established human PEL xenograft model. Complimentary ex vivo analyses revealed suppression of signal transduction and increased KSHV lytic gene expression within drug-treated tumors, with the latter validated in vitro through demonstration of dose-dependent viral lytic gene expression within PEL cells exposed to ABC294640. Collectively, these results implicate interrelated mechanisms and SphK2 inhibition in the induction of PEL cell death by ABC294640 and rationalize evaluation of ABC294640 in clinical trials for the treatment of KSHV-associated lymphoma.

Targeting HGF/c-MET induces cell cycle arrest, DNA damage, and apoptosis for primary effusion lymphoma

“…We have previously shown that several small-molecule compounds induced by PEL apoptosis are connected to reactivate KSHV lytic gene expression. 30,31 However, here we only found a slight increase of viral latent/lytic gene expression (but with no statistical significance) within PF-2341066-treated BCBL-1 cells (supplemental Figure 2).…”

Recent advances in the development of sphingosine kinase inhibitors

“…ABC294640 was found to reduce pro-proliferative signalling through the Akt and MAPK pathways via reduction in S1P receptor signalling. More recent studies with ABC294640 have implied roles for SK2 in regulating autophagy [119], transcription of key cancer-promoting genes such as c-Myc [36,98] and pro-inflammatory mediators through NF-κB [120][121][122][123]. ABC294640 also induced proteasomal degradation of SK1 and Des1 [80], Myc and other targets such as androgen receptor [53,98] and Mcl-1 [37] through an as yet undetermined mechanism that appears to be related to its ability to inhibit Des1 [80].…”

“…ABC294640 has been used extensively in vivo where it has shown some efficacy in animal models of solid tumours [50,98,113,114,116,118,124,125], blood cancers [36,37,121], and inflammatory conditions such as osteoarthritis [126], transplantation [120], stroke/ischemia [122,127] and colitis [128,129] (Table 2). It has been shown to dose-dependently decrease circulating S1P in mice [50] and S1P levels in xenograft tumours [50,112].…”

Therapeutic potential of targeting sphingosine kinases and sphingosine 1-phosphate in hematological malignancies

“…The binding of S1P to hTERT prevents its interaction with makorin ring finger protein 1 (MKRN1), 115 an E3 ubiquitin ligase that polyubiquitinates hTERT and promotes its proteasomal degradation (see 116 6 for details).…”