Exploitation of the transcytotic pathway in polarised cells by camelid single domain antibodies

Delivery of drugs to sites of disease can be hampered by the presence of cellular barriers in the human body. The presence of such barriers reduces the therapeutic activity of drugs on the disease target. The barrier present between the bloodstream and the brain for instance, stringently controls what goes into the brain and what not. Diseases that take place in such enclosed systems may be difficult to reach for pharmaceutical compounds because of these barriers and this can reduce their therapeutic effectivity. In this thesis we have described the development of molecules that interact with specific barriers in the human body and that mediate translocation across these barriers. As platform we used antibodies from the llama. Llama antibodies have several favourable properties as compared with other mammalian antibodies. The llama antibody platform was used in the described studies to make entities capable of translocating across cellular barriers. Part of the described studies has looked at the removal of compounds from the body by efflux via the intestinal wall (a cellular barrier). We developed molecules which can interact specifically with that barrier and mediate the passage of unwanted molecules. These molecules can be used for example for the removal of viruses that have infected the body. Fusion of the translocation molecules with compounds that bind viruses would enable the resulting compounds to both bind the virus and mediate its translocation across the intestinal wall. Such therapeutic strategies could tackle the infections of persistent viruses such as HIV. The other part of the described studies has looked at the delivery of blood borne compounds across the blood brain barrier to the central nervous system. Efficient platforms that mediate brain delivery from the bloodstream are scarce/ non-existent. We found molecules which have favourable properties in artificial model systems mimicking the blood-brain barrier. Application of these molecules to mice showed that there was a significant proportion of the injected dose able to accumulate in the brain, which indicates that our molecules indeed can target the brain. Further genetic adaptation of the antibodies might improve the translocation process to the brain environment and deliver a bigger pool of therapeutics to the site of disease. Development of these molecules might yield entities capable of delivering therapeutically relevant compounds to the brain. At the moment, brain delivery of pharmaceuticals is still a feature that is hardly possible without invasive procedures. Due to this aberrant delivery, there is no proper treatment possible of diseases like Alzheimer’s, Parkinson’s and brain cancer. We hope that with further development, our molecules will be able to give a solution to the brain delivery problem and thereby aid in the treatment of brain afflictions. This thesis has given examples of how antibodies from the llama can be used as retargeting agents. We have shown that they can be designed to translocate across cellular barriers and to take along cargo in this process. Development of the antibodies may yield molecules which can help in the diagnosis and treatment of several diseases.