Cisplatin Pharmacodynamics Following Endobronchial Ultrasound-Guided Transbronchial Needle Injection into Lung Tumors

Intratumoral delivery of cisplatin by endobronchial ultrasound-guided transbronchial needle injection (EBUS-TBNI) has recently emerged as a therapy for treating peribronchial lung cancers. It remains unclear, however, where best to inject drug into a tumor, and at how many sites, so current cisplatin delivery strategies remain empirical. Motivated by the need to put EBUS-TBNI treatment of lung cancer on a more objective footing, we developed a computational model of cisplatin pharmacodynamics following EBUS-TBNI. The model accounts for diffusion of cisplatin within and between the intracellular and extracellular spaces of a tumor, as well as clearance of cisplatin from the tumor via the vasculature and clearance from the body via the kidneys. We matched the tumor model geometry to that determined from a thoracic CT scan of a patient with lung cancer. The model was calibrated by fitting its predictions of cisplatin blood concentration versus time to measurements made up to 2 hrs following EBUS-TBNI of cisplatin into the patient's lung tumor. This gave a value for the systemic volume of distribution for cisplatin of 12.2 L and a rate constant of clearance from the tumor into the systemic compartment of 1.46 × 10^-4 s^-1. Our model indicates that the minimal dose required to kill all cancerous cells in a lung tumor can be reduced by roughly 3 orders of magnitude if the cisplatin is apportioned between 5 optimally spaced locations throughout the tumor rather than given as a single bolus to the tumor center. Our findings suggest that optimizing the number and location of EBUS-TBNI sites has a dramatic effect on the dose of cisplatin required for efficacious treatment of lung cancer.