Cytotoxicity of dual function nitrofurans in rodent and human tumor cells

Solvent effects on the stability of nifuroxazide complexes with cobalt(II), nickel(II) and copper(II) in alcohols

A spectrophotometric study of the complexation of nifuroxazide with cobalt(II), nickel(II) and copper(II) was carried out in different alcohols. The formation of a complex in each case is reported and their stability constants have been calculated. For a given solvent, the stability of the complexes increases from cobalt to copper. In the case of copper(II), the stability varies as an inverse function of the dielectric constant of the solvent. A possible structure of the complex is proposed.

Chemosensitization of CCNU in KHT murine tumor cells in vivo and in vitro by the agent RB 6145 and its isomer PD 144872

The cytotoxicity and chemosensitizing potential of the nitrohetercyclic agent RB 6145 and its R enantiomer PD 144872 were determined in rodent tumor cells grown in tissue culture or as solid tumors. Using a clonogenic cell survival assay the degree of selective cytotoxicity of these bioreductive drugs was first determined in KHT/iv cells. Cells treated under hypoxic conditions were observed to be approximately 50-80-fold more susceptible to the action of RB 6145 or PD 144872 than were cells exposed under air. To assess the in vitro chemosensitizing potential of RB 6145 and PD 144872, doses of these agents which led to survival values between 0.5 and 1.0 under hypoxic conditions were administered, and were then combined concomitantly with variable doses of the nitrosourea CCNU. Exposure to the nitrosourea was for 1 h. The results showed that inclusion of either sensitizer enhanced the cell killing of the chemotherapeutic agent 2.4-2.6-fold. Subsequent experiments evaluated the therapeutic benefit of combining these bioreductive agents with CCNU in KHT sarcoma-bearing C3H/HeJ mice. When given at times ranging from 90 min before to 60 min after CCNU exposure, these bioreductive drugs increased the tumoricidal activity of the chemotherapeutic agent. Complete dose response curves combining RB 6145 and PD 144872 and a range of CCNU doses also were evaluated. The sensitizers (0.75 mmol/kg) were administered 30 min prior to the chemotherapeutic agent and survival of clonogenic tumor cells 22-24 h after treatment was used to assay tumor response.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro cytotoxicity and chemosensitizing activity of the dual function nitroimidazole RB 6145

PURPOSE

To determine the cytotoxicity and chemosensitizing potential of RG 6145 in mouse KHT/iv and human A549 tumor cells.

METHODS AND MATERIALS

RSU 1069, the lead compound in a series of nitroimidazoles containing an alkylating aziridine function, has been shown to possess a high degree of selective cytotoxicity for hypoxic cells in addition to being a potent sensitizer of radiation and chemotherapy. Unfortunately, preliminary clinical studies have revealed a dose-limiting gastrointestinal toxicity for RSU 1069. Recently RB 6145, the ring-opened analogue of RSU 1069, has been found to be less emetic than RSU 1069. In the present studies, we assessed both the differential hypoxic cell cytotoxicity of RB 6145 and its chemosensitizing potential when combined concomitantly with variable doses of the activated form of cyclophosphamide (4-hydroperoxy-cyclophosphamide, 4-OOH-CP) or the nitrosourea CCNU.

RESULTS

As we had observed previously for RSU 1069, RB 6145 was found to be less cytotoxic to human than rodent tumor cells. In addition, the degree of selective cytotoxicity toward hypoxic cells was (a) less in A549 than in KHT/iv cells (factor of 9 vs. 80) but (b) comparable to that seen with RSU 1069. For both cell lines, inclusion of the sensitizer enhanced the cell killing of the chemotherapeutic agent 4-OOH-CP by a factor of approximately 1.5-1.7-fold. When combined with CCNU, RB 6145 increased the killing of A549 cells approximately 1.8-fold. Similar hypoxic cell preferential cytotoxicity and enhancement in anti-tumor treatment efficacy were seen when A549 cells were exposed to the R enantiomer of RB 6145 (PD 144872) either alone or in combination with CCNU.

CONCLUSION

These data support the notion that further consideration should be given to the clinical application of these bioreductive agents.

Potentiation of alkylating chemotherapy by dual function nitrofurans in multi-cell spheroids and solid tumors

The cytotoxicity and chemosensitizing potential of four dual function nitrofurans was determined in human HT-29 multi-cell spheroids and rodent KHT sarcoma solid tumors. Spheroids were treated with a range of doses of the bioreductive drugs for a period of up to 48 h and the extent of cell kill was assessed at various times after treatment. Cytotoxicity was determined using a clonogenic cell-survival assay. The results demonstrated that two of the nitrofurans were even more toxic to spheroid cells than was the potent bioreductive nitroimidazole aziridine RSU 1069. The dose of the nitrofuran which, after a 24-h exposure, led to a survival value between 0.5 and 1.0, then was chosen for subsequent studies aimed at assessing the ability of these agents to potentiate the efficacy of the nitrosourea CCNU. Exposure to this chemotherapeutic agent was for a period of 1 h. The results indicated that all four dual function nitrofurans enhanced the cell killing of the conventional chemotherapeutic agent by factors ranging from 1.1 to 1.7. Subsequent studies evaluated the therapeutic benefit of combining these bioreductive agents and CCNU in KHT sarcoma-bearing C3H/HeJ mice. The nitrofurans were administered i.p. 0.5 h prior to the chemotherapy and tumor response was assessed by measuring the survival of clonogenic KHT cells 22-24 h after treatment. Normal tissue toxicity was determined using a bone marrow stem cell (CFU-GM) assay. Combining these bioreductive agents with CCNU increased the tumor cell kill by factors of 1.2 to 1.7.(ABSTRACT TRUNCATED AT 250 WORDS)