德国Essen大学皮肤科Dirk Schadendorf教授专访

　　《肿瘤瞭望》：RAF-MEK-ERK通路是恶性黑色素瘤发展和出现药物抵抗的主要通路之一。请您介绍一下，如何判断BRAF抑制剂耐药，以及耐药的发生率和发生时间等？

　　Oncology Frontier: We are aware of Ras-Raf-MEK-ERK signaling pathway is one of the major pathways for the development of drug resistance and malignant melanoma. Please give us a brief introduction on how to define BRAF inhibitor resistance as well as its incidence and timing.

　　Dr. Schadendorf: The Ras-Raf-MEK-ERK pathway is critical for driving proliferation and initiation of metastasis of tumor cells in melanoma. It is driven by gene mutation. One of the most frequently affected genes is BRAF gene. The mutation of BRAF gene is upregulation of this pathway and leads to the oncogenicbehavior of tumor cells. So what we are doing is that we try to interfere with this upregulation of MAPK/ERK pathway by using BRAF inhibitor like Vemurafenib and Dabrafenib. And we found in most of patients this hyperactive pathway is shut down in most of the tumor cells. This can be very nicely visualized by PET scanning which is used for observe metabolic activity of tumor cells. For example， patients who have metastatic melanoma and getting BRAF inhibitors， you can see within hours within days the metabolic activity of the metastasis is shut down. This metabolism shut down is leading with some delay or shrinkage of the tumor. This effect does not happen in all tumor cells and is not for unlimited period of time. This is only a transient phenomenon. As a result， the time when tumor is being controlled depends on how long the BRAF inhibitor is really able to work. On average， the tumor control is in the range of 6 to 7 months. This is the median. We also have patients who are still benefiting from BRAF inhibitor treatment for more than 4 years. On the other hand， there are also patients who have tumor progression after receiving BRAF inhibitor treatment for 8 to 10 weeks. When we do CT scanning we see that there is no effect on the tumor cells and the tumor still grows. So resistance which leads to failure of controlling tumor proliferation varies quite substantially. The mechanisms of resistance are multiple. We have mechanisms which explain in part of this early resistance that BRAF inhibitors have not clinical effect. We have identified numbers of mechanisms which are developed over the treatment course over weeks and months.

　　《肿瘤瞭望》：您提到了耐药机制，请详细介绍一下。

　　Oncology Frontier: So you have mentioned the mechanisms already. Could you be more specific about the mechanisms?

　　Dr. Schadendorf: Yes. So what we have learnt about tumors which escaped from BRAF inhibitor treatment is that around 60-70% of the patients have a reactivation of the MAPK/ERK pathway. So that this pathway which is originally upregulated by the BRAF mutation then is shut down by the BRAF inhibitor for a certain period of time is reactivated by several mechanisms which are part of the MAPK/ERK pathway including NRAS mutations in around 20-30% of the patients. Amplification of BRAF shows a special BRAF splicing variant is a most frequent alteration of BRAF gene. Also in around 20-30% of the patients we found the downstream molecules MEK1 and MEK2 gene mutations which would also lead to resistance.

　　《肿瘤瞭望》：耐药的发生发展是多种机制作用的结果，什么时候我们需要警惕可能发生了耐药，耐药患者需要换用其他抑制剂吗？

　　Oncology Frontier: So it’s coming from multiple mechanisms keeping that resistance going. What kind of circumstance do we need to see for BRAF inhibitors resistance? Would patients need to be changed to different inhibitors?

　　Dr. Schadendorf: Yes. I think understanding resistance is obviously critical in advance. Our treatment approaches need a rational time point to switch to a different treatment modality or adding something additional inhibitors for example. However， we are lacking good techniques at the moment to monitor if our patients are being reactive， if the tumor has really relapse， if there is new gross， for examples， CT scanning. We definitely need a modality which has a different model of action， for example， the combination of patients who have undergone BRAF inhibitor treatment with MEK inhibition with check point of blockade. So principles which work in multiple mechanisms could have a longer lasting in tumor control and patients could survive even longer.

　　《肿瘤瞭望》：在免疫监测点抑制剂和针对信号通路的靶向药物的夹击下，您认为化疗在晚期恶性黑色素瘤的治疗中处于什么样的地位，是否有新的化疗药物可用于晚期恶性黑色素瘤？

　　Oncology Frontier: With so many different emerging effective immune therapies and target drugs what is the status of chemotherapy now. Do we have any advancement for new chemo agencies?

　　Dr. Schadendorf : Target therapy in clinical reality in many parts of the world having access to BRAF inhibitors and we expect the further benefit would be available with magnification by combination of BRAF and MEK inhibition but this will benefit only these patients subset with BRAF mutation which is around 40% in the location in American and Australian patient population. All others which are BRAF wild type not mutant we are still facing huge medical needs. We do see that PD1 antibodies will bring some benefits for these patients who will extend to patients subset with acral melanoma and mucosal melanoma. We need more data on that to make this point finally. Everyone believes that this is not limited to a certain subset of melanoma patients. That for， I think as soon as PD1 antibodies are being approved， there is no real need for chemotherapy in first line. Where that you would need  chemotherapy in 2nd or 3rd line depends on the mutations status and availability of clinical studies and also biological behavior of how quickly the tumor escapes the initial treatment modalities that there will be certain patients who still require chemotherapy. But in 3 years， most of the patients will either see target therapy approaches or immune oncology approaches and then the other way around before they consider chemotherapy.

　　《肿瘤瞭望》：毫无疑问，在中国，能获得新药是治疗开展的关键步骤。您觉得中国百姓还需多久才能获得这些BRAF抑制剂和PD-1抗体等这类药物，而且负担得起？

　　Oncology Frontier: There is no doubt that access to the new drug is the big steppingstone here in China. So how soon do you think there would be available access to affordable BRAF drugs and PD-1 antibody?

　　Dr. Schadendorf: Access to the drugs is critical. We have seen that we have not made any progress in treating melanoma patients for about 30 years. Only the availability of these new drugs has made some progress but it is still far away from being cured. Also in Europe， because the reimbursement issue， some of the new drugs are still not available. Specific procedure in approving the drugs and have money available to pay for the drugs are important. I think in China， one has to think of a way to get things approved quicker and better. For companies who are producing these drugs getting closer contact with regulatory agencies. Here in China， I think those conferences will increase awareness of doctors and Chinese politicians as well as bring together of the drug companies with health regulatory agencies to speed up drug approval process for Chinese patients.

　　BRAF抑制剂在黑色素瘤治疗中的应用

　　既往研究表明，RAS－RAF－MEK－ERK信号传导通路（MARK通路）是驱动黑色素瘤肿瘤细胞生长、增殖和转移的关键分子通路。该通路上信号分子的基因突变，如常见的BRAF基因突变，可造成该通路活性过度增高，诱导肿瘤生成和转移。在此研究基础上，BRAF抑制剂，如维罗非尼（Vemurafenib）和达拉非尼（dabrafenib）先后通过研究和临床试验，获美国FDA批准用于治疗晚期黑色素瘤。这些药物通过抑制过度活化的BRAF分子，来抑制过度激活的RAS/RAF通路，从而抑制肿瘤细胞的代谢活性。在使用了BRAF抑制剂的患者中行PET/CT检查，可直观地发现肿瘤细胞的代谢活性大大降低。转移性黑色素瘤患者在服用了BRAF抑制剂后几个小时或几天内，就可以观察到肿瘤代谢活性明显减退。当肿瘤细胞代谢活性大力削减后，肿瘤体积便会缩小。

　　BRAF抑制剂的耐药现象

　　由于肿瘤的异质性，并不是每个肿瘤细胞都能被BRAF抑制剂所控制。该类药物也无法维持长期有效，肿瘤控制也只呈现短暂效果。目前临床试验数据显示，该类药物的中位无进展生存期（PFS）是6~7个月。虽然有些患者的肿瘤有效控制期已达4年多之久，但也有些患者在服用该类药物8~10个星期之后，CT检查显示肿瘤未被控制，呈现持续增长趋势。所以，总体而言，BRAF抑制剂耐药现象不容忽视。有些患者对BRAF抑制剂完全不敏感，从治疗之初就无任何效果，也有一些患者在使用了几周或是几个月之后才出现耐药。

　　BRAF抑制剂的耐药机制

　　目前研究表明，耐药的患者中，60%~70%有MARK通路的再激活。这些初治时具备BRAF突变的患者，最初由BRAF突变引起的该通路活性增加，在使用BRAF抑制剂后，通路活性得到有效抑制，肿瘤也在一定时间内得到控制，然而使用一段时间之后，信号通路再次被激活，导致肿瘤出现耐药。这其中有多种机制，涉及MARK通路上的不同基因分子，包括NRAS突变、BRAF扩增（如BRAF的剪切变异体的扩增）和MEK1/2突变等。

　　BRAF抑制剂耐药后的应对策略

　　根据耐药机制，我们可以采用其他治疗方案，或者联合运用其他类型抑制剂，比如在使用BRAF抑制剂的基础上联合运用MEK抑制剂、检验点阻断剂（免疫治疗）等。然而，如何及时准确地发现BRAF抑制剂发生耐药，意义更为深远。目前我们尚未建立相应的技术平台，来监测肿瘤的药物反应。哪些患者会提早复发，或是对治疗完全无反应，又或是有长期收益，这些都是目前尚无法及时准确回答的问题。这是未来需要进一步研究的方向之一，以便及时发现耐药的萌芽，及早调整治疗方案，从而让肿瘤得到更为长期有效的控制，延长患者的生存期。

　　加快新药审批以保障患者获得及时有效的治疗

　　获取最新研发并通过临床试验的治疗药物对患者的及时有效治疗相当关键。在欧洲一些地区，患者因为报销问题而无法获得这些药物，因此，我们需要推进药物的审核批准及相关的保险制度，保障患者及时用药、并在经济上能够负担。中国也面临着同样的问题，这就需要制药公司同相关法规部门尽早协调审核，政府部门、卫生行业相关机构、一线医务工作者、研究人员、药剂工作者等需通力合作，共同推动新药的审核批准及推广，以使患者能及时获得有效的治疗药物，保障治疗进行。