A single-cell derived spheroid approach to dissect intratumoural heterogeneity in colorectal cancer: cell lines show changes in proteomes and therapeutic response to 5-FU.

[PURPOSE] Colorectal cancer (CRC) stands as a significant contributor to cancer-related mortality. Owing to its prognostic and therapeutic implications, intratumoural heterogeneity (ITH) presents a considerable challenge. We have developed an experimental framework integrating single-cell derived spheroids with proteomic profiling to facilitate a molecular, proteomic, and therapeutic characterization of intratumoural heterogeneity during CRC progression.

[METHODS] Single cells from the commercially available colorectal cancer cell lines SW480 (primary colorectal adenocarcinoma) and SW620 (locoregional lymph node metastasis of the same donor) were isolated using fluorescence-activated cell sorting (FACS) and subsequently cultured forming spheroids. This platform allowed controlled interrogation of clonal diversity through proliferation and viability assays, alongside deep proteomic characterization using label-free liquid chromatography-mass spectrometry (LC-MS) with data-independent acquisition. To evaluate its utility for therapeutic testing, chemotherapy response was measured after 72 h of incubation with 5-fluorouracil (5-FU).

[RESULTS] The single-cell derived spheroid system demonstrated significant heterogeneity, as evidenced by variations in morphology, growth dynamics, viability, and proteomic signatures. Protein profiling identified ITH-associated proteins (WDR5, CKB, IPO11, ATP6V1F, DCXR and PCCB) and underscored pathway variations including tumour suppressor and proto-oncogenic signalling, vascularization and metabolic regulation. Furthermore, individual spheroids exhibited differential sensitivities to 5-fluorouracil, demonstrating the platform's capacity to resolve heterogeneous therapeutic responses.

[CONCLUSION] Our study establishes a robust and scalable method that integrates single-cell spheroids with proteomics to model and quantify ITH in CRC. By capturing clinically relevant diversity across morphology, viability, proteomic profiles and drug response, this approach provides a foundation for translating spheroid- and proteomics-based assays into personalized therapeutic testing.