Author: Scott James Bright, Vered Domankevich-Bachar, Mandira Manandhar, Poliana Marinello, Yogesh Rai, Marco Freitas Reis, Alexandre Rubinstein, Gabriel O. Sawakuchi, Ronen Segal, Walison Augusto Silva Brito, Mark Wasley, Amy Wu 👨🔬
Affiliation: MD Anderson Cancer Center, Alpha Tau Medical Ltd, Alpha Tau Medical LTD, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center 🌍
Purpose: Immunologically cold breast cancers are aggressive and difficult to treat due to their lack of immune cell infiltration. The combination of high-LET radiation with DNA repair inhibitors offers a promising strategy to stimulate the immune system and enhance therapeutic efficacy. This study aimed to investigate the immunomodulatory potential of combining alpha particles with a selective Poly (ADP-ribose) polymerase (PARP) inhibitor in breast cancer.
Methods: Cells (MDA-MB-436, MDA-MB-436 BRCA1, and 4T1) were treated with AZD5305, a PARP1 inhibitor 2 h before irradiation using an alpha particle irradiator (Americium-241) or x-rays (X-Rad320, Precision X-Ray). Radiosensitization was assessed using the clonogenic survival assay. The expression of surface proteins related with immune activation was investigated by flow cytometry, while DNA damage and intracellular immune signaling proteins were determined by western blotting. Diffusing Alpha-emitter Radiation Therapy (Alpha DaRT) was employed to deliver alpha particles intratumorally, by the implantation of 224Ra-loaded sources in mice bearing 4T1 subcutaneous leg tumors. AZD5305 (1 mg/kg) was daily administered by oral gavage for 6 consecutive days, starting 24 h before Alpha DaRT implantation. Tumor growth delay and survival were assessed.
Results: AZD5305 enhanced radiosensitization to both X-rays and alpha particles. In 4T1 cells, AZD5305+X-rays significantly increased the expression of the costimulatory proteins CD80 and CD86, which have the potential to activate TCD8+ cells. The combination also upregulated immune checkpoint molecules, including Tim-3, CTLA-4, PD-1, and Lag-3. Treatment with AZD5305 and alpha particles promoted more persistent DNA damage (detectable 72 h after irradiation) and elevated levels of intracellular immune signaling proteins compared to AZD5305 combined with X-rays. In vivo, Alpha DaRT+AZD5305 achieved the greatest tumor growth delay and improved survival outcomes.
Conclusion: The combination of alpha particles with selective PARP1 inhibition enhances immune stimulation, induces persistent DNA damage, and sensitizes immunologically cold breast cancer both in vitro and in vivo.