Abstract

Introduction: Tropomyosin receptor kinase-C (TrkC) has been reported to be overexpressed in cancer and regulates its survival and metastasis. In addition, tumour microenvironment is immunosuppressive and associated with high expression of immunosuppressive mediators including regulatory T cells (Tregs), TGF-β and myeloid-derived suppressor cells. This study was aimed to study the antitumour efficacy of TrkC-targeting dinitrophenol (DNP) conjugate (IYIY-DNP) combined with Cyclophosphamide (CYP) for immunotherapy. CYP is an FDA-approved anticancer drug and has been reported to selectively suppress Treg cells at low dose. Methods: Female Balb/c mice was immunised with DNP-KLH (Keyhole Limpet Hemocyanin) to stimulate anti-DNP antibodies. After immunisation, TrkC expressing-4T1 cells were implanted, and tumour bearing mice at the size of 60-80mm3 were randomly divided to group of 10 mg/kg IYIY-DNP (I.V), 25 mg/kg CYP (I.P), 10 mg/kg IYIY-DNP + 25 mg/kg CYP for treatment on every alternative day, for five cycles (n=8 for each group including control saline). Tumour size were recorded using calliper on every two days, for 30 days. Results: No toxicity was observed on mice treated with all groups throughout 14 days of observation. Mice treated with low dose of 25 mg/kg CYP displayed delayed tumour growth by 6.29%, however, mice treated with 10 mg/kg IYIY-DNP + 25 mg/kg CYP delayed tumour growth by 36.14%, both compared to saline-treated mice. The average area under the tumour growth curve vs. day post treatment for 10 mg/kg IYIY-DNP + 25 mg/kg CYP group is significantly smaller compared with saline-treated group (P<0.05). Conclusion: These findings suggest that combination therapy of IYIY-DNP and CYP is able to decrease the tumour growth preclinically and have a potential to be developed to become new immunotherapy treatment strategy. 

Keywords: Tropomyosin Receptor Kinase C (TrkC), 4T1 cells, Cyclophosphamide (CYP), Immunotherapy