AusBiotech special: how Oncaidia hopes to target cancer

La is an essential ribonucleoprotein that has a number of roles in the cell, both in protein transcription and translation. It is of great interest to immunologists, as it is an autoantigen and has been linked to systemic autoimmune diseases such as lupus. And recently, Adelaide researchers have found that the La protein is significantly overexpressed in cancer cells.

Dr Michael Brown, a medical oncologist from the Royal Adelaide Hospital, happens to have a background in immunology and has been investigating novel immunotherapeutics for a number of years. His experimental therapeutics lab at the Hanson Institute on the RAH campus has also been developing a fowlpox virus-based vaccine for advanced prostate cancer.

In the lab, Brown and colleagues, including co-inventors Dr Fares Al-Ejeh and research assistant Jocelyn Darby, have been looking at La very closely indeed. This team has been working with a La-specific monoclonal antibody, trademarked as Apomab, that is being commercialised through a new company called Oncaidia.

Previously known by its brand name, Apomab Ltd was a subsidiary of Adelaide company LabTech System but was demerged in 2005 so the parent could concentrate on developing its microbiological pathology technology. Apomab Ltd has become Oncaidia and has now launched itself on the public, opening a share offer in late July.

The new company's managing director, Keith Smith, says Oncaidia hopes to offer a technology that will target cancer in three ways: initially as a diagnostic imaging product to locate cancer, then as a prognostic to assist with conventional treatment, and finally as a therapeutic to treat cancer itself. Since La is an essential component of all cancers, the potential coverage could be broad indeed.

"The monoclonal antibody that we have branded Apomab is able to identify a protein which we have found to be upregulated in cancer cells compared to healthy cells, the La protein," Smith says.

"If we can identify the cancer cell we can use that information in a number of ways. We can use it to identify where cancer cells are in the body, by using a radio label and the techniques of nuclear medicine to identify the location of cancer cells in the body, so that helps with the diagnosis of cancer.

"While La is upregulated in cancer cells compared to normal cells, we've also found that it is further upregulated when cancer cells are stressed. When they enter apoptosis and they start to die, you get even higher concentrations of La, so that enables us to determine whether chemotherapy is actually working or not."

Currently, chemotherapy patients typically go through about three cycles of chemo before the clinician can understand whether it's actually working, but Oncaidia believes with its technology, there is the opportunity to measure whether chemotherapy is working or not after just the first dose.

"That of course has important implications as the clinician can change the medication to a form that will be more effective."

Smith says that in addition to its role as a diagnostic product, the company is working on attaching the mAb to the potent radioisotope yttrium-90, which could be developed into a therapeutic product. In animal studies, the company has been able to generate very effective tumour control in a range of different models, he says.

"Another thing that is really exciting is the fact that La is found in all cancer cells so it is potentially applicable to many forms of cancer. From a commercial perspective that makes it a very exciting prospect."

Dead cells

How the discovery came about is a common enough story. Brown's team had been looking at C1q, a molecule that is part of the C1 complex and which triggers off the complement cascade, as well as binding dead cells. Genetically engineered mice that lack C1q do not clear dead cells efficiently, and in rare cases, humans that lack C1q develop severe lupus.

"Although I had retrained as a medical oncologist, I continued to think along immunological lines, and mulled over the connection between antibodies and dead cells," Brown says. "We had a hybridoma that recognised the La autoantigen and tested whether it would bind to dead cells and how it would actually do that.

"The inventive step is that the antibody doesn't just bind to dead cells but more so to cells that have died because of DNA damage."

Brown says La, a nuclear phosphoprotein, is multifunctional. In transcription it acts as a "molecular chaperone", he says.

La is an RNA binding protein that binds particular motifs on the transfer RNA and ribosomal RNA molecules needed to build the translational apparatus of the cell. The synthesis of transfer and ribosomal RNA molecules is catalysed by RNA polymerase III, which is overactive in malignancy.

Consistent with this overactivity of RNA polymerase III, the team discovered that, like other RNA binding proteins, La is overexpressed in malignant cells.

"Histopathologists describe malignant cells as larger cells with prominent nucleoli, which are the ribosome factories of the cell. More ribosomes mean more protein," Brown says.

"Cancer cells usually divide more often than normal cells, and when they divide, they have to replicate everything. So the demand for protein generally increases as does the amount of La, which we find doubles in dividing cells.

"In systemic autoimmune diseases such as lupus, the La antigen is the target of autoantibodies but these antibodies are not themselves pathogenic. This is where C1q comes in again. For whatever reason, it seems that patients with these autoimmune diseases don't clear dead cells well.

"Considering the huge number of cells in the human body, there is a significant proportion that dies and needs to be cleared every second. Cells are generally cleared very efficiently, but if there is something wrong with that process and they are not, they undergo secondary necrosis or post-apoptopic necrosis. Then different proteolytic processing occurs and reveals new epitopes.

"That is one of views of how it might happen. It may go some of the way in explaining how autoantibodies are also found in the serum of cancer patients because cancers also turn over cells some of which don't get cleared efficiently."

Exactly how aberrant translational control, cancer, and autoimmunity may be linked, no one is quite certain. It has opened up a new sphere of study, however. There was a whole issue of Oncogene devoted to it in 2004 and Brown points in particular to a Nature Reviews Cancer paper in March 2003 by Pier Paolo Pandolfi from the Sloan-Kettering Institute in the US, called "Does the ribosome translate cancer?"

"This is a burgeoning area of research and we sort of fell into that," Brown says. ---PB---

Fireships

So, in malignancies there is an overexpression of La, which is a highly abundant protein anyway. This discovery has prompted the development of Oncaidia's mAb as a diagnostic tool for clinicians and potentially as a new cancer treatment.

In addition, La is even further upregulated when cells enter apoptosis, a feature that can be used by clinicians to test whether conventional chemotherapy is working. Another goal, of course, is the hope that it can be developed as a therapeutic, by tracking down dead and dying cells and delivering a radionuclide to the surrounding live cancer cells.

Brown likes to use the analogy of Elizabethan fireships, thought to have been used by Francis Drake against the Spanish Armada in 1588. The hulks of wrecked ships were filled with pitch, set alight and sent in to disrupt the enemy ships' formation.

"The hulk is the dead cell - we set it alight to affect the other ships in the formation," Brown says.

The team has also undertaken experiments with histone deacetylase inhibitors, now being explored for their pro-apoptopic effects. "We find that effect that we have is maintained," Brown says.

"The dogma being that one of the hallmarks of cancer is the evasion of apoptosis. However, these new classes of drugs, when used in conjuction with conventional treatments, do increase the rate of apoptosis. We think that will be to the advantage of our product.

"We haven't explored all of the ways in which you can induce apoptosis - we've looked mainly at intrinsic rather than extrinsic pathways. There are new agents, for example TRAIL by Genentech, which we haven't fully explored yet." (TRAIL is a pro-apoptopic agonist designed to activate two receptors, DR4 and DR5.)

Also overexpressed in tumours is transglutimase 2 (TG2), an enzyme that gets switched on during apoptosis and stabilises dying cells by crosslinking the proteins inside with covalent bonds.

Brown believes that this protein-protein crosslinking will add to the technology's effectiveness as the monoclonal antibody as well as its target antigen appears to be crosslinked in the dying cancer cell.

In addition to the Apomab technology, Oncaidia also owns other intellectual property relating to the telomerase enzyme and its role in cancer, Keith Smith says. At the moment, however, Oncaidia is focusing on the Apomab technology.

"We need to be focused on this, and as funds become available we will give more attention to other technologies, but from a corporate perspective we don't want to be seen as having a single platform, and we don't," he says. "We are looking at other licences as well, as we intend to build a cancer company."