Evaluation of Trastuzumab Anti-Tumor Efficacy and its Correlation with HER-2 Status in Patient-Derived Gastric Adenocarcinoma Xenograft Models

Abstract

The aim of the study was to investigate trastuzumab anti-tumor efficacy and its correlation with HER-2 status in primary xenograft models derived from Chinese patients with gastric adenocarcinoma. Patient-derived gastric adenocarcinoma xenograft (PDGAX) mouse models were firstly generated by implanting gastric adenocarcinoma tissues from patients into immune deficient mice. A high degree of histological and molecular similarity between the PDGAX mouse models and their corresponding patients' gastric adenocarcinoma tissues was shown by pathological observation, HER-2 expression, HER-2 gene copy number, and mutation detection. Based on Hoffmann's criteria in gastric cancer, three models (PDGAX001, PDGAX003 and PDGAX005) were defined as HER-2 positive with fluorescence in situ hybridization (FISH) amplification or immunohistochemistry (IHC) 2+/ 3+, while two models (PDGAX002, PDGAX004) were defined as HER-2 negative. Upon trastuzumab treatment, significant tumor regression (105 % TGI) was observed in model PDGAX005 (TP53 wt), while moderate sensitivity (26 % TGI) was observed in PDGAX003, and resistance was observed in PDGAX001, 002 and 004. A significant increase in HER-2 gene copy number was only observed in PDGAX005 (TP53 wt). Interestingly, trastuzumab showed no efficacy in PDGAX001 (HER2 IHC 3+ and FISH amplification, but with mutant TP53). Consistent with this finding, phosphor-HER2 modulation by trastuzumab was observed in model PDGAX005, but not in PDGAX001.

Fig. 1

PDGAX model tumor growth curves. All five patient-derived gastric adenocarcinoma samples showed growth after subcutaneous implantation in SCID mice and subsequently in nude mice

Fig. 2

Histological evaluation of the PDGAX mouse models and matched human primary tumors. Representative images showing similar histological features (adenocarcinoma) between each PDGAX mouse model (top row) and the corresponding patient GA tissue (bottom row). AC: adenocarcinoma

Fig. 3

HER-2 IHC and FISH analysis. Representative images showing HER-2 IHC and FISH results on PDGAX mouse models (top row) and matched human primary tumor tissues (bottom row). HER-2 strong staining (3+) and FISH amplification (AMP) were detected in models PDGAX005 and PDGAX001 and matched primary tumor tissues. PDGAX001, PDGAX002, PDGAX003, and PDGAX004 were shown to be HER-2 IHC (0 ~ 3+) and FISH non-AMP. For FISH data, red signals represent HER2 and green signals represent CEP17

Fig. 4

Trastuzumab anti-tumor efficacy in PDGAX models. Xenograft tumors from stable passages of the PDGAX models were implanted subcutaneously into nude mice and treated with vehicle control or trastuzumab 15 mg/kg twice a week for two or 4 weeks, based on tumor growth rates in the different models when tumors reached 150 ~ 250 mm³ post implantation. Significant tumor regression was only observed in model PDGAX005 (TGI 105 %), while moderate or no responses (0 ~ 26 % TGI) were observed in PDGAX001, PDGAX002, PDGAX003 and PDGAX004 models. Tumor volumes were measured twice a week. Tumor growth inhibition (%TGI) was calculated based on tumor volumes of the control and treatment groups

Fig. 5

Detection of pHER2 IHC modulation in models PDGAX001 and PDGAX005. Representative images showing pHER2 modulation in trastuzumab-treated tissues from model PDGAX005 compared with vehicle control group. No modulation observed in model PDGAX001

Fig. 6

TP53 gene mutation detected by PCR-direct sequencing. An illustration of the mutation (G - > A) identified in TP53 gene (both on forward and reverse sequences). This mutation led to an amino acid change from cysteine to tyrosine at the 176th peptide of TP53 protein