Synthesis and biological activity of fluoroquinolone-pyrrolo[2,1-c][1,4]benzodiazepine conjugates

"Click" reaction mediated synthesis of costunolide and dehydrocostuslactone derivatives and evaluation of their cytotoxic activity

As part of pharmacological-phytochemical integrated studies on medicinal plants from Indian flora, costunolide (1) and dehydrocostus lactone (2), were isolated as major phytochemicals from Saussurea lappa, a plant traditionally used in different Asian systems of medicine. A series of 1,4-disubstituted-1,2,3-triazoles conjugates were synthesized through diastereo selective Michael addition followed by regioselective Huisgen 1,3-dipolar cycloaddition reactions. All these triazolyl derivatives (5a-5j) & (7a-7j) were well characterized using modern spectroscopic techniques and evaluated for their anticancer activity against a panel of five human cancerous celllines. The results indicated that all the analogs displayed moderate cytotoxic activity.

Fe(OTs)3/SiO2: a novel catalyst for the multicomponent synthesis of dibenzodiazepines under solvent-free conditions

An Fe(OTs)₃/SiO₂ catalyst was used as an efficient, recyclable, heterogeneous catalyst for the multicomponent synthesis of dibenzodiazepines.

Computational studies support the role of the C7-sibirosamine sugar of the pyrrolobenzodiazepine (PBD) sibiromycin in transcription factor inhibition

The pyrrolo[2,1-c][1,4]benzodiazepines (PBDs) are a group of sequence-selective, DNA minor-groove binding agents that covalently attach to guanine residues. Originally derived from Streptomyces species, a number of naturally occurring PBD monomers exist with varying A-Ring and C2-substituents. One such agent, sibiromycin, is unusual in having a glycosyl residue (sibirosamine) at its A-Ring C7-position. It is the most cytotoxic member of the naturally occurring PBD family and has the highest DNA-binding affinity. Recently, the analogue 9-deoxysibiromyin was produced biosynthetically by Yonemoto and co-workers.1 Differing only in the loss of the A-Ring C9-hydroxyl group, it was reported to have a significantly higher DNA-binding affinity than sibiromycin based on DNA thermal denaturation studies, although these data have since been retracted.2 As deletion of the C9-OH moiety, which points toward the DNA minor groove floor, might intuitively be expected to reduce DNA-binding affinity through the loss of hydrogen bonding, we carried out molecular dynamics simulations on the interaction of both molecules with DNA over a 10 ns time-course in explicit solvent. Our results suggest that the two molecules may differ in their sequence-selectivity and that 9-deoxysibiromycin should have a lower binding affinity for certain sequences of DNA compared to sibiromycin. Our molecular dynamics results indicate that the C7-sibirosamine sugar does not form hydrogen bonding interactions with groups in the DNA minor-groove wall as previously reported, but instead points orthogonally out from the minor groove where it may inhibit the approach of DNA control proteins such as transcription factors. This was confirmed through a docking study involving sibiromycin and the GAL4 transcription factor, and these results could explain the significantly enhanced cytotoxicity of sibiromycin compared to other PBD family members without bulky C7-substituents.

Pyrrolobenzodiazepines (PBDs) do not bind to DNA G-quadruplexes

The pyrrolo[2,1-c][1,4] benzodiazepines (PBDs) are a family of sequence-selective, minor-groove binding DNA-interactive agents that covalently attach to guanine residues. A recent publication in this journal (Raju et al, PloS One, 2012, 7, 4, e35920) reported that two PBD molecules were observed to bind with high affinity to the telomeric quadruplex of Tetrahymena glaucoma based on Electrospray Ionisation Mass Spectrometry (ESI-MS), Circular Dichroism, UV-Visible and Fluorescence spectroscopy data. This was a surprising result given the close 3-dimensional shape match between the structure of all PBD molecules and the minor groove of duplex DNA, and the completely different 3-dimensional structure of quadruplex DNA. Therefore, we evaluated the interaction of eight PBD molecules of diverse structure with a range of parallel, antiparallel and mixed DNA quadruplexes using DNA Thermal Denaturation, Circular Dichroism and Molecular Dynamics Simulations. Those PBD molecules without large C8-substitutents had an insignificant affinity for the eight quadruplex types, although those with large π-system-containing C8-substituents (as with the compounds evaluated by Raju and co-workers) were found to interact to some extent. Our molecular dynamics simulations support the likelihood that molecules of this type, including those examined by Raju and co-workers, interact with quadruplex DNA through their C8-substituents rather than the PBD moiety itself. It is important for the literature to be clear on this matter, as the mechanism of action of these agents will be under close scrutiny in the near future due to the growing number of PBD-based agents entering the clinic as both single-agents and as components of antibody-drug conjugates (ADCs).

Synthesis and anticancer activity of chalcone-pyrrolobenzodiazepine conjugates linked via 1,2,3-triazole ring side-armed with alkane spacers

Aiming to develop multitarget drugs for the anticancer treatment, a new class of chalcone-pyrrolo[2,1-c] [1,4]benzodiazepine (PBD) conjugates linked through a 1,2,3-triazole moiety containing alkane spacers has been designed and synthesized. Combining these two core pharmacophore structures with modifications at A-C8/C-C2-position of PBD ring system yielded analogs with improved efficacy and have shown promising in vitro anticancer activity ranging from <0.1-2.92 μM. These PBD-conjugates caused G1 cell cycle arrest with effect on G1 cell cycle regulatory proteins such as Cyclin D1 and Cdk4. These conjugates also exhibited inhibitory effect on NF-kB, Bcl-XL proteins that play a vital role in breast cancer cell proliferation. These findings suggest that one of the compound 4d among this series is most effective and has potential for detailed investigations.

1,2,4-Benzothiadiazine linked pyrrolo[2,1-c][1,4]benzodiazepine conjugates: Synthesis, DNA-binding affinity and cytotoxicity

Benzothiadiazine-pyrrolobenzodiazepine conjugates linked through different alkane spacers have been prepared. These new classes of hybrid molecules exhibit cytotoxicity against many cancer cell lines. Their DNA thermal denaturation studies have been carried out and one of the compounds (4b) elevates the DNA helix melting temperature of the CT-DNA by 6.7 degrees C after incubation for 36 h.

Synthesis and in vitro photodynamic activities of water-soluble fluorinated tetrapyridylporphyrins as tumor photosensitizers

A series of water-soluble fluorinated cationic porphyrins were designed, synthesized, and characterized. In vitro photocytotoxicity of these compounds was evaluated by MTT assay on HeLa cells. Their photocytotoxicity was dependent on the positions of the cations and the fluorines in the pyridine ring, and 5,10,15,20-tetrakis-(N-methyl-2-fluoro-pyridin-3-yl)-porphyrin (8) showed the most potent photo-induced cytotoxicity without photobleaching. PDT-induced ROS inside HeLa cells was measured with flow cytometry using ROS-sensitive fluorometric probe, 2,7-dichlorofluororescin (DCF), which revealed high correlations of ROS with cellular cytotoxicity. FACS analysis shows that PDT with porphyrin 8 induced apoptosis in HeLa cells. In summary, efficient generation of ROS, biological effectiveness, and good photostability of porphyrin 8 indicate its potential application in photodynamic therapy (PDT) in the near future.