LAL test and RPT for endotoxin detection of CPT-11/DSPE-mPEG2000 nanoformulation: What if traditional methods are not applicable?

Endotoxin can be measured mainly by two methods: the Rabbit Pyrogen Test (RPT) and Limulus Amebocyte Lysate (LAL) assay. We found that a chemotherapeutic drug nanoformulation composed of irinotecan hydrochloride and an amphiphilic molecule DSPE-mPEG2000 can interfere with the LAL. Furthermore, the RPT results indicated that at a relatively high dosage, the drug irinotecan hydrochloride can induce a hypothermia effect which forces us to reduce the dose. So it is necessary to develop new methods for the detection of endotoxin. Endotoxin detection is an important step in drug characterization. Herein we found that a chemotherapeutic drug nanoformulation composed of irinotecan hydrochloride (CPT-11) and an amphiphilic molecule DSPE-mPEG2000 can interfere with the limulus amebocyte lysate assay (LAL). Furthermore, the rabbit pyrogen test (RPT) results indicated that at a relatively high dosage, the drug irinotecan hydrochloride can induce a hypothermia effect which may render the RPT results ambiguous in determination of the safety of the drug formulation.Our findings demonstrate limitations of endotoxin detection in micellar drugs, and call for the necessity of developing reliable endotoxin detection methods that can overcome the interference of nanomaterials in order to better ensure the drug safety of patients in future pharmaceutical drug development.