Natural plants derivatives have gained enormous merits in cancer therapy applications upon formulation with nanomaterials. Curcumin, as a popular research focus has acquired such improvements surpassing its disadvantageous low bioavailability. To this point, the available research data had confirmed the importance of nanomaterial type in orienting cellular response and provoking different toxicological and death mechanisms that may range from physical membrane damage to intracellular changes. This in turn underlines the poorly studied field of nanoformulation interaction with cells as the key determinant in toxicology outcomes. In this work, curcumin-AuNPs-reduced graphene oxide nanocomposite (CAG) was implemented as a model, to study the impact on cellular membrane integrity and the possible redox changes using colon cancer in vitro cell lines (HT-29 and SW-948), representing drug-responsive and resistant subtypes. Morphological and biochemical methods of transmission electron microscopy (TEM), apoptosis assay, reactive oxygen species (ROS) and antioxidants glutathione and superoxide dismutase (GSH and SOD) levels were examined with consideration to suitable protocols and vital optimizations. TEM micrographs proved endocytic uptake with succeeding cytoplasm deposition, which unlike other nanomaterials studied previously, conserved membrane integrity allowing intracellular cytotoxic mechanism. Apoptosis was confirmed with gold-standard morphological features observed in micrographs, while redox parameters revealed a time-dependent increase in ROS accompanied with regressive GSH and SOD levels. Collectively, this work demonstrates the success of graphene as a platform for curcumin intracellular delivery and cytotoxicity, and further highlights the importance of suitable in vitro methods to be used for nanomaterial validation.