Targeting Tumor-Associated Carbohydrate Antigens
The glycocalyx is the thick, dense, and dynamic layer of highly heterogeneous glycans surrounding all cells on earth. The interaction of specific glycan structures with different lectins activates pathways that are indispensable for the proper function of cells, tissues, and organisms.
The glycocalyx varies in size, shape, and composition between species but also within the same organism. The glycan repertoire on cell membranes changes dynamically depending on the cells' role, function, age, and developmental stage.
The Glycan Code, or the structure-to-function secrets of specific glycan structures, is by far the most complicated language encoded on our cell membrane and mostly remains to be deciphered.
More than 70 years ago, it was discovered that cancer cells display aberrant glycans termed Tumor-Associated Carbohydrate Antigens or TACAs. Over the years since first described, TACA expression became a hallmark of cancer with a pivotal role that directly affects ALL aspects of cancer biology. Moreover, TACAs were proven valuable as markers and targets for cancer diagnostics and therapeutics that effectively distinguish healthy from malignant cells.
Nevertheless, the inherent structural heterogeneity and immense efforts involved in purifying glycans from native sources limited the development of TACA-targeting tools. The entire field changed dramatically with the appearance of synthetic glycan assembly that enabled homogeneous and well-defined TACAs, and the development of vaccines and monoclonal antibodies (mAbs) against different TACAs in multiple cancers.
To date, the main bottleneck is still the availability of synthetic glycan structures. However, additional challenges arise from the insufficient immunogenicity of the glycoconjugates used for immunization and undesired broad glycan-specificity of the developed mAbs. Thus, despite the urgent need for anti-TACA mAbs, the number of antibodies under clinical trials is still extremely low.
To improve glycoconjugate vaccines for mAb production, we examine different glycoconjugate linker chemistry, adjuvants, and carrier proteins in several animal models (Fig. 2). Our goal is to produce high-affinity and glycan-epitope-specific mAbs and add valuable tools to our thin and insufficient toolbox against cancer.
Developing glycan-binding nanobodies
During the late 80s, it was discovered that the Camelidae family (camels, llamas, alpacas, vicuñas) produces unique antibodies lacking the light chain of conventional ones. The antigen-binding domain in each of these unusual heavy chain antibodies (hcAbs) is formed only by a single domain, designated VHH or "Nanobody" (Nb).
As shaped by evolution, Nbs have higher stability and solubility compared to engineered single domain antibodies. In addition, due to their ultra-small size (~13kDa), Nbs can penetrate and bind unique epitopes that are simply inaccessible to conventional antibodies.
Moreover, Nbs are easily engineered with a vast range of functionalization properties. Using basic cloning methods or site-specific labeling, Nbs can be modified as desired, either with fluorescent probes, radiotracers, or therapeutic drugs (Fig 2). Due to their easier genetic manipulation, Nbs can be expressed as monomers, dimers, or higher oligomers to form multivalent and/or multispecific tools, an attractive property when targeting heterogeneous TACA populations on cancer cells.
We previously immunized alpacas with multiple synthetic TACAs and developed several Nbs. The Nbs target different TACAs from the Globo family, including Globo-H, a key marker for breast cancer. Current work functionalizes these Nbs for further inspection in animal models towards clinical trials.
Deciphering the glycobiology aspects behind Plasmodium-host interactions
One of our current lab projects started after we developed nanobodies that specifically target different human pathogenic parasites. We examine the role of glycans in the pathogenicity of the malaria parasites Plasmodium falciparum and the fascinating ways these intracellular parasites hijack and exploit host glycans for their survival (Fig 3).