Resistance to Pyrrolobenzodiazepine Dimers Is Associated with SLFN11 Downregulation and Can Be Reversed through Inhibition of ATR

by Selleckchem | Jun 30 2023

Resistance to antibody-drug conjugates (ADCs) has been observed in both preclinical models and clinical studies. However, mechanisms of resistance to pyrrolobenzodiazepine (PBD)-conjugated ADCs have not been well characterized and thus, this study was designed to investigate development of resistance to PBD dimer warheads and PBD-conjugated ADCs. We established a PBD-resistant cell line, 361-PBDr, by treating human breast cancer MDA-MB-361 cells with gradually increasing concentrations of SG3199, the PBD dimer released from the PBD drug-linker tesirine. 361-PBDr cells were over 20-fold less sensitive to SG3199 compared with parental cells and were cross-resistant to other PBD warhead and ADCs conjugated with PBDs. Proteomic profiling revealed that downregulation of Schlafen family member 11 (SLFN11), a putative DNA/RNA helicase, sensitizing cancer cells to DNA-damaging agents, was associated with PBD resistance. Confirmatory studies demonstrated that siRNA knockdown of SLFN11 in multiple tumor cell lines conferred reduced sensitivity to SG3199 and PBD-conjugated ADCs. Treatment with EPZ011989, an EZH2 inhibitor, derepressed SLFN11 expression in 361-PBDr and other SLFN11-deficient tumor cells, and increased sensitivity to PBD and PBD-conjugated ADCs, indicating that the suppression of SLFN11 expression is associated with histone methylation as reported. Moreover, we demonstrated that combining an ataxia telangiectasia and Rad3-related protein (ATR) inhibitor, AZD6738, with SG3199 or PBD-based ADCs led to synergistic cytotoxicity in either resistant 361-PBDr cells or cells that SLFN11 was knocked down via siRNA. Collectively, these data provide insights into potential development of resistance to PBDs and PBD-conjugated ADCs, and more importantly, inform strategy development to overcome such resistance.

Comments:

The study you described aimed to investigate the development of resistance to pyrrolobenzodiazepine (PBD)-conjugated antibody-drug conjugates (ADCs). The researchers established a PBD-resistant cell line called 361-PBDr by gradually increasing the concentrations of SG3199, a PBD dimer released from the PBD drug-linker tesirine, in human breast cancer MDA-MB-361 cells.

The results showed that the 361-PBDr cells were over 20-fold less sensitive to SG3199 compared to the parental cells. Additionally, these resistant cells demonstrated cross-resistance to other PBD warheads and ADCs conjugated with PBDs. To understand the underlying mechanisms of resistance, the researchers conducted proteomic profiling and identified downregulation of Schlafen family member 11 (SLFN11), a DNA/RNA helicase known to sensitize cancer cells to DNA-damaging agents, as being associated with PBD resistance.

Confirmatory studies using siRNA knockdown of SLFN11 in multiple tumor cell lines showed reduced sensitivity to SG3199 and PBD-conjugated ADCs. Further experiments revealed that treatment with EPZ011989, an EZH2 inhibitor, led to the derepression of SLFN11 expression in 361-PBDr cells and other SLFN11-deficient tumor cells, consequently increasing their sensitivity to PBDs and PBD-conjugated ADCs. This finding suggested that the suppression of SLFN11 expression may be associated with histone methylation, as previously reported.

Moreover, the researchers demonstrated that combining an ataxia telangiectasia and Rad3-related protein (ATR) inhibitor called AZD6738 with SG3199 or PBD-based ADCs resulted in synergistic cytotoxicity in both resistant 361-PBDr cells and cells in which SLFN11 was knocked down via siRNA. These findings provide insights into the potential development of resistance to PBDs and PBD-conjugated ADCs. Furthermore, they inform the development of strategies to overcome such resistance, such as the use of EZH2 inhibitors and ATR inhibitors in combination with PBD-based therapies.