The core problem is delivery. The blood–brain barrier, a tightly packed layer of endothelial cells lining the brain’s blood vessels, blocks more than 98 percent of small-molecule drugs and virtually all large molecules. In glioblastoma, a second obstacle appears: the blood–brain–tumor barrier, which is patchy and inconsistent, leaving large regions of the tumor effectively unreachable. Even where drugs do penetrate, elevated interstitial fluid pressure inside the tumor pushes fluid—and anything dissolved in it—back toward healthy tissue, while a dense extracellular matrix physically impedes the diffusion of nanoparticles. Efflux pumps such as P-glycoprotein actively expel chemotherapy agents that manage to enter tumor cells. The result is that standard-of-care temozolomide, the oral alkylating agent given after surgery and radiotherapy, reaches only a fraction of the tumor mass, and the disease almost invariably recurs.

The review’s central argument is that these barriers can be turned into an advantage by exploiting a molecular quirk of glioblastoma cells: they overexpress folate receptors. These receptors, normally responsible for capturing vitamin B9 from the bloodstream, sit on the cell surface and bind folic acid with extraordinarily high affinity. Crucially, folate receptor uptake occurs through receptor-mediated endocytosis, a process in which the cell literally swallows anything attached to the ligand. By chemically grafting folic acid onto the surface of a nanoparticle, researchers create a vehicle that tumor cells actively pull inside themselves. Because folate receptors are largely absent from most healthy adult tissues, the strategy offers a built-in selectivity mechanism that conventional chemotherapy lacks entirely.

The chemistry behind this targeting is more sophisticated than simply sticking a vitamin onto a particle. The review describes two principal conjugation routes. Direct ligand coupling attaches folic acid straight to functional groups on the nanoparticle surface, typically through the gamma carboxyl group of glutamate, which preserves the vitamin’s binding face for the receptor. Linker-assisted surface modification, by contrast, uses spacer molecules—often polyethylene glycol—to project the folate ligand away from the particle surface, reducing steric hindrance and improving receptor engagement. Common coupling reagents include carbodiimide chemistry such as EDC and NHS esters, which form stable amide bonds between the folate and amine- or carboxyl-bearing polymer surfaces. The length and flexibility of these linkers matter enormously: a folate buried against the particle surface may never contact its receptor, while one tethered on a sufficiently long spacer can bind even when the particle itself is too bulky to approach the membrane closely.

The nanocarriers themselves span a remarkable range of materials. Poly(lactic-co-glycolic acid), or PLGA, a biodegradable polymer approved by regulators for other uses, can encapsulate hydrophobic drugs and release them slowly as it erodes. Liposomes, spherical vesicles built from phospholipid bilayers, carry both water-soluble and lipid-soluble payloads. Human serum albumin nanoparticles, magnetic iron oxide particles known as SPIONs, quantum dots, carbon nanotubes, and boron nitride nanotubes have all been folate-functionalized in experimental studies. Each platform brings its own theranostic capability: SPIONs serve as magnetic resonance imaging contrast agents and can generate heat under alternating magnetic fields for magnetic hyperthermia, while quantum dots and near-infrared dyes such as IR-780 enable fluorescence imaging that can guide surgical resection or monitor treatment response in real time.

Preclinical evidence reviewed by the authors suggests the strategy delivers measurable gains. In rat models of glioma, temozolomide loaded into folate-conjugated magnetic triblock copolymer nanoparticles improved therapeutic outcomes compared with free drug, with the magnetic component additionally enabling image-guided delivery and hyperthermia sensitization. Folate-targeted erlotinib, an epidermal growth factor receptor inhibitor, delivered in human serum albumin nanoparticles reduced tumor size and extended survival in glioblastoma-bearing rats. Liposomal formulations carrying combinations of temozolomide and the antimalarial artesunate have shown activity against drug-resistant tumors, while folate-modified lipid–polymer hybrid nanoparticles have improved paclitaxel delivery to intracranial disease. Dual-targeting systems that pair folate with glucose or other brain-shuttle ligands aim to solve the two-stage problem—first crossing the blood–brain barrier, then engaging tumor cells—by combining a transcytosis trigger with a receptor-homing ligand on the same particle.

The theranostic concept is what distinguishes these systems from ordinary targeted drug delivery. A single nanoparticle can simultaneously carry a chemotherapeutic payload, an imaging agent, and sometimes a physical therapy modality such as photothermal or photodynamic activation. This integration means clinicians could, in principle, visualize exactly where a drug has accumulated before and during treatment, adjusting dosing on the basis of real-time tumor mapping rather than population averages. For a disease like glioblastoma, where surgical margins are notoriously ambiguous and response assessment with conventional MRI is complicated by treatment-related changes that mimic progression, the diagnostic half of the theranostic pair could be as valuable as the therapeutic half.

Safety, however, remains the field’s unresolved question. The review notes that folate-armed nanotheranostics have so far shown good biocompatibility and low systemic toxicity in experimental settings, a benefit attributed partly to the reduced off-target exposure that receptor targeting provides. Yet the authors are explicit that long-term safety has not been established. Nanoparticles can persist in organs of the reticuloendothelial system, accumulate in the liver and spleen, and interact with the protein corona that forms on their surfaces in blood—a layer of adsorbed proteins that can alter both targeting behavior and immune recognition. Degradation products of some nanomaterials raise their own toxicological concerns, and the behavior of these particles over years rather than weeks is essentially unknown. Translating encouraging rodent data into human trials will require answering these questions systematically.

There are also biological caveats. Folate receptor expression varies between patients and even between regions of the same tumor, meaning a folate-targeted therapy could miss receptor-negative cell populations and select for resistant clones. The reduced folate carrier, an alternative folate transport pathway, complicates the targeting picture in some tissues. And the fundamental delivery problem of crossing an intact blood–brain barrier has not vanished; folate targeting addresses the tumor-cell engagement step far better than the barrier-crossing step, which is why combination strategies and convection-enhanced delivery techniques continue to be explored alongside receptor targeting.

Even with these caveats, the convergence of folate chemistry, nanomaterial engineering, and imaging technology represents a genuinely integrated response to a disease that has defeated nearly every conventional approach. The review by Bari and Pardeshi consolidates a decade and a half of work—from the foundational demonstration that folate receptors could be exploited for tumor imaging and drug delivery, through the structural determination of how folic acid is recognized by its receptor, to the current generation of multifunctional, dual-targeted, image-guided platforms. No folate-armed nanotheranostic has yet completed clinical development for glioblastoma, and the gap between mouse and human brain remains wide. But the logic of the approach—turning the tumor’s own appetite for folate into a delivery mechanism that carries both medicine and a camera—offers something glioblastoma patients have rarely had: a way to see the target and hit it at the same time. Whether that promise survives the long road of safety testing and clinical validation will be one of the more consequential stories in neuro-oncology over the coming decade.

Subject of Research: Folate-conjugated nanotheranostic platforms for targeted diagnosis and treatment of glioblastoma

Article Title: Nanotheranostics armed with folate: an integrated approach for precision targeting of glioblastoma

Article References: Bari, D. B., & Pardeshi, C. V. (2026). Nanotheranostics armed with folate: an integrated approach for precision targeting of glioblastoma. Medical Oncology, 43(10), Article 283. https://doi.org/10.1007/s12032-026-03363-x

Image Credits: AI Generated

DOI: 10.1007/s12032-026-03363-x

Keywords: glioblastoma, nanotheranostics, folate receptors, blood–brain barrier, drug delivery, nanoparticles, temozolomide, targeted therapy, brain cancer, theranostics, nanomedicine, molecular imaging