Trojan horses released into bloodstream to kill cancer cells

Linker must be cleaved

The antibody is a key part of the ADC as it makes sure that that chemical package recognizes the cancer cell and is invited in. This happens via an antigen on the outside of the cancer cell. The antigen is unique in being present on cells that grow rapidly, which is the case for many cancer cells.

The antigen acts as a receptor, so when the ADC antibody meets the cancer cell’s antigen, recognition occurs, and our Trojan friend is ‘invited’ inside. Unfortunately, similar antigens are found in certain healthy cells that by nature grow rapidly, such as hair, nail and bone marrow cells, and these cells will perish if the ADC is let in.

So Katrine Qvortrup and her colleagues started looking at ways of ensuring that the toxic payload is only released in cancer cells and not in the other fast-growing cells. This involved taking a close look at the inside of the cancer cell, and how it differs from the inside of healthy cells. Perhaps they could spot a difference that could be used to make sure that the ADC is only activated in the cancer cell.

“For a linker to release the drug inside the cell, it must first be cleaved. Something needs to trigger the cleaving. Linkers can be cleaved in several ways, one method involving the use of enzymes. Encountering a certain enzyme, the linker opens up, and the drug is released,” explains Katrine Qvortrup.

Special enzyme in certain cancer cells

This led the researchers to take an interest in an enzyme called sulfatase, which is found in higher concentrations inside certain cancer cells. High sulfatase concentrations are usually seen in hormone-dependent cancers such as prostate cancer and certain types of breast cancer. Based on this knowledge, the research group designed a linker that is cleaved only when it meets sulfatase.

During the development of the linker, the researchers worked closely with the Finsen Laboratory, which is the cancer research department at Rigshospitalet in Copenhagen. The Finsen Laboratory was involved in testing the various versions of the linker that were developed until DTU researchers succeeded in achieving the desired properties.

“With our new linker, we have added a kind of extra level of security, which means that the ADC is first taken up by a fast-growing cell and can then only be triggered if sulfatase is present. This means that should the ADC enter a fast-growing, healthy cell, nothing happens because there is not enough sulfatase present. In this way, we target the drug even more precisely at the cancer cells, resulting in greater efficacy and fewer side-effects, because healthy cells are not targeted,” says Katrine Qvortrup.

Changing antibody size

The researchers have also succeeded in improving the linker in several ways by changing its chemical functionalities, for example by increasing its water solubility. This helps to stabilize the ADC design, which in turn increases the efficacy of the drug. In addition, they succeeded in designing a linker capable of conjugating several types of drugs, which makes it possible to use ADCs to attack far more diseases.

Last but not least, they started changing the size of the antibody, so you can use a smaller molecule to deliver the toxic drug.

“An antibody is a fairly large molecule, and it prevents the ADC from penetrating metastases, where the cancer cells are very densely packed. We have therefore developed ‘nanobodies’, which are significantly smaller molecules than the antibodies used so far in ADCs. In this way, we can sneak the ADC into metastases,” says Katrine Qvortrup.

The solution was inspired by the scientific literature, which describes a special receptor on cancer cells that has not been exploited before. The researchers made sure that their ‘nanobodies’ would recognize this receptor, so that an ADC can now enter the metastatic cancer cells.

DTU researchers have had the new linker technology further analysed by Abzena, a private company specializing in this field. The technology has been patented.

“We’re now in the process of fine-tuning our linker, while also having more tests done in order to gather more knowledge about its functionalities. Having published all our research in spring 2023, we will soon be ready to sell the technology so that it can be used in the fight against cancer,” says Katrine Qvortrup.