Synthetic lethality of a cell-penetrating anti-RAD51 antibody in PTEN-deficient melanoma and glioma cells

Abstract

PTEN is a tumor suppressor that is highly mutated in a variety of human cancers. Recent studies have suggested a link between PTEN loss and deficiency in the non-homologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair. As a means to achieve synthetic lethality in this context, we tested the effect of 3E10, a cell-penetrating autoantibody that inhibits RAD51, a key factor in the alternative pathway of DSB repair, homology dependent repair (HDR). We report here that treatment of PTEN-deficient glioma cells with 3E10 leads to an accumulation of DNA damage causing decreased proliferation and increased cell death compared to isogenic PTEN proficient controls. Similarly, 3E10 was synthetically lethal to a series of PTEN-deficient, patient-derived primary melanoma cell populations. Further, 3E10 was found to synergize with a small molecule inhibitor of the ataxia telangiectasia and Rad3-related (ATR) protein, a DNA damage checkpoint kinase, in both PTEN-deficient glioma cells and primary melanoma cells. These results point to a targeted synthetic lethal strategy to treat PTEN-deficient cancers through a combination designed to disrupt both DNA repair and DNA damage checkpoint signaling.

Regulation and pharmacological targeting of RAD51 in cancer

“…3E10 directly interacts with the N-terminus of RAD51, and this interaction prevents RAD51 from assembling as a filament onto ssDNA ( 183 ). An expanded role for 3E10 was demonstrated as 3E10 exposure results in increased toxicity in PTEN-deficient glioma and melanoma cancer cells, which already have a significant propensity for DNA damage ( 185 ). Additionally, 3E10 sensitizes tumor cells to various cancer therapies, including radiation, doxorubicin and ATR inhibitors ( 185 , 186 ).…”

“…An expanded role for 3E10 was demonstrated as 3E10 exposure results in increased toxicity in PTEN-deficient glioma and melanoma cancer cells, which already have a significant propensity for DNA damage ( 185 ). Additionally, 3E10 sensitizes tumor cells to various cancer therapies, including radiation, doxorubicin and ATR inhibitors ( 185 , 186 ). Recently, a novel RAD51 inhibitor, Fab-F2-iPTD, was created by fusing a cell-penetrating peptide to an antigen-binding fragment (Fab) that inhibits RAD51–ssDNA binding activity ( 187 ).…”

Targeting Rad51 as a strategy for the treatment of melanoma cells resistant to MAPK pathway inhibition

“…It is a synthetic lethality of the additional inhibition of the remaining DNA repair mechanisms. For example, a recent study postulates a synthetic lethality of PTEN-deficient melanoma cells to Rad51 inhibition, as PTEN affects non-homologous end joining repair (NHEJ) as an alternative DNA double-strand break repair pathway to HRR 43 . A synthetic lethal relationship is also possible between the NER and the HR mechanism and several mutations and polymorphisms in NER genes are significantly associated with melanoma formation 44,45 .…”

The Mechanisms Underlying PTEN Loss in Human Tumors Suggest Potential Therapeutic Opportunities

“…RAD51 is a key regulator involved in DNA double strand break repair and homology-directed repair. Treatment of PTEN-deficient glioma cells with a cell-penetrating antibody against RAD51, 3E10, leads to an accumulation of DNA damage causing decreased proliferation and increased cell death compared to isogenic PTEN-proficient controls [185]. ITGA5 knockdown and the pharmacologic inhibition of BCL2-BCLX L had a synergistic effect with PI3K/AKT inhibitors in PTEN-mutant prostate cancer cells, such as LNCap and PC3, but not in PTEN-proficient DU145 cells [186].…”