Pyrrolobenzodiazepines (PBDs) are a group of naturally occurring compounds that were discovered in the cultures of Streptomyces in the 1960s. Some natural PBDs discovered in these cultures, such as anthramycin and sibiromycin, were shown to possess a broad spectrum of anti-tumor activity. Since cancer is still a leading cause of death globally, the development of novel anti-proliferative derivatives of PBDs is essential for human welfare worldwide. Further synthesis and structure-activity relationship (SAR) studies of the parent natural products and their tetracyclic analogs will lead to the discovery of drug candidates. In this work, thirteen PBD analogues were synthesized using no more than three to four synthetic steps, beginning with commercially obtainable L-proline and isatoic anhydride. The MTT assay, which is a colorimetric assay that uses 3-(4,5-Dimethylthiazol-2-Yl)-2,5-diphenyltetrazolium bromide (MTT) to assess cell metabolic activity, was initially implimented to test the in vitro cytotoxicity of the compounds using multiple cell lines, namely: SKBR-3, MCF-7, SKMEL-2, CaCo 2, HCT 116, and Mia Paca. Nearly all of the compounds decreased the cell viability of MCF-7 by roughly 20%. Additionally, the anti-proliferative activity of the PBD products were further evaluated by the NCI-60 Human Tumor Cell Lines Screen, which is a part of the National Cancer Institute’s Development Therapeutics Program - Drug Synthesis and Chemistry Branch.

Pyrrolo [2,1-c] [1,4] benzodiazepine (PBD) is a class of natural products obtained from various actinomycetes which have both anti-tumor and antibiotic activities and can bind to specific sequences of DNA. PBD-dilactam was initially produced using isatoic anhydride and (L)-proline which was then converted to the PBD-thiolactam using Lawesson's reagent. Reaction of thiolactam with hydrazine in ethanol afforded PBD-11-hydrazinyl. Condensation of 11-hydrazinyl PBD with aldehydes possessing various substitutions was performed to obtain (S,E)-11-[2-(arylmethylene) hydrazono] pyrrolo [2,1-c] [1,4] benzodiazepine derivatives. 1HNMR, 13C-NMR, DEPT, IR, GC-MS and X-ray crystallography were used for the characterization. Inhibition activity of the products were carried out using TEM-1, AmpC and P99 β-lactamases. A minimal inhibition growth of 25% was observed for one of the selected PBDs on cancer cell line. A promising result was observed on preliminary cannabinoid binding activity test on one of the compounds.

This study aimed to investigate the pharmacology of selected pyrrolobenzodiazepine (PBD) compounds shown to have cytotoxic activity with predicted DNA sequence selectivity. Research focused upon the PBD dimer, SJG-136, selected for clinical trials, and the novel PBD monomer compounds D709119, MMY-SJG and SJG-303. SJG-136, a novel sequence-selective DNA minor groove cross-linking agent, was shown to have potent tumour cell type selective cytotoxicity in in vitro assays. Pharmacokinetic studies in mice via both the i.p. and i.v. route (dosed at the maximum tolerated dose (MTD)) showed that SJG-136 reaches concentrations in plasma well in excess of the in vitro IC50 values for 1 h exposure, and was detected in tumour and brain samples also above the in vitro IC50 values. Furthermore, SJG-136 showed linear pharmacokinetics over a 3-fold drug dose range. Metabolism studies showed SJG-136 is readily metabolised in vitro by hepatic microsomes, predominantly to a monodemethylated metabolite; this metabolite could be detected in vivo. Analytical method development work was also conducted for the imminent Phase I clinical trial of SJG-136 resulting in a sensitive and selective bio-analytical detection protocol. Comet analysis showed that SJG-136 dosed at the MTD and ⅓MTD causes significant interstrand DNA cross-linking in lymphocytes in vivo. In vitro studies demonstrated that SJG-136 localises within the cell nucleus, and acts to disrupt cell division via a G2/M block in the cell cycle at realistic concentrations and exposure times that are achievable in vivo. In vivo pharmacokinetic studies of D709119 showed the compound is easily detectable in mouse plasma following i.p. dosing at the MTD, but could not be detected in either tumour or brain samples. In vitro cytotoxicity studies revealed D709119 to have potent activity across a selection of tumour cell lines. SJG-136, D709119, MMY-SJG, SJG-303 and DC-81 demonstrated a non-enzyme-catalysed reactivity with the biologically relevant thiol, reduced glutathione (GSH). Studies demonstrated that reactivity of the PBD compounds toward GSH was dependent on GSH concentrations. At levels of GSH found in plasma, the PBD compounds showed considerably lower reactivity with GSH than at intracellular GSH levels. SJG-136 and D709119 also showed favourable pharmacokinetic profiles in mice, and warrant further study for anti-tumour activity in vivo and progression to use in patients.

This study aimed to investigate the pharmacology of selected pyrrolobenzodiazepine (PBD) compounds shown to have cytotoxic activity with predicted DNA sequence selectivity. Research focused upon the PBD dimer, SJG-136, selected for clinical trials, and the novel PBD monomer compounds D709119, MMY-SJG and SJG-303. SJG-136, a novel sequence-selective DNA minor groove cross-linking agent, was shown to have potent tumour cell type selective cytotoxicity in in vitro assays. Pharmacokinetic studies in mice via both the i.p. and i.v. route (dosed at the maximum tolerated dose (MTD)) showed that SJG-136 reaches concentrations in plasma well in excess of the in vitro IC50 values for 1 h exposure, and was detected in tumour and brain samples also above the in vitro IC50 values. Furthermore, SJG-136 showed linear pharmacokinetics over a 3-fold drug dose range. Metabolism studies showed SJG-136 is readily metabolised in vitro by hepatic microsomes, predominantly to a monodemethylated metabolite; this metabolite could be detected in vivo. Analytical method development work was also conducted for the imminent Phase I clinical trial of SJG-136 resulting in a sensitive and selective bio-analytical detection protocol. Comet analysis showed that SJG-136 dosed at the MTD and ⅓MTD causes significant interstrand DNA cross-linking in lymphocytes in vivo. In vitro studies demonstrated that SJG-136 localises within the cell nucleus, and acts to disrupt cell division via a G2/M block in the cell cycle at realistic concentrations and exposure times that are achievable in vivo. In vivo pharmacokinetic studies of D709119 showed the compound is easily detectable in mouse plasma following i.p. dosing at the MTD, but could not be detected in either tumour or brain samples. In vitro cytotoxicity studies revealed D709119 to have potent activity across a selection of tumour cell lines. SJG-136, D709119, MMY-SJG, SJG-303 and DC-81 demonstrated a non-enzyme-catalysed reactivity with the biologically relevant thiol, reduced glutathione (GSH). Studies demonstrated that reactivity of the PBD compounds toward GSH was dependent on GSH concentrations. At levels of GSH found in plasma, the PBD compounds showed considerably lower reactivity with GSH than at intracellular GSH levels. SJG-136 and D709119 also showed favourable pharmacokinetic profiles in mice, and warrant further study for anti-tumour activity in vivo and progression to use in patients.