Poster Presentation The 16th Australian Peptide Conference 2025

Unleashing telomere maintenance toxicity in ALT cancers: A FANCM-RMI inhibiting bioactive peptide (#227)

Joshua Mills 1 , Lisa J Alcock 1 , Rohan Bythell-Douglas 2 , Haritha K Sudhakar 1 , Chandrika Deshpande 3 , Toby Passioura 3 , Andrew J Deans 2 , Yu Heng Lau 1 4
  1. School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia
  2. Genome Stability Unit, St Vincent’s Institute of Medical Research, Fitzroy, Vic, Australia
  3. Sydney Analytical Core Research Facility, The University of Sydney, Camperdown, New South Wales, Australia
  4. ARC Centre of Excellence for Innovations in Peptide and Protein Science, The University of Sydney, Camperdown, New South Wales, Australia

Alternative Lengthening of Telomeres (ALT) is a telomerase-independent mechanism for telomere maintenance that 15% of all human cancers rely upon to survive. The ALT pathway inadvertently generates toxic telomeric replication stress that is suppressed in cancer cells by the recruitment of two protein partners to the telomere – FANCM and the Blooms complex - where FANCM directly interacts with the RMI1/RMI2 subunits of the Blooms complex. Disrupting the FANCM-RMI interaction is selectively lethal to ALT-positive cancers, however, no inhibitors with demonstrated cellular activity have been reported to date.

In this work, we report the first cell-active peptide inhibitor of the FANCM–RMI interaction. Hits from a RaPID screening campaign were evaluated in biophysical binding assays, where linear peptides unexpectedly displayed more potent binding than their cyclic counterparts, suggesting inefficient cyclisation occurred during selection. The top linear peptide, P4, exhibited high solubility and sub-micromolar affinity (IC50 = 120 nM) for RMI. A crystal structure of P4 bound to RMI was elucidated, enabling rational truncation to a minimal pharmacophore tP4 without loss of binding affinity (IC50 = 100 nM).

To enable cellular uptake, tP4 was conjugated to the cyclic cell-penetrating peptide, CPP12. The resulting conjugate tP4-CPP12 exhibited cytotoxicity in ALT-positive U2OS cancer cells, with lower toxicity in ALT-negative SJSA-1 cancer cells. These results suggest that inhibition of the FANCM-RMI interaction exacerbates ALT-specific replication stress, leading to cell death in cancer cells.

 

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