Abstract: Nedisertib, also known as M3814 or Peposertib, is a highly potent, orally available, and selective inhibitor of the DNA-dependent protein kinase (DNA-PK). DNA-PK plays a pivotal role in the repair of DNA double-strand breaks (DSBs) through the non-homologous end joining (NHEJ) pathway. By inhibiting DNA-PK, Nedisertib prevents the repair of DSBs induced by ionizing radiation and DNA-damaging chemotherapeutic agents, thereby acting as a powerful radiosensitizer and chemosensitizer in solid tumors. Preclinical studies have demonstrated its synergistic antitumor effects when combined with various therapies, and it has shown the ability to reverse drug resistance. Currently, Nedisertib is undergoing Phase I and Ib clinical trials. While monotherapy has not yielded partial responses, its combination with radiotherapy, chemotherapy, and radioimmunotherapy presents a highly promising therapeutic strategy for advanced solid tumors.
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 of lesion [1]. In eukaryotic cells, DSBs are predominantly repaired through homologous recombination (HR) and non-homologous end joining (NHEJ) [1][2]. The DNA-dependent protein kinase (DNA-PK), composed of a catalytic subunit (DNA-PKcs) and a Ku70/Ku80 heterodimer, acts as a critical 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].
Nedisertib, also referred to in the literature as M3814 or Peposertib, is a new-generation, orally bioavailable, and highly selective small-molecule inhibitor of DNA-PK [1][2]. Discovered through drug library screening, it was developed to overcome the limitations of older DNA-PK inhibitors, which often lacked selectivity due to structural similarities with phosphatidylinositol 3-kinases (PI3Ks) [1][2]. Nedisertib is currently being evaluated in clinical trials for its potential to radiosensitize and chemosensitize solid tumors [1].
2. Pharmacological Activity
Nedisertib exhibits potent pharmacological activity both in vitro and in vivo. In cellulo, it enhances cellular radiosensitivity at submicromolar concentrations in a DNA-PKcs-dependent manner [1]. It also sensitizes cancer cells to various chemotherapeutic agents, including topoisomerase II inhibitors (daunorubicin, etoposide), microtubule polymerization inhibitors (paclitaxel), and calicheamicin [1]. Furthermore, Nedisertib has been shown to bind to the ATP-binding cassette transporter family G2 (ABCG2), effectively reversing multidrug resistance [1].
In preclinical in vivo models, oral or intragastrical administration of Nedisertib at doses ranging from 5 to 100 mg/kg significantly augmented tumor growth suppression when combined with radiation and chemotherapies such as paclitaxel, etoposide, pegylated liposomal daunorubicin (PLD), and 5-fluorouracil [1]. It also demonstrated synergistic antitumor effects in non-small cell lung cancer (NSCLC) models [2] and potentiated radioimmunotherapy using bintrafusp α (an inhibitor of TGFβ and PD-L1) [1].
Clinically, Phase 1 studies have shown that Nedisertib is well-tolerated, establishing a recommended Phase 2 dose (RP2D) of 400 mg twice daily (BID) [1][2]. In a Phase I study combining the drug with radiotherapy, 12 patients achieved stable disease [2]. A Phase Ib trial evaluating its combination with capecitabine and radiotherapy for rectal cancer has also been completed [2].
3. Molecular Mechanism of Action
The primary mechanism of action of Nedisertib is the potent and selective inhibition of DNA-PKcs. By blocking DNA-PK activity, Nedisertib effectively halts the NHEJ repair pathway, preventing cancer cells from repairing radiation- or chemotherapy-induced DSBs [1][2]. At the molecular level, Nedisertib inhibits the autophosphorylation of DNA-PKcs at the Ser2056 residue. This inhibition has been observed in cellulo at concentrations of 0.1–1 μM and has been confirmed in vivo through concentration-dependent reductions of DNA-PKcs autophosphorylation in the peripheral blood mononuclear cells of patients in clinical trials [1].
The ultimate cellular fate following Nedisertib treatment and ionizing radiation depends heavily on the tumor's p53 status. In p53-proficient cells, the accumulation of unrepaired DNA damage leads to cell cycle checkpoint activation, senescence, or apoptosis. Conversely, in p53-deficient cells, the treatment drives the cells into mitotic catastrophe, resulting in cell death [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]. It was discovered through extensive drug library screening and exhibits exceptional selectivity for DNA-PK; when tested against a panel of 284 lipid and protein kinases, only eight showed an IC50 value below 1 μM [1]. The IC50 for DNA-PKcs is highly potent, measured at 0.6 nM in the presence of 10 μM ATP and 20 nM in the presence of 1 mM ATP [1].
Recent structural analyses using cryo-electron microscopy (cryo-EM) have elucidated the precise binding interactions that confer this high affinity and selectivity. The morpholine and quinazoline groups of Nedisertib fit snugly into the deepest hydrophobic pocket of the kinase [1]. The chloro-fluorobenzene ring forms critical interactions with specific amino acid residues, including Met3729, Ser3731, Pro3735, Leu3751, and Ile3940. Additionally, the pyridazine group fits into a distinct groove formed by Met3729, Trp3805, Thr3811, Asn3926, and Met3929, which further stabilizes the drug-target complex [1]. This deep insertion and extensive contact with specific residues explain its superior selectivity compared to older generation inhibitors.
5. Current Limitations
Despite its high potency and excellent tolerability, Nedisertib has limitations as a standalone therapy. In Phase 1 clinical trials, Nedisertib monotherapy did not yield any partial responses in patients with advanced solid tumors [1]. Because its mechanism relies on inhibiting the repair of DNA damage, the drug exhibits modest growth inhibition on its own and is fundamentally dependent on the presence of exogenous DNA-damaging agents (such as ionizing radiation or cytotoxic chemotherapy) to exert a significant antitumor effect [1].
6. Future Perspectives
The future clinical utility of Nedisertib lies in rational combination therapies. Because it acts as a potent radiosensitizer and chemosensitizer, ongoing and future clinical trials are heavily focused on combining Nedisertib with radiotherapy and DNA-damaging chemotherapeutics [1][2]. The completion of Phase Ib trials combining it with capecitabine and radiotherapy for rectal cancer paves the way for Phase II evaluations [2]. Furthermore, preclinical evidence suggesting that Nedisertib can potentiate radioimmunotherapy (such as combinations with bintrafusp α) opens new avenues for integrating DNA repair inhibition with immune checkpoint blockade and tumor microenvironment modulation [1]. Exploiting the synthetic lethality observed in p53-deficient tumors also represents a promising biomarker-driven strategy for future clinical development [1].
