Radiosensitisation by olaparib through focused ultrasound delivery in a diffuse midline glioma model

BACKGROUND AND PURPOSE

Diffuse midline glioma H3K27-altered (DMG) is an aggressive, inoperable, predominantly paediatric brain tumour. Treatment strategies are limited, resulting in a median survival of only 11 months. Currently, radiotherapy (RT), often combined with temozolomide, is considered the standard of care but remains palliative, highlighting the urgency for new therapies. Radiosensitisation by olaparib, an inhibitor of PARP1 and subsequently PAR-synthesis, is a promising treatment option. We assessed whether PARP1 inhibition enhances radiosensitivity in vitro and in vivo following focused ultrasound mediated blood-brain barrier opening (FUS-BBBO).

METHODS

Effects of PARP1 inhibition were evaluated in vitro using viability, clonogenic, and neurosphere assays. In vivo olaparib extravasation and pharmacokinetic profiling following FUS-BBBO was measured by LC-MS/MS. Survival benefit of FUS-BBBO combined with olaparib and RT was assessed using a patient-derived xenograft (PDX) DMG mouse model.

RESULTS

Treatment with olaparib in combination with radiation delayed tumour cell proliferation in vitro through the reduction of PAR. Prolonged exposure of low olaparib concentration was more efficient in delaying cell growth than short exposure of high concentration. FUS-BBBO increased olaparib bioavailability in the pons by 5.36-fold without observable adverse effects. A Cmax of 54.09 μM in blood and 1.39 μM in the pontine region was achieved following administration of 100 mg/kg olaparib. Although RT combined with FUS-BBBO mediated olaparib extravasation delayed local tumour growth, survival benefits were not observed in an in vivo DMG PDX model.

CONCLUSIONS

Olaparib effectively radiosensitises DMG cells in vitro and reduces primary tumour growth in vivo when combined with RT. Further studies are needed to investigate the therapeutic benefit of olaparib in suitable preclinical PDX models.

A real or apparent decrease in glomerular filtration rate in patients using olaparib?

Purpose

Olaparib is a poly (ADP-ribose) polymerase (PARP) inhibitor indicated for ovarian and metastatic breast cancer. Increased serum creatinine levels have been observed in patients taking olaparib, but the underlying mechanism is unknown. This study aimed to investigate if patients receiving olaparib have increased creatinine levels during olaparib treatment and whether this actually relates to a declined glomerular filtration rate (GFR).

Methods

We retrospectively identified patients using olaparib at the Netherlands Cancer Institute – Antoni van Leeuwenhoek (NKI-AVL) from 2012 until 2020. Patients with at least one plasma or serum sample available at baseline/off treatment and during olaparib treatment were included. Cystatin C levels were measured, creatinine levels were available and renal function was determined by calculating the estimated glomerular filtration rate (eGFR) using the Creatinine Equation (CKD-EPI 2009) and the Cystatin C Equation (CKD-EPI 2012).

Results

In total, 66 patients were included. Olaparib treatment was associated with a 14% increase in median creatinine from 72 (inter quartile range (IQR): 22) μmol/L before/off treatment to 82 (IQR: 20) μmol/L during treatment (p < 0.001) and a 13% decrease in median creatinine-derived eGFR from 86 (IQR: 26) mL/min/1.73 m² before/off treatment to 75 (IQR: 29) mL/min/1.73 m² during treatment (p < 0.001). Olaparib treatment had no significant effect on median cystatin C levels (p = 0.520) and the median cystatin C–derived eGFR (p = 0.918).

Conclusions

This study demonstrates that olaparib likely causes inhibition of renal transporters leading to a reversible and dose-dependent increase in creatinine and does not affect GFR, since the median cystatin C–derived eGFR was comparable before/off treatment and during treatment of olaparib. Using the creatinine-derived eGFR can give an underestimation of GFR in patients taking olaparib. Therefore, an alternative renal marker such as cystatin C should be used to accurately calculate eGFR in patients taking olaparib.

Development and validation of an integrated LC-MS/MS assay for therapeutic drug monitoring of five PARP-inhibitors

An liquid chromatography-mass spectrometry (LC-MS/MS) assay was developed for the combined analysis of the five poly (ADP-ribose) polymerase (PARP) inhibitors niraparib, olaparib, rucaparib talazoparib and veliparib. A simple and fast sample pre-treatment method was used by protein precipitating of plasma samples with acetonitrile and dilution of the supernatant with formic acid (0.1% v/v in water). This was followed by chromatographic separation on a reversed-phase UPLC BEH C18 column and detection with a triple quadrupole mass spectrometer operating in the positive mode. A simplified validation procedure specifically designed for bioanalytical methods for clinical therapeutic drug monitoring (TDM) purposes, was applied. This included assessment of the calibration model, accuracy and precision, lower limit of quantification (LLOQ), specificity and selectivity, carry-over and stability. The validated range was 30-3000 ng/mL for niraparib, 100-10,000 ng/mL for olaparib, 50-5000 ng/mL for rucaparib, 0.5-50 ng/mL for talazoparib and 50-5000 for veliparib. All results were within the criteria of the US Food and Drug Administration (FDA) guidance and European Medicines Agency (EMA) guidelines on method validation. The assay has been successfully implemented in our laboratory.