**5. EVs as drug delivery tool in cancer**

Effective therapeutic agents have been extensively studied and tried for many decayed to be developed in order to deliver an effective therapeutic agent to its target specifically with minimal side effects. It is well known that non-targeted drugs are inefficient and have side effects when they are delivered systemically. The purpose of a drug delivery system (DDS) is to deliver a drug efficiently, improve the effect of the drug and minimise its side effects [85, 86]. Many useful drug delivery tools and cargos have been developed, such as PEG, liposome, nanoparticles and cell penetrating peptides (CPPs) [87–89]. However, despite the persistent efforts of researchers, the delivery to specific organ and the side effect of DDS remain unsolved completely. DDSs are desirable for use in cancer therapy, and EVs have been recently proposed as promising natural drug delivery tool to serve different diseases [90, 91]. It has been noticed that EVs have a tropism to some organs or cells, and because of their biological significance, they have gain a potential benefit in drug delivery field to target organs or cells. Furthermore, EV-based DDSs are expected to have huge impact and revolution in drug delivery industry field because of their minimal side effects, as they are naturally occurring in the body, in addition to their ability to mediate tumour-selective drug delivery or to mediate organ-specific drug delivery.

#### **5.1. Drug delivery techniques**

#### *5.1.1. Encapsulation of drugs to EVs*

Drugs should be conjugated or encapsulated in EVs in order to be used as DDSs cargo or vehicle. Several methods have been utilized for encapsulating existing drugs in EVs using methods, such as sonication, extrusion and electroporation [92]. One study investigated four different methods for incorporating catalase into EVs from a Raw 264.7 macrophage cell line, where incubation at room temperature, freeze-thaw cycles, sonication and extrusion were applied [93]. Interestingly, it has been reported that melanoma cells treated with the anticancer drug cisplatin eliminated the cisplatin through EVs [94]. When human pancreatic adenocar‐ cinoma CFPAC-1 cells were treated with EVs containing paclitaxel, this produced an antitumour effect [95].
