Does Oncocalyxone A (oncoA) have intrinsic fluorescence?

Background: Oncocalyxone A (oncoA) is a quinone extracted from the Cordia oncocalyx plant. This compound has pharmacological properties, such as anti-inflammatory, analgesic, and cytotoxic activities, among others. OncoA presents a similar chemical structure to doxorubicin, a drug used in cancer treatment, which possesses an intrinsic fluorescence explored in various studies, including those using doxorubicin-loaded nanoparticles. Thus, due to the chemical structural similarity, the question arose whether oncoA could also show autofluorescence. Therefore, this study proposed to characterize the absorption and emission spectral profiles of oncoA and analyze if this compound could be used as a fluorescent probe.

Methods: For this, fucoidan-coated polyisobutylcyanoacrylate (PIBCA) nanoparticles containing oncoA were prepared, and an uptake study was performed using a human metastatic breast cancer cell line (MDA-MB-231 cells).

Results: OncoA presented a maximum emission wavelength in the blue region, near 430 nm, at 350 nm excitation, compatible with standard microscope optics. Fluorescence microscopy analyses showed that oncoA-loaded PIBCA nanoparticles were internalized by MDA-MB-231 cells under incubation times as shorter as 15 min.

Conclusion: According to these findings, oncoA-encapsulated nanoparticles are promising fluorescent probes and could be useful for cellular uptake studies.