伍斯特理工學院（Worcester Polytechnic Institute，WPI）機械工程師開發了一款芯片，只要從癌症患者身上抽取少量的血，這款芯片就能捕獲並確認轉移性癌細胞。與很多采用的微流控技術的現有裝置所相比，這一依賴於簡單機械方法的突破性技術在捕獲癌細胞方面顯得更有效。
伍斯特理工學院所開發出來的裝置將抗體附著在微小阱（well）底部的碳納米管陣列上面。癌細胞沉澱到阱的底部，然後有選擇性地與基於表面標記物的抗體結合（不同於其它裝置，芯片也能捕獲由癌細胞生成，被稱為外來體的微小結構）。發表在最新一期《納米技術》雜誌上的“液體活檢”技術將有可能成為簡單實驗測試的基礎，該技術能快速檢測早期轉移跡象並幫助醫生針對特定癌細胞制定治療方案。
癌症從某一器官擴散到身體其它部分的過程稱之為轉移，通常會進入血液。不同類型的腫瘤對特定器官和組織也有偏好，例如，循環乳腺癌細胞就青睞於紮根在骨頭、肺和大腦內。癌症轉移的預後（也稱為癌症第四期）普遍較差，因此，在身體其它部位形成新的腫瘤群體之前，需要一項能夠檢測循環腫瘤細胞的技術，這樣才能大大增加病人存活的機率。
伍斯特理工學院機械工程系副教授兼微系統實驗室主任Balaji Panchapakesan表示，“把重點放在捕獲循環腫瘤細胞的概念還很新。這個挑戰非常艱難，無異於大海撈針。人體有數十億的紅細胞和成千上萬的白細胞，在這其中流動的腫瘤細胞只有很小的一部分。而我們所開發的裝置就能以超高精度捕獲上述細胞。”
由Panchapakesan團隊開發的裝置包括微型元件陣列，每個大約十分之一英寸寬（3毫米）。每個元件都包含一個微阱，碳納米管的底部則由抗體附著。每個微阱擁有特定抗體，基於微孔表面的基因標記物，這些抗體有選擇地與其中一種癌細胞類型相結合。通過將各種抗體附著其中，只需單個血液樣品，裝置就能夠捕獲多種不同類型的癌細胞。在實驗室內，研究人員只需要液體盎司（0.85毫升）的血液就能填充170個微阱。即使是如此小的樣本，每個裝置也能捕獲1-1000個細胞，捕獲效率介於62%-100%。
Panchapakesan團隊在期刊《納米技術》雜誌上發表了一篇名為《靜態微陣列隔離，動態時間序列分類，捕獲並列舉血液中上升的乳腺癌細胞：CTC納米管芯片》的文章，這篇文章的寫作人員包括主要作者博士後研究員Farhad Khosravi，以及來自路易斯維爾大學和托馬斯杰斐遜大學的研究人員，他們在文中描述了對轉移性乳腺癌的兩種特定標記物抗體的研究，這兩種名為EpCam和Her2的抗體被附著在碳納米芯片之上。當血樣與標有標記物的細胞放置在芯片上時，該裝置將快速定位並捕獲被標記的細胞。
除了捕獲腫瘤細胞，Panchapakesan表示，該芯片也能捕獲由癌細胞生成，帶有相同標記物，被稱為外來體的微小結構。Panchapakesan指出，“對於其它類型的液體活檢裝置而言，3納米結構太小而難以捕獲，如微流控裝置，因為剪切力將有可能破壞它們。我們所開發的裝置，是目前為止唯一能直接在芯片上捕獲循環腫瘤細胞和外來體的芯片，這將為檢測循環腫瘤細胞的轉移提供新的可能。新的研究證據顯示，外來體排出的微小蛋白能夠驅動循環腫瘤細胞進行反應，這將成為有效癌症藥物傳輸和治療最主要的障礙。因此我們的研究顯得非常重要。”
與其它液體活檢裝置相比，尤其是那些使用微流控技術捕獲癌細胞的裝置（隨液體流動的細胞必須附著在錨定抗體之上），Panchapakesan認為他們團隊開發出來的芯片具有額外優勢。除了能夠更為高效的捕獲循環腫瘤細胞，通過差分沉降，WPI裝置在將癌細胞從其它細胞和血液物質中進行分離方面也顯得極為高效。
雖然最初將芯片測試重點放在乳腺癌領域，Panchapakesan表示該裝置也能檢測各種各樣的腫瘤類型，開髮用於測量其它癌症類型（包括肺癌和胰腺癌）的先進裝置計劃也已經開始運行。他希望某一天一款類似於他們的裝置不僅僅可以用於癌症患者的定期跟進，也可以用於常規癌症篩查。
Panchapakesan補充說道，“想像一下你每年去做體檢，抽一次血，血樣經過癌細胞標記物綜合陣列檢測，就能在癌症早期或其它發展期捕獲癌細胞，醫生從這些被捕獲的癌細胞中獲取必要的蛋白質或遺傳信息，並根據癌症特定標記物定制你的治療方案，可謂將自己的健康一手掌握。白細胞是一個尤其要注意的問題，因為他們在血液中的數量很大，很可能會被誤認為是癌細胞。我們所開發的裝置使用了一種被稱為被動白細胞過濾的策略。由於密度的差異，癌細胞將會沉降到微阱底部（只發生在窗口較為狹窄的情境下），在那裡，癌細胞將會與抗體正面交鋒。剩餘的血液內容物則保留在微阱頂部，被沖走也非常容易。”
Circulating tumor cells (CTC) are key early indicators of metastasis, which is the process by which cancer cells move from one organ group in the body to another. Once cancer spreads, the prognosis is generally not good. So, early identification of CTCs can help prevent them from creating new colonies of malignant cells.
Researchers at Worcester Polytechnic Institute (WPI) in Massachusetts have developed a new approach to microfluidics to detect CTCs in blood. The WPI researchers believe that their technique could form the basis of a simple lab test for quick detection of early signs of metastasis and help physicians select treatments targeted at the specific cancer cells identified.
Current microfluidic techniques used in tumor cell isolation have been dependent on flow rate and require off-chip post-processing. The WPI researchers’ technique employs static isolation of tumor cells from the blood by fractionation of the blood into small droplets.
In research described in the journal Nanotechnology, the WPI researchers were able to create a chip design in which antibodies are attached to an array of carbon nanotubes at the bottom of a tiny well in the chip. The chips have an array of these tiny wells, each about three millimeters across.
When the blood droplets are put into the well, the heavier cancer cells drop to the bottom where they become attached to the antibodies. Each of the wells holds a specific antibody that will bind to one type of cancer cell. The chip’s electrodes detect electrical changes that occur when the cancer cells are captured by the antibodies.
Using an array of antibodies makes it possible to identify several different types of cancer cells within a single blood sample. To put that in perspective, the researchers could fill 170 wells with just 0.85 millileter of blood. The chips were able to capture between one and a thousand cells per device, equating to an efficiency of between 62 and 100 percent.
You can see a video that offers a demonstration of how the chip works below.
The advantages of this technique over traditional microfluidic methods are numerous and significant. But let’s just focus on the advantages derived from the use of carbon nanotubes.
First, the nanotube-based microarrays include both detection and capture technology, unlike traditional microfluidics, which only capture. Second, the nanotube microarray allows for a wide variety of antibodies so that it can attract and identify different types of cells that may need to be fought in different ways.
Another one of the advantages of this approach over other microfluidics is that it can capture exosomes, which are produced by cancer cells and carry the same markers.
“These highly elusive 3-nanometer structures are too small to be captured with other types of liquid biopsy devices, such as microfluidics, due to shear forces that can potentially destroy them,” said Balaji Panchapakesan, associate professor of mechanical engineering at WPI and director of the Small Systems Laboratory, in a press release. “Our chip is currently the only device that can potentially capture circulating tumor cells and exosomes directly on the chip, which should increase its ability to detect metastasis.” Panchapakesan adds that this is important because research is showing that tiny proteins excreted with exosomes can actually suppress cancer drug delivery and hinder treatment.
Panchapakesan believes the technology is ready for commercialization, but his team just needs more data on patients (delineated by stage of cancer) to move the technology along further in its development.
In an e-mail interview with IEEE Spectrum, Panchapakesan added: “If there is any equipment that needs to be developed more, [it’ll probably be] the automation and robotic handling of the entire system from drop deposition to microscopy. But really we just need patients, patients, patients.”
Source:IEEE
留言列表
生技醫療產業 (1)