The thioesterase domain catalyzes chain termination and release of the mature lipopeptide.The molecular engineering of daptomycin, the only marketed acidic lipopeptide antibiotic to date (Figure 8), has seen many advances since its inception into clinical medicine in 2003. It is an attractive target for combinatorial biosynthesis for many reasons: second generation derivatives are currently in the clinic for development;Streptomyces roseosporus, the producer organism of daptomycin, is amenable to genetic manipulation; the daptomycin biosynthetic gene cluster has been cloned, sequenced, and expressed in S. lividans; the lipopeptide biosynthetic machinery has the potential to be interrupted by variations of natural precursors, as well as precursor-directed biosynthesis, gene deletion, genetic exchange, and module exchange; the molecular engineering tools have been developed to facilitate the expression of the three individual NRPS genes from three different sites in the chromosome, using ermEp* for expression of two genes from ectopic loci; other lipopeptide gene clusters, both related and unrelated to daptomycin, have been cloned and sequenced, thus providing genes and modules to allow the generation of hybrid molecules; derivatives can be afforded via chemoenzymatic synthesis; and lastly, efforts in medicinal chemistry are able to further modify these products of molecular engineering.New derivatives of daptomycin (Figure 9) were originally generated by exchanging the third NRPS subunit (dptD) with the terminal subunits from the A54145 (Factor B1) or calcium-dependent antibiotic pathways to create molecules containing Trp13, Ile13, or Val13. dptD is responsible for incorporating the penultimate amino acid, 3-methyl-glutamic acid (3mGlu12), and the last amino acid, Kyn13, into the chain.
Pharmacology
Pharmacodynamics
Darolutamide is a second- or third-generation nonsteroidal antiandrogen (NSAA). It acts as a selective competitive silent antagonist of the androgen receptor (AR), the biological target of androgens like testosterone and dihydrotestosterone (DHT). Its affinity (Ki) for the AR is 11 nM and its functional inhibition (IC50) of the AR is 26 nM. The major metabolite of darolutamide, ketodarolutamide, has similar antiandrogenic activity relative to darolutamide (Ki = 8 nM; IC50 = 38 nM). In addition to its actions as an AR antagonist, darolutamide has been found to act as a silent antagonist of the progesterone receptor (PR), with approximately 1% of the potency of its AR antagonism.A dosage of darolutamide of 1,200 mg/day has been found to result in a mean decrease in prostate specific antigen (PSA) levels of more than 90% in men with prostate cancer. The addition of darolutamide to castration has been found to decrease PSA levels by more than 50% in about 50% of men at 200 mg/day, 69% of men at 400 mg/day, 83% of men at 1,200 mg/day, and 86% of men at 1,400 mg/day.Darolutamide shows some advantages in comparison to enzalutamide and apalutamide, two other second-generation NSAAs. It appears to negligibly cross the blood–brain barrier, and hence has reduced risk of seizures and other central side effects from off-target GABAA receptor inhibition. In accordance with its diminished central penetration, darolutamide does not appear to increase testosterone levels.