The effects of Efaproxyn (efaproxiral) on subcutaneous RIF-1 tumor oxygenation and enhancement of radiotherapy-mediated inhibition of tumor growth in mice

Efaproxiral, an allosteric modifier of hemoglobin, reduces hemoglobin-oxygen binding affinity, facilitating oxygen release from hemoglobin, which is likely to increase tissue pO(2). The purpose of this study was to determine the effect of efaproxiral on tumor oxygenation and growth inhibition of RIF-1 tumors that received X radiation (4 Gy) plus oxygen breathing compared to radiation plus oxygen plus efaproxiral daily for 5 days. Two lithium phthalocyanine (LiPc) deposits were implanted in RIF-1 tumors in C3H mice for tumor pO(2) measurements using EPR oximetry. Efaproxiral significantly increased tumor oxygenation by 8.4 to 43.4 mmHg within 5 days, with maximum increases at 22-31 min after treatment. Oxygen breathing alone did not affect tumor pO(2). Radiation plus oxygen plus efaproxiral produced tumor growth inhibition throughout the treatment duration, and inhibition was significantly different from radiation plus oxygen from day 3 to day 5. The results of this study provide unambiguous quantitative information on the effectiveness of efaproxiral to consistently and reproducibly increase tumor oxygenation over the course of 5 days of treatment, modeling the clinical use of efaproxiral. Also, based on the tumor growth inhibition, the study shows the efaproxiral-enhanced tumor oxygenation was radiobiologically significant. This is the first study to demonstrate the ability of efaproxiral to increase tumor oxygenation and to increase the tumor growth inhibition of radiotherapy over 5 days of treatment.     

Antitumor carboplatin is more toxic in tumor cells when photoactivated: enhanced DNA binding

Carboplatin, an analogue of "classical" cis-diamminedichloridoplatinum(II) (cisplatin), is a widely used second-generation platinum anticancer drug. Cytotoxicity of cisplatin and carboplatin is mediated by platinum-DNA adducts. Markedly higher concentrations of carboplatin are required, and the rate of adduct formation is considerably slower. The reduced toxic effects in tumor cells and a more acceptable side-effect profile are attributable to the lower reactivity of carboplatin with nucleophiles, since the cyclobutanedicarboxylate ligand is a poorer leaving group than the chlorides in cisplatin. Recently, platinum complexes were shown to be particularly attractive as potential photochemotherapeutic anticancer agents. Selective photoactivation of platinum complexes by irradiation of cancer cells may avoid enhancement of toxic side-effects, but may increase toxicity selectively in cancer cells and extend the application of photoactivatable platinum complexes to resistant cells and to a wider range of cancer types. Therefore, it was of interest to examine whether carboplatin can be affected by irradiation with light to the extent that its DNA binding and cytotoxic properties are altered. We have found that carboplatin is converted to species capable of enhanced DNA binding by UVA irradiation and consequently its toxicity in cancer cells is markedly enhanced. Recent advances in laser and fiber-optic technologies make it possible to irradiate also internal organs with light of highly defined intensity and wavelength. Thus, carboplatin is a candidate for use in photoactivated cancer chemotherapy.     

Improvement of tumor oxygenation by mild hyperthermia

There is now abundant evidence that oxygenation in rodent, canine and human tumors is improved during and for up to 1-2 days after heating at mild temperatures. An increase in tumor blood perfusion along with a decline in the oxygen consumption rate appears to account for the improvement of tumor oxygenation by mild hyperthermia. The magnitude of the increase in tumor pO(2), determined with oxygen-sensitive microelectrodes, caused by mild hyperthermia is less than that caused by carbogen breathing. However, mild hyperthermia is far more effective than carbogen breathing in increasing the radiation response of experimental tumors, probably because mild hyperthermia oxygenates both (diffusion-limited) chronically hypoxic and (perfusion-limited) acutely hypoxic cells, whereas carbogen breathing oxygenates only the chronically hypoxic cells. Mild hyperthermia is also more effective than nicotinamide, which is known to oxygenate acutely hypoxic cells, in enhancing the radiation response of experimental tumors. The combination of mild hyperthermia with carbogen or nicotinamide is highly effective in reducing the hypoxic cell fraction in tumors and increasing the radiation response of experimental tumors. A primary rationale for the use of hyperthermia in combination with radiotherapy has been that hyperthermia is equally cytotoxic toward fully oxygenated and hypoxic cells and that it directly sensitizes both fully oxygenated and hypoxic cells to radiation. Such cytotoxicity and such a radiosensitizing effect may be expected to be significant when the tumor temperature is elevated to at least 42-43 degrees C. Unfortunately, it is often impossible to uniformly raise the temperature of human tumors to this level using the hyperthermia devices currently available. However, it is relatively easy to raise the temperature of human tumors into the range of 39-42 degrees C, which is a temperature that can improve tumor oxygenation for up to 1-2 days. The potential usefulness of mild hyperthermia to enhance the response of human tumors to radiotherapy by improving tumor oxygenation merits continued investigation.     

Role of the DNA Base Excision Repair Protein,APE1 in Cisplatin,Oxaliplatin, or Carboplatin Induced Sensory Neuropathy

Although chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting side effect of platinum drugs, the mechanisms of this toxicity remain unknown. Previous work in our laboratory suggests that cisplatin-induced CIPN is secondary to DNA damage which is susceptible to base excision repair (BER). To further examine this hypothesis, we studied the effects of cisplatin, oxaliplatin, and carboplatin on cell survival, DNA damage, ROS production, and functional endpoints in rat sensory neurons in culture in the absence or presence of reduced expression of the BER protein AP endonuclease/redox factor-1 (APE1). Using an in situ model of peptidergic sensory neuron function, we examined the effects of the platinum drugs on hind limb capsaicin-evoked vasodilatation. Exposing sensory neurons in culture to the three platinum drugs caused a concentration-dependent increase in apoptosis and cell death, although the concentrations of carboplatin were 10 fold higher than cisplatin. As previously observed with cisplatin, oxaliplatin and carboplatin also increased DNA damage as indicated by an increase in phospho-H2AX and reduced the capsaicin-evoked release of CGRP from neuronal cultures. Both cisplatin and oxaliplatin increased the production of ROS as well as 8-oxoguanine DNA adduct levels, whereas carboplatin did not. Reducing levels of APE1 in neuronal cultures augmented the cisplatin and oxaliplatin induced toxicity, but did not alter the effects of carboplatin. Using an in vivo model, systemic injection of cisplatin (3 mg/kg), oxaliplatin (3 mg/kg), or carboplatin (30 mg/kg) once a week for three weeks caused a decrease in capsaicin-evoked vasodilatation, which was delayed in onset. The effects of cisplatin on capsaicin-evoked vasodilatation were attenuated by chronic administration of E3330, a redox inhibitor of APE1 that serendipitously enhances APE1 DNA repair activity in sensory neurons. These outcomes support the importance of the BER pathway, and particularly APE1, in sensory neuropathy caused by cisplatin and oxaliplatin, but not carboplatin and suggest that augmenting DNA repair could be a therapeutic target for CIPN.     

Adult Respiratory Distress Syndrome

Many causes for the adult respiratory distress syndrome (ARDS) have been reported, all with common pathologic, pathophysiologic and biochemical end results. The final common pathway may involve changes in lung content of a critical enzyme, superoxide dismutase, or alterations in surfactant metabolism, or both. The early assumption that the disorder is partially due to oxygen toxicity from inspired oxygen concentrations greater than 60 percent is consistent with findings of recent biochemical studies. Although the lung normally maintains its alveoli dry, during ARDS increased permeability of small pulmonary vessels results in primary pulmonary edema, in contrast to edema from increased vascular pressure. These data have been obtained mainly in animals; whether they apply to humans with ARDS is not certain. Tissue oxygenation is improved by increasing end-expiratory pressure in an animal model of ARDS, more effectively during spontaneous breathing than during mechanical ventilation. During spontaneous breathing, adverse ventilatory effects were caused by stimulation of pulmonary reflexes.     

Enhancement of tumor perfusion and oxygenation by carbogen and nicotinamide during single- and multifraction irradiation

Numerous experimental and clinical studies have been completed regarding the effects of carbogen and nicotinamide on tumor oxygenation and radiosensitivity. The current study incorporates three physiological measurement techniques to further define spatial variations in oxygen availability and development of hypoxia after single- and multifraction irradiation in KHT murine fibrosarcomas. Distances to anatomical and perfused blood vessels were measured using immunohistochemical and fluorescent staining, intravascular oxygen levels were determined cryospectrophotometrically, and tumor hypoxia was quantified using uptake of EF5, a marker of hypoxia. Carbogen, nicotinamide, and the combination of both all increased intravascular oxygen availability compared to controls. While nicotinamide had no effect on the number of perfused blood vessels in nonirradiated tumors, carbogen produced a substantial closing of vessels. After a single dose of 4 Gy, only the combination of nicotinamide and carbogen produced significant improvements in oxygen availability, while numbers of perfused vessels were significantly increased for nicotinamide, unchanged for the combination of nicotinamide and carbogen, and significantly decreased for carbogen. After 4 x 4-Gy fractions, oxygen availability was increased substantially with the combination of nicotinamide and carbogen, somewhat with carbogen, and not at all with nicotinamide. Tumor oxygenation changes were estimated by EF5/Cy3 intensity distributions, which demonstrated that manipulative agents could produce disparate effects on tumor hypoxia when combined with either single- or multifraction irradiation.     

Effect of a perfluorochemical emulsion on the radiation response of BA1112 rhabdomyosarcomas

The effect of treatment with a perfluorochemical emulsion (Fluosol DA, 20%), carbogen, or the combination of these two agents on the radiation response of BA1112 tumors in WAG/rij rats was examined. Fluosol and carbogen as single agents had only small effects on the tumor cell survival curve. The combination of Fluosol plus carbogen had a larger effect on tumor cell survival, reducing the hypoxic fraction of the tumor from 23 to 1.6%. The amount of sensitization was a function of the Fluosol dose, with maximal augmentation of the radiation response obtained at doses of 7.5-15 ml/kg. Carbogen pretreatments ranging from 5 to 60 min in duration all had similar effects on tumor radiosensitivity. The effect of the perfluorochemical emulsion plus carbogen on the survival of irradiated tumor cells appears to reflect changes in tumor oxygenation, rather than cytotoxic or immunological effects, since the perfluorochemical emulsion (with or without carbogen) had no effect on the viability of cells in unirradiated tumors. These experiments extend previous studies by ourselves and others using mouse tumors to show that the combination of a perfluorochemical emulsion and carbogen breathing can also increase the radiation response of a nonimmunogenic rat tumor.     

Preclinical studies of porfiromycin as an adjunct to radiotherapy

The bioreductive alkylating agent porfiromycin (POR) is more toxic to EMT6 cells that are hypoxic at the time of treatment than to aerobic cells. The toxicity of POR to hypoxic EMT6 cells in vitro was similar to that of mitomycin C (MC): the aerobic toxicity of POR was considerably less than that of MC. Treatment of cells in vitro with POR before and during irradiation did not sensitize either hypoxic or aerobic cells to X rays; instead, only additive cytotoxicity was produced. In contrast, treatment of solid EMT6 tumors in vivo with POR plus radiation produced supra-additive cytotoxicity, as assessed by analyses of the complete dose-response curves for the killing of tumor cells by radiation alone or by POR alone. The supra-additivity of the combination regimens appeared to reflect the preferential killing by each agent of those tumor cells which were in an environment conferring resistance to the other agent. In contrast, combinations of POR and X rays produced only additive cytotoxicities to marrow CFU-GM. Supra-additive antineoplastic effects were obtained at doses of POR which produced little hematologic or other host toxicity. The complementary cytotoxicities of radiation and POR to cells in different microenvironments in solid tumors and the absence of a similar effect in normal tissue make optimized regimens combining radiotherapy and POR unusually promising for the treatment of solid tumors.     

Regional tumor oxygenation and measurement of dynamic changes.

We recently described a novel approach to measuring regional tumor oxygen tension using (19)F pulse burst saturation recovery (PBSR) nuclear magnetic resonance (NMR) echo planar imaging (EPI) relaxometry of hexafluorobenzene. We now compare oxygen tension measurements in a group of size-matched R3327-AT1 Dunning prostate rat tumors made using this new method with those using a traditional polarographic method: the Eppendorf histograph. Similar oxygen tension distributions were found using the two methods, and both techniques showed that tumors with volume greater than 3.5 cm(3) were significantly (P < 0.0001) less well oxygenated than smaller tumors (volume less than 2 cm(3)). Using the (19)F EPI approach, we also examined the response to respiratory challenge. Increasing the concentration of inspired oxygen from 33% to 100% O(2) produced a significant increase (P < 0.0001) in tumor oxygenation for a group of small tumors. In contrast, no change was observed in the mean pO(2) for a group of large tumors. Consideration of individual tumor regions irrespective of tumor size showed a strong correlation between the maximum pO(2) observed when breathing 100% O(2) compared with mean baseline pO(2). These results further demonstrate the usefulness of (19)F EPI to assess changes in regional tumor oxygenation.     

Measuring tumor cycling hypoxia and angiogenesis using a side‐firing fiber optic probe

Hypoxia and angiogenesis can significantly influence the efficacy of cancer therapy and the behavior of surviving tumor cells. There is a growing demand for technologies to measure tumor hypoxia and angiogenesis temporally in vivo to enable advances in drug development and optimization. This paper reports the use of frequency‐domain photon migration with a side‐firing probe to quantify tumor oxygenation and hemoglobin concentrations in nude rats bearing human head/neck tumors administered with carbogen gas, cycling hypoxic gas or just room air. Significant increase (with carbogen gas breathing) or decrease (with hypoxic gas breathing) in tumor oxygenation was observed. The trend in tumor oxygenation during forced cycling hypoxia (CH) followed that of the blood oxygenation measured with a pulse oximeter. Natural CH was also observed in rats under room air. The studies demonstrated the potential of the technology for longitudinal monitoring of tumor CH during tumor growth or in response to therapy. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Cytotoxicity of carboplatin on human glioblastoma cells is reduced by the concomitant exposure to an extremely low-frequency electromagnetic field (50 Hz, 70 G)

Glioblastoma multiforme (GBM) is a malignant brain cancer that causes high mortality in patients. GBM responds weakly to the common cancer treatments such as chemotherapy and radiotherapy and even surgery. Carboplatin is an alkylating agent widely used to treat cancer. However, resistance to this drug is a common problem in its use in cancer treatment. Concomitant exposure to extremely low-frequency electromagnetic fields (ELF-EMFs) and carboplatin is one unexplored possibility for overcoming this resistance. Indeed, many lines of evidence show that EMF affects cancer cells and drug action. In this study, we evaluated the effect of concomitant administration of carboplatin and EMF (50 Hz, 70 G) and also concomitant administration of carboplatin and static magnetic field (SMF) (70 G) on human glioma cell line (U-87). The results showed that cotreatment reduced the efficiency of carboplatin in U-87 cells, by decreasing caspase-3 in comparison to drug groups. Overall, EMF reduced the apoptotic effect of carboplatin, possibly through a redox regulation mechanism. Therefore, we have to avoid coadministration of magnetic field (MF) and carboplatin in tumor area, because the MF decreased the toxicity of the drug. However, further studies are needed to reveal the action mechanism of this combination therapeutic method.     

Inhibition of ABC-transporter(s)' function in non-small cell lung cancer cells by platinum drugs]

With an account of the literature data that platinum drugs react with many cellular targets, including ATP and proteins, the authors suggested that disturbance of the function of energy-dependent ABC-transporters (markers of multidrug resistance, MDR) under the effect of platinum drugs could be a cause of increased efficacy of MDR agents (agents, MDR to which is developed by the classical mechanism) when used in combination with platinum drugs even in the treatment of multidrug resistant lung cancer. The cisplatin and carboplatin effect on accumulation of MDR doxorubicin in cells of non-small cell cancer was studied by flow cytometry with the use of biopsy specimens. The MDR phenotype of the tumors was determined by a change in doxorubicin intracellular accumulation under the action of the ABC-transporter(s)' inhibitors: verapamil and genistein (specific inhibitors of Pgp and MRP respectively) and sodium azide (an inhibitor of all energy-dependent ABC-transporters). The MDR phenotypes, i.e. Pgp-MRP+ or Pgp+MRP+, were detected in all the tumors investigated. Two types of changes in doxorubicin intracellular accumulation under the action of the inhibitors and the platinum drugs were shown: (a) an increase in doxorubicin cytoplasmic accumulation and (b) a change in subcellular distribution of the anthracycline (increased accumulation of doxorubicin in the cell nucleus and its higher binding to DNA). Cisplatin and carboplatin had an inhibitory effect on ABC-transporter(s) in all the tumors investigated but the effect of carboplatin was less pronounced. It was concluded that cisplatin and carboplatin stimulation of doxorubicin intracellular accumulation, as well as a change in subcellular distribution of the anthracycline under the action of the platinum drugs (increased doxorubicin accumulation in the cell nucleus) in multidrug resistant lung tumors could be at least partly explained by inhibition of the MDR transporter(s)' function. The results could provide a basis for the use of the sequential combination cisplatin (or carboplatin)-->doxorubicin in the treatment of multidrug resistant lung cancer.     

Comparisons among pimonidazole binding, oxygen electrode measurements, and radiation response in C3H mouse tumors.

Pimonidazole binding was compared with oxygen electrode measurements and with measurements of the radiobiologically hypoxic fraction in C3H mammary tumors in which oxygenation was manipulated by means of subjecting tumor-bearing CDF1 mice to air breathing, carbogen breathing, oxygen breathing, hydralazine injection or tumor clamping. Hypoxia measured by pimonidazole binding could be correlated with both pO2 (r2 = 0.81) and radiobiologically hypoxic fraction (r2 = 0.85) in this system. The scope and limitation of pimonidazole as an immunohistochemical marker for tumor hypoxia is discussed.     

Effects of radiation on tumor intravascular oxygenation, vascular configuration, development of hypoxia, and clonogenic survival

The underlying physiological mechanisms leading to tumor reoxygenation after irradiation have elicited considerable interest, but they remain somewhat unclear. The current study was undertaken to determine the effects of a single dose of 10 Gy gamma radiation on both tumor pathophysiology and radiobiologically hypoxic fraction. Immunohistochemical staining and perfusion markers were used to quantify tumor vasculature, uptake of the hypoxia marker EF5 to assess the distribution of hypoxia, and intravascular HbO(2) measurements to determine oxygen availability. Tumor radiosensitivity was measured by a clonogenic assay. At 24 h postirradiation, oxygen availability increased, perfused vessel numbers decreased, EF5 uptake decreased, and the radiobiologically hypoxic fraction was unchanged. Together, these results demonstrate that tumor hypoxia develops at an increased distance from perfused blood vessels after irradiation, suggesting a decrease in oxygen consumption at 24 h. By 72 h postirradiation, all physiological parameters had returned to the levels in volume-matched, nonirradiated controls. These studies clearly show that single measures of either tumor oxygenation or vascular structure are inadequate for assessing the effects of radiation on tumor clonogenicity. Although such direct measurements have previously proven valuable in predicting tumor response to therapy or oxygen manipulation, a combination of parameters is required to adequately describe the mechanisms underlying these changes after irradiation.     

Tropisetron attenuates tumor growth and progression in an experimental model of mouse lung cancer

The antineoplastic effects of 5-hydroxytryptamine (5-HT) receptor antagonists have been shown in previous studies. However, the exact underlying mechanisms mediating these antineoplastic effects are unclear. In the present study, we assessed the antineoplastic effects of tropisetron, a 5-HT receptor antagonist, in an experimental model of lung cancer in BALB/c mouse. Lewis lung carcinoma cell line was used to induce lung cancer. Mice were divided into four groups (n = 6) as follows: tumor-bearing mice + tropisetron (5 mg/kg intraperitoneally [IP]), tumor-bearing mice + tropisetron (10 mg/kg IP), tumor-bearing mice + saline, healthy mice + tropisetron (10 mg/kg). Tumor burden, interferon-γ (IFN-γ), interleukin (IL)-4, pathological response, Ki-67, and E-cadherin were assessed using enzyme-linked immunosorbent assay, and real-time polymerase chain reaction. Comet assay was used to assess DNA toxicity. Tropisetrone-treated animals (either 5 or 10 mg/kg) showed significantly lower tumor sizes at the day 24th after tumor induction. Tropisetron received animals also showed significantly higher levels of IFN-γ, E-cadherin, pathologic response, and necrotic cells compared to the saline-treated counterparts. In addition, the levels of IL-4, and Ki-67 were significantly lower in tropisetrone treated mice in comparison with control. Furthermore, tropisteron coadministration signifcantly reduced H₂O₂-induced DNA toxicity while treatment with tropisteron alone showed no adverse effect on DNA. Tropisetrone can be used as a potential antineoplastic drug in lung cancer. This agent can promote its antineoplastic effects in part through modulating inflammatory and proliferating markers.     

Effects of the calcium channel blocker flunarizine on the hemodynamics and oxygenation of tumor microvasculature.

Flunarizine is a diphenylpiperazine calcium entry blocker that has been shown previously to increase tumor blood flow and sensitivity to radiotherapy via reduction in the radiobiologically significant hypoxic fraction. Two mechanisms of action have been proposed previously (vasodilation, altered blood viscosity), but no studies have been performed to examine its mechanisms of action in vivo. Such information would be invaluable in determining the role of flunarizine in multimodality approaches to reduce tumor hypoxia. Fisher-344 rats bearing R3230Ac tumors transplanted into dorsal flap window chambers were used to examine microcirculatory changes after administration of flunarizine (1.0 mg/kg, iv). The drug increased the diameters of the microvasculature and red cell velocities specifically in central tumor regions (producing an average increase in vessel flow by a factor of 1.96), which was accompanied by an increase in perivascular pO2 of 12 mm Hg, on the average. The drug did not change the diameters of tumor "feeding" vessels, nor did it change vascular length densities. Thus the improvement in central tumor blood flow and oxygenation could not be attributed to dilation of feeding vessels. The oxygen-carrying capacity of the blood was not altered either since hemoglobin saturation (measured in vitro) and the hematocrits of the microvasculature were unchanged after drug administration. Therefore, by a process of elimination, the most likely explanation for the effect of the drug is modification of blood viscosity. Additional studies are under way in this laboratory to examine whether changes in viscosity occur after flunarizine administration.     

Correlation of tumor oxygen dynamics with radiation response of the dunning prostate R3327-HI tumor

Our previous studies have shown that oxygen inhalation significantly reduces tumor hypoxia in the moderately well-differentiated HI subline of the Dunning prostate R3327 rat carcinoma. To test our hypothesis that modifying hypoxia could improve the radiosensitivity of these tumors, we performed experimental radiotherapy to compare the tumor response to ionizing radiation alone or in combination with oxygen inhalation. Tumor pO(2) measurements were performed on size-selected tumors several hours before radiotherapy using (19)F nuclear magnetic resonance echo planar imaging relaxometry (FREDOM) of the reporter molecule hexafluorobenzene. In common with our previous findings, the larger tumors (>3.5 cm(3)) exhibited greater hypoxia than the smaller tumors (<2 cm(3); P < 0.001), and oxygen inhalation reduced the hypoxic fraction (<10 Torr): In the larger tumors, hypoxic fraction dropped significantly from a mean baseline value of 80% to 17% (P < 0.001). The effect of oxygen administered 30 min before and during irradiation on tumor response to a single 30-Gy dose of photons was evaluated by growth delay. For the smaller tumors, no difference in growth delay was found when treatment was given with or without oxygen breathing. By contrast, breathing oxygen before and during irradiation significantly enhanced the growth delay in the larger tumors (additional 51 days). The differential behavior may be attributed to the low baseline hypoxic fraction (<10 Torr) in small tumors (20%) as a target for oxygen inhalation. There was a strong correlation between the estimated initial pO(2) value and the radiation-induced tumor growth delay (R > 0.8). Our histological studies showed a good match between the perfused vessels marked by Hoechst 33342 dye and the total vessels immunostained by anti-CD31 and indicated extensive perfusion in this tumor line. In summary, the present results suggest that the ability to detect modulation of tumor pO(2), in particular, the residual hypoxic fraction, with respect to an intervention, could have prognostic value for predicting the efficacy of radiotherapy.     

Recent Progress in the Treatment of Advanced Prostate Cancer With Intermittent Dose-Intense Calcitriol (DN-101)

Docetaxel is becoming standard therapy for androgen-independent prostate cancer (AIPC), and investigational agents are being added to docetaxel to assess potential additive effects and synergy. Although one of these agents, calcitriol, has repeatedly demonstrated antiproliferative properties against cancer of the prostate, breast, colon, and lung, the antineoplastic activity of calcitriol requires superphysiologic levels. Unfortunately, chronic exposure to superphysiologic levels of calcitriol causes hypercalcemia and resulting toxicity. Therefore, a host of analogues of calcitriol have been investigated for antineoplastic function, including intermittent dose-intense calcitriol, or DN-101. Because of encouraging results from phase II studies of DN-101 combined with docetaxel, the ASCENT (AIPC Study of Calcitriol Enhancement of Taxotere) phase II trial investigated docetaxel plus DN-101 versus docetaxel plus placebo in 250 men with metastatic AIPC and an abnormal baseline prostate-specific antigen (PSA) level. Although the ASCENT trial did not achieve its primary endpoint for increased PSA response, there was a significant trend in PSA response rate in the DN-101 arm. DN-101 in combination with docetaxel seems to improve overall survival and, interestingly, has a favorable safety profile compared with docetaxel alone. The DN-101/docetaxel combination is currently being studied in a much larger international trial, ASCENT-2.     

Mini-review: discovery and development of platinum complexes designed to circumvent cisplatin resistance

The discovery and development of new platinum-containing anticancer drugs have represented an integral part of anticancer drug development at the Institute of Cancer Research, Sutton, over almost 20 years. As part of a collaboration with chemists at Johnson Matthey, later AnorMED, four major new classes of platinum drug have been discovered, three of which have entered clinical trial. Earlier studies led to the clinical development of the less toxic analogue carboplatin and JM216, the first orally administerable platinum drug. In recent years, the focus has been on two lead complexes designed to overcome the major mechanisms of tumour resistance to cisplatin: JM335 (trans-ammine (cyclohexylaminedichlorodihydroxo) platinum(IV)), an active trans platinum complex; and ZD0473 (cis-amminedichloro(2-methylpyridine) platinum(II)), a sterically hindered complex shown to be less reactive towards thiol-containing molecules than cisplatin. JM335 shows some circumvention of acquired cisplatin resistance in vitro and exhibits unique cellular pharmacological properties in comparison to cisplatin or its cis-isomer in terms gene-specific repair of adducts on DNA and the rate of induction of apoptosis. ZD0473 is now in phase I clinical trial. Myelosuppression is the dose-limiting toxicity at a dose of 130 mg/m2 given i.v. every 3 weeks and there has been evidence of antitumour activity. ZD0473-resistant human ovarian carcinoma cell lines have been established in vitro. Some mechanisms of resistance common to those described for cisplatin (decreased drug uptake, increased glutathione) have been observed plus, in one cell line, increased BCL2 levels and loss of the DNA mismatch repair protein MLH1.     

Apparent synergism between radiation and the carcinogen 1,2-dimethylhydrazine in the induction of colonic tumors in rats

We have evaluated the interaction of radiation and 1,2-dimethylhydrazine (DMH) with respect to colon carcinogenesis in the Fischer 344 rat and have demonstrated the utility of this model for future more detailed mechanistic studies. In initial experiments, single doses of abdomen-only radiation (9 Gy) or DMH (150 mg/kg) were employed alone or in combination. Radiation was administered 3.5 days prior to the DMH. At 8 months post-treatment, the incidence of DMH-induced colon tumors was doubled by prior radiation exposure. When the protocol was repeated employing a DMH dose of 135 mg/kg with a 6-month observation period, the incidence of tumors induced by DMH alone was reduced, but the combination of radiation plus DMH still resulted in an augmentation of tumor incidence. When the protocol of radiation plus DMH was repeated three times at monthly intervals, a 15-fold increase in tumor incidence (from 5 to 74%) was observed at 6 months post-treatment. This finding demonstrates an apparent synergy between the radiation and the chemical carcinogen. Throughout these studies, the appearance of carcinomas was associated with preexisting colonic lymphoid nodules. The reproducibility of tumor induction as well as range of tumor incidence generated by variations in this system may be adequately sensitive to examine the combination of much lower doses of radiation and/or chemical carcinogen. The relationship between existing lymphoid aggregates which alter local epithelial cell kinetics and which are associated with fenestrations in the basement membrane, and the development of colon cancer in congruent sites may assist in defining dose-response curves for combined agents as well as providing a system for evaluating the mechanisms underlying their interactions.