Discovery of In Vivo Active Sphingosine-1-phosphate Transporter (Spns2) Inhibitors

Sphingosine 1-phosphate (S1P) is a pleiotropic signaling molecule that interacts with five G-protein-coupled receptors (S1P1-5) to regulate cellular signaling pathways. S1P export is facilitated by Mfsd2b and spinster homologue 2 (Spns2). While mouse genetic studies suggest that Spns2 functions to maintain lymph S1P, Spns2 inhibitors are necessary to understand its biology and to learn whether Spns2 is a viable drug target. Herein, we report a structure-activity relationship study that identified the first Spns2 inhibitor 16d (SLF1081851). In vitro studies in HeLa cells demonstrated that 16d inhibited S1P release with an IC50 of 1.93 μM. Administration of 16d to mice and rats drove significant decreases in circulating lymphocyte counts and plasma S1P concentrations, recapitulating the phenotype observed in mice made deficient in Spns2. Thus, 16d has the potential for development and use as a probe to investigate Spns2 biology and to determine the potential of Spns2 as a drug target.

Copper-boryl mediated organic synthesis

Organoboron compounds are valuable synthetic intermediates that find application in a diverse variety of processes including both C-X and C-C bond-forming transformations. This has been achieved by using a variety of boron derivatives. Of these, boronate esters are probably the most versatile and, reflecting this, methods for the generation of boronate esters are of considerable current interest. Given the mild reaction conditions, good functional group tolerance, and low cost of the metal catalyst, the use of copper-boryl reagents is particularly attractive. In this review, methodologies in copper-boryl chemistry are discussed and the many different transformations possible are surveyed.

Abstract P3-03-06: Characterization of HER2-positive breast cancer (BC) cells selected for tolerance to trastuzumab-induced antibody-dependent cell-mediated cytotoxicity (ADCC)

Cellular mechanisms of trastuzumab resistance include alteration(s) in cell signaling pathways (PTEN loss, activation of PI3K/Akt signaling), steric hindrance of antibody binding (by Muc-1/Muc-3), over-activation of alternate receptor kinases (HER3/c-Met/IGF-1R), and proteolysis of HER2 extracellular domain harboring target epitopes for antibody-based therapeutics. Prior studies of trastuzumab resistance have focused largely on cells selected ex vivo with the antibody in absence of human immune effector cells. We developed a selection model, wherein human HER2 positive BC cells (BT474, SKBR3) were subjected to acute ADCC (>90% cell death), trastuzumab concentration 100ug/mL, effector-target ratio 100:1, using human peripheral blood mononuclear cells (PBMCs) as effectors. Surviving cells were allowed to recover to confluence over 8-10 weeks, for 10 total rounds of ADCC selection ex vivo. Mock-treated parent, IgG1 isotype control, trastuzumab, and PBMCs alone were used as controls. ADCC assays based on calcein fluorescent labeling of live target cells, revealed significant reduction (maximum 20%, p<0.005) in cell lysis in immune-selected BT474 cell lines compared to parental controls (immune-selected SKBR3 cells exhibited a non-significant trend towards reduced ADCC). Transcriptome-wide next-generation RNA sequencing (Illumina NextSeq 500, 2 x 75 bp paired-end, median of 46 million paired-end reads/sample), coupled with pathway enrichment analysis (Reactome), followed by q-PCR validation, confirmed significant changes in expression in immune-selected cells (compared to parent control) for genes including: ALDH1, ANK1, TMPRSS3, HINT1, DNM2, TNNC1, COL4A4 in BT474; and ALDH1, ANK1, CAMP1, CPE, IDO1 in SKBR3 cells. Whole-genome sequencing (Illumina HiSeq X, 150 bp paired end, 30x coverage) elucidated 180 genes with single nucleotide variations (SNVs) in immune-selected cells compared to parent in BT474 cells, and 215 genes in SKBR3 cells. Thirty-four SNVs were shared in both cell lines. Further screening and validation confirm genes with SNVs demonstrating significant transcript up-regulation. These include: COL4A3, LEP, SOX-9 in BT474; and HLA-B, TNFRSF10B, HLA-B, PSMA6 in SKBR3. In further phenotypic analysis, ADCC-conditioned BT474 cells exhibit an elongated fibroblast-like morphology with multiple processes, in contrast to control. Immune-selected SKBR3 cells (and not BT474 cells) demonstrate significantly increased motility compared to control in transwell migration assays (p<0.001), and demonstrated increased cell proliferation (MTT assay, 10-15%, 48h; p=0.0242) as compared to parent controls. Our data indicate immune-selection by effector cells contributes to ADCC tolerance in vitro, and is associated with distinct genotypic and phenotypic alterations. Future investigation will determine whether Fc-engineered MAbs (afucosylated), antibody drug conjugates (T-DM1), or potentiation of ADCC by co-stimulatory agonist CD137 antibodies will re-sensitize ADCC-tolerance. This investigation will help to elucidate potentially targetable pathways that emerge from immune-selection with trastuzumab.

Citation Format: Biswas T, Fritzemeier R, Mark A, Meißner T, Young B, Jones BL, Pegram M. Characterization of HER2-positive breast cancer (BC) cells selected for tolerance to trastuzumab-induced antibody-dependent cell-mediated cytotoxicity (ADCC) [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P3-03-06.