A sunlight-driven synthesis turns a chemotherapy formulation into gold nanoparticles in minutes, raising questions about how the drug behaves once bound to the particles.
Paper: Synthesis of vincristine-mediated gold nanoparticles and evaluation of their anticancer potential against human colon cancer cells (Colo-205). AI-generated abstract conceptual image created using ChatGPT/OpenAI
In a recent article published in the journal Next Nanotechnology, researchers developed a rapid, one-pot, sunlight-assisted synthesis of vincristine-mediated gold nanoparticles and evaluated their anticancer potential against human colon cancer cells.
Vincristine-AuNPs synthesis rationale
Gold nanoparticles (AuNPs) have gained considerable interest as carriers for chemotherapeutic agents because their unique physicochemical properties can improve drug delivery and anticancer efficacy.
Vincristine (VCR), an alkaloid derived from Catharanthus roseus, is a potent chemotherapy drug used to treat several cancers and studied against colorectal cancer in preclinical models. Conventional methods for preparing drug-loaded AuNPs typically involve multiple steps, including separate reduction, stabilization, and linker chemistry, which complicate the process.
Previous studies have linked vincristine to pre-formed gold nanoparticles using linkers or coatings, but the authors say no prior work reported direct synthesis using vincristine as the reducing and capping agent.
Colorectal cancer is a leading cause of cancer deaths worldwide, which has driven research into safer and more precise treatments. The study aimed to develop a simple, rapid, green approach to synthesize vincristine-associated gold nanoparticles (VCR-AuNPs) via a one-pot photochemical process, using vincristine sulfate injectable solution during sunlight-dependent particle formation.
This approach offers a simpler route to prepare drug-bearing nanoparticles for testing against human colon cancer cells (Colo-205).
Sunlight-assisted one-pot synthesis
The synthesis involved exposing a mixture of gold precursor solution and commercial vincristine sulfate injectable formulation to sunlight at room temperature. Gold nanoparticles formed within 5 minutes without additional reducing or stabilizing agents. Control experiments showed that both light and vincristine, or compounds produced from vincristine during illumination, were required.
Citrate-capped AuNPs were also prepared as controls. The formation and characteristics of VCR-AuNPs were monitored by their surface plasmon resonance (SPR) spectra using UV-Vis spectroscopy.
Structural analysis was performed using X-ray diffraction (XRD) and selected area electron diffraction (SAED), confirming the crystalline nature and face-centered cubic lattice of gold nanoparticles.
Transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA) evaluated morphology, size distribution, and hydrodynamic diameter. The particles were predominantly quasi-spherical, with some triangular and hexagonal plates; the mean core size was around 18 nm, and the modal hydrodynamic diameter was 27 nm.
Fourier-transform infrared spectroscopy (FTIR) was conducted to identify functional groups associated with particle-surface interactions. High-performance liquid chromatography (HPLC) quantified residual vincristine in supernatants to estimate the amount removed from solution during synthesis.
Antioxidant properties were assessed via DPPH radical scavenging assays comparing free vincristine, VCR-AuNPs, and citrate-capped AuNPs. The anticancer potential was evaluated using the sulforhodamine B assay against human colon carcinoma Colo-205 cells to measure growth inhibition, comparing VCR-AuNPs, free vincristine, and citrate AuNPs. Phase-contrast microscopy examined morphological changes in treated cells.
Characterization and anticancer evaluation
The sunlight-assisted synthesis produced VCR-AuNPs within 5 minutes. Longer-term colloidal stability was not measured. The SPR band of VCR-AuNPs was red-shifted to 541 nm compared with citrate-capped AuNPs at 507 nm, consistent with differences in particle size, shape, and the surrounding organic layer.
XRD and SAED confirmed a crystalline face-centered cubic gold lattice.
TEM images showed mainly quasi-spherical nanoparticles with an average core diameter of approximately 18 nm, along with smaller amounts of triangular and hexagonal shapes.
NTA gave a modal hydrodynamic diameter of 27 nm and a mean of 49 ± 44 nm, showing several particle-size populations, including larger particles and aggregates.
FTIR spectra suggested that hydroxyl, amine, and carbonyl groups in vincristine participate in surface interactions and capping. Mannitol in the injectable formulation did not reduce gold in control tests. Its possible contribution to capping was not assessed separately.
HPLC analysis revealed that about one-third (~32.7%) of the initial vincristine was removed from solution, representing an upper bound of intact drug loading onto the nanoparticles because some VCR may have been consumed during reduction or altered by light exposure.
In antioxidant assays, VCR-AuNPs scavenged more DPPH radicals than free vincristine at 10, 20, and 40 µg/mL and more than drug-free citrate AuNPs across the tested range. At 10 µg/mL, VCR-AuNPs scavenged 50.7 ± 1.2%, compared with 31.8 ± 0.7% for free VCR (p < 0.001). This cell-free assay does not show whether the formulation reduces oxidative damage in living tissue.
The cytotoxicity assessment showed that VCR-AuNPs inhibited Colo-205 colon cancer cell proliferation as effectively as free vincristine, with no statistically significant difference between the treatments (p = 0.56) and GI50 values below 10 µg/mL.
Both treatments exceeded 50% growth inhibition at the lowest concentration tested, so the study could not determine their exact potency or show that VCR-AuNPs were more potent than free VCR.
Citrate-capped AuNPs without drug showed minimal toxicity, supporting the interpretation that the antiproliferative effect came from the vincristine payload rather than the gold core. Microscopy images of treated cells showed morphological alterations consistent with antiproliferative effects.
The one-pot synthesis strategy, which uses the vincristine formulation during particle formation, reduces preparation steps by eliminating the need for separate reducing and stabilizing agents.
Implications and future directions
This research describes a one-pot, sunlight-assisted method that avoids separate chemical reducing agents and stabilizers.
The study calls for further work on the reduction mechanism, vincristine photostability, drug release, colloidal stability, particle charge, safety in non-cancerous cells, other colorectal cancer models, and in vivo pharmacokinetics and efficacy. A calibrated light source would also be needed for reproducible scale-up.
Overall, whether this approach offers a therapeutic advantage over free vincristine still needs testing in broader cell models and animals.