Sphingosine 1-phosphate (S1P) is a phospholipid that binds to a set of G protein-coupled receptors (S1P1 – S1P5) to initiate an array of signaling cascades that impact cell survival, differentiation, proliferation, and migration. On a larger physiological scale, the effects of S1P on immune cell trafficking, vascular barrier integrity, angiogenesis, and heart rate have also been observed. An impetus for the characterization of S1P-initiated signaling effects came with the discovery that FTY720 (Fingolimod) modulates the immune system by acting as an agonist at S1P1. In the course of structure-activity relationship studies to understand better the functional chemical space around FTY720, we discovered conformationally-constrained FTY720 analogs that behave as S1P receptor (S1PR) type-selective antagonists. Here we present a pharmacological profile of a lead S1P1/3 antagonist prodrug, 1-(hydroxymethyl)-3-(3-octylphenyl)cyclobutane (VPC03090). VPC03090 is phosphorylated by sphingosine kinase 2 to form the competitive antagonist species, 3-(3-octylphenyl)-1-(phosphonooxymethyl)cyclobutane (VPC03090-P) as observed in GTP[gamma-35S] binding assays, with effects on downstream S1PR signaling confirmed by Western blot and calcium mobilization assays. Oral dosing of VPC03090 results in an approximate 1:1 phosphorylated : alcohol species ratio with a half-life of 30 hours in mice. As aberrant S1P signaling has been implicated in carcinogenesis, we applied VPC03090 in an immunocompetent mouse mammary cancer model to assess its anti-neoplastic potential. Treatment with VPC03090 significantly inhibited the growth of 4T1 primary tumors in mice. This result calls to attention the value of 51PR antagonists as not only research tools but also potential therapeutic agents.