pH-Sensitive doxorubicin delivery using zinc oxide nanoparticles as a rectified theranostic platform: anti-proliferative, apoptotic, cell cycle arrest and radio-distribution studies.

Despite enormous advancements in its management, cancer is the world's primary cause of mortality. Therefore, tremendous strides were made to produce intelligent theranostics with mitigated side effects and improved specificity and efficiency. Thus, we developed a pH-sensitive theranostic platform composed of dextran immobilized zinc oxide nanoparticles, loaded with doxorubicin and radiolabeled with the technetium-99m radionuclide (Tc-labelled DOX-loaded ZnO@dextran). The platform measured 11.5 nm in diameter with -12 mV zeta potential, 88% DOX loading efficiency and 98.5% radiolabeling efficiency. It showed DOX release in a pH-responsive manner, releasing 93.1% cumulatively at pH 5 but just 7% at pH 7.4. It showed improved intracellular uptake, which resulted in a high growth suppressive effect against MCF-7 cancer cells as compared to the free DOX. It boasted a 4 times lower IC than DOX, indicating its significant anti-proliferative potential (0.14 and 0.55 μg ml, respectively). The biological evaluation revealed that its molecular mode of anti-proliferative action included downregulating Cdk-2, which provoked G1/S cell cycle arrest, and upregulating both the intracellular ROS level and caspase-3, which induced apoptosis and necrosis. The experiments in Ehrlich-ascites carcinoma bearing mice demonstrated that DOX-loaded ZnO@dextran showed a considerable 4-fold increase in anti-tumor efficacy compared to DOX. Moreover, by utilizing the diagnostic radionuclide (Tc), the radiolabeled platform (Tc-labelled DOX-loaded ZnO@dextran) was monitored in tumor-bearing mice, revealing high tumor accumulation (14% ID g at 1 h p.i.) and reduced uptake in non-target organs with a 17.5 T/NT ratio at 1 h p.i. Hence, Tc-labelled DOX-loaded ZnO@dextran could be recommended as a rectified tumor-targeted theranostic platform.