A Novel Anticancer Agent, 8-Methoxypyrimido[4′,5′:4,5]thieno(2,3-b) Quinoline-4(3H)-One Induces Neuro 2a Neuroblastoma Cell Death through p53-Dependent,Caspase-Dependent and -Independent Apoptotic Pathways

Neuroblastoma is the most common cancer in infants and fourth most common cancer in children. Despite recent advances in cancer treatments, the prognosis of stage-IV neuroblastoma patients continues to be dismal which warrant new pharmacotherapy. A novel tetracyclic condensed quinoline compound, 8-methoxypyrimido [4′,5′:4,5]thieno(2,3-b) quinoline-4(3H)-one (MPTQ) is a structural analogue of an anticancer drug ellipticine and has been reported to posses anticancer property. Study on MPTQ on neuroblastoma cells is very limited and mechanisms related to its cytotoxicity on neuroblastoma cells are completely unknown. Here, we evaluated the anticancer property of MPTQ on mouse neuro 2a and human SH-SY5Y neuroblastoma cells and investigated the mechanisms underlying MPTQ-mediated neuro 2a cell death. MPTQ-mediated neuro 2a and SH-SY5Y cell deaths were found to be dose and time dependent. Moreover, MPTQ induced cell death reached approximately 99.8% and 90% in neuro 2a and SH-SY5Y cells respectively. Nuclear oligonucleosomal DNA fragmentation and Terminal dUTP Nick End Labelling assays indicated MPTQ-mediated neuro 2a cell death involved apoptosis. MPTQ-mediated apoptosis is associated with increased phosphorylation of p53 at Ser15 and Ser20 which correlates with the hyperphosphorylation of Ataxia-Telangiectasia mutated protein (ATM). Immunocytochemical analysis demonstrated the increased level of Bax protein in MPTQ treated neuro 2a cells. MPTQ-mediated apoptosis is also associated with increased activation of caspase-9, -3 and -7 but not caspase-2 and -8. Furthermore, increased level of caspase-3 and cleaved Poly (ADP Ribose) polymerase were observed in the nucleus of MPTQ treated neuro 2a cells, suggesting the involvement of caspase-dependent intrinsic but not extrinsic apoptotic pathway. Increased nuclear translocation of apoptosis inducing factor suggests additional involvement of caspase-independent apoptosis pathway in MPTQ treated neuro 2a cells. Collectively, MPTQ-induced neuro 2a cell death is mediated by ATM and p53 activation, and Bax-mediated activation of caspase-dependent and caspase-independent mitochondrial apoptosis pathways.     

Pharmacokinetic, biodistribution, and biophysical profiles of TNF nanobodies conjugated to linear or branched poly(ethylene glycol)

Covalent attachment of poly(ethylene glycol) (PEG) to therapeutic proteins has been used to prolong in vivo exposure of therapeutic proteins. We have examined pharmacokinetic, biodistribution, and biophysical profiles of three different tumor necrosis factor alpha (TNF) Nanobody-40 kDa PEG conjugates: linear 1 × 40 KDa, branched 2 × 20 kDa, and 4 × 10 kDa conjugates. In accord with earlier reports, the superior PK profile was observed for the branched versus linear PEG conjugates, while all three conjugates had similar potency in a cell-based assay. Our results also indicate that (i) a superior PK profile of branched versus linear PEGs is likely to hold across species, (ii) for a given PEG size, the extent of PEG branching affects the PK profile, and (iii) tissue penetration may differ between linear and branched PEG conjugates in a tissue-specific manner. Biophysical analysis (R(g)/R(h) ratio) demonstrated that among the three protein-PEG conjugates the linear PEG conjugate had the most extended time-average conformation and the most exposed surface charges. We hypothesized that these biophysical characteristics of the linear PEG conjugate accounts for relatively less optimal masking of sites involved in elimination of the PEGylated Nanobodies (e.g., intracellular uptake and proteolysis), leading to lower in vivo exposure compared to the branched PEG conjugates. However, additional studies are needed to test this hypothesis.     

Investigation of the probable homo-dimer model of the Xeroderma pigmentosum complementation group A (XPA) protein to represent the DNA-binding core

The Xeroderma pigmentosum complementation group A (XPA) protein functions as a primary damage verifier and as a scaffold protein in nucleotide excision repair (NER) in all higher organisms. New evidence of XPA’s existence as a dimer and the redefinition of its DNA-binding domain (DBD) raises new questions regarding the stability and functional position of XPA in NER. Here, we have investigated XPA’s dimeric status with respect to its previously defined DBD (XPA_98-219) as well as with its redefined DBD (XPA_98-239). We studied the stability of XPA_98-210 and XPA_98-239 homo-dimer systems using all-atom molecular dynamics simulation, and we have also characterized the protein–protein interactions (PPI) of these two homo-dimeric forms of XPA. After conducting the root mean square deviation (RMSD) analyses, it was observed that the XPA_98-239 homo-dimer has better stability than XPA_98-210. It was also found that XPA_98-239 has a larger number of hydrogen bonds, salt bridges, and hydrophobic interactions than the XPA_98-210 homo-dimer. We further found that Lys, Glu, Gln, Asn, and Arg residues shared the major contribution toward the intermolecular interactions in XPA homo-dimers. The binding free energy (BFE) analysis, which used the molecular mechanics Poisson–Boltzmann method (MM-PBSA) and the generalized Born and surface area continuum solvation model (GBSA) for both XPA homo-dimers, also substantiated the positive result in favor of the stability of the XPA_98-239 homo-dimer.

Communicated by Ramaswamy H. Sarma