In vitro potentiation of BCNU activity in rat brain tumour cells pretreated with misonidazole

Syntheses and biological studies of nitroimidazole conjugated heteroscorpionate ligands and related Cu(I) and Cu(II) complexes

Copper(I) and copper(II) complexes of 5-nitroimidazole conjugated heteroscorpionate ligands have been synthesized. In particular, the new 2,2-bis(pyrazol-1-yl)-N-(2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl)acetamide ligand (L^HMN) was synthesized by direct coupling of preformed side chain acid with 5-nitroimidazole and its coordination chemistry was investigated towards Cu(I) and Cu(II) acceptors and compared with that of the related 2,2-bis(3,5-dimethyl-1-H-pyrazol-1-yl)-N-(2-(2-methyl-5-nitro-1H-imidazol-1-yl)ethyl)acetamide ligand (L^MeMN). The copper(II) complexes {[(L^MeMN)₂Cu]Cl₂} and {[(L^HMN)₂Cu]Cl₂} were prepared by the reaction of CuCl₂·2H₂O with L^HMN or L^MeMN ligands in methanol solution. The water soluble copper(I) complexes {[(L^MeMN)Cu(PTA)₂]}(PF₆) and {[(L^HMN)Cu(PTA)₂]}(PF₆) were prepared by the reaction of Cu(CH₃CN)₄PF₆ and 1,3,5-triaza-7-phosphaadamantane (PTA) with L^HMN or L^MeMN ligands in acetonitrile solution. The new Cu(I) and Cu(II) complexes as well as the corresponding uncoordinated ligands were evaluated for their cytotoxic activity against 2D monolayer cultures of multiple human cancer cell lines and 3D-cultured HCT-15 colon cancer spheroids. Morphological analysis by Transmission Electron Microscopy (TEM) revealed the induction of a massive cytoplasmic vacuolization consistent with a paraptotic-like cancer cell death.

γ radiation-induced damage of nucleic acid bases, calf thymus DNA and DNA within MCF-7 breast cancer cells by [Cu2(OAc)4(tnz)2]: a potential radiosensitizer

A Cu(ii) complex of tinidazole is more radiosensitizing than it in radiation-induced damage of nucleic acids, calf thymus DNA and DNA in MCF-7 breast cancer cells. NO₂˙⁻ was modulated to strike a balance between efficacy and toxic side effects.

Chemosensitization of the nitrosoureas by 2-nitroimidazoles in the subcutaneous 9L tumor model: pharmacokinetic and structure-activity considerations

Alterations of the pharmacokinetics and cytotoxic effects of the nitrosoureas, 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and 1-(2-chloroethyl)-3-(cyclohexyl)-1-nitrosourea (CCNU) by the 2-nitroimidazoles, misonidazole (MISO) and SR-2508 were investigated using the subcutaneous (sc) 9L tumor model in male Fisher 344 rats. When 50 mg/kg of CCNU was given i.p., the peak plasma concentration of CCNU was about 3 micrograms/ml. CCNU was eliminated with biphasic kinetics that had a terminal half-time (T1/2) of approximately 47 min. When 2.5 mmole/kg of MISO was given i.p. 150 min before CCNU, the peak plasma concentration of CCNU was increased by approximately 63% with no change in the elimination kinetics. Clamping did not change the pharmacokinetics of CCNU in either plasma or tumors. MISO pretreatment increased the peak CCNU concentration in unclamped tumors by 3-fold, but had no effect on the CCNU pharmacokinetics in clamped tumors. With the exception of a decrease in the peak BCNU concentration in tumors similar to that observed with MISO, SR-2508 (3.75 mmole/kg, i.p.) did not change the pharmacokinetics of BCNU or CCNU in plasma and tumors. CCNU had no effect on the MISO concentration in plasma and unclamped tumors. However, in the clamped tumors, CCNU delayed the return of the MISO concentration to the unclamped tumor level by about an additional 60 min after the clamp was released. SR-2508 was eliminated from the plasma with biphasic kinetics having an initial and terminal T1/2 of approximately 11 and approximately 76 min, respectively. SR-2508 reached a peak tumor concentration of about 500 micrograms/ml in 30 min. The elimination T1/2 for SR-2508 in unclamped and clamped tumors was approximately 81 and approximately 42 min, respectively. When the clamp was released, the SR-2508 concentration returned to the level found in the unclamped tumors approximately 90 min after it reached its nadir; BCNU and CCNU had no effect on the kinetics of this process. MISO significantly potentiated the cytotoxicity of BCNU in clamped tumors at surviving fractions less than or equal to 0.5. MISO did not potentiate the cytotoxicity of CCNU until the surviving fraction reached 0.05. SR-2508 did not potentiate the cytotoxicity of either BCNU or CCNU.(ABSTRACT TRUNCATED AT 400 WORDS)

Biodistribution of misonidazole and 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) in rats bearing unclamped and clamped 9L subcutaneous tumors

The biodistribution of misonidazole (MISO) and 1,3bis(2-chloroethyl)-1-nitrosourea (BCNU) was studied using the subcutaneous (s.c.) 9L tumor model in male Fisher 344 rats. A transient hypoxia in these tumors was created by clamping the blood supply to the tumor. Reoxygenation occurred upon release of the clamp. The plasma and tumor concentrations of MISO and BCNU were quantitated by high pressure liquid chromatography. When 12 mg/kg of BCNU was given i.p. without MISO, the peak plasma concentration was about 6 micrograms/ml, and the elimination half-time was about 16 min. When 2.5 mmole/kg of MISO was given i.p. 150 min before the BCNU, the peak plasma concentration of BCNU increased by approximately 33%, and the plasma elimination half-time increased by approximately 57%. Clamping the tumor for 120 min did not significantly change the BCNU concentration in plasma, but in tumors the time to reach the peak level was delayed slightly, and the peak concentration was reduced when compared to that in the unclamped tumors. MISO pretreatment decreased the BCNU peak concentration in both unclamped and clamped tumors, but the decrease was more pronounced in the unclamped tumors. In both unclamped and clamped tumors, the BCNU concentration and its rate of disappearance were identical about 30 min after BCNU administration, with or without MISO pretreatment. The elimination half-time of MISO from the plasma (approximately 142 min) was identical for rats with unclamped or clamped tumors. The half-time for the disappearance of MISO from unclamped tumors was about 98 min. BCNU had no effect on the MISO concentration in plasma and unclamped tumors. MISO disappeared in the clamped tumors with a half-time of about 40 min. When the clamp was released, the MISO concentration returned to the level in the unclamped tumors after about 45 min. BCNU delayed the return of the MISO concentration to the unclamped tumor level by about 60 min. Two conclusions can be drawn from this study. First, the pharmacokinetics of each drug changed when the two drugs were combined. Second, the data indicate that alterations in the tumor BCNU pharmacokinetics are not the major mechanism responsible for the chemopotentiation previously measured in s.c. 9L tumors.

Potentiation of in vitro cytotoxic effects of misonidazole on human colon tumor cells by the differentiation-inducing agent N-methylformamide

Human colon tumor cells (clone A) were studied in vitro with regard to modification of dose-dependent cytotoxicity to misonidazole (MISO) treatment by pre-exposure growth in medium containing the differentiation-inducing agent N-methylformamide (NMF). Cells were grown as exponential cultures and were exposed for 2 passages to 170 mM NMF before exposure to graded doses of MISO (0-100 mM, 3 hours at 37 degrees C, oxic or hypoxic). Both oxic and hypoxic cells could be sensitized to MISO cell killing. Using the 10% level of survival for comparison, the calculated MISO doses (mM) were: 105, 37, 50, and 10 for oxic control cells, hypoxic control cells, oxic-NMF treated cells, and hypoxic-NMF treated cells, respectively. Therefore, for NMF treated oxic cells, cell killing was increased by a factor of about 2.1, while for NMF treated hypoxic cells, cell killing increased by a factor of about 3.7. These data indicate that NMF treatment, while potentiating effects on both oxic and hypoxic cells, appears to have selectivity towards hypoxic cells. NMF may therefore have use in combined modality radiation therapy of solid tumors with electron-affinic radiosensitizers.

Chemopotentiation in vivo: no loss of sensitization with fractionation

The response of KHT sarcomas to one, two, five or ten daily fractions of 1-(2-chloroethyl)-3-cyclohexyl-1-nitrosourea (CCNU), with and without misonidazole (MISO), was evaluated using delay of tumour regrowth as the measure of response. When CCNU was given as 2 dose fractions separated by 24 h rather than as a single treatment, no extra dose was necessary to achieve a particular level of damage, suggesting a lack of damage repair. With increasing fraction number, however, an increasing total dose of drug was required to achieve a given effect, presumably to compensate for proliferation. Increasing drug doses also were readily tolerated (almost twice the LD50/7 for a single dose of CCNU resulted in no deaths when given in a 10 fraction treatment) indicating a large sparing of normal tissue toxicity when CCNU treatments were fractionated. The addition of MISO enhanced the tumour response to CCNU in all treatment schemes. When single doses of CCNU were combined with 0.5 mg g-1 MISO, an enhancement ratio (ER) of approximately 1.5 was observed. This ER was maintained for all fractionated treatment schedules including the 10 daily fraction protocol. In addition, no loss of sensitization with increasing fractionation was observed when a lower dose of 0.2 mg g-1 MISO was combined with each of 5 or 10 daily fractions of CCNU. Similar experiments were performed to test the combination of cyclophosphamide (Cy) and MISO (0.5 mg g-1) in the RIF-1 tumour; again chemopotentiation was maintained with increasing fractionation. These results of combined MISO and fractionated chemotherapy are in contrast to the rapid loss of sensitization observed when MISO is used as a radiation sensitizer and combined with small doses of X-rays, thus providing in vivo evidence of the mechanistic difference between the effects of MISO used as a radiation sensitizer or chemopotentiator. Peripheral white blood cell counts performed on mice receiving 5 daily fractions of CCNU +/- MISO displayed no significant enhancement of normal tissue toxicity by MISO. Thus combining MISO with repeated low dose treatments of a chemotherapeutic agent results in a therapeutic gain.

Modification of chemotherapy by nitroimidazoles

The potentiation of chemotherapeutic agents by radiation sensitizers has been extensively studied for several years. There is little doubt that the effectiveness of certain anti-cancer drugs, primarily alkylating agents, can readily be enhanced both in vitro and in vivo through the addition of a sensitizer. While enhanced effects have been observed in certain critical normal tissues, in general most animal model studies have demonstrated a therapeutic gain at large sensitizer doses. This approach to combination therapies therefore appears promising. Yet many questions concerning the interaction between chemotherapeutic agents and radiosensitizers, particularly in the area of mechanisms of action, still remain. This overview attempts to focus on some of these questions. Four aspects of modification of chemotherapy by nitroimidazoles are reviewed and discussed. These address the importance in chemopotentiation of i) hypoxia, ii) alterations in DNA damage and/or repair, iii) depletion of intracellular sulfhydryls and iv) modification of drug pharmacokinetics. It is concluded that: i) even though chemopotentiation can occur at intermediate oxygen levels, hypoxia ultimately plays a pivotal role, ii) no single unifying mechanism for chemopotentiation exists; alterations in drug pharmacokinetics, cellular SH levels and DNA damage/repair all are involved, the relative importance of each factor is dependent on the particular drug-sensitizer combination, iii) it is important to continue the evaluation of chemopotentiation under conditions mimicking clinically achievable sensitizer pharmacokinetics and iv) further investigations into more effective utilization of chemopotentiation are warranted.