Novel 18F-Labeled Affibody Molecule Used with Pet to Measure Response of Breast Cancer to Therapeutic Intervention
Researchers from the US NIH have created a new 18F-containing radioactive compound and used it to label affibody molecules for use in a positron emission tomography (PET) study of HER2, a protein that is known to be overexpressed in approximately 20% of breast cancers. The 18F-labeled molecule N-2-(4-18F-fluorobenzamido)ethyl]maleimide (18F-FBEM)–ZHER2:342 was used to assess the effectiveness of a new therapeutic agent, 17 (dimethylaminoethylamino)-17-demethoxygeldanamycin.
Traditional methods to measure HER2 expression involve surgical removal and biopsy of tumor samples, although these are often inaccurate. The newly developed molecular imaging method overcomes these problems, and also presents a solution for measuring the disease progression over a prolonged time period.
The new technique was experimentally determined using BT474- and MCF7/clone18-type breast cancer xenografts implanted into mice. Four doses were administered and each was separately imaged by PET. The results of the disease progression were verified using biodistribution, ELISA and Western blot studies.
Speaking to Future Medicinal Chemistry about the significance of his group’s study, Jacek Capala of the NIH’s National Cancer Institute said, “Our work showed that PET can be used for in vivo assessment of HER2 expression. Current ex-vivo methods (e.g. immunohistochemistry techniques [IHC]and Fluorescent in situ hybridization analyses) are restricted to a limited tissue sample obtained at a single time point. After initial diagnosis, follow-up biopsies are routinely not performed and, currently, there are no means to obtain information concerning how long it takes a therapeutic agent (e.g. Herceptin™) to reach the target, how effective it is and how long its effect lasts. Our results indicated that PET imaging using the 18F-labeled affibody molecules might detect a two- to three-fold decrease in HER2 expression, while IHC was not only less sensitive but also misclassified some tumors.”
Inaccuracies in the estimation of HER2 levels using IHC could lead to misdiagnosis, with the potential severe clinical consequences. The study therefore suggests that PET imaging may be an attractive alternative strategy for providing a quantitative and objective assessment of HER2 expression in a noninvasive manner, also allowing several scans to be performed during the course of therapy.
The study has led the researchers to suggest that their technique could permit better selection of patients for HER2-targeted therapies as well as allow the early detection of tumors that either do not respond or acquire resistance to such therapies. They also propose that, because affibody molecules may be selected to target specific cell proteins, similar compounds could be developed to target proteins unique to other tumors types.
Looking forward to further planned studies, Capala commented, “In spite of the development of new HER2-targeted therapies (e.g. trastuzumab), there is a significant number of patients with HER2-positive tumors who do not respond or acquire resistance to these therapies … We are currently investigating the possible application of affibody molecules to develop HER2-specific therapeutic agents. For instance, in recent work, we have genetically fused HER2-specific affibody molecule with a truncated and optimized version of Pseudomonas Exotoxin A. In addition, we are also planning to investigate whether our strategy can be used to target HER2 for diagnosis and therapy of breast cancer metastasis in the brain.”
Source: Kramer-Marek G, Kiesewetter DO, Capala J. Changes in HER2 expression in breast cancer xenografts after therapy can be quantified using PET and 18F-labeled affibody molecules. J. Nuc. Med. 50(7), 1131–1139 (2009).
Possible Anti-Sense Method Against Muscular Dystrophy
A study conducted by researchers at the University of Rochester, NY, USA, may have implications for the development of novel therapeutic approaches against the most common form of adult-onset muscular dystrophy, myotonic dystrophy type 1 (DM1).
DM1, which results in the wasting of muscle cells in the face, hands and legs, is caused by ‘toxic’ RNA containing repeating sequences of three nucleotides. The stretch of cytosine-uridine-guanine repeats, which causes the genome to stutter, is in fact located in a part of the RNA that is normally not translated into a protein. The repetitive RNA forms a hairpin configuration in the nucleus and is strongly attractive to the muscleblind-like 1 (MBNL1) protein, which, when bound to the RNA, forms toxic aggregates. This has the effect of preventing the RNA from being able to move out to the cytosol to be translated into a viral protein kinase.
The research group, led by Thurman Wheeler and Charles Thornton, proposed a approach to distract the troublesome, repeat sections of RNA using complementary sequences of Morpholino antisense nucleotides. When inserted into mice with muscular dystrophy, the antisense sequence blocked the harmful coupling of MBNL1 and the RNA containing the expanded repeats, in turn reducing many of the symptoms of DM1. The researchers suggest that their results may lead to an alternative use of antisense methods in the inhibition of deleterious interactions of proteins with pathogenic RNAs. One major challenge, however, to further developments remains strategies for delivering potential therapeutics to the nucleus.
Source: Wheeler TM, Sobczak K, Lueck J et al. Reversal of RNA dominance by displacement of protein sequestered on triplet repeat RNA. Science 325(5938), 336 – 339 (2009).
UK Parliamentary Report Warns of HIV ‘Treatment Timebomb’
A group of British politicians has called on pharmaceutical companies to grant rival manufacturers the right to produce their HIV medicines as part of the effort to increase access to treatment at a time when demand for such therapeutics is surging in the developing world.
The report, entitled A treatment timebomb, published by the all-party parliamentary group on AIDS, states that new companies and government donors will need to provide better access to more expensive antiretrovirals, especially in light of estimates that by 2030 around 55 million people will require HIV drugs – in contrast to the current figure of 4 million. As part of its proposals, the report states that companies should publish independent audits of their efforts to increase access to anti-HIV drugs.
“We are sitting on a treatment time bomb. We must reduce the price of second-line medicines and less toxic first-line medicines before millions need them. We cannot sleepwalk into a situation where we can only afford to treat a tiny proportion of those infected,” said David Borrow, MP, who chairs the group.
The report also analyzes the the impact of patents on HIV-related R&D, and shows support for ‘patent pooling’, the concept in which pharmaceutical companies agree to allow low-cost generic producers to make their patented products subject to the terms of an agreement.
The UK-based company GlaxoSmithKline (GSK) took the lead earlier this year by becoming the first major drug maker to announce its intention to establish a ‘patent pool’ for neglected disease drugs. However, the company has stopped short of including HIV drugs as part of its initiative.
In a recent move, the company has announced its intention to grant South African company Aspen the right to make its second-line antiretroviral therapy abacavir (Ziagen®) in a royalty-free licensing deal. While welcoming the initiative, Borrow stressed that more could be done, “[We welcome] GSK’s new commitments especially on preventing mother to child transmission of HIV, and increasing research on pediatric drugs… The announcement about working with other companies to make fixed-dose combinations may also be welcome – but we have no detail yet on what those companies will be and for which medicines.”
Commenting further, Borrow said, “GSK is taking positive steps, but they are broadly unilateral, which will limit their impact. We would like to see them work with UNITAID to create a patent pool that gives fair royalties for their patents.”
Source: The treatment timebomb www.aidsportal.org/repos/APPGTimebomb091.pdf
Alnylam Rnai Technology Pledged for Gsk Patent Pool
US-based company Alnylam Pharmaceuticals has made the first pledge to the GlaxoSmithKline’s (GSK) patent pool, with 1500 patents for RNA interference (RNAi) technology. The new additions will triple the contents of the patent pool, which already contains 800 of GSK’s own patents, donated when the pool was set up in March 2009.
The patents dontated by Alnylam are a mixture of granted and pending patents on RNAi therapeutics. The company’s RNAi platform uses gene-silencing technology, which prevents proteins linked to diseases from forming by targeting disease-specific mRNAs. The company has also been involved in the identification of malaria therapeutic targets.
Andrew Witty, CEO of GSK, commented on the development of the patent pool: “The key objective of the pool is to make it easier for researchers across the world to access intellectual property that may be useful in the search for new medicines to treat neglected tropical diseases. The more companies, academic institutions and foundations that join the pool, the more effective it will be.”
The GSK patent pool aims to target 16 diseases from the US FDA Neglected Tropical Diseases initiative, including malaria, tuberculosis and leprosy, in the regions specified within the United Nations’ list of least developed countries. Patents in the pool will be available on a royalty-free basis for organizations wanting to conduct research into neglected disease therapeutics.
“We are committed to the innovation of medicines for patients, so we cannot ignore the potential of our technology to make a difference in the discovery of important new medicines for neglected diseases that afflict millions of people each year,” explained John Maraganore, CEO of Alnylam.
Source: GlaxoSmithKline press release: Alnylam joins GSK in donating intellectual property to patent pool for neglected tropical diseases www.gsk.com/media/pressreleases/2009/2009_pressrelease_10071.htm
Breast Cancer-Promoting Gene Identified
A study published by researchers based at the Genome Institute of Singapore has identified a new gene that potentially contributes to aggressive breast cancer behavior.
Using microarray informatics, the group identified the Rab-coupling protein (RCP), also known as RAB11FIP1, as a potential candidate. RCP is located in a chromosomal region regularly amplified in breast cancer (8p11–12).
In vitro analyses indicated that overexpression of RCP in MCF10A normal human mammary epithelial cells resulted in their acquiring tumorigenic properties, which include loss of contact inhibition, growth factor independence, and anchorage-independent growth. However, knockdown of RCP in human breast cancer cell lines reduced in vitro colony formation, invasion and migration, in addition to significantly reducing tumor formation and metastasis in mouse xenograft models. The researchers found that overexpression of RCP enhanced extracellular signal-regulated protein kinase phosphorylation and increased Ras activation in vitro.
The authors conclude that, as their results indicate, RCP is a multifunctional gene regularly amplified in breast cancer that encodes a protein with Ras-activating function. They therefore suggest that targeting RCP could provide a novel approach for inhibiting this tumor-promoting pathway.
Source: Zhang J, Liu X, Datta A et al.RCP is a human breast cancer–promoting gene with Ras-activating function. J. Clin. Invest. DOI: 10.1172/JCI37622 (Epub ahead of print).