A Pilot Study of Tc-94m Sestamibi PET MDR Imaging

Background: * A pilot study of PET imaging with Tc-94m sestamibi to assess activity of the multidrug transporter, MDR-1 (Multi Drug Resistance Protein 1)/P-glycoprotein, an ATP (adenosine 5'-triphosphate)-binding cassette protein that transports drug out of the cell, thereby reducing intracellular drug accumulation. * Tariquidar is a safe, nontoxic antagonist of P-glycoprotein. Previous studies demonstrated that tariquidar increased retention of the radioimaging agent, Tc99 sestamibi in normal liver and in a subset of tumors. These studies were limited by the semiquantitative nature of total body imaging by conventional radionuclide scintigraphy * In collaboration with the Clinical Center Nuclear Medicine Department, a PET imaging agent has been developed, Tc-94m sestamibi, and the FDA (Food and Drug Administration) has granted approval for its use in humans. Objectives: -To evaluate the feasibility of Tc-94m sestamibi as a PET imaging agent, which should allow greater resolution and quantitation and thereby make possible direct quantitative comparisons of tumor uptake before and after treatment with a P-glycoprotein antagonist. Eligibility: * Patients over 18 years of age, who are eligible for, or have completed enrollment in an active NCI (National Cancer Institute) protocol for treatment of cancer. * Negative pregnancy test within 24 hrs of Tc-94m injection. * An index lesion greater than 2cm will be required to optimize the PET images. * Prior treatment with a P-glycoprotein antagonist is allowed. Design: * Designed as a feasibility study. Patients meeting the eligibility criteria and signing informed consent will undergo a PET sestamibi imaging scan in the Department of Nuclear Medicine. Seventy-two hours later, a dose of tariquidar will be administered before a repeat imaging study. * Blood will be obtained for analysis of the pharmacokinetics of Tc-94m sestamibi, and for isolation of peripheral blood mononuclear cells to assay P-glycoprotein inhibition in circulating CD56+ cells. These assessments are needed to confirm the impact of tariquidar on P-glycoprotein in normal cells - for example, those involved in drug excretion and in circulating mononuclear cells. These results will then be used to inform the findings in the PET imaging study. * Fifteen patients will be enrolled and pairwise comparisons will be made between the sestamibi residence times in tumor, normal liver, kidney, and heart. All comparisons are noted to be exploratory.