Abstract: Nedisertib, also known as M3814 or peposertib, is a highly potent, selective, and orally available inhibitor of the DNA-dependent protein kinase (DNA-PK). DNA-PK is a critical molecular sensor for DNA double-strand breaks (DSBs) and plays a pivotal role in DNA repair through the non-homologous end joining (NHEJ) pathway. By inhibiting DNA-PK, Nedisertib effectively blocks NHEJ, thereby profoundly sensitizing cancer cells to DNA-damaging agents such as ionizing radiation and various chemotherapeutics. Structural analyses reveal that Nedisertib binds deeply into the hydrophobic pocket of the DNA-PK catalytic subunit (DNA-PKcs). While monotherapy has shown limited clinical efficacy, Nedisertib exhibits significant promise in combination regimens. Notably, recent preclinical evidence highlights its potential in targeted radionuclide and immunotherapy combinations, where it amplifies radiation-induced inflammatory micronucleation and enhances the efficacy of TGFβ/PD-L1 targeted cancer immunotherapies. Nedisertib is currently undergoing multiple Phase I clinical trials to evaluate its safety and efficacy in combination with chemoradiotherapy.
1. Introduction
Ionizing radiation (IR) and a subset of anticancer drugs exert their biological effects primarily by inducing DNA damage, with DNA double-strand breaks (DSBs) being the most deleterious type [1]. In eukaryotes, DSBs are repaired mainly through homologous recombination (HR) and non-homologous end joining (NHEJ) [1]. DNA-dependent protein kinase (DNA-PK), composed of a catalytic subunit (DNA-PKcs) and a Ku80-Ku70 heterodimer, acts as the primary molecular sensor for DSBs and plays a pivotal role in the NHEJ repair pathway [1]. Cells deficient in DNA-PKcs exhibit hypersensitivity to IR and DNA-damaging agents, a vulnerability that can be pharmacologically exploited [1]. Nedisertib (also known as M3814 or peposertib) is a recently developed, new-generation oral DNA-PK inhibitor discovered through drug library screening at Merck KGaA [1][2]. It was designed to overcome the limited selectivity of older DNA-PK inhibitors and is currently being evaluated in clinical trials as a potent radio- and chemosensitizer for cancer therapy [1][2].
2. Pharmacological Activity
Nedisertib (M3814) demonstrates robust pharmacological activity by enhancing cellular radiosensitivity and chemosensitivity in a DNA-PKcs-dependent manner at submicromolar concentrations [1]. In preclinical models, it sensitizes cells to various chemotherapeutic agents, including calicheamicin, microtubule polymerization inhibitors (paclitaxel), and topoisomerase II inhibitors (daunorubicin and etoposide) [1]. In vivo, oral or intragastrical administration of M3814 (5–100 mg/kg) significantly augmented tumor growth suppression when combined with radiation, Mylotarg (humanized anti-CD33 antibody conjugated to N-acetyl γ-calicheamicin), paclitaxel, etoposide, 5-fluorouracil, and pegylated liposomal daunorubicin (PLD) [1][2]. Furthermore, M3814 has been shown to bind to the ATP-binding cassette transporter family G2 (ABCG2), effectively reversing multidrug resistance [1].
In the context of targeted radionuclide and immunotherapy combinations, M3814 has shown highly promising results. Recent studies demonstrate that M3814 potentiates in vivo tumor growth suppression when combined with radioimmunotherapy using bintrafusp α, an agent that inhibits profibroblastic TGFβ and immunosuppressive PD-L1 [1]. The DNA-PK inhibitor amplifies radiation-induced inflammatory micronucleation, thereby enhancing the efficacy of TGFβ/PD-L1 targeted cancer immunotherapy [1]. In a Phase 1 clinical study, M3814 was well tolerated, establishing a recommended phase 2 dose (RP2D) of 400 mg twice daily (BID) [1][2].
3. Molecular Mechanism of Action
M3814 functions as a highly potent and selective inhibitor of DNA-PK. It inhibits the autophosphorylation of DNA-PKcs at Ser2056 in cellulo at concentrations ranging from 0.1 to 1 µM [1]. In vitro, the IC50 for DNA-PKcs is exceptionally low, measured at 0.6 nM in the presence of 10 µM ATP, and 20 nM in the presence of 1 mM ATP [1]. Its selectivity profile is highly favorable; when tested against a panel of 284 lipid or protein kinases, only eight exhibited IC50 values below 1 µM [1]. By inhibiting DNA-PK, M3814 effectively blocks radiation-induced NHEJ repair, thereby preventing cancer cells from recovering from DNA double-strand breaks [2]. The ultimate cellular fate following M3814 exposure and DNA damage depends on the p53 status of the tumor: p53-proficient cells typically undergo cell cycle checkpoint arrest, senescence, or apoptosis, whereas p53-deficient cells are driven toward death by mitotic catastrophe [1].
4. Structure-Activity Relationship (SAR)
The chemical structure of M3814 is (S)-[2-chloro-4-fluoro-5-(7-morpholinoquinazolin-4-yl)phenyl]-(6-methoxypyridazin-3-yl)methanol [1]. Recent structural analyses using cryo-electron microscopy (cryo-EM) have elucidated its precise binding interactions with DNA-PKcs. The morpholine and quinazoline groups of M3814 fit snugly into the deepest hydrophobic pocket of the kinase, a binding mode similar to that of older inhibitors like NU7441 [1]. The chloro-fluorobenzene ring forms critical interactions with specific amino acid residues, including Met3729, Ser3731, Pro3735, Leu3751, and Ile3940 [1]. Additionally, the pyridazine group fits into a distinct groove formed by Met3729, Trp3805, Thr3811, Asn3926, and Met3929, which serves to further stabilize the interaction between the inhibitor and the DNA-PKcs enzyme [1].
5. Current Limitations
Despite its high potency and excellent selectivity profile, M3814 has limitations when used as a standalone treatment. In Phase 1 clinical studies, M3814 monotherapy did not yield partial responses in patients with advanced solid tumors [1]. Like many DNA repair inhibitors, its therapeutic efficacy is heavily reliant on the presence of DNA damage. Therefore, M3814 must be administered in combination with exogenous DNA-damaging modalities, such as radiotherapy or cytotoxic chemotherapy, to achieve significant tumor regression [1][2].
6. Future Perspectives
The future clinical development of Nedisertib (M3814) is strongly focused on combination strategies. Multiple Phase 1 and Phase Ib clinical trials are currently ongoing to evaluate its efficacy in combination with radiotherapy and chemotherapy [1]. For instance, a Phase Ib trial investigating the combination of M3814 with capecitabine and radiotherapy for the treatment of rectal cancer has been completed, paving the way for potential Phase II studies [2]. Most notably, the research direction combining M3814 with targeted radionuclide therapy and immunotherapy represents a highly promising frontier. Preclinical evidence showing that M3814 amplifies radiation-induced inflammatory micronucleation and synergizes with TGFβ/PD-L1 targeted immunotherapies (such as bintrafusp α) suggests that DNA-PK inhibition could become a cornerstone strategy for overcoming immunosuppressive tumor microenvironments and enhancing the efficacy of radioimmunotherapy [1].
