Spin-lattice relaxation in murine tumors after in vivo treatment with interferon alpha/beta or tumor necrosis factor alpha.

1H NMR spin-lattice relaxation times (T1) were measured in vitro and in vivo in Friend leukemia cell tumors during subcutaneous tumor growth in syngeneic mice and after in vivo administration of either purified murine interferon alpha/beta (IFN) or recombinant tumor necrosis factor alpha (TNF). Untreated tumors exhibited monoexponential T1 relaxation independently of tumor age at least until Day 16 after implantation. Histological examinations showed that under these conditions tumors were highly homogeneous and substantially free of necrotic areas. Peritumoral administrations of either IFN or TNF did not significantly alter the tumor relaxation properties at early stages of inhibition of tumor growth. The longitudinal relaxation decay became instead clearly biexponential at later stages (more than 7 days of IFN treatment or 2 days after TNF administration). While the T1 relaxation behavior could be unequivocally correlated with the presence of necrotic areas in these tumors, it could not be considered as an early marker of the altered growth capability, induced by administration of either IFN or TNF.