Phospholipid-drug conjugates as a novel oral drug targeting approach for the treatment of inflammatory bowel disease

The enzyme phospholipase A(2)(PLA(2)) is overexpressed in the inflamed intestine in inflammatory bowel disease (IBD) patients, and in this work we aimed to exploit PLA(2) as a prodrug-activating enzyme for a novel PL-drug conjugate, thereby liberating the free drug specifically in the targeted diseased tissue(s). The proposed prodrug contains a drug moiety covalently bound through a linker to the sn-2 position of a phospholipid (PL). The NSAID diclofenac was used as model molecule, and four different linker lengths (2, 4, 6 and 8 - CH2 units) were studied. The four PL-diclofenac conjugates were synthesized and characterized by LC/MS and NMR. PLA(2)- mediated activation of the prodrugs was analyzed in-vitro, and the remaining intact complex and free drug liberation were assessed after incubation with PLA(2). The rate and degree of PLA(2)- mediated activation were highly dependent on the linker length; 2- and 4-carbon linker conjugates were activated to lower extent than the 6-carbon conjugate, and longer linker again decreased the affinity towards PLA2. The 6-carbon linker conjugate was found to be the optimal and released similar to 95% of the free drug after incubation with PLA2, whereas only similar to 20% were delivered by the 2- carbon linker prodrug. The 6-carbon linker conjugate was shown to be stable in intestinal perfusate, fresh plasma, and pH 4.0 and 6.8 buffers, but not at pH 1.0. In conclusion, the results of this work confirm the feasibility of our general aim to exploit PLA(2) as a prodrug-activating enzyme of PL-drug conjugates. This may provide a novel oral drug targeting approach in IBD therapy.