RAS/RAF突变与MSI状态在结直肠癌治疗中的研究进展

近几年,结直肠癌中的分子研究取得了相当大的进展,对如何通过分子表达的不同来选择最佳治疗方案也有了更深的认识。RAS/RAF基因是染色体不稳定性(CIN)通路中最重要的组成部分之一。最近的研究显示RAS/RAF突变的患者有机会接受靶向MAP激酶信号传导通路中的EGFR-KRAS/BRAF-MEK抑制剂的联合治疗,从而为预后不良的RAS/RAF突变患者提供一种新的治疗方式。日前,微卫星不稳定性(MSI)已经被确认为结直肠癌患者接受PD-1治疗的分子标志物。但是MSI对患者是否应接受免疫治疗的预测仍存在些许偏差,相信更为完美的预测靶点肿瘤突变负荷(TMB)将在不久的将来应用于指导临床进行免疫治疗。RAS/RAF突变及MSI状态的研究进展,为改善结直肠癌患者的预后提供了美好前景。     

RAS signaling pathways, mutations and their role in colorectal cancer

Two of the main cellular pathways in which the RAS protein operates are the mitogen-activated protein kinases (MAPK) and phosphoinositide-3 kinase (PI3K) pathways. In a normal cell, these are important in controlling several functions, such as cell growth and survival. It becomes self-evident that these events will be disrupted in a malignant cell with a deregulated MAPK or PI3K pathway. Mutations in genes involved in these pathways and interacting with RAS, as well as RAS itself will be discussed. The second part of this review concentrates on how crucial RAS signaling is in colorectal cancer progression, with references to treatment response and prognosis when RAS or other related mutations are present.     

结直肠癌APC、K-ras、p53基因突变检测

目的:探讨结直肠癌中APC、K-ras、p53基因突变模式。方法:应用酚/氯仿法提取48例结直肠癌组织及其相应正常黏膜组织的DNA,用聚合酶链反应(PCR)、单链构象多态性分析(SSCP)和DNA测序等方法检测APC基因第15外显子突变密集区(mutation cluster region,MCR)区段、K-ras和p53基因的突变。结果:APC、K-ras和p53基因的突变率分别为37.5%(18/48)、43.8%(21/48)和35.4%(17/48)。48例结直肠癌组织中,有42例发生APC、K-ras或p53基因突变,突变率高达87.5%(42/48),其中仅有APC、K-ras或p53 1种基因发生突变的发生率分别为16.7%(8/48)、25.0%(12/48)和20.8%(10/48)。单独1种基因发生突变的总发生率为62.5%(30/48)。APC和p53,APC和K-ras或p53和K-ras 2种基因均有突变的发生率分别为6.3%(3/48)、10.4%(5/48)和4.2%(2/48)。APC、K-ras和p53 3种基因均发生突变的发生率为4.2%(2/48)。2种和3种基因均发生突变的总发生率为25%(12/48)。结论:结直肠癌的发生、发展并不完全遵循由正常结直肠黏膜上皮细胞向腺瘤和侵袭性癌转化的过程中,及依次发生“APC→K-ras→p53→DCC”突变累积这一经典的结直肠癌发生发展模式,可能存在其他结直肠癌发病机制。     

RAS Signaling in Colorectal Carcinomas through Alteration of RAS, RAF, NF1, and/or RASSF1A

More than half of all colorectal carcinomas are known to exhibit an activated mitogen-activated protein kinase pathway. The NF1 gene, a negative regulator of KRAS, has not previously been examined in a series of colorectal cancer. In the present study, primary colorectal carcinomas stratified according to microsatellite instability status were analyzed. The whole coding region of NF1 was analyzed for mutations using denaturing high-performance liquid chromatography and sequencing, and the copy number alterations of NF1 were examined using multiple ligation-dependent probe amplification and real-time polymerase chain reaction. The mutational hot spots in KRAS and BRAF were sequenced, and promoter hypermethylation status of RASSF1A was assessed with a methylation-specific polymerase chain reaction. One sample had two missense mutations in NF1, whereas nine additional tumors had intronic mutations likely to affect exon splicing. Interestingly, 8 of these 10 tumors were microsatellite-unstable. Four other tumors showed a duplication of NF1. Mutations in KRAS and BRAF were mutually exclusive and were present at 40% and 22%, respectively. RASSF1A was hypermethylated in 31% of the samples. We show that the RAS signaling network is extensively dysregulated in colorectal carcinomas, because more than 70% of the tumors had an alteration in one or more of the four examined components.     

An Update on the Biology of RAS/RAF Mutations in Colorectal Cancer

Deaths caused by colorectal cancer (CRC) are among the leading causes of cancer-related death in the United States and around the world. Approximately 150,000 Americans are diagnosed with CRC each year and around 50,000 will die from it. Mutations in many key genes have been identified that are important to the pathogenesis of CRC. Among the genes mutated in CRC, RAS and RAF mutations are common events. Both RAS and RAF are critical mediators of the mitogen-activated protein kinase (MAPK) pathway that is involved in regulating cellular homeostasis, including proliferation, survival, and differentiation. In this review, we provide a historical perspective and update on RAS/RAF mutations as related to colorectal cancer. Additionally, we will review recent mouse models of RAS and RAF mutations that have an impact on CRC research.     

Alterations in K-ras, APC and p53-multiple genetic pathway in colorectal cancer among Indians

The incidence of colorectal cancer (CRC) is increasing rapidly in Asian countries during the past few decades, but no comprehensive analysis has been done to find out the exact cause of this disease. In this study, we investigated the frequencies of mutations and expression pattern of K-ras, APC (adenomatosis polyposis coli) and p53 in tumor, adjoining and distant normal mucosa and to correlate these alterations with patients clinicopathological parameters as well as with the survival. Polymerase chain reaction (PCR)-restriction digestion was used to detect mutations in K-ras and PCR-SSCP (Single Strand Conformation Polymorphism) followed by DNA sequencing was used to detect mutations in APC and p53 genes. Immunohistochemistry was used to detect the expression pattern of K-ras, APC and p53 proteins. The frequencies of mutations of K-ras, APC and p53 in 30 tumor tissues samples were 26.7 %, 46.7 % and 20 %, respectively. Only 3.3 % of tumors contained mutations in all the three genes. The most common combination of mutation was APC and p53 whereas mutation in both p53 and K-ras were extremely rare. There was no association between the mutations and expression pattern of K-ras, APC and p53 (p?>?0.05). In Indians, the frequency of alterations of K-ras and APC is similar as in Westerns, whereas the frequency of p53 mutation is slightly lower. The lack of multiple mutations in tumor specimens suggests that these genetic alterations might have independent influences on CRC development and there could be multiple alternative genetic pathways to CRC in our present study cohort.     

FGFR3 and P53 characterize alternative genetic pathways in the pathogenesis of urothelial cell carcinoma

Fibroblast growth factor receptor 3 (FGFR3) and P53 mutations are frequently observed in bladder cancer. We here describe the distribution of FGFR3 mutations and P53 overexpression in 260 primary urothelial cell carcinomas. FGFR3 mutations were observed in 59% and P53 overexpression in 25%. Interestingly, FGFR3 and P53 alterations were mutually exclusive, because they coincided in only 5.7% of tumors. Consequently, we propose that they characterize two alternative genetic pathways in urothelial cell carcinoma pathogenesis. The genetic alterations were reflected in the pathology and the clinical outcome, i.e., FGFR3 mutations were found in low-stage/-grade tumors and were associated with a favorable disease course, whereas P53 alterations were tied to adverse disease parameters.     

Oncogenic activation of the RAS/RAF signaling pathway impairs the response of metastatic colorectal cancers to anti-epidermal growth factor receptor antibody therapies

Monoclonal antibodies (mAbs) against the extracellular domain of the epidermal growth factor receptor (EGFR) have been introduced for the treatment of metastatic colorectal cancer (mCRC). We have reported recently that increased copy number of the EGFR can predict response to anti-EGFR mAbs and that patients might be selected for treatment based on EGFR copy number. Here, we show that mutations activating the RAS/RAF signaling pathway are also predictive and prognostic indicators in mCRC patients, being inversely correlated with response to anti-EGFR mAbs. In cellular models of CRCs, activation of the RAS signaling pathway by introduction of an activated K-RAS allele (Gly(12)Val) impairs the therapeutic effect of anti-EGFR mAbs. In cancer cells carrying constitutively active RAS, the pharmacologic inhibition of the mitogen-activated protein kinase (MAPK) signaling cascade improves anti-EGFR treatment based on mAbs. These results have implications for the identification of patients who are likely to respond to anti-EGFR treatment. They also provide the rationale for combination therapies, targeted simultaneously to the EGFR and RAS/RAF/MAPK signaling pathways in CRC patients.     

Phase II Trial of Trametinib and Panitumumab in RAS/RAF Wild Type Metastatic Colorectal Cancer

IntroductionMEK inhibition may overcome resistance to EGFR inhibition in patients with RAS wildtype (wt) metastatic colorectal cancer (mCRC). We evaluated antitumor activity of trametinib (MEK1/2 inhibitor) with panitumumab (EGFR monoclonal antibody) in a phase II trial.MethodsPatients with KRAS, NRAS, and BRAF wt mCRC with prior 5-FU, irinotecan, oxaliplatin, +/- bevacizumab and no prior anti-EGFR therapy were treated with trametinib 1.5 mg oral daily and panitumumab 4.8 mg/kg IV every 2 weeks. Primary endpoint was clinical benefit rate (CB; CR, PR, or SD ≥24 weeks) by RECIST v1.1. A 2-stage minimax design was used. Serial plasma circulating free DNA (cfDNA) was collected and profiled using Oncomine Lung cfDNA assay.ResultsFourteen patients were enrolled from November 2015 to April 2019. CB rate was 38% (5/13) and median progression free survival (PFS) was 4.4 months (95% CI, 2.9-7.1). Confirmed overall response rate was 38% (5/13). Treatment-related AE (trAE) included acneiform rash (85%), diarrhea (62%), maculopapular rash (54%), mucositis (46%), and others. Dose modifications and interruptions of trametinib occurred in 69% and panitumumab in 54% of patients. The trial did not progress to stage II accrual due to tolerability and short duration of response. RAS or BRAF mutations cfDNA were detected in 3/13 patients (23%) before radiographic disease progression.ConclusionThe addition of trametinib to panitumumab led to a high rate of tumor shrinkage in RAS/RAF wt metastatic colorectal cancer, with poor tolerability due to a high incidence of skin toxicity. Median PFS was similar to panitumumab alone in historical control data.     

Mutations of APC,K-ras,and p53 are associated with specific chromosomal aberrations in colorectal adenocarcinomas

It is widely accepted that both large-scale chromosomal abnormalities and mutation of specific genes, such as APC, K-ras, and/or p53, occur in the majority of colorectal adenocarcinomas. Whether or not a relationship exists between these different forms of genetic abnormalities was previously unknown. Using comparative genomic hybridization and mutational analysis of APC, K-ras, and p53 to evaluate 50 colorectal adenocarcinomas, we have shown that mutation of p53 is significantly associated with gain of 20q, 13q, and 8q and loss of 18q (P = 0.000, 0.02, 0.044, and 0.001, respectively). Conversely, APC mutation did not associate with any of the above-mentioned aberrations but did associate significantly with gain of 7p (P = 0.01). Gain of chromosomal arm 12p, although a less common aberration, was significantly associated with K-ras mutation (P = 0.011). The associations we have described should refine the search for candidate genes underlying chromosomal aberrations and assist in the definition of distinct pathways in colorectal tumorigenesis.     

P53-dependent effects of RAS oncogene on chromosome stability and cell cycle checkpoints.

Mutations activating the function of ras proto-oncogenes are often observed in human tumors. Their oncogenic potential is mainly due to permanent stimulation of cellular proliferation and dramatic changes in morphogenic reactions of the cell. To learn more on the role of ras activation in cancerogenesis we studied its effects on chromosome stability and cell cycle checkpoints. Since the ability of ras oncogenes to cause cell transformation may be dependent on activity of the p53 tumor-suppressor the cells with different p53 state were analysed. Ectopic expression of N-ras(asp12) caused in p53-deficient MDAH041 cell line an augmentation in the number of chromosome breaks in mitogenic cells, significant increase in the frequency of metaphases showing chromosome endoreduplication and accumulation of polyploid cells. Similar effects were induced by different exogenous ras genes (N-ras(asp12), H-ras(leu12), N-ras proto-oncogene) in Rat1 and Rat2 cells which have a defect in p53-upstream pathways. In contrast, in REF52 and human LIM1215 cells showing ras-induced p53 up-regulation, ras expression caused only slight increase in the number of chromosome breaks and did not enhance the frequency of endoreduplication and polyploidy. Inactivation in these cells of p53 function by transduction of dominant-negative C-terminal p53 fragment (genetic suppressor element #22, GSE22) or mutant p53s significantly increased the frequency of both spontaneous and ras-induced karyotypic changes. In concordance with these observations we have found that expression of ras oncogene caused in p53-defective cells further mitigation of ethyl-metansulphonate-induced G1 and G2 cell cycle arrest, but did not abrogate G1 and G2 cell cycle checkpoints in cells with normal p53 function. These data indicate that along with stimulation of cell proliferation and morphological transformation ras activation can contribute to cancerogenesis by increasing genetic instability.     

APC、β-catenin、C-myc和Cyclin D1在大肠癌组织中的表达及其意义

背景与目的:Wnt信号转导通路成员各癌基因、抑癌基因的异常,激活下游相关靶基因的转录,在肿瘤发生发展中起重要作用.本研究通过检测不同大肠组织中APC、β-catenin、C-myc和Cyclin D1的表达情况,探讨其在大肠癌发生中的意义.方法:应用免疫组织化学方法检测30例正常大肠粘膜、30例大肠腺瘤、10例大肠腺瘤恶变及50例大肠癌组织中APC、β-catenin、C-myc和Cyclin D1蛋白的表达情况.以β-catenin在细胞膜表达为正常表达,而在胞浆和/或胞核表达为异位表达.结果:大肠癌和大肠腺瘤恶变组织APC阳性率分别为44.0%和40.0%,显著低于大肠腺瘤(86.7%)和正常大肠粘膜(100%)(P＜0.01).大肠癌、大肠腺瘤恶变组织和大肠腺瘤β-catenin胞浆和/或胞核异位表达率分别为62.0%、50.0%、30.0%,均显著高于正常大肠粘膜(0%)(P＜0.01),大肠癌β-catenin异位表达率显著高于大肠腺瘤(P＜0.01).大肠癌、大肠腺瘤恶变组织、大肠腺瘤中C-myc表达率分别为56.0%、60.0%、46.7%,均显著高于正常大肠粘膜(0%)(P＜0.01),而Cyclin D1阳性率分别为66.0%、60.0%、30.0%,均显著高于正常大肠粘膜(0%)(P＜0.01).大肠癌Cyclin D1表达率显著高于大肠腺瘤(P＜0.01).大肠癌中β-catenin异位表达与C-myc和Cyclin D1表达呈正相关关系(r=0.63,P＜0.01;r=0.57,P＜0.01),而与APC表达呈负相关关系(r=-0.39,P＜0.05).结论:大肠癌组织中存在APC低表达和/或β-catenin异位表达,以及C-myc和Cyclin D1的过度表达,4种基因蛋白可能在大肠癌发生过程中起重要作用.     

大肠癌中APC、β-catenin和cyclinD1的表达及其临床意义

目的：探讨APC、β-catenin和cyclinD1在大肠癌发生、发展过程中的作用。方法：应用免疫组织化学方法检测30例正常大肠黏膜、30例大肠腺瘤、10例大肠腺瘤恶变及50例大肠癌组织中APC、β-catenin和cyclinD1蛋白的表达情况。结果：大肠癌和大肠腺瘤恶变APC阳性率分别为44.0%,40.0%,显著低于大肠腺瘤（86.7%）和正常大肠黏膜（100%）（P〈0.01）。大肠癌、大肠腺瘤恶变和大肠腺瘤β-catenin胞浆和/或胞核异位表达率分别为：62.0%,50.0%,30.0%,显著高于正常大肠黏膜（0）（P〈0.01）,大肠癌β-catenin异位表达率显著高于大肠腺瘤（P〈0.01）。大肠癌中β-catenin膜表达缺失率为：46.0%,显著高于大肠腺瘤（10.0%）和正常大肠黏膜（0）（P〈0.01）。大肠癌、大肠腺瘤恶变、大肠腺瘤cyclinD1阳性率分别为：66.0%,60.0%,30.0%,显著高于正常大肠黏膜（0）（P〈0.01）,大肠癌cyclinD1阳性率显著高于大肠腺瘤（P〈0.01）。β-catenin膜表达缺失和cyclinD1高表达与大肠癌组织分化程度、浸润深度、淋巴结转移、Dukes分期有关。APC蛋白表达与大肠癌组织分化程度有关。大肠癌中β-catenin异位表达与cyclinD1阳性表达呈正相关关系（r=0.57,P〈0.01）,而与APC阳性表达呈负相关关系（r=-0.39,P〈0.05）。结论：APC失表达和/或β-catenin异位表达,可能是原癌基因cyclinD1激活的重要原因,并在大肠癌发生过程中起重要作用,可能是大肠癌发生的早期事件。β-catenin膜表达缺失和cyclinD1高表达与大肠癌的侵袭、转移有关。     

Prognostic significance of p53 overexpression in gastric and colorectal carcinoma.

p53 expression was examined in 55 gastric and 107 colorectal carcinomas with an immunoperoxidase technique, using the polyclonal antibody CM1 on routinely fixed, paraffin embedded tissue. p53 protein was detected in 47% gastric and in 46% colorectal carcinomas and found to correlate with stage of disease and unfavourable clinical outcome (P less than 0.001). Thus, the proportion of positively reacting neoplasms increased as the stage progressed, tumours which had invaded regional lymph-nodes overexpressed p53 more frequently than localised carcinomas and an elevated level of p53 was associated with early relapse and death. In colorectal carcinoma p53 positivity was also linked with site and macroscopic configuration of the primary tumour and was most frequently expressed in carcinomas from the rectum and in ulcerative tumours. p53 overexpression was irrespective of tumour grade. Uniform negative reactivity with anti-p53 antibody was seen in normal epithelium adjacent to carcinoma, intestinal metaplasia, atrophic gastritis and in colonic adenomas. There was a good correlation between immunohistochemical staining on paraffin and frozen sections. These studies suggest that in gastric and colorectal carcinoma, immunohistochemical detection of p53 protein in routinely fixed tissue can be used along with other established parameters to assess prognostic outcome, especially to identify patients with poor short-term prognosis.     

LOSS OF HETEROZYGOSITY INVOLVING THE APC TUMOR SUPPRESSOR GENE IN HUMAN COLORECTAL CARCINOMA

ＬＯＳＳＯＦＨＥＴＥＲＯＺＹＧＯＳＩＴＹＩＮＶＯＬＶＩＮＧＴＨＥＡＰＣＴＵＭＯＲＳＵＰＰＲＥＳＳＯＲＧＥＮＥＩＮＨＵＭＡＮＣＯＬＯＲＥＣＴＡＬＣＡＲＣＩＮＯＭＡ￥ＸｕＷｅｎｈｕａｉ；徐文怀；ＹａｎｇＤｉｎｇｃｈｅｎｇ；杨定成（Ｄｅｐａｒｔｍｅｎｔｏｆ...     

p53 and RAS gene mutations in multiple myeloma.

We analysed genomic DNA from 30 patients with multiple myeloma (MM), searching for alterations in the p53 and RAS genes by a combination of polymerase chain reaction and single-strand conformation polymorphism techniques. Mutations in the p53 gene were observed in 20% (6 out of 30) of the patients, and were located in conserved sequence blocks within exons 5 and 7. These were single-nucleotide substitutions and consisted predominantly (4/6) of G:C to A:T transitions. Of the six patients with a mutated p53 gene, four were in the terminal phase of the disease. RAS gene mutations were found more frequently since they occurred in 47% (14 out of 30) of the patients. Mutations consisted of single-nucleotide substitutions, located in codons 12, 13 and 61 of either K- or N-RAS, to the exclusion of H-RAS. Moreover, one patient bore two simultaneous mutations, affecting simultaneously the K- and the N-RAS genes. RAS gene mutations were more frequently observed in patients with fulminating disease (10/15, 67%) than in patients with less aggressive forms of the disease (4/15, 26%). We also analysed genomic DNAs from 10 human myeloma cell lines, of which two bore mutations affecting codon 12 of the K-RAS gene, and one codon 12 of the N-RAS gene. The first two cell lines were obtained from freshly explanted tumor cells in which we observed identical mutations. Results presented here show that activating mutations in the RAS genes are, in MM, more frequent than those affecting the p53 gene and suggest that both events are related to terminal phases of the disease.