Abstract B18: Intratumor lysophosphatidylinositol metabolites in a treatment naïve patient-derived bone metastatic prostate cancer xenograft

Abstract A patient-derived bone metastatic prostate cancer (PCa) xenograft (MDA-PCa-183) was used to investigate early resistance mechanisms after androgen deprivation therapy (ADT). The patient-derived xenograft (PDX) expresses wild-type androgen receptor (AR), TMPRSS2-ERG and was found to have homozygous loss of PTEN [1]. MDA-PCa-183 PDX was established as described by Li et al. [2] using a bone biopsy procured from a patient with metastatic PCa prior to ADT. Tumors were grown in intact male immunodeficient mice (n=23) with a subset of mice (n=16) castrated when they reached a size of approximately 900 mm3. At day 11 after castration tumors from 6 mice were harvested and these were considered at maximal androgen ablation (MAA). Of the remaining ten castrated mice, seven responded to androgen ablation by tumor shrinkage or detention of tumor growth (responsive tumors). Tumors of three mice demonstrated sustained growth after castration (relapsed tumors), were harvested between 30 to 40 days after castration and prostate specific antigen (PSA) blood levels were measured. The androgen signaling biomarkers, AR, cytochrome P450 17-alpha-hydroxylase/17,20-lyase (CYP17) and TMPSSR2-ERG protein expression were determined using immunohistochemistry. A biochemical profile consisting of lipid, amino acid, bioenergy, nucleotide (Metabolon, Inc.) and steroid were measured. The levels of testosterone, androstenedione, dihydrotestosterone, progesterone and 17-alpha-hydroxy-progestone were <0.1 pg/mg tissue in MAA and relapsed tumors. Immunostaining showed that tumors from castrate mice expressed AR and CYP17, but were negative for TMPSSR2-ERG. AR and CYP17 were localized in cytoplasm of epithelial cells. PSA levels were low for all castrate tumors (<35 ng/dL). Notably, the lipid profile showed that the lysolipids (LL); 1-palmitoylglycerophosphoinositol, 1-stearoylglycerophosphoinositol, 2-stearoylglycerophosphoinositol, were increased in MAA and relapsed tumors (P<0.05) and 2-oleoylglycerophosphoinositol, 1-oleoylglycerophosphoinositol, 2-arachidonoylglycerophosphoinositol levels were higher in MAA tumors versus intact control tumors (P<0.05). Arachidonic acid levels were also increased in MAA and relapsed tumors (P<0.05). In contrast, the eicosanoids (prostaglandin D2, prostaglandin E2 and 5-HETE) levels were similar in the MAA, relapse and control tumors. The long chain fatty acids, palmitate and oleate, levels were similar in MAA, relapsed and control tumors, however stearate levels decreased in MAA and relapsed tumors (P<0.05). Inositol 1-phosphate (I1P), a metabolite of glycerophosphoinositols (GPIs), levels are similar in MAA and control tumors but are increased in relapsed tumors versus control (P<0.05). Our data supports a possible mechanism of AR independent cell proliferation in relapsed MDA-PCa-183 PDX by LL activation of G protein-coupled receptor-55 (GPR55) signaling. The intracellular LL together with ABCC1 and GPR55 generate an autocrine loop that promotes epithelial cell growth [3] after ADT. LL signaling may also support endothelial cell proliferation within the PDX during ADT. I1P levels, a metabolite of LL, indicate that GPIs may act as a paracrine regulator of osteoblast differentiation. Overall, LL biosynthesis and metabolic metabolites may support early resistance to ADT. References: 1) Roychowdhury, S., et al., Personalized oncology through integrative high-throughput sequencing: a pilot study. Sci Transl Med. 2011. 3(111):p.111ra121. 2) Li, Z.G., et al., Androgen Receptor-Negative Human Prostate Cancer Cells Induce Osteogenesis in Mice Through FGF9-Mediated Mechanisms. J Clin Invest. 2008. 118(8);p.2697-710. 3) Piñeiro, R., et al., The putative cannabinoid receptor GPR55 defines a novel autocrine loop in cancer cell proliferation. Oncogene. 2011. 30(2);p.142-52. Citation Format: Mark Titus, John Araujo, Jun Yang, Sumankalai Ramachandran, Eleni Efstathiou, Patricia Troncoso, Christopher Logothetis, Nora Navone. Intratumor lysophosphatidylinositol metabolites in a treatment naïve patient-derived bone metastatic prostate cancer xenograft. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr B18.