Elucidation of the composition of Photosystem I Light-Harvesting Complex I from the green microalga <em>Botryococcus braunii</em> and its cytotoxic evaluation in breast cancer cells

Abstract

Natural products have contributed to the development of protein formulations currently used as biotherapeutic agents. The topic of this thesis investigates the green microalga <em>Botryococcus braunii</em> (<em>B. braunii</em>) Photosystem I light-harvesting antenna complex I (PSI-LHCI) and its delivery to one of the most aggressive types of breast cancer with fewer treatment options, triple-negative breast cancer cells (TNBC), exhibiting notable anticancer activity. The PSI-LHCI multiprotein supercomplex plays a significant role in the highly efficient photosynthetic conversion of light energy to chemical energy while generating reactive oxygen species (ROS). Intracellular ROS-regulating anticancer therapeutic strategies emphasize ROS's ability to trigger programmed cell death by selectively killing cancer cells after inducing oxidative stress and exceeding cytotoxic thresholds. In Chapter 3, PSI-LHCI isolation, purification and characterization will be introduced, followed by Chapter 4, an investigation of the role and cell death mechanism determined after the delivery of <em>B. braunii</em> PSI-LHCI to TNBC MDA-MB-231 cells. A discontinuous sucrose density gradient by ultracentrifugation produced PSI-LHCI complex, and <em>in vitro</em> experiments were conducted by incubating MDA-MB-231 cells under serum starvation conditions with PSI-LHCI. In the absence of an LED light source, we conclude that <em>B. braunii</em> PSI-LHCI naturally generates intracellular ROS, significantly reducing cell viability compared to typical positive controls while inducing necrosis by autophagy cell death mechanism.