Camptothecin (
CPT), a potent inhibitor of
topoisomerase I and HIF-1α, failed to demonstrate utility as an anti-
cancer agent in early clinical trial investigations, primarily due to limited clinical activity and significant toxicity attributable to unfavorable physicochemical properties (e.g. low plasma solubility, pH-labile
lactone ring).
NLG207 (formerly
CRLX101), a nanoparticle-
drug conjugate (NDC) of
CPT designed to optimize plasma pharmacokinetics and facilitate
drug delivery to
tumors, is included as part of combination treatment in two Phase II clinical trials ongoing at the National Cancer Institute (NCT02769962 and NCT03531827). To better understand the potential for
drug-drug interactions and to correlate
drug exposure to clinical outcomes and pharmacodynamic
biomarkers, a robust analytical method was developed to measure
CPT in human plasma. Two sample processing methods were developed to quantify both NDC-bound
CPT and free
CPT, primarily via alteration of pH conditions. A solid-phase extraction recovered >79 % of
CPT prior to quantitative analysis by ultra HPLC-MS/MS. Dynamic calibration ranges of 10 to 10,000 ng/mL and 1 to 1000 ng/mL for total and free
CPT, respectively were utilized to capture clinical ranges.
NLG207 NDCs demonstrated significant rates of
CPT release in human plasma at room temperature after 2 h but were shown to be stable at 4 °C for 24 h and through 4 freeze/thaw cycles. This assay was used to quantitate
CPT plasma concentrations in clinical samples to confirm clinical utility following
NLG207 treatment in subjects with advanced
prostate cancer.