Evaluation of non-invasive metabolic imaging biomarkers for novel RAF/MEK1/2-targeted anti-cancer agents

Our increased knowledge of the precise processes that lead to cancer has revealed a key role for RAF-MEK proteins in the initiation and progression of this disease. In fact many drugs are now in development that aim to block RAF/MEK1/2 (also known as RAF/MEK1/2 inhibitors) and the recent FDA approval of the drug vemurafenib, which inhibits the BRAF member of the RAF family of proteins, for the treatment of skin cancers (also known as melanomas) with BRAF mutation provides key evidence for the effectiveness of this strategy.
Treatments based on giving drugs to block RAF/MEK are now in clinical testing. As these forms of treatment are not expected to lead to immediately visible changes in tumour size, the traditional gold-standard for measuring clinical response, early indicators (or biomarkers) that the therapy is achieving its desired effects are required to help assess how the patient is responding and if necessary adjust the treatment plan. Of importance, in particular for the patient, are the biomarkers that do not require surgical intervention, i.e. non-invasive. Imaging techniques such as magnetic resonance (MR) provide a useful tool to follow the biology of tumours in a non-invasive way.
This project will use non-invasive imaging approaches (mainly MR spectroscopy (MRS) and imaging (MRI)) to track a key feature of tumour biology that is known to be abnormally regulated in cancer, namely metabolism, and inform on how the cancer cells are affected by RAF/MEK1/2 inhibition and how any affects change when cancer cells become unresponsive to treatment. Studies will be performed in cancer cells and human tumours implanted in mice as well as samples from patients participating in a clinical trial of a drug that inhibits RAF/MEK1/2 proteins.
Our experimental plan will include various cellular and molecular tests that will be combined with MRS and MRI measurements to provide information on the metabolic status of cells and tumours and understand how this relates to the anti cancer effects such as cell death caused by the RAF-MEK1/2 inhibitors.
This research will help us relate our laboratory findings to what the RAF/MEK inhibitor drugs actually do in the patients. This information is crucial and will in the future help doctors determine whether a drug is acting as it is meant to and, crucially, when the therapy is no longer effective so other treatment options may be sought without delay.

RAF-MEK1/2-ERK1/2 signalling is a focus for targeted cancer drug development with many RAF-MEK1/2 inhibitors now in clinical trials. Detecting biomarkers of pathway blockade, particularly those that are non-invasive, is key for assessing target modulation and drug efficacy and thereby aiding identification of promising pharmaceuticals in early stage trials to prioritise for pivotal trials.

Using magnetic resonance spectroscopy (MRS), we have shown a reduction in lactate levels in BRAF mutant human melanoma cells and xenografts following treatment with MEK1/2 selective inhibitors.
Here we will a) identify and assess the metabolic biomarkers of response to novel classes of RAF/MEK1/2 inhibitors (BRAF-selective, MEK1/2 selective and RAF+MEK1/2 selective) in human cancer cells with varying BRAF and RAS mutation status, b) investigate the metabolic mechanisms involved in response and resistance to treatment and c) assess the translatability of any metabolic biomarkers in in vivo tumour models and patient tumour tissues, to identify the value of incorporating in vivo measurements into clinical trials.

We will assess the effect of RAF/MEK1/2 signalling inhibition in human cancer cells with varying BRAF and RAS mutation status in vitro using 1H, 31P and 13C MRS combined with molecular and biochemical assays to investigate changes in metabolism and metabolic pathway fluxes and enzyme activities associated with response and resistance to treatment. These investigations will then be extended to a) tumour models in vivo where we aim to delineate the impact of any therapy-driven physiological changes (using MR imaging) on metabolism and b) RAF-MEK1/2 inhibitor-treated patient samples to assess the clinical relevance of our findings.

This work will define the potential of metabolic changes as non-invasive imaging biomarkers for the action of RAF/MEK1/2-targeted agents and will be a major step in translating findings from the laboratory to the clinic.

The research proposed here will help advance our understanding of tumour metabolic regulation by oncogenic signalling and validate the metabolic biomarkers observed in the pre-clinical setting to clinically relevant readouts of drug response that could be used clinically for advance the development of targeted anticancer agents and help treatment monitoring and patient follow-up. This investigation in centered on NRAS mutant melanoma, which has poor patient prognosis, limited treatment options and where new effective treatments are urgently required. Findings could also apply to other RAF/MEK driven cancers.

The likely beneficiaries of this research will include:
1. Academics working in the fields of drug development, cancer metabolism and cancer imaging.
These scientists will benefit from the scientific output of this project which can then inform their own work in the various fields described and help refocus effort on the key questions that need to be tackled to make a real impact in the field.

2. Clinicians responsible for treating patients and running clinical trials.
Clinicians administering molecularly targeted drugs need to be guided by pharmacodynamic biomarkers of drug response at an early stage. Currently, this assessment involves taking surgical biopsy samples from the tumour and running molecular assays to investigate molecular biomarker changes. Some tumours are difficult to access and may be too risky to biopsy. Furthermore, longitudinal assessment involves taking repeat biopsy, which comes with patient acceptability and ethical issues. The availability of a non-invasive biomarkers for drug response will bypass the need for surgical biopsy and is likely to lead to increased patient participation in early phase trials. This will in turn increase the statistical power of the data and the intellectual value derived from the trials.
In addition, the project will assess the translatability of metabolic changes observed from pre-clinical models to patient tumours and will enable retrospective correlation of patient baseline metabolite profiles to eventual clinical outcome. This information will be key to assess if patient response to treatment can be predicted based on a) data from pre-clinical models, and b) pre-treatment metabolite profiles.

3. Commercial and private sector companies.
Drug development is a lengthy and costly business. The availability of robust pharmacodynamic biomarkers of drug activity at every stage of the process is key to help with target validation through to patient response assessment. Imaging biomarkers offer the advantages described above and are increasingly playing a key role in clinical trials. Pharmaceutical companies have a keen interest in such readouts as they are likely to optimise the drug development process and minimise late stage drug failures and associated high costs. This will then enable them to run cost-effective drug development programmes which will eventually reduce the cost of producing cancer drugs leading to wider availability worldwide. Savings could also be passed on to government departments such as the NHS thus making more funds available for the treatment of other life threatening diseases.

4. Public sector organizations and patients.
The spending of the NHS on cancer treatment could be massively reduced if robust early biomarkers of drug activity can be obtained so that if necessary alternative treatment options may be sought without delay and without incurring the high and unnecessary costs of unsuccessful therapies.
For the patient, the availability of such "efficacy readouts" could spare the need for unnecessary treatment (which may be associated with unwanted side effects) and may mean that more effective therapies may be identified early on.
The non-invasive biomarker research described here will contribute to making Britain a world centre of excellence for advancing cancer drug development and delivering improved patient care.