BIODISTRIBUTION OF RADIOLABELED LIPID - DNA COMPLEXES AND DNA IN MICE

The tissue biodistribution and expression of [8](Z)-heptadecenyl]-3-[h ydroxyethyl]imidazolinium chloride (DOTIM):cholesterol complexes and P -33- radiolabeled DNA expressing chloramphenicol acetyl transferase (C AT; 4.7 kB) were studied after intravenous (iv) injection in ICR mice. Mice were injected with 200 mu L of complex containing DNA at 3 mg/kg or DNA alone. One group received 8 mu Ci of radioactivity and were sa crificed at 5 and 20 min, and 1, 2, 4 and 24 h post-dose (n = 4/time p oint). A second group received the equivalent of 3.9 mu Ci of radioact ivity and were sacrificed at 20 min, and 2 and 24 h for subsequent who le body autoradiographic analysis (WBA; n = 2/time point). The tissue distribution of intact DNA was assessed by Southern blot at 24 h post- dose, whereas the integrity of complexes and DNA incubated in heparini zed whole blood was studied separately. In further studies, the time c ourse of expression in lung tissue over a 48-h period was examined, an d the relative lung-expression bf purified open circular (OG) versus s upercoiled (SG) DNA-at 24 h was evaluated. Approximately 42% of the ra dioactivity was found in the lungs 5 min after injection and about hal f this percentage was found in the liver. By 2 h, only 5% remained in the lungs, but 48% was present in the liver. No other tissue accumulat ed >5% of the dose throughout the duration of the study. WBA radiogram s confirmed the tissue distribution results and highlighted significan t accumulation of radioactivity in bone over time. Southern Blot analy sis demonstrated intact DNA in many tissues 24 h after dosing. In cont rast, the majority of DNA incubated in blood was degraded within 2 h, although the complexes afforded some protection relative to DNA alone. The OC DNP expressed equivalently to SC DNA in lung tissue (OC = 1035 +/- 183 pg; SC = 856 +/- 257 pg/mg soluble protein, n = 6, mean +/- S EM) at 24 h, and detectable levels of CAT were present within 2 h of d osing (21.3 +/- 7.2 pg, n greater than or equal to 8, mean +/- SD). Th e results confirm that DNA-DOTIM:cholesterol complexes are initially d eposited in the lungs after iv administration.