Ovarian cancer is a formidable adversary, claiming the lives of 207,000 women annually and ranking as the second most lethal gynecological malignancy worldwide. While initial treatment with platinum-based therapies often yields positive results, many patients eventually succumb to platinum resistance. This resistance is characterized by a complex interplay of various molecular mechanisms, including reduced drug uptake, enhanced detoxification, and increased DNA repair mechanisms. Among the factors implicated in acquired drug resistance, the role of superoxide dismutase 1 (SOD1) has emerged as a potential therapeutic target. In this blog post, we delve into our research journey, where we aimed to reverse cisplatin resistance in ovarian cancer using PEGylated graphene oxide nanoparticles as a delivery system for SOD1-targeting siRNA.
Identifying SOD1 as a Therapeutic Target
Our research began with the identification of SOD1 as a pivotal player in cisplatin resistance in ovarian cancer cells. SOD1, a 32 kDa enzyme, neutralizes superoxide anions, counteracting oxidative damage. Furthermore, SOD1 is essential for cellular adaptation to oxidative stress, making it an attractive target for reversing resistance induced by ROS-generating platinum compounds. We successfully demonstrated previously the chemosensitizing effect of SOD1 downregulation through RNA interference (RNAi) in vitro.
The Development of GOPEI-mPEG Nanoparticles
To translate our findings into a potential clinical therapy, we developed a novel graphene-based nanoparticle platform called GOPEI-mPEG. This platform combines nano-graphene oxide (GO) with polyethyleneimine (PEI) and polyethylene glycol (PEG) to deliver SOD1 siRNA in vivo. The incorporation of GO ensures uniform nanoparticle sizes, enhancing translational drug delivery.
Characteristics of GOPEI-mPEG
GOPEI-mPEG exhibited favorable physicochemical properties, including hydrodynamic diameter, ζ-potential, and polydispersity index. PEGylation of the nanoparticles facilitated endosomal escape, a crucial step in effective siRNA delivery. Our cellular uptake studies confirmed the biocompatibility of GOPEI-mPEG, and the siRNA cargo remained protected from RNase degradation.
Challenges and Insights
Despite these promising results, we encountered challenges related to cytotoxicity, particularly in the liver. We attributed this cytotoxicity to oxidative stress induced by PEI, resulting in SOD1 mRNA overexpression. This unexpected outcome raised concerns about potential clonal selection favoring cisplatin resistance in surviving cell populations.
Exploring Nanoparticle Toxicity
The toxicity of graphene nanoparticles depends on factors such as size, shape, surface charge, and functionalization. Concentration-dependent treatment with graphene increased ROS generation, causing oxidative stress-mediated mitochondrial damage and activating stress-reactive transcription factors. Remarkably, both GOPEI and GOPEI-mPEG nanoparticles and cisplatin triggered mitochondrial dysfunction, activating the unfolded protein response in the mitochondria (UPRmt). This discovery is the first report of cisplatin-induced activation of all three signalling arms of UPRmt in ovarian cancer. While further exploration of these pathways were beyond the scope of this study, based on the striking differences in the activation of UPRmt pathways between baseline and upon cisplatin treated cells, it would be intriguing to explore further the potential involvement of these pathways in intrinsic or acquired cisplatin resistance in other cell lines as well.
Our in vivo results indicated that SOD1 knockdown had a partial chemosensitizing effect in cisplatin-resistant tumors, consistent with our previous in vitro findings. However, the SOD1 mRNA induction by the nanoparticles limited the efficacy of siSOD1 dosing, potentially due to the toxicity of the cationic polymer component. To fully unlock the therapeutic potential of SOD1 knockdown, we plan to investigate alternative drug delivery platforms, such as lipid nanoparticles, and explore their effectiveness in other xenograft models.
Our journey in targeting SOD1 via RNAi with PEGylated graphene oxide nanoparticles has unveiled promising insights into the potential reversal of cisplatin resistance in ovarian cancer. While challenges remain, our findings pave the way for further exploration of SOD1 as a therapeutic target and the development of innovative drug delivery systems. The fight against platinum resistance continues, and we are committed to advancing our understanding and finding new solutions for the benefit of patients worldwide.