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Identification of substituted pyrimido[5,4-b]indoles as selective Toll-like receptor 4 ligands.

Chan M, Hayashi T, Mathewson RD, Nour A, Hayashi Y, Yao S, Tawatao RI, Crain B, Tsigelny IF, Kouznetsova VL, Messer K, Pu M, Corr M, Carson DA, Cottam HB - J. Med. Chem. (2013)

Bottom Line: Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively.Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound.Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex.

View Article: PubMed Central - PubMed

Affiliation: Moores Cancer Center, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0695, USA.

ABSTRACT
A cell-based high-throughput screen to identify small molecular weight stimulators of the innate immune system revealed substituted pyrimido[5,4-b]indoles as potent NFκB activators. The most potent hit compound selectively stimulated Toll-like receptor 4 (TLR4) in human and mouse cells. Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively. Specifically, a subset of compounds bearing phenyl and substituted phenyl carboxamides induced lower IL-6 release while maintaining higher IP-10 production, skewing toward the type I interferon pathway. Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound. Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex. These small molecules, which stimulate innate immune cells with minimal toxicity, could potentially be used as adjuvants or immune modulators.

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SAR regionsof modification of hit compound 1.
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fig6: SAR regionsof modification of hit compound 1.

Mentions: The primary HTS library contained a familyof 452 compounds in the pyrimido[5,4-b]indole classand therefore represented a valuable initial indication of structuralfeatures important for activation of NFκB. Upon inspection ofthe NFκB activation values in the initial HTS relative to thevarious structural features, several trends were apparent. There wasa requirement for a hydrophobic moiety in the region of the cyclohexylgroup of compound 1. In this same region, the carboxamidefunction was essential. Furthermore, a hydrophobic group at N-3, preferablya phenyl group, was also required for activity. Substitutions on theN-3 phenyl, other than fluorine atoms, resulted in loss of activity.Removal of the benzo ring of the indole portion of the scaffold alsoresulted in loss of activity. When the C-4 oxo was replaced by NHto form a triazine ring, loss of activity was observed. Finally, exchangeof the entire acetamide moiety on the C-2 thiol with the N-3 phenylgroup, such that the acetamide was attached at N-3 and the phenylwas attached at the C-2 thiol, resulted in loss of activity. Withthese SAR features as an initial guide, we elected to investigatemodifications of hit compound 1 at three regions whilemaintaining the core pyrimido[5,4-b]indole ring system:the N-substitution of the S-acetamide, the N-3 substituent,and the N-5 substituent (Figure 6).


Identification of substituted pyrimido[5,4-b]indoles as selective Toll-like receptor 4 ligands.

Chan M, Hayashi T, Mathewson RD, Nour A, Hayashi Y, Yao S, Tawatao RI, Crain B, Tsigelny IF, Kouznetsova VL, Messer K, Pu M, Corr M, Carson DA, Cottam HB - J. Med. Chem. (2013)

SAR regionsof modification of hit compound 1.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3722616&req=5

fig6: SAR regionsof modification of hit compound 1.
Mentions: The primary HTS library contained a familyof 452 compounds in the pyrimido[5,4-b]indole classand therefore represented a valuable initial indication of structuralfeatures important for activation of NFκB. Upon inspection ofthe NFκB activation values in the initial HTS relative to thevarious structural features, several trends were apparent. There wasa requirement for a hydrophobic moiety in the region of the cyclohexylgroup of compound 1. In this same region, the carboxamidefunction was essential. Furthermore, a hydrophobic group at N-3, preferablya phenyl group, was also required for activity. Substitutions on theN-3 phenyl, other than fluorine atoms, resulted in loss of activity.Removal of the benzo ring of the indole portion of the scaffold alsoresulted in loss of activity. When the C-4 oxo was replaced by NHto form a triazine ring, loss of activity was observed. Finally, exchangeof the entire acetamide moiety on the C-2 thiol with the N-3 phenylgroup, such that the acetamide was attached at N-3 and the phenylwas attached at the C-2 thiol, resulted in loss of activity. Withthese SAR features as an initial guide, we elected to investigatemodifications of hit compound 1 at three regions whilemaintaining the core pyrimido[5,4-b]indole ring system:the N-substitution of the S-acetamide, the N-3 substituent,and the N-5 substituent (Figure 6).

Bottom Line: Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively.Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound.Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex.

View Article: PubMed Central - PubMed

Affiliation: Moores Cancer Center, University of California, San Diego, 9500 Gilman Drive, La Jolla, California 92093-0695, USA.

ABSTRACT
A cell-based high-throughput screen to identify small molecular weight stimulators of the innate immune system revealed substituted pyrimido[5,4-b]indoles as potent NFκB activators. The most potent hit compound selectively stimulated Toll-like receptor 4 (TLR4) in human and mouse cells. Synthetic modifications of the pyrimido[5,4-b]indole scaffold at the carboxamide, N-3, and N-5 positions revealed differential TLR4 dependent production of NFκB and type I interferon associated cytokines, IL-6 and interferon γ-induced protein 10 (IP-10) respectively. Specifically, a subset of compounds bearing phenyl and substituted phenyl carboxamides induced lower IL-6 release while maintaining higher IP-10 production, skewing toward the type I interferon pathway. Substitution at N-5 with short alkyl substituents reduced the cytotoxicity of the leading hit compound. Computational studies supported that active compounds appeared to bind primarily to MD-2 in the TLR4/MD-2 complex. These small molecules, which stimulate innate immune cells with minimal toxicity, could potentially be used as adjuvants or immune modulators.

Show MeSH
Related in: MedlinePlus