Pharmacological inhibition of the DNA damage checkpoint prevents radiation-induced oocyte death

Abstract

Summary sentence: Oocytes, which are highly sensitive to DNA damage caused by certain cancer treatments, can be protected from radiation-induced death by an inhibitor 20 of the checkpoint protein CHK2.Key Words: fertility, primordial follicles, premature ovarian failure, oncofertility. 25Corresponding author: Ewelina.Bolcun-filas@jax.org; 207-288-6985; The Jackson Laboratory, 600 Main Street, Bar Harbor, Maine, 04609 USA All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.The copyright holder for this preprint (which . http://dx.doi.org/10.1101/132779 doi: bioRxiv preprint first posted online May. 1, 2017; 2 ABSTRACT 30Ovarian function is directly correlated with survival of the primordial follicle reserve.Women diagnosed with cancer have a primary imperative of treating the cancer, but since the resting oocytes are hypersensitive to the DNA-damaging modalities of certain chemo-and radiotherapeutic regimens, such patients face the collateral outcome of 35 premature loss of fertility and ovarian endocrine function. Current options for fertility preservation primarily include collection and cryopreservation of oocytes or in vitro fertilized oocytes, but this necessitates a delay in cancer treatment and additional assisted reproductive technology (ART) procedures. Here, we evaluated the potential of pharmacological preservation of ovarian function by inhibiting a key element of the 40 oocyte DNA damage checkpoint response, checkpoint kinase 2 (CHK2; CHEK2).Whereas non-lethal doses of ionizing radiation (IR) eradicate immature oocytes in wild type mice, irradiated Chk2 -/-mice retain their oocytes and thus, fertility. Using an ovarian culture system, we show that transient administration of the CHK2 inhibitor 2-(4-(4-Chlorophenoxy)phenyl)-1H-benzimidazole-5-carboxamide-hydrate ("CHK2iII") blocked 45 activation of the CHK2 targets TRP53 and TRP63 in response to sterilizing doses of IR, and preserved oocyte viability. After transfer into sterilized host females, these ovaries proved functional and readily yielded normal offspring. These results provide experimental evidence that chemical inhibition of CHK2 is a potentially valid treatment for preserving fertility and ovarian endocrine function of women exposed to DNA-50 damaging cancer therapies such as IR.All rights reserved. No reuse allowed without permission.was not peer-reviewed) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity.

CHK2 inhibition provides a strategy to suppress hematological toxicity from PARP inhibitors

“…This suggests co-targeting CHK2 could alleviate some side effects of PARPi in the blood, without a detrimental impact on the efficacy of these agents against the cancer. Others have suggested cotargeting CHK2 to boost the activity of PARPi (26,27), but our findings point to a distinct rationale, more in keeping with recent efforts to harness CHK2 inhibitors to limit the toxic influence of radiation (28,29) or cytotoxic chemotherapy (30).…”

Transient inhibition of p53 homologs protects ovarian function from two distinct apoptotic pathways triggered by anticancer therapies

“…Because fertility-preserving adjuvant therapies deceive this safeguard system, thereby allowing oocytes that were destined to die to persist, genomic integrity becomes a concerning issue [47]. Previous studies have concluded adjuvant therapies were safe, as no visible abnormalities were detected in pups born to female mice treated with genotoxic agents and adjuvants [4,5,[7][8][9]25]. However, the limitation of phenotype-based mutagenesis assay has been demonstrated by the ENU (N-ethyl-Nnitrosourea) mutagenesis in the mouse, which increases de novo single nucleotide variants in progenies by 133-fold (7.18 × 10 −7 per nucleotide, 2105 de novo SVNs per generation) [48], resulting in~25 mutations with functional consequences per diploid genome.…”

“…However, in vivo the activity of most inhibitors rapidly declines, as they are cleared from the system [38]. Therefore, results based on the assays in which ovaries are treated in vitro do not convey a practicable ovarian function-preserving therapy [25]. Hence, we tested the efficacy of CK2II for the preservation of ovarian functions against CDDP and X-ray in mice.…”

“…When DNA damage occurs, CHEK2 phosphorylates the transactivation inhibitory domain at S621, which in turn promotes the phosphorylation and formation of active tetramers in TAp63α [21,24]. A study by Rinaldi and coworkers suggests that CHEK2 can be a target of ovarian reserve preservation: In ovarian organ culture, a CHEK2 inhibitor protected PFs from γ-irradiation, and the transplantation of these treated ovaries produced healthy pups [25]. A recent study by Tuppi et al [26] has identified CK1 is an essential kinase that activates TAp63α via phosphorylation in response to DNA damage.…”

Germline genome protection: implications for gamete quality and germ cell tumorigenesis

“…It is intriguing that genetic depletion of Chek2, which is an important mediator of germ cell apoptosis following IR (Bolcun‐Filas et al ., ; Rinaldi et al ., ), did not rescue PGCs in the Fancm C4/C4 mutant, while deficiencies in Atm, Tp53, and p21 did. There are several possible explanations for these observations, one of which is that Chek2 deficiency does not rescue PGC numbers because the DNA lesions that occur in the Fancm C4/C4 mutant may not be DSBs that would activate CHK2.…”