In vitro pharmacokinetics and pharmacodynamics of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU)

The relationship between treatment efficacy and the pharmacokinetics (PK) and pharmacodynamics (PD) of anticancer drugs is poorly defined. 1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) is an alkylating agent used in the treatment of brain and other forms of cancer. It is postulated that BCNU kills cells by forming DNA interstrand cross-links. The present study was undertaken to characterize the PK and PD of BCNU in mouse L1210 cells. L1210 cells were exposed to BCNU (0-160 microM) and analyzed for intracellular BCNU concentrations, DNA interstrand cross-links, cell cycle phase, and cytotoxicity. The half-life of BCNU in cells was approximately 40 min. The maximum reduction of mitochondrial enzyme activity (maximum cell death) achieved within 24 hr after exposure to BCNU was concentration-dependent and could be described by a Hill equation. At lower concentrations, the area under the DNA interstrand cross-link-time curve linearly correlated with the maximum cell death and the area under the BCNU concentration-time curve. BCNU induced cell accumulation in the G(2)/M phase of the cell cycle, which continued even after apparent completion of cross-link repair. Loss of membrane permeability was minimal (approximately 2%) during the first 24 hr. Thereafter, cells died exponentially over the next 9 days, primarily by necrosis. In conclusion, while cytotoxicity was concentration-dependent, an indirect relationship was found among the time-course of BCNU concentrations, DNA interstrand cross-links, and cell death. Because of the disparity between the time-scale of PK and PD, focusing only on the early events may provide limited information about the process of anticancer drug-induced cell death.     

O~6-苄基鸟嘌呤增强 1,3-二 (2 -氯乙基)-亚硝基脲对人肝癌细胞及其移植瘤的抗肿瘤作用(英文)

应用噻唑蓝 (MTT)法检测 O6-苄基鸟嘌呤(O6- BG)与 1 ,3-二 (2 -氯乙基 ) -亚硝基脲 (BCNU)合用的细胞毒作用及透射电镜检测凋亡细胞的方法研究了 O6- BG对 O6-烷基鸟嘌呤 - DNA烷基转移酶(O6- AGT )阳性的人肝癌细胞 SMMC- 772 1对BCNU细胞毒作用敏感性的影响及其与 BCNU合用治疗移植瘤的协同效果 .结果显示 :1 .5- 6.0 mg· L-1的 O6- BG预先作用 2 h后 ,SMMC- 772 1细胞对 BCNU的敏感性明显增加 ;0 .75- 6.0 mg· L-1的 O6- BG可完全快速地抑制肿瘤细胞的 AGT活性并持续 1 2 h;ip 90 mg· kg-1的 O6- BG预处理 2 h后给予 2 5mg·kg-1的 BCNU治疗 ,可使动物 sc接种的人肝癌移植瘤生长延迟 38.6d,诱导肿瘤细胞凋亡 ,并且可明显抑制肿瘤组织的转移酶活性 .说明 O6- BG与 BCNU合用于 AGT阳性的肿瘤将具有明显的治疗效果     

Temozolomide in patients with advanced cancer: phase I and pharmacokinetic study

STUDY OBJECTIVE: To determine the maximum tolerated dose, dose-limiting toxicity, pharmacokinetics, and potential antitumor activity of temozolomide administered as a single dose every 28 days. DESIGN: Open label, phase I, dose-escalation trial. SETTING: University-affiliated cancer center. PATIENTS: Eleven patients aged 33-73 years with a documented solid tumor or lymphoma who failed therapy of proven efficacy for their disease or had a disease for which no conventional therapy was available. INTERVENTION: Temozolomide 500 mg/m2 was administered as a single oral dose every 28 days. Doses were escalated to 750 or 1000 mg/m2. No intrapatient dose escalation was allowed. At least two patients were enrolled at each dose level. Patients who did not have progressive disease and did not experience a dose-limiting toxicity, or experienced a dose-limiting toxicity but were eligible for dose reduction, were eligible to continue on the study. MEASUREMENTS AND MAIN RESULTS: Pharmacokinetic analysis was performed for temozolomide and its active metabolite, 5-(3-methyltriazeno)-imidazole-4-carboxamide (MTIC). Neutropenia and thrombocytopenia were dose limiting at 1000 mg/m2. Temozolomide was absorbed rapidly (mean time to maximum concentration 1.4 hrs) and eliminated, with average half-life and apparent oral systemic clearance values of 1.8 hours and 97 ml/minute/m2, respectively. Mean systemic exposure to MTIC was 3.7% of temozolomide. No objective responses were observed. The maximum tolerated dose of temozolomide was 750 mg/m2. CONCLUSION: Temozolomide 750 mg/m2 administered orally every 28 days was well tolerated. Alternate temozolomide dosing schedules such as continuous daily administration may enhance antitumor activity through sustained depletion of the DNA repair protein O6-alkylguanine DNA alkyltransferase.     

Biological properties of 5,11-dimethyl-6H-pyrido[3,2-b]carbazoles: a new class of potent antitumour drugs

Thirteen 5,11-dimethyl-6H-pyrido[3,2-b]carbazoles, structurally related to the antitumour drug ellipticine, were tested for their cytotoxicity against the L1210 murine leukaemia cell line and their antitumour activity against both leukaemias and solid tumours. Most of them showed an interesting antitumour activity against L1210 leukaemia, 4-hydroxy-9-chloro-2,3, 5,11-tetramethyl-6H-pyrido[3,2-b]carbazole displaying a high antitumour activity against L1210 and P388 leukaemias, B16 melanoma and M5076 sarcoma. Despite promising cytotoxic activity, 4-ethoxy-5,11-dimethyl-6H-pyrido-[3,2-b]carbazole had no antitumour activity. The ability of four drugs to induce strand breaks in DNA was studied using the single cell gel electrophoresis assay (comet assay). Most of the molecules induced DNA breaks that were totally or partially repaired after 1 h. The effects of these compounds on the L1210 cell cycle were tested as well as their abilities to induce apoptosis in these cells. Three of them induced a G2/M blockade, without any obvious evidence of apoptosis. The other compound, 4-ethoxy-5,11-dimethyl-6H-pyrido[3,2b]carbazole, did not lead to phase-specific blockade, but was a strong inductor of apoptosis in L1210 cells.     

铂类络合物引起的DNA O6-AGT的耗竭及染色体损伤

本文测定了KB,CHL,HL-60和L1210细胞DNA鸟嘌呤O⁶-烷基转移酶(O⁶-AGT)活性。结果表明,KB细咆有较高的O⁶-AGT活性,系Mer⁺细胞。而CHL,HL-60和L1210细胞的O⁶-AGT活性低,属于Mer^-细胞。在此基础上我们观察了顺铂(DDP)、宁辛铂(樟脑胺氯乙酸铂,CCP)和碳铂(JM-8)对KB(Mer⁺)细胞O⁶-AGT的影响及Mer⁺和Mer^-细胞的杀伤及微核的诱发作用。结果表明,三种络合物在等毒性浓度下对O⁶-AGT耗竭程序是CCP>DDP>JM-8,但这种耗竭与杀细胞作用无明显相关性而与微核诱发作用相关。此结果提示铂类络合物对DNA鸟嘌呤O⁶的损伤可能是其致痛致突变的原因之一。     

Triazene compounds: mechanism of action and related DNA repair systems.

Triazene compounds of clinical interest (i.e. dacarbazine and temozolomide) are a group of alkylating agents with similar chemical, physical, antitumour and mutagenic properties. Their mechanism of action is mainly related to methylation of O(6)-guanine, mediated by methyldiazonium ion, a highly reactive derivative of the two compounds. The cytotoxic/mutagenic effects of these drugs are based on the presence of DNA O(6)-methylguanine adducts that generate base/base mismatches with cytosine and with thymine. These adducts lead to cell death, or if the cell survives, provoke somatic point mutations represented by C:G-->T:A transition in DNA helix. Triazene compounds have excellent pharmacokinetic properties and limited toxicity. Dacarbazine requires hepatic activation whereas temozolomide is spontaneously converted into active metabolite in aqueous solution at physiological pH. Moreover, temozolomide is fully active when administrated orally (100% bioavailability). The biological effects of triazene compounds and cell resistance to them depend on at least three DNA repair systems, (a) O(6)-alkylguanine-DNA-alkyltransferase, called also methyl-guanine methyl-transferase (MGMT); (b) mismatch repair (MMR), and (c) base excision repair (BER). MGMT is a small enzyme-like protein that removes small alkyl adducts from the O(6) position of DNA guanine through a stoichiometric and auto-inactivating reaction. This reaction consists in a covalent transfer of the alkyl group from the alkylated site in DNA to an internal cysteine residue of MGMT protein. High levels of MGMT are responsible for normal and tumour cell resistance to triazenes. Therefore, pre-treatment with MGMT inhibitors - i.e. O(6)-benzylguanine or O(6)-(4-bromotenyl)guanine (Lomeguatrib) - is followed by a great increase in the activity of triazenes against target cells expressing high MGMT levels. MMR is represented by a protein complex dedicated to the repair of biosynthetic errors generated during DNA replication. The MMR system recognizes base mismatches and insertion-deletion loops, cuts the nucleotide sequence containing the lesion, and restores the correct base sequence. Therefore, not only MGMT but also MMR is involved in target cell susceptibility to triazenes. However, the system does not suppress, but instead promotes the cytotoxic effects of triazenes. In fact, MMR is not able to repair the incorrect base pairing determined by treatment with triazenes and, according to a predominant hypothesis, it causes reiterated "futile" attempts of damage repair leading to the activation of cell cycle arrest and apoptosis. BER removes lesions due to cellular metabolism, or to physical or chemical agents. BER is able to repair N(7)-methylguanine and N(3)-methyladenine determined by treatment with triazenes. Therefore, triazene compounds can also kill tumour cells by a N(3)-methyladenine-mediated mechanism if BER activity is inhibited by chemical agents (i.e. PARP inhibitors). In conclusion, in selected cases, triazenes can represent a therapeutic alternative to treatment of neoplastic diseases including haematological malignancies. Moreover, the susceptibility of neoplastic cells to these compounds can be substantially increased through pharmacological modulation of the expression level and functional activity of DNA repair enzymes.     

Enhanced DNA excision repair in CCRF-CEM cells resistant to 1,3-bis(2-chloroethyl)-1-nitrosourea,quantitated using the single cell gel electrophoresis (Comet) assay

Enhanced DNA repair activity is important for the development of cellular resistance to alkylating agents. Here, we quantitated the kinetics of DNA excision repairs initiated by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in human leukemia CCRF-CEM cells. CEM cells that had been established resistant to BCNU (CEM-R) were evaluated in comparison with parental CEM cells (CEM-S). The excision repair kinetics were quantitated as the amount of DNA single strand breaks, which were generated from the incision/excision of the damaged DNA and were diminished by the rejoining of renewed DNA, using the single cell gel electrophoresis (Comet) assay. CEM-R cells were 10-fold more resistant to BCNU than CEM-S cells, and also showed cross-resistance to melphalan and cisplatin. In response to the treatment with BCNU, both CEM-S and CEM-R cells initiated an incision/excision reaction at the end of the incubation period, and completed the rejoining process within 4 hr. While CEM-S cells could not repair the damage induced by the high concentration of BCNU, CEM-R cells completed the repair process regardless of BCNU concentrations, suggesting enhanced excision repairs in CEM-R cells. The excision repair activity of CEM-R cells was increased with regard to the incision reaction and to the rate of the repair. Similar results were obtained using ultraviolet C, suggesting enhanced nucleotide excision repair in CEM-R cells. Thus, the enhanced DNA excision repairs were successfully quantitated in the resistant leukemic cell line using the Comet assay. The evaluation of the repair activity may predict the sensitivity of cancer cells to chemotherapy and provide a clue to overcome the resistance.     

DNA repair, ADP-ribosylation and pyridine nucleotide metabolism as targets for cancer chemotherapy

DNA repair mechanisms serve as useful targets for modulating the cytotoxic and chemotherapeutic effects of many agents whose mechanism of action involves the induction of DNA damage. For example, the modified base O6-methylguanine can inactivate the repair protein O6-alkylguanine alkyltransferase, thereby sensitizing cells to the cytotoxic effects of clinically useful nitrosoureas such as BCNU. Some of the cytotoxic DNA adducts induced by BCNU are repaired by O6-alkylguanine alkyltransferase; thus, inactivation of the protein by O6-methylguanine converts cells that are relatively resistant to BCNU into sensitive cells. Another cellular enzyme, poly(ADP-ribose) polymerase, responds to DNA strand breaks by cleaving its substrate, NAD+, and using the resultant ADP-ribose moieties to synthesize homopolymers of ADP-ribose. The use of agents such as benzamide derivatives to inhibit enzyme function results in the accumulation of DNA strand breaks and potentiates the tumoricidal effects of some DNA strand-breaking agents such as bleomycin. Poly(ADP-ribose) polymerase can also affect pyridine nucleotide metabolism in a manner that initiates biochemical alterations leading directly to cell death. Thus, the amount of NAD used in the synthesis of poly(ADP-ribose) is dependent on the number of DNA strand breaks present in the cells. DNA damage can sufficiently activate the enzyme to rapidly consume NAD and consequently deplete ATP levels, resulting in the cessation of all energy-dependent functions and cell death. Understanding this biochemical pathway that leads to cell death provides a new basis for modulating chemotherapy. For example, agents such as Tiazofurin and/or 6-aminonicotinamide can each be used to alter pyridine nucleotide metabolism, lower NAD pools and potentiate the cytotoxic effects of other chemotherapeutic agents whose primary target is the induction of DNA damage.     

Inhibition of the hepatic O6-alkylguanine-DNA alkyltransferase in vivo by pretreatment with antineoplastic agents

The mammalian DNA repair enzyme O6-alkylguanine-DNA alkyltransferase (AT) is inactivated during the repair process and its activity can only be restored by de novo synthesis. We have made use of this property to determine whether and to what extent various chemotherapeutic agents alkylate DNA in the O6-position of guanine, ie. produce lesions susceptible to AT repair. Adult female Fischer rats received a single i.p. injection of a high dose (LD50) of the respective agent and, 5 hr later, a chasing dose of N-nitroso-[14C]dimethylamine (0.2 mg/kg; 4 hr survival). The amount of 7-[14C]methylguanine formed was approximately 95 mumol/mol guanine and not significantly altered by pretreatment with any of the drugs. The ratio of O6-[14C]methylguanine/7-[14C]methylguanine was 0.019 for control animals, indicating that during the observation period of 4 hr, 83% of the O6-[14C]methylguanine produced had been removed by the hepatic AT. Little or no effect was found in rats that received spirohydantoin mustard, hexamethylmelamine, cis-platinum or mitomycin C. A significant increase in the O6-/7-[14C]methylguanine ratio was found after pretreatment with AZQ (0.026) and cyclophosphamide (0.028), agents for which lesions involving the O6-position of guanine have not yet been identified. N-(2-Hydroxyethyl)-N-nitrosourea and the cytostatic haloethylinitrosoureas, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), 1-(2-chloroethyl)-3-(2,6-dioxo-3-piperidyl)-1-nitrosourea (PCNU), and N-chloroethyl-N-hydroxyethylnitrosourea (HECNU) inhibited the hepatic AT, producing a ratio of 0.025-0.035. Considerably higher ratios of 0.059 and 0.101 were observed after administration of the methylating agents procarbazine and 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide (DTIC), respectively. Complete saturation of the repair system (O6-/7-[14C]methylguanine ratio, 0.11) was only achieved with N-methyl-N-nitrosourea.     

Inhibition of DNA repair as a means of increasing the antitumor activity of DNA reactive agents

Chemotherapeutic alkylnitrosoureas (BCNU, CCNU, streptozotocin) and alkyltriazenes (DTIC, temozolomide) produce a cytotoxic lesion at the O(6)-position of guanine. The DNA repair protein, O(6)-alkylguanine-DNA alkyltransferase removes damage from the O(6)-position in a single-step mechanism without co-factors. There is extensive evidence that this protein is one of the most important factors contributing to alkylnitrosourea and alkyltriazene treatment failure. There is an inverse correlation between the level of this protein and the sensitivity of cells to the cytotoxic effects of O(6)-alkylating agents. Attempts have been made to modulate AGT activity using anti-sense technology, methylating agents, O(6)-alkylguanines, and O(6)-benzylguanine analogs. O(6)-Benzylguanine and its analogs are clearly the most potent direct inactivators of the AGT protein. The mechanism involves O(6)-benzylguanine acting as a low-molecular weight substrate with transfer of the benzyl group to the cysteine residue within the active site of the repair protein. Pretreatment of cells with non-toxic doses of O(6)-benzylguanine results in an increase in the sensitivity to O(6)-alkylating agents. Animal studies revealed that the therapeutic index of BCNU increased when administered in combination with O(6)-benzylguanine. This drug is currently in phase I clinical trials. Evidence from animal studies indicates that myelosuppression may be the dose-limiting toxicity, thus, efforts are aimed at improving the therapeutic index by the stable expression of O(6)-benzylguanine-resistant AGT proteins into targeted normal tissue such as bone marrow. The successful modulation of alkyltransferases brings on an exciting new era for alkylnitrosoureas and alkyltriazenes.     

The cytotoxicity of helenalin, its mono and difunctional esters, and related sesquiterpene lactones in murine and human tumor cells.

Naturally occurring sesquiterpene lactones and their semisynthetic derivatives, such as the O = C-C = CH-bearing helenalin and its esters, have been shown to demonstrate potent cytotoxicity against the growth of murine L1210 lymphoid leukemia and human Tmolt3 leukemia, colon adenocarcinoma, HeLaS3, lung bronchogenic, KB, osteosarcoma, and glioma cells. The modes of action of helenalin in L1210 cells are the inhibition of DNA, RNA, and protein syntheses. This study confirms that thiol bearing enzymes of nucleic acid metabolism were significantly inhibited, e.g. DNA polymerase alpha, IMP hydrogenase, and ribonucleoside reductase. The addition of GSH to the reaction medium demonstrated total recovery of L1210 ribonucleoside reductase activity. Helenalin reduced cellular GSH levels in L1210 cells. Helenalin also reduced all four pool levels of d(NTP)s which would account for part of the observed inhibition of DNA synthesis. Reductions in the ribonucleotide pool levels were also generally evident after drug treatment. Thus, the sesquiterpene lactones appear to have more than one mode of action in L1210 cells. All of the modes of actions of helenalin are feasible mechanisms to lower nucleic acid synthesis and cause cell death of the L1210 leukemia cells.     

A phase II study of Temozolomide in advanced untreated pancreatic cancer

Temozolomide (SCH 52365) is an imidazotetrazine derivative which exhibits broad spectrum activity against murine tumors and is structurally related to dacarbazine (DTIC). Temozolomide cytotoxicity is schedule dependent in vivo with a daily × 5 schedule showing the highest activity. Oral temozolomide is rapidly and completely absorbed with minimal interpatient and intrapatient variability in pharmacokinetics. Clinical studies have demonstrated activity against melanoma and glioma. The present study examined the activity of oral temozolomide against patients with pancreatic cancer. Patients with advanced pancreatic adenocarcinoma previously untreated with chemotherapy received temozolomide 200 mg/m²/day once daily orally for 5 days with cycles repeated every 28 days. There were 16 patients entered on study with 15 evaluable for response and toxicity. There were no responses seen in 15 evaluable patients with 14 manifesting progressive disease within 2 months of starting therapy. Toxicity was primarily hematological with 3 patients experiencing ≥ grade 3 neutropenia and thrombocytopenia respectively. Other toxicities were relatively modest. In conclusion, temozolomide in the once daily × 5 schedule is inactive against adenocarcinoma of the pancreas.     

Modulation of nitrosourea resistance in human colon cancer by O6-methylguanine.

Human colon cancer is resistant to a variety of alkylating agents including the nitrosoureas. To specifically evaluate nitrosourea resistance, we studied the role of O6-alkylguanine-DNA alkyltransferase (alkyltransferase) which is known to repair nitrosourea-induced cytotoxic DNA damage. Alkyltransferase activity varied over a similar wide range in 25 colon cancer biopsies and 14 colon cancer cell lines but the activity was not correlated with differentiation status, Dukes' classification or in vitro growth characteristics. 1,3-Bis-(2-chloroethyl)-1-nitrosourea (BCNU) resistance and alkyltransferase activity were highly correlated (R2 = 0.929, P less than 0.001) in 7 different colon cancer cell lines, suggesting that the alkyltransferase is an important component of nitrosourea resistance in colon cancer cells. In the BCNU-resistant, high alkyltransferase VACO 6 cell line, inactivation of the alkyltransferase by O6-methylguanine caused a proportional decrease in the BCNU IC50, consistent with that predicted by the regression line. Enzyme inactivation was also associated with a marked increase in DNA cross-link formation. Because alkyltransferase correlates with BCNU resistance in colon cancer, and resistance can be reversed by inactivating the protein, the alkyltransferase may have an important role in nitrosourea resistance in human colon cancer cells. These data provide the rationale for clinical trials in colon cancer with biochemical modulators of the alkyltransferase to increase the therapeutic response to nitrosoureas.     

Synthesis and antitumor activity of methyltriazene prodrugs simultaneously releasing DNA-methylating agents and the antiresistance drug O(6)-benzylguanine

Active resistance of tumor cells against DNA alkylating agents arises by the production of high levels of the DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT). This resistance during treatment with, for example, the anticancer agent temozolomide can be reversed by administration of O(6)-benzylguanine, a purine that transfers its benzyl group to AGT and irreversibly inactivates it. Stimulated by the favorable therapeutic properties of temozolomide we designed and synthesized DNA-methylating triazenes built on the antiresistance benzylguanine ring system. The condensation reaction between 2-nitrosopurines and acylhydrazines proved to be very suitable to prepare acylated methyltriazenes. Fine-tuning of the release rate of both the methylating agent (diazomethane) and of O(6)-benzylguanine was accomplished by variation of the hydrolysis-sensitive acyl substituent in 5. Hydrolysis studies were performed with (1)H NMR and revealed that the p-nitrophenyl substituted triazene 26 showed an optimal hydrolysis rate (t(1/2) = 23 min) and almost 100% selectivity for the desired fragmentation route. In vitro antitumor studies in the 60 human tumor cell line panel of the National Cancer Institute confirmed the superior properties of p-nitrophenyl-protected methyl triazene 26, showing mean IC(50) values of 10 microM compared to 100 microM for temozolomide. In analogy with temozolomide, triazene 26 showed however low preference for each of the cancer subpanels, with IC(50) values between 8 and 14 microM.     

2-amino-O4-benzylpteridine derivatives: potent inactivators of O6-alkylguanine-DNA alkyltransferase

2-amino-O4-benzylpteridine (1), 2-amino-O4-benzyl-6,7-dimethylpteridine (2), 2-amino-O4-benzyl-6-hydroxymethylpteridine (4), 2-amino-O4-benzylpteridine-6-carboxylic acid (5), 2-amino-O4-benzyl-6-formylpteridine (6), and O4-benzylfolic acid (7) are shown to be as potent or more potent inactivators of the human DNA repair protein O6-alkylguanine-DNA alkyltransferase (alkyltransferase) in vitro than O6-benzylguanine, the prototype alkyltransferase inactivator currently in clinical trials. Additionally, the negatively charged (at physiological pH) inactivators 2-amino-O4-benzylpteridine-6-carboxylic acid (5) and O4-benzylfolate (7) are far more water soluble than O6-benzylguanine. The activity of O4-benzylfolic acid (7) is particularly noteworthy because it is roughly 30 times more active than O6-benzylguanine against the wild-type alkyltransferase and is even capable of inactivating the P140K mutant alkyltransferase that is resistant to inactivation by O6-benzylguanine. All the pteridine derivatives except 2-amino-O4-benzylpteridine-6-carboxylic acid are effective in enhancing cell killing by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). However, the effectiveness of O4-benzylfolate as an adjuvant for cell killing by BCNU appears to be a function of a cell's alpha-folate receptor expression. Thus, O4-benzylfolate is least effective as an adjuvant in A549 cells (which express little if any receptor), is moderately effective in HT29 cells (which express low levels of the receptor), but is very effective in KB cells (which are known to express high levels of the alpha-folate receptor). Therefore, O4-benzylfolic acid shows promise as an agent for possible tumor-selective alkyltransferase inactivation, which suggests it may prove to be superior to O6-benzylguanine as a chemotherapy adjuvant.     

Synthesis and biological activity of several amino nucleoside-platinum(II) complexes

Several platinum(II) complexes of 3',5'-diamino-3',5'-dideoxythymidine (compound 1), 5'-amino-5'-deoxythymidine (compound 2), and 3'-amino-3'-deoxythymidine (compound 3) and the respective 2'-deoxyuridine amino nucleoside complexes, 4-6, have been synthesized. Whereas compounds 1, 2, and 4-6 had no inhibitory effect on the replication of murine L1210 cells in cell culture, compound 3 [(3'-AdThd)2PtCl2] inhibited these cells with an ED50 of 0.8 microM. Incubation of L1210 cells with 10-20 microM compound 3 for 2 h produced less than 18% inhibition of RNA, DNA, or protein synthesis, which is of questionable significance. However a 16-h incubation resulted in an increased uptake of labeled thymidine into DNA (77%), labeled uridine into RNA (17%), and labeled amino acids into protein (100%). These unexpected results indicate that inhibition of macromolecules may not be involved in the inhibition of the replication of L1210 cells. The increased incorporation of labeled metabolites into macromolecules may be related to the increase in cell volume after a 2-h incubation of L1210 cells with compound 3 plus a marked increase after 2 h in the proportion of cells in their S phase. Compound 3 appears to delay the progression of cells through their cell cycle. A marked inhibitory effect on the transport of methionine or aminoisobutyric acid into L1210 cells was found with compound 3, which was slightly greater than that produced with cisplatin. Compound 3 had a dose-dependent effect on the survival of mice bearing the L1210 ascites neoplasm, with a T/C X 100 of 175 at a dose of 320 mg/kg. Investigation of the kinetics of decomposition in aqueous systems demonstrated that the primary UV-absorbing decomposition product is 3'-amino-3'-deoxythymidine and that only a limited amount of the compound is formed (less than 8%). Although 3'-amino-3'-deoxythymidine could account for a part of the inhibition of the replication of L1210 cells in culture, it cannot account for the inhibition of amino acid transport by compound 3, the platinum complex of 3'-amino-3'-deoxythymidine. Compound 3 has been shown to limit part of the amino acid uptake into L1210 cells in a similar manner to cisplatin.     

A phase II study of Temozolomide in advanced untreated pancreatic cancer

Temozolomide (SCH 52365) is an imidazotetrazine derivative which exhibits broad spectrum activity against murine tumors and is structurally related to dacarbazine (DTIC). Temozolomide cytotoxicity is schedule dependent in vivo with a daily × 5 schedule showing the highest activity. Oral temozolomide is rapidly and completely absorbed with minimal interpatient and intrapatient variability in pharmacokinetics. Clinical studies have demonstrated activity against melanoma and glioma. The present study examined the activity of oral temozolomide against patients with pancreatic cancer. Patients with advanced pancreatic adenocarcinoma previously untreated with chemotherapy received temozolomide 200 mg/m²/day once daily orally for 5 days with cycles repeated every 28 days. There were 16 patients entered on study with 15 evaluable for response and toxicity. There were no responses seen in 15 evaluable patients with 14 manifesting progressive disease within 2 months of starting therapy. Toxicity was primarily hematological with 3 patients experiencing grade 3 neutropenia and thrombocytopenia respectively. Other toxicities were relatively modest. In conclusion, temozolomide in the once daily × 5 schedule is inactive against adenocarcinoma of the pancreas.     

Pharmacological strategies to increase the antitumor activity of methylating agents

Among methylating agents of clinical interest, temozolomide is a novel antitumor compound that has raised particular interest due to its acceptable safety profile and activity against tumors poorly responsive to conventional chemotherapy, such as malignant glioma and metastatic melanoma. Moreover, the drug has recently shown promising antitumor activity in a patient affected by primary brain lymphoma and is currently under phase II clinical trials for leptomeningeal metastases from leukemia and lymphoma or for brain metastases from lung and breast cancers. The antitumor activity of TMZ, that generates different types of methyl adducts (70% N7-methylguanine, 10% N3-methyladenine and 9% O6-methylguanine), has been mainly attributed to the formation of O6-methylguanine adducts. Indeed, tumor cell susceptibility to TMZ is strongly affected by the functional status of DNA repair systems, involved either in the removal of methyl adducts from O6G or in the apoptotic signaling triggered by O6-methylG:T mispairs. This review will focus on the different pharmacological strategies aimed at overcoming tumor resistance to TMZ such as new formulations of the drug or dosing schedules, and combined treatments with other chemotherapeutic agents, modulators of DNA repair systems, or gene therapy. The potential use of N3-methyladenine selective agents in the case of tumors tolerant to O6-methylguanine will be also discussed.