Acquisition of resistance to antitumor alkylating agent ACNU: a possible target of positron emission tomography monitoring

Preclinical Applications of 3'-Deoxy-3'-[18F]Fluorothymidine in Oncology - A Systematic Review

The positron emission tomography (PET) tracer 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) has been proposed to measure cell proliferation non-invasively in vivo. Hence, it should provide valuable information for response assessment to tumor therapies. To date, [18F]FLT uptake has found limited use as a response biomarker in clinical trials in part because a better understanding is needed of the determinants of [18F]FLT uptake and therapy-induced changes of its retention in the tumor. In this systematic review of preclinical [18F]FLT studies, comprising 174 reports, we identify the factors governing [18F]FLT uptake in tumors, among which thymidine kinase 1 plays a primary role. The majority of publications (83 %) report that decreased [18F]FLT uptake reflects the effects of anticancer therapies. 144 times [18F]FLT uptake was related to changes in proliferation as determined by ex vivo analyses. Of these approaches, 77 % describe a positive relation, implying a good concordance of tracer accumulation and tumor biology. These preclinical data indicate that [18F]FLT uptake holds promise as an imaging biomarker for response assessment in clinical studies. Understanding of the parameters which influence cellular [18F]FLT uptake and retention as well as the mechanism of changes induced by therapy is essential for successful implementation of this PET tracer. Hence, our systematic review provides the background for the use of [18F]FLT in future clinical studies.

Delivery of temozolomide to the tumor bed via biodegradable gel matrices in a novel model of intracranial glioma with resection

INTRODUCTION

We have completed in vivo safety and efficacy studies of the use of a novel drug delivery system, a gel matrix-temozolomide formulation that is injected intracranially into the post-resection cavity, as a candidate for glioma therapy.

METHODS

A rat intracranial resection model of C6-GFP intracranial glioma was used for safety and toxicity studies. Biodistribution studies were performed using gel matrix-gallocyanine formulations and were evaluated at various time intervals using real-time analysis of dye distribution. Additionally, the resection model was used to determine the efficacy of gel matrix-temozolomide as compared to blank gel matrix. A subcutaneous human xenograft glioma model was used to further assess the efficacy of gel matrix-temozolomide in reducing the overall tumor load.

RESULTS

Gel matrix-temozolomide exhibited minimal cytotoxicity toward normal brain tissue while displaying high levels of oncolytic activity toward glioma cells. In the intracranial glioma resection and subcutaneous glioma model, administration of gel matrix-temozolomide directly to the tumor bed was well tolerated and effective at reducing the tumor load. A significant reduction of tumor load was observed (P < 0.0001) in the 30% temozolomide group (approximately 95%) as compared to blank control. There was little morbidity and no mortality associated with gel matrix treatment.

CONCLUSIONS

Gel matrix-temozolomide appears to be safe and effective when used in vivo to treat intracranial glioma and warrants further development as a potential adjuvant therapy.

Feasibility studies of 4'-[methyl-(11)C]thiothymidine as a tumor proliferation imaging agent in mice

This study reports on the radiosynthesis and feasibility studies of 4'-[methyl-(11)C]thiothymidine ([methyl-(11)C]S-dThd) as a tumor proliferation imaging agent. [Methyl-(11)C]S-dThd was synthesized by rapid methylation of corresponding 5-trimethylstannyl- or 5-tributylstannyl-precursor via a palladium-promoted Stille cross-coupling reaction with [(11)C]methyl iodide. The decay-corrected radiochemical yields of [methyl-(11)C]S-dThd synthesized by the corresponding 5-trimethylstannyl-precursor and 5-tributylstannyl-precursor based on [(11)C]CO(2) were 18.9% and 14.5%, respectively. The radiochemical purity of [methyl-(11)C]S-dThd was always greater than 99%. The specific activities of [methyl-(11)C]S-dThd synthesized by the corresponding 5-trimethylstannyl-precursor and 5-tributylstannyl-precursor were 47 GBq/mumol and 121 GBq/mumol, respectively, at the end of the synthesis. The total synthesis time was 30 min after the end of bombardment. The comparison between in vivo distribution of [methyl-(14)C]S-dThd and that of [methyl-(3)H]FLT showed that tracer uptake was comparable in nonproliferating tissues. In contrast, [methyl-(14)C]S-dThd showed significantly higher uptake in proliferating tissues than did [methyl-(3)H]FLT. [Methyl-(11)C]S-dThd uptake levels in five different tumor tissues were well correlated with the DNA synthesis levels determined by [2-(14)C]thymidine DNA incorporation. At 30 min after injection, plasma analysis found 95% of the activity in unmetabolized form. The microPET imaging of the C6 glioma xenograft showed significantly high uptake in the tumor and urinary bladder, followed by the intestine and marrow. Our results demonstrated that the tumor uptake of [methyl-(11)C]S-dThd was higher than that of [methyl-(3)H]FLT and was well correlated with the DNA synthesis level. Consequently, 4'-[methyl-(11)C]thiothymidine has promise for the imaging of tumor cell proliferation by positron emission tomography.