Investigation of metal–organic frameworks (MOFs) for biomedical applications has attracted much attention in recent years. MOFs are regarded as a promising class of nanocarriers for drug delivery owing to well-defined structure, ultrahigh surface area and porosity, tunable pore size, and easy chemical functionalization. In this review, the unique properties of MOFs and their advantages as nanocarriers for drug delivery in biomedical applications were discussed in the first section. Then, state-of-the-art strategies to functionalize MOFs with therapeutic agents were summarized, including surface adsorption, pore encapsulation, covalent binding, and functional molecules as building blocks. In the third section, the most recent biological applications of MOFs for intracellular delivery of drugs, proteins, and nucleic acids, especially aptamers, were presented. Finally, challenges and prospects were comprehensively discussed to provide context for future development of MOFs as efficient drug delivery systems.

BackgroundWhen DNA double-strand breaks (DSB) are induced by ionizing radiation (IR) in cells, histone H2AX is quickly phosphorylated into γ-H2AX (p-S139) around the DSB site. The necessity of DNA-PKcs in regulating the phosphorylation of H2AX in response to DNA damage and cell cycle progression was investigated.ResultsThe level of γH2AX in HeLa cells increased rapidly with a peak level at 0.25 - 1.0 h after 4 Gy γ irradiation. SiRNA-mediated depression of DNA-PKcs resulted in a strikingly decreased level of γH2AX. An increased γH2AX was also induced in the ATM deficient cell line AT5BIVA at 0.5 - 1.0 h after 4 Gy γ rays, and this IR-increased γH2AX in ATM deficient cells was dramatically abolished by the PIKK inhibitor wortmannin and the DNA-PKcs specific inhibitor NU7026. A high level of constitutive expression of γH2AX was observed in another ATM deficient cell line ATS4. The alteration of γH2AX level associated with cell cycle progression was also observed. HeLa cells with siRNA-depressed DNA-PKcs (HeLa-H1) or normal level DNA-PKcs (HeLa-NC) were synchronized at the G1 phase with the thymidine double-blocking method. At ~5 h after the synchronized cells were released from the G1 block, the S phase cells were dominant (80%) for both HeLa-H1 and HeLa-NC cells. At 8 - 9 h after the synchronized cells released from the G1 block, the proportion of G2/M population reached 56 - 60% for HeLa-NC cells, which was higher than that for HeLa H1 cells (33 - 40%). Consistently, the proportion of S phase for HeLa-NC cells decreased to ~15%; while a higher level (26 - 33%) was still maintained for the DNA-PKcs depleted HeLa-H1 cells during this period. In HeLa-NC cells, the γH2AX level increased gradually as the cells were released from the G1 block and entered the G2/M phase. However, this γH2AX alteration associated with cell cycle progressing was remarkably suppressed in the DNA-PKcs depleted HeLa-H1 cells, while wortmannin and NU7026 could also suppress this cell cycle related phosphorylation of H2AX. Furthermore, inhibition of GSK3β activity with LiCl or specific siRNA could up-regulate the γH2AX level and prolong the time of increased γH2AX to 10 h or more after 4 Gy. GSK3β is a negative regulation target of DNA-PKcs/Akt signaling via phosphorylation on Ser9, which leads to its inactivation. Depression of DNA-PKcs in HeLa cells leads to a decreased phosphorylation of Akt on Ser473 and its target GSK3β on Ser9, which, in other words, results in an increased activation of GSK3β. In addition, inhibition of PDK (another up-stream regulator of Akt/GSK3β) by siRNA can also decrease the induction of γH2AX in response to both DNA damage and cell cycle progression.ConclusionDNA-PKcs plays a dominant role in regulating the phosphorylation of H2AX in response to both DNA damage and cell cycle progression. It can directly phosphorylate H2AX independent of ATM and indirectly modulate the phosphorylation level of γH2AX via the Akt/GSK3 β signal pathway.

Consistent discrepancies in the p16/HPV-positivity have been observed in head and neck squamous cell carcinoma (HNSCC). It is therefore questionable, if all HPV+ and/or p16+ tested cancers are HPV-driven. Patients down-staged according to the HPV-dependant TNM are at risk for undertreatment and data in clinical trials may be skewed due to false patient inclusion. We performed a meta-analysis to classify clinical outcomes of the distinct subgroups with combined p16 and HPV detection. 25 out of 1677 publications fulfilled the inclusion criteria. The proportion of the subgroups was 35.6% for HPV+/p16+, 50.4% for HPV−/p16−, 6.7% for HPV−/p16+ and 7.3% for HPV+/P16−. The HPV+/p16+ subgroup had a significantly improved 5-year overall-survival (OS) and disease-free-survival in comparison to others both for HNSCC and oropharyngeal cancers. The 5-year OS of the HPV−/p16+ HNSCC was intermediate while HPV+/p16− and HPV−/p16− had the shortest survival outcomes. The clearly distinct survival of HPV−/p16+ cancers may characterize a new relevant HPV-independent subtype yet to be biologically characterized. The possibility also exists that in some HPV+/p16+ cancers HPV is an innocent bystander and p16 is independently positive. Therefore, in perspective, HPV-testing should distinguish between bystander HPV and truly HPV-driven cancers to avoid potential undertreatment in HPV+ but non-HPV-driven HNSCC.