The present study confirmed that the GA loaded-NLC-RGD could significantly improve the anticancer potential of DOX. Previously synergistic effects of Gallatin and the chemotherapeutic agents have been reported in cancer treatment (Ren et al., 2016, Yu et al., 2018). However, low bioavailability and flavonoid first-pass metabolism attenuate the anticancer effects of GA (Wu et al., 2011, Zhu et al., 2018). Based on our results, NLC-RGD is an appropriate carrier for delivering GA into the adenocarcinoma human alveolar basal epithelial cells. Nanoparticles in a size range of 30–200 nm are suitable for drug delivery (Hajipour et al., 2021). Nanoparticles larger than 30 nm are easily omitted by the reticuloendothelial system, and those smaller than 20 nm are removed by renal excretion (Hajipour et al., 2018). Zeta potential as an indicator of nanoparticle surface charge controls the repulsive force among nanoparticles and the stability of the drug delivery system (Hufschmid et al., 2019). It is also reported that neutral or faintly negative ZP is more compatible to interact with the cell membrane (Lane et al., 2015). The Zeta potential of prepared nanoparticles is high enough to provide acceptable stability, and also is not too negative to prevent nanoparticles and cell membrane interaction.
To develop targeted nanoparticles, RGD was added to the formulation that can deliver the drug directly to a cancer cell by binding to integrins. Given to overexpression of αvβ3 and αvβ6 integrin on the surface of the A549 lung cancer cells (Heikkilä et al., 2009), the presence of RGD in NLC formulation increases the cellular uptake of nanoparticles and enhances their therapeutic efficiency (Yoo et al., 2019). Furthermore, overexpression of integrins (RGDs receptors) in vascular endothelial cells of tumor tissue, makes RGD a well-known tumor-targeting peptide (Nieberler et al., 2017). Moreover, given the key role of integrins in cell adhesion and cancer development, RGD containing nanoparticles can inhibit metastasis by blocking the integrins (Hajipour et al., 2019). Comparison accumulation of NLC with NLC-RGD in the cell in uptake experiments established that RGD containing nanoparticles have a great binding affinity to cancerous cells. Due to the in-vitro nature of our study, all beneficial aspects of nanoparticle delivery systems were not observable. In in-vivo systems, NLC-RGD not only deliver their cargo by RGD mediated active targeting, but also provide the drug accumulation into tumor tissue by EPR mediated passive targeting (Kang et al., 2020). In addition, in in-vivo systems nanoparticles are absorbed by Peyer’s patches (M cells) in the small intestine, which results in bypassing the liver and therefore decrease first-pass metabolism (Kakran et al., 2011).
Cell viability and apoptosis experiments showed that co-treatment of A549 cells with GA and DOX is more toxic and more apoptotic compared to DOX. These observations are in accordance with previous studies, which reported that GA prevents cancer development by reversal of the Warburg effect (Ji et al., 2019), motivate reactive oxygen species (ROS) mediated apoptosis, or the mitochondrial-dependent apoptosis pathway (Zhang et al., 2012), G0/G1 phase cell cycle arrest (Gwak et al., 2011), and inhibition of multidrug resistance (MDR) (Lorendeau et al., 2014). In this regard, Yu et al. (Yu et al., 2018) showed that GA decreases the Cisplatin resistance of human lung cancer cells and potentiates apoptosis via Bcl-2 suppression. Inactivating Akt and promoting the Caspase-3 pathway are other mechanisms by which GA inhibits retinoblastoma cell proliferation (Zou and Xu, 2018). Given to Over-expression of specific ABC transporters in several types of cancers and their roles in tumor-initiating (Muriithi et al., 2020), the main aim of this study was to investigate the expression of ABC transporter under the influence of GA loaded NLC-RGD. Downregulation or inhibition of the ABC transporter sensitizes cancer cells to chemotherapeutic agents (Nanayakkara et al., 2018). To our knowledge, this is the first study that reports the downregulation of ABCB1, ABCC1, and ABCC2 as another mechanism by which GA enhances the apoptotic effects of DOX. However, in the opposite of these results, Critchfield et al. (Critchfield et al., 1994) reported that GA stimulates P-glycoprotein efflux of adriamycin in HCT-15 colon carcinoma cells. There is no logical interpret for this controversial report. Our experiments also revealed that the effects of GA on the expression of ABC transporter were strengthened when used in the form of GA loaded-NLC-RGD, confirming the appropriateness of prepared nanoparticles. Results showed that improved targeting of GA makes the DOX more effective for apoptosis induction. Therefore, low doses of DOX can be more effective for cancer inhibition, which in turn decreases the side effects of DOX.