Mitochondria targeted small molecule-mediated chemo-photodynamic therapy induces apoptosis in cancer cells

Mitochondria, the powerhouse of the cell, play a vital role in bioenergetics, biosynthesis, and stress signaling, making them a promising target for anti-cancer therapy. However, achieving precise mitochondrial targeting remains challenging. Recently, phototherapy has gained attention for its non-invasive nature, yet the development of mitochondria-targeted small molecule probes for phototherapy is still limited. To address this, we design and synthesize Cy-(Indo)₂, a mitochondria-targeted small molecule featuring a pentamethine cyanine-based donor-π-acceptor system for simultaneous fluorescence imaging and phototherapy along with Cox-2 inhibition via conjugation with indomethacin V. Cy-(Indo)₂ self-assembles into nanoscale particles in water with a high positive surface charge, localizes in the mitochondria of HCT-116 colon cancer cells within 3 h, and generates ROS within 20 min under 740 nm LED irradiation. Molecular dynamic (MD) simulations and time-dependent density functional theory (TD-DFT) confirmed the self-assembly of Cy-(Indo)2 into nanoparticles as well as effective spin-orbit coupling in the excited states to stabilize the T1 state for efficient photodynamic therapy (PDT). Under 740 nm LED light (0.9 W/cm²), Cy-(Indo)₂ induces mitochondrial outer membrane permeabilization (MOMP), triggering mitochondrial impairment, ROS generation, and apoptosis via Bcl-2, Cas-3, Cas-9, PARP and Cox-2 inhibition as well as BAX upregulation. This mitochondria-targeted chemo-photodynamic effect results in selective HCT-116 death without showing toxicity to non-cancerous Cos-7 cells. Our findings establish Cy-(Indo)₂ as a promising organelle-specific therapeutic, opening new avenues for light-based, non-invasive cancer treatment.