Abstract 1430: Anti-CD3 x anti-EGFR bispecific antibody armed T cells (EGFR BATs) kills resistant pancreatic cancer cell lines and increases sensitivity to chemotherapy

Chemotherapy (chemoT) responses of pancreatic cancer (PC) are short and PC rapidly develop multidrug resistance (MDR) with median overall survival (OS) of locally advanced PC and metastatic PC patients of 7 months. Several MPC patients developed dramatic responses to the same chemoT after receiving multiple infusions of EGFR BATs. Novel therapeutic strategies are needed to improve clinical results. This study asks whether pre-targeting tumor cells with EGFR BATs can “sensitize” drug resistant tumor cell lines so that subsequent treatment can not only kill the MDR PC lines but also decrease the doses of chemotherapy required to kill tumor cells. Gemcitabine (Gem) and cisplatin (CIS) were used to generate drug-resistant MiaPaCa-2 and L3.6 by exposing step-wise increasing concentrations of Gem and Cis. MiaPaCa-2 and L3.6 survive to become resistant to Gem and CIS. Specific cytotoxicity was measured by 51Cr release. Flow cytometry data showed increased CD44+/CD24+/EpCAM+ cancer stem like cells and increased ABC transporter ABCG2+ cells in resistant cell lines compared to parental lines. EGFR or HER2 BATs from normal donors would kill Gem or CIS resistant MiaPaCa-2 or L3.6 (n = 6-8 normals) in 51Cr release assays and secrete Th1cytokines, IFN-γ and TNF-α, MIP-1b, and RANTES. We assessed whether pretreatment with EGFR BATs modify the effective dose of CIS activity directed at MiaPaCa-2 and PANC-1 cells using the xCelligence system. EGFR BATs at an E:T of 2:1 were added to the target cells for 24 hours, washed out, and CIS was added at concentrations of 3.5, 7, and 14 µM (IC50 by MTT) and MiaPaCa-2 at concentrations of 4.7, 9.3, and 18.6 µM (IC50 by MTT). The survival of the MiaPaCa2-2 cells was monitored continuously to track survival of the tumor cells. The mean cytotoxicity directed at MiaPaCa-2 increased with BATs priming at concentrations lower than the IC50 (4.7 and 9.3 µM). At the 4.7 µM dose, cytotoxicity increased from CIS alone (31±15%) to BATs primed followed by CIS (57±17%), and BATs together with CIS (77±12%). In PANC-1 cells, there was no specific cytotoxicity of with CIS concentrations at 3.5, 7.0, and 14 µM. BATs priming before addition of CIS increased specific cytotoxicity to 51±13%, 60±9%, and 84±5% at CIS concentrations of 3.5, 7.0, and 14 µM, respectively. Similar data have been obtained for 5-fluorouracil and preliminary data show similar trends for CIS resistant MiaPaCa-2 and PANC-1. In summary, we showed that: 1) BATs can kill chemo resistant tumor cells; and 2) pretreatment or sensitization of the tumor with BATs lowers the threshold for effective cytotoxic doses of CIS against MiaPaCa2-2 and PANC-1. This BATs priming strategy may augment clinical responses, decrease chemoT toxicities, and improve overall survival for pancreatic cancer patients. Citation Format: Lawrence G. Lum, Johnson Ung, Archana Thakur. Anti-CD3 x anti-EGFR bispecific antibody armed T cells (EGFR BATs) kills resistant pancreatic cancer cell lines and increases sensitivity to chemotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1430.