Neomorphic mutations targeting amino acid R132 of the TCA cycle enzyme, IDH1, have been identified in multiple cancer types and lead to a build up of (R)-2-hydroxyglutarate (R)-2HG.
Several mechanisms have been proposed to account for mutant-IDH1-mediated transformation:
- (R)-2HG may compete with alpha-ketoglutarate (α-KG) dependent enzymes that act as tumour suppressors such as TET2 or EGLN
- (R)-2HG might inhibit electron transport chain function
- Rapid (R)-2HG generation may deplete the cellular pool of α-KG leading to depletion of NADPH.
According to some reports in the literature, heterodimer formation between mutant and wild-type alleles of IDH1 is important for the production of high levels of (R)-2HG1.
We were interested in exploring novel ways to target tumour cells bearing mutant IDH1 alleles that were distinct from the obvious opportunity available to identify mutant-specific IDH1 inhibitors. The potential metabolic vulnerabilities of mutant IDH1 cancers raised the possibility that wild-type IDH1 might be essential for tumourigenesis or tumour maintenance in this context.
We therefore employed Horizon’s rAAV-mediated homologous recombination gene engineering technology to generate conditional knockouts of the IDH1+ or IDH1R132C alleles in the fibrosarcoma cell line, HT1080.
During the course of this work we:
- Generated a HT-1080 IDH1(+cKO/R132C) X-MAN™ isogenic cell line that lack expression of the wild type allele. Cre-mediated excision of exon 5 was not necessary to silence expression of targeted allele.
- Found that cells lacking expression of the wild type allele are able to undergo tumorigenesis in xenograft models.
- Observed inhibition of the mutant protein prevents the IDH1(R132H/+) mediated growth of MCF10A cells. MCF10A IDH1(R132H/+) cells enable facile proliferation assays to track activity of IDH1 inhibitors .
- Conclude that wild type IDH1 is dispensable for tumour growth in IDH1 mutant cancer cells.