Targeting Aberrant DNA Double-Strand Break Repair in Triple-Negative Breast Cancer with Alpha-Particle Emitter Radiolabeled Anti-EGFR Antibody

Abstract

The higher potential efficacy of alpha-particle radiopharmaceutical therapy lies in the 3 to 8-fold greater biological effectiveness (RBE) of alpha particles relative to photon or beta-particle radiation. This greater RBE, however, also applies to normal tissue, thereby reducing the potential advantage of high RBE. Since alpha particles typically cause DNA double strand breaks (DSBs), targeting tumors that are defective in DSB repair effectively increases the RBE, yielding a secondary, RBE-based differentiation between tumor and normal tissue that is complementary to conventional, receptor-mediated tumor targeting. In some triple negative breast cancers (TNBC, ER−/PR−/HER-2−), germline mutation in BRCA-1, a key gene in homologous recombination (HR) DSB repair, predisposes patients to early onset of breast cancer. These patients have few treatment options once the cancer has metastasized. In this study, we investigated the efficacy of alpha particle emitter, 213Bi labeled anti-EGFR antibody, Cetuximab, in BRCA-1 defective TNBC. 213Bi-Cetuximab was found to be significantly more effective in the BRCA-1 mutated TNBC cell line HCC1937 than BRCA-1 competent TNBC cell MDA-MB-231. siRNA knockdown of BRCA-1 or DNA-PKcs, a key gene in non-homologous end joining (NHEJ) DSB repair pathway, also sensitized TNBC cells to 213Bi-Cetuximab. Furthermore, the small molecule inhibitor of DNA-PKcs, NU7441, sensitized BRCA-1 competent TNBC cells to alpha particle radiation. Immunofluorescent staining of γH2AX foci and comet assay confirmed that enhanced RBE is caused by impaired DSB repair. These data offer a novel strategy for enhancing conventional receptor-mediated targeting with an additional, potentially synergistic radiobiological targeting that could be applied to TNBC.

Modulation of ionizing radiation-induced effects by NU7441, KU55933 and VE821 in peripheral blood lymphocytes

“…On the other hand, it significantly increased radiation-induced cytotoxicity and genotoxicity, indicating no direct relation between early H2AX phosphorylation and DNA damage repair capacity in human peripheral lymphocytes. Our results and data reported by others show NU7441 to be a potent radiosensitizing agent (Song et al, 2013;Ciszewski et al, 2014;Tichy et al, 2014). However, lymphocytes and highly differentiated (G 0/ G 1 ) tissues might be significantly affected by its non-selective action.…”

Evaluation of cetuximab as a candidate for targeted α-particle radiation therapy of HER1-positive disseminated intraperitoneal disease

“…[32][33][34] Studies from this laboratory and others have reported on the potential of HER1 as a target for molecular imaging and for targeted radiation therapy. [21][22][23][24]26,[35][36][37][38] Cetuximab has been the focus of several imaging studies with the objective of assessing the value of this mAb for disease monitoring, HER1 expression and distribution, patient selection and for performing dosimetric calculations. [23][24][25][26] The preclinical studies from this laboratory demonstrated excellent targeting of s.c. tumor by 111 In-cetuximab given intravenously.…”

Targeted and Nontargeted α-Particle Therapies

“…The RBE under these circumstances ranges from three to seven. Higher values (RBE = 21) may be achieved if cell signaling pathways associated with DNA double-strand break repair are inhibited (32). Because the RBE may be thought of as a ratio of radiosensitivities, increases in the RBE require that the sensitivity to high LET radiation increase while the sensitivity to low LET radiation either remain unchanged or decrease.…”

“…From this perspective one may envision a combination of α-particle-emitter-based radiopharmaceutical therapy with a DNA double-strand break repair inhibitor. Targeting of the α-particle-emitter-labeled agent to cancer cells confers a first-order level of synthetic lethality; the high LET radiation and increased propensity for double-strand break damage, coupled with a double-strand break repair inhibitor, confer another layer of synthetic lethality (32). …”