Imatinib (STI571) br Drug release kinetics br Macromolecules
3.2. Drug release kinetics
Macromolecules and nanoparticles are reported for their cell inter-nalization by endocytosis. Endocytotic pathway involves acidic mem-brane-vesicles such as endosomes and lysosomes and their fusion. As tumour regions have slightly acidic extracellular environment , Ru-Fu release rate was evaluated employing the diﬀerent pH conditions: pH 5.5 (simulates the pH in mature endosomes of cancer cells); pH 6.8 (the pH of cancer tissue) and pH 7.4 (corresponds to the circulatory environment of blood) at 37 °C, the physiological temperature. Ob-servations showed that the acidic pH enhanced the rate of molecule release from Ru-Fu complex. The percentage of cumulative release of rutin and fucoidan were as follows: 45.2% and 43.8% at pH 7.4 (Fig. 3c); 58.8% and 57.2% at pH 6.8 (Fig. 3b); 78.5% and 72.5% at pH 5.5 (Fig. 3a) respectively. No initial burst release was observed using the formulation. The results demonstrated that the release process of compounds at pH 7.4 was much slower than that pH 5.5. The carboxylic and hydroxyl linkages enable Ru-Fu complex to remain slightly stable
for a considerable period of time during circulation at pH 7.4 and thereby eliminates the premature burst release. The stability of the complex might reduce the risk of adverse eﬀects of compounds against normal Imatinib (STI571) due to their premature release by disintegration in circu-lation. Though at pH 6.8, the drug release behaviour was higher than that at pH 7.4, the eﬀect was lesser than at pH 5.5 and the slight change in the behaviour could also be due to the possible changes in the degree of protonation . At lower pH 5.5, the destabilization of weaker hydrogen bonds between Ru-Fu contributes to the release of the com-pounds. A recent study also stated that rutin and EGCG molecules could interact with ferritin to form stable complexes through hydrophobic or Vander Waals interactions resulting in an improved and sustained re-lease of compounds in the simulated gastrointestinal conditions .
3.3. Anti-cell proliferative eﬀects of compounds and the complex
Natural bioactive compounds exhibiting toxicity to cancer cells can serve as anticancer drugs. To evaluate the eﬀects of cytotoxicity in-duced by rutin, fucoidan and complex, HeLa and HaCaT cells (control) were treated with various concentrations of rutin, fucoidan and com-plex for 24 h and performed the MTT reduction assay. The generation of formazan due to the reduction of MTT denotes the decreased mi-tochondrial activity of cells  and the absorbance directly associates with the number of cells whose mitochondrial metabolism is impaired after the 24 h exposure of bioactive compounds. These observations, made an inferrence that the rutin and fucoidan had better growth in-hibitory eﬀects on HeLa cells than HaCaT cells with the display of concentration-dependent eﬀect (Fig. 4a and b). The IC50 values of rutin, fucoidan and Ru-Fu complex in Hela cells were 30 μg/ml, 200 μg/ ml and 20 μg/ml respectively, whereas they were 60 μg/ml, 400 μg/ml and 80 μg/ml for HaCaT cells. The observed IC50 values of HeLa were much lower than HaCaT cells, indicating the intrinsic toxic nature of compounds and complex against HeLa cancer cells but less toxic to
Fig. 3. Cumulative release (%) profiles of rutin and fucoidan from Ru-Fu complex at 37 °C under pH 5.5 (a), 6.8 (b) and 7.4 (c). The error bars denote mean values ± SD of three independent experiments, each performed in tri-plicates.
normal HaCaT cells (Fig. 4a–c). Moreover, Ru-Fu complex showed higher growth inhibitory eﬀects on HeLa cells than HaCaT cells in a concentration dependent manner and drastic reduction in the IC50 value of Ru-Fu for HeLa cells was observed when compared to in-dividual compounds (rutin and fucoidan) (Fig. 4c). The treatment by mixtures of the compounds (Ru + Fu) at lower concentrations also in-creased the anti-proliferative eﬀect in Hela cells than individual treat-ment (Fig. 4d). The percentages of cell viability at the selected sub-IC50 were found to be 75.3% (Rutin), 81.6% (Fucoidan), and 41% (Ru + Fu mixture) compared to control (Fig. 4d). But, the enhanced eﬀect was observed with Ru-Fu complex, and the HeLa cell growth was found to be reduced to 14.8% by the treatment with the complex (Fig. 4d).