Introduction Tumour dormancy and cellular quiescence have recently been strongly implicated in disease recurrence after adjuvant therapy in colorectal cancer (CRC). CRC is increasingly recognised as a heterogeneous disease with significant implications for medical and surgical management. Little is known about the control of cellular quiescence and the molecular features of dormant cells in CRC. Here we present the molecular and functional features of dormant intestinal tumour cells and describe the paracrine signalling pathways that govern their behaviour.
Method Transgenic Apc1322t/H2BYFP mice were generated to allow the characterisation, both functionally and molecularly of dormant tumour cells. A drug screen was performed on ex vivo 3D matrigel-cultured tumour spheroids. Proliferation kinetics, growth characteristics and molecular alterations were correlated with known signalling pathways implicated in intestinal tumorigenesis. Selected compounds were then advanced to validation using six human colorectal cancer cell lines, that represent the three main subtypes of CRC, in 2D and 3D culture experiments.
Results Dormant tumour cells represent a small population of tumour cells that are highly clonogenic, chemoresistant and share many features similar to reserve intestinal stem cells. The Hedgehog and BMP pathways play a dominant role in controlling the growth of tumour spheroids in culture. Antagonism of the Hedgehog pathway causes spheroid growth collapse, the activation of dormant tumour cells and yet no cytotoxicity. The effects of Hedgehog antagonism appears to be CRC sub-type specific; with the most marked effects in the commonest CCSN1 (CIN) subtype of CRC.
Conclusion Here we provide the first molecular and functional characterisation of dormant tumour cells, showing them to represent the hypothesised quiescent cancer stem cell. Interestingly, our data confirms that of others, in demonstrating Wnt inactivation fails to effect the growth of Apc-mutant tumour cells. However we show that the Hedgehog pathway appears to control not only spheroid growth at a global level but also and uniquely the activation of dormant tumour cells. Manipulation of the Hedgehog pathway in combination with standard-of-care chemotherapy may provide significant benefits for patients with classical Apc-mutated and Wnt driven CRC.
Disclosure of interest None Declared.
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Buczacki SJA, Davies RJ. The confounding effects of tumour heterogeneity and cellular plasticity on personalized surgical management of colorectal cancer. Colorectal Dis. 2014;16(5):329–31