Conditionally replicating adenoviruses kill tumor cells via a basic apoptotic machinery-independent mechanism that resembles necrosis-like programmed cell death

Conditionally replicating adenoviruses (CRAds) represent a promising class of novel anticancer agents that are used for virotherapy. The E1ADelta24 mutation-based viruses, Ad5-Delta24 [CRAd(E3-); E3 region deleted] and infectivity-enhanced Ad5-Delta24RGD [CRAd(E3+)] have been shown to potently eradicate tumor cells. The presence of the E3 region in the latter virus is known to improve cell killing that can be attributed to the presence of the oncolysis-enhancing Ad death protein. The more precise mechanism by which CRAds kill tumor cells is unclear, and the role of the host cell apoptotic machinery in this process has been addressed only in a limited way. Here, we examine the role of several major apoptotic pathways in the CRAd-induced killing of non-small-cell lung cancer H460 cells. As expected, CRAd(E3+) was more potent than CRAd(E3-). No evidence for the involvement of the p53-Bax apoptotic pathway was found. Western blot analyses demonstrated strong suppression of p53 expression and unchanged Bax levels during viral replication, and stable overexpression of human papillomavirus type 16-E6 in H460 cells did not affect killing by both CRAds. CRAd activity was also not hampered by stable overexpression of anti-apoptotic Bcl2 or BclXL, and endogenous Bcl2/BclXL protein levels remained constant during the oncolytic cycle. Some evidence for caspase processing was obtained at late time points after infection; however, the inhibition of caspases by the X-linked inhibitor of apoptosis protein overexpression or cotreatment with zVAD-fmk did not inhibit CRAd-dependent cell death. Analyses of several apoptotic features revealed no evidence for nuclear fragmentation or DNA laddering, although phosphatidylserine externalization was detected. We conclude that despite the known apoptosis-modulating abilities of individual Ad proteins, Ad5-Delta24-based CRAds trigger necrosis-like cell death. In addition, we propose that deregulated apoptosis in cancer cells, a possible drug resistance mechanism, provides no barrier for CRAd efficacy.     

Identification and evaluation of glutathione conjugate gamma-l-glutamyl-l-cysteine for improved drug delivery to the brain

Abstract

Glutathione (GU), an endogenous antioxidant tripeptide, is frequently transferred in the human brain through N-methyl-d-aspartate receptor (NMDAR), profusely expressed at the blood–brain barrier (BBB) junction. GU, also modifies the characteristics of tight junction proteins (occludin and claudin) at the site of BBB by depolarizing the enzyme, protein tyrosine phosphatase that manifests its usefulness for passive delivery of nanocarriers to the brain. GU, thus, represents itself as an ideal ligand for the surface decoration of nanocarriers to successfully administer them across the brain via receptor-mediated drug delivery pathway. Hence, we have employed here, in-silico approaches to identify the potential GU-like molecules, as appropriate ligand(s) for surface engineering of nanoconstruct with the purpose of attaining targeted drug delivery to the brain. Structure-based virtual screening methods was used to filter PubChem database for the identification of bioactive compounds with >95% structure similarity with GU. We have further screened the compounds against NMDAR using molecular docking approach. Top hits were selected based on their high binding affinities and selectivity towards NMDAR, and their binding pattern was analysed in detail. Finally, all atom molecular dynamics simulation for 100?ns was carried out on free NMDAR and in-presence of the selected GU-like compound, gamma-l-glutamyl-l-cysteine to evaluate complex stability and structural dynamics. In conclusion, gamma-l-glutamyl-l-cysteine may act as potential binding partner of NMDAR which can further be evaluated in drug delivery system to brain across the BBB.

Communicated by Ramaswamy H. Sarma