Actinium's Technology Platform
Actinium's Alpha Particle Immunotherapy (APIT) platform is a highly potent and selective form of targeted radiotherapy. It is based on attaching the powerful alpha-emitting radioisotope Actinium 225 to monoclonal antibodies (mAbs), which are large molecules capable of binding specifically to cancer cells. By virtue of carrying alpha-emitters, mAbs bring them directly to cancer cells where these alpha emitters can selectively kill the targeted cell. The figure below presents a schematic of a drug based on the Company’s APIT technology.
APIT based drug construct and its components
The power of alpha emitters is best understood when compared to beta emitters, an alternative form of radioisotope used in cancer drugs. The killing power of a radioactive particle is directly proportional to its energy and inversely proportional to its range. Alpha particle carries the most energy but travels the shortest path, while beta particle has less energy but goes farther in the body.
Comparison between α and β irradiation’s effect on cancer cells and healthy tissues
Being 100 times more powerful than beta particles, alpha therapy is effective in cancers that are not sensitive to beta irradiation. Prime examples are the past and current clinical trials in AML. APIT has demonstrated extremely high cancer cell kill levels even though AML is not considered particularly radiosensitive and radiotherapy is not used in treating the disease. Based on these inherent isotope traits, the Company and Dr. David Scheinberg, Chairman of the Molecular Pharmacology Program at Memorial Sloan Kettering Cancer Center (MSKCC), ATNM’s key scientific collaborator, developed alpha particles as an ideal payload for targeted cancer radiotherapy. While their potency is 100-fold higher than beta’s and cytotoxins’ significantly increases the killing power of alpha particle drugs against targeted tumor cells, their extremely short range limits any damage inflicted on healthy tissues.
In addition to its potency and range of emission, there are other key considerations for evaluating the suitability of particular radioisotopes for medical use. Among them are half-life of the isotope, which is an indication of the period over which it remains radioactive, and its pharmacokinetics, i.e. its distribution in the body and its eventual elimination from it. For these reasons, Actinium 225 (Ac-225) and the isotope derived from it, Bismuth 213 (Bi-213), were selected as lynchpins of the Company’s technology. Both isotopes have relatively short half-lives and favorable and controllable pharmacokinetics. However, for efficacy, logistics and cost reasons ATNM has decided to focus its efforts on Actinium 225 which has a 10 day half life versus Bismuth-213’s half life of 46 minutes.