A Mechanistic Insight into Doxorubicin Adsorption on N-isopropyl Acrylamide Grafted Nanotube: Optimization Study of Loading Temperature

24 Background : The drug development process is costly and time-consuming; hence, nowadays, 25 enormous efforts have been established through computational studies for finding appropriate 26 strategies, methods and solutions for enhancing the drug production and administration 27 procedures. Hydrogels that undertake deformation upon pertinent changes in temperature have 28 significant aptitude as drug delivery systems. These biomaterials have made a substantial impact 29 on the development of drugs for critical diseases, especially cancer therapy. Drug loading and 30 uptake are primary and fundamental steps of the drug development and discovery process. N- 31 isopropyl acrylamide is a common and well-known thermo-sensitive and injectable hydrogel for 32 the drug uptake under the lower critical solution temperature (LCST). In the current study, 33 carbon nanotube (CNT) as a nanocarrier was modified via N-isopropyl acrylamide. On the other 34 hand, Doxorubicin as an anti-cancer drug applied on mentionted systems to develop drug 35 packing at three different temperatures. 36 Results: After computational parametrization of the system via bioinformatics software and 37 databases, Molecular dynamics (MD) simulation was run. To this end, the detailed simulations 38 were carried out to reveal the interaction energy, numbers of hydrogen bonds, the gyration 39 radius, mean square displacement, and radial distribution function as well as Gibss free energy. 40 Besides, the optimal loading temperature for doxorubicin was determined. The results achieved 41 from simulating the polymer demonstrated a decrease in the gyration radius at a higher 42 temperature. A decrease of gyration radius resulted in more concentrated aggregation with 43 stronger bonds. 44 Conclusions: Therefore, at the higher temperature, the more stable polymer interaction and 45 better doxorubicin loading were acquired. The smart absorption of doxorubicin onto the CNT modified via N-iso-propyl acrylamide (NIPA) give a significant and valuable view on the future 47 studies regarding the drug development and novel, biocompatible, and biodegradable stimuli- 48 sensitive drug delivery system.


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Background 62 Cancer is one of the global, critical and life-threatening diseases which was the third leading 63 causal factor of death in 1990, while it rose to be the second leading cause of mortality in 2013. 64 In 2013, around 15 million cancerous patients were identified, and cancer led to around 8.2 65 million deaths. In that year, statistical analysis showed that the cancer resulted in 196.3 million 66 cancer cases (1).

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(DOX) is one of the essential and common anti-cancer drugs which fights against the 69 proliferation and metastasis of cancerous cells. DOX binds to the DNA and inhibits the nucleic 70 acid production (2). As such, it disrupts the molecular structure as well as the spatial blockage.

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DOX is used to treat various cancers such as gastric, lung, breast, bladder, ovary, thyroid, bone, 72 nerve tissue, muscles, joints, and soft tissue malignancies (3). It is also used to heal Hodgkin's 73 lymphoma and multiple types of leukemia (4). On the contrary, the drawback of the DOX which 74 has an adverse effect, is the fact that it can also damage healthy human cells and prevent their 75 growth as well (5). This requires implementing novel techniques to minimize these drug-related 76 systemic toxic effects. There are multiple methods to achieve such a goal; one of them is 77 nanostructures which provide the targeted drug delivery. Targeted and smart drug delivery via 78 the nanoparticles not only minimize the doxorubicin adverse and unwanted effects on the non-79 cancerous and healthy cells but also maximizes the efficiency of the drug on tumor cells (6). 80 Novel nanostructured drug delivery systems have dramatically improved drug therapies (7). 81 Various polymeric (8), carbon-based (9), and ceramic nanostructures (10) have been studied for 82 this purpose. These structures have specific features including targeted drug delivery (11), high 83 5 biocompatibility (12), enhancing drug viability in the bloodstream (12), controlling and 84 decelerating the drug release (13), protecting drug molecules (14), having a smaller size than the 85 cells (15), and the ability to cross biological barriers to deliver a drug to the targeted site (16). 86 Therefore, nanostructures can be a suitable carrier for doxorubicin delivery. Because of the high 87 therapeutic utility of doxorubicin in oncology and clinical fields, the DOX drug development can 88 decrease the manufacturing cost and increase the efficacy and minimize the drawbacks (17) Hydrophilic polymers can stabilize nanotubes in the aquatic environment. The pH-sensitive 107 polymers such as polyacrylic acid have been used as a carbon nanotube functional group, in 108 which the nanotubes are dispersed in water based on the degree of polymer ionization and pH.

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For nanotubes, the use of temperature-sensitive polymers instead of the pH-sensitive polymers is 110 a more suitable option in the aqueous environment. The pores in the hydrogels facilitate the 111 loading of the drug on/into the carriers and may serve as a drug delivery system (30). The  transformed from a distended hydrophilic structure below the critical solution temperature to a 124 condensed hydrophobic structure above this temperature (33).

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The polymer of our current study, NIPA, is one of the conventionals, biocompatable, 126 biodegradebale and thermo-sensitiver injectable hydrogels which are physiologically and 127 chemicaly capatable to load and delivery Therapeutic agents. Anticancer agents are naturally 128 7 entrapped in the thermo-sensitive hydrogel by mixing with precursor solution and then after by 129 sterilization procedure the hydrogel is capable to inject to the body biofluids (34,35). 130 Other studies showed that the essential solution temperature of the NIPA could be increased by     The comparison of the figures reveals that at 310.15 K, the chart has a higher slope. Therefore, at 264 310.15 K, the diffusion coefficient was more significant. The higher diffusion coefficient means 265 that the drug is absorbed more rapidly ovo the surface of the CNT and the hydrogel; accordingly, 266 the efficiency and rate of the drug absorption will be higher. So, the drug loading takes place In this equation, 'ρ' is the density of the particle at 'r' distance.
356 Figure 1 shows a three-dimensional schematic of the 5-mer, 10-mer, and 15-mer polymer 357 molecules of the N-isopropyl acrylamide.  There are noticeable Hydrogen bonds and electrostatic interactions between the drug and N-383 isopropyl acrylamide. Therefore, measuring the surface charges of the system is very important.

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One popular and appropriate mathematical method to precisely calculate the surface charge in 385 quantum mechanics (QM) is the Bond Charge Correction (BCC) method. Table 1 shows the 386 monomer parameters in the polymer according to the surface charge correction method.   The number of simulations was three and the duration was 30 nanoseconds. In the first 403 simulation, 15 5-unit polymers with five drugs and one nanotube were used. In the second 404 26 simulation, eight polymers of 10 units with five drugs and one nanotube were used and in the 405 third simulation, five polymers of 15 units with five drugs and one nanotube were used. As 406 reported in our last study, the optimum length of the NIPA chains was obtained to be 5-mer 407 hydrogel; hence, we developed this polymer for our current study to investigate the DOX 408 loading. In particular, three different temperatures including 288.15 K, 298.15 K, and 310.15 K 409 were assumed as the critical points and the loading of drugs was developed at these three 410 temperatures. Furthermore, by applying the Umbrella Sampling simulation method, we 411 calculated the Gibbs free energy of the system during our MD simulations.   Figure 1