Bowden, DL
(2019)
Evaluation of Acid Ceramidase as Response Predictor and Therapeutic Target in Neoadjuvant Chemoradiotherapy for Rectal Cancer.
Doctor of Medicine thesis, University of Liverpool.
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Abstract
Introduction Colorectal cancer represents the second commonest cause of cancer-related mortality in the UK, with one-third of cases involving the rectum. Response to chemoradiotherapy (CRT) in rectal cancer varies from pathological complete response (pCR, with associated survival benefit) to disease progression. Predicting response is not currently possible but biomarkers to do this would facilitate personalised treatment, minimise morbidity from CRT and prevent delays in the systemic and local management of the disease in non-responders. Therapeutic targets may also be revealed to improve the efficacy of CRT, and further facilitate non-operative or rectal-preservation strategies. Initial proteomic profiling of rectal cancer has revealed differential expression of acid ceramidase (AC) between relative responders and non-responders to CRT. Aims 1) Validation of initial proteomic findings. 2) Confirmation of biological manipulation of AC in vitro. 3) Subsequent assessment of cell survivability post-irradiation. Methods Tissue microarrays (TMAs) were constructed, comprising pre-CRT biopsies and post-CRT resection specimens from 111 rectal cancer patients, and used to correlate immunohistochemical expression of AC with pathological response to CRT (χ2). Genetic (siRNA) and pharmacological (carmofur) manipulation were used independently to inhibit AC expression and activity in a colorectal cancer cell line. Cells were subsequently irradiated, and survival measured by clonogenic assay. Results TMA analysis demonstrated low AC expression in tumour stroma to correlate with pCR (p=0.003) and relative responders to CRT (p=0.048), whereas high AC expression in normal colonic epithelium correlated with a non-response (p=0.012). High AC expression in residual cancer epithelium post-CRT also correlated with an increased risk of local disease recurrence (p=0.031). Preliminary in vitro modelling demonstrated no irradiation specific benefit to pharmacological or genetic inhibition of AC activity. Genetic manipulation of AC resulted in reduced cell viability and higher caspase activity, suggesting an apoptotic mechanism. Conclusions This study supports a role for AC in the response to CRT, implicating tumour-stromal interaction and apoptosis as potential mechanisms of action. Inhibition of AC, by drugs such as carmofur, may yet provide a promising therapeutic strategy as an adjunct to CRT in patients with rectal cancer. Further prospective analysis of AC in a wider clinical dataset and further evaluation of the potential mechanism of AC-dependent radio-resistance in rectal cancer and apoptosis is required.
| Item Type: | Thesis (Doctor of Medicine) |
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| Divisions: | Faculty of Health and Life Sciences > Institute of Life Courses and Medical Sciences > School of Medicine |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 28 Jun 2019 13:36 |
| Last Modified: | 19 Jan 2023 00:42 |
| DOI: | 10.17638/03043404 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3043404 |
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