Macrolide and Ketolide Antibiotics Inhibit the Cytotoxic Effect of Trastuzumab Emtansine in HER2-Positive Breast Cancer Cells: Implication of a Potential Drug-ADC Interaction in Cancer Chemotherapy

Macrolides are widely used for the long-term treatment of infections and chronic inflammatory diseases. The pharmacokinetic features of macrolides include extensive tissue distribution because of favorable membrane permeability and accumulation within lysosomes. Trastuzumab emtansine (T-DM1), a HER2-targeting antibody-drug conjugate (ADC), is catabolized in the lysosomes, where Lys-SMCC-DM1, a potent cytotoxic agent, is processed by proteinase degradation and subsequently released from the lysosomes to the cytoplasm through the lysosomal membrane transporter SLC46A3, resulting in an antitumor effect. We recently demonstrated that erythromycin and clarithromycin inhibit SLC46A3 and attenuate the cytotoxicity of T-DM1; however, the effect of other macrolides and ketolides has not been determined. In this study, we evaluated the effect of macrolide and ketolide antibiotics on T-DM1 cytotoxicity in a human breast cancer cell line, KPL-4. Macrolides used in the clinic, such as roxithromycin, azithromycin, and josamycin, as well as solithromycin, a ketolide under clinical development, significantly attenuated T-DM1 cytotoxicity in addition to erythromycin and clarithromycin. Of these, azithromycin was the most potent inhibitor of T-DM1 efficacy. These antibiotics significantly inhibited the transport function of SLC46A3 in a concentration-dependent manner. Moreover, these compounds extensively accumulated in the lysosomes at the levels estimated to be 0.41-13.6 mM when cells were incubated with them at a 2 μM concentration. The immunofluorescence staining of trastuzumab revealed that azithromycin and solithromycin inhibit the degradation of T-DM1 in the lysosomes. These results suggest that the attenuation of T-DM1 cytotoxicity by macrolide and ketolide antibiotics involves their lysosomal accumulation and results in their greater lysosomal concentrations to inhibit the SLC46A3 function and T-DM1 degradation. This suggests a potential drug-ADC interaction during cancer chemotherapy.

Resistance phenotypes conferred by macrolide phosphotransferases

This study aims to compare the resistance phenotypes conferred by various genes encoding enzymes that phosphorylate erythromycin. The mph genes were cloned into Escherichia coli AG100A susceptible to macrolides and ketolides following disruption of the AcrAB pump. An 882 bp sequence containing a premature stop codon, homologous to the three other previously described mph genes and present widely among Enterobacteriaceae, was found to confer resistance to erythromycin by phosphorylation. The mph(C) gene, as reported for mph(B), also conferred resistance to spiramycin. The mph(A) gene was unique in conferring resistance to azithromycin. The four investigated genes conferred resistance to telithromycin.

The influence of macrolide antibiotics on the uptake of organic anions and drugs mediated by OATP1B1 and OATP1B3

Macrolides may cause severe drug interactions due to the inhibition of metabolizing enzymes. Transporter-mediated uptake of drugs into cells [e.g., by members of the human organic anion transporting polypeptide (OATP) family] is a determinant of drug disposition and a prerequisite for subsequent metabolism. However whether macrolides are also inhibitors of uptake transporters, thereby providing an additional mechanism of drug interactions, has not been systematically studied. The human OATP family members OATP1B1 and OATP1B3 mediate the uptake of endogenous substances and drugs such as antibiotics and HMG-CoA reductase inhibitors (statins) into hepatocytes. In this study we investigated the potential role of these uptake transporters on macrolide-induced drug interactions. By using sulfobromophthalein (BSP) and the HMG-CoA reductase inhibitor pravastatin as substrates, the effects of the macrolides azithromycin, clarithromycin, erythromycin, and roxithromycin and of the ketolide telithromycin on the OATP1B1- and OATP1B3-mediated uptake were analyzed. These experiments demonstrated that the OATP1B1- and OATP1B3-mediated uptake of BSP and pravastatin can be inhibited by increasing concentrations of all macrolides except azithromycin. The IC50 values for the inhibition of OATP1B3-mediated BSP uptake were 11 microM for telithromycin, 32 microM for clarithromycin, 34 microM for erythromycin, and 37 microM for roxithromycin. These IC50 values were lower than the IC50 values for inhibition of OATP1B1-mediated BSP uptake (96-217 microM). These macrolides also inhibited in a concentration-dependent manner the OATP1B1- and OATP1B3-mediated uptake of pravastatin. In summary, these results indicate that alterations of uptake transporter function by certain macrolides/ketolides have to be considered as a potential additional mechanism underlying drug-drug interactions.

Effects of acute renal failure on the pharmacokinetics of telithromycin in rats: negligible effects of increase in CYP3A1 on the metabolism of telithromycin

It was reported that the expression of CYP3A1 increased in rats with acute renal failure induced by uranyl nitrate (rat model of U-ARF) compared with controls. It was shown that telithromycin was mainly metabolized via CYP3A1/2 in rats in this study. Hence, the pharmacokinetic parameters of telithromycin were compared after both intravenous and oral administration at a dose of 50 mg/kg to control rats and a rat model of U-ARF. After intravenous administration of telithromycin to rats with U-ARF, the AUC and renal clearance (Cl(r)) were significantly greater (35.0% increase) and slower (99.1% decrease), respectively, than the controls. Unexpectedly, the nonrenal clearance (Cl(nr)) of telithromycin was comparable between the two groups of rats, suggesting that CYP3A isozyme responsible for the metabolism of telithromycin seemed not to be expressed considerably in the rat model of U-ARF. After oral administration of telithromycin to rats with U-ARF, the AUC was also significantly greater (127% increase) than the controls and the value, 127%, was considerably greater than 35.0% after intravenous administration of telithromycin. This may be due mainly to the decrease in the intestinal first-pass effect of telithromycin compared with controls in addition to significantly slower Cl(r) than controls.

Sampling the antibiotic resistome

Microbial resistance to antibiotics currently spans all known classes of natural and synthetic compounds. It has not only hindered our treatment of infections but also dramatically reshaped drug discovery, yet its origins have not been systematically studied. Soil-dwelling bacteria produce and encounter a myriad of antibiotics, evolving corresponding sensing and evading strategies. They are a reservoir of resistance determinants that can be mobilized into the microbial community. Study of this reservoir could provide an early warning system for future clinically relevant antibiotic resistance mechanisms.

Probing the breadth of macrolide glycosyltransferases: in vitro remodeling of a polyketide antibiotic creates active bacterial uptake and enhances potency

The glycan portion of macrolide antibiotics modulates their efficacy. High-level expression of three macrolide GTs and kinetic analysis has revealed a highly selective synthetic "tool kit" with such plasticity that 12 glycan-modified macrolide antibiotics have been readily created. One of these (1-Gal) is enhanced over its parent oleandomycin (1) by "glycotargeting", allowing higher uptake through active internalization by virtue of the attachment of a glycan (Gal) not normally found on 1. Subsequent release of the targeting glycan by endogenous galactosidase activity releases 1.

Ketolide resistance inStreptococcus pyogenescorrelates with the degree of rRNA dimethylation by Erm

Macrolide and ketolide antibiotics inhibit protein synthesis on the bacterial ribosome. Resistance to these antibiotics is conferred by dimethylation at 23S rRNA nucleotide A2058 within the ribosomal binding site. This form of resistance is encoded by erm dimethyltransferase genes, and is found in many pathogenic bacteria. Clinical isolates of Streptococcus pneumoniae with constitutive erm(B) and Streptococcus pyogenes with constitutive erm(A) subtype (TR) are resistant to macrolides, but remain susceptible to ketolides such as telithromycin. Paradoxically, some strains of S. pyogenes that possess an identical erm(B) gene are clinically resistant to ketolides as well as macrolides. Here we explore the molecular basis for the differences in these streptococcal strains using mass spectrometry to determine the methylation status of their rRNAs. We find a correlation between the levels of A2058-dimethylation and ketolide resistance, and dimethylation is greatest in S. pyogenes strains expressing erm(B). In constitutive erm strains that are ketolide-sensitive, appreciable proportions of the rRNA remain monomethylated. Incubation of these strains with subinhibitory amounts of the macrolide erythromycin increases the proportion of dimethylated A2058 (in a manner comparable with inducible erm strains) and reduces ketolide susceptibility. The designation 'constitutive' should thus be applied with some reservation for most streptococcal erm strains. One strain worthy of the constitutive designation is S. pyogenes isolate KuoR21, which has lost part of the regulatory region upstream of erm(B). In S. pyogenes KuoR21, nucleotide A2058 is fully dimethylated under all growth conditions, and this strain displays the highest resistance to telithromycin (MIC > 64 microg ml-1).

Cellular uptake and efflux of azithromycin, erythromycin, clarithromycin, telithromycin, and cethromycin

Macrolide antibiotics have an outstanding ability to concentrate within host cells, particularly phagocytes. In the study described in this paper five different macrolide antibiotics were compared regarding the uptake and release kinetics in human peripheral blood polymorphonuclear neutrophils (PMNs) and three different cell lines, two phagocytic cell lines (RAW 264.7 and THP-1) and an epithelial cell line (MDCK). Based on the results obtained, the substances tested could be clustered into different groups. Azithromycin constituted the first group, characterized by rapid and nonsaturable uptake into phagocytic cells and a high degree of retention in the preloaded cells. The second group included erythromycin and clarithromycin. These two substances do not exhibit cell specificity; consequently, they are taken up to a similar extent and are released by all cell types studied. Ketolides constituted the last group. Their uptake was saturable in cells of monocytic lineage as well as in nondifferentiated cells of myeloid lineage, and they were rapidly released from all the cell lines studied. However, in PMNs, ketolide uptake was not saturable; and unlike telithromycin, cethromycin rapidly egressed from the loaded cells.

Structures of MLSBK antibiotics bound to mutated large ribosomal subunits provide a structural explanation for resistance

Crystal structures of H. marismortui large ribosomal subunits containing the mutation G2099A (A2058 in E. coli) with erythromycin, azithromycin, clindamycin, virginiamycin S, and telithromycin bound explain why eubacterial ribosomes containing the mutation A2058G are resistant to them. Azithromycin binds almost identically to both G2099A and wild-type subunits, but the erythromycin affinity increases by more than 10(4)-fold, implying that desolvation of the N2 of G2099 accounts for the low wild-type affinity for macrolides. All macrolides bind similarly to the H. marismortui subunit, but their binding differs significantly from what has been reported in the D. radioidurans subunit. The synergy in the binding of streptogramins A and B appears to result from a reorientation of the base of A2103 (A2062, E. coli) that stacks between them. The structure of large subunit containing a three residue deletion mutant of L22 shows a change in the L22 structure and exit tunnel shape that illuminates its macrolide resistance phenotype.

Telithromycin activity is reduced by efflux in Streptococcus pyogenes

OBJECTIVES

To investigate whether telithromycin is a substrate for efflux pumps in Streptococcus pyogenes.

METHODS

The distribution of telithromycin MICs was analysed for two distinct collections of Italian (n=486) and Spanish (n=210) S. pyogenes strains. The effect of an efflux mechanism was investigated using [(3)H]telithromycin.

RESULTS

Telithromycin MIC ranges were < or = 0.004-0.06 mg/L (MIC(50) and MIC(90), 0.01 mg/L) in erythromycin-susceptible strains (lacking both mef and erm genes) and 0.01-1 mg/L (MIC(50) and MIC(90), 0.5 mg/L) in strains endowed with the M phenotype and expressing the mef(A) gene. A distinct telithromycin efflux was detected in the strains expressing the mef(A) gene, but not in those expressing the erm(B) gene, nor in the susceptible strains lacking mef(A) or erm genes. Efflux reversibility by addition of an inhibiting compound (sodium arsenate) was demonstrated. An msr-like sequence was also found in all strains effluxing telithromycin, but not in the others.

CONCLUSIONS

This study shows that telithromycin can be removed from S. pyogenes by efflux. That the efflux is related to the presence of the mef(A) gene is demonstrated, but-owing to the increasingly evident complexity of S. pyogenes efflux systems-the possibility that other genes may contribute to the efflux cannot be excluded.

Binding site of the bridged macrolides in the Escherichia coli ribosome

Ketolides represent the latest group of macrolide antibiotics. Tight binding of ketolides to the ribosome appears to correlate with the presence of an extended alkyl-aryl side chain. Recently developed 6,11-bridged bicyclic ketolides extend the spectrum of platforms used to generate new potent macrolides with extended alkyl-aryl side chains. The purpose of the present study was to characterize the site of binding and the action of bridged macrolides in the ribosomes of Escherichia coli. All the bridged macrolides investigated efficiently protected A2058 and A2059 in domain V of 23S rRNA from modification by dimethyl sulfate and U2609 from modification by carbodiimide. In addition, bridged macrolides that carry extended alkyl-aryl side chains protruding from the 6,11 bridge protected A752 in helix 35 of domain II of 23S rRNA from modification by dimethyl sulfate. Bridged macrolides efficiently displaced erythromycin from the ribosome in a competition binding assay. The A2058G mutation in 23S rRNA conferred resistance to the bridged macrolides. The U2609C mutation, which renders E. coli resistant to the previously studied ketolides telithromycin and cethromycin, barely affected cell susceptibility to the bridged macrolides used in this study. The results of the biochemical and genetic studies indicate that in the E. coli ribosome, bridged macrolides bind in the nascent peptide exit tunnel at the site previously described for other macrolide antibiotics. The presence of the side chain promotes the formation of specific interactions with the helix 35 of 23S rRNA.

Verapamil Toxicity Resulting from a Probable Interaction with Telithromycin

OBJECTIVE:

To report a case of hypotension and bradyarrhythmia caused by verapamil toxicity in a patient prescribed telithromycin.

CASE SUMMARY:

A 76-year-old white woman receiving verapamil 180 mg/day for hypertension experienced a sudden onset of shortness of breath and weakness and was found to be profoundly hypotensive and bradycardic, with a systolic blood pressure of 50–60 mm Hg and a heart rate of 30 beats/min. She had been taking telithromycin 800 mg/day for 2 days previously for acute sinusitis. The patient was treated with crystalloids, vasopressors, and transvenous pacing. Approximately 72 hours after admission, her blood pressure and heart rate rapidly returned to normal, and she was discharged several days later.

DISCUSSION:

Telithromycin is a known substrate of the CYP3A4 system, and several pharmacokinetic interactions can occur by displacement of other drugs from this system. Verapamil is metabolized through several cytochrome P450 isoenzyme systems. Although there are no previous reports of an interaction between these drugs, other possible causes for the patient's symptoms were excluded and the diagnosis of a probable interaction between verapamil and telithromycin leading to verapamil toxicity was made.

CONCLUSIONS:

Telithromycin is a ketolide antibiotic approved for treatment of respiratory tract infections and acute sinusitis. The potential for clinically significant drug interactions should be considered before using this agent, especially in patients taking other drugs that are metabolized through the CYP3A system. Caution should be exercised when considering the use of this antibiotic in patients receiving verapamil.

Species-specific antibiotic-ribosome interactions: implications for drug development

In the cell, the protein synthetic machinery is a highly complex apparatus that offers many potential sites for functional interference and therefore represents a major target for antibiotics. The recent plethora of crystal structures of ribosomal subunits in complex with various antibiotics has provided unparalleled insight into their mode of interaction and inhibition. However, differences in the conformation, orientation and position of some of these drugs bound to ribosomal subunits of Deinococcus radiodurans (D50S) compared to Haloarcula marismortui (H50S) have raised questions regarding the species specificity of binding. Revisiting the structural data for the bacterial D50S-antibiotic complexes reveals that the mode of binding of the macrolides, ketolides, streptogramins and lincosamides is generally similar to that observed in the archaeal H50S structures. However, small discrepancies are observed, predominantly resulting from species-specific differences in the ribosomal proteins and rRNA constituting the drug-binding sites. Understanding how these small alterations at the binding site influence interaction with the drug will be essential for rational design of more potent inhibitors.

Effects of Itraconazole or Grapefruit Juice on the Pharmacokinetics of Telithromycin

STUDY OBJECTIVE

To determine whether coadministration of the cytochrome P450 3A4 (CYP3A4) inhibitors itraconazole or grapefruit juice will modify the pharmacokinetic profile of telithromycin, and to assess the safety of telithromycin.

DESIGN

Two single-center, open-label studies; the itraconazole study was nonrandomized, sequential, and multiple dose, and the grapefruit juice study was randomized, two-period crossover, and single dose.

SETTING

Two clinical investigative centers in the United States.

SUBJECTS

Thirty-four healthy, nonsmoking male volunteers aged 18-45 years.

INTERVENTION

All patients received telithromycin 800 mg/day; 18 patients received concomitant itraconazole 200 mg/day, and 16 received concomitant single-dose, single-strength grapefruit juice.

MEASUREMENTS AND MAIN RESULTS

Standard pharmacokinetic and safety measurements were performed. Itraconazole given concomitantly with telithromycin increased the steady-state area under the plasma concentration-time curve from 0-24 hours of telithromycin by 53.8% (p<0.0001). Coadministration of grapefruit juice did not affect telithromycin pharmacokinetic parameters, and telithromycin was well tolerated in both studies.

CONCLUSION

Only modest changes in the pharmacokinetics of telithromycin were seen with concomitant administration of itraconazole. Telithromycin pharmacokinetics were unaffected by concomitant administration of grapefruit juice.