Our program is focused on producing new therapeutic candidates to prolong remission and potentially cure highly lethal cancers where patients have few alternative treatment options. We have selected Acute Myelogenous Leukemia (AML) as the initial clinical indication for evaluating our novel therapeutics, but anticipate a full development program encompassing many other types of solid tumor cancers.
Our strategy is to develop an antibody that binds to and eliminates the cancer-forming stem cells in leukemia and other solid tumors. While current cancer treatments (e.g. surgery, chemotherapy, radiation) will frequently get rid of the bulk of the tumor, they rarely touch the tiny number of cancer stem cells that actually re-generate the masses of cancer cells that have been eliminated. When the latter occurs, the patient is described as having a relapse, leading to a disease recurrence with poor prognosis. Our strategy is to eliminate the small number of cancer-regenerating stem cells by targeting cell membrane proteins expressed by these cells.
We have discovered that many cancer cells coat themselves with a protein called CD47 that prevents them from being eaten and disposed of by the patient’s blood cells. In this context, CD47 can be considered a ‘don’t eat me’ signal that protects the cancer cells from being phagocytosed i.e. ‘eaten’. The antibody we are developing binds to and covers the ‘don’t eat me’ CD47 protein, so that the patient’s blood cells are now able to ‘eat’ the cancer cells by standard physiological responses, and eliminate them from the body.
Developing an antibody such as this for use in humans requires many steps to evaluate it is safe, while at the same ensuring it targets and eliminates the cancer forming stem cells. The antibody must also ‘look’ like a human antibody, or else the patient will ‘see’ it as a foreign protein and reject it. To achieve these criteria, we have made humanized antibodies that bind to human CD47. We have shown that the antibodies eliminate cancer cells in two ways: (i) blood cells from healthy humans rapidly “ate” and killed leukemia cells collected from separate cancer patients when the anti-human CD47 antibody was added to a mixture of both cell types in a research laboratory test tube; (ii) the anti-human CD47 antibody eliminates human leukemia cells collected from patients, then transferred into special immunodeficient mice which are unable to eliminate the human tumor cells themselves. In these experiments, the treated mice remained free of the human leukemia cells for many weeks post-treatment, and could be regarded as being cured of malignancy.
To show the antibodies were safe, we administered to regular mice large amounts of a comparable anti-mouse CD47 antibody on a daily basis for a period of many months. No adverse effects were noted. Unfortunately our antibody to human CD47 did not bind to mouse CD47, so it’s safety could not be evaluated directly in mice. Since the anti-human CD47 antibody does bind to non-human primate CD47, safety studies for our candidate therapeutic need to be conducted in non-human primates. These studies have been initiated and are in progress. Following administration of the anti-human CD47 antibodies, the non-human primates will be monitored for clinical blood pathology, which, as in humans, provides information about major organ function as well as blood cell function in these animals.
The next step after identifying an antibody with strong anti-cancer activity, but one that can be safely administered to non-human primates without causing any toxic effects, is to make large amounts of the antibody for use in humans. Any therapeutic candidate that will be administered to humans must be made according to highly regulated procedures that produce an agent that is extremely “clean”, meaning free of viruses, other infectious agents, bacterial products, and other contaminating proteins. This type of production work can only be performed in special facilities that have the equipment and experience for this type of clinical manufacturing. We have contracted such an organization to manufacture clinical grade anti-human CD47 antibodies. This organization has commenced the lengthy process of making anti-CD47 antibody that can be administered to humans with cancer. It will take another 18 months to complete the process of manufacturing clinical grade material in sufficient quantities to run a Phase I clinical trial in patients with Acute Myelogenous Leukemia.