Ezequiel Wexselblatt

What do we know about the reduction of Pt(IV) pro-drugs?

Platinum(IV) pro-drugs are an important class of molecules that might improve the pharmacological properties of the platinum(II) anticancer agents that are currently used in the clinic. Their axial ligands that are detached during cellular activation by reductive elimination can be used to confer favorable pharmacological properties to the complexes allowing for potentially lower toxicity and improved efficacy. This manuscript describes the various approaches taken to design and prepare Pt(IV) complexes that will be effective anticancer agents. We review the working hypotheses guiding the researchers in the field while pointing out some more recent results that contradict some of the accepted paradigms in the hope of triggering some rethinking of the existing working hypotheses.

c-di-AMP reports DNA integrity during sporulation in Bacillus subtilis

The bacterium Bacillus subtilis produces the DNA integrity scanning protein (DisA), a checkpoint protein that delays sporulation in response to DNA damage. DisA scans the chromosome and pauses at sites of DNA lesions. Structural analysis showed that DisA synthesizes the small molecule cyclic diadenosine monophosphate (c‐di‐AMP). Here, we demonstrate that the intracellular concentration of c‐di‐AMP rises markedly at the onset of sporulation in a DisA‐dependent manner. Furthermore, exposing sporulating cells to DNA‐damaging agents leads to a global decrease in the level of this molecule. This drop was associated with stalled DisA complexes that halt c‐di‐AMP production and with increased levels of the c‐di‐AMP‐degrading enzyme YybT. Reduced c‐di‐AMP levels cause a delay in sporulation that can be reversed by external supplementation of the molecule. Thus, c‐di‐AMP acts as a secondary messenger, coupling DNA integrity with progression of sporulation.

Relacin, a novel antibacterial agent targeting the Stringent Response.

Finding bacterial cellular targets for developing novel antibiotics has become a major challenge in fighting resistant pathogenic bacteria. We present a novel compound, Relacin, designed to inhibit (p)ppGpp production by the ubiquitous bacterial enzyme RelA that triggers the Stringent Response. Relacin inhibits RelA in vitro and reduces (p)ppGpp production in vivo. Moreover, Relacin affects entry into stationary phase in Gram positive bacteria, leading to a dramatic reduction in cell viability. When Relacin is added to sporulating Bacillus subtilis cells, it strongly perturbs spore formation regardless of the time of addition. Spore formation is also impeded in the pathogenic bacterium Bacillus anthracis that causes the acute anthrax disease. Finally, the formation of multicellular biofilms is markedly disrupted by Relacin. Thus, we establish that Relacin, a novel ppGpp analogue, interferes with bacterial long term survival strategies, placing it as an attractive new antibacterial agent.

Platinum(IV) Prodrugs with Haloacetato Ligands in the Axial Positions can Undergo Hydrolysis under Biologically Relevant Conditions

Losing ligands rapidly: Pt(IV) complexes with haloacetato ligands can hydrolyze rapidly under biological conditions (pH 7 and 37 °C, see scheme) and the rate increases with increasing pH value. Possible mechanisms for this hydrolysis are examined using H2(18)O and ESI-MS analysis.

Design, synthesis and structure–activity relationship of novel Relacin analogs as inhibitors of Rel proteins

Rel proteins in bacteria synthesize the signal molecules (p)ppGpp that trigger the Stringent Response, responsible for bacterial survival. Inhibiting the activity of such enzymes prevents the Stringent Response, resulting in the inactivation of long-term bacterial survival strategies, leading to bacterial cell death. Herein, we describe a series of deoxyguanosine-based analogs of the Relacin molecule that inhibit in vitro the synthetic activity of Rel proteins from Gram positive and Gram negative bacteria, providing a deeper insight on the SAR for a better understanding of their potential interactions and inhibitory activity. Among the inhibitors evaluated, compound 2d was found to be more effective and potent than our previously reported Relacin.

On the Stability of PtIV Pro‐Drugs with Haloacetato Ligands in the Axial Positions

The design of Pt(IV) pro-drugs as anticancer agents is predicated on the assumption that they will not undergo substitution reactions before entering the cancer cell. Attempts to improve the cytotoxic properties of Pt(IV) pro-drugs included the use of haloacetato axial ligands. Herein, we demonstrate that Pt(IV) complexes with trifluoroacetato (TFA) or dichloroacetato (DCA) ligands can be unstable under biologically relevant conditions and readily undergo hydrolysis, which results in the loss of the axial TFA or DCA ligands. The half-lives for Pt(IV) complexes with two TFA or DCA ligands at pH 7 and 37 °C range from 6 to 800 min, which is short relative to the duration of cytotoxicity experiments that last 24-96 h. However, complexes with two monochloroacetato (MCA) or acetato axial ligands are stable under biologically relevant conditions. The loss of the axial ligands depends primarily on the electron-withdrawing strength of the axial ligands, but also upon the nature of the equatorial ligands. We were unable to find obvious correlations between the structures of the Pt(IV) complexes and the rates of decay of the parent compounds. The X-ray crystal structures of the bis-DCA and bis-MCA Pt(IV) derivatives of oxaliplatin did not reveal any significant structural differences that could explain the observed differences in stability.