Improving response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer

Wanigasooriya, Kasun Shalitha ORCID: 0000-0002-3683-1864 (2023). Improving response to neoadjuvant chemoradiotherapy in locally advanced rectal cancer. University of Birmingham. Ph.D.

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Abstract

Introduction:
Response to neoadjuvant chemoradiotherapy (NCRT) for locally advanced rectal cancer (LARC) varies considerably. There is a need to unravel the elusive biological mechanisms behind treatment resistance in LARC and discover radiosensitising treatments using the latest experiment models.

Methods:
Next generation sequencing (NGS) was performed on archival specimens from 23 LARC patients (retrospective cohort) to identify differentially expressed genes associated with NCRT response. Six patient derived organoid (PDO) models were derived (prospective cohort) from colorectal cancer (CRC) patients; genetically and immunohistochemically characterised. In vitro viability assays were conducted to determine PDO response to radiotherapy. NGS was performed on PDOs pre- and post-irradiation. Chemoradiotherapy viability assays using targeted pathway inhibitors were performed using HCT116 CRC cell line and PDOs. AKT phosphorylation following chemoradiotherapy was assessed using western blots.

Results:
The first 6 out of 16 CRC PDO lines successfully derived in the laboratory were characterised through genomics and immunohistochemistry. Several genes and biological pathways of interest in radiotherapy response (sensitivity or resistance) were identified on differential expression analyses and Gene Set Enrichment Analysis of the retrospective FFPE sample and prospective organoid sample transcriptomes. The PI3K/AKT/mTOR pathway upregulation was associated with radiotherapy resistance in retrospective and prospective cohort sample transcriptomic analyses. Radiotherapy was associated with significantly increased AKT phosphorylation in HCT116. The use of PI3K and mTOR dual inhibitors apitolisib and dactolisib radiosensitised HCT116 and PDOs in vitro and led to inhibition of radiation induced AKT phosphorylation. These drugs radiosensitised radioresistant PDO lines and HCT116 with maximal inhibitory concentration levels within previously published ranges for humans. Dual inhibitors may also possess chemotherapy sensitising properties in the absence of radiotherapy.

Conclusion:
The PI3K/AKT/mTOR pathway upregulation is associated with NCRT resistance. The role of dual PI3K and mTOR inhibitors as radiosensitisers in LARC patients warrants further preclinical and clinical research.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):