Ahmanson Translational Imaging Division, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
J Nucl Med. 2012 Feb;53(2):275-80. doi: 10.2967/jnumed.111.090407.
The ability to measure tumor determinants of response to nucleoside analog (NA) chemotherapy agents such as gemcitabine and related compounds could significantly affect the management of several types of cancer. Previously we showed that the accumulation in tumors of the new PET tracer 1-(2'-deoxy-2'-(18)F-fluoro-β-d-arabinofuranosyl)cytosine ((18)F-FAC) is predictive of responses to gemcitabine. (18)F-FAC retention in cells requires deoxycytidine kinase (dCK), a rate-limiting enzyme in the deoxyribonucleoside salvage metabolism and in gemcitabine conversion from an inactive prodrug to a cytotoxic compound. The objectives of the current study were to determine whether (18)F-FAC tumor uptake is also influenced by cytidine deaminase (CDA), a determinant of resistance to gemcitabine; to develop a new PET assay using (18)F-FAC and the related probe 1-(2'-deoxy-2'-(18)F-fluoro-β-l-arabinofuranosyl)-5-methylcytosine (l-(18)F-FMAC) to profile tumor lesions for both dCK and CDA enzymatic activities; and to determine whether this PET assay can identify the most effective NA chemotherapy against tumors with differential expression of dCK and CDA.
Isogenic murine leukemic cell lines with defined dCK and CDA activities were generated by retroviral transduction. A cell viability assay was used to determine the sensitivity of the isogenic cell lines to the dCK-dependent NA prodrugs gemcitabine and clofarabine. In vitro enzymatic and cell-based tracer uptake assays and in vivo PET with (18)F-FAC and l-(18)F-FMAC were used to predict tumor responses to gemcitabine and clofarabine.
dCK and CDA activities measured by kinase and tracer uptake assays correlated with the sensitivity of isogenic cell lines to gemcitabine and clofarabine. Coexpression of CDA decreased the sensitivity of dCK-positive cells to gemcitabine treatment in vitro by 15-fold but did not affect responses to clofarabine. Coexpression of CDA decreased (18)F-FAC but not l-(18)F-FMAC, phosphorylation, and uptake by dCK-positive cells. (18)F-FAC and l-(18)F-FMAC PET estimates of the enzymatic activities of dCK and CDA in tumor implants in mice were predictive of responses to gemcitabine and clofarabine treatment in vivo.
These findings support the utility of PET-based phenotyping of tumor nucleoside metabolism for guiding the selection of NA prodrugs.
确定氟代胞嘧啶脱氨酶 (CDA) 是否也会影响氟代胞苷 ((18)F-FAC) 肿瘤摄取，CDA 是吉西他滨耐药的决定因素；开发一种使用 (18)F-FAC 和相关探针 1-(2'-脱氧-2'-(18)F-氟-β-L-阿拉伯呋喃基)-5-甲基胞嘧啶 (l-(18)F-FMAC) 的新 PET 测定法，以对肿瘤病变进行 dCK 和 CDA 酶活性分析；并确定该 PET 测定法是否可以识别针对具有不同 dCK 和 CDA 表达的肿瘤的最有效的 NA 化疗药物。
通过逆转录病毒转导生成具有明确 dCK 和 CDA 活性的同基因鼠白血病细胞系。细胞活力测定法用于确定同基因细胞系对 dCK 依赖性 NA 前药吉西他滨和克拉屈滨的敏感性。体外酶和细胞内示踪剂摄取测定法以及体内 (18)F-FAC 和 l-(18)F-FMAC 的 PET 用于预测吉西他滨和克拉屈滨对肿瘤的反应。
激酶和示踪剂摄取测定法测量的 dCK 和 CDA 活性与同基因细胞系对吉西他滨和克拉屈滨的敏感性相关。CDA 的共表达使 dCK 阳性细胞对吉西他滨处理的体外敏感性降低了 15 倍，但不影响对克拉屈滨的反应。CDA 的共表达降低了 dCK 阳性细胞的 (18)F-FAC 但不降低 l-(18)F-FMAC、磷酸化和摄取。在小鼠肿瘤植入物中，(18)F-FAC 和 l-(18)F-FMAC PET 对 dCK 和 CDA 酶活性的估计可预测体内吉西他滨和克拉屈滨治疗的反应。
这些发现支持基于 PET 的肿瘤核苷代谢表型分析用于指导 NA 前药选择的实用性。
