3169 - Radiotherapy Enhances TROP-2 Antibody Drug Conjugate Efficacy By Upregulating TROP-2 Membrane Expression, and Increasing Apoptosis and DNA Damage

05:00pm - 06:00pm PT

Hall F

Screen: 7

POSTER

Presenter(s)

Wen-Chi Yang, MD - National Taiwan University Hospital, Taipei, 100

W. C. Yang^1,2, M. F. Wei³, C. S. Huang⁴, and S. H. Kuo^2,5; ¹Department of Radiation Oncology, National Taiwan University Cancer Center, Taipei, Taiwan, ²Graduate Institute of Oncology, National Taiwan University College of Medicine, Taipei, Taiwan, ³Division of Radiation Oncology, Department of Oncology, National Taiwan University, Taipei, Taiwan, ⁴Departments of Surgery, National Taiwan University Hospital, Taipei, Taiwan, ⁵Division of Radiation Oncology, Department of Oncology, National Taiwan University Hospital, Taipei, Taiwan

Purpose/Objective(s):

Sacituzumab govitecan (SG), a TROP-2-directed antibody-drug conjugate, has demonstrated significant anti-tumor activity in triple-negative breast cancer (TNBC); however, its effectiveness varies among patients. This study investigates whether combining radiotherapy (RT) with SG enhances therapeutic efficacy in TNBC

Materials/Methods:

We utilized three human TNBC cell lines—MDA-MB-231, MDA-MB-453, and MDA-MB-468—to evaluate the radiosensitizing effects of SG. Clonogenic assays were performed to assess the impact of SG in combination with RT. Double-stranded DNA (dsDNA) damage response proteins, including ?H2AX, ATM, phospho (p)-ATM, DNA-PKC, and p-DNA-PKC, along with the apoptosis-related protein cleaved PARP, were analyzed via western blotting. TROP-2 membrane expression and apoptotic cell populations (Annexin V/PI staining) were quantified through flow cytometry. MDA-MB-231 and MDA-MB-468 xenograft models were used to assess whether RT pretreatment enhances SG’s anti-tumor efficacy.

Results:

SG cytotoxicity was evaluated in MDA-MB-231, MDA-MB-453, and MDA-MB-468, with IC50 values of 4.53 µM, 315.7 nM, and 126.6 nM, respectively. These values correlated with TROP-2 expression levels, with MDA-MB-231 exhibiting the lowest and MDA-MB-468 the highest expression. Clonogenic assays demonstrated a synergistic effect of RT and SG across all TNBC cell lines. Combination treatment with SG and RT resulted in increased DNA damage, indicated by higher expression of ?H2AX, p-ATM, and p-DNA-PKC compared to control, SG alone, or RT alone. RT significantly increased TROP-2 expression on the tumor cell surface in a dose-dependent manner (5 Gy, 10 Gy, and 15 Gy) at 24 hours post-RT. Proliferation assays showed that RT followed by SG (24 hours post RT) significantly reduced cell proliferation compared to SG pretreatment (1 hour before RT) followed by RT in MDA-MB-231 and MDA-MB-453 (P < 0.05 and P < 0.01). Additionally, RT followed by SG resulted in significantly higher ?H2AX expression, cleaved PARP expression, and apoptotic cell populations compared the reverse sequence. In MDA-MB-468 xenografts (a high TROP-2 expression model), SG alone and RT alone significantly reduced tumor growth compared to the control group (P < 0.05 for both), while RT pretreatment followed by SG further enhanced tumor suppression compared to control, SG alone, and RT alone (P < 0.001, P < 0.05, and P < 0.01, respectively). In MDA-MB-231 xenografts (a low TROP-2 expression model), SG alone did not exhibit significant anti-tumor effects. However, RT pretreatment followed by SG significantly reduced tumor growth compared to the control, SG alone, and RT alone groups (P < 0.001, P < 0.001, and P < 0.01, respectively).

Conclusion:

Our findings indicate that RT pretreatment followed by SG effectively inhibits TNBC tumor growth, irrespective of TROP-2 expression, both in vitro and in vivo. This effect is mediated through the upregulation of TROP-2 expression, increased apoptosis, and enhanced dsDNA damage.