The focus of our section's research program is to develop therapeutic strategies aimed at overcoming drug resistance in cancer. Our research has been dedicated to the translation of drug resistance reversal strategies to the clinic. The design of our clinical trials has been enhanced by laboratory support that has allowed us to analyze clinical samples and interpret the clinical trial findings. Our clinical trials involve studies of inhibition of resistance to conventional agents such as that mediated by P-glycoprotein, and studies of novel agents such as DMS612 and GRN1005, intended to directly improve treatment of cancer. A number of clinical trials evaluated inhibition of P-glycoprotein, an ABC transporter mediating resistance through outward transport of anticancer agents. In trials carried out here and across the globe, there was disappointment in this therapeutic strategy of drug resistance reversal, ie no benefit from adding an inhibitor to reverse drug resistance. Nonetheless, continued effort in the study of drug uptake is warranted -- few if any studies on a national or international level actually query drug uptake in cancer. To that end we are collaborating with Peter Choyke and Karen Kurdziel to evaluate F18-labeled paclitaxel (FPAC), which is then evaluated by PET imaging. This, in addition to the sestamibi study described below constitute two studies aimed at evaluating drug accumulation in tumors, actually an understudied mechanism of drug resistance. The project can be viewed as high risk with potentially high gain for multiple tumor types and thus very appropriate for the NCI intramural program. We completed and published two studies with third generation inhibitors tariquidar (XR9576) and CBT-1. In both studies we examined Pgp-mediated drug efflux was observed in circulating CD56+ cells, inhibition of rhodamine efflux observed for both agents. 99mTc-sestamibi imaging was employed as a surrogate for altered drug accumulation in normal and tumor tissues. Although the 99mTc-sestamibi studies provided proof-of-concept showing increased radionuclide accumulation in normal tissue, particularly in the liver, tumor uptake was much less prevalent and often did not change with the addition of the Pgp inhibitor. The 99mTc studies are poorly quantitative because they are planar images and background often overwhelms differences. The Clinical Center PET department developed a method to label sestamibi with 94mTc for positron emission imaging, promising a more quantitative imaging agent. Our clinical trial testing this imaging agent is open but was on hold much of the year due to lack of drug. It is now reopened. It is our hope that the quantitative PET imaging will allow us to better answer the question of how much impact tariquidar can have on patient tumors. The question of why sestamibi uptake fails in many patient tumors whether or not tariquidar is present is an important one and suggests that drug uptake, independent of a Pgp efflux mechanism, may be an important new area for study. In addition to the PET-sestamibi trial, we have initiated collaborations with Dr. Robert Innis, Dr. Pete Choyke, and Dr. Karen Kurdziel aimed at evaluating drug accumulation using PET agents 11C-N-desmethyl-loperamide and 18F-paclitaxel (FPAC). These PET studies offer the opportunity to move the field forward in a significant way;we will accrue our first patient to the FPAC study this month.These studies offer the opportunity to ask the more general question - to assess interpatient variation in drug uptake in tumor tissue. The assumption among treating physicians is that patients have uniform anticancer drug uptake in tumors. This question has never been systematically studied. It is our hope that radiolabeled imaging studies will begin to assess this question. Also important is the question of CNS uptake of anticancer agents. This work is directly relevant to our work with ABC transporters, since these comprise some of the blood-brain barrier obstacle to drug accumulation. In this we will join a collaboration already ongoing that includes Drs. Pat Steeg and JoAnne Zujewski. Studies of CNS metastases are very difficult to carry out. We have initiated a study with GRN1005, a conjugated taxane that promises to have CNS uptake due to conjugate with a peptide that binds the LRP receptor for transit across the blood brain barrier. The compound is being developed by Geron Pharmaceuticals. We have initiated a pilot surgery trial that will allow us to measure tubulin stabilization in CNS metastases removed at medically indicated surgical procedures after GRN1005 administration. We are also participating in the company?s Phase II efficacy study. This is a critical research area ? today, patients have increasing control of systemic disease and CNS relapse is emerging as a major medical problem. Patients who have conventional CNS radiation often do not have CNS disease completely eradicated and are also at risk for long-term cognitive problems, particularly with increasing control of CNS disease. This again is an area where the intramural program can contribute significantly - high-risk research with important long-term impact. Our laboratory also maintains an interest in studying drug resistance in other model systems. Several years ago, in collaboration with the NCI's Developmental Therapeutics Program, we identified a number of compounds with selectivity against renal cell caner, based on COMPARE analysis using cytotoxicity data in the 60 cell line panel. These compounds were evaluated in our laboratory and the renal selectivity confirmed. One new compound class, the dimethane sulfonates, has been continuously in preclinical development at DTP and one, NSC-281612, was approved for Phase I testing. The Phase I trial is now open at the NIH clinical center and accruing patients. The study is a multi-institutional Phase 1 trial with one site at University of Pittsburgh and the other at Hershey Medical Center. We have identified bone marrow toxicity as the chief cumulative toxicity, and have changed the schedule to mitigate this. Thrombocytopenia is the primary toxicity observed. One of the goals in the Phase I trial has been the development of biomarkers to evaluate the presence of DNA damage in tumor cells or surrogate tissues following treatment with the DMS compound. This has been successful to date in the laboratory of Dr. Yves Pommier, with Dr. Christophe Redon already documenting evidence of DNA damage in blood and hair follicle samples.
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