DEVELOPING RECOMBINANT ANTIBODIES FOR SORTING RECEPTOR SORLA

Abstract

Breast cancer is the most common malignancy and the leading cause of cancer-related death among women. About 15 to 20% of breast cancers has amplification of the HER2 oncogene. HER2 is a member of the epidermal growth factor receptor (EGFR) family that promotes cell survival, proliferation, motility, and resistance to apoptosis. Despite many advances in treatment options targeting HER2, anti-HER2 therapy resistance remains a relevant issue. SorLA is a sorting receptor of the vacuolar protein sorting 10 proteins (vps10p) domain receptor family, a family of sorting receptors transporting cargo between cell surface and intracellular compartments such as the trans-Golgi network, endosomes, and lysosomes. A link between HER2 cancer signaling and the expression of SorLA has recently been discovered. SorLA was shown to promote HER2 recycling by preventing its lysosomal degradation. Depletion of SorLA decreased HER2 signaling, promoted HER2’s accumulation in dysfunctional lysosomes and sensitized the cancer cells to a lysosometargeting cationic amphiphilic drug ebastine. High SorLA expression correlated with poor patient outcomes in HER2-amplified breast cancer patients. These findings make SorLA an attractive target for drug therapy.

The aim of this study was to develop anti-SorLA antibody fragments (binders), the most promising of which will later be developed into a full-length humanized anti-SorLA antibody ultimately testable in patients. The binders were developed using phage display targeting either full-length SorLA or its binding domain. In the first round 576 clones were screened. In the second round 68 clones were screened and subsequently sequenced, producing 41 different sequences. These most promising 34 clones were then used to immunoprecipitated SorLA to further test for binding activity. Out of these 34 binders 23 successfully immunoprecipitated SorLA. The most promising clones will be tested in vitro in HER2 positive cancer cell lines to assess their cancer growth -halting capabilities. The most successful clone will be developed into a full-length human antibody that can be tested in patients.