Tumor Kinase Inhibitor Concentrations Measured by PET

Rationale: Multiple agents targeting specific signaling proteins important for tumor growth and angiogenesis, including (tyrosine) kinase inhibitors and monoclonal antibodies, have been developed and have reached clinical approval. In general, however, these targeted agents induce a response only in a subgroup of cancer patients, while all are exposed to potential toxic therapies. Prior to treatment, it is unknown which patients will respond and why kinase inhibitors are only effective in some, but not all, patients. Clearly, there is a need for a non-invasive in vivo technique to identify those patients who may benefit from treatment with a specific drug.

Positron emission tomography (PET) is a non-invasive technique that enables quantitative measurements of molecular pathways and interactions with picomolar sensitivity and, as such, it has the potential to fulfill the need mentioned above. We expect that response to kinase inhibitors is dependent on achieving active drug levels in tumor tissue. Currently, intratumoral kinase inhibitor levels are being investigated at our institution (ICK study). However, these measurements require fresh tumor biopsies. We hypothesize that radiolabeled kinase inhibitor PET imaging can quantify concentrations of labeled drug in tumor lesions, thereby avoiding burdensome biopsies in the future.

Objective: The main objective of this study is to determine whether tumor concentrations of kinase inhibitors at pharmacological active doses can be predicted from PET studies using tracer amounts (microdosing) of corresponding radiolabeled kinase inhibitors. This objective includes the development and validation of pharmacokinetic models for radiolabeled kinase inhibitors as well as validation of the microdosing concept for kinase inhibitors.

The secondary objectives include exploration whether kinase inhibitor kinetics depend on perfusion (as measured by [15O]water PET) or size (as measured by diagnostic CT/MRI) of tumor lesions, to investigate the presence of a sink that accumulates kinase inhibitor, and to investigate (in)activation of key pathways targeted by the specific kinase inhibitor.

Study design: Single center, non-randomized, interventional proof of concept study.

Study population: Adult patients with advanced, biopsy accessible tumors for whom standard palliative treatment with the kinase inhibitor investigated in this study, i.e. erlotinib and sorafenib, is indicated.

Intervention: Patients will be treated with the kinase inhibitor according to standard treatment. [11C] kinase inhibitor PET (i.e. sorafenib and erlotinib in this study, with the aim to investigate others in future studies) and [15O]water PET will be performed before and after two weeks of treatment. Tumor biopsies will be performed before and during therapy.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Enrollment in this study will require two tumor biopsies, 2x [11C] kinase inhibitor PET, 2x [15O]water PET and arterial blood sampling. The biopsies may cause physical discomfort. During therapy, follow-up will include standard laboratory analysis as well as regular visits to the outpatient clinic. The radiation exposure is acceptable. Patients treated with a kinase inhibitor as standard therapy may benefit from disease regression or stabilization as it has proven clinical benefit in the patient population under investigation. The results of this kinase inhibitor PET imaging study will be strongly supportive for the development of non-invasive, personalized treatment strategies thereby avoiding 1) cumbersome tumor biopsies, 2) unwanted exposure to potentially toxic drugs and 3) costly therapy without clinical benefit.