High-throughput mutation profiling of CTCL samples reveals KRAS and NRAS mutations sensitizing tumors toward inhibition of the RAS/RAF/MEK signaling cascade

Abstract

Cutaneous T-cell lymphomas (CTCLs) are malignancies of skin-homing lymphoid cells, which have so far not been investigated thoroughly for common oncogenic mutations. We screened 90 biopsy specimens from CTCL patients (41 mycosis fungoides, 36 Sé zary syndrome, and 13 non-mycosis fungoides/Sé zary syndrome CTCL) for somatic mutations using OncoMap technology. We detected oncogenic mutations for the RAS pathway in 4 of 90 samples. One mycosis fungoides and one pleomorphic CTCL harbored a KRAS G13D mutation; one Séz-ary syndrome and one CD30 ؉ CTCL harbored a NRAS Q61K amino acid change. All mutations were found in stage IV patients (4 of 42) who showed significantly decreased overall survival compared with stage IV patients without mutations (P ‫؍‬ .04). In addition, we detected a NRAS Q61K IntroductionCutaneous T-cell lymphomas (CTCLs) are rare malignancies of skin-homing T lymphocytes. Curative modalities have thus far proven elusive. CTCL microarray studies have revealed natural clusters in association with prognosis. 1 Array-based comparative genomic hybridization (CGH) combined with gene expression profiling identified highly recurrent chromosomal alterations both in mycosis fungoides (MF) and Sézary syndrome (SS) patient specimens. 2,3 For example, FASTK and SKAP1 gene loci showed recurrent gains, and these genes also exhibited increased expression, whereas RB1 and DLEU tumor suppressor genes displayed diminished expression associated with loss. In another study, recurrent deletion of tumor suppressor genes BCL7A, SMAC/ DIABLO, and RHOF in MF was observed. 4 Genomic patterns characteristic of MF differ markedly from SS. 5 This might implicate discriminative molecular pathogenesis and different therapeutic requirements.The RAS-RAF-MEK-ERK signaling pathway regulates cell responses to environmental stimuli and plays a crucial role in many cancers. 6 Thus, RAF and MEK are attractive therapeutic targets. 7,8 RAS is a small guanine-nucleotide binding protein that is attached to the inner side of the plasma membrane. Activation of RAS causes RAF recruitment and activation by phosphorylation. Activated RAF kinase phosphorylates and activates MEK, which phosphorylates ERK. Three RAS (KRAS, NRAS, and HRAS), 3 RAF (ARAF, BRAF, and CRAF), 2 MEK (MEK1 and MEK2), and 2 ERK (ERK1 and ERK2) isoforms compose the "canonical" mitogen-activated protein kinase pathway. Somatic mutations that are found in many cancers, including colon carcinoma, melanoma, or pancreatic cancer, occur almost exclusively in BRAF, KRAS, or NRAS isoforms. 9-11 Typical mutations affect glycine 12 (G12), glycine 13 (G13), or glutamine 61 (Q61) and keep RAS in an activated form. The RAS pathway regulates survival, proliferation, senescence, and differentiation. However, in tumor cells, mutated (oncogenic) RAS preferentially promotes survival and proliferation. Thus, RAF and MEK kinases serve as suitable drug targets. RAF is targeted by inhibitors in preclinical or clinical development, including, for example, RAF265 and PLX4720. 12,13 However, target...

Simultaneous inhibition of pan-phosphatidylinositol-3-kinases and MEK as a potential therapeutic strategy in peripheral T-cell lymphomas

“…We did not find any known mutation in PIK3CA, AKT1, PTEN, KRAS and BRAF genes in any cell line. The described 14 NRAS mutation Q61K was confirmed in the HuT78 cell line, but was absent from the other PTCL cell lines (data not shown). Although no mutations have yet been reported in the PIK3CD gene, 15 two described variants 16 were also studied in PTCL cell lines.…”

Combined targeting of MEK and PI3K/mTOR effector pathways is necessary to effectively inhibit NRAS mutant melanoma in vitro and in vivo

“…Staining intensity was significantly higher for the MEK/ERK than for the PI3K/mTOR pathway (MEK/ERK 1.2 ± 0.2 PI3K/ mTOR 0.86 ± 0.3 P = 0.015), suggesting a predominance of this pathway in NRAS mutant melanomas stained. Recent studies demonstrate that cells with activating mutations in the RAS pathway respond to MEK inhibitors; however, in melanoma, this is especially true for RAF mutant tumors with no other activating alternations (12,30,31). To test whether NRAS mutant melanoma cell lines are sensitive to MEK inhibition, we characterized their response to two different MEK inhibitors.…”

Romidepsin and Azacitidine Synergize in their Epigenetic Modulatory Effects to Induce Apoptosis in CTCL

“…In CTCL, various cytogenetic studies found multiple genetic alterations that recur in a subset of mycosis fungoides and/or S ezary syndrome patients (36)(37)(38). But few common genetic variants including targetable mutations have been identified (39).…”