On the mutagenic action of adenine

The deamination of cytosine and adenine is mutagenic; the deamination of guanine is not. The deamination of cytosine leads to G = C → A = T point mutation and to G → A and C → T transition in the DNA molecule; the deamination of adenine leads to the opposite A → G and T → C transition. It is shown that adenine lack could be as mutagenic as adenine deamination and it is also shown schematically that adenine lack through defective adenine synthesis could give rise to a population of genetically abnormal cells incapable of any degree of differentiation, a state perhaps reminiscent of the most acute of leukaemias and the most anaplastic of cancers.     

A pharmacokinetic study of intra-CSF administered encapsulated cytarabine (DepoCyt®) for the treatment of neoplastic meningitis in patients with leukemia,lymphoma, or solid tumors as part of a phase III study

Summary Introduction Cytarabine liposome injection (DepoCyt^?), a sterile suspension of the antimetabolite cytarabine, encapsulated into multivesicular, lipid-based particles, has been developed to improve the treatment of neoplastic meningitis (NM) through sustained release of cytarabine. The objective of this study was to determine the pharmacokinetics (PK) of cytarabine after intrathecal administration of 50 mg encapsulated cytarabine (DepoCyt^?) in patients with neoplastic meningitis up to 336 h (14 days) after dosing. Methods This was an open-label study wherein two 50-mg doses of DepoCyt^? were administered 14 days apart via the intraventricular (IVT) route or by lumbar puncture (LP). Cerebrospinal fluid (CSF) samples were collected from eight adult patients at various times up to 14 days after each dose. Plasma samples were also collected within the same time period. CSF samples were analyzed for unencapsulated (free) and encapsulated cytarabine and the cytarabine metabolite, ara-U. Plasma samples were analyzed for free cytarabine and ara-U. The limit of detection was 0.003 μg/mL cytarabine and 0.016 μg/ml for ara-U. Results The concentration of free and encapsulated cytarabine in the ventricular and lumbar CSF ranged from 0.01 to 1500 μg/mL and were detectable up to 14 days post-dosing. Free cytarabine concentrations in plasma were only sporadically detectable. CSF and plasma concentrations of ara-U were low in all samples. Conclusions The administration of intrathecal encapsulation cytarabine prolongs sustained tumor exposure to cytotoxic concentrations of cytarabine (>0.02 μg/ml) with a slow continuous release of cytarabine from the DepoFoam^TM particles, so drug exposure is prolonged over time, resulting in lower peak cytarabine levels and a longer duration of exposure compared with standard cytarabine (Ara-C). This work was performed at Moffitt Cancer Center, Tampa, Florida and University of Florida College of Medicine, Gainesville, Florida. This work was presented in part at the 12th␣International Conference on Brain Tumor Research and Therapy at Keble College, Oxford, United Kingdom on September 20–23, 1997.     

组织特异性胞嘧啶脱氨酶和5-氟胞嘧啶热化疗对裸鼠结肠癌肝脏转移的影响

目的 探讨组织特异性胞嘧啶脱氨酶/5-氟胞嘧啶(CD/5-FC)系统热化疗对裸鼠结肠癌肝脏转移的影响.方法 将45只裸鼠按随机数字表法分为3组:对照组、非热疗组、热疗组,每组15只.门静脉注射法建立结肠癌肝脏转移动物模型,3组分别给予不同的治疗方法.采用χ2检验和单因素方差分析3组肝脏肿瘤转移率、转移数目;观察各组病理学变化、肿瘤细胞凋亡指数;荧光定量RT-PCR和Westernblot检测肿瘤组织中CD基因的表达情况.结果 对照组、非热疗组、热疗组肝脏平均转移癌结节数目和转移率分别为(4.6±1.3)、(2.2±1.0)、(0.5±0.8)个和100.0%、60.0%、13.3%,3组比较差异有统计学意义(F=25.898,χ2=5.208,19.548,5.168,P<0.05);肿瘤细胞凋亡指数平均为4.6%、9.9%和17.4%.热疗组可见大量细胞空泡变性、坏死、溶解现象,有较多的凋亡小体形成.3组均可以检测到CD基因的表达.结论 组织特异性CD/5-FC系统热化疗对转CD基因结肠癌LoVo细胞裸鼠肝脏转移有明显的抑制作用.     

Intrathecal chemotherapy for hematologic malignancies: drugs and toxicities

Intrathecal (IT) chemotherapy is an important component of the prophylaxis or treatment of hematologic malignancies in the central nervous system (CNS), especially in patients with acute lymphoblastic leukemia and aggressive lymphomas. Different regimens of IT chemotherapies have been formulated, often in conjunction with systemic high-dose chemotherapy leading to penetration of the drugs into the cerebrospinal fluid (CSF). The three commonest IT drugs are methotrexate, cytosine arabinoside (Ara-C), and corticosteroids. The CSF half-lives of methotrexate and Ara-C are much prolonged, a factor to be considered if these drugs are also administered systemically in high doses. Neurotoxicities attributed to IT chemotherapy have been reported, including spinal cord lesions, seizures, and encephalopathy. Spinal cord lesions, manifesting as tetraplegia, paraplegia, and cauda equina syndrome, are the commonest neurotoxicity. It is mostly related to combined IT methotrexate and Ara-C, or Ara-C as the sole IT agent when given at high doses or as a slow-release preparation. Cord lesions rarely recover and patients are left with motor deficits, bowel and urinary disabilities. Seizures and encephalopathy are reported in relatively fewer patients, with variable manifestations and prognosis. Knowledge of the pharmacokinetics, dosing schedules and potential toxicities of IT chemotherapeutic drugs is important in the design of CNS prophylaxis and treatment in hematologic malignancies.     

CD/5-FC系统对胰腺癌裸鼠移植瘤的抗血管形成作用的初步探讨

目的　探讨自杀基因系统对胰腺癌裸鼠移植瘤的微血管形成的抑制作用。方法　构建含大肠杆菌胞嘧啶脱氨酶 (cytosinedeaminase ,CD)基因的腺病毒穿梭载体 pAdTrack CMV CD ,与骨架载体pAdEasy 1在细菌内重组为 pAd CD ,经 2 93细胞包装、扩增 ,氯化铯密度梯度离心制备纯化高效的CD腺病毒液 ,建立胰腺癌裸鼠皮下移植瘤模型 ,观察CD基因的原位治疗及微血管形成抑制情况。结果　含CD基因腺病毒载体经酶切鉴定正确 ,包装纯化后 ,检测病毒滴度为 2× 10 11pfu/ml,体内实验显示CD基因原位转导对裸鼠胰腺癌移植瘤的微血管形成具有较明显的抑制效应。结论　腺病毒介导CD/ 5 FC自杀基因系统 ,不仅可以直接杀灭癌细胞 ,而且还可通过抑制移植瘤微血管的形成来抑制胰腺癌细胞的生长 ,可作为胰腺癌基因治疗的有效方法。     

Cytosine arabinoside in the treatment of acute myeloid leukemia: The role and place of high-dose regimens

Summary Cytosine arabinoside (AraC) is one of the most active drugs in the treatment of acute leukemias and is widely applied at all phases of therapy. In spite of extensive clinical and experimental investigations, its intracellular metabolism and especially its mechanism of action are still not fully elucidated. Controversy also continues about the most appropriate way and dose of administration; which differs by more than 100 fold in clinical studies ranging from low-dose, over standard and intermediate dose regimens, to high-dose protocols.The present review is focused on the role and place of high-dose AraC treatment in acute myeloid leukemia (AML). Based on available clinical and experimental data, the following conclusions can be drawn: Not considering possible but not yet demonstrated beneficial long-term effects, the incorporation of high-dose AraC intoinduction therapy has not resulted in an improvement of overall remission rate, with the possible exception of patients with slow initial cytoreduction after a first course of conventional treatment. Promising results, however, emerge from high-dose AraC-basedconsolidation protocols, which need confirmation in prospectively randomized comparative trials. Inrelapsed and refractory AML, higher than conventional doses undoubtedly enhance the efficacy of AraC salvage therapy. The question of whether the antileukemic activity of intermediate-dose regimens with 500–1,000 mg/m² AraC is equivalent to that of high-dose protocols applying 2,000–3,000 mg/m² AraC, however, remains open but may soon be answered by ongoing controlled clinical and pharmacologic investigations.     

Therapy of childhood acute myelogenous leukemias

Acute myelogenous leukemia (AML) accounts for approximately 20% of acute leukemias in children. Although AML is more resistant to chemotherapy than acute lymphoblastic leukemia (ALL), significant progress in improving outcome for AML patients has been achieved over the past 15 years. This can be attributed to intensification of chemotherapy, increased use of bone marrow transplantation, and improved supportive care. Thus 30–50% of children with AML achieve long-term event-free survival with current treatment strategies [61, 66, 85, 96]. This review gives an overview about the evolution of and rationale for current pediatric treatment protocols, with special emphasis on the German Berlin-Frankfurt-Münster (BFM) studies, and discusses new directions for the future. Received: 26 January 1996 / Accepted: 2 April 1996     

Cytosine arabinoside (Ara-C) plus alpha-interferon (αIFN) determine prolonged complete remissions in patients with aggressive non-Hodgkin's lymphoma partially responsive to first-line doxorubicin-containing regimens

Summary. Ten patients with aggressive NHL who failed to achieve a complete remission with first-line chemotherapy were treated with Ara-C and αIFN. Ara-C was administered subcutaneously at 100mg on day 1, 150mg on day 2 and 200 mg on days 3,4 and 5 of a 28 d cycle; αIFN was given at 3 million International Units three times a week and continued for 2 years in CR patients. Six CR were attained with a median duration of 36+ months. Toxicity was mild. A new approach to second-line therapy for aggressive NHL is proposed.     

CpG underrepresentation and the bacterial CpG-specific DNA methyltransferase M.MpeI

Cytosine methylation promotes deamination. In eukaryotes, CpG methylation is thought to account for CpG underrepresentation. Whether scarcity of CpGs in prokaryotic genomes is diagnostic for methylation is not clear. Here, we report that Mycoplasms tend to be CpG depleted and to harbor a family of constitutively expressed or phase variable CpG-specific DNA methyltransferases. The very CpG poor Mycoplasma penetrans and its constitutively active CpG-specific methyltransferase M.MpeI were chosen for further characterization. Genome-wide sequencing of bisulfite-converted DNA indicated that M.MpeI methylated CpG target sites both in vivo and in vitro in a locus-nonselective manner. A crystal structure of M.MpeI with DNA at 2.15-Å resolution showed that the substrate base was flipped and that its place in the DNA stack was taken by a glutamine residue. A phenylalanine residue was intercalated into the “weak” CpG step of the nonsubstrate strand, indicating mechanistic similarities in the recognition of the short CpG target sequence by prokaryotic and eukaryotic DNA methyltransferases.