Direct inhibition of tumor hypoxia response with synthetic transcriptional repressors

Area of Science:

• Molecular Biology
• Cancer Research
• Drug Discovery

Background:

• Oncogenic transcription factors (TFs) are challenging drug targets due to large interface requirements.
• Hypoxia-inducible factors (HIFs) and X-box-binding protein 1 (XBP1) are key TFs in solid tumors, activated by hypoxia and other stressors.
• These TFs bind to specific DNA motifs (UPRE and HRE) to drive oncogenic gene programs.

Purpose of the Study:

• To develop a novel strategy for targeting undruggable transcription factors.
• To create synthetic transcriptional repressors (STRs) that mimic TF DNA-binding domains.
• To validate the efficacy of a lead STR molecule (STR22) in preclinical cancer models.

Main Methods:

• Designed STRs to mimic the basic leucine zipper domain of XBP1, targeting UPRE and HRE motifs.
• Assessed STR22's DNA binding affinity and its ability to compete with endogenous TFs in cellular assays.
• Evaluated STR22's effect on HIF1α binding, hypoxia-induced gene expression, and protumorigenic phenotypes in triple-negative breast cancer (TNBC) cells.
• Tested STR22 efficacy in vivo via intratumoral and systemic administration in TNBC tumor models.

Main Results:

• STR22 demonstrated high-fidelity binding to UPRE and HRE DNA sequences.
• STR22 successfully competed with HIFs and XBP1 in cellular contexts.
• Under hypoxic conditions, STR22 inhibited global HIF1α binding, suppressed hypoxia-induced gene expression, and blocked protumorigenic phenotypes in TNBC cells.
• In vivo, STR22 treatment reduced tumor growth and metastasis in TNBC models by inhibiting hypoxia-dependent gene expression.

Conclusions:

• A novel strategy using synthetic transcriptional repressors (STRs) can effectively target oncogenic transcription factors.
• STR22 represents a promising therapeutic candidate for inhibiting the tumor hypoxia response.
• This approach offers a new avenue for targeting TF-DNA interactions in cancer therapy.