LAUSR

Breast cancer is a heterogeneous disease and is currently diagnosed using clinical biomarkers to classify tumors and guide therapy. However, drug resistance is a major cause of treatment failure and current methods can only detect resistance after several months following drug therapy. Thus, there is a need for novel biomarkers to track breast cancer prognosis, diagnosis, and to monitor therapeutic efficacy. Polyamines are polycations that support the production of nucleic acids and are necessary for transcription, DNA replication and cell cycle progression. The rate-liming step in polyamine catabolism is the acetylation of spermine and spermidine by spermine/spermidine acetyl-transferase (SAT1). Indeed, diacetylspermine has been identified as a clinical urinary biomarker of early and late stage breast cancer. Despite multiple clinical studies citing the potential for diacetylspermine as a cancer biomarker, the oncogenic events contributing to increased diacetylspermine production are largely unknown. To identify metabolic biomarkers of breast cancer progression and therapeutic efficacy, an untargeted metabolomics study was performed using urine samples from mice implanted with breast cancer patient derived xenografts (PDXs). NSG mice were engrafted with a doxorubicin sensitive (Dox-Sens) or a doxorubicin resistant (Dox-Res) PDX. When tumors reached 100-200 mm 3 , mice were administered intravenous doxorubicin (2 mg/kg) or vehicle control once weekly for three weeks. Mice were placed in metabolic cages for 24 hours after each treatment to collect urine. At 28 days, a final 24-hour urine collection was performed in the absence of drug treatment followed by euthanization (n = 9). Untargeted metabolomics revealed diacetylspermine as the most significantly altered metabolite in urine samples by two-way repeated measures ANOVA (p = 1.26x10 -11 , q = 4.82 x 10 -8 ). Urinary diacetylspermine was correlated with growth of the Dox-Sens tumors and undetectable in urine from mice with Dox-Res tumors. Remarkably, when Dox-Sens mice were treated with doxorubicin, there was a further increase in diacetylspermine despite the decrease in tumor size. These results demonstrate the potential utility of urinary diacetylspermine as a biomarker for monitoring tumor growth and doxorubicin treatment efficacy. Furthermore, these breast cancer PDX models have provided an opportunity to characterize the mechanism of oncogenic diacetylspermine production and response to drug treatment. Citation Format: Thomas J. Velenosi, Kristopher W. Krausz, Frank J. Gonzalez. Characterization of diacetylspermine as a metabolic urinary biomarker in breast cancer using patient-derived xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4366.