Green Nanotechnology Through Papain Nanoparticles: Preclinical in vitro and in vivo Evaluation of Imaging Triple-Negative Breast Tumors.

Background: Recent advancements in nanomedicine and nanotechnology have expanded the scope of multifunctional nanostructures, offering innovative solutions for targeted drug delivery and diagnostic agents in oncology and nuclear medicine. Nanoparticles, particularly those derived from natural sources, hold immense potential in overcoming biological barriers to enhance therapeutic efficacy and diagnostic accuracy. Papain, a natural plant protease derived from Carica papaya, emerges as a promising candidate for green nanotechnology-based applications due to its diverse medicinal properties, including anticancer properties.

Purpose: This study presents a novel approach in nanomedicine and oncology, exploring the potential of green nanotechnology by developing and evaluating technetium-99m radiolabeled papain nanoparticles (^99mTc-P-NPs) for imaging breast tumors. The study aimed to investigate the efficacy and specificity of these nanoparticles in breast cancer models through preclinical in vitro and in vivo assessments.

Methods: Papain nanoparticles (P-NPs) were synthesized using a radiation-driven method and underwent thorough characterization, including size, surface morphology, surface charge, and cytotoxicity assessment. Subsequently, P-NPs were radiolabeled with technetium-99m (^99mTc), and in vitro and in vivo studies were conducted to evaluate cellular uptake at tumor sites, along with biodistribution, SPECT/CT imaging, autoradiography, and immunohistochemistry assays, using breast cancer models.

Results: The synthesized P-NPs exhibited a size mean diameter of 9.3 ± 1.9 nm and a spherical shape. The in vitro cytotoxic activity of native papain and P-NPs showed low cytotoxicity in HUVEC, MDA-MB231, and 4T1 cells. The achieved radiochemical yield was 94.2 ± 3.1% that were sufficiently stable (≥90%) for 6 h. The tumor uptake achieved in the 4T1 model was 2.49 ± 0.32% IA/g at 2 h and 1.51 ± 0.20% IA/g at 6 h. In the spontaneous breast cancer model, 1.19 ± 0.20% IA/g at 2 h and 0.86 ± 0.31% IA/g at 6 h. SPECT/CT imaging has shown substantial tumor uptake of the new nanoradiopharmaceutical and clear tumor visualization. ^99mTc-P-NPs exhibited a high affinity to tumoral cells confirmed by ex vivo autoradiography and immunohistochemistry assays.

Conclusion: The findings underscore the potential of green nanotechnology-driven papain nanoparticles as promising agents for molecular imaging of breast and other tumors through SPECT/CT imaging. The results represent a substantial step forward in the application of papain nanoparticles as carriers of diagnostic and therapeutic radionuclides to deliver diagnostic/therapeutic payloads site-specifically to tumor sites for the development of a new generation of nanoradiopharmaceuticals.