Design, synthesis, and biological evaluation of pyrrolo[2,1-c][1,4]benzodiazepine and indole conjugates as anticancer agents

A series of novel pyrrolo[2,1-c][1,4]benzodiazepine (PBD) hybrids linked with indole carboxylates is described. These compounds were prepared by linking C-8 of 3 (DC-81) with an indole 2-carbonyl moiety (9) through carbon chain linkers to afford PBD hybrid agents 17-21 in good yields. Preliminary in vivo tests show that these hybrid agents have potent antitumor activity. The cytotoxic studies of the hybrid agents on human melanoma A2058 cells indicate most of the hybrids induced higher cytotoxicity, better DNA-binding ability, an increase in the apoptotic sub-G1 population, and a significant reduction in deltapsi(mt) relative to compound 3. In addition, DNA flow cytometric analysis shows that hybrids actively induce a marked loss of cells from the G2/M phase of the cell cycle, which progresses to early apoptosis as detected by flow cytometry after double-staining with annexin V and propidium iodide (PI). Thus, we suggest that the hybrid agents are potent inducers of cell apoptosis in A2058 cells.     

Interaction between A 3-nitrobenzothiazolo (3,2-a) quinolinium antitumour drug and deoxyribonucleic acid

The interaction of 3-nitrobenzothiazolo (3,2-a) quinolinium (NBQ) perchlorate with DNA was studied by u.v.-visible and fluorescence spectrophotometry as well as by hydrodynamic methods. On binding to DNA, the absorption spectrum underwent bathochromic and hypochromic shifts, and the fluorescence was quenched. Binding parameters, determined from spectrophotometric measurements by Scatchard analysis according to an excluded-site model, indicated a binding constant of 2.4 × 10⁵ M^?1 for calf thymus DNA at ionic strength 0.01. The interaction was markedly suppressed by increasing the salt concentration. Binding to the GC-rich DNA of Micrococcus lysodeikticus was weaker than the binding to calf thymus DNA at ionic strength 0.01. NBQ increased the viscosity of sonicated rod-like DNA fragments, producing a calculated increment in length of 2.4 Å/bound drug molecule. It removed and reversed the supercoiling of closed circular duplex plasmid pBR322 DNA by virtue of a helix-unwinding angle estimated as approximately 13°/bound ligand molecule. We conclude that the binding of NBQ to DNA occurs by a mechanism of intercalation, which probably accounts for its reported antitumor activity.     

Platinum antitumour agents: A review of (bio)analysis

This paper summarizes analytical techniques in order to get a clear picture of the ins and outs of the (bio)analysis of platinum-containing compounds. The antitumour agent cisplatin has become an indispensable drug for the cure of a variety of cancer diseases. Since its introduc-tion in the early seventies, about 2,000 related platinum complexes were designed to devoid the dose-limiting nephrotoxicity. Some of them were introduced for clinical trial, such as carboplatin and iproplatin. To investigate the mechanism of action and pharmaco-kinetic behaviour, several interesting assays for total and specific platinum determination in biological matrices have been developed, each with its own possibilities and limitations.     

Design, synthesis and in vitro cytotoxicity studies of novel pyrrolo[2,1-c][1,4]benzodiazepine (PBD)--polymade conjugates and 2,2'-PBD dimers

A series of novel pyrrolo[2,1-c][l,4]benzodiazepine (PBD)-polyamide conjugates (1 and 2) and 2,2'-PBD dimers (3, 4 and 5) were synthesized and evaluated for cytotoxicity in >60 human tumor cell lines. In general PBD-polyamide conjugates (1 and 2) exhibit higher cytotoxic potency compared with 2,2'-PBD dimers (3, 4 and 5). Compound 2 exhibits a wide spectrum of anticancer activities against 17 cell lines in six cancer panels with LC50 values of <9 microM, and is especially effective against colon cancer, melanoma, renal cancer and breast cancer. Compound 1 selectively affects cell growth against renal cancer A 498 cell line and compound 4 affects cell growth against breast cancer MDA-MB-231/ATCC cell line with an LC50 value 0.06 microM. Increases in the chain length of the linker in 2,2'-PBD dimers significantly increase the cytotoxic potency and increases in the number of pyrrole groups in the PBD-polyamide conjugates similarly increase the cytotoxic potency.     

Synthesis and antitumour activities of quinolone antineoplastic agents.

DNA topoisomerases, found in all prokaryotic and eukaryotic cells, play a key role in controlling the topological state of DNA. Quinolone antibacterial agents have been shown to be inhibitors of DNA gyrase, a bacterial topoisomerase II enzyme. The eukaryotic topoisomerase II is the target of various cytotoxic agents such as adriamycin and etoposide. Recently, several quinolones having C-8 fluoro and C-8 chloro substituents have been found to have cytotoxic activities and to interact with mammalian topoisomerase II. In searching for an antitumour agent of the quinolone class, we identified several quinolones having excellent in vitro cytotoxic activity. A-74932 also possesses good activity in vivo against both systemic tumour and subcutaneously implanted murine solid tumours as well as human tumour xenografts. The chemical synthesis as well as biological properties of A-74932 are described.     

Synthesis and benzodiazepine receptor binding of 5H-pyrido[2,1-C][1,4]benzothiazines

The pyrido[2,1-c][1,4]benzothiazines 1a-t and the pyrido[2,1-c][1,4]thiazines 7a,b were prepared and tested for their ability to displace specific [3H]diazepam binding from rat brain membranes. Some of the examined compounds of type 1 and 7b showed moderate binding affinity for the benzodiazepine receptor.     

NAD(P)H (quinone acceptor) oxidoreductase (DT-diaphorase)-mediated two-electron reduction of anthraquinone-based antitumour agents and generation of hydroxyl radicals.

The anthraquinone-based antitumour agents mitoxantrone, daunorubicin and ametantrone were found to be substrates for NAD(P)H (quinone acceptor) oxidoreductase (DT-diaphorase) [QAO] isolated from rat liver. This was indicated by the stimulation of QAO-dependent NADPH oxidation by these agents. This effect followed Michaelis-Menten kinetics and was dependent on the concentration of QAO, inhibited by the specific QAO inhibitor dicumarol (15 microM) and enhanced by the QAO activators bovine serum albumin (0.01%) and Triton X-100 (0.03%). As indicated by the Vmax/Km ratio, mitoxantrone (26.53) was considerably more active than ametantrone (11.25) or daunorubicin (7.35). Metabolism of these anthraquinones was associated with the formation of superoxide anions, hydrogen peroxide and hydroxyl radicals as indicated by electron spin resonance spin trapping studies with 5,5-dimethyl-1-pyrroline-N-oxide. This is likely to be due to the slow auto-oxidation of the respective dihydroquinones in the presence of molecular oxygen. QAO needs to be considered as a possible route of bioreductive activation of these agents.     

Enhancement of benzodiazepine binding by progabide (SL 76002) and SL 75102

The new GABA derivatives, progabide (SL 76002) and SL 75102 (the corresponding carboxylic acid), enhanced [³H]diazepam binding to rat cortical membranes. SL 75102 was as effective as GABA, and both were less active than muscimol. Similar to other GABA agonists, progabide and SL 75102 enhanced binding in vitro by an increase in affinity. The elevation of [³H]diazepam binding in the presence of SL 75102 was antagonized by bicuculline. In ex vivo experiments, brain membrane preparations of mice pretreated with progabide were found to bind a greater amount of [³H]diazepam. This increased binding was characterized by an elevation in B_max, while K_D was unaffected. [³H]Flunitrazepam binding to brain in vivo was also enhanced in mice pretreated with progabide. Other GABA agonists (muscimol, THIP, isoguvacine) and GABAergic agents (sodium valproate) elicited an increase in [³H]flunitrazepam binding in vivo. Binding of intravenous [³H]flunitrazepam in vivo may be useful for discovering enhancers of benzodiazepine binding.     

Synthesis and benzodiazepine receptor binding of 1H-pyrrolo[2,1-C][1,4]benzothiazines

The pyrrolo[2,1-c][1,4]benzothiazines 2a-n and the pyrrolo[2,1-c][1,4]thiazine 13 were prepared and tested for their ability to displace specific [3H]diazepam binding from rat brain membranes. Such compounds were found essentially devoid of binding affinity for the benzodiazepine receptor.