Abstract 590: Co-injection of human monocytes improves the in vivo antitumoral activity of bevacizumab in two NSCLC PDX models

Nowadays, an increasing number of monoclonal antibodies (mAbs) that specifically target malignant cells or interfere with different compartments of the tumor microenvironment are available for cancer therapy. They take effect via different modes of action including the initiation of a tumor-targeting immune response. Preclinical platforms such as PDX models have to be improved to better recapitulate all possible modes of action for mAbs as well as other immune-modulating agents. In the current study, we evaluated the antitumoral activity of Bevacizumab in two NSCLC PDX growing subcutaneously in NMRI nu/nu mice with and without co-injection of human monocytes. Two NSCLC PDX, LXFA 2478 and LXFA 677, were subcutaneously implanted into 4-6 weeks old female NMRI nu/nu mice (Harlan, Denmark). Tumor models were chosen based on their VEGFA expression level. Additionally, LXFA 2478 and LXFA 677 show high expression of TLR2 and CD14 respectively, two factors known to be involved in monocyte attraction. When median tumor size reached 150 - 300 mm3, mice were equally distributed to treatment groups (n = 4/group). Animals were treated once weekly for 7 cycles with a) control vehicle b) control vehicle + 5×106 human monocytes c) Bevacizumab at 40 mg/kg/d and d) Bevacizumab + 5×106 human monocytes. Tumor volume was determined twice weekly by caliper measurement. At the end of the study, tumor and lymphatic organs of the animals were harvested and subsequent IHC analysis for human CD14, CD68 and CD163 was performed. In both investigated tumor models, Bevacizumab showed moderate antitumoral activity with a maximal tumor load reduction of 71% (LXFA 2478) and 84% (LXFA677) as compared to untreated controls on days 39 and 35. The co-injection of human monocytes markedly enhanced the therapeutic effect of Bevacizumab in both NSCLC PDX: maximal tumor load reduction was 89% in LXFA 2478 and 95% in LXFA 677 in combination groups. The injection of monocytes alone did not affect tumor growth as compared to untreated control. As predicted by the high VEGFA expression, NSCLC PDX showed high sensitivity against Bevacizumab. This antitumoral activity was increased by 18% and 11% for LXFA 2478 and LXFA 677, respectively, through the additional injection of monocytes. Monocyte recruiting factors (namely CD14 and TLR2) likely contribute to the mechanism of action. Monocytes and macrophages have been reported to induce antibody-dependent cytotoxicity and phagocytosis of tumor cells in the