*DOI: http://dx.doi.org/10.5772/intechopen.103688 Advances in Graphene Platforms for Drug Delivery in Cancer and Its Biocompatibility*

and accumulation in the digestive tract [96]. Apparently, the accumulation of QDs depends on the stage of development of the zebrafish (embryo, larva, adult). Studies in adult zebrafish using GQDs at different concentrations (0.1 ng/mL to 100 μg/mL) and exposure times (8 h to 6 days) showed distribution in the heart, blood vessels, brain, intestine, head, and tail [97–101]. The effects that have been found in zebrafish are morphological and functional alterations, while mortality is attributed to the generation of ROS, oxidative stress, and, finally, apoptosis [102]. On the other hand, studies carried out in chicken embryos have also shown evidence of GQDs-induced toxicity. It was found this affected survival but did not produce morphological or biochemical alterations in the embryo [103]. However, another study found morphological alterations and hemolysis of erythrocytes [104], as well as ultrastructural alterations of the brain, suggesting neurotoxicity [105]. These results suggest that GQDs can alter key processes, not only in adulthood but also during embryonic development.

Biodistribution studies in rodents have shown that GQDs are distributed in various tissues and produce certain toxic effects as well. For example, in mice that received GQDs in a single dose of 10 mg/kg intravenously, it was found that 6 hours after inoculation the QDs were distributed in several organs. Clearance began after 3 days and, at 14 days, the QDs had been completely removed. Histological and biochemical studies did not reveal alterations, only weight loss [106]. However, in another biodistribution study carried out in rodents treated with a single dose of 5 and 15 mg/kg of GQDs intravenously, they produced morphological alterations compatible with inflammation and biochemical damage in the lungs after 7 days of exposure [107]. Additionally, yet another study using repeated doses of 5, 10, and 15 mg/kg every third day for 30 days, showed a reduction in blood cells, morphological alterations in the liver, lipofuscin deposits in the kidney, and the presence of inflammatory infiltrate in the lungs. These alterations were dose-dependent [108]. Taken together, these data suggest that GQDs produce acute toxicity at both single and repeated doses in mammals.

Today there are no reports of long-term studies (chronic toxicity), studies on reproduction and development, or of any other type that allow a general overview of the toxicological profile of GQDs. However, there is experimental evidence showing that other materials derived from graphene can produce a series of toxic effects that must be considered. For example, studies of the distribution of graphene and its derivatives after aerial exposure showed toxic effects in the lungs of rodents [109, 110]. In a chronic inhalation toxicity study of graphene nanoplates, deposits of the nanomaterial were observed in the lungs and pulmonary lymph nodes in mice [111]. In a distribution study in rats using doses of 10, 20, and 40 mg/kg of graphene oxide orally, it was found that it produced nephrotoxic effects due to oxidative stress [112]. While in another study, the administration of multiple doses of oxidized graphene (4 mg/kg) for 4 weeks showed deposits of the material in different tissues in rats [113]. Mutagenic effects have been observed in rats when exposed to graphene oxide at a dose of 4 mg/kg for 4 weeks [114]. Likewise, toxic effects on the reproductive capacity and development of offspring have also been reported after the administration of oxidized graphene to mice with doses from 6.25 mg/kg [115]. Unfortunately, when reviewing the subject, we noted there are no toxicity studies regarding the GQDs platforms employed for drug delivery in cancer research. In fact, all the studies have focused on evaluating its efficiency and specificity toward the tumor cell. That is, what has mattered so far is to demonstrate their possible therapeutic applications in cancer, but not the possible toxic effects they may produce. Therefore, we could say that biosafety studies on GQDs platforms are null.

To date, GQDs have been widely studied as carriers with a large surface area favoring drug transport and particular interest has been placed on characterizing their therapeutic bio properties *in vitro*. However, the preclinical studies carried out so far are hardly enough. Most of the studies in cells and animals have focused on evaluating the efficiency of drug/gene delivery at the site of interest. The dosage of the treatments used in animals has been empirical, since no study has demonstrated the real drug/QD concentration within the body, and it is not known if there could be pharmacological interactions between these platforms and other therapies used in the clinic. One aspect that has been completely neglected is the bioavailability of GQDs. What will be the appropriate route of administration? Do they bind to plasma proteins? Do they accumulate? Where do they metabolize? In the route of excretion? There are many questions that remain unanswered. In addition, long-term toxicity studies are required in different species of animals to test the effects on reproduction, carcinogenicity, and teratogenicity, among others. Many preclinical studies are still needed if GQDs are to be used for diagnosis and treatment in humans.

Concern regarding the toxicity of graphene not only stems from the findings mentioned above, but also from the long-standing concern about environmental and occupational exposure to graphene [116]. Inhalation toxicity data of graphene analyzed in experimental animals suggest that acute exposure by repeated inhalation to graphene-derived materials could induce inflammatory/fibrotic reactions, suggesting that it could also induce fibrotic disease in humans [117, 118]. Hence the importance of conducting preclinical biosafety studies of graphene nanomaterials and their derivatives using specific criteria, for these are not necessarily the same as those used for chemical products. The toxicological evaluation must be extrapolated with special care due to the size of the nanomaterials and the chemical groups they contain. If there is no complete toxicological profile that meets the standards required by the guidelines of administrative agencies such as the US Food and Drug Administration (FDA), the European Medicines Agency (EMA) or the European Medicines Evaluation Agency (EMEA), and the Japanese Agency for Pharmaceutical and Medical Devices Agency (PMDA), the research will not leave the laboratory.
