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Is Stability a Key Parameter in the Accumulation of Phospholipid Vesicles in Tumors?

Division of Medical Physics, Radiological Sciences, University of California at Los Angeles, Los Angeles
Department of Radiology, City of Hope National Medical Center, Duarte, California

Correspondence: For reprints contact: L. E. Williams, Dept. of Radiology, City of Hope National Medical Center Duarte, CA 91010.

ABSTRACT

Phospholipid vesicle (liposome) stability in human plasma was determined using perturbed angular correlation (PAC) with ¹¹¹In as the aqueous phase marker. Using compositions given in earlier tumor imaging slides, liposomes were made with either egg iecithin (EL) or distearoyl phosphatdylcholine (DSPC) as the dominant phospholipid. With fresh human plasma at 37°C, EL vesicles lysed much more rapidly with survival half times being7 hr at 6.7 mg lipid/ml plasma. DSPC liposomes had a half-time of 130 hr independent of lipid concentration. No lysis occurred with plasma previousty stored for 1 wk at 5°C.The addition of 143 USP units of heparin per 4.5 ml sample decreased both half-times by two orders of magnitude. We conclude that EL vesicles exhibit plasma survival times much shorter than those found with DSPC liposomes; this may preclude the former agents from having significant tumor accumulation in vivo.

FOOTNOTES

^* Present address: Department of Astronomy and Physics, California State University, Northridge, CA 91330.