New Chloramphenicol Derivatives from the Viewpoint of Anticancer and Antimicrobial Activity

Abstract

Over the last years, we have been focused on chloramphenicol conjugates that combine in their structure chloramphenicol base with natural polyamines, spermine, spermidine and putrescine, and their modifications. Conjugate 3, with spermidine (SPD) as a natural polyamine linked to chloramphenicol base, showed the best antibacterial and anticancer properties. Using 3 as a prototype, we here explored the influence of the antibacterial and anticancer activity of additional benzyl groups on N1 amino moiety together with modifications of the alkyl length of the aminobutyl fragment of SPD. Our data demonstrate that the novel modifications did not further improve the antibacterial activity of the prototype. However, one of the novel conjugates (4) showed anticancer activity without affecting bacterial growth, thus emerging as a promising anticancer agent, with no adverse effects on bacterial microflora when taken orally.

Keywords: Chloramphenicol; antibiotics; anticancer activity; antimicrobial activity; conjugates; mitochondrial ribosome; molecular dynamics simulations; polyamines; protein biosynthesis.

Figure 1

Structures of compounds encountered in the present work.

Scheme 1

Synthesis of polyamine (PA)–chloramphenicol (CAM) conjugates 4–7. Reagents and reaction conditions: (i) (a) Me₃SiCl, DCM/MeCN (5:1), reflux, (b) TrtCl/Et₃N, (c) MeOH, 85–97%; (ii) (PhCH₂) ₂NH, O-(benzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU), Et₃N, 65–80%; (iii) lithium aluminium hydride (LAH), THF, reflux, 60–80%; (iv) trifluoroacetic acid (TFA)/CH₂Cl₂(1:9 or 2:8 v/v), Et₃SiH, 85–95%; (v) succinic anhydride, DIEA, DMF; (vi) (PhCH₂)NH, HBTU, ethyldiisopropylamine (DIEA), 90% over the two steps; (vii) (a) succinic anhydride, DMF, (b) 10a-c or 12, HBTU, DIEA, DMF, 60–73%.

Figure 2

Cytotoxicity of compounds 3 (A,B) and 4 (C,D) on ZL34 mesothelioma cells and Met5A mesothelial immortalized cells. * Significantly different values from those measured in control samples (p < 0.05).

Figure 3

Effect of CAM or PA–CAM conjugates on cytoplasmic and mitochondrial protein synthesis. Western blot analysis on total protein extracts, derived from (Α) ZL34 and (B) Met5A cells. (C,D) Quantification of COX2 protein levels compared to actin levels after normalization. * Significantly different values from those measured in control samples (p < 0.05).

Figure 4

Changes in the polyamine levels of cells (A) ZL34 and (B) Met5A, after treatment with 60 μΜ of compound 3 or 4. (C) Intracellular concentration of compounds 3 and 4, detected in cell extracts.

Figure 5

Molecular modeling of compounds binding mode in the vicinity of the catalytic center of hmLRS, derived from molecular dynamics (MD) simulations. Possible hydrogen bonds are shown with yellow bullets. For clarity only, relevant nucleotides of the environment are shown. Nucleotides A2938 and C2939 of the catalytic center are shown for orientation purposes in gray. (A) Compound 3. Four possible hydrogen bonds stabilize compound 3 in the region, as shown in Table 5. (B) Compound 4. Four possible hydrogen bonds (Table 5) as well as two stacking interactions stabilize compound 4 in the region. Note the hydrogen bond between N1 nitrogen of adenine in A2938 with a hydroxyl oxygen of compound 4 nearest to the CAM ring.