Transformation by HrasG12V is consistently associated with mutant allele copy gains and is reversed by farnesyl transferase inhibition

Abstract

RAS-driven malignancies remain a major therapeutic challenge. The two-stage 7,12-dimethylbenz(a)anthracene (DMBA)/12-o-tetradecanoylphorbol-13-acetate (TPA) model of mouse skin carcinogenesis has been used to study mechanisms of epithelial tumor development by oncogenic Hras. We used mice with a HrasG12V knock-in allele to elucidate the early events after Hras activation, and to evaluate the therapeutic effectiveness of farnesyltransferase (FTI) inhibition. Treatment of Caggs-Cre/FR-HrasG12V mice with TPA alone was sufficient to trigger papilloma development with shorter latency and a ~10-fold greater tumor burden than DMBA/TPA-treated WT controls. HrasG12V allele copy number was increased in all papillomas induced by TPA. DMBA/TPA treatment of HrasG12V knock-in mice induced an even greater incidence of papillomas, which either harbored HrasG12V amplification, or developed a HrasQ61L mutation in the second allele. Laser-capture microdissection of normal skin, hyperplastic skin and papillomas showed that amplification occurred only at the papilloma stage. HRAS mutant allelic imbalance was also observed in human cancer cell lines, consistent with a requirement for augmented oncogenic HRAS signaling for tumor development. The FTI SCH66336 blocks HRAS farnesylation and delocalizes it from the plasma membrane. NRAS and KRAS are not affected as they are alternatively prenylated. When tested in lines harboring HRAS, NRAS or KRAS mutations, SCH66336 delocalized, inhibited signaling and preferentially inhibited growth only of HRAS-mutant lines. Treatment with SCH66336 also induced near-complete regression of papillomas of TPA-treated HrasG12V knock-in mice. These data suggest that farnesyl transferase inhibitors should be reevaluated as targeted agents for human HRAS-driven cancers, such as those of bladder, thyroid and other epithelial lineages.

NF2 Loss Promotes Oncogenic RAS-Induced Thyroid Cancers via YAP-Dependent Transactivation of RAS Proteins and Sensitizes Them to MEK Inhibition

“…A requirement for intensification of mutant Ras signaling through copy-number imbalances is supported by studies in Hras mutant fibroblasts, in which transformation is strongly associated with amplification of the mutant allele (35). Increased mutant allele copy number is an obligate early event in Hras G12V -induced papilloma development (31, 36, 37). Similarly, the aggressiveness of myeloproliferative neoplasms expressing Nras G12D is augmented when the mutant allele is homozygous (38).…”

Paternal uniparental disomy 11p15.5 in the pancreatic nodule of an infant with Costello syndrome: Shared mechanism for hyperinsulinemic hypoglycemia in neonates with Costello and Beckwith–Wiedemann syndrome and somatic loss of heterozygosity in Costello syndrome driving clonal expansion

“…Angiosarcoma and forestomach papillomata showed similar increase in the copy number of the mutant allele [Chen et al, 2009], leading to the conclusion that further augmentation of the signal output from a single oncogenic Hras mutation is required for tumor development. HRAS allelic imbalance favoring the mutant allele was observed in human thyroid cancer cell lines, supporting this conclusion [Chen et al, 2014]. …”

“…In a Hras G12V knock-in mouse model of Costello syndrome developing skin papillomata, amplification of the mutant allele occurred only at the papilloma stage [Chen et al, 2009, 2014]. Angiosarcoma and forestomach papillomata showed similar increase in the copy number of the mutant allele [Chen et al, 2009], leading to the conclusion that further augmentation of the signal output from a single oncogenic Hras mutation is required for tumor development.…”

Modeling RASopathies with Genetically Modified Mouse Models

“…Interestingly, farnesyltransferase inhibition, which blocks H-RAS farnesylation and delocalizes the protein from the plasma membrane (with the subsequent signaling blockade), induced near complete regression of papillomas of TPA-treated H-Ras G12V knockin mice. These data suggest that farnesyltransferase inhibitors should be evaluated in CS patients as well as in tumors induced by H-Ras oncogenes [ 141 ].…”