Objective As the modulation of autophagic processes can be therapeutically beneficial to cancer treatment, the identification of novel autophagic enhancers is highly anticipated. However, current autophagy-inducing anticancer agents exert undesired side effects owing to their non-specific biodistribution in off-target tissues. This study aims to develop a multifunctional agent to integrate cancer targeting, imaging and therapy and to investigate its mechanism.
Design A series of mitochondria-targeting near-infrared (NIR) fluorophores were synthesised, screened and identified for their autophagy-enhancing activity. The optical properties and biological effects were tested both in vitro and in vivo. The underlying mechanism was investigated using inhibitors, small interfering RNA (siRNA), RNA sequencing, mass spectrometry and human samples.
Results We have screened and identified a new NIR autophagy-enhancer, IR-58, which exhibits significant tumour-selective killing effects. IR-58 preferentially accumulates in the mitochondria of colorectal cancer (CRC) cells and xenografts, a process that is glycolysis-dependent and organic anion transporter polypeptide-dependent. IR-58 kills tumour cells and induces apoptosis via inducing excessive autophagy, which is mediated through the reactive oxygen species (ROS)-Akt-mammalian target of rapamycin (mTOR) pathway. RNA sequencing, mass spectrometry and siRNA interference studies demonstrate that translocase of inner mitochondrial membrane 44 (TIM44)-superoxide dismutase 2 (SOD2) pathway inhibition is responsible for the excessive ROS, autophagy and apoptosis induced by IR-58. TIM44 expression correlates positively with CRC development and poor prognosis in patients.
Conclusions A novel NIR small-molecule autophagy-enhancer, IR-58, with mitochondria-targeted imaging and therapy capabilities was developed for CRC treatment. Additionally, TIM44 was identified for the first time as a potential oncogene, which plays an important role in autophagy through the TIM44-SOD2-ROS-mTOR pathway.
- COLORECTAL CANCER
- MOLECULAR MECHANISMS
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Contributors YH performed the experiments, analysed the data and drafted the manuscript. JZ and SLL took part in the IHC experiments and analysis of optical properties. YW, JTH, PL, ZLC, TL and XT participated in the qRT-PCR and western blot analysis. JZ, JJO, HMM and HJL contributed to collecting human tissues. CMS designed the study, supervised the experiments and revised the manuscript. All authors have read and approved the final manuscript.
Funding This work was supported by the National Natural Science Foundation of China (Grant No. 81130026 and 81372727), State Key Basic Research Development Program (2012CB518103), Program of New Century Excellent Talents in University (NCET-11-0869) from the Ministry of Education.
Competing interests None.
Patient consent Obtained.
Ethics approval The Ethics Committee of the Third Military Medical University.
Provenance and peer review Not commissioned; externally peer reviewed.