Our Science

Peptide targeted radiotherapy (PTRT) is a promising new approach to cancer therapy that has been widely validated in clinical studies and is in routine clinical use in Europe. Our approach systemically delivers a molecularly targeted, radiolabeled peptide which is designed to target with high affinity and specificity the receptors overexpressed on tumors.  Guidelines for effectively employing PTRT have been published, further supporting the promise and acceptance of this therapeutic modality (Zaknun JJ et al, Eur J Nucl Med Mol Imaging 2013, 40(5):800-16). Our technology represents the next generation of PTRT, employing superior peptide targeting and a radioisotope with more desirable characteristics than conventional radioisotopes.

We have developed a novel peptide, P2045, that contains an intelligently designed sequence that forms a chelate complex with radioisotopes. P2045 has been specifically optimized for binding both an imaging agent, Technetium (Tc99), and the therapeutic radionuclide Rhenium (Re188). Our peptide specifically and selectively binds to cancer cells that over-express the somatostatin receptor, particularly those in lung, pancreatic and neuroendocrine cancers. The high energy beta emission of the radioisotope allows delivery of cytotoxic radiation not only to tumor cells in which it is internalized but also to neighboring tumor cells. Our product candidates therefore benefit from the specificity of a targeted therapeutic coupled with the tumoricidal effect of radiation therapy. Additionally, the unique mechanism of action allows PTRT to be combined with other therapies to potentially increase the clinical response for patients.

Tozaride (Rhenium 188 P2045)

Rhenium (Re) 188 P2045 is a targeted therapy that combines a high-affinity somatostatin receptor-binding peptide with the high-energy, beta-emitting radionuclide Rhenium-188.  Both small cell (~84%), and non-small cell (~87%) lung cancers, as well as neuroendocrine cancers (>90%) are characterized by a high over-expression of the somatostatin receptor (SSTR).  SSTR2 is the most widely up-regulated subtype and is the primary mediator of somatostatin effects in cancer cells. P2045 is rapidly internalized by SSTR2 allowing it to be a highly specific targeting agent. In studies with nude mice, Re188 P2045 caused almost complete inhibition of SSTR-bearing pancreatic tumors with no acute damage to any other organ or tissue.   In other preclinical studies, Re188 P2045  demonstrated significant growth delay in xenografts of small cell lung and other cancers (Cyr et al, J Med Chem 2007, 50:1354-1364).

Companion Diagnostics

The key to delivering personalized cancer therapy is selecting the most appropriate patients for a therapy that is targeted to the patient’s specific molecular subtype.  Our diagnostic imaging agent is based on Technitium (Tc) 99, a widely used imaging isotope. Tc99 conjugated to P2045 targets tumors expressing high levels of SSTR2.  Our Phase 1 clinical trial demonstrated the feasibility of using Tc99-P2045 to image patients in real time to identify the most appropriate patients (those with a high density of the SSTR2 target) for the therapeutic dose with Tozaride.