Assessing the Potential Mechanisms of Isomerization Reactions of Isoprene Epoxydiols on Secondary Organic Aerosol.

Laboratory and field measurements have demonstrated that isoprene epoxydiol (IEPOX) is the base component of a wide range of chemical species found in isoprene-derived secondary organic aerosol (SOA). To address newly raised questions concerning the chemical identities of IEPOX-derived SOA, the results of laboratory experiments carried out in bulk aqueous and organic media and analyzed via nuclear magnetic resonance spectroscopy and computed free energies of possible products are reported. The IEPOX nucleophilic addition product 2-methyltetrol was found to react too slowly in aqueous solution to explain the previous observation of tetrahydrofuran-based species. The IEPOX isomerization reactions in organic media were shown to mainly produce 3-methyltetrahydrofuran-2,4-diols, which were also established by the computational results as one of the most thermodynamically favorable possible IEPOX reaction products. However, these isomerization reactions were found to be relatively slow as compared to nucleophilic addition reactions, indicating that their occurrence on ambient SOA might be limited to low water content situations. No evidence was found for the production of the C5 alkene triols or 3-methyltetrahydrofuran-3,4-diols previously reported for IEPOX reaction on SOA as analyzed via the gas chromatography/electron ionization-quadrupole mass spectrometry with prior trimethylsilyl derivatization method.

Prognosis Related to Metastatic Burden Measured by ¹8F-Fluorocholine PET/CT in Castration-Resistant Prostate Cancer.

UNLABELLED: This study investigated the prognostic significance of metabolically active tumor volume (MATV) measurements applied to (18)F-fluorocholine PET/CT in castration-resistant prostate cancer (CRPC). METHODS: (18)F-fluorocholine PET/CT imaging was performed on 30 patients with CRPC. Metastatic disease was quantified on the basis of maximum standardized uptake value (SUV(max)), MATV, and total lesion activity (TLA = MATV × mean standardized uptake value). Tumor burden indices derived from whole-body summation of PET tumor volume measurements (i.e., net MATV and net TLA) were evaluated as variables in Cox regression and Kaplan-Meier survival analyses. RESULTS: Net MATV ranged from 0.12 cm(3) to 1,543.9 cm(3) (median, 52.6 cm(3)). Net TLA ranged from 0.40 to 6,688.7 g (median, 225.1 g). Prostate-specific antigen level at the time of PET correlated significantly with net MATV (Pearson r = 0.65, P = 0.0001) and net TLA (r = 0.60, P = 0.0005) but not highest lesional SUV(max) of each scan. Survivors were followed for a median 23 mo (range, 6-38 mo). On Cox regression analyses, overall survival had a significant association with net MATV (P = 0.0068), net TLA (P = 0.0072), and highest lesion SUV(max) (P = 0.0173) and a borderline association with prostate-specific antigen level (P = 0.0458). Only net MATV and net TLA remained significant in univariate-adjusted survival analyses. Kaplan-Meier analysis demonstrated significant differences in survival between groups stratified by median net MATV (log-rank P = 0.0371), net TLA (log-rank P = 0.0371), and highest lesion SUV(max) (log-rank P = 0.0223). CONCLUSION: Metastatic prostate cancer detected by (18)F-fluorocholine PET/CT can be quantified on the basis of volumetric measurements of tumor metabolic activity. The prognostic value of (18)F-fluorocholine PET/CT may stem from this capacity to assess whole-body tumor burden. With further clinical validation, (18)F-fluorocholine PET-based indices of global disease activity and mortality risk could prove useful in patient-individualized treatment of CRPC.