Introduction Circulating Tumour Cells (CTCs) are important biomarkers in many solid tumours including gastroesophageal cancer. Cultures derived from CTCs provide many potential benefits, including an in vitro model to assist selection of systemic treatment for personalised treatments. This study aimed to determine the sensitivity of a CTC derived primary culture to commonly used chemotherapeutics and radiation.
Material and methods RFCTC is the first described long term primary CTC culture derived from a patient with a metastatic, high-grade neuroendocrine tumour of the distal oesophagus. The in vitro chemo sensitivity of RFCTC to 7 different cytotoxic drugs alone and in fixed ratio dose combination was determined using standard cell proliferation assays, and reported as IC50 ±SD or Combination Indices (CI) as determined using median-effect analysis (CalcuSyn software, Biosoft, UK). The sensitivity of the cells to radiation with drug pretreatment was also investigated using clonogenic survival as the radiobiological endpoint. Cells were exposed to 2 Gy X-ray radiation ±Carboplatin (CP) sensitisation (5 µM). Data are presented as percent Plating Efficiency (PE).
Results and discussions Paclitaxel (IC508.4±0.7 nM) and Vinblastine (IC500.4±0.1 nM) were the most effective single agent cytotoxins. Doxorubicin (IC500.15±0.05 µM), Oxaliplatin (IC501.48±0.59 µM), Etoposide (EP) (IC501.68±1.3 µM), and 5-Fluorouracil (IC507.7±0.28 µM) were all effective. RFCTC was relatively insensitive to CP (IC5039.24+0.86 µM), likely due to the patient’s pre-exposure to systemic CP treatment prior to CTC isolation. CP and EP, the standard chemotherapy regimen used in this disease, showed synergism with CI <0.9.
The PE of untreated RFCTCs was relatively low (3.41%+0.34) and this was significantly affected by exposure to either radiation (0.44%+0.08) or CP treatment (0.21%+0.08) alone. Pre-sensitisation of RFCTCs with CP prior to receiving radiation resulted in negligible PE (0.025%±0.025). This result indicates that cells are extremely sensitive to radiation in combination with CP pretreatment.
Conclusion Our results show the feasibility of drug testing on a primary CTC derived cell line, and replicated expected clinical sensitivities to the standard first-line chemotherapies (CP and EP) for this tumour. We also identified vinblastine as a potential efficacious agent in this rare disease. RFCTC has an effective response to 2 Gy radiation, which is even more pronounced when combined with CP pre-sensitisation.