Citrus Flavonoid Meets Nuclear Medicine in Twin Radiometal Design for Breast Cancer

A molecule found in orange and lemon peels may be on its way to becoming a two-in-one weapon against breast cancer. In a new computational study published in Heliyon, researchers in Indonesia have modeled what happens when hesperidin, a citrus-derived flavonoid long prized for its antioxidant and anticancer properties, is bound to two of nuclear medicine’s most important metals: technetium and rhenium. Their conclusion is that the two metal complexes are electronically near-twins, yet they behave differently when confronted with breast cancer proteins, a difference that could one day let doctors image a tumor and treat it with the same molecular scaffold.

The idea behind the study is theranostics, a portmanteau of therapy and diagnostics that has become one of the most exciting frontiers in oncology. A theranostic agent combines a targeting molecule with a radioactive payload that can either emit gamma rays for imaging or beta particles for destroying tumor cells. Technetium-99m, with its 140 keV gamma emission and short six-hour half-life, is the workhorse of single-photon emission computed tomography and delivers a minimal radiation burden to patients. Rhenium-186 and rhenium-188, by contrast, emit beta particles that can kill cancer cells, making them therapeutic counterparts. Because technetium and rhenium share nearly identical electronic configurations, they form closely related coordination complexes, which is precisely what makes the pair attractive for matched diagnostic and therapeutic agents built from the same ligand.

Hesperidin is an appealing ligand for this purpose. Abundant in citrus fruits, it carries multiple hydroxyl and phenolic groups that can chelate metal ions effectively, and it has already shown cytotoxic effects in various cancer models through modulation of apoptosis and suppression of cell proliferation. Earlier experimental work showed that flavonoids such as quercetin and genistein can be labeled with technetium with radiochemical purities above 90 percent, reinforcing the idea that polyphenolic scaffolds are well suited to radiometal coordination. The research team, led by Taufik Muhammad Fakih and Muchtaridi Muchtaridi, set out to determine computationally whether hesperidin could serve the same dual role for both technetium and rhenium.

The first stage of the investigation relied on density functional theory. The team built three-dimensional models of both metal-hesperidin complexes, optimized their geometries using the B3LYP hybrid functional, and treated the heavy metal centers with the LANL2DZ effective core potential to capture relativistic effects. Frequency calculations confirmed that each optimized structure represented a true energy minimum with no imaginary frequencies. The frontier molecular orbital analysis revealed striking similarity between the two complexes: the HOMO-LUMO energy gap was 0.08848 Hartree for the rhenium complex and 0.08689 Hartree for the technetium complex, indicating nearly identical chemical reactivity. In both cases, the frontier orbitals remained localized on the aromatic rings and oxygen-containing substituents of hesperidin, showing that metal coordination does not disrupt the ligand’s intrinsic electronic distribution or its pharmacophoric structure.

Subtle differences did emerge from the global reactivity descriptors. The technetium complex showed a slightly higher ionization potential, electron affinity, electronegativity, and electrophilicity index, suggesting a marginally stronger tendency to accept electron density. The rhenium complex, meanwhile, exhibited a higher dipole moment of 7.02 Debye compared with 6.52 Debye for technetium, and greater polarizability, hinting at stronger electrostatic interactions in polar environments. A control calculation using the HSEH1PBE functional on the technetium complex produced broadly consistent trends, supporting the internal reliability of the electronic-structure analysis while underscoring that all of these values remain theoretical predictions.

With the electronic groundwork laid, the researchers turned to molecular docking against five breast cancer-related proteins: the estrogen receptor alpha, HER2, AKT1, EGFR, and PIK3CA. After validating the docking protocol by re-docking each receptor’s co-crystallized ligand, with root-mean-square deviations well below 2.0 angstroms for four of the five targets, they ran 100 independent docking simulations per receptor-ligand pair. The results pointed decisively toward kinase targets. Rhenium-hesperidin bound AKT1 with a binding energy of minus 7.49 kcal/mol, corresponding to a micromolar inhibition constant of 3.21 micromolar, the strongest interaction in the entire panel, supported by an extensive hydrogen-bonding network involving residues such as Asn54, Gln59, and Thr211, and hydrophobic contacts with Trp80, Val270, and Leu264. EGFR followed at minus 5.62 kcal/mol, while the hormone receptor ERα and HER2 showed only weak, millimolar-range binding.

The technetium complex told a complementary story. It also favored AKT1, but with a weaker binding energy of minus 5.17 kcal/mol and an inhibition constant of 163.59 micromolar, and its interactions across the panel were generally less potent and less persistent than those of the rhenium analogue. The researchers interpret this asymmetry as functionally meaningful: the stronger, more stable binding of rhenium-hesperidin suits a therapeutic role, while the weaker, more transient engagement of technetium-hesperidin fits the requirements of an imaging agent, which must bind briefly, reveal its location, and clear away.

To test whether these static snapshots would hold up in a dynamic, water-filled environment, the team ran 100-nanosecond molecular dynamics simulations of the two complexes bound to AKT1 and EGFR, using the AMBER99SB-ILDN force field and custom parameters for the metal centers. Both complexes remained stably accommodated in the binding pockets, with acceptable radius of gyration and solvent-accessible surface area profiles. Hydrogen-bond occupancy analysis was particularly revealing: rhenium-hesperidin achieved a total hydrogen-bond occupancy of 407.72 percent against EGFR, far exceeding the 9.11 percent of the native ligand, with persistent contacts at Met793, Lys745, Ser720, and Thr854, residues central to EGFR kinase activity. Technetium-hesperidin also outperformed the native ligand but with lower overall occupancy, again consistent with more reversible binding.

The binding free-energy estimates from MM-PBSA calculations added a final, and deliberately cautious, layer of nuance. For AKT1, the technetium complex produced the most negative mean binding free energy at minus 282.81 kJ/mol, driven by strong van der Waals contributions, compared with minus 220.48 kJ/mol for rhenium. For EGFR, the picture reversed: rhenium-hesperidin averaged minus 47.73 kJ/mol while the technetium complex averaged a slightly positive 20.15 kJ/mol. The authors are careful to stress that these single-trajectory estimates carry large standard deviations, particularly for EGFR, and should be read as comparative trends rather than a definitive ranking. The apparent discrepancy between docking and MM-PBSA reflects the different theoretical foundations of the two methods, one evaluating static poses with empirical scoring and the other incorporating flexibility and solvation from dynamic trajectories.

The study’s limitations are candidly acknowledged: no experimental validation has yet been performed, the PIK3CA docking failed its re-docking criterion, and each molecular dynamics system was simulated only once. Even so, the work lays a credible theoretical foundation for a genuinely elegant concept, a single citrus flavonoid that could carry a gamma-emitting technetium label into the clinic for imaging breast tumors and a beta-emitting rhenium label for therapy, preferentially engaging the AKT1 and EGFR kinases that drive cancer proliferation and survival. Turning that computational promise into a bedside radiopharmaceutical will require radiolabeling experiments, stability and biodistribution studies, and ultimately clinical testing, but the molecular blueprint now exists, and it smells faintly of oranges.

Subject of Research: Computational evaluation of technetium- and rhenium-labeled hesperidin complexes as radiotheranostic agents for breast cancer

Article Title: Theoretical evaluation of technetium-to-rhenium substitution in hesperidin complexes for breast cancer theranostic potential

Article References: Fakih, T. M., Novitasari, D., Syaifudin, M., & Muchtaridi, M. (2026). Theoretical evaluation of technetium-to-rhenium substitution in hesperidin complexes for breast cancer theranostic potential. Heliyon, 12(15), Article e45458. https://doi.org/10.1016/j.heliyon.2026.e45458

Image Credits: AI Generated

DOI: 10.1016/j.heliyon.2026.e45458

Keywords: hesperidin, technetium-99m, rhenium-188, theranostics, breast cancer, molecular docking, molecular dynamics, DFT, AKT1, EGFR, radiopharmaceuticals, flavonoids