Liposomal Formulations for Efficient Delivery of a Novel, Highly Potent Pyrimidine-Based Anticancer Drug

<b>Background/Objectives:</b> Cancer is one of the deadliest diseases worldwide. Despite the existing treatments, the adverse side effects and the increasing drug resistance to the current therapies lead to a reduced quality of life for patients and poor prognosis. The pyrimido[5,4-<i>d</i>]pyrimidine compound (<b>PP</b>) was identified as a promising new anticancer drug due to its potent activity against colorectal and triple-negative breast cancers; however it showed poor aqueous solubility and safety profile. This study aimed the synthesis of compound <b>PP</b>, its encapsulation in liposomal formulations based on phosphatidylcholines (PC), the characterization of liposomal formulations and its biological evaluation. <b>Methods:</b> A new synthesis method for <b>PP</b> was developed. The compound was incorporated into different liposomal formulations. The hydrodynamic size, polydispersity, and zeta potential of loaded and non-loaded formulations were measured by DLS. The cytotoxic effects of compound <b>PP</b>, placebo nanoformulations, and <b>PP</b>-loaded nanoformulations were assessed in colorectal (HCT 116) and triple-negative breast cancer (MDA-MB-231) cell lines, as well as in non-tumor BJ-5ta cells. <b>Results:</b> The <b>PP</b> compound was efficiently synthesized. The <b>PP</b>-loaded liposomal formulations exhibit sizes below 150 nm, low polydispersity, and long-time stability upon storage at 4 °C. The antitumor compound was encapsulated with excellent efficiency, and sustained release profiles were obtained. The <b>PP</b> compound showed high activity against HCT 116 (IC₅₀ = 2.04 ± 0.45 µM) and MDA-MB-231 (IC₅₀ = 5.24 ± 0.24 µM) cell lines. DPPC-containing formulations were effective against cancer cells, but showed toxicity comparable to free <b>PP</b> in BJ-5ta normal cells. Conversely, <b>PP-EggPC-Chol-L</b> formulation displayed strong anticancer activity with residual toxicity to normal cells. <b>Conclusions:</b> The <b>PP</b>-loaded liposomal formulation, composed of 70% PC from egg yolk (EggPC) and 30% cholesterol (Chol), designated as <b>PP-EggPC-Chol-L</b>, was the most promising formulation, showing effective anticancer activity in both cancer cell lines and a significant improvement in the safety profile which is of utmost importance to progress to the next phase of drug development.