Establishing Drosophila melanogaster as part of the pre-clinical pipeline for anti-metastatic cancer drug discovery

Lead Research Organisation: University of Sheffield
Department Name: Biomedical Science

Abstract

Every two minutes in the UK someone is diagnosed with cancer. Currently this leads to around 164,000 cancer deaths in the UK every year, mainly from metastasis. Although some types of metastatic cancer can be cured with existing treatments, most cannot, and current treatments are aimed at simply stopping or slowing the growth of the cancer, or to relieve symptoms caused by it. This means that there is an urgent need for new therapies.

Innovative new drug screens are being developed in vitro, that are very promising in terms of anti-metastatic cancer drug discovery. One such screen has been developed by the Berx and Goossens labs, which is targeted at finding compounds that block a general cell process called the epithelial-to-mesenchymal transition (EMT). While EMT is required during normal, regulated development, when activated in cancer cells it can facilitate the escape of cells into the body, as well as drive chemoresistance. Given that many mutations can contribute to cancer metastasis, and that these can differ greatly between individuals, our approach is to find compounds that block EMT regardless of the upstream triggers. Berx and Goossens have designed a sophisticated high-throughput in vitro screen aimed at finding such compounds, that has already produced a number of very exciting hits.

While these compound and drug library screens can be done on cells in a dish, unfortunately cancer spreading and metastasis is a complex multi-step process that can only be fully mimicked in a whole animal. Therefore, before moving on to testing new compounds on human patients, preclinical studies in whole animals are of utmost important to test that they work in this context. The next step in the Berx/Goossens labs after in vitro screens, as in many other studies, is therefore to test the efficacy of their identified anti-EMT compounds in mouse models. Many compounds identified in vitro often fail when tested on mice, due to issues such as toxicity, stability or ability to be absorbed into the body.

Here we propose to that instead of moving directly from in vitro studies - to mice, to introduce a step where compounds are first tested on Drosophila melanogaster, as a first port of call to see if the compounds will work in a whole animal context. We hypothesise that establishing Drosophila as the first test for in vivo efficacy has huge potential to eliminate false positives, along with compounds that are toxic in vivo or simply cannot be absorbed into the body. While in the past, this would have been limited by a lack of fly models where cells can be followed from initiation of migration - to seeding and growth in adult organisms, we recently overcame this longstanding limitation. We have recently generated a Drosophila model for metastatic colorectal cancer, as well as robust, sensitive assays to quantify primary tumour burden, circulating tumour cells and formation of macroscopic secondary metastases. We propose to introduce this model into the Berx/Goossens anti-EMT drug discovery pipeline, as the first step for whole animal testing. While compounds will still need to be tested in a mammalian model closer to humans before clinical trials, by only moving forward with compounds that have demonstrated robust efficacy in Drosophila, preliminary results from our labs suggest that this will lead to at least 75% drop in the use of mice. While this proposal is focused towards establishing Drosophila as a step in the pipeline for anti-metastatic cancer drug discovery, we expect that the development of further models, and demonstrating the power of such a Drosophila-mouse lab collaboration, will lead to a wide uptake of this approach, and have a great impact in reducing the numbers of mice used in the drug discovery pipeline.

Technical Summary

Colorectal cancer (CRC) is the second most frequent cause of cancer-related mortality, which in 75% of cases is due to metastasis. There is therefore an urgent need for new anti-metastatic therapies.

Drug discovery has traditionally been based on the identification of a disease-causing protein and search for chemical compounds able to alter its function using in vitro cell culture and biochemical assays. However, the number of new drugs that reach the market has been dropping over the last decades. A key issue is that most small molecules identified in vitro, lack the desirable characteristics for absorption, distribution, metabolism, excretion and toxicity required in vivo. Given these issues, and the complexity of metastasis, the likelihood of molecules brought forward from in vitro stages being effective in an animal model is low. Therefore, it is expected that a large number of in vitro positive hits will not be effective when tested in mammalian models, primarily rodents, to fully understand the properties of new drugs.

The Berx and Goossens labs have developed a sophisticated in vitro screen that has identified several compounds able to block the epithelial-to-mesenchymal transition, a key step initiating metastasis. To reduce the number of rodents required to analyse which of positive hits may have beneficial effects in vivo, we propose to use our recently developed metastatic Drosophila melanogaster model for CRC as a first step to test the in vivo effects of anti-metastatic compounds identified in vitro. This model permits not only the assessment in vivo efficacy in a complex 3D environment, but also the assessment of drug absorption, distribution, metabolic stability and toxicity, reducing the possibilities of false positives.

While testing in mammalian models will still be required, by replacing mice with Drosophila as the first in vivo step in the pre-clinical pipeline we estimate that this will reduce the number of mice used an estimated 70%.

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