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

• DOI: 10.1038/leu.2016.244
• Publication Date: 2016-08-30T06:49:04Z
• Authors: A N McCracken; R J McMonigle; J Tessier; R Fransson; M S Perryman; B Chen; A Keebaugh; E Selwan; S A Barr; S M Kim; S G Roy; G Liu; D Fallegger; L Sernissi; C Brandt; N Moitessier; A J Snider; S Clare; M Müschen; A Huwiler; M T Kleinman; S Hanessian; A L Edinger
• Keywords: 0301 basic medicine; Clinical Sciences; Oncology and Carcinogenesis; Immunology; Drug Resistance; 610; Clinical sciences; Antineoplastic Agents; Apoptosis; Cardiovascular medicine and haematology; Article; Cell Line; Mice; 03 medical and health sciences; Rare Diseases; Cardiovascular Medicine and Haematology; Cell Line, Tumor; Receptors; Animals; Humans; Phosphorylation; Cancer; Tumor; Leukemia; Biomedical and Clinical Sciences; Animal; Fingolimod Hydrochloride; Oncology and carcinogenesis; Hematology; Xenograft Model Antitumor Assays; 3. Good health; Disease Models, Animal; Phosphotransferases (Alcohol Group Acceptor); Receptors, Lysosphingolipid; 5.1 Pharmaceuticals; Drug Resistance, Neoplasm; Disease Models; Lysosphingolipid; Neoplasm; Female

The frequency of poor outcomes in relapsed leukemia patients underscores the need for novel therapeutic approaches. The Food and Drug Administration-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.