Folic acid (FA) binds with high affinity to folate receptor (FR) alpha, which is involved in receptor-mediated transport. FR-alpha levels are elevated in specific malignant tissues and thus FA serves as a useful targeting moiety for the diagnosis and detection of FR+ cancers. It has been established that apoferritin, a 440 kD iron transport protein ~70 nm in diameter, is capable of being dissociated into its respective 24 subunits at low pH (pH ~ 3) and re-associated at pH ~ 7 to re-form the full apoferritin cluster. This re-association enables compounds to be easily entrapped within the cage-like protein. In this report, we describe a method for the synthesis and characterization of a folate-PEG-apoferritin based imaging probe. Folate-PEG apoferritin loaded with fluorescein was readily endocytosed by FR+ L1210 leukemia cells. More importantly, uptake was blocked by excess folic acid, demonstrating receptor-mediated cellular uptake of the folate conjugated agent.

Synthesis and evaluation of a folate PEG conjugated apoferritin imaging agent

244th National Meeting (2012)

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