Development of tumor-specific anti-angiogenic inhibitor Cet-Grab and combined treatment strategies of Cetuximab and L-ascorbic acid

Abstract

Cetuximab is a monoclonal antibody directed against EGFR which is overexpressed in most of the human solid tumors. As an effective clinical therapy for patients with wild-type KRAS, Cetuximab blocks EGFR mediated proliferative signaling on basis of the strong binding affinity to EGFR. In the first part of the research, we described the development of Cet-Grab which has a strong affinity to VEGFA, PlGF, and EGFR. VEGF decoy receptor VEGF-Grab, the earlier version of Cet-Grab, was limited its wider application due to insufficient tumor localization. To achieve tumor-specific vascular disruption, we adopted Cetuximab and generated Cet-Grab by biochemical fusion of Cetuximab and VEGF-Grab. Compared to VEGF-Grab, Cet-Grab showed effective anti-proliferative potential by inhibiting EGFR-mediated signaling. Moreover, Cet-Grab specifically localized around tumor region and resulting in improved anti-angiogenic potential in A431 xenograft mouse model. First part of the study could provide an insight for designing multi-paratopic Fc-fusion protein and highlights the efficiency of tumor-specific localization of angiogenic inhibitor. In the second part of the research, we suggested L-ascorbic acid as the partner of Cetuximab in abrogating Cetuxi-mab resistance caused by mutant KRAS. The treatment of L-ascorbic acid to mutant KRAS human colon cancer cell lines synergistically induced cellular death with Cetuximab in a SVCT-2 (Sodium-dependent Vit-amin C Transporter 2) dependent manner. Consistently, substantial tumor regression was observed under the treatment of L-ascorbic acid with Cetuximab in mice bearing SVCT-2 positive, Cetuximab resistant colon cancer cells. Interestingly, treatment of L-ascorbic-acid with Cetuximab-induced both apoptotic and necrotic cell death which is accompanied by the inactivation of RAFs and activation of the ASK-1-p38 pathway. These results demonstrate that the Cetuximab resistance in patients with mutant KRAS could be overcome by the combined treatment of L-ascorbic acid and Cetuximab in an SVCT-2 dependent manner.