Dose-dependent bioavailability, absorption-rate limited elimination, and tissue distribution of the ATR inhibitor BAY-1895344 (elimusertib) in mice.

PURPOSE

Ataxia Telangiectasia and Rad3-related (ATR) is a pivotal component of the DNA damage response and repair pathways that is activated in responses to cytotoxic cancer treatments. Several ATR inhibitors (ATRi) are in development that block the ATR mediated DNA repair and enhance the damage associated with cytotoxic therapy. BAY-1895344 (elimusertib) is an orally available ATRi with preclinical efficacy that is in clinical development. Little is known about the pharmacokinetics (PK) which is of interest, because tissue exposure and ATR inhibition may relate to toxicities or responses.

METHODS

To evaluate BAY-1895344 PK, a sensitive LC-MS/MS method was utilized for quantitation in mouse plasma and tissues. PK studies in mice were first conducted to determine dose linearity. In vivo metabolites were identified and analyzed semi-quantitatively. A compartmental PK model was developed to describe PK behavior. An extensive PK study was then conducted in tumor-bearing mice to quantitate tissue distribution for relevant tissues.

RESULTS

Dose linearity was observed from 1 to 10 mg/kg PO, while at 40 mg/kg PO bioavailability increased approximately fourfold due to saturation of first-pass metabolism, as suggested by metabolite analyses and a developed compartmental model. Longer half-lives in PO treated mice compared to IV treated mice indicated absorption-rate limited elimination. Tissue distribution varied but showed extensive distribution to bone marrow, brain, and spinal cord.

CONCLUSIONS

Complex PK behavior was limited to absorption processes which may not be recapitulated clinically. Tissue partition coefficients may be used to contrast ATR inhibitors with respect to their efficacy and toxicity.