ALKERMES启动ALKS-4230联合K药的临床
可瑞达就在默沙东
这棵大树有阴凉
你与他们常来往
想必是安排照应更周详
看到这个标题时，脑子里过的沙家浜里小刁的唱词。
ALKERMES启动 ALKS-4230联合KEYTRUDA® (pembrolizumab)治疗进展性实体瘤的1期临床，原文内容见最后，标题看下来，首先是一个问题：什么是ALKS-4230?
直接copy Journal of Clinical Oncology 35, no. 15_suppl
ALKS 4230 is an engineered fusion protein comprised of a circularly permuted interleukin-2 (IL-2) and IL-2 Receptor (IL-2R) α designed to selectively activate the intermediate-affinity (ia) IL-2R, comprised of IL-2Rβ and γc. The iaIL-2R is expressed predominantly on effector lymphocytes, which play an important role in driving antitumor immune responses. In contrast, unmodified IL-2 activates high-affinity (ha) IL-2R, driving the expansion of haIL-2R-expressing cell types including immunosuppressive CD4+ regulatory T (Treg) cells at concentrations below those at which iaIL-2R bearing effector cells are activated. Also, the haIL-2R is expressed on endothelial cells and may contribute to IL-2 mediated toxicity via capillary leak syndrome. Thus, selective activation of the iaIL-2R by ALKS 4230 has the potential to provide enhanced tumor killing as well as improved tolerability.
看到IL-2之后，大家肯定会想起NKTR-214，ALKS-4230和NKTR-214都是通过对IL-2的修饰或改造，使其能够相对特异性的结合表达在NK细胞及CD8+T细胞表面的IL2受体复合物（IL2R β/γ or CD122/CD132）来激活免疫系统，和PD-1单抗合用会有好的协同作用。
那么ALKS-4230和普通的IL-2及NKTR-214有什么不同呢？首先还是要从IL-2受体的组成说起。
IL-2R由α、β和γ三个不同亚基组成，三个亚基可以组成不同亲和力的受体：
单独的α亚基（IL-2α即CD25）组成低亲和力的受体，Kd~10nM，其胞内很短，单独存在不参与信号转导；
β亚基（IL-2Rβ即CD122）和γ亚基（IL-2Rγ即CD132）组成中等亲和力受体，Kd~1nM，其中IL-2Rβ结合IL2亲和力很低Kd~100nM，而IL-2γ单独几乎不结合IL-2，IL-2Rβ/γ受体主要表达在NK细胞或者CD8+ T细胞表面；
三亚集一起组成最高亲和力受体，Kd~10pM，主要表达在活化T细胞和Treg表面；
IL-2Ｒβ/γ 在结合IL-2后活化JAK-1和JAK-3 ，激活细胞内信号转导通路从而发挥生物学效应，因此对不同细胞各异的生物学效应与其复杂的信号转导机制有关。
IL-2是最早的免疫治疗药物，20世纪90年代FDA就批准IL-2用于晚期肾癌和恶黑，ORR 15%-20%，5年OS 10-15%，但IL-2剂量高且副作用很大，会引起严重的低血压和血管渗漏综合征，必须住院密切观察，因此限制了临床的大规模使用。
那下面来看NKTR-214，在IL-2上修饰6个PEG分子，形成了无活性的前药（prodrug，紫色），给患者注射之后，PEG会从前药会逐渐脱落，形成了有活性的2-PEG和1-PEG的形式（绿色），这个过程都是不可逆的。活性药物会偏向和CD122亚基结合(bias CD122)，从而更容易激活NK细胞和CD8+ T细胞，提升抗肿瘤免疫，而不是激活Treg细胞来抑制免疫。
为什么bias CD122?其实应该是“The PEG chains on NKTR-214 are located at the region of IL2 that contacts the alpha (α) subunit of the heterotrimeric IL2 receptor complex, IL2Rαβγ, reducing its ability to bind and activate the heterotrimer.”保留的PEG分子对结合IL-2Rαβγ的影响力更大，但是对结合IL-2Rβγ的影响较小，下表格中用IL-2Rαβ和IL-2Rβ模拟IL-2Rαβγ和IL-2Rβγ。
最后来看主角ALKS-4230，ALKERMES用了circularly permuted即环状结构重组的方法来构建全新的IL-2。环状结构重组原本是将蛋白质中原本的N与C端被相接，然后在另一处产生开口，原有的结构与活性在新蛋白中得到部分保留，同时在一些结构或功能上又区别于原来的蛋白。
但参考他家专利US20130336924A1（Ligands Modified by Circular Permutation as Agonists and Antagonists），改造基于晶体结构2B5I，具体细节如下描述：
首先生成IL2的一个vriant，最终是IL-2 variant融合到IL-2Rα的N端，定义IL-2的95和94位氨基酸为新的N和C末端，这是将C端通过2个氨基酸的linker连接到IL--2原本N端的第4个氨基酸，这时产生的C末端(即原来的94位氨基酸)通过一个6个氨基酸的间隔序列融合到IL-2Rα的N端，最后在IL-2Rα的C端加上一个人Ig G1 型Fc片段，这个就是最早的RDB1405，也就是现在的ALKS-4230。
文字太绕，可以直接看图：
可以看出，
IL-2和IL-2R的四聚体中最关键的相互作用是IL-2红色部分也就是IL-2的N端部分，灰色部分原本是和IL-2Rγ接近，也有微弱的相互作用，这里移到N端并不影响与IL-2Rβ的结合
IL-2Rα起到捕获IL-2的作用，原本IL-2与IL-2Rβ/γ相互作用中等，这时增加了IL-2Rα，可以形成较强相互作用的的四元复合体，另外某种程度上IL-2Rα也起NKTR-214中PEG的作用，通过位阻降低了和Treg等细胞表面IL-2Rαβγ的结合亲和力
最后Fc融合还有利于提高半衰期
因此整个ALKS-2430就可以较高亲和力去特异性激活那些不表达IL-2Rα的细胞表面的IL-2R，这部分细胞主要NK和CD8+ T细胞，机制的方向上和NKTR-214是相反的。
2B5I的结构由斯坦福大学医学院免疫与结构大佬Garcia组在05年完成，这几年Garcia组又发表了正交IL-2/CD122等相关的研究，希望为免疫细胞治疗提供增强疗效减少毒性的策略等，anyway，罗马不是一天建成的，今天任何一点的进展都可能是昨天无数次的积累甚至是失败推动的。
今天讲讲基础技术，下次整理IL-2R激动剂类的临床。
-- Ongoing Phase 1 Study Expanded to Assess Safety and Anti-Tumor Activity of ALKS 4230 With Pembrolizumab in Patients With Advanced Solid Tumors --
DUBLIN, Sept. 10, 2018 /PRNewswire/ -- Alkermes plc (Nasdaq: ALKS) today announced that it has expanded its ongoing phase 1 study for ALKS 4230, the company's immuno-oncology drug candidate, to evaluate its safety and anti-tumor activity when administered in combination with the FDA-approved PD-1 inhibitor KEYTRUDA® (pembrolizumab) in patients with advanced solid tumors. ALKS 4230 is an engineered fusion protein designed to preferentially bind and signal through the intermediate affinity interleukin-2 (IL-2) receptor complex, thereby selectively activating and increasing the number of immunostimulatory tumor-killing immune cells while avoiding the expansion of immunosuppressive cells that interfere with anti-tumor response. Pembrolizumab is an anti-PD-1 therapy that works by increasing the ability of the body's immune system to help detect and fight tumor cells.
"The emergence of therapeutics targeting the PD-1 pathway has revolutionized the field of oncology, yet there remains significant opportunity to improve the clinical benefit of checkpoint inhibitors for the treatment of solid tumors. There is strong scientific rationale supporting the combination of PD-1 pathway inhibition with cytokine therapy such as ALKS 4230 to activate the body's own immune system to fight cancer, and the potential synergies of ALKS 4230 and pembrolizumab on anti-tumor activity may expand treatment options for patients in a variety of tumor settings," said Craig Hopkinson, M.D., Chief Medical Officer and Senior Vice President of Medicines Development and Medical Affairs at Alkermes. "We've accelerated clinical evaluation of ALKS 4230 in combination with pembrolizumab based on data from our ongoing monotherapy dose-escalation stage of the phase 1 study, where ALKS 4230 demonstrated dose-dependent pharmacodynamic effects on circulating natural killer cells and CD8+ T cells, and minimal and non-dose dependent effects on immunosuppressive regulatory T cells. These data validate our design rationale for ALKS 4230, and we look forward to sharing initial data from our dose-escalation cohorts at a medical meeting later this year."
Evaluation of the safety and anti-tumor activity of ALKS 4230 in combination with pembrolizumab will be assessed in certain PD-1 approved tumor types in both refractory and treatment naïve patients, including non-small cell lung cancer (NSCLC), head and neck squamous cell carcinoma, gastric cancer, urothelial carcinoma and microsatellite instability-high cancers. Melanoma and renal cell carcinoma will also be evaluated in the cohort of treatment naïve patients. The combination of ALKS 4230 and pembrolizumab will also be assessed in certain PD-1 unapproved tumor types, including colorectal cancer, triple-negative breast cancer, ovarian carcinoma, soft tissue sarcomas, and patients with metastatic NSCLC whose tumors express low or undetectable PD-L1 (tumor proportion score <1%).