**2.2 Preparation of microemulsions**

Microemulsions can be prepared by the following methods:

1.Phase titration method: In this method, the microemulsion is formed by the spontaneous emulsification method. The phase diagram is useful in determining the various interactions that happens when the components of the microemulsion


**Table 2.** *Indicating the types of surfactants.* *Perspective Chapter: Microemulsion as a Game Changer to Conquer Cancer with an Emphasis… DOI: http://dx.doi.org/10.5772/intechopen.101479*

is being mixed [19]. Mainly from the phase diagram, the microemulsion region can be determined [20]. Later, the optimized formulation can be obtained by implementing any of the experimental models [21, 22].

2.Phase inversion method: While coming to the phase inversion method, the microemulsion undergoes phase inversion on addition of excess dispersed phase. During this, change in the particle size occurs that can affect the drug release both *in-vitro* as well as *in-vivo* [23]. In this case, when the non-ionic surfactant is used for the preparation of microemulsion, the change in temperature decides the formation of the microemulsion by the method called phase inversion temperature (PIT) method. Suppose when there is an increase in temperature, it leads to the water in oil microemulsion, whereas when the temperature decreases it leads to oil in water microemulsion [24]. While coming to the phase inversion composition, the addition of the water or oil makes the difference [25]. In which, when water is added to oil phase or oil is added to water phase, the surfactant exhibits both the hydrophilic and lipophilic property at one point, and that point is called as emulsion inversion point. After which an addition of water or oil makes the changes in the curvature of the microemulsion and leads to the formation of o/w microemulion or w/o microemulsion [26–28].

#### **3. Herbal based microemulsion for cancer treatment**

Various herbal based components are being tested by researchers for determining the anti-cancer activity. But some of the components have low bioavailability because of low solubility. Thus, the microemulsion acts as a carrier for the delivery of such components and helps in improved bioavailability and resulting in enhanced therapeutic effect [29].

Dibenzoylmethane (DBM) is one such compound that has poor water solubility because of which they have low bioavailability. In order to overcome this condition, DBM has been incorporated into microemulsion [30]. The microemulsions are also capable of protecting the drug molecule form enzymatic hydrolysis and oxidation etc., thus allowing the drug to reach the target site. In the study conducted with DBM, peppermint oil has been used and oil in water microemulsion has been made because of poor solubility of DBM in water. This is one of the advantage of microemulsion were both the hydrophilic as well as hydrophobic drug can be incorporated into them. This formulation has exhibited its action as effective chemopreventive agent in forestomach tumor. It has also been stated that the microemulsion decreases the interfacial tension between the vehicle and the intestinal cells and leads to enhanced permeation. This can eventually result in increased therapeutic activity [31].

There are also many medicinal values present in the food compounds that we consume in our day to day life. One such compound is turmeric. The turmeric which is also known as *Curcuma longa L. (C. longa)* possesses various biological activities like anti-cancer, anti-oxidant and anti-inflammation etc. [32]. Various studies have been carried out with curcumin on different cancer cells like melanoma, prostate, hepatoma and breast cancer cells. Yen Chu Chen et al. has worked on curcuminoid microemulsion to improve the inhibitory effect on the colon cancer cells. The microemulsion has been prepared by soya bean oil, anhydrous ethanol (co-solvent) and tween 80. Both the early and late apoptosis has been observed in cancer cells and also the cell cycle arrest at S phase. Additionally, the up regulation in p53 (tumor suppressor) has been observed in the p21- independent manner. Increase in caspase 8, caspase 9, and caspase 3 have also been observed. Thus, it can be said that

curcumin can produce a wide range of anticancer activity by focusing on extensive mechanism [33].

As said earlier even though various natural compounds are available for the rehabilitation of cancer, they fail to produce the complete desired action because of low bioavailability and poor solubility. Thus, microemulsion helps in enhancing the bioavailability and improving the solubility with the aid of their lipid based drug delivery system. One such study has been carried out by Salma A. El-Sawi et al., to improve the delivery of the extracts of *Salix mucronata* that possesses antiproliferative activity. The extracts from the *Salix mucronata* has been loaded into the microemulsion, so as to improve the penetration of compounds through the biological barriers and produce a desired pharmacological action with less quantity of dose [34].

When a drug is having low solubility in water but lipophilic in nature, it will be loaded into the microemulsion because of its lipid based delivery. Additionally, because of the lipid based drug delivery, they not only improve the solubility, it can also enhance the permeability of the drugs through various barriers. In which the blood brain barrier (BBB), one of the strongest barriers which do not allow the entry of drugs into the target site, acts as a main hurdle for various drugs in targeting the brain tumor [35]. Even though various flavonoids, terpenes, and carotinoids are being studied to determine their anti-cancer activity, most of them fail to reach the target site because of BBB. Thus, it is important to breach the BBB to get a therapeutic activity. Most of the techniques for delivery of the drug into the brain by crossing the BBB involves invasive or a semi-invasive technique, whereas the nasal route of drug delivery acts as a non-invasive method. But the direct administration of active ingredient into the nasal cavity may lead to degradation of drug by various enzymes and clearance of drug. Thus, in order to overcome these drawbacks, the microemulsion can be used as carrier because of their property to improve the permeability of the drug [36, 37].

Quercetin is a flavonoid that has been widely studied for their anti-cancer activity [38]. They have the ability to inhibit the proliferation of various cancer cells like lung, prostate, liver, breast, cervical and colon cancer [39]. Quercetin is also being used as a synergistic agent along with other chemotherapeutic drugs [40]. But because of their low permeability, they are unable to reach the target site and produce a complete therapeutic activity. Thus, if they are being loaded by any of the carrier or drug delivery system, one can meet the expected outcome. Sagar Kishor Savale in 2017, has prepared the quercetin microemulsion, in order to target the brain tumor assuming that this carrier would help in increasing the permeability of the drug. Quercetin has been dissolved in oleic acid and later tween 80 and polyethylene glycol 400 has been used as surfactant and co-surfactant respectively for the preparation of microemulsion. Though the *in-vitro* permeability study has been done, the in-depth molecular mechanism and *in-vivo* studies should be determined [41].

Another flavonoid that is helpful in targeting the cancer cells is myricetin. It is also structurally similar to that of quercetin and luteolin. Myricetin exhibits anticancer activity [42] by interacting with various oncoproteins like Janus kinase – signal transducer and activator of transcription 3 (JAK1-STAT3), protein kinase B (PKB) and mitogen activated kinase 1 (MEK 1). They also act on the over expressed cyclin- dependent kinase 1 to exert an anti-mitotic effect on the liver cancer cells [43]. Though, they exhibit various anticancer activities, the main struggle comes when there is low bioavailability. But this problem can be eradicated by using microemulsion. Studies are also being carried out for the preparation myricetin

#### *Perspective Chapter: Microemulsion as a Game Changer to Conquer Cancer with an Emphasis… DOI: http://dx.doi.org/10.5772/intechopen.101479*

microemulsion that can improve the bioavailability of the compound [44]. Shujun Wang et al. have formulated myricetin microemulsion for oral delivery. It was stated that the incorporation of microemulsion delivery system could decrease the dose of the myricetin because improved drug availability at the target site. Since, the microemulsion is involved; the author says that the enhanced bioavailability of myricetin at the target site may because of the presence of payers patch and the M (Microfold) cell in the intestine and also because of the presence of lipid in the microemulsion, which makes the enhanced absorption via the lymphatic system [45].

Ruixue Guo et al. has prepared a myricetin microemulsion, for enhancing the bioavailability of the compound, anti-proliferative activity and also the anti-oxidant activity. In this study, the effect of myricetin microemulsion was tested on the liver cancer cells (HepG2). Since, the excess addition of surfactant in the microemulsion may lead to toxicity, it is important that we need to use the surfactant in the minimum quantity. Thus focusing on these criteria, the work has been carried out by screening various oils, surfactant and co-surfactant to get stable and optimized formulation. As a result of it, labrafac lipophile WL 1349 was selected as oil phase, tween 80 and cremophor RH 40 was used as surfactant and transcutol HP has been used a co-surfactant. The prepared miroemulsion has shown enhanced oral bioavailability as compared to that of the myricetin suspension (Sodium carboxy methylcellulose suspension) [46].

The microemulsion can also be a self-micro-emulsifying drug delivery system (SMEDDS). They are given as a preconcentrate so that after reaching the target site, they may get converted into a microemulsion giving a prodrug effect. The advantage of such delivery system is that, the stability of the formulation can be maintained as a result the bioavailability can also be improved. In the SMEDDS, the lipid phase used can also be liquid or solid. While comparing both, it has been said that S-SMEDDS (i.e.): use of solid lipid is preferred because, it involves the solidification of liquid excipients into a powder form (solid form) that helps in obtaining a more stable formulation compared to liquid lipid. One such solid SMEDDS has been prepared by Wenli Huang et al. [47]. In this work, *Brucea javanica* oil is being loaded into S-SMEDDS (BJOS) to enhance the anti-cancer activity. *Brucea javanica* oil is a traditional herbal medicine in China that has the ability to treat various cancers like gastrointestinal cancer, lung cancer and prostate cancer. Since, the oil itself is producing various anti-cancer activity, they were used as a main component in the study that can act as the anti-cancer agent. The BJOS formulation was prepared by using *Brucea javanica* as oil phase, Cremophor RH40 and PEG 6000 as surfactant and co-surfactant respectively. Compared to the Brucea javanica oil emulsion alone, the BJOS formulation had a better antiproliferative activity. This may be because; the S-SMEDDS would have carried the BJO into the cancer cells via endocytosis.

Apart from the above said compounds, there are also other herbal compounds that exhibits anti-cancer activity by acting on various pathways by inhibiting the cell cycle arrest, maintaining the genetic stability, inducing apoptosis exhibiting anti-angiogenic activity and also anti-metastatic activity. Thus, as a nutshell, it can be said that it would be a better option if we choose microemulsion as a drug delivery system or a carrier for the delivery of herbal compounds that exhibits anti-cancer activity. Because unless the conventionally available drugs or synthetic drugs, the herbal compounds may not cause much side effects or harm the normal cells. Even the herbal compounds are also being taken by us on regular basis. Thus, it will lead to great endeavors if natural compounds are being delivered in an accurate manner by using this kind of delivery system.
