Preparation iiand characterization of mucoadhesive microcapsules of paclitaxel

The objective of the present work was to develop paclitaxel encapsulated mucoadhesive microcapsules with an aim to enhance its efficacy and control the drug release in cancer patients. Paclitaxel microcapsules with a coat consisting of sodium alginate and mucoadhesive polymer such as acacia, Carbomer 941, Povidone K-30, Macrogol (PEG 6000) were prepared by ionotropic gelation technique and were evaluated for morphological characters, drug content, loading efficiency, drug–polymer interactions, swelling ratio, mucoadhesive properties and in vitro drug release. The resulting microcapsules were discrete, spherical, and free-flowing with a particle size range of 534 to 822 µm. The microencapsulation efficiency was 45.09–99.83%. The microcapsules prepared with alginate along with macrogol (F4M) have exhibited good mucoadhesive property in the in vitro wash off test. The swelling ratio of microcapsules was enhanced with increased alginate concentration and the formulation (F4) showed highest swelling index of 2666. Paclitaxel release from these mucoadhesive microcapsules was slow and extended over a period of 6 h and further depends upon the concentration of the alginate. The percent drug release of alginate-acacia microcapsules (F4Ac) was higher than other formulations in the present study. In conclusion, alginate-acacia mucoadhesive microcapsules could be promising vehicle for oral controlled release of paclitaxel.


INTRODUCTION
Multiple unit dosage forms such as microspheres or beads have gained popularity as oral drug delivery systems. The acceptance is because of their uni-form distribution of the drug in the gastrointestinal tract, uniform drug absorption, reduced local irritation, and elimination of unwanted intestinal retention of polymeric material, than non-disintegrating unit dosage form (Varshosaz et al., 2009;Menon and Sajeeth, 2013). Muco-adhesive microcapsules are a better choice of dosage forms compared to intravenous infusion or bolus injections to sustain the drug for a more extended period (Jin et al., 2015). Paclitaxel could be used orally along with cyclosporine as a irst-line treatment in patients with advanced gastric cancers (Kruijtzer et al., 2003). Currently, paclitaxel is administered only through the intravenous route with a dosage regimen of once in three weeks, which incur a massive cost to the patient in terms of treatment (Paclitaxel, 2017). This snag could be overcome by a formula-tion approach of paclitaxel into an oral dosage form. As paclitaxel is a high molecular weight compound, its bioavailability can be enhanced by reducing its size to micro or nano range (Haggar and Boushey, 2009). The incidence of colorectal cancer in India is lower than that in western countries, and it is the seventh leading cancer in India (Gu et al., 2016). As per Globocan database in the year 2018, around 27,500 new cases of colorectal cancer have been found in India with about 19,500 death cases, and a total number of patients living with the disease was around 53,700 (Bray et al., 2018).

MATERIALS AND METHODS
Paclitaxel was obtained as a gift sample from Neon Laboratories Pvt. Ltd. and Naprod Life Science Pvt. Ltd., Boisor, India. Polymers such as acacia, carbomer 941, povidone K-30 and macrogol (PEG 6000) were obtained as gift samples from IPCA Laboratories Ltd., Athal, India. Sodium alginate, Eudragit S-100 and calcium chloride were procured from Thomas Baker, Merck and Loba Chemie Pvt. Ltd. All other chemicals used were of analytical grade.
Microcapsules of paclitaxel with sodium alginate in a (drug: sodium alginate) ratio of 1:1, 1:2, 1:3 and 1:4 and with co-polymer (drug: sodium alginate: co-polymer) in a ratio of 1:2:2 were prepared by ionotropic gelation process. The drug was dissolved in methanol followed by puri ied water to make 2 mL of drug solution in methanol. Sodium alginate and co-polymers were dispersed in distilled water according to the formula given in Table 1 by using a stirrer. The drug solution was added into the polymer dispersion with continuous stirring. Then the drug-polymer dispersion was added dropwise at the rate of 1 mL/ m into 100 ml of CaCl 2 solution (10% w/v) through a syringe with needle number-24 (0.55X 25 mm).
Further, the medium was stirred for 20 m at 200 rpm to complete the curing reaction and to produce spherical, rigid microcapsules. The microcapsules were collected by decantation, and the product thus separated was washed repeatedly with water, dried at 40 • C for 12 h and stored in a desiccator. The microcapsule compositions are listed in Table 1.

Evaluation of microcapsules
The prepared microcapsules were evaluated for particle size analysis, drug content, loading ef iciency, swelling ratio, muco-adhesive properties, invitro release, morphological characters and drugpolymer interactions (Al-najjar and Hussain, 2017).

Size Analysis
The micro-particles were analyzed for particle size by using optical microscopy method. The instrument was calibrated, and a size of 100 microparticles was calculated under magni ication.

Per cent drug content
About 100 mg of prepared microcapsules were pow-  Results obtained are presented as an average of 3 determinations dered, and a weighed quantity of 50 mg powder was transferred to a 100-mL volumetric lask. It was dissolved in 0.5% w/v Sodium Lauryl Sulfate followed by volume made up to 100 mL with distilled water. The solution was kept for an hour with occasional shaking and iltered through Whatman Filter Paper No -42. The iltrate was collected and diluted with a suf icient amount of distilled water, maintaining the concentration of the drug within the standard plot range. The diluted solution was analyzed for paclitaxel content by UV-Vis spectrophotometer (UV-1800 Shimadzu Corporation, Japan) at 228 nm (Sharma et al., 2016).

Microencapsulation ef iciency (ME)
Accurately weighed micro-particles containing 25 mg of the drug were transferred to a beaker containing 100 mL in 0.5% w/v Sodium Lauryl Sulfate in distilled water. The mixture was allowed to stand for 24 hours. The amount of drug-loaded was determined spectro-photometrically at 228 nm. All the experiments were carried out in triplicate (n=3) (Liu et al., 2017). M E (%) = Experimental drug content theoretical drug content * 100  Accurately weighed microcapsules (50 mg) were placed in a glass vial containing 10 mL of phosphate buffer pH 6.8 at 37±0.5 • C in an incubator with occasional shaking and allowed to stand at room temperature for 6 hours. The microcapsules were removed, blotted with ilter paper, and the swollen microcapsules were weighed. Each experiment was carried out in triplicate (n=3) (Clercq et al., 2019). The swelling index was obtained by using the following Where W 0 and W t are the initial weight of the microparticles and weight of the micro-particles at time t respectively.

In-vitro drug-release studies
Dissolution study was carried out using a rotating basket method (Model TDT6P Electrolab, Mumbai). About 900 mL of the dissolution medium (0.5% w/v sodium lauryl sulfate in distilled water, pH 6.8)

Figure 5: DSC Thermograms.
was taken in a covered vessel, and the temperature was maintained at 37±0.5 • C. The speed of the paddle was set at 100 rpm. Prepared microcapsules containing drug equivalent to 10 mg was used for the study. The dissolution test was carried out by withdrawing 5 mL of dissolution media at speci ic time intervals and was replaced by the same amount of fresh medium. Samples were assayed at 228 nm for paclitaxel using the UV spectrophotometer. Each experiment was carried out in triplicate (n=3) (Achim et al., 2008).

Mucoadhesion characteristics
The muco-adhesive properties of microcapsules were evaluated by an in vitro adhesion testing method known as wash off method. Freshly excised piece of the intestinal mucosa (2 x 2 cm) from albino rat was mounted on to glass slides (3 x 1 inch) with cyanoacrylate glue. The glass slides were connected with suitable support to the arm of a USP tablet disintegrating test apparatus. About 25 microcapsules were spread onto the intestinal mucosa. When the disintegrating test machine was operated, the tissue specimen was given slowly in regular up and down movement in the test luid (900 mL of simu-lated intestinal luids) at 37±0.5 • C contained in a one-litre vessel of the machine. At the end of 0.5 h, one hour, and subsequently at hourly intervals up to 6 h, the machine was stopped, and numbers of microcapsules still adhering to the tissue was calculated. The studies were carried out in triplicate (n=3) (Xu et al., 2019).

Fourier transform infrared(FTIR) Studies
FT-IR studied the chemical compatibility between paclitaxel and the other formulation components (excipients). The FTIR spectra of moisture-free powdered samples of drug, excipients and prepared formulations were recorded using IR Af inity-1 FTIRspectrophotometer, Shimadzu, Japan. The samples were mixed with potassium bromide and compressed into a pellet before recording the spectra (Ahmad et al., 2014).

Differential scanning calorimeter (DSC) studies
DSC scans were performed on accurately weighed paclitaxel and formulations (Perkin Elmer, Singapore Make DSC-4000). Sealed and perforated aluminium pans were used for placing the samples. Temperature calibrations were performed using indium as standard. An empty pan was sealed in the same way as the sample was used as a reference. The samples were run at a scanning rate of 40 • C/m from 40-300 • C (Martins et al., 2014).

Scanning electron microscope (SEM) analysis
The particle size, shape, and surface morphology of microcapsules were examined by scanning electron microscopy. Microcapsules were ixed on aluminium studs and coated with gold using a sputter coater SC 502, under vacuum (0.1 mmHg). The microcapsules were then analyzed by using SEM (Model LEICA S-430, London, UK) (Aukunuru et al., 2013).

Size of Microcapsules
Microcapsules were found to be spherical, oblong, large and free-lowing. The sizes vary from one formulation to another. The particle size was in the range of 534 to 822µm. Nagarajan Sriram et al., obtained similar-sized microcapsules, working with pioglitazone hydrochloride using ionotropic external gelation technique (Sriram and Katakam, 2016). The size of microcapsules was increased with the incorporation of acacia, carbomer 941, povidone K-30 and macrogol (PEG 6000). The size was also reduced with higher levels of calcium chloride and reaction time. The results were depicted in Table 2.

Drug content and microencapsulation ef iciency
The drug content and microencapsulation ef iciency are given in Table 2. The drug content was found to be uniform in each formulation and could be reproducible in each batch of prepared microcapsules The microencapsulation ef iciency was in the range of 45.09-99.83% which is better as compared to the method of preparation of paclitaxel loaded poly(lactide-co-glycolide) microspheres by Zongrui Zhang et al., which gave an encapsulation ef iciency of 92.82% (Zhang et al., 2018b). Microencapsulation ef iciency was enhanced by the incorporation of co-polymers like acacia, carbomer 941, povidone K-30 and macrogol (PEG 6000). It was also observed that the entrapment ef iciency was enhanced slightly with an increase in cross-linking time. In contrast, an increase in cross-linking concentration did not in luence the drug-loading process.

Swelling characteristics
The swelling characteristics were presented as a swelling index in Table 2. The swelling property depends on the polymer concentration, ionic strength, as well as the presence of water. The dynamic process of mucoadhesion in-vitro occurs with optimum water content-overall hydration results in the formation of a wet, slippery mucilage without adhesion. The swelling index of prepared microcapsules was found in the range of 1200-2666 at the end of 3 h. The result showed that the swelling index was enhanced by the incorporation of acacia, whereas the ratio reduced when combined with other co-polymers. This result was similar to the results obtained by Patil et al., who worked on salbutamol using methylcellulose, sodium carboxymethylcellulose, carbopol and hydroxyl propyl methyl cellulose where they obtained microcapsules with the high swelling index for hydroxypropyl methylcellulose and less for methylcellulose (Rao et al., 2010).

Drug release characteristics
The drug release characteristics of the prepared formulations were presented in Figures 1 and 2. Paclitaxel release from microcapsules was slow, spread over extended periods, and depended on the composition of the coat. Microcapsules of alginate-acacia gave relatively fast release when compared to others. The order of increasing release rate observed with various microcapsules was alginate-acacia<alginate-povidone<alginate-carbomer<alginate-macrogol. It indicates that alginate-acacia microcapsules gave relatively higher release (t 50% , 1.5 h) than alginate-macrogol (t 50% , 1.8 h) microcapsules. Kim CK et al. also reported similar indings (Chong-Kook et al., 1994). The concentrations of calcium chloride have little in luence on the release of different concentration levels, namely 20 and 30% w/v solutions. However, a minimum concentration of 10% w/v solution of calcium chloride was found suf icient. Prepared microcapsules alginate (F4), alginate-acacia (F4Ac), alginate-carbomer (F4C), alginate-macrogol (F4M), alginate-povidone (F4P) were compared for controlled release pattern of the drug. The per cent drug release of microcapsules follows the order F4Ac>F4P>F4M>F4C>F4. The drug release was maximum of 99.5% with F4Ac formulation. Jagadeesh G Hiremath et al. prepared paclitaxel loaded poly (caprolactone) microspheres by solvent evaporation method and found that the cumulative per cent drug release was 62.54±1.6 at the end of 30 days. It shows that the ionic gelation method could be a better choice as compared to solvent evaporation method . Hence, controlled release pattern of alginate-acacia microcapsules (F4Ac) was comparable to the commercially available dosage form of paclitaxel. In the case of the currently marketed intravenous drug formulations, paclitaxel injection is administered intravenously over three hours at a dose of 175 mg/m 2 followed by cisplatin at a dose of 75 mg/m 2 or paclitaxel injection administered intravenously over 24 hours at a dose of 135 mg/m 2 followed by cisplatin at a dose of 75 mg/m 2 (Martín, 2015). The result of the in vitro drug release showed that there was no signi icant change in percentage drug content, and the microcapsules could release the drug periodically for four hours in a controlled manner.

Mucoadhesion characteristics
The microcapsules exhibited suitable mucoadhesive property in the in-vitro wash-off test. The results are given in Table 3. The strength for mucoadhesion was found to be directly proportional to the concentration of polymer. Although the combination of polymers attained the maximum value of muco-adhesive strength, signi icant muco-adhesive strengths were also shown by individual polymers in simulated intestinal luids. The optimized formulation F4M showed considerable higher muco-adhesive strength as compared to other formulations with a muco-adhesive time over more than 4 hours (Pal and Nayak, 2012).

Scanning electron microscope (SEM) studies
The morphological characterization revealed that the alginate microcapsules (F4) were spherical. The surface of the microcapsules was almost smooth, free from pores and deposits. The SEM photographs of alginate-acacia microcapsules (F4Ac) showed that microcapsules were nearly spherical, as shown in Figure 3. The surface was smooth but contained longitudinal depression, whereas the F4Ac resulted in better morphological structure and more smooth surface as compared to the F4formulation (Zhang et al., 2018a).

Fourier transforms infrared (FTIR) Studies.
In paclitaxel FTIR spectrum, major peaks were obtained at 3497.09 cm −1 , along with broad-band in the region of 3600-3100cm −1 which may be attributed to the presence of -NH and -OH stretching due to secondary amine and hydroxyl groups (D and Prabhakar, 2017). The peak at 3035.12 cm −1 indicates the presence of C-H stretching in aromatic hydrocarbons. The peak can detect the presence of C-H stretching due to -CH 3 and -CH 2 -of aliphatic chain at 2954.11 cm −1 . The carbonyl group, C=O stretching peak at 1732.15 cm −1 may be attributed to carboxylic ester group and C=O stretching peak at 1647.28 cm −1 to amide group. The peak at 1073.43 cm −1 indicates the presence of C-O-C coupling interaction and peak at 710.80 cm −1 may be attributed to out of plane deformation of a methylene group. Compatibility of paclitaxel with excipients was studied using polymers such as sodium alginate, povidone, carbomer, macrogol and gum acacia. The FTIR spectra of the prepared microcapsules (F4Ac, F4P, F4C, F4M) showed characteristic peaks for drug and excipients with no signi icant shift in positions indicating that there was no chemical interaction between the drug and polymers, thus con irming the drug compatibility with the excipients. The FT-IR spectra are showed in Figure 4 shows that A: FTIR spectra of F4Ac,Paclitaxel,Sodium alginate, Acacia presented from top to bottom respectively B: FTIR spectra of F4M,Macrogol,Paclitaxel, Sodium alginate presented from top to bottom respectively C: FTIR spectra of F4P,Povidone, Paclitaxel, Sodium alginate presented from top to bottom respectively D: FTIR spectra of F4C, Carbomer, Paclitaxel, Sodium alginatepresented from top to bottom respectively.

Differential scanning calorimeter (DSC) studies
The DSC thermograms of paclitaxel showed a characteristic peak at 223.83 0 C, which corresponds to the melting point of the drug (Mu and Feng, 2001). The peak started at 213.84 0 C and ended at 231.03 0 C with an area of 187.172 mJ, height of 11.0802 mW and ∆H value of 50.5869 J/g. The formulations F4Ac, F4P, F4C showed characteristic peaks for drug and excipients with a peak shift towards lower temperature region, which may be due to the presence of additives. The formulation F4M showed small peaks around 223.83 0 C, which could be due to less drug content in the formula. DSC thermograms of different polymers and prepared microcapsules with their peak areas are showed in Figure 5 shows that A: DSC thermogram of F4Ac, B: DSC thermogram of F4C, C: DSC thermogram of F4P, D: DSC thermogram of F4M.
Muco-adhesive polymers as carriers that sustain the drug release seem to be a promising polymer for colonic delivery of a drug(s) (Sudheer, 2018). Among such polymers, sodium alginate is widely used natural polymer for mucoadhesion, but it is unable to effectively prevent the drug release during transit through upper gastrointestinal tract (Sachan et al., 2009). Sodium alginate polymers are crosslinked using acacia, povidone, macrogol and carbomer as a co-polymers, to overcome this dif iculty.

CONCLUSIONS
The above research was unique as the effect of co-polymers such as acacia, povidone, macrogol and carbomer along with the primary polymer sodium alginate was studied to obtain an optimized muco-adhesive microcapsule of paclitaxel. The results revealed that alginate-acacia microcapsule gave relatively higher per cent release than alginatecarbomer. The concentrations of calcium chloride and reaction time exposure have little effects on the release rate. The controlled-release pattern of alginate-acacia microcapsule was observed to release paclitaxel for six h. Microcapsules prepared with alginate-acacia and alginate-povidone was found good with respect to release, swelling ratio, mucoadhesion, and morphological characteristics. Hence, these are suitable carriers for oral controlled release of paclitaxel.

ACKNOWLEDGEMENT
Authors deeply acknowledge the Head, Post Graduate Department of Zoology, Berhampur University and the Director, Royal College of Pharmacy and Health Sciences, Berhampur for providing the necessary laboratory facilities. Further, we are deeply indebted to Neon Laboratories, Naprod Life Sciences, Mumbai for providing the drug in the test as gift samples.