Clarity Pharmaceuticals (ASX:CU6) combined trastuzumab with its proprietary copper-chelating, or SAR, technology for the development of copper-67-based radioimmunotherapy for human epidermal growth factor receptor 2 (HER2)-positive breast cancer patients, according to a Tuesday Australian bourse filing.

Preclinical evidence showed a dose-response reduction in tumor size and prolonged survival using copper-67-SAR-trastuzumab compared to trastuzumab, an antibody that targets HER2, alone in a HER2-positive tumor mouse model, the filing said.

The firm collaborated with the University of Melbourne for the combination of the trastuzumab antibody with the SAR chelator and radiolabeling with copper-64 for diagnostic imaging, the filing added.

The firm plans to conduct a phase 1/2a theranostic study with copper-64 and copper-67 SAR trastuzumab in HER2-positive breast cancer patients, per the filing.

It also signed a supply agreement with EirGenix for the clinical development and future commercial supply of clinical-grade good manufacturing practice trastuzumab biosimilar, EG12014.

Its shares fell 6% in early trading on Tuesday.