Molecular determinants of Radiosensitivity

Radiation remains second only to surgery in curing cancer, but there is wide variation from patient to patient is the effectiveness of radiation treatment. Some of this is due to the fact that some cancers are much more sensitive to radiation treatment than others. We aim to try to discover what causes this difference in effectiveness to see whether we could find drugs that could be used with radiation to make the cancers more sensitive to treatment. If successful this could increase our chance of curing the cancer and might even allow us to use lower doses of radiation to achieve the maximum effect.

Significant gains in the therapeutic ratio of radiotherapy could be made if treatments could be developed that selectively rendered tumour cells specifically more sensitive to IR without altering the sensitivity of normal tissues. We plan to identify clinically exploitable targets that may enable tumours to be made more sensitive to radiotherapy using siRNA screens.
We will screen a druggable genome library using HeLa cells, and a library of 800 kinase genes using NSCLC cell lines containing specific mutations. The aim is to identify novel genes whose depletion induces tumour-specific radiosensitisation. The clinical significance of those genes confirmed as being involved in tumour cell radioresistance will be assessed by correlating the clinical outcomes of retrospective series of cancer patients with the tumour RNA expression levels of these genes.
We will also continue to investigate the mechanism of action of a gene (POLQ) that we have recently been shown to be involved in tumour cell radiosensitivity. We have previously shown that tumour cells depleted of POLQ are rendered more sensitive to ionising radiation and chemotherapy as a result of reduced homologous recombination efficiency. The structural basis for this will be examined using truncated POLQ constructs to determine which parts of POLQ are involved in altering radiosensitivity. This may enable us to identify which parts of POLQ could be targeted pharmacologically to inhibit POLQ.

The future plans also focus on understanding the mechanisms that lead to vascular normalisation and decreased hypoxia in tumours after PI3K/mTOR inhibtition and determining whether these events occur in human tumours. We propose two approaches.

We will evaluate the time course of changes in hypoxia and perfusion after inhibitor treatment. We know that approximately 75% of the improvement in perfusion and oxygenation has occurred by 72h. We will now evaluate the changes at earlier times along with evaluation of drug efficacy based on IHC at these times. We will also determine the reversibility of the events after drug withdrawal. Knowing the timing of the changes will allow us to determine whether alterations in vascular morphology for example precede or follow changes in oxygenation.

We will determine whether the increased oxygen level after inhibition of PI3K might be due to decreased oxygen consumption using tissue culture and spheroid models. At the same time we will measure ATP levels, lactate and pH after drug treatment. If there are detectable shifts we will also measure other key metabolites.