N nitroso n methylurea

Animal procedures were conducted in accordance with a protocol approved by the Institutional Animal Care and Use Committee at the University of Illinois at Urbana-Champaign. To induce mammary tumors in the female Wistar-Furth rats (Harlan, IN), NMU (N-Nitroso-N-methylurea) (Sigma, St. Louis, MO) diluted in distilled water (12.5 mg mL⁻¹) was injected intraperitoneally at a concentration of 55 mg per kg into the left side of the abdomen when the animals (Fisher 344, Harlan, Indianapolis, IN) were 7 weeks old. One week later, the same amount of NMU was injected intraperitoneally into the right side of the abdomen. After ~12 weeks of age, when mammary tumors became palpable, the rat was prepared for in vivo imaging. Surgery to expose the primary tumor and its neighboring mammary tissue was performed under isoflurane anesthesia. During the imaging sessions, each rat was anesthetized with 1% isoflurane mixed with O₂, at a flow rate of 1 L min⁻¹. Physiological temperature was maintained by a heating blanket. Imaging duration was kept under 3 h to avoid complications of long-term anesthesia. Rats were euthanized after imaging.

All chemicals were of analytical purity. Hydrogen peroxide was obtained from the firm “Ferraine” (Russia). Mitomycin C (MitC), methyl methanesulfonate (MMS), 5-vinyl-2-norbornene, acetic acid, methanol, diethyl ether, N-nitroso-N-methyl urea and other compounds were obtained from Sigma-Aldrich (St. Louis, MO, USA). For comparative measurements, EBH, synthetized earlier in study [14 ], was used.