Phosphorylation of a constrained azacyclic FTY720 analog enhances anti-leukemic activity without inducing S1P receptor activation

Abstract

The frequency of poor outcomes in relapsed leukemia patients underscores the need for novel therapeutic approaches. The FDA-approved immunosuppressant FTY720 limits leukemia progression by activating protein phosphatase 2A and restricting nutrient access. Unfortunately, FTY720 cannot be re-purposed for use in cancer patients due to on-target toxicity associated with S1P receptor activation at the elevated, anti-neoplastic dose. Here we show that the constrained azacyclic FTY720 analog SH-RF-177 lacks S1P receptor activity but maintains anti-leukemic activity in vitro and in vivo. SH-RF-177 was not only more potent than FTY720, but killed via a distinct mechanism. Phosphorylation is dispensable for FTY720’s anti-leukemic actions. However, chemical biology and genetic approaches demonstrated that the sphingosine kinase 2- (SPHK2) mediated phosphorylation of SH-RF-177 led to engagement of a pro-apoptotic target and increased potency. The cytotoxicity of membrane-permeant FTY720 phosphonate esters suggests that the enhanced potency of SH-RF-177 stems from its more efficient phosphorylation. The tight inverse correlation between SH-RF-177 IC50 and SPHK2 mRNA expression suggests a useful biomarker for SH-RF-177 sensitivity. In summary, these studies indicate that FTY720 analogs that are efficiently phosphorylated but fail to activate S1P receptors may be superior anti-leukemic agents compared to compounds that avoid cardiotoxicity by eliminating phosphorylation.

Mission Possible: Advances in MYC Therapeutic Targeting in Cancer

“…However, FTY720 functions primarily through immunosuppression by internalizing and activating the sphingosine 1 phosphate receptor (S1PR) [136]. FTY720 analogs, such as SH-RF-177, induce cell death in part through PP2A activation without the activation of S1PR, increasing the clinical significance of these compounds [137].…”

The sphingosine 1‐phosphate receptor agonist FTY720 interfered the distribution of dendritic cell and induced the maternal‐fetal immune tolerance

“…FTY720 acts directly on lymphocytes, and exerts immunosuppressive effects. [8][9][10][11][12] Therefore, FTY720 was once widely recognized in the field of transplantation immune tolerance. Whether FTY720, which plays a key role in the migration, differentiation and homing of lymphocytes, can fully regulate the maternal immune system and the local immunity of the maternal-fetal interface by creating the microenvironment for pregnancy immune tolerance?…”

Sphingosine 1-Phosphate Signaling and Its Pharmacological Modulation in Allogeneic Hematopoietic Stem Cell Transplantation

“…Thus S1P signaling may directly impact the GvL effect by regulating leukemia cells sensitivity to apoptosis. Various studies have shown that FTY720 has direct effects on certain leukemia growth and survival though this has been shown not to be due to S1P signaling by using FTY720 analogues that lack S1PR activity [ 65 ]. However, a recent study has shown that S1PR1 signaling enhances cell survival in naïve T cells via the modulation and mitochondrial function and metabolism.…”