Optoacoustic Imaging Reveals Normalized Tumor Oxygenation following Sepiapterin Treatment

1147 Objectives Nitric Oxide Synthase (NOS) activities in various types of tumor cells are uncoupled. The underlying mechanism for uncoupling is a reduced ratio between the tetrahydrobiopterin (BH4) and dihydrobiopterin (BH2) levels leading to reduced NO bioavailability and corresponding enhanced superoxide and peroxynitrite generation. One consequence of this is endothelial dysfunction leading to poor tumor vascularization and reduced oxygenation. This study aims to improve normalization of tumor vasculature and tumor oxygenation by increasing the BH4:BH2 ratio. Methods We used A549 lung cancer xenograft and MMTVneu spontaneous breast cancer tumor models in mice. These tumor bearing animals were treated, by oral gavage (1mg/kg), with sepiapterin (SP), a metabolic precursor of BH4. We then measured tumor oxygenation by multi-spectral optoacoustic tomography (MSOT). In MSOT, differences in the absorption properties of oxyhemoglobin and deoxyhemoglobin were exploited to measure the oxygenation of tumor hemoglobin in SP-treated animals to control animals (n=8 mice per group). Tumor bearing athymic mice were treated with SP daily for six days. The animals were imaged as at three time points: prior to the first SP treatment, day 3 after the first SP treatment, and day 6 after the first SP treatment. The same experiments were repeated with the spontaneous MMTVneu tumor model also. The mice were treated with SP daily for six days. The animals were imaged at four time points: prior to the first SP treatment, day 5 after the first SP treatment, day 8 after the first SP treatment, and day 16 after the first SP treatment. Results MSOT data demonstrated that SP treatment increased the percentage of oxygenated hemoglobin in xenograft tumors when compared to vehicle treated control tumors. The percentage of oxygenated hemoglobin in the control tumors decreased over time. This was expected, since hypoxia increases as tumors grow. There is a significantly higher (p Conclusions The results proved the hypothesis that recoupling NOS in tumors enhances tumor oxygenation. These results also highlight the spontaneous tumors having more normal vasculature than the subcutaneous xenograft tumors. The outcomes could have potential applications in enhancing radio- and chemo-sensitivities.