Acid‐sphingomyelinase triggered fluorescently labeled sphin‐gomyelin containing liposomes in tumor diagnosis after radiation‐induced stress

In liposomal delivery, a big question is how to release the loaded material into the correct place. Here, we will test the targeting and release abilities of our sphingomyelin‐consisting liposome. A change in release parameters can be observed when sphingomyelin‐containing liposome is treated with sphingomyelinase enzyme. Sphingomyelinase is known to be endogenously released from the different cells in stress situations. We assume the effective enzyme treatment will weaken the liposome making it also leakier. To test the release abilities of the SM‐ liposome, we developed several fluorescence‐based experiments. In in vitro studies, we used molecular quenching to study the sphingomyelinase enzyme‐based release from the liposomes. We could show that the enzyme treatment releases loaded fluorescent markers from sphingomyelin‐containing liposomes. Moreover, the release correlated with used enzymatic activities. We studied whether the stress‐related enzyme expression is increased if the cells are treated with radiation as a stress inducer. It appeared that the radiation caused increased enzymatic activity. We studied our liposomes’ biodistribution in the animal tumor model when the tumor was under radiation stress. Increased targeting of the fluorescent marker loaded to our liposomes could be found on the site of cancer. The liposomal targeting in vivo could be improved by radiation. Based on our studies, we propose sphingomyelincontaining liposomes can be used as a controlled release system sensitive to cell stress.