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Tipifarnib deprenylates HRAS in vivo

Tipifarnib is Highly Active in HRAS-mutant Head and Neck Squamous Cell Carcinoma (HNSCC) Tumor Models Mara Gilardi2, Zhiyong Wang2, Linda Kessler1, Antonio Gualberto1, Yi Liu1, J. Silvio Gutkind2, Francis Burrows1

1Kura Oncology, Inc., San Diego, CA, USA, 2University of California, San Diego

Tipifarnib is a potent and selective inhibitor of farnesyltransferase (FT). FTcatalyzes the post-translational attachment of farnesyl groups to signalingproteins that are requisite for localization to the inner cell membrane.Although all RAS isoforms are FT substrates, only HRAS is exclusivelydependent upon farnesylation for membrane localization and signalingactivation, making HRAS mutant tumors uniquely susceptible to tipifarnibmediated inhibition of FT. Based upon this rationale, the safety and efficacyof tipifarnib is currently being evaluated in patients with HRAS mutant headand neck squamous cell carcinoma (HNSCC) in an international, multicenter,open-label 2 cohort, non-comparative, pivotal Phase 2 trial (NCT03719690).Here we report the characterization of tipifarnib in CDX and PDX models ofHRAS-mutant HNSCC in vitro and in vivo

BACKGROUND AND RATIONALE

• HRAS is a targetable oncogene in squamous cell carcinomas using tipifarnib• Tipifarnib prevents HRAS prenylation and membrane insertion• HRAS-mutant cells are highly sensitive in vitro under both adherent and

anchorage-independent conditions• Tipifarnib induced stasis or regression in HRAS-mutant HNSCC xenograft

models, independently of HRAS genotype• Antitumor activity in vivo is associated with inhibition of MAPK and PI3K-

mTOR signaling, cell cycle arrest and robust activation of apoptosis• Direct antitumor effects may be enhanced by antiangiogenic activity of

tipifarnib in vivo• Tipifarnib is under active clinical evaluation in HRAS-mutant SCC including

HNSCC

CONCLUSIONS

TIPIFARNIB IS SELECTIVELY CYTOTOXIC TO HRAS-MUTANT HNSCC CELLS IN VITRO

Poster PB-083, EORTC-NCI-AACR Molecular Targets and Cancer Therapeutics Symposium November13-16th, 2018

HRAS MUTATIONS DEFINE A UNIQUE MOLECULAR SUBSET OF HNSCC

NRASKRAS

Molecular basis of tipifarnib activity in HRAS-mutant HNSCC

TIPIFARNIB DEPRENYLATES AND DISPLACES HRAS FROM MEMBRANES

• HNSCC express high levels of HRAS2

• HRAS mutant SCCHN (~6% at initial diagnosis) characterized by frequent CASP8 mutations and low rate of TP53 mutation3

• HRAS mutation may result from toxin (e.g. tobacco) exposure4

• HRAS mutation is associated with innate and acquired resistance to cetuximab5

– 3/13 (23%) of patients with on-treatment disease progression during cetuximab/platinum/5-FU therapy acquired HRAS mutations

1

1. TCGA data. Gao et al. 2013. Sci Signal 6:pl1; Cerami et al 2012. Cancer Discov. 2:401-42. Cancer Genome Atlas Network 2015. Nature 517:576-82.3. Cancer Genome Atlas Research Network 2012. Nature 489:519-254. Sathyan et al. 2007. Modern Path 20, 1141-85. Braig et al. Oncotarget. 2016. 7, 42988-42995

1

HRAS colocalization with cellular membranes is lost in tipifarnib-treated HNSCC cells

Control Tipifarnib

TIPIFARNIB IS HIGHLY ACTIVE IN HRAS-MUTANT HNSCC XENOGRAFTS

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HRAS-mutant UMSCC17B and ORL214 cellswere treated with tipifarnib (100nM, 48h) andstained with anti-HRAS antibodies by westernblotting (left) or immunofluorescence (right).The fluorescence profile relative to thedistribution of HRAS (green) was compared tothat of DAPI (blue) and the membrane markerWGA lectins (red) by confocal microscopy

HNSCC cells were treated with a titration of tipifarnib for 72 h (left panel) or with vehicle or 300 nM tipifarnib under anchorage-independent conditions for 14 days (right panels)

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ACTIVITY OF TIPIFARNIB IN HRAS-MUTANT SCC IS INDEPENDENT OF GENOTYPE

TIPIFARNIB INHIBITS ONCOGENIC SIGNALING AND PROLIFERATION ANDINDUCES APOPTOSIS IN HRAS-MUTANT HNSCC XENOGRAFTS IN VIVO

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