DHES0815A, a novel antibody-drug conjugate targeting HER2/neu, is highly active against uterine serous carcinomas in vitro and in vivo

Abstract

Objective: Uterine serous carcinoma (USC) is an aggressive histologic variant of endometrial cancer which portends a poor prognosis. DHES0815A is a novel antibody-drug-conjugate (ADC) which binds specifically to HER2 overexpressing tumors at a distinct epitope from that bound by trastuzumab and pertuzumab after which it delivers the toxic payload, PBD-MA, a DNA mono-alkylating agent. The objective of this study was to evaluate the preclinical activity of DHES0815A against primary USC cell lines and xenografts.

Methods: Twelve primary USC cell lines were assessed by immunohistochemistry (IHC) for HER2 protein expression and for C-erbB2 gene amplification using fluorescent in situ hybridization (FISH) analysis. Cell viability and bystander killing in USC cell lines after exposure to DHES0815A, the non-targeted ADC, and the unconjugated antibody (i.e. MHES0488A) were evaluated using flow cytometry-based-assays. In vivo activity of DHES0815A was tested against HER2/neu overexpressing USC xenografts.

Results: High HER2/neu protein expression was seen in 25% (3/12) of the primary USC cell lines. USC cell lines overexpressing HER2/neu were significantly more sensitive to DHES0815A when compared to the non-targeted control ADC (p < 0.001). DHES0815A did not induce significant bystander killing of HER2/neu negative tumors when admixed with HER2/neu positive tumors. DHES0815A caused growth-inhibition and increased survival in USC HER2/neu overexpressing xenografts when compared to controls (p < 0.01).

Conclusions: DHES0815A is both highly selective and toxic to USC tumors overexpressing HER2/neu both in vitro and in vivo. HER2-directed ADCs, alone or in combination with other HER2/neu targeted agents may represent a novel treatment option for patients with tumors harboring HER2/neu overexpression refractory to trastuzumab and traditional chemotherapy.

Keywords: Antibody drug conjugate (ADC); DHES0815A; Uterine cancer; Uterine serous carcinoma.

Figure 1:

IC₅₀ of DHES0815A compared to control (non-targeted control in USC cell lines with high level of HER2/neu expression versus negative HER2/neu expression. High HER2/neu (3+) expressing USC cell lines (ARK2, ARK20, ARK1) demonstrated significantly lower IC₅₀ values when compared to the non-targeted control ADC (53-fold, 19-fold, and a 11-fold decrease, p<0.05). USC cell lines with negative HER2/neu (0/1+) expression (ARK4) showed no difference in IC₅₀ values of DHES0815A when compared to the non-targeted control ADC.

Figure 2:. Bystander assay-

Solid gray bar no-border: Low/negative HER2/neu expressing ARK4 cell (ARK4-GFP cells), co-cultured without any treatment (control, CTRL). Stripes bar with no-border: Low/negative HER2/neu expressing ARK4 cell (ARK4-GFP cells), co-cultured with high HER2/neu expressing cells (ARK2) and treated with control ADC at 1 μg/mL. Squares bar no-border: Low/negative HER2/neu expressing ARK4 cell (ARK4-GFP cells), co-cultured with high HER2/neu expressing cells (ARK2) and treated with DHES0815A at 1 μg/mL concentration.

Figure 3A:. In vivo efficacy of DHES0815A.

Antitumor activity of DHES0815A was compared to controls including the non-targeted ADC, the unconjugated antibody (MHES0488A), and saline (control) in xenograft models with 3+ HER2/neu expression. (i.e. ARK-2). Mice were treated with a single intravenous injection as described in the methods section. The treatment with DHES0815A, showed a statistically significant difference in tumor growth inhibition compared to the control (p=0.0001) and the non-targeted control ADC (p=0.006) that began at days 16 and 19 of the treatment respectively. Figure 3B: Overall survival. DHES0815A caused growth-inhibition and increased survival in HER2/neu overexpressing xenografts when compared to control (p<0.01). Figure 3C: Animal weight change. Animals tolerated DHES0815A well treatments with no significant change in their body weight.