(640d) Enzyme Catalysis-Based Circulating Tumor Cell Detection

According to estimates from the World Health Organization (WHO) in 2024, cancer is still the leading cause of death before the age of 70 years worldwide. Most cancer patients died of metastasis. If they can be diagnosed and cured effectively at early stage, the therapeutic effect and survival rates will be significantly improved. In addition, the information about tumor location, type, staging, and prognosis could guide precise treatment, alleviating patient suffering.

Circulating tumor cells (CTCs) are the "seeds" of cancer metastasis. They are shed from tumor and transfer to distant organ through blood circulation. After further proliferation, metastatic lesions will be gradually formed. Due to their intact cellular structure, the genomic, transcriptomic, proteomic, and metabolomic information of CTCs can be obtained, making CTCs detection a hot topic of liquid biopsy. Current CTCs detection techniques are mostly based on the differences in physical properties (size, charge) and surface antigen expression between CTCs and white blood cells. However, CTCs are extremely rare in the peripheral blood, with only a few to dozens of CTCs per milliliter of blood. Additionally, CTCs exhibit high heterogeneity in size, morphology, and surface antigen expression. Such rarity and heterogeneity pose high demand on the sensitivity and specificity of detection methods. Existing techniques have high false-negative rates and yield low purity of isolated CTCs, which makes it difficult for downstream clinical applications. It's urgently needed to develop novel CTCs detection methods with both high sensitivity and specificity.

Despite significant differences in genomics and proteomics, it has been found that there are similarities in metabolomics of CTCs. The lactate content in cancer cells is much higher than normal cells due to "Warburg effect". Metabolite-based CTCs detection methods hold promise for overcoming the low sensitivity. What's worth mentioning is that the intracellular microenvironment is complex, with plenty of similar metabolites and relatively low lactate concentration, demanding high detection sensitivity and specificity. Enzymes, as highly specific catalysts, ensure the efficient and independent occurrence of various metabolic reactions within cells. Inspired by this, a new enzyme catalysis-based CTCs detection method was developed. We proposed a method based on transplanting an enzyme catalytic route targeting lactate to detect CTCs. Lactate oxidase (LOx) was encapsulated in nanoparticles with ultra high activity and stability for the detection of lactate, which improved the signal to noise ratio by ~650 fold. LOx catalyzed lactate that has a considerably higher concentration in cancer cells than in normal cells to generate fluorescence signal for cancer cell identification.

At the best working condition, the sensitivity and specificity of cancer cell detection reached over 90% and 95%, respectively. We applied this method to sample from lung cancer patients. The detection performance of 0.84 CTC per mL blood by our method surpassed the threshold of 0.67 CTC per mL blood proposed by CellSearch^TM, showing high efficiency for CTCs detection.