Effects of mitomycin C and porfiromycin on exponentially growing and plateau phase cultures

Insight into enzyme-catalyzed aziridine formation mechanism in ficellomycin biosynthesis

Ficellomycin is an aziridine-containing antibiotic, produced by Streptomyces ficellus. Based on the newly identified ficellomycin gene cluster and the assigned functions of its genes, a possible pathway for aziridine ring formation in ficellomycin was proposed, which is a complex process involving at least 3 enzymatic steps. To obtain support for the proposed mechanism, the targeted genes encoding sulfate adenylyltransferase, adenylsulfate kinase, and a putative sulfotransferase were respectively disrupted and the subsequent analysis of their fermentation products revealed that all the three genes were involved in aziridine formation. To further confirm the mechanism, the key gene encoding a putative sulfotransferase was over expressed in Escherichia coli Rosseta (DE3). Enzyme assays indicated that the expressed sulfotransferase could specifically transfer a sulfo group from 3'-phosphoadenosine-5'-phosphosulfate (PAPS) onto the hydroxyl group of (R)-(-)-2-pyrrolidinemethanol. This introduces a good leaving group in the form of the sulfated hydroxyl moiety, which is then converted into an aziridine ring through an intramolecular nucleophilic attack by the adjacent secondary amine. The sulfation/intramolecular cyclization reaction sequence maybe a general strategy for aziridine biosynthesis in microorganisms. Discovery of this mechanism revealed an enzyme-catalyzed route for the synthesis of aziridine-containing reagents and provided an important insight into the functional diversity of sulfotransferases.

Biocompatibility and therapeutic evaluation of magnetic liposomes designed for self-controlled cancer hyperthermia and chemotherapy

Magnetic liposome-mediated combined chemotherapy and hyperthermia is gaining importance as an effective therapeutic modality for cancer. However, control and maintenance of optimum hyperthermia are major challenges in clinical settings due to the overheating of tissues. To overcome this problem, we developed a novel magnetic liposomes formulation co-entrapping a dextran coated biphasic suspension of La_0.75Sr_0.25MnO₃ (LSMO) and iron oxide (Fe₃O₄) nanoparticles for self-controlled hyperthermia and chemotherapy. However, the general apprehension about biocompatibility and safety of the newly developed formulation needs to be addressed. In this work, in vitro and in vivo biocompatibility and therapeutic evaluation studies of the novel magnetic liposomes are reported. Biocompatibility study of the magnetic liposomes formulation was carried out to evaluate the signs of preliminary systemic toxicity, if any, following intravenous administration of the magnetic liposomes in Swiss mice. Therapeutic efficacy of the magnetic liposomes formulation was evaluated in the fibrosarcoma tumour bearing mouse model. Fibrosarcoma tumour-bearing mice were subjected to hyperthermia following intratumoral injection of single or double doses of the magnetic liposomes with or without chemotherapeutic drug paclitaxel. Hyperthermia (three spurts, each at 3 days interval) with drug loaded magnetic liposomes following single dose administration reduced the growth of tumours by 2.5 fold (mean tumour volume 2356 ± 550 mm³) whereas the double dose treatment reduced the tumour growth by 3.6 fold (mean tumour volume 1045 ± 440 mm³) compared to their corresponding control (mean tumour volume 3782 ± 515 mm³). At the end of the tumour efficacy studies, the presence of MNPs was studied in the remnant tumour tissues and vital organs of the mice. No significant leaching or drainage of the magnetic liposomes during the study was observed from the tumour site to the other vital organs of the body, suggesting again the potential of the novel magnetic liposomes formulation for possibility of developing as an effective modality for treatment of drug resistant or physiologically vulnerable cancer.

Preclinical evaluation of Laromustine for use in combination with radiation therapy in the treatment of solid tumors

PURPOSE

These studies explored questions related to the potential use of Laromustine in the treatment of solid tumors and in combination with radiotherapy.

MATERIALS AND METHODS

The studies used mouse EMT6 cells (both parental and transfected with genes for O(6)-alkylguanine-DNA transferase [AGT]), repair-deficient human Fanconi Anemia C and Chinese hamster VC8 (BRCA2(-/-)) cells and corresponding control cells, and EMT6 tumors in mice assayed using cell survival and tumor growth assays.

RESULTS

Hypoxia during Laromustine treatment did not protect EMT6 cells or human fibroblasts from this agent. Rapidly proliferating EMT6 cells were more sensitive than quiescent cultures. EMT6 cells expressing mouse or human AGT, which removes O(6)-alkyl groups from DNA guanine, thereby protecting against G-C crosslink formation, increased resistance to Laromustine. Crosslink-repair-deficient Fanconi Anemia C and VC8 cells were hypersensitive to Laromustine, confirming the importance of crosslinks as lethal lesions. In vitro, Laromustine and radiation produced additive toxicities to EMT6 cells. Studies using tumor cell survival and tumor growth assays showed effects of regimens combining Laromustine and radiation that were compatible with additive or subadditive interactions.

CONCLUSIONS

The effects of Laromustine on solid tumors and with radiation are complex and are influenced by microenvironmental and proliferative heterogeneity within these malignancies.

New Method to Prepare Mitomycin C Loaded PLA-Nanoparticles with High Drug Entrapment Efficiency

The classical utilized double emulsion solvent diffusion technique for encapsulating water soluble Mitomycin C (MMC) in PLA nanoparticles suffers from low encapsulation efficiency because of the drug rapid partitioning to the external aqueous phase. In this paper, MMC loaded PLA nanoparticles were prepared by a new single emulsion solvent evaporation method, in which soybean phosphatidylcholine (SPC) was employed to improve the liposolubility of MMC by formation of MMC-SPC complex. Four main influential factors based on the results of a single-factor test, namely, PLA molecular weight, ratio of PLA to SPC (wt/wt) and MMC to SPC (wt/wt), volume ratio of oil phase to water phase, were evaluated using an orthogonal design with respect to drug entrapment efficiency. The drug release study was performed in pH 7.2 PBS at 37 degrees C with drug analysis using UV/vis spectrometer at 365 nm. MMC-PLA particles prepared by classical method were used as comparison. The formulated MMC-SPC-PLA nanoparticles under optimized condition are found to be relatively uniform in size (594 nm) with up to 94.8% of drug entrapment efficiency compared to 6.44 mum of PLA-MMC microparticles with 34.5% of drug entrapment efficiency. The release of MMC shows biphasic with an initial burst effect, followed by a cumulated drug release over 30 days is 50.17% for PLA-MMC-SPC nanoparticles, and 74.1% for PLA-MMC particles. The IR analysis of MMC-SPC complex shows that their high liposolubility may be attributed to some weak physical interaction between MMC and SPC during the formation of the complex. It is concluded that the new method is advantageous in terms of smaller size, lower size distribution, higher encapsulation yield, and longer sustained drug release in comparison to classical method.

In vivo evaluation of a new polymer-lipid hybrid nanoparticle (PLN) formulation of doxorubicin in a murine solid tumor model

The purpose of this study is to evaluate the in vivo efficacy, unwanted toxicity and loco-regional distribution of a doxorubicin-loaded polymer-lipid hybrid nanoparticle (Dox-PLN) formulation in a murine solid tumor model after intratumoral injection. Dox-PLN were prepared by dispersing Dox in stearic acid and tristearin, with subsequent addition of a novel anionic polymer HPESO (hydrolyzed polymer of epoxidized soybean oil) to enhance the drug incorporation in the lipids. Solid tumors were obtained by injecting EMT6 mouse mammary cancer cells intramuscularly into the hind legs of BALB/c mice. Dox-PLN, blank PLN or surfactant formulations were injected intratumorally (IT) when tumors reached approximately 0.3 g. In vivo efficacy of treatment was measured by tumor growth delay (TGD), defined as the delay in time for the tumor to grow to 1.13 g relative to the untreated control. Signs of unwanted drug toxicity, the histology and morphology of tumor and heart tissues, and the IT distribution of Dox-PLN after IT treatment were examined or monitored. IT-administered Dox-PLN resulted in 70% and 100% TGD (p<0.01) for Dox doses of 0.1 and 0.2 mg, respectively. Dox-PLN treated tumors developed substantially larger central necrotic regions than the untreated tumors, with Dox-PLN residues extensively distributed among the dead cell debris, suggesting that the anticancer effect of Dox-PLN was mainly a combined result of IT nanoparticle distribution and short-ranged, sustained drug release. Except for two of fifteen mice receiving the higher 0.2 mg Dox dose showing transient fur-roughing, all Dox-PLN treated mice showed no signs of toxicity. The present study demonstrates that Dox-PLN possess significant in vivo cytotoxic activity against solid tumors with minimal systemic toxicity. IT administered Dox-PLN have the potential to improve the therapeutic index of loco-regional solid tumor chemotherapy.

In vivo efficacy and toxicity of intratumorally delivered mitomycin C and its combination with doxorubicin using microsphere formulations

The efficacy and toxicity of intratumorally (i.t.) administered anticancer drugs mitomycin C (MMC) and doxorubicin (Dox) incorporated in polymeric microspheres were investigated. Biodegradable sulfopropyl dextran microspheres and their oxidized products were used to load Dox and MMC, respectively. EMT6 mouse mammary cancer cells were injected into the hind leg of BALB/c mice. MMC microspheres, alone or combined with Dox microspheres, were injected i.t. once tumors had reached around 0.3 g. The tumor-plus-leg diameter was measured daily and the delay in time for the tumor to grow to 1.13 g relative to control (TGD) was employed as an indication of therapeutic effect. General toxicity was determined by monitoring weight, appearance and behavior of the mice. Morphology and histology of tumor and heart tissues were also examined. An average 79% TGD was observed after i.t. injection of MMC microspheres. The i.t. co-administration of MMC and Dox microspheres resulted in a 185% TGD. The i.t. injections of the microsphere formulations did not result in visible signs of toxicity in animals. In contrast, systemic (i.e. i.p.) injections of MMC solutions caused considerable general toxicity. This study suggests that i.t. delivery of anticancer drugs by polymeric microspheres is an effective way of improving the therapeutic index for cancer chemotherapy of selected solid tumors under special conditions.

Concurrent chemo-radiotherapy with mitomycin C compared with porfiromycin in squamous cell cancer of the head and neck: Final results of a randomized clinical trial

PURPOSE

Previous randomized trials have shown a benefit with concurrent use of the hypoxic cell cytotoxin mitomycin C (MC) and radiation (RT) in the management of squamous cell cancer of the head and neck (SCCHN). We conducted a randomized trial comparing MC with porfiromycin (POR) in combination with RT in the management of SCCHN.

METHODS AND MATERIALS

Between 1992 and 1999, 128 patients with SCCHN were enrolled in this prospective randomized trial. Patients were stratified by management intent, and balanced with respect to stage and site of disease. They were randomized to receive MC (15 mg/M(2)) or POR (40 mg/M(2)) on Days 5 and 47 (or last day) of RT. Of 121 evaluable patients, 61 were randomized to MC and 60 to POR. Patients were treated with standard daily RT to a total median dose of 64 Gy over 47 days. Patients were well balanced with respect to management intent, stage, site, age, sex, hemoglobin levels, tumor grade, radiation dose, and days on treatment.

RESULTS

There were no significant differences between the two arms with respect to acute hematologic or nonhematologic toxicities. As of January 2003 with a median follow-up of 6.3 years, there have been 19 local relapses (4 MC vs. 15 POR), 21 regional relapses (7 MC vs. 14 POR), 24 distant metastases (11 MC vs. 13 POR), and 66 deaths (33 MC vs. 33 POR). MC was superior to POR with respect to 5-year local relapse-free survival (91.6% vs. 72.7%, p = 0.01), local-regional relapse-free survival (82% vs. 65.3%, p = 0.05), and disease-free survival (72.8% vs. 52.9%, p = 0.026). There were no significant differences between the two arms with respect to overall survival (49.2% vs. 54.4%) or distant metastasis-free rate (79.9% vs. 75.9%).

CONCLUSIONS

Despite promising preclinical data, and an acceptable toxicity profile, POR was inferior to MC as an adjunct to RT in the management of SCCHN. This randomized trial emphasizes the need for randomized studies to evaluate new agents in the management of SCCHN.

Cytotoxicity of the bioreductive agent RH1 and its lack of interaction with radiation

BACKGROUND AND PURPOSE

RH1 is a new bioreductive agent that was developed as a cytotoxic agent with selectivity for tumour cells expressing high levels of the enzyme DT-diaphorase (DTD). The aim of the present study was to investigate the cytotoxicity of RH1 in relation to cellular levels of reducing enzymes and any interaction of RH1 with ionizing radiation under oxic and hypoxic conditions.

PATIENTS AND METHODS

The MB-MDA231 human breast cancer cell line (WT) and WT cells transfected with the NQO1 gene encoding DTD (the D7 cell line) were used to examine the dependency of RH1's cytotoxicity on cellular DTD activity. The role of the 1-electron reducing enzyme P450 reductase was also studied using a P450 reductase-transfected isogenic cell line (R4). A clonogenic assay was used to investigate the cytotoxicity of RH1 with and without irradiation in air and in nitrogen. In all cases drug exposure was for 3 h.

RESULTS

DTD levels were around 300-fold higher in D7 compared to WT and R4 cells. RH1 was cytotoxic at nanomolar concentrations to all the cell lines, and was 2-3 times more toxic in the D7 cells with high DTD than in the other two cell lines. Doses of RH1 was around 2-fold more effective in hypoxic than in oxic WT cells, but not by as much in D7 cells. RH1 did not radiosensitise the cells but showed an additive effect when combined with irradiation under oxic and hypoxic conditions.

CONCLUSIONS

RH1 shows high clonogenic cytotoxicity to MDA231 cells with high DTD activity but its selectivity based on the presence of DTD is much less than as shown in previous reports. RH1 showed an additive cell killing effect when combined with irradiation under both oxic and hypoxic conditions.