Abstract: Nedisertib, also known as M3814 or Peposertib, is a highly potent, orally available, and selective inhibitor of 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 via the non-homologous end joining (NHEJ) pathway. While older generations of DNA-PK inhibitors lacked selectivity due to structural similarities with phosphoinositide 3-kinases (PI3Ks), Nedisertib was developed to overcome these limitations, demonstrating high specificity for DNA-PK. Preclinical and early clinical studies indicate that while Nedisertib has modest efficacy as a monotherapy, it acts as a powerful sensitizer when combined with ionizing radiation (IR) and various DNA-damaging chemotherapeutic agents. Currently, Nedisertib is undergoing clinical evaluation in combination with radiotherapy and chemotherapy for the treatment of advanced solid malignancies, showing a manageable safety profile and promising synergistic antitumor activity.
1. Introduction
DNA double-strand breaks (DSBs) are considered the most deleterious type of DNA damage, typically generated by ionizing radiation (IR) and a subset of anticancer chemotherapeutic drugs [1]. In eukaryotic cells, DSBs are primarily repaired through two mechanisms: homologous recombination (HR) and non-homologous end joining (NHEJ) [1]. DNA-dependent protein kinase (DNA-PK), which consists of a catalytic subunit (DNA-PKcs) and a Ku80-Ku70 heterodimer, acts as the primary molecular sensor for DSBs and is essential for the NHEJ repair pathway [1] [2]. Cells deficient in DNA-PKcs exhibit hypersensitivity to IR and DNA-damaging agents, making DNA-PK an attractive target for cancer therapy [1].
Historically, the development of DNA-PK inhibitors was hindered by their structural similarity to phosphoinositide 3-kinases (PI3Ks) and PI3K-related kinases (PIKKs), which limited their selectivity [1] [2]. Nedisertib (M3814, also referred to as Peposertib) represents a new generation of orally active, highly potent, and selective DNA-PK inhibitors discovered through extensive drug library screening [1] [2]. It is currently being investigated as a combination partner in chemoradiotherapy regimens for advanced malignancies [1].
2. Pharmacological Activity
Nedisertib exhibits exceptional potency and selectivity for DNA-PK. In vitro assays demonstrate an IC50 for DNA-PKcs of 0.6 nM and 20 nM in the presence of 10 µM and 1 mM ATP, respectively [1]. When tested against a panel of 284 lipid or protein kinases, only eight showed IC50 values below 1 µM, underscoring its high selectivity [1]. In cellular models, Nedisertib effectively inhibits the autophosphorylation of DNA-PKcs at Ser2056 at submicromolar concentrations (0.1–1 µM) [1].
The primary pharmacological value of Nedisertib lies in its ability to enhance cellular radiosensitivity and chemosensitivity. Preclinical studies show that it sensitizes cancer cells to various chemotherapeutic agents, including calicheamicin, microtubule polymerization inhibitors (paclitaxel), and topoisomerase II inhibitors (daunorubicin, etoposide, and pegylated liposomal daunorubicin) [1]. In non-small cell lung cancer (NSCLC) models, Nedisertib demonstrated synergistic antitumor effects when combined with paclitaxel and etoposide [2]. In vivo, oral or intragastrical administration of 5–100 mg/kg of Nedisertib significantly augmented tumor growth suppression when paired with radiation, chemotherapy, or radioimmunotherapy (such as bintrafusp α) [1].
In human Phase 1 clinical trials, Nedisertib was well tolerated, establishing a recommended phase 2 dose (RP2D) of 400 mg twice daily (BID) [1] [2]. A concentration-dependent reduction in DNA-PKcs autophosphorylation was observed in peripheral blood mononuclear cells [1]. In a study combining Nedisertib with radiotherapy, 12 patients achieved stable disease [2].
3. Molecular Mechanism of Action
Nedisertib functions by competitively inhibiting the ATP-binding site of DNA-PKcs, thereby blocking the NHEJ pathway required for repairing radiation- and chemotherapy-induced DNA double-strand breaks [1] [2]. The ultimate fate of the cancer cell following Nedisertib exposure depends heavily on its p53 status. Upon treatment with DNA-damaging agents and Nedisertib, p53-proficient cells typically undergo cell cycle checkpoint arrest, senescence, or apoptosis. In contrast, p53-deficient cells are forced into death by mitotic catastrophe [1].
Additionally, Nedisertib has been shown to bind to the ATP-binding cassette transporter family G2 (ABCG2), which allows it to reverse certain mechanisms of multidrug resistance in cancer cells [1].
4. Structure-Activity Relationship (SAR)
Chemically, Nedisertib 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 within the DNA-PKcs pocket. The morpholine and quinazoline groups of Nedisertib fit snugly into the deepest hydrophobic pocket of the enzyme [1].
Furthermore, the chloro-fluorobenzene ring forms critical interactions with specific amino acid residues, including Met3729, Ser3731, Pro3735, Leu3751, and Ile3940. The pyridazine group fits into a distinct groove formed by Met3729, Trp3805, Thr3811, Asn3926, and Met3929, which significantly stabilizes the drug-target interaction and contributes to its high selectivity over other PIKK family members [1].
5. Current Limitations
Despite its high potency and selectivity, Nedisertib exhibits significant limitations when used as a standalone treatment. In Phase 1 clinical studies, Nedisertib monotherapy failed to elicit partial responses in patients with advanced solid tumors [1]. Preclinical data also confirm that the compound shows only modest growth inhibition on its own [1]. Its therapeutic utility is almost entirely dependent on its ability to act as a sensitizer; therefore, it must be administered concurrently with exogenous DNA-damaging agents (IR or cytotoxic chemotherapy) to achieve meaningful antitumor efficacy [1] [2].
6. Future Perspectives
Because Nedisertib lacks objective response as a monotherapy, its future clinical development is firmly directed toward combination regimens. Numerous Phase 1 and Phase 2 clinical trials are currently underway to evaluate its safety and efficacy in combination with radiotherapy and various chemotherapies [1]. For instance, a Phase Ib trial combining Nedisertib with capecitabine and radiotherapy for the treatment of rectal cancer has been completed, paving the way for further Phase II evaluations [2].
Moreover, the recent elucidation of the DNA-PKcs and Nedisertib complex structure via cryo-EM opens the door for structure-guided drug design. This structural insight could facilitate the development of next-generation DNA-PK inhibitors with optimized pharmacokinetic properties or the ability to induce synthetic lethality in specific genetically defined cancer subsets [1].
