Engineering self-homing circulating tumour cells as novel cancer theranostics

Purpose: New ways to target and treat metastatic disease are urgently needed. Tumor \"self-homing\" describes the recruitment of circulating tumor cells (CTCs) back to a previously excised primary tumor location, contributing to tumor recurrence, as well as their migration to established metastatic lesions. Recently, self-homing CTCs have been exploited as delivery vehicles for anti-cancer therapeutics in preclinical primary tumor models. However, the ability of CTCs to self-home and treat metastatic disease is largely unknown. Methods: Here, we employ molecular imaging to explore whether systemically-administered CTCs home to metastatic lesions and if CTCs armed with both a reporter gene and a cytotoxic prodrug gene therapy can be used to visualize and treat metastatic disease. Results: Bioluminescence imaging (BLI) performed over time revealed a remarkable ability of CTCs to home to primary and metastatic tumors throughout the body. Mice that received therapeutic CTCs had less BLI signal as well as less primary tumour burden than control mice. Preliminary data also showed self-homing therapeutic CTCs may be effective at treating disseminated breast cancer metastases. Conclusion: Using dual-luciferase BLI, this study demonstrates the noteworthy ability of experimental CTCs to home to disseminated breast cancer lesions. Moreover, by incorporating a prodrug gene therapy system into our self-homing CTCs, we show exciting progress towards effective and targeted delivery of gene-based therapeutics to treat both primary and metastatic lesions.