Abstract 2800: Pharmacokinetics, bioavailability, and pharmacodynamics of oral triapine

Background: Locally advanced cervical cancer accounts for most deaths from disease. Standard of care includes treatment with cisplatin-based chemoradiation with a 70% response rate. The addition of intravenous (IV) triapine to chemoradiation has shown promising clinical activity in phase 1 and 2 studies but comes with a more intensive treatment regimen. An ongoing phase 1 trial has finished the escalation phase, and we report the pharmacokinetics (PK) and pharmacodynamics (PD) of oral (PO) triapine. Methods: This phase 1 study followed a 3+3 design for dose escalation of oral triapine, starting with initial dose of 100 mg five days a week for five weeks combined with external beam pelvic radiation and weekly IV cisplatin. PK was determined by LC-MS/MS, and PD included methemoglobin levels at 4 h post dose. Within patient PK variability after IV and PO dosing and PO bioavailability were calculated. Results: PK data were available for 10 patients at 100 (the MTD) and 150 mg. PO parameter values were Tmax 1.3 h, t1/2 1.4 h, CL/F 104 L/h, and Vz/F 214 L. There was no discernable difference between triapine exposure at 100 vs. 150 mg PO (Cmax 520 (2.5) vs. 344 (1.9) µg/L; AUC 1209 (2.53) vs. 1034 (1.41) µg/L•h), and between patient variability at each dose level was substantial. The correlation of PO Vz/F vs Cl/F was high at R2=0.86, suggesting that the apparent clearance and volume variability is primarily due to variability in the oral bioavailability F. PO within patient variability of Cmax and AUC was also large at 43% and 55%. IV PK was less variable with lower geometric standard deviations across all parameters, including within patients where variability of Cmax and AUC was modest at 10 and 12% coefficient of variation, respectively. Oral bioavailability was estimated at 66%. We found a non-significant trend of smoking almost doubling triapine oral clearance from 68 to 156 L/h (p=0.056). There was no apparent relationship between occurrence of DLT and either IV or PO triapine AUC. Methemoglobin levels directly correlated with triapine exposure expressed as AUC or Cmax. Conclusions: Triapine PK parameter values for PO and IV administration and PO bioavailability values observed in this trial were comparable to previous reports. Correlation of methemoglobin with exposure highlights the importance of optimizing triapine exposure. Additional data may support the exploration of a dose specific to current smokers. Citation Format: Jan H. Beumer, Sarah Behr, Ho