Functionalized nanodiamond-conjugated apoptotic siRNA acts synergistically with sorafenib in a cellular model for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has poor prognosis due to its high resistance rates to chemotherapy. Myeloid cell leukemia-1 (MCL1), a potent anti-apoptotic regulator is emerging as a potential molecular target to overcome this resistance. Derived from its initial discovery in leukemia, the MCL1 oncoprotein is overexpressed in more than half of hepatic cancer cells. We developed a novel RNA interference (RNAi) strategy designed to suppress MCL1 oncogene in HCC by utilizing functionalized nanodiamonds (fNDs) as nucleic acid delivery vehicles. Two distinct amino acid-fNDs were engineered, forming diamoplexes (complexes with siRNA): HK-NDs (histidine was attached to all lysine residues on the ND surface), and H 50 K 50 -NDs (histidine was conjugated to 50% of surface lysine). Scanning transmission X-ray microscopy and transmission electron microscopy were performed to map their intracellular fate in human HCC model (HepG2), confirming efficient cellular uptake and distribution. Metabolic activity-based cell viability assays analyzed via Combenefit software confirmed the synergy between anti-MCL1 siRNA diamoplexes and standard-of-care drug, sorafenib (an apoptotic-inducer). Cells exposed to diamoplexes led to MCL knockdown, thereby compromising their viability post-sorafenib treatment. Synergy was most significant (α < 0.05) between the lowest dose of sorafenib (0.525 μM) at all tested diamoplex concentrations (4.5 to 72 pmol). fNDs themselves demonstrated high biocompatibility (cell viability >70%), meeting the critical expectations of a safe gene delivery vector. Overall, this work provides a proof-of-concept for fND-based nucleic acid therapy. Platform's biosafety and high transfection efficiency is promising to augment treatment paradigm by combining gene and drug therapy, thus improving overall therapeutic outcomes.