靶向AKT的抗肿瘤药物研究曙光已见

作者：朱孝峰　 中山大学肿瘤防治中心华南肿瘤学国家重点实验室
AKT可能成为抗肿瘤药物的新靶点
    PI3K/AKT途径为受体酪氨酸激酶信号转导通路的下游途径，也是细胞内一条重要的生存通路。
    在肿瘤发生、发展的过程中，由于酪氨酸激酶受体过表达或突变、PI3KCA突变、PTEN突变或缺失、AKT扩增或突变等导致AKT持续活化。当AKT在细胞膜上被过度激活后，能够向细胞质或细胞核转运，并与相应部位的底物蛋白发生作用，使底物蛋白特定部位的丝氨酸/苏氨酸发生磷酸化而激活或灭活底物蛋白，如BAD、FOXO、GSK-3β、P27、P21、procaspase-9、IKK、Mdm2、mTOR、EZH2、内皮细胞NO合成酶、端粒酶、基质金属蛋白酶等，从而抑制肿瘤细胞凋亡，促进其生长、增殖、侵袭、血管生成，以及对化疗、放疗耐受。
    近来，有研究证实PTEN/ PI3K/AKT/GSK-3/-catenin和PTEN/ PI3K/AKT /mTOR等途径的过度激活在维持肿瘤干细胞的干性及生存中发挥重要作用。因此，AKT可能是一个具有广泛开发前景的抗肿瘤药物靶点。

靶向AKT的抗肿瘤药物研究正蓬勃发展
    近年来，基于AKT为靶点的抗肿瘤药物研究正在蓬勃发展，并且取得了一些具有开发前景的抑制剂。这些抑制剂主要有以下几类。
    靶向AKT的ATP结合位点  竞争性抑制ATP结合位点的抑制剂。目前AKT抑制剂GSK2141795与MEK抑制剂GSK1120212联合正在进行Ⅰ期临床试验。
    磷脂酰肌醇类似物  因为PIP3能直接与AKT的PH域相结合，故PIP3类似物可竞争性地与AKT相结合，阻止AKT移位至胞膜并被激活。其代表性化合物是Keryx公司研发的Perifosine。目前Perifosine 联合放疗、吉西他滨、多西他赛、紫杉醇的Ⅰ期临床试验以及单独应用治疗复发的乳腺癌、前列腺癌、头颈部肿瘤以及肺癌的临床Ⅱ期试验正在进行中。
    变构抑制剂  能与AKT的PH结构域或连接PH结构域与激酶区的连接结构域结合，引起AKT构象的改变，从而阻碍PDK-1与AKT活化位点的靠近，使AKT308位点苏氨酸残基不能被磷酸化而抑制AKT的活化。其代表性化合物是默克公司研发的MK2206，在Ⅰ期临床试验中，该化合物单药取得了较好的疗效。为了阻止AKT抑制后的反馈途径从而提高疗效，默克公司和阿斯利康公司已决定联手，将MK2206与MEK抑制剂AZD6244联合用于NSCLC的Ⅱ期临床试验。
    我们研究组多年来一直从事AKT调控的信号通路及其靶向药物的研究，发现Excisanin A（从大萼香茶菜中分离得到的一种二萜类单体化合物）可通过抑制AKT的活性并阻断其下游信号转导途径进而诱导肿瘤细胞凋亡，SYUNZ-16（紫草素衍生物）也可通过抑制AKT活性并阻断AKT/FOXO信号途径诱导肿瘤细胞凋亡。针对AKT的ATP结合位点设计合成筛选发现一类新型AKT抑制剂——2-嘧啶-5-酰胺基噻唑类化合物，其中DC120抑制AKT激酶活性在纳摩尔浓度，在体内外能显著抑制肿瘤细胞增殖，阻断AKT下游信号通路，诱导细胞凋亡；在悬浮培养条件下，化合物DC120能显著抑制MCF-7干细胞微球囊的形成。体内外研究发现，DC120抑制了AKT促进增殖和抗凋亡的作用，但是AKT激酶活性的抑制却反馈增强了MEK/ERK通路，在联合MEK抑制剂后显著增强其抗瘤作用。

AKT抑制剂联合其他靶向药物初见曙光
    PI3K/AKT途径是细胞内一条重要的生存通路，AKT活性抑制后细胞会反馈激活一些重要信号通路维持细胞的存活。已证实抑制AKT途径可反馈性上调酪氨酸激酶受体的表达或激活mTORC2等从而激活MAPK信号通路等，AKT下游的mTOR抑制剂如雷帕霉素和替西罗莫司（Temsirolimus）可通过IGF-1途径反馈性地激活PI3K/AKT途径。AKT抑制剂单药的效果不理想可能与其激活的反馈通路有关，这些反馈通路的形成是这一类抑制剂的最大特征，也是这一类抑制剂开发成抗癌药物的障碍。近年来，对AKT抑制剂作用的反馈机制的了解不断深入，研究者们提出联合不同通路的药物阻断其反馈机制可能是AKT抑制剂研发的正确方向。目前有许多AKT抑制剂联合酪氨酸激酶抑制剂、mTOR抑制剂或MEK抑制剂等在进行Ⅰ/Ⅱ期临床试验，并且已初见曙光。

Phase I clinical trial of an allosteric AKT inhibitor, MK-2206, using a once weekly (QW) dose regimen in patients with advanced solid tumors.
http://www.asco.org/ascov2/Meeti ... mp;abstractID=79123
2011 ASCO Annual Meeting
Background: AKT is a key regulator of cellular proliferation, apoptosis and growth. A range of cancers have genetic aberrations that involve the PI3K/AKT pathway, leading to abnormal AKT hyperactivation and tumor progression. MK-2206 is a novel potent investigational AKT inhibitor, which was initially administered orally in a QOD schedule, where the maximum tolerated dose (MTD) was established at 60mg, based on safety and biomarker studies (Yap et al, ASCO 2010). In view of a long half-life (t1/2) (60-80h), a QW schedule was subsequently pursued to explore the potential of less frequent dosing to circumvent feedback activation of alternative signaling pathways in response to sustained and uninterrupted AKT inhibition. Methods: Eligible patients with advanced solid tumors were recruited in a phase I, multi-center, dose escalation study. Patients had regular safety assessments and blood sampling for pharmacokinetic (PK) studies. Pharmacodynamic (PD) and/or predictive biomarker analyses were undertaken on paired tumor samples (mandatory biopsies at MTD), platelet-rich plasma, hair follicles and circulating nucleic acids in plasma. Results: 30 patients (17 M; median age 60 yr; ECOG PS 0/1: 11/19) received MK-2206 at 90, 135, 200, 250 and 300 mg QW（每周一次）. Grade 3 rash was the dose limiting toxicity (DLT) at 300mg (n=3) and 250mg (n=2). Expansion of the 200mg QW resulted in grade 3 rash DLT in 4 of 15 patients. An intermediate dose of 150mg QW is being investigated. Common reversible MK-2206-related toxicities included rash (32.3%)（皮疹）, fatigue (9.7%) （疲劳）and nausea（恶心）, vomiting（呕吐）, diarrhea（腹泻）, pruritus（皮肤瘙痒）, stomatitis（口腔炎）, dry skin（皮肤干燥） and dysgeusia (味觉障碍), each occurring at 6.5%. No MK-2206-related grade 5 toxicities were observed. PK analysis showed a median Tmax of 6 hr and a mean apparent terminal t1/2 of 78.6 hr. PD analysis of platelet-rich plasma at 200mg QW (n=9) showed suppression of pAKT up to 96 hours post-dose (p<0.001). Biomarker analyses of tumor samples are ongoing. Conclusions: MK-2206 has shown an acceptable toxicology profile, significant and sustained AKT blockade and a PK-PD profile allowing for QW dosing.

A phase I dose-escalation study of oral MK-2206 (allosteric AKT inhibitor) with oral selumetinib (AZD6244; MEK inhibitor) in patients with advanced or metastatic solid tumors.
2011 ASCO Annual Meeting
Background: The PI3K-Akt and RAF/MEK/ERK pathways represent two of the most frequently activated growth factor signaling pathways in human cancer. Inhibition of both pathways could yield greater benefits than inhibiting either pathway alone. The objectives of this phase I study were to examine the safety, pharmacokinetics (PK), pharmacodynamics (PD) and preliminary antitumor activity of the novel combination of MK-2206 with selumetinib. This investigational study represents a new approach to early-stage drug development with the collaboration of two pharmaceutical companies co-developing early stage targeted agent combinations (NCT01021748). Methods: Eligible patients with advanced solid tumors were treated with MK-2206 either every other day (QOD) （隔日一次）or once weekly (QW), in combination with selumetinib administered continuously either once daily (QD) or twice daily (BID). Results: To date, 33 patients have been treated on five dose levels. In the MK-2206 QOD dosing schedule, dose-limiting Grade 3 macular skin rash was reported in 2/3 evaluable patients at MK-2206 45 mg QOD with selumetinib 75mg BID; the tolerable dose was MK-2206 45 mg QOD with selumetinib 75 mg QD. For QW MK-2206, dose-limiting acneiform rash (n=1), stomatitis (n=1) and detached retinal pigment epithelium (n=1) were observed in 3/7 evaluable patients treated at MK-2206 90 mg QW with selumetinib 75mg BID; dose reduction to MK-2206 90mg QW/ selumetinib 50 mg BID was not tolerated due to dose-limiting acneiform rash in 2/ 4 evaluable patients. An intermediate dose of MK-2206 90mg once weekly with selumetinib 75mg QD was tolerable. Preliminary assessment of PK/PD data suggest no apparent drug-drug interactions with the PK profile of each drug administered in this combination. Conclusions: MK2206 at 45 mg QOD, or 90 mg QW is well tolerated in combination with selumetinib 75 mg QD in patients with advanced cancer.

Impact of AKT inhibitor MK-2206 on erlotinib resistance in non-small cell lung cancer (NSCLC).
2011 ASCO Annual Meeting
Background: Mechanisms of acquired resistance to erlotinib (E) in NSCLC include aberrant activation of alternative receptor tyrosine kinases and/or their downstream signal transduction cascades (e.g, c-Met and AKT), indicating a need for strategies to detect such resistance mechanisms and agents to overcome them. The effects of MK2206, a selective AKT inhibitor, on E activity in NSCLC cell lines with diverse oncogenic mutation profiles and a range of E sensitivity were investigated. We hypothesized that inhibition of AKT signaling would augment E activity and reverse resistance. Methods: Four cell lines were evaluated: HCC827 (EGFR-mutant, E-hypersensitive), H1666 (EGFR-wild type, E-sensitive), H358 (EGFR-wild type, E-sensitive) and A549 (EGFR-wild type, E-resistant). Treatment effects were assessed by MTT assay, colony formation, flow cytometry and immunoblotting for signaling and apoptosis. Results: The combination of MK2206 and E showed significantly enhanced growth inhibition compared to single-agent treatment in all lines tested, including E-resistant cells. Addition of the c-Met ligand, HGF, blocked anti-proliferative and cytotoxic effects of E. Treatment with MK-2206 restored E sensitivity in cells rendered resistant by HGF. In comparison, c-Met inhibition (using PHA665752) effectively overcame HGF-mediated resistance, but was ineffective as a single agent or in combination with E. In E-resistant A549 cells, the addition of MK2206 significantly reduced colony formation compared to the single agents. Conclusions: MK2206 enhanced E activity in both E-sensitive and E-resistant NSCLC cell lines, and re-sensitized cells rendered resistant through c-Met activation by HGF. This paradigm is currently being tested in an ongoing NCI-sponsored phase II trial of MK-2206 in combination with E in patients with advanced NSCLC (stratified by EGFR mutational status) who have previously benefited from E-based therapy.

A phase I trial of MK 2206 in children with refractory solid tumors: A Children’s Oncology Group study.
http://abstract.asco.org/AbstView_114_100590.html
Results: Forty-five patients [23 males, median age 13.6 years (range 3.1-21.9)] with malignant glioma (14), ependymoma (4), hepatocellular carcinoma (3), gliomatosis cereberi (2) or other tumors (22) were enrolled; 34 were fully evaluable for toxicity (schedule 1 n=17; schedule 2 n=17). Schedule 1 DLTs included: grade 3 dehydration（脱水）in 1/6 patients at 28 mg/m2; grade 4 hyperglycemia（高血糖）and neutropenia（嗜中性白血球减少症）in 1/6 patients at 45 mg/m2. There were no DLTs at 35 mg/m2 and dose level 4 (58 mg/m2) is currently open for patient accrual with one enrollment. Schedule 2 DLTs included: grade 3 alkaline phosphatase（碱性磷酸酶）in 1/6 patients at 90 mg/m2; grade 3 rash（皮疹） in 1/6 patients at 120 mg/m2), and grade 3 rash in 2/6 patients at 155 mg/m2. Conclusions: The recommended pediatric phase II dose of weekly MK2206 is 120 mg/m2 and the last cohort of patients to the every other day dosing schedule of MMK206 is enrolling. PK and PD data are currently being analyzed and will be presented.

https://www.inspire.com/groups/l ... ion/mk2206-tarceva/

MK-2206, an Allosteric Akt Inhibitor, Enhances Antitumor Efficacy by Standard Chemotherapeutic Agents or Molecular Targeted Drugs In vitro and In vivo
http://mct.aacrjournals.org/content/9/7/1956.full#T1

顶老马，第一次离老马这么近

谢谢老马。虽然看不明白，老马辛苦来。

坚持就是胜利，又有新靶点了！