Transcription Factor Inhibition

Transcription Factor Inhibition

 

Metals in Medicine

The use of metals in medicine has grown impressively in recent years as the result of a greatly advanced understanding of the structures of biologically active metal complexes and metal-containing proteins. This area of research focuses on the interaction of inorganic therapeutic agents that can be specifically coupled to a biologically active site by cooperative ligation.

Cobalt(III) Schiff Base Complexes

The Meade lab seeks to understand and utilize Co(III)-Schiff base complexes (Co(III)-sb) as research tools and potential therapeutics. The complexes we study consist of a Co(III) center coordinated to an acetylacetonatoethylenediamine (acacen) backbone. The backbone can be modified to contain a targeting group, and axial ligand exchange dynamics can be exploited for biological or chemical utility.

Structure of the Co(III) Schiff base complex with ammine axial ligands
Structure of the Co(III) Schiff base complex with ammine axial ligands

Regulating Gene Transcription

Co(III)-sb complexes have been shown to irreversibly inhibit the activity of histidine-containing proteins by binding to histidine residues in the active site. Zinc finger transcription factors often contain a Cys2His2 type zinc finger that can be inhibited by Co(III)-sb. Co(III)-sb displaces Zn(II) and disrupts protein structure. For targeting, Co(III)-sb is tethered to the DNA consensus sequence of a specific transcription factor (making Co(III)-DNA). By inhibiting the activity of transcription factor proteins, gene transcription can be regulated. This can be exploited for use in cancer, developmental, and disease biology.

When Co(III)-sb binds histidine residues in a Cys2His2 zinc finger motif, Zn(II) is displaced and protein structure is disrupted.
When Co(III)-sb binds histidine residues in a Cys2His2 zinc finger motif, Zn(II) is displaced and protein structure is disrupted.
By attaching the DNA binding sequence of a particular transcription factor, highly specific protein targeting is achieved.
By attaching the DNA binding sequence of a particular transcription factor, highly specific protein targeting is achieved.

Epithelial-to-Mesenchymal Transition (EMT) Inhibition

Co(III)-DNA targeted to inhibit Snail family transcription factors has been synthesized and tested in Xenopus laevis. The Co(III)-DNA prevents Slug, Snail, and Sip1 from binding their DNA targets, while leaving other transcription factors unaffected. The attachment of the oligonucleotide to the Co(III) complex increases specificity 150-fold over the unconjugated complex. Slug, Snail, and Sip1 have been implicated in the regulation of epithelial-to-mesenchymal transition in development and cancer metastasis. A complex targeted to inactivate their transcriptional activity could prove valuable as an experimental tool and a cancer therapeutic.

Xenopus embryos treated with Co(III)-Ebox grown at 27°C show impaired neural crest migration (red arrowheads) visualized by in situ hybridization for Twist and Krox20.
Xenopus embryos treated with Co(III)-Ebox grown at 27°C show impaired neural crest migration (red arrowheads) visualized by in situ hybridization for Twist and Krox20.

Hedgehog Pathway Inhibition (Cancer)

Targeted Co(III)-DNA has also shown remarkable specificity in inhibiting Ci protein, the final step in the Drosophila hedgehog signaling pathway. The hedgehog signaling pathway is overactivated in cancers such as basal cell carcinoma (skin) and medulloblastomas (brain), so inhibiting the pathway has therapeutic potential. Studies are currently underway to inhibit Gli protein, the mammalian analog of Ci. In order to deliver this to mammalian tissues, gold nanoparticles are being utilized.

Injection of Co(III)-Ci but not Co(III)-CiMut is able to phenocopy loss of ci function in vivo. Drosophila cuticle mounts showing denticle belt patterning of 48 h old embryos. Wild-type embryos between 0 and 45 min old were microinjected with 1μM (C) Co(III)-CiMut or (D) Co(III)-Ci, allowed to develop for 48 h, mounted and imaged by phase contrast light microscopy. Arrow points to denticle belt fusion characteristic of a ci mutant.
Injection of Co(III)-Ci but not Co(III)-CiMut is able to phenocopy loss of ci function in vivo. Drosophila cuticle mounts showing denticle belt patterning of 48 h old embryos. Wild-type embryos between 0 and 45 min old were microinjected with 1μM (C) Co(III)-CiMut or (D) Co(III)-Ci, allowed to develop for 48 h, mounted and imaged by phase contrast light microscopy. Arrow points to denticle belt fusion characteristic of a ci mutant.

 

Inhibiting Amyloid-β Aggregation (Alzheimer’s)

Oligomers of the Aβ42 peptide are significant neurotoxins linked to Alzheimer’s disease (AD). Histidine (His) residues present at the N terminus of Aβ42 are believed to influence toxicity by either serving as metal–ion binding sites (which promote oligomerization and oxidative damage) or facilitating synaptic binding. HPLC-MS, NMR, fluorescence, and DFT studies demonstrated that Co(III)-sb complexes could interact with the His residues in a truncated Aβ16 peptide representing the Aβ42 N terminus. Coordination of Co(III)-sb complexes altered the structure of Aβ42 peptides and promoted the formation of large soluble oligomers. Interestingly, this structural perturbation of Aβ correlated to reduced synaptic binding to hippocampal neurons. These results demonstrate the promise of Co(III)-sb complexes in anti-AD therapeutic approaches.

Proposed scheme of the modulation of Aβ activity by Co–acacen. Co–acacen is believed to coordinate the His residues of Aβ through the two axial positions. Computational studies suggest the simultaneous coordination of His6 and either His13 or His14 as the most stable conformation. His-coordination alters the Aβ structure, disrupting oligomerization pathways and synaptic binding.
Proposed scheme of the modulation of Aβ activity by Co–acacen. Co–acacen is believed to coordinate the His residues of Aβ through the two axial positions. Computational studies suggest the simultaneous coordination of His6 and either His13 or His14 as the most stable conformation. His-coordination alters the Aβ structure, disrupting oligomerization pathways and synaptic binding.

 

Chemistry at Northwestern University