Differential Activity of ATR and WEE1 Inhibitors in a Highly Sensitive Subpopulation of DLBCL Linked to Replication Stress

Abstract

DNA damage checkpoint kinases ATR and WEE1 are among key regulators of DNA damage response pathways protecting cells from replication stress, a hallmark of cancer that has potential to be exploited for therapeutic use. ATR and WEE1 inhibitors are in early clinical trials and success will require greater understanding of both their mechanism of action and biomarkers for patient selection. Here, we report selective antitumor activity of ATR and WEE1 inhibitors in a subset of non-germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL) cell lines, characterized by high MYC protein expression and CDKN2A/B deletion. Activity correlated with the induction of replication stress, indicated by increased origin firing and retardation of replication fork progression. However, ATR and WEE1 inhibitors caused different amounts of DNA damage and cell death in distinct phases of the cell cycle, underlying the increased potency observed with WEE1 inhibition. ATR inhibition caused DNA damage to manifest as 53BP1 nuclear bodies in daughter G 1 cells leading to G 1 arrest, whereas WEE1 inhibition caused DNA damage and arrest in S phase, leading to earlier onset apoptosis. In vivo xenograft DLBCL models confirmed differences in single-agent antitumor activity, but also showed potential for effective ATR inhibitor combinations. Importantly, insights into the different inhibitor mechanisms may guide differentiated clinical development strategies aimed at exploiting specific vulnerabilities of tumor cells while maximizing therapeutic index. Our data therefore highlight clinical development opportunities for both ATR and WEE1 inhibitors in non-GCB DLBCL subtypes that represent an area of unmet clinical need.Significance: ATR and WEE1 inhibitors demonstrate effective antitumor activity in preclinical models of DLBCL associated with replication stress, but new mechanistic insights and biomarkers of response support a differentiated clinical development strategy.

Resistance to the CHK1 inhibitor prexasertib involves functionally distinct CHK1 activities in BRCA wild-type ovarian cancer

“…Instead, a large subpopulation of G2 cells was CyclinB1-negative along with the low levels of mitotic marker pHH3-S10. The differential effects of ATR, CHK1, and WEE1 on DNA replication may present different mechanisms of resistance to ATR, CHK1, and WEE1 inhibitors although all involved the delayed G2 phase [32], warranting further investigation. Also, given that BRCA mutation status is associated with PARPi resistance/sensitivity in HGSOC [6,7], it is imperative to study potential mechanisms of resistance to CHK1i separately for BRCA mutant HGSOC models.…”

A WEE1 family business: regulation of mitosis, cancer progression, and therapeutic target

“…Regarding the mechanism of action, adavosertib induces S and/or G2/M cell cycle checkpoints override, depending on cancer types, when used in monotherapy. Cell cycle perturbation is associated with a progressive accumulation of DNA damages and by the induction of apoptosis [ 35 , 99 , 119 – 122 ]. This last event is cell cycle phase-dependent and can occur (i) as a consequence of S phase checkpoint override, when cancer cells start DNA replication even in the presence of DNA damages (replicative catastrophe); (ii) following G2/M phase checkpoint override, that results in forced entry into mitosis, even in the presence of DNA damages (mitotic catastrophe).…”

Combined PARP and ATR inhibition potentiates genome instability and cell death in ATM-deficient cancer cells

“…ATM and DNA-PK inhibitors are being explored as chemo-and radiosensitisers due to their fundamental role in DNA DSB repair [21,22]. Conversely, ATR's functions in regulating G2-M checkpoint activation, replication fork stability and late-origin firing [23] appear to dominate ATRinhibitor efficacy, with ATR and WEE1 inhibitors showing efficacy in tumours with high replication stress [24][25][26]. ATM-deficient cells are also hypersensitive to ATR inhibition, at least partly due to a greater dependency on ATR for DNA repair and checkpoint control [27][28][29].…”