Viedma ripening is the attrition-induced spontaneous chiral amplification of a conglomerate crystal mixture. To demonstrate the general nature of this deracemization process, we have extended attrition-enhanced chiral amplification to 10 achiral organic molecules that form conglomerate chiral crystals: benzil (1), diphenyl disulfide (2), benzophenone (3), tetraphenylethylene (4), guanidine carbonate (5), butylated hydroxytoluene (6), hippuric acid (7), ninhydrin (8), cytosine (9), and adeninium dinitrate (10). In these experiments the time required to reach homochirality was as low as 3 h and typically ranged from 25 to 50 h. In most cases amplification to homochirality of both enantiomers was observed in repeat experiments, although often in a nonstochastic fashion, reflecting the scalemic nature of the starting material. We have also demonstrated the utility of quantitative circular dichroism (CD) to determine enantiomeric excess in systems where chirality exists only in the solid-state.
Resistance to chemotherapy in advanced cancers can be mediated by different factors such as epidermal growth factor receptor (EGFR) overexpression and DNA repair enzymes. Therefore, current standards of care usually involve combinations of multiple treatments. Here, to reduce the adverse effects of multiple drug combinations and improve outcome, we proposed a single drug approach to block multiple overlapping effects that characterize chemoresistance. Thus, we designed a new linker that allows assembly of multiple functions (e.g., inhibition of EGFR phosphorylation, induction of DNA lesions, and blockade of their repair) into a single molecule. This led to the successful synthesis of a novel and potent combi-molecule JS230. Here, we demonstrated that in resistant prostate cancer cells overexpressing EGFR, it was capable of (a) inhibiting EGFR in a dose-dependent manner, (b) damaging DNA, and (c) sustaining the damage by inhibiting the DNA repair protein poly(ADP-ribose) polymerase (PARP). The triple mechanism of action of JS230 cumulated into growth inhibitory potency superior to that of classical two-or three-drug combinations.
BackgroundMutations of the DNA repair proteins BRCA1/2 are synthetically lethal with the DNA repair enzyme poly(ADP-ribose) polymerase (PARP), which when inhibited, leads to cell death due to the absence of compensatory DNA repair mechanism. The potency of PARP inhibitors has now been clinically proven. However, disappointingly, acquired resistance mediated by the reactivation of wild type BRCA1/2 has been reported. In order to improve their efficacy, trials are ongoing to explore their combinations with temozolomide (TMZ). Here, in order to enhance potency in BRCA1/2-mutant cells, we report on the design of single molecules termed “combi-molecules” capable of not only inhibiting PARP but also damaging DNA like TMZ, which is known to induce a large number of DNA adducts. The majority of these lesions are processed through PARP-dependent base-excision repair machinery. Paradoxically, the least abundant lesion, the O6-methylguanine adduct is the most cytotoxic. Its repair by the O6-methylguanine DNA methyl transferase (MGMT) confers robust resistance to TMZ. Thus, we surmise that a combi-molecule designed to generate the same DNA adducts as TMZ, with an additional ability to block PARP, could induce BRCA1/2 mutant selective potency and a growth inhibitory profile independent of MGMT status.MethodsThe hydrolysis of EG22 and its stabilized form ZSM02 was analyzed by HPLC and fluorescence spectroscopy. Growth inhibitory potency was determined by SRB assay. PARP inhibition was determined by an enzyme assay and DNA damage by the comet assay. Subcellular distribution was visualized by confocal microscopy.ResultsStudies on EG22 showed that: (a) it inflicted anomalously higher levels of DNA damage than TMZ (b) it induced PARP inhibitory potency in the same range as ANI, a known PARP inhibitor (IC50 = 0.10 μM) (c) it showed strong potency in both BRCA1/2 wild type and mutated cells with 6-fold selectivity for the mutants and it was 65–303-fold more potent than TMZ and 4–63-fold than ANI alone and 3–47-fold than their corresponding equimolar combinations and (d) its potency was independent of MGMT expression.ConclusionThe results in toto suggest that a combi-molecular approach directed at blocking PARP and damaging DNA can lead to single molecules with selective and enhanced potency against BRCA1/2 mutant and with activity independent of MGMT, the major predictive biomarker for resistance to TMZ.
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