Chemotherapy together with surgery and/or radiotherapy are the most common therapeutic methods for treating cancer. However, the off-target effects of chemotherapy are known to produce side effects and dose-limiting toxicities. Novel delivery platforms based on natural and synthetic polymers with enhanced pharmacokinetic and therapeutic potential for the treatment of cancer have grown tremendously over the past 10 years. Polymers can facilitate selective targeting, enhance and prolong circulation, improve delivery, and provide the controlled release of cargos through various mechanisms, including physical adsorption, chemical conjugation, and/or internal loading. Notably, polymers that are biodegradable, biocompatible, and physicochemically stable are considered to be ideal delivery carriers. This biomimetic and bio-inspired system offers a bright future for effective drug delivery with the potential to overcome the obstacles encountered. This review focuses on the barriers that impact the success of chemotherapy drug delivery as well as the recent developments based on natural and synthetic polymers as platforms for improving drug delivery for treating cancer.

The blood–brain barrier (BBB) is a highly selective and natural protective membrane that restricts the entry of therapeutic agents into the central nervous system (CNS). This restrictive nature poses a major challenge for pharmacological treatment of a wide range of CNS disorders, including neurodegenerative disorders, brain tumors, and psychiatric conditions. Many chemical drugs and biopharmaceuticals are unable to cross the BBB, and conventional drug delivery methods often fail to achieve sufficient brain concentrations, leading to reduced therapeutic efficacy and increased risk of systemic toxicity. In recent years, targeted drug delivery strategies have emerged as promising approaches to overcome the BBB and enhance the delivery of therapeutic agents to the brain. Among these, receptor-mediated transcytosis (RMT) and transporter-mediated transcytosis (TMT) are two of the most extensively studied mechanisms for transporting drugs across brain endothelial cells into the brain parenchyma. Advances in materials science and nanotechnology have facilitated the development of multifunctional carriers with optimized properties, improving drug targeting, stability, and release profiles within the brain. This review summarizes the physiological structure of the BBB and highlights recent innovations in RMT- and TMT-mediated brain drug delivery systems, emphasizing their potential not only to overcome current challenges in CNS drug development, but also to pave the way for next-generation therapies that enable more precise, effective, and personalized treatment of brain-related diseases.

Conformationally restrained polyamine analog PG11047 is a well-known drug candidate that modulates polyamine metabolism and inhibits cancer cell growth in a broad spectrum of cancers. Here, we report a structure–activity relationship study of the PG11047 analogs (HPGs) containing alkyl chains of varying length, while keeping the unsaturated spermine backbone unchanged. Synthesis of higher symmetrical homologues was achieved through a synthetic route with fewer steps than the previous route to PG11047. The amphiphilic HPG analogs underwent self-assembly and formed spherically shaped nanoparticles whose size increased with the hydrophobic alkyl group’s increasing chain length. Assessment of the in vitro anticancer activity showed more than an eight-fold increase in the cancer cell inhibition activity of the analogs with longer alkyl chains compared to PG11047 in human colon cancer cell line HCT116, and a more than ten-fold increase in human lung cancer cell line A549. Evaluation of the inhibition of spermine oxidase (SMOX) showed no activity for PG11047, but activity was observed for its higher symmetrical homologues. Comparison with a reference SMOX inhibitor MDL72527 showed nine-fold better activity for the best performing HPG analog.

Systemically administered lipid nanoparticles (LNPs) predominantly target the liver, limiting their use for extrahepatic applications. Here, we introduce cyclam-based ionizable lipids that confer selective lung tropism after intravenous dosing. A ten-member library spanning three linker chemotypes and varied hydrophobic tails produced LNPs that consistently delivered mRNA to the lung. Lipids with aromatic linkers yielded compact nanoparticles (50–80 nm), with high encapsulation and RNA recovery, and outperformed DLin-MC3-DMA in vitro and in vivo. In Ai9 reporter mice, two intravenous doses of Cre mRNA formulated with lead cyclam lipid achieved ~30% lung editing with minimal off-organ activity. Structure–property analyses showed that increasing lipophilicity and aromatic content correlated inversely with particle size and positively with encapsulation, establishing design rules for macrocycle-guided delivery. Cyclam-based ionizable lipids thus enable systemically administered, lung-selective expression and provide a versatile platform for mRNA and gene-editing therapies.

Overexpression of protein arginine methyltransferase 5 (PRMT5) is pivotal in MYC-driven primary medulloblastoma tumors, suggesting PRMT5 as a potential therapeutic target. JNJ, a potent PRMT5 inhibitor currently in clinical trials, notably for non-Hodgkin lymphoma and lung cancer, was evaluated in this study. We report a validated LC–MS/MS bioanalytical method for quantifying JNJ in plasma and tissue matrices. The method demonstrated acceptable sensitivity, selectivity, and robustness in accordance with regulatory guidelines. The assay was linear over the range 0.2–500 ng mL⁻¹ (r² = 0.99), with plasma recovery exceeding 84% using only 100 µL of sample. Precision (%RSD < 15%) and accuracy (~91–108%) were within acceptable limits. JNJ showed >94% plasma protein binding and moderate Caco-2 permeability (3.4 ± 0.4 × 10⁻⁶ cm s⁻¹). Hepatic intrinsic clearance was higher in mouse liver microsomes than in human (41 ± 19 vs. 7 ± 0.6 mL min⁻¹ kg⁻¹). Following oral dosing in mice (10 mg kg⁻¹), T_max was 30 min with a C_max of 2781 ± 1033 ng mL⁻¹. Oral bioavailability was low (15%). The validated method was successfully applied to in vitro and in vivo studies and will guide dosing in animal models of medulloblastoma.