Biodegradable Microalgae‐Based Carriers for Targeted Delivery and Imaging‐Guided Therapy toward Lung Metastasis of Breast Cancer

High delivery efficiency, prolonged drug release, and low systemic toxicity are effective weapons for drug delivery systems to win the battle against metastatic breast cancer. Herein, it is shown that Spirulina platensis (S. platensis) can be used as natural carriers to construct a drug-loaded system for targeted delivery and fluorescence imaging-guided chemotherapy on lung metastasis of breast cancer. The chemotherapeutic doxorubicin (DOX) is loaded into S. platensis (SP) via only one facile step to fabricate the DOX-loaded SP (SP@DOX), which exhibits ultrahigh drug loading efficiency and PH-responsive drug sustained release. The rich chlorophyll endows SP@DOX excellent fluorescence imaging capability for noninvasive tracking and real-time monitoring in vivo. Moreover, the micrometer-sized and spiral-shaped SP carriers enable the as-prepared SP@DOX to passively target the lungs and result in a significantly enhanced therapeutic efficacy on lung metastasis of 4T1 breast cancer. Finally, the undelivered carriers can be biodegraded through renal clearance without notable toxicity. The SP@DOX described here presents a novel biohybrid strategy for targeted drug delivery and effective treatment on cancer metastasis.