Enhanced\nSynergistic Efficacy Against Breast Cancer\nCells Promoted by Co-Encapsulation of Piplartine and Paclitaxel in\nAcetalated Dextran Nanoparticles

Malignant breast tumors constitute the most frequent\ncancer diagnosis\namong women. Notwithstanding the progress in treatments, this condition\npersists as a major public health issue. Paclitaxel (PTX) is a first-line\nclassical chemotherapeutic drug used as a single active pharmaceutical\ningredient (API) or in combination therapy for breast cancer (BC)\ntreatment. Adverse effects, poor water solubility, and inevitable\nsusceptibility to drug resistance seriously limit its therapeutic\nefficacy in the clinic. Piplartine (PPT), an alkaloid extracted from <i>Piper longum</i> L., has been shown to inhibit cancer cell proliferation\nin several cell lines due to its pro-oxidant activity. However, PPT\nhas low water solubility and bioavailability <i>in vivo</i>, and new strategies should be developed to optimize its use as a\nchemotherapeutic agent. In this context, the present study aimed to\nsynthesize a series of acetalated dextran nanoparticles (Ac-Dex NPs)\nencapsulating PPT and PTX to overcome the limitations of PPT and PTX,\nmaximizing their therapeutic efficacy and achieving prolonged and\ntargeted codelivery of these anticancer compounds into BC cells. Biodegradable,\npH-responsive, and biocompatible Ac-Dex NPs with diameters of 100–200\nnm and spherical morphologies were formulated using a single emulsion\nmethod. Selected Ac-Dex NPs containing only PPT or PTX as well as\nthose coloaded with PPT and PTX achieved excellent drug-loading capabilities\n(PPT, ca. 11–33%; PTX, ca. 2–14%) and high encapsulation\nefficiencies (PPT, ∼57–98%; PTX, ∼80–97%).\nUnder physiological conditions (pH 7.4), these NPs exhibited excellent\ncolloidal stability and were capable of protecting drug release, while\nunder acidic conditions (pH 5.5) they showed structural collapse,\nreleasing the therapeutics in an extended manner. Cytotoxicity results\ndemonstrated that the encapsulation in Ac-Dex NPs had a positive effect\non the activities of both PPT and PTX against the MCF-7 human breast\ncancer cell line after 48 h of treatment, as well as toward MDA-MB-231\ntriple-negative BC cells. PPT/PTX@Ac-Dex NPs were significantly more\ncytotoxic (IC<sub>50/PPT</sub> = 0.25–1.77 μM and IC<sub>50/PTX</sub> = 0.07–0.75 μM) and selective (SI = 2.9–6.7)\nagainst MCF-7 cells than all the control therapeutic agents: free\nPPT (IC<sub>50</sub> = 4.57 μM; SI = 1.2), free PTX (IC<sub>50</sub> = 0.97 μM; SI = 1.0), the single-drug-loaded Ac-Dex\nNPs, and the physical mixture of both free drugs. All combinations\nof PPT and PTX resulted in pronounced synergistic antiproliferative\neffects in MCF-7 cells, with an optimal molar ratio of PPT to PTX\nof 2.3:1. PPT/PTX-2@Ac-Dex NPs notably promoted apoptosis, cell cycle\narrest at the G2/M, accumulation of intracellular reactive oxygen\nspecies (ROS), and combined effects from both PPT and PTX on the microtubule\nnetwork of MCF-7 cells. Overall, the combination of PTX and PPT in\npH-responsive Ac-Dex NPs may offer great potential to improve the\ntherapeutic efficacy, overcome the limitations, and provide effective\nsimultaneous delivery of these therapeutics for BC treatment.