The role of molecular genetics in the clinical management of sporadic medullary thyroid carcinoma: A systematic review.
Fussey Jonathan Mark,Vaidya Bijay,Kim Dae,Clark Jonathan,Ellard Sian,Smith Joel Anthony
BACKGROUND:The significant variation in the clinical behaviour of sporadic medullary thyroid carcinoma (sMTC) causes uncertainty when planning the management of these patients. Several tumour genetic and epigenetic markers have been described, but their clinical usefulness remains unclear. The aim of this review was to evaluate the evidence for the use of molecular genetic and epigenetic profiles in the risk stratification and management of sMTC. METHODS:MEDLINE and Embase databases were searched using the MeSH terms "medullary carcinoma", "epigenetics", "molecular genetics", "microRNAs"; and free text terms "medullary carcinoma", "sporadic medullary thyroid cancer", "sMTC", "RET", "RAS" and "miR". Articles containing less than ten subjects, not focussing on sMTC, or not reporting clinical outcomes were excluded. Risk of bias was assessed using a modified version of the Newcastle-Ottawa Scale. RESULTS:Twenty-three studies met the inclusion criteria, and key findings were summarized in themes according to the genetic and epigenetic markers studied. There is good evidence that somatic RET mutations predict higher rates of lymph node metastasis and persistent disease, and worse survival. There are also several good quality studies demonstrating associations between certain epigenetic markers such as tumour miR-183 and miR-375 expression and higher rates of lymph node and distant metastasis, and worse survival. CONCLUSIONS:There is a growing body of evidence that tumour genetic and epigenetic profiles can be used to risk stratify patients with sMTC. Further research should focus on the clinical applicability of these findings by investigating the possibility of tailoring management to an individual's tumour mutation profile.
Correlative analyses of RET and RAS mutations in a phase 3 trial of cabozantinib in patients with progressive, metastatic medullary thyroid cancer.
Sherman Steven I,Clary Douglas O,Elisei Rossella,Schlumberger Martin J,Cohen Ezra E W,Schöffski Patrick,Wirth Lori J,Mangeshkar Milan,Aftab Dana T,Brose Marcia S
BACKGROUND:Cabozantinib significantly prolonged progression-free survival (PFS) versus a placebo in patients with progressive, metastatic medullary thyroid cancer (MTC; P < .001). An exploratory analysis of phase 3 trial data evaluated the influence of rearranged during transfection (RET) and RAS (HRAS, KRAS, and NRAS) mutations on cabozantinib clinical activity. METHODS:Patients (n = 330) were randomized to cabozantinib (140 mg/day) or a placebo. The primary endpoint was PFS. Additional outcome measures included PFS, objective response rates (ORRs), and adverse events in RET and RAS mutation subgroups. RESULTS:Among all study patients, 51.2% were RET mutation-positive (38.2% with RET M918T), 34.8% were RET mutation-unknown, and 13.9% were RET mutation-negative. Sixteen patients were RAS mutation-positive. Cabozantinib appeared to prolong PFS versus the placebo in the RET mutation-positive subgroup (hazard ratio [HR], 0.23; 95% confidence interval [CI], 0.14-0.38; P < .0001), the RET mutation-unknown subgroup (HR, 0.30; 95% CI, 0.16-0.57; P = .0001), and the RAS mutation-positive subgroup (HR, 0.15; 95% CI, 0.02-1.10; P = .0317). The RET M918T subgroup achieved the greatest observed PFS benefit from cabozantinib versus the placebo (HR, 0.15; 95% CI, 0.08-0.28; P < .0001). The ORRs for RET mutation-positive, RET mutation-negative, and RAS mutation-positive patients were 32%, 22%, and 31%, respectively. No PFS benefit was observed in patients lacking both RET and RAS mutations, although the ORR was 21%. The safety profile for all subgroups was similar to that for the overall cabozantinib arm. CONCLUSIONS:These data suggest that cabozantinib provides the greatest clinical benefit to patients with MTC who have RET M918T or RAS mutations. However, a prospective trial is needed to confirm the relation between genetic variation and the response to cabozantinib. Cancer 2016;122:3856-3864. © 2016 American Cancer Society.
Exomic sequencing of medullary thyroid cancer reveals dominant and mutually exclusive oncogenic mutations in RET and RAS.
Agrawal Nishant,Jiao Yuchen,Sausen Mark,Leary Rebecca,Bettegowda Chetan,Roberts Nicholas J,Bhan Sheetal,Ho Allen S,Khan Zubair,Bishop Justin,Westra William H,Wood Laura D,Hruban Ralph H,Tufano Ralph P,Robinson Bruce,Dralle Henning,Toledo Sergio P A,Toledo Rodrigo A,Morris Luc G T,Ghossein Ronald A,Fagin James A,Chan Timothy A,Velculescu Victor E,Vogelstein Bert,Kinzler Kenneth W,Papadopoulos Nickolas,Nelkin Barry D,Ball Douglas W
The Journal of clinical endocrinology and metabolism
CONTEXT:Medullary thyroid cancer (MTC) is a rare thyroid cancer that can occur sporadically or as part of a hereditary syndrome. OBJECTIVE:To explore the genetic origin of MTC, we sequenced the protein coding exons of approximately 21,000 genes in 17 sporadic MTCs. PATIENTS AND DESIGN:We sequenced the exomes of 17 sporadic MTCs and validated the frequency of all recurrently mutated genes and other genes of interest in an independent cohort of 40 MTCs comprised of both sporadic and hereditary MTC. RESULTS:We discovered 305 high-confidence mutations in the 17 sporadic MTCs in the discovery phase, or approximately 17.9 somatic mutations per tumor. Mutations in RET, HRAS, and KRAS genes were identified as the principal driver mutations in MTC. All of the other additional somatic mutations, including mutations in spliceosome and DNA repair pathways, were not recurrent in additional tumors. Tumors without RET, HRAS, or KRAS mutations appeared to have significantly fewer mutations overall in protein coding exons. CONCLUSIONS:Approximately 90% of MTCs had mutually exclusive mutations in RET, HRAS, and KRAS, suggesting that RET and RAS are the predominant driver pathways in MTC. Relatively few mutations overall and no commonly recurrent driver mutations other than RET, HRAS, and KRAS were seen in the MTC exome.
Somatic RAS mutations occur in a large proportion of sporadic RET-negative medullary thyroid carcinomas and extend to a previously unidentified exon.
Boichard A,Croux L,Al Ghuzlan A,Broutin S,Dupuy C,Leboulleux S,Schlumberger M,Bidart J M,Lacroix L
The Journal of clinical endocrinology and metabolism
CONTEXT:Medullary thyroid carcinoma (MTC) is characterized by proto-oncogene RET mutations in almost all hereditary cases as well as in more than 40% of sporadic cases. Recently, a high prevalence of RAS mutations was reported in sporadic MTC, suggesting an alternative genetic event in sporadic MTC tumorigenesis. OBJECTIVE:This study aimed to extend this observation by screening somatic mutational status of RET, BRAF, and the three RAS proto-oncogenes in a large series of patients with MTC. MATERIALS AND METHODS:Direct sequencing of RET (exons 8, 10, 11, 13, 14, 15, 16), BRAF (exons 11 and 15), and KRAS, HRAS, and NRAS genes (exons 2, 3, and 4) was performed on DNA prepared from 50 MTC samples, including 30 sporadic cases. RESULTS:Activating RET mutations were detected in the 20 hereditary cases (germline mutations) and in 14 sporadic cases (somatic mutations). Among the 16 sporadic MTC without any RET mutation, eight H-RAS mutations and five K-RAS mutations were found. Interestingly, nine RAS mutations correspond to mutation hot spots in exons 2 and 3, but the other four mutations were detected in exon 4. The RET and RAS mutations were mutually exclusive. No RAS gene mutation was found in hereditary MTC, and no BRAF or NRAS mutation was observed in any of the 50 samples. CONCLUSIONS:Our study confirms that RAS mutations are frequent events in sporadic MTC. Moreover, we showed that RAS mutation analysis should not be limited to the classical mutational hot spots of RAS genes and should include analysis of exon 4.
Evidence of a low prevalence of RAS mutations in a large medullary thyroid cancer series.
Ciampi Raffaele,Mian Caterina,Fugazzola Laura,Cosci Barbara,Romei Cristina,Barollo Susi,Cirello Valentina,Bottici Valeria,Marconcini Giulia,Rosa Pelizzo Maria,Borrello Maria Grazia,Basolo Fulvio,Ugolini Clara,Materazzi Gabriele,Pinchera Aldo,Elisei Rossella
Thyroid : official journal of the American Thyroid Association
BACKGROUND:Approximately 60% of sporadic medullary thyroid carcinomas (sMTC) remain orphan of a recognized genetic cause. Recently, a high percentage of RAS point mutations have been described in RET-negative sMTC. The aim of this study was to assess the prevalence of RAS point mutations in a large series of MTC collected in four Italian centers. METHODS:For this purpose, we studied codons 12, 13, and 61 of H-, K-, and N-RAS genes in 188 MTC samples, either hereditary or sporadic, by direct sequencing. Correlations between the RAS mutational status and the clinical-pathological features of MTC patients as well as a meta-analysis of all published data were performed. RESULTS:The prevalence of RAS mutations in the present series of MTC was 10.1%, and 17.6% when considering only RET-negative cases. RAS mutations were found in MTC tumoral tissue, but not in peripheral blood indicating their somatic origin. A novel mutation in codon 72 (M72I) was found, but with a low or null transforming potential. No association was found between the presence of RAS mutations and the clinical-pathological features of the patients. Although not statistically significant, a positive association between the presence of RAS mutations and a better outcome was observed. The meta-analysis of all published studies confirmed a prevalence of 8.8% for RAS mutations in MTC. CONCLUSIONS:The prevalence of RAS mutations in our MTC series was relatively low and consistent with the meta-analysis data. Only somatic RAS mutations were found and only in RET-negative sMTC. Likewise, MTCs that harbor a RAS mutation identify a subgroup of tumors with less aggressive behavior. To our knowledge, this is the largest series of MTCs studied for the presence of mutations in RAS genes and the first meta-analysis on this specific topic.
Mutational screening of RET, HRAS, KRAS, NRAS, BRAF, AKT1, and CTNNB1 in medullary thyroid carcinoma.
Schulten Hans-Juergen,Al-Maghrabi Jaudah,Al-Ghamdi Khalid,Salama Sherine,Al-Muhayawi Saad,Chaudhary Adeel,Hamour Osman,Abuzenadah Adel,Gari Mamdooh,Al-Qahtani Mohammed
BACKGROUND:Screening medullary thyroid carcinomas (MTCs) for rearranged during transfection (RET) mutations becomes increasingly important for clinical assessment of the disease. The role of mutations in other genes including RAS (i.e. HRAS, KRAS, and NRAS), v-raf murine sarcoma viral oncogene homolog B1 (BRAF), v-akt murine thymoma viral oncogene homolog 1 (AKT1), and CTNNB1 (β-catenin) is unknown or not fully explored yet for this disease. MATERIALS AND METHODS:Formalin-fixed and paraffin-embedded (FFPE) material was the primary source for screening 13 sporadic and inherited MTCs and matched non-tumor specimens. Multiplex PCR was included in the PCR protocol. Sequence analysis encompassed mutational hotspot regions in RET exons 5, 8, 10, 11, and 13 to 16; HRAS exons 1 and 2; KRAS exons 1 and 2; NRAS exons 1 and 2; BRAF exon 15; AKT1 exon 2, and CTNNB1 exon 3. RESULTS:We identified RET mutations in seven of 13 MTCs: five RET-positive cases revealed a mutation in exon 16 (M918T) and two a mutation in exon 10 (C618S and C620S). In four of the RET-positive cases, the mutation was inherited, out of which three were reportedly associated with a multiple endocrine neoplasia type 2 (MEN2) syndrome, i.e. MEN2A (C618S), MEN2A/familial MTC (FMTC) (C620S), and MEN2B (M918T). These cases reflect the known MEN2 genotype-phenotype correlation. Three of the five stage IVc MTCs were inherited RET-positive cases. Mutational screening in HRAS, KRAS, NRAS, BRAF, AKT1, and CTNNB1 disclosed one sporadic RET-negative MTC (stage III) with mutation in HRAS codon 13 (G13R). CONCLUSION:Our study supports the clinical relevance of screening MTC patients for RET mutations. The role of RAS mutations, in particular HRAS mutations, in sporadic RET-negative MTC has not been fully explored yet. Mutations in BRAF, AKT1, and CTNNB1 are likely not to play a role in MTC.
Analysis of somatic mutations in BRAF, CDKN2A/p16 and PI3KCA in patients with medullary thyroid carcinoma.
Nascimento Fabrício P,Cardoso Mirian G,Lindsey Susan C,Kunii Ilda S,Valente Flávia O F,Kizys Marina M L,Delcelo Rosana,Camacho Cléber P,Maciel Rui M B,Dias-Da-Silva Magnus R
Molecular medicine reports
Medullary thyroid carcinoma (MTC), a neuroendocrine tumor originating from thyroid parafollicular cells, has been demonstrated to be associated with mutations in RET, HRAS, KRAS and NRAS. However, the role of other genes involved in the oncogenesis of neural crest tumors remains to be fully investigated in MTC. The current study aimed to investigate the presence of somatic mutations in BRAF, CDKN2A and PI3KCA in MTC, and to investigate the correlation with disease progression. DNA was isolated from paraffin‑embedded tumors and blood samples from patients with MTC, and the hotspot somatic mutations were sequenced. A total of 2 novel HRAS mutations, p.Asp33Asn and p.His94Tyr, and polymorphisms within the 3' untranslated region (UTR) of CDKN2A (rs11515 and rs3088440) were identified, however, no mutations were observed in other genes. It was suggested that somatic point mutations in BRAF, CDKN2A and PI3KCA do not participate in the oncogenesis of MTC. Further studies are required in order to clarify the contribution of the polymorphisms identified in the 3'UTR of CDKN2A in MTC.
Clinical significance of RET and RAS mutations in sporadic medullary thyroid carcinoma: a meta-analysis.
Vuong Huy Gia,Odate Toru,Ngo Hanh T T,Pham Thong Quang,Tran Thao T K,Mochizuki Kunio,Nakazawa Tadao,Katoh Ryohei,Kondo Tetsuo
There are ongoing debates with respect to the prognostic roles of molecular biomarkers in sporadic medullary thyroid carcinoma (MTC). In this study, we aimed at investigating the prognostic value of and mutations - the two most common mutations in sporadic MTCs. A search was conducted in four electronic databases. Relevant data were extracted and pooled into odds ratios (OR), mean differences (MD) and corresponding 95% confidence intervals (CI) using the random-effect model. We used Egger's regression test and visual of funnel plots to assess the publication bias. From 2581 studies, we included 23 studies with 964 MTCs for meta-analysis. Overall, the presence of mutation was associated with an elevated risk for lymph node metastasis (OR = 3.61; 95% CI = 2.33-5.60), distant metastasis (OR = 2.85; 95% CI = 1.64-4.94), advanced tumor stage (OR = 3.25; 95% CI = 2.02-5.25), tumor recurrence (OR = 3.01; 95% CI = 1.65-5.48) and patient mortality (OR = 2.43; 95% CI = 1.06-5.57). mutation had no significant prognostic value in predicting tumor aggressiveness. To summarize, our results affirmed that mutation is a reliable molecular biomarker to identify a group of highly aggressive sporadic MTCs. It can help clinicians better assess patient prognosis and select appropriate treatment decisions.
Comprehensive Genomic Profiling of Clinically Advanced Medullary Thyroid Carcinoma.
Heilmann Andreas M,Subbiah Vivek,Wang Kai,Sun James X,Elvin Julia A,Chmielecki Juliann,Sherman Steven I,Murthy Ravi,Busaidy Naifa L,Subbiah Ishwaria,Yelensky Roman,Nangia Chaitali,Vergilio Jo-Anne,Khan Saad A,Erlich Rachel L,Lipson Doron,Ross Jeffrey S,Miller Vincent A,Shah Manisha H,Ali Siraj M,Stephens Philip J
OBJECTIVE:The aim of this study was to determine the genomic alterations of cancer-related genes in advanced medullary thyroid carcinoma during the course of clinical care. METHODS:Hybrid-capture-based comprehensive genomic profiling was performed on 34 consecutive medullary thyroid carcinoma cases to identify all four classes of genomic alterations, and outcome for an index patient was collected. RESULTS:RET was mutated in 88% (30/34) of cases, with RET M918T being responsible for 70% (21/30) of the RET alterations. The other RET alterations were RET E632_L633del, C634R, C620R, C618G/R/S, V804M, and RET amplification. Two of the four RET wild-type patients harbored mutations in KRAS or HRAS (1/34 each). The next most frequent genomic alterations were amplifications of CCND1, FGF3, and FGF19 and alterations in CDKN2A (3/34 each). One case with a RET M918T mutation developed acquired resistance to progressively dose-escalated vandetanib. When the mTOR inhibitor everolimus was added to continued vandetanib treatment, the patient achieved a second 25% reduction of tumor volume (RECIST 1.1) for 8 months. CONCLUSIONS:Comprehensive genomic profiling identified the full breadth of RET alterations in metastatic medullary thyroid carcinoma and possible cooperating oncogenic driver alterations. This approach may refine the use of targeted therapy for these patients.
Alternative RNA splicing of calcitonin/calcitonin gene-related peptide minigene transcripts in a thyroid C-cell line.
Cote G J
Biochemical and biophysical research communications
RNA transcripts derived from the calcitonin (CT)/calcitonin gene-related peptide (CGRP) gene are differentially processed in a tissue-specific fashion to produce two unique mRNAs. This RNA processing decision is deregulated in malignant thyroid C-cells. To examine this mechanism of RNA processing, CT/CGRP minigene constructs were transfected into the human medullary thyroid carcinoma TT cell line. RNA derived from the normal CT/CGRP construct paralleled the endogenous pathway to produce both CT and CGRP mRNAs. Mutation analysis and RNA/protein crosslinking were performed in order to clarify trans-acting factor interactions. The data suggest that CGRP production in TT cells results from the coexpression of facilitative and inhibitory factors.
Interplay between Ret and Fap-1 regulates CD95-mediated apoptosis in medullary thyroid cancer cells.
Nicolini Valentina,Cassinelli Giuliana,Cuccuru Giuditta,Bongarzone Italia,Petrangolini Giovanna,Tortoreto Monica,Mondellini Piera,Casalini Patrizia,Favini Enrica,Zaffaroni Nadia,Zunino Franco,Lanzi Cinzia
Emerging evidence suggests that Ret oncoproteins expressed in medullary thyroid cancer (MTC) might evade the pro-apoptotic function of the dependence receptor proto-Ret by directly impacting the apoptosis machinery. Identification of the molecular determinants of the interplay between Ret signaling and apoptosis might provide a relevant contribution to the optimization of Ret-targeted therapies. Here, we describe the cross-talk between Ret-M918T oncogenic mutant responsible for type 2B multiple endocrine syndrome (MEN2B), and components of death receptor-mediated extrinsic apoptosis pathway. In the human MEN2B-type MTC cell line MZ-CRC-1 expressing Ret-M918T, Ret was found associated with Fap-1, known as inhibitor of the CD95 death receptor trafficking to the cell membrane, and with procaspase-8, the initiator pro-form caspase in the extrinsic apoptosis pathway. Cell treatment with the anti-tumor Ret kinase inhibitor RPI-1 inhibited tyrosine phosphorylation of procaspase-8, likely inducing its local activation, followed by downregulation of both Ret and Fap-1, and translocation of CD95 into lipid rafts. According to the resulting increase of CD95 cell surface expression, the CD95 agonist antibody CH11 enhanced RPI-1-induced cell growth inhibition and apoptosis. RET RNA interference downregulated Fap-1 protein in MZ-CRC-1 cells, whereas exogenous RET-M918T upregulated Fap-1 in HEK293 cells. Overall, these data indicate that the Ret oncoprotein exerts opposing controls on Fap-1 and CD95, increasing Fap-1 expression and decreasing CD95 cell surface expression. The functional interplay of the Ret mutant with the extrinsic apoptosis pathway provides a mechanism possibly contributing to MTC malignant phenotype and a rational basis for novel therapeutic strategies combining Ret inhibitors and CD95 agonists.
Diversity of mutations in the RET proto-oncogene and its oncogenic mechanism in medullary thyroid cancer.
Hedayati Mehdi,Zarif Yeganeh Marjan,Sheikholeslami Sara,Afsari Farinaz
Critical reviews in clinical laboratory sciences
Thyroid cancer is the most common endocrine malignancy and accounts for nearly 1% of all of human cancer. Thyroid cancer has four main histological types: papillary, follicular, medullary, and anaplastic. Papillary, follicular, and anaplastic thyroid carcinomas are derived from follicular thyroid cells, whereas medullary thyroid carcinoma (MTC) originates from the neural crest parafollicular cells or C-cells of the thyroid gland. MTC represents a neuroendocrine tumor and differs considerably from differentiated thyroid carcinoma. MTC is one of the aggressive types of thyroid cancer, which represents 3-10% of all thyroid cancers. It occurs in hereditary (25%) and sporadic (75%) forms. The hereditary form of MTC has an autosomal dominant mode of inheritance. According to the present classification, hereditary MTC is classified as a multiple endocrine neoplasi type 2 A & B (MEN2A & MEN2B) and familial MTC (FMTC). The RET proto-oncogene is located on chromosome 10q11.21. It is composed of 21 exons and encodes a transmembrane receptor tyrosine kinase. RET regulates a complex network of signal transduction pathways during development, survival, proliferation, differentiation, and migration of the enteric nervous system progenitor cells. Gain of function mutations in RET have been well demonstrated in MTC development. Variants of MTC result from different RET mutations, and they have a good genotype-phenotype correlation. Various MTC related mutations have been reported in different exons of the RET gene. We proposed that RET genetic mutations may be different in distinct populations. Therefore, the aim of this study was to find a geographical pattern of RET mutations in different populations.
Quantitative Proteomics Analysis of Sporadic Medullary Thyroid Cancer Reveals FN1 as a Potential Novel Candidate Prognostic Biomarker.
Zhan Shaohua,Li Jinming,Wang Tianxiao,Ge Wei
BACKGROUND:Sporadic medullary thyroid cancer (MTC) is a rare neuroendocrine tumor. Currently, although the diagnosis of sporadic MTC is relatively simple, the need to discover novel candidate prognostic biomarkers for sporadic MTC and investigate the underlying mechanism involved in this rare disease is urgent. MATERIALS AND METHODS:We employed tandem mass tag-based liquid chromatography-mass spectrometry to identify and analyze differentially expressed proteins (DEPs) in sporadic MTC. Western blotting was used to validate the DEPs. Immunohistochemistry was performed to investigate FN1 and RPS6KA3 in an independent set of sporadic MTC tissues. Immunohistochemical data were analyzed by different statistical methods. RESULTS:Three hundred eighty-eight DEPs were identified in mass spectrometry, mainly involved in the extracellular matrix, cytoskeletal remodeling, or oxidoreductase activity. Among them, THBS1, MMP9, FN1, RPS6KA3, SYT1, and carcinoembryonic antigen were successfully validated by Western blot. In addition, FN1 and RPS6KA3, enriched in extracellular matrix (ECM) remodeling and the mitogen-activated protein kinase (MAPK) signaling pathway, respectively, were investigated in an independent set of sporadic MTC tissues. Receiver-operator characteristic curve analysis showed that FN1 and RPS6KA3 can be used for discriminating sporadic MTC tumorous tissues from paired normal thyroid tissues, and the clinical biomarker calcitonin was positively correlated with FN1 and RPS6KA3 in tumorous tissues. Furthermore, the immunohistochemical scores of FN1 in tumorous tissue showed an inverse relationship with tumor classification, lymph node classification, and American Joint Committee on Cancer stage. Through univariate and multivariate analysis for progression-free survival, we also found that low FN1 expression in tumorous tissues was an independent worse prognostic factor for progression-free survival. CONCLUSION:We identified that the pathophysiology of sporadic MTC involve numerous pathways, including the synaptic vesicle pathway, the MAPK signaling pathway, and the ECM remodeling pathway. Furthermore, our study also identified FN1 as novel prognostic biomarkers related to the pathophysiologic changes in sporadic MTC. IMPLICATIONS FOR PRACTICE:Proteomic dissection and prognostic biomarkers are scarce in sporadic medullary thyroid cancer (MTC). This article reports the use of proteomics technology to comprehensively investigate the molecular mechanisms of sporadic MTC, which resulted in the identification of FN1 as a novel candidate prognostic biomarker.
Transcriptional targeting of oncogene addiction in medullary thyroid cancer.
Valenciaga Anisley,Saji Motoyasu,Yu Lianbo,Zhang Xiaoli,Bumrah Ceimoani,Yilmaz Ayse S,Knippler Christina M,Miles Wayne,Giordano Thomas J,Cote Gilbert J,Ringel Matthew D
Metastatic medullary thyroid cancer (MTC) is incurable and FDA-approved kinase inhibitors that include oncogenic RET as a target do not result in complete responses. Association studies of human MTCs and murine models suggest that the CDK/RB pathway may be an alternative target. The objective of this study was to determine if CDKs represent therapeutic targets for MTC and to define mechanisms of activity. Using human MTC cells that are either sensitive or resistant to vandetanib, we demonstrate that palbociclib (CDK4/6 inhibitor) is not cytotoxic to MTC cells but that they are highly sensitive to dinaciclib (CDK1/2/5/9 inhibitor) accompanied by reduced CDK9 and RET protein and mRNA levels. CDK9 protein was highly expressed in 83 of 83 human MTCs and array-comparative genomic hybridization had copy number gain in 11 of 30 tumors. RNA sequencing demonstrated that RNA polymerase II-dependent transcription was markedly reduced by dinaciclib. The CDK7 inhibitor THZ1 also demonstrated high potency and reduced RET and CDK9 levels. ChIP-sequencing using H3K27Ac antibody identified a superenhancer in intron 1 of RET. Finally, combined inhibition of dinaciclib with a RET kinase inhibitor was synergistic. In summary, we have identified what we believe is a novel mechanism of RET transcription regulation that potentially can be exploited to improve RET therapeutic targeting.
Role of RET protein-tyrosine kinase inhibitors in the treatment RET-driven thyroid and lung cancers.
Roskoski Robert,Sadeghi-Nejad Abdollah
RET is a transmembrane receptor protein-tyrosine kinase that is required for the development of the nervous system and several other tissues. The mechanism of activation of RET by its glial-cell derived neurotrophic factor (GDNF) ligands differs from that of all other receptor protein-tyrosine kinases owing to the requirement for additional GDNF family receptor-α (GFRα) co-receptors (GFRα1/2/3/4). RET point mutations have been reported in multiple endocrine neoplasia (MEN2A, MEN2B) and medullary thyroid carcinoma. In contrast, RET fusion proteins have been reported in papillary thyroid and non-small cell lung adenocarcinomas. More than a dozen fusion partners of RET have been described in papillary thyroid carcinomas, most frequently CCDC6-RET and NCOA4-RET. RET-fusion proteins, commonly KIF5B-RET, have also been found in non-small cell lung cancer (NSCLC). Several drugs targeting RET have been approved by the FDA for the treatment of cancer: (i) cabozantinib and vandetanib for medullary thyroid carcinomas and (ii) lenvatinib and sorafenib for differentiated thyroid cancers. In addition, alectinib and sunitinib are approved for the treatment of other neoplasms. Each of these drugs is a multikinase inhibitor that has activity against RET. Previous X-ray studies indicated that vandetanib binds within the ATP-binding pocket and forms a hydrogen bond with A807 within the RET hinge and it makes hydrophobic contact with L881 of the catalytic spine which occurs in the floor of the adenine-binding pocket. Our molecular modeling studies indicate that the other antagonists bind in a similar fashion. All of these antagonists bind to the active conformation of RET and are therefore classified as type I inhibitors. The drugs also make variable contacts with other residues of the regulatory and catalytic spines. None of these drugs was designed to bind preferentially to RET and it is hypothesized that RET-specific antagonists might produce even better clinical outcomes. Currently the number of new cases of neoplasms bearing RET mutations or RET-fusion proteins is estimated to be about 10,000 per year in the United States. This is about the same as the incidence of chronic myelogenous leukemia for which imatinib and second and third generation BCR-Abl non-receptor protein-tyrosine kinase antagonists have proven clinically efficacious and which are commercially successful. These findings warrant the continued development of specific antagonists targeting RET-driven neoplasms.