# The Exploitation of Lysosomes in Cancer Therapy with Graphene-Based Nanomaterials
## 5 The Role of Lysosomes in GNM-Based Cancer Therapy  
_5.1. Lysosomes Enable Drug Release from GNM-Containing Nanocarriers, Whereupon Drugs Escape from Lysosomes_  
Since most chemotherapeutic agents achieve their anticancer effects by acting on cell organelles other than lysosomes (e.g., the cell nucleus, mitochondria, and endoplasmic reticulum), they must escape from the endosome/lysosome to exert their effect and avoid degradation by acid hydrolases [54]. Recently, many novel polymers, pH-sensitive peptides, proteins, and other endosymolytic agents have been synthesized to facilitate the endosomal escape [55]. Several mechanisms that are responsible for the lysosomal escape of nanoparticles could also apply to graphene-based DDSs (Figure 3). (1) The proton sponge effect is the ability of molecules, such as polyethylenimine (PEI) and polyamidoamine (PAMAM) dendrimers, that contain amine groups with buffering capacity to absorb protons, which prevents the acidification of endosomes/lysosomes. To achieve the desired pH, ATPase continues to pump protons into the endosome/lysosome, causing an influx of chloride ions and water osmosis. This process leads to an increase in pressure within the lysosomes and ultimately results in a lysosomal burst. (2) The umbrella effect is an extension of the proton sponge effect. When amines are protonated, charge repulsions cause the structure of nanoparticles to expand, leading to the rupture of endosomes/lysosomes. (3) Pore formation: Nanoparticles can fuse directly with the membrane of endosomes/lysosomes, inducing membrane stress and internal membrane tension, which can lead to the formation of pores. (4) Photochemical disruption is a mechanism in which a photosensitizer, when exposed to light, generates ROS that can destroy the integrity of the endosomal/lysosomal membrane [55; 56; 57]. For an anti-cancer effect, it is not necessary for the entire graphene-based DDS to leave the endosome/lysosome, only the anti-cancer drug. To achieve this, the drugs must first be separated from the GNM-containing nanocarrier. This can happen in several ways. (1) The low pH environment within lysosomes triggers the protonation of graphene-based DDSs, leading to electrostatic repulsion between positively charged drugs and nanocarriers [39; 40]. (2) Low pH triggers the breakdown of the \(\pi\)-\(\pi\) interaction, the supramolecular forces that arise between unsaturated (poly)cyclic molecules with \(\pi\)-orbitals [58]. This has been observed for the \(\pi\)-\(\pi\) interaction between GNMs and doxorubicin [59; 60; 61], proflavine [61], or Chlorin e6 [62]. (3) The breakdown of chemical bonds. For example, the diselenide bond between GO and PAMAM was broken by a low lysosomal pH [15] or a high lysosomal ROS [13], resulting in the release of the drug. Next, we list studies describing how anti-cancer drugs are released from GNM-containing nanocarriers and the mechanisms of their endosomal/lysosomal escape (Table 1). [PERSON] and colleagues constructed the smart vehicle GPCP, which is composed of PLL-modified graphene conjugated with citraconine (Cit) as a charge-convertible inner layer, and PAMAM dendrimer as a cationic outer layer. GPCP was loaded with photosensitizer indocyanine green (ICG), which generates heat and ROS when irradiated in the near-infrared (NIR) and miR-2 li, an oligonucleotide inhibitor of oncogenic microRNA 21. After endocytosis of the GPCP/miR-2 li/ICG by MDA-MB-231 triple-negative breast cancer cells, both ICG and miR-2 li were released at the acidic pH of lysosomes due to the acid-triggered charge reversal effect. Furthermore, charge-reversed GPCP destabilized the endosomal membrane through the proton sponge effect, allowing both ICG and miR-2 li to escape from the endosomes/lysosomes and exert their anticancer effects. Importantly, the complex demonstrated potent antitumor activity in the NIR-irradiated MDA-MB-231 mouse model [12]. [PERSON] and colleagues modified GO with a Poloxamer 188-modified PAMAM dendrimer, which exhibits a strong proton sponge effect.