01 July, 2009

Llamas Against Breast Cancer

ResearchBlogging.orgWe all knew llamas were kind of weird. They're fluffy. They're smelly. They spit. They're like Sanrio (the Hello Kitty company) tried to make over a camel. But that's not all. Llamas are also immunologically strange. Whereas most all other organisms with a humoral immune system produce large, multi-domain antibodies with several distinct genetic and structural motifs, llamas instead make nanobodies. Nanobodies are, basically, tiny little antibodies. Normal antibodies contain 2 heavy chains and 2 light chains, which each have V (variable, where the epitope binds) and J (joining) regions; and the heavy chains also have C (constant, these make up the Fc fragment) regions. All of those chains are bound together by disulfide bonds and the resulting antibody typically has 2 binding sites, each at the tip of the Y shape. Nanobodies dispense with all of that and only retain a functional binding site with a single variable light chain domain. As a result, nanobodies are much much smaller and can access and bind to sequestered epitopes or complex 3D epitopes that may otherwise be hidden inside a molecular cleft.


Figure A: Structual phylogenetic picture, much like a family picture. This is only an approximation as Good Images are copyrighted and Photoshopping ribbon-style molecules is difficult.

The point of this study is not that nanobodies are weird and cool. Instead, Alvarez-Rueda et al harnessed the complex 3D structural variability of nanobodies to mimic the immunogenic structure of HER2. HER2 is a surface protein normally only expressed in fetal development that is reexpressed in 20-40% of breast cancers and 30% of ovarian cancers. It is a member of the epidermal growth factor (EGF) family and is suspected to help cancerous cells proliferate more rapidly and aggressively. Tumor expression of HER2 correlates strongly with increased metastatisis and decreased survival. We've known about HER2 for a while now and it has been a target of intense research. There are now genetic tests available for HER2 alleles that correlate with increased morbidity from breast cancer. There was also a passive immunotherapeutic treatment against HER2 approved for use in combination with chemotherapy in 1998 called Trastuzumab (marketed as Herceptin(R) and manufactured by Roche). Trastumuzab is a humanized antibody therapy that targets HER2 directly; it is thought that it mimics the natural humoral immune response to HER2, which is observed to slow down tumor growth in early tumors but unfortunately sometimes fails to stop it. The primary problem with Trastuzumab is that it must be repeatedly administered over the course of cancer treatment to have any effect. While Trastumuzab is an invaluable tool in the fight against these cancers, it has long been recognized that inducing a robust host immune response would help to combat the tumor itself, and subsequent induction of a host immune memory against HER2 would help to prevent relapse of the cancer.

The best way to do this is with a vaccine.

Simply injecting HER2 with an adjuvant could produce a strong immune response, but the HER2 itself could make the cancer worse meanwhile. The ideal vaccine would be a molecule that mimics the structure of HER2 closely enough to induce cross-reactive immunity but that doesn't have the biological activity of HER2.

Enter the llama and its nanobodies.

Alvarez-Rueda et al injected Trastuzumab into a llama and the llama kindly produced nanobodies. Because Trastuzumab is an antibody against HER2, the llama's immune system produced a molecule against it that is somewhat structurally similar to HER2. When this nanobody molecule was isolated and expressed via transgenic clone library, it was found to strongly bind both Trastuzumab as well as isolated human anti-HER2 antibodies. So they then took the nanobody (called 1HE) and injected it into mice (along with Freund's adjuvant). As expected, the mice produced antibodies against the nanobody. These antibodies then, in turn, bound strongly to both 1HE and the HER2 protein. This strongly implies that immunization of a human with the 1HE nanobody and adjuvant would induce a strong anti-HER2 antibody response, effectively immunizing them against HER2-expressing breast or ovarian cancers or arresting the growth of existing tumors as part of chemotherapy*. Additionally, the polyclonal antibodies produced by the mice in response to the nanobody were found to inhibit growth of HER2-expressing carcinoma cell lines. The data have not yet been validated in vivo.

Either way, this is a cool advance in the fight against breast cancer, and I sincerely hope that something therapeutically useful in humans will soon come out of this. Thank you, llamas.

*This is technically known as an anti-idiopathic vaccine.

Alvarez-Rueda, N., Ladjemi, M., Béhar, G., Corgnac, S., Pugnière, M., Roquet, F., Bascoul-Mollevi, C., Baty, D., Pèlegrin, A., & Navarro-Teulon, I. (2009). A llama single domain anti-idiotypic antibody mimicking HER2 as a vaccine: Immunogenicity and efficacy Vaccine DOI: 10.1016/j.vaccine.2009.05.067

6 comments:

Ambivalent Academic said...

Cool! I had no idea that llamas were the shit! Thanks for sharing.

Becca said...

here's a llama there's a llama, and another little llama fuzzy llama funny llama llama llama duck!

I'm still having trouble wrapping my brain around the fact that the antibodies bound to both 1HE and the HER2 protein. Does this mean that some antibodies were produced that bound each, or that a single antibody could actually bind both (the 'lock' and 'key', so to speak)?

Stephanie Zvan said...

Okay, that's utterly awesome, but I'm a little sad now that you felt you had to explain Sanrio.

Mike said...

Anyone with breast cancer or interested in preventing this condition should know about the data on vitamin D. The data on vitamin D deficiency leading to cancer is as strong as the evidence that smoking causes cancer. The Canadian Cancer society started recommending that everyone take vitamin D to prevent cancer over two years ago but still very few outside Canada know this. There is also very good data suggesting that breast cancer patients do much better when their vitamin D levels are optimal. www.vitaminD3world.com is a good resource for more information and has recently launched a new preparation of vitamin D in a micro-pill formulation. The pills have been formulated with cellulose which absorbs water very quickly. This ensures that the pill breaks up very quickly to provide for maximum absorption. The micro pill is tiny and tasteless. Many vitamin D pills on the market have very poor dissolution properties resulting in poor absorption.
The site also offers to supply customers with a free supply of 400IU for their children and it also has a good newsletter.

Toaster Sunshine said...

@Becca:
Essentially, yes. Herceptin, which is a drug of humanized antibodies against HER2, bound both HER2 and 1HE. 1HE was similar enough to HER2 that the antibodies could bind both, but was different enough from HER2 that it didn't also have the EGF effector function that would make cancer worse. It would instead get the body to make antibodies against HER2 without acting like HER2, just looking like it.

@Mike:
I don't believe that the complexity of most cancers, if any, can simply be reduced to Vitamin D deficiency. Rather than try to sell us a "micro pill", could you perhaps instead explain the mechanism by which Vitamin D deficiency leads to development of cancerous lesions? Are cancers seen more frequently in populations prone to Vitamin D deficiency (e.g., Scandinavia)?

Sir, I publicly challenge you to a PubMed duel!

nanobodies said...

This is so cool and interesting. I learned so much with this post and I am going to share it.