Ro 63-9141 is a new member of the pyrrolidinone-3-ylidenemethyl cephem series of cephalosporins. Its antibacterial spectrum was evaluated against significant gram-positive and gram-negative pathogens in comparison with those of reference drugs, including cefotaxime, cefepime, meropenem, and ciprofloxacin. Ro 63-9141 showed high antibacterial in vitro activity against gram-positive bacteria except ampicillin-resistant enterococci, particularly vancomycin-resistant strains of Enterococcus faecium. Its MIC at which 90% of the isolates tested were inhibited (MIC 90 ) for methicillin-resistant Staphylococcus aureus (MRSA) was 4 g/ml. Ro 63-9141 was bactericidal against MRSA. Development of resistance to the new compound in MRSA was not observed. Ro 63-9141 was more potent than cefotaxime against penicillin-resistant Streptococcus pneumoniae (MIC 90 ‫؍‬ 2 g/ml). It was active against ceftazidime-susceptible strains of Pseudomonas aeruginosa and against Enterobacteriaceae except Proteus vulgaris and some isolates producing extended-spectrum ␤-lactamases. The basis for the antibacterial spectrum of Ro 63-9141 lies in its affinity to essential penicillin-binding proteins, including PBP 2 of MRSA, and its stability towards ␤-lactamases. The in vivo findings were in accordance with the in vitro susceptibilities of the pathogens. These data suggest the potential utility of Ro 63-9141 for the therapy of infections caused by susceptible pathogens, including MRSA. Since insufficient solubility of Ro 63-9141 itself precludes parenteral administration in humans, a water-soluble prodrug, Ro 65-5788, is considered for development.Methicillin-resistant staphylococci (MRS) have become a serious problem in many parts of the world. Although the incidence of strains of methicillin-resistant Staphylococcus aureus (MRSA), methicillin-resistant Staphylococcus epidermidis (MRSE), and other MRS varies from country to country and from hospital to hospital (3, 5), it has been steadily increasing worldwide in the last decade (10,18,19). MRS are resistant not only to the available ␤-lactam antibiotics, but also, in most instances, to structurally unrelated classes of antibacterials (for mainly unknown reasons) and thus represent a prime target in the current search for new antimicrobials.MRS are characterized by the expression of a special penicillin-binding protein (PBP), PBP 2Ј, that is not present in methicillin-susceptible staphylococci. This PBP is causally connected with methicillin resistance, as it functions as a transpeptidase and is not efficiently inhibited by commercially available ␤-lactams, in contrast to the other transpeptidases in staphylococci, PBP 1, PBP 2, and PBP 3. However, the poor affinity of PBP 2Ј for ␤-lactam antibiotics does not seem to be inherent in the ␤-lactam structure since new carbapenems and cephalosporins that are good inhibitors of PBP 2Ј have recently been described (1,6,11,12,14,20).Ro 63-9141, the active principle of the water-soluble prodrug Ro 65-5788, is a novel parenteral cephalosporin with broad-spe...

Resistance to cefotaxime (CTA) and ceftriaxone (CTR) in Enterobacter cloacae and Pseudomonas aeruginosa was investigated in several strains which are susceptible or resistant to these agents. All strains produced a chromosomally mediated cephalosporinase of the Richmond type I. P-Lactamases in susceptible strains were inducible, whereas resistant strains produced the enzymes constitutively. CTA and CTR were very poor substrates but potent inhibitors of all enzymes. Binding to, rather than hydrolysis by, ,B-lactamases was assumed to be a major reason for resistance, and combination experiments supported this assumption. Dicloxacillin, which did not inhibit the growth and which was a poor inducer but a strong inhibitor of these P-lactamases, exerted strong synergistic activity when combined with CTA or CTR in strains which produced large amounts of Plactamase constitutively. Cefoxitin, on the other hand, poorly active alone, but a good inducer, strongly antagonized CTA or CTR in susceptible strains producing inducible enzymes. In marked contrast to CTA and CTR were the findings with cefsulodin. Cefsulodin was active against CTA-and CTR-resistant Pseudomonas, and its activity was hardly influenced by dicloxacillin or cefoxitin. Since cefsulodin was found to have a very low affinity for all cephalosporinases, these findings corroborate the assumption that binding of nonhydrolyzable cephalosporins, rather than hydrolysis by cephalosporinases, may play an important role in resistance to these agents and other newer cephalosporins in Enterobacteriaceae, as well as in other gram-negative bacteria.

Cyclothialidine (1, Ro 09-1437) is a potent DNA gyrase inhibitor that was isolated from Streptomyces filipinensis NR0484 and is a member of a new family of natural products. It acts by competitively inhibiting the ATPase activity exerted by the B subunit of DNA gyrase but barely exhibits any growth inhibitory activity against intact bacterial cells, presumably due to insufficient permeation of the cytoplasmic membrane. To explore the antibacterial potential of 1, we developed a flexible synthetic route allowing for the systematic modification of its structure. From a first set of analogues, structure-activity relationships (SAR) were established for different substitution patterns, and the 14-hydroxylated, bicyclic core (X) of 1 seemed to be the structural prerequisite for DNA gyrase inhibitory activity. The variation of the lactone ring size, however, revealed that activity can be found among 11- to 16-membered lactones, and even seco-analogues were shown to maintain some enzyme inhibitory properties, thereby reducing the minimal structural requirements to a rather simple, hydroxylated benzyl sulfide (XI). On the basis of these "minimal structures" a modification program afforded a number of inhibitors that showed in vitro activity against Gram-positive bacteria. The best activities were displayed by 14-membered lactones, and representatives of this subclass exhibit excellent and broad in vitro antibacterial activity against Gram-positive pathogens, including Staphylococcus aureus, Streptococcus pyogenes, and Enterococcus faecalis, and overcome resistance against clinically used drugs. By improving the pharmacokinetic properties of the most active compounds (94, 97), in particular by lowering their lipophilic properties, we were able to identify congeners of cyclothialidine (1) that showed efficacy in vivo.

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Ro 13-9904, a new parenteral cephalosporin, was found to have high in vitro activity against Enterobacteriaceae and other gram-negative bacteria, including various isolates resistant to cefuroxime, cefamandole, cefoxitin, and cefazolin. It showed promising activity against Pseudomonas aeruginosa. Although inhibitory against Staphylococcus aureus at concentrations readily achievable in plasma, it was less potent against this pathogen than cefamandole, cefazolin, or cefuroxime.Isolates of Streptococcus faecalis were uniformly resistant to all the cephalosporins tested. Ro 13-9904 was more active than cefotaxime against Proteus mirabilis, Neisseria gonorrhoeae, Neisseria meningitidis, and Haemophilus influenzae, but less active against S. aureus. Ro 13-9904 was stable to various types of f,-lactamases. Its therapeutic efficacy against experimental septicemias in mice was equal to or slightly superior to that of cefotaxime and SCE-1365 when the antibiotics were administered in repeated subcutaneous doses after bacterial challenge. Cefoperazone, and particularly cefamandole nafate, cefazolin, and mezlocillin were less effective. Although structurally related to cefotaxime and SCE-1365, Ro 13-9904 was found to differ from them in one important respect, namely, in having a long duration of action; this was observed with single-dose treatment given before bacterial challenge. Its broad spectrum of activity coupled with favorable pharmacokinetic properties make Ro 13-9904 a promising compound for clinical studies.Since the development of cephalothin and cephaloridine, the first cephalosporins on the market, the antibacterial potency of this attractive class of antibiotics has undergone profound improvement over the years. The newest semi-