First-in-Human Study of the Ataxia Telangiectasia and Rad3-Related (ATR) Inhibitor Tuvusertib (M1774) as Monotherapy in Patients with Solid Tumors

PURPOSE

Tuvusertib (M1774) is a potent, selective, orally administered ataxia telangiectasia and Rad3-related (ATR) protein kinase inhibitor. This first-in-human study (NCT04170153) evaluated safety, tolerability, maximum tolerated dose (MTD), recommended dose for expansion (RDE), pharmacokinetics (PK), pharmacodynamics (PD), and preliminary efficacy of tuvusertib monotherapy.

PATIENTS AND METHODS

Ascending tuvusertib doses were evaluated in 55 patients with metastatic or locally advanced unresectable solid tumors. A safety monitoring committee determined dose escalation based on PK, PD, and safety data guided by a Bayesian 2-parameter logistic regression model. Molecular responses (MR) were assessed in circulating tumor DNA samples.

RESULTS

Most common grade ≥3 treatment-emergent adverse events were anemia (36%), neutropenia, and lymphopenia (both 7%). Eleven patients experienced dose-limiting toxicities, most commonly grade 2 (n = 2) or 3 (n = 8) anemia. No persistent effects on blood immune cell populations were observed. The RDE was 180 mg tuvusertib QD (once daily), 2 weeks on/1 week off treatment, which was better tolerated than the MTD (180 mg QD continuously). Tuvusertib median time to peak plasma concentration ranged from 0.5 to 3.5 hours and mean elimination half-life from 1.2 to 5.6 hours. Exposure-related PD analysis suggested maximum target engagement at ≥130 mg tuvusertib QD. Tuvusertib induced frequent MRs in the predicted efficacious dose range; MRs were enriched in patients with radiological disease stabilization, and complete MRs were detected for mutations in ARID1A, ATRX, and DAXX. One patient with platinum- and PARP inhibitor-resistant BRCA wild-type ovarian cancer achieved an unconfirmed RECIST v1.1 partial response.

CONCLUSIONS

Tuvusertib demonstrated manageable safety and exposure-related target engagement. Further clinical evaluation of tuvusertib is ongoing.

Development of a Practical Nomogram for Personalized Anemia Management in Patients Treated with Ataxia Telangiectasia and Rad3-related Inhibitor Camonsertib

PURPOSE

Camonsertib is a highly selective and potent inhibitor of ataxia telangiectasia and Rad3-related (ATR) kinase. Dose-dependent anemia is a class-related on-target adverse event often requiring dose modifications. Individual patient risk factors for the development of significant anemia complicate the selection of a "one-size-fits-all" ATR inhibitor (ATRi) dose and schedule, possibly leading to suboptimal therapeutic doses in patients at low risk of anemia. We evaluated whether early predictors of anemia could be identified to ultimately inform a personalized dose-modification approach.

PATIENTS AND METHODS

On the basis of preclinical observations and a mechanistic understanding of ATRi-related anemia, we identified several potential factors to explore in a multivariable linear regression modeling tool for predicting hemoglobin level ahead of day 22 (cycle 2) of treatment.

RESULTS

In patients treated with camonsertib monotherapy (NCT04497116), we observed that hemoglobin decline is consistently preceded by reticulocytopenia, and dose- and exposure-dependent decreases in monocytes. We developed a nomogram incorporating baseline and day 8 hemoglobin and reticulocyte values that predicted the day 22 hemoglobin values of patients with clinically valuable concordance (within 7.5% of observations) 80% of the time in a cross-validation performance test of data from 60 patients.

CONCLUSIONS

The prediction of future hemoglobin decrease, after a week of treatment, may enable a personalized, early dose modification to prevent development of clinically significant anemia and resulting unscheduled dose holds or transfusions.

Durable responses to ATR inhibition with ceralasertib in tumors with genomic defects and high inflammation

BACKGROUNDPhase 1 study of ATRinhibition alone or with radiation therapy (PATRIOT) was a first-in-human phase I study of the oral ATR (ataxia telangiectasia and Rad3-related) inhibitor ceralasertib (AZD6738) in advanced solid tumors.METHODSThe primary objective was safety. Secondary objectives included assessment of antitumor responses and pharmacokinetic (PK) and pharmacodynamic (PD) studies. Sixty-seven patients received 20-240 mg ceralasertib BD continuously or intermittently (14 of a 28-day cycle).RESULTSIntermittent dosing was better tolerated than continuous, which was associated with dose-limiting hematological toxicity. The recommended phase 2 dose of ceralasertib was 160 mg twice daily for 2 weeks in a 4-weekly cycle. Modulation of target and increased DNA damage were identified in tumor and surrogate PD. There were 5 (8%) confirmed partial responses (PRs) (40-240 mg BD), 34 (52%) stable disease (SD), including 1 unconfirmed PR, and 27 (41%) progressive disease. Durable responses were seen in tumors with loss of AT-rich interactive domain-containing protein 1A (ARID1A) and DNA damage-response defects. Treatment-modulated tumor and systemic immune markers and responding tumors were more immune inflamed than nonresponding.CONCLUSIONCeralasertib monotherapy was tolerated at 160 mg BD intermittently and associated with antitumor activity.TRIAL REGISTRATIONClinicaltrials.gov: NCT02223923, EudraCT: 2013-003994-84.FUNDINGCancer Research UK, AstraZeneca, UK Department of Health (National Institute for Health Research), Rosetrees Trust, Experimental Cancer Medicine Centre.

The schedule of ATR inhibitor AZD6738 can potentiate or abolish antitumor immune responses to radiotherapy

Inhibitors of the DNA damage signaling kinase ATR increase tumor cell killing by chemotherapies that target DNA replication forks but also kill rapidly proliferating immune cells including activated T cells. Nevertheless, ATR inhibitor (ATRi) and radiotherapy (RT) can be combined to generate CD8+ T cell-dependent antitumor responses in mouse models. To determine the optimal schedule of ATRi and RT, we determined the impact of short-course versus prolonged daily treatment with AZD6738 (ATRi) on responses to RT (days 1-2). Short-course ATRi (days 1-3) plus RT caused expansion of tumor antigen-specific, effector CD8+ T cells in the tumor-draining lymph node (DLN) at 1 week after RT. This was preceded by acute decreases in proliferating tumor-infiltrating and peripheral T cells and a rapid proliferative rebound after ATRi cessation, increased inflammatory signaling (IFN-β, chemokines, particularly CXCL10) in tumors, and an accumulation of inflammatory cells in the DLN. In contrast, prolonged ATRi (days 1-9) prevented the expansion of tumor antigen-specific, effector CD8+ T cells in the DLN, and entirely abolished the therapeutic benefit of short-course ATRi with RT and anti-PD-L1. Our data argue that ATRi cessation is essential to allow CD8+ T cell responses to both RT and immune checkpoint inhibitors.

Dose-dependent bioavailability and tissue distribution of the ATR inhibitor AZD6738 (ceralasertib) in mice

PURPOSE

Ataxia telangiectasia and Rad3-related (ATR) initiates and regulates cellular responses to DNA damage, such as those caused by cancer treatments. Several ATR inhibitors (ATRi) are in clinical development including AZD6738. Therapeutic indices among ATRi may differ as a result of varying potencies and concentrations at both tumor and off-target sites. Additionally, AZD6738 contributes to anti-tumor immune responses necessitating evaluation of exposure at immunological sites.

METHODS

Using mouse models and a highly sensitive LC-MS/MS assay, the pharmacokinetics of AZD6738 were studied, including dose linearity, bioavailability, metabolism, and tissue distribution in tumor-bearing mice.

RESULTS

Initial studies identified dose-dependent bioavailability, with greater than proportional increases in exposure as dose increased resulting in a ~ twofold increase in bioavailability between the lowest and highest investigated doses. These behaviors were successfully captured with a compartmental PK model. Analysis of metabolite PK revealed decreasing metabolic ratios with increasing dose, indicative of saturable first-pass metabolism. Further analysis revealed that intestinal and gut metabolism contribute to metabolism and these saturable mechanisms. Studies of tumor and tissue distribution found rapid and extensive drug distribution to most tissues except brain and spinal cord.

CONCLUSION

The complex non-linear behavior of AZD6738 PK in mice was due to pre-systemic saturation and which appears to be recapitulated clinically at low doses. PK reported here will allow future correlation of tissue related toxicities with drug exposure as well as exposure with immunological responses. These results can also be compared with those from similar studies of other ATRi to contrast drug exposure with responses.