Poster Presentation Royal Australian Chemical Institute National Congress 2026

Chemical inhibition of FANCM-RMI unleashes telomere maintenance toxicity in osteosarcoma cells (#526)

Joshua S Mills 1 , Lisa J Alcock 2 , Rohan Bythell-Douglas 3 , Haritha K Sudhakar 1 , Chandrika Deshpande 4 , Toby Passioura 4 , Andrew J Deans 3 , Yu Heng Lau 1 5
  1. School of Chemistry, The University of Sydney, Sydney, New South Wales, Australia
  2. School of Molecular and Life Sciences (MLS), Curtin University, Perth, Western Australia, Australia
  3. Genome Stability Unit, St Vincent’s Institute of Medical Research, Fitzroy, Vic, Australia
  4. Sydney Analytical Core Research Facility, The University of Sydney, Camperdown, New South Wales, Australia
  5. ARC Centre of Excellence for Innovations in Peptide and Protein Science, The University of Sydney, Camperdown, New South Wales, Australia

Telomeres are protective chromosomal caps that shorten during replication, signalling for senescence or programmed cell death once they reach a critically short length. To prevent the shortening of their telomeres, approximately 15% of human cancers utilise the Alternative Lengthening of Telomeres (ALT) pathway. As the ALT pathway inadvertently generates toxic replication stress, ALT-positive cells manage this stress by recruiting FANCM and the Bloom’s complex. Disrupting the interaction of FANCM with the RMI1/RMI2 subunits of the Bloom’s complex offers a therapeutic window to selectively unleash ALT-associated replication stress. However, no cell-active chemical inhibitors had been reported to date.

We report the first cell-active peptide inhibitor of the FANCM-RMI interaction, identified via an mRNA display screening campaign. Surprisingly, linear peptide hits were more potent than their cyclic counterparts in biophysical binding assays, likely due to incomplete cyclization with the trans-dibromobutene linker during selection. Our lead linear peptide, P4, demonstrated high solubility and sub-micromolar affinity (IC50 = 120 nM). By elucidating the crystal structure of P4 bound to RMI, we performed a rational truncation to a minimal pharmacophore, tP4, which maintained potent binding (IC50 = 100 nM). To enhance cellular uptake and proteolytic stability, tP4 was conjugated to the cyclic cell-penetrating peptide CPP12. This conjugate, tP4-CPP12, demonstrated selective cytotoxicity in ALT-positive U2OS cells, with lower cytotoxicity observed in ALT-negative SJSA-1 cells. These findings suggest that inhibition of the FANCM-RMI interaction exacerbates ALT-specific replication stress, leading to cell death in osteosarcoma cancer cells.

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