Drug delivery systems (DDSs) offer efficient and localized drug transportation as well as reduce associated side effects. In order to better understand DDSs, precise observation of drug release and delivery is required. Here, we present a strategy, plasmonic-tunable Raman/fluorescence imaging spectroscopy, to track the release and delivery of an anticancer drug (doxorubicin) from gold nanoparticle carriers in real time at a single living cell level. A pH-responsive drug release profile was attained through the conjugation of doxorubicin (DOX) to the nanoparticle surface via a pH-sensitive hydrazone linkage. When DOX is bound to the surface of the gold nanoparticle, its surface-enhanced Raman spectrum can be seen, but its fluorescence is quenched. When released, due to the lysosomes' acidic pH, its Raman enhancement is greatly reduced, changing the acquired Raman spectrum and in turn allowing for the visualization of its fluorescence signal. The plasmonic-tunable Raman/fluorescence properties enabled the tracking of the DOX release and delivery process from the gold nanoparticle surface to the lysosomes of single living cells under the acidic pH change of their microenvironments. This technique offers great potential to follow the molecular mechanisms of drug delivery and release in living cells, as well as the cellular response to drug action.

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Nanoparticles as potential drug delivery vectors are drawing more attention every day. Here, we used gold nanopspheres (AuNSs) to selectively target the Wnt signaling pathway in human oral squamous cell carcinoma (HSC-3) cells. In a previously conducted study, XAV939, a small inhibiter, was found to strongly regulate the Wnt pathway by inhibiting the tankyrase enzyme and subsequent stabilization of cytoplasmic axin levels. In the present study, conjugating XAV939 molecules to AuNSs is found to enhance its potency by a factor of 20 over its free form in killing the HSC-3 cancer cells. Additionally, XAV 939 uptake studies have demonstrated an enhanced XAV939 bioconjugate delivery to the targeted cells compared to the passive cellular diffusion of the free drug at the same concentration. Furthermore, our study revealed that drug delivery and cytotoxicity are directly related to the size of the functionalized nanoparticles.

Objectives Gold nanoparticles (AuNPs) are used to deliver drugs and therapeutic small molecule inhibitors to cancer cells. Evidence shows that AuNPs coated with nuclear localization sequence can cross the nuclear membrane and induce cellular apoptosis. To determine the therapeutic role of AuNPs, we compared two nanoconstructs conjugated to doxorubicin (DOX) through pH‐sensitive and pH‐resistant linkers. Materials and Methods We tested DOX nanoconjugates' cytotoxicity, cellular and nuclear uptake in oral squamous cell carcinoma cell line. Furthermore, we evaluated the therapeutic effect of pH‐sensitive and pH‐resistant DOX bioconjugates in hamster buccal pouch carcinoma model. Results Our data indicate that pH‐resistant and pH‐sensitive DOX‐nanoconjugates were equally localized in cancer cells, but the pH‐resistant DOX nanoparticles were more localized in the nuclei inducing a 2‐fold increase in the apoptotic effect compared with the pH‐sensitive DOX nanoparticles. Our in vivo results show significantly higher tumor shrinkage and survival rates in animals treated with DOX pH‐resistant AuNPs compared with pH‐sensitive ones. Conclusion Our findings suggest that AuNPs enhance the cytotoxic effect against cancer cells in addition to acting as drug carriers. DOX pH‐resistant AuNPs enhanced accumulation of AuNPs in cancer cells’ nuclei inducing a significant cellular apoptosis which was confirmed using in vitro and in vivo experiments without deleterious effects on blood cell count.

The G1-S checkpoint is thought to prevent cells with damaged DNA from entering S phase and replicating their DNA and efficiently arrests cells at the G1-S transition. Here, using time-lapse imaging and single-cell tracking, we instead find that DNA damage leads to highly variable and divergent fate outcomes. Contrary to the textbook model that cells arrest at the G1-S transition, cells triggering the DNA damage checkpoint in G1 phase route back to quiescence, and this cellular rerouting can be initiated at any point in G1 phase. Furthermore, we find that most of the cells receiving damage in G1 phase actually fail to arrest and proceed through the G1-S transition due to persistent cyclin-dependent kinase (CDK) activity in the interval between DNA damage and induction of the CDK inhibitor p21. These observations necessitate a revised model of DNA damage response in G1 phase and indicate that cells have a G1 checkpoint.