DEVELOPMENT OF CANCER THERAPY USING NANOPARTICLES ENCLSOSING CANCER DRUGS IN ZEBRAFISH EMBRYOS
The zebrafish embryo has emerged as a powerful system for transplantation of a range of foreign cancer cells that can develop into tumours. The transparency of the embryo allows the tumour progression to be followed in great detail, when the cancer cells for example express fluorescent proteins. The reason this system works so well is that the embryos lack an adaptive immune system until around 4-6 weeks postfertilisation. This means they lack the capacity to reject foreign cells without the need for selecting immunocompromised animals as in mice, or for immuno-suppressive drugs, as in mice and in adult zebrafish. The Griffiths group established a system whereby fluorescent human or mouse cancer cells are injected into the zebrafish embryo blood vessels or trunk, at two days post fertilisation (pf). By 4-5 days the cells grow into tumours by microscopy and all indications argue that these tumors do not visibly affect the behavior or the development of the embryo. When fluorescent nanoparticles were injected into embryos having tumours at day 4 pf their ability to localise into the tumour could be monitored. In this proposal we seek permission to develop these tumour-containing embryos up until 12 days pf. This will allow us to assess the ability of nanoparticles (NP) encapsulating anti cancer drugs that are injected into the embryos at days 4-6 pf to reach the tumours and selectively kill the cancer cells. This process can be evaluated over the next 6-7 days. By comparing different NP made by our collaborators we can use the zebrafish embryo as a screen tool to select the most promising NP to be tested at the next level, in mouse models of cancer. This strategy allows us to reduce the number of mice needed for screening NP, in conformity with the 3R principles. The concept of using NP allows one to selectively target a small quantum of drug into the vicinty of the tumour, where the drug can be locally released. This is far superior in essence from the conventional therapy using free drugs, that are more in non-tumour sites than in the tumour itself; this non-selectivity in localization is associated with the severe side-effects that are well known with conventional cancer therapy. In support of this claim, the few NP already in clinical practice, such as doxil (liposomes filled with doxorubicin) are much less toxic to patients than the free drug, although their therapeutic capacity is similar to the free drug. While the embryos that have developed tumors by day 5 are indistinguishable from control embryos by all criteria (as noted below) we will monitor their health and behaviour closely over the next 6 days. At visible signs of distress the fish will be euthanized with a high concentration of tricaine anaesthetic.
On a smaller group of larvae, these experiments, up to day 10 post fertilization will be performed in presence or absence of feed to assess the potential bias that the feeding regime could introduce experiments.
On a smaller group of larvae, these experiments, up to day 10 post fertilization will be performed in presence or absence of feed to assess the potential bias that the feeding regime could introduce experiments.