Enhanced Synergistic Efficacy Against Breast Cancer Cells Promoted by Co-Encapsulation of Piplartine and Paclitaxel in Acetalated Dextran Nanoparticles.

Malignant breast tumors constitute the most frequent cancer diagnosis among women. Notwithstanding the progress in treatments, this condition persists as a major public health issue. Paclitaxel (PTX) is a first-line classical chemotherapeutic drug used as a single active pharmaceutical ingredient (API) or in combination therapy for breast cancer (BC) treatment. Adverse effects, poor water solubility, and inevitable susceptibility to drug resistance seriously limit its therapeutic efficacy in the clinic. Piplartine (PPT), an alkaloid extracted from Piper longum L., has been shown to inhibit cancer cell proliferation in several cell lines due to its pro-oxidant activity. However, PPT has low water solubility and bioavailability in vivo, and new strategies should be developed to optimize its use as a chemotherapeutic agent. In this context, the present study aimed to synthesize a series of acetalated dextran nanoparticles (Ac-Dex NPs) encapsulating PPT and PTX to overcome the limitations of PPT and PTX, maximizing their therapeutic efficacy and achieving prolonged and targeted codelivery of these anticancer compounds into BC cells. Biodegradable, pH-responsive, and biocompatible Ac-Dex NPs with diameters of 100-200 nm and spherical morphologies were formulated using a single emulsion method. Selected Ac-Dex NPs containing only PPT or PTX as well as those coloaded with PPT and PTX achieved excellent drug-loading capabilities (PPT, ca. 11-33%; PTX, ca. 2-14%) and high encapsulation efficiencies (PPT, ∼57-98%; PTX, ∼80-97%). Under physiological conditions (pH 7.4), these NPs exhibited excellent colloidal stability and were capable of protecting drug release, while under acidic conditions (pH 5.5) they showed structural collapse, releasing the therapeutics in an extended manner. Cytotoxicity results demonstrated that the encapsulation in Ac-Dex NPs had a positive effect on the activities of both PPT and PTX against the MCF-7 human breast cancer cell line after 48 h of treatment, as well as toward MDA-MB-231 triple-negative BC cells. PPT/PTX@Ac-Dex NPs were significantly more cytotoxic (IC_50/PPT = 0.25-1.77 μM and IC_50/PTX = 0.07-0.75 μM) and selective (SI = 2.9-6.7) against MCF-7 cells than all the control therapeutic agents: free PPT (IC₅₀ = 4.57 μM; SI = 1.2), free PTX (IC₅₀ = 0.97 μM; SI = 1.0), the single-drug-loaded Ac-Dex NPs, and the physical mixture of both free drugs. All combinations of PPT and PTX resulted in pronounced synergistic antiproliferative effects in MCF-7 cells, with an optimal molar ratio of PPT to PTX of 2.3:1. PPT/PTX-2@Ac-Dex NPs notably promoted apoptosis, cell cycle arrest at the G2/M, accumulation of intracellular reactive oxygen species (ROS), and combined effects from both PPT and PTX on the microtubule network of MCF-7 cells. Overall, the combination of PTX and PPT in pH-responsive Ac-Dex NPs may offer great potential to improve the therapeutic efficacy, overcome the limitations, and provide effective simultaneous delivery of these therapeutics for BC treatment.