Intra-cerebral ventricular infusion of 5-iodo-2-deoxyuridine (IUDR) as a radiosensitizer in the treatment of a rat glioma

Body weight algorithm predicts humane endpoint in an intracranial rat glioma model

Humane endpoint determination is fundamental in animal experimentation. Despite commonly accepted endpoint criteria for intracranial tumour models (20% body weight loss and deteriorated clinical score) some animals still die before being euthanized in current research. We here systematically evaluated other measures as surrogates for a more reliable humane endpoint determination. Adult male BDIX rats (n = 119) with intracranial glioma formation after BT4Ca cell-injection were used. Clinical score and body weight were assessed daily. One subgroup (n = 14) was assessed daily for species-specific (nesting, burrowing), motor (distance, coordination) and social behaviour. Another subgroup (n = 8) was implanted with a telemetric device for monitoring heart rate (variability), temperature and activity. Body weight and clinical score of all other rats were used for training (n = 34) and validation (n = 63) of an elaborate body weight course analysis algorithm for endpoint detection. BT4Ca cell-injection reliably induced fast-growing tumours. No behavioural or physiological parameter detected deteriorations of the clinical state earlier or more reliable than clinical scoring by experienced observers. However, the body weight course analysis algorithm predicted endpoints in 97% of animals without confounding observer-dependent factors. Clinical scoring together with the novel algorithm enables highly reliable and observer-independent endpoint determination in a rodent intracranial tumour model.

Impact of IUdR on Rat 9L glioma cell survival for 25-35 keV photon-activated auger electron therapy

The goal of the current study was to measure the energy dependence of survival of rat 9L glioma cells labeled with iododeoxyuridine (IUdR) that underwent photon-activated Auger electron therapy using 25-35 keV monochromatic X rays, i.e., above and below the K-edge energy of iodine. Rat 9L glioma cells were selected because of their radioresistance, ability to be implanted for future in vivo studies and analogy to radioresistant human gliomas. Survival curves were measured for a 4 MV X-ray beam and synchrotron produced monochromatic 35, 30 and 25 keV X-ray beams. IUdR was incorporated into the DNA at levels of 0, 9 and 18% thymidine replacement for 4 MV and 35 keV and 0 and 18% thymidine replacement for 30 and 25 keV. For 10 combinations of beam energy and thymidine replacement, 62 data sets (3-13 per combination) provided 776 data points (47-148 per combination). Survival versus dose data taken for the same combination, but on different days, were merged by including the zero-dose points in the nonlinear, chi-squared data fitting using the linear-quadratic model and letting the best estimate to the zero-dose plating efficiency for each of the different days be a fitting parameter. When comparing two survival curves, the ratio of doses resulting in 10% survival gave sensitization enhancement ratios (SER10) from which contributions due to linear energy transfer (LET) (SER10,LET), IUdR radiosensitization (SER10,RS), the Auger effect (SER10,AE) and the total of all effects (SER10,T) were determined. At 4 MV and 35, 30 and 25 keV, SER10,LET values were 1.00, 1.08 ± 0.03, 1.22 ± 0.02 and 1.37 ± 0.02, respectively. At 4 MV SER10,RS values for 9 and 18% IUdR were 1.28 ± 0.02 and 1.40 ± 0.02, respectively. Assuming LET effects were independent of percentage IUdR and radiosensitization effects were independent of energy, SER10,AE values for 18% IUdR at 35, 30 and 25 keV were 1.35 ± 0.05, 1.06 ± 0.03 and 0.98 ± 0.03, respectively. The value for 9% IUdR at 35 keV was 1.01 ± 0.04. First, we found the radioresistant rat 9L glioma cell line exhibited an SER10 due to the Auger effect of 1.35 at (35 keV, 18% IUdR) and an SER10 due to the radiosensitizing effect of 1.40 at (4 MV, 18% IUdR), both significantly less than values for previously reported cell lines. These low individual values emphasize the benefit of their combined value (SER10 of approximately 1.9) for achieving clinical benefit. Second, as expected, we observed that energies below the K-edge of iodine (25 and 30 keV), for which there are L, M and higher shell photoelectric events creating Auger electrons, show no promise for Auger electron therapy. Third, to proceed with future in vivo studies, additional data from 35-65 keV are needed to determine the optimal X-ray energy for IUdR Auger electron therapy. Only then can there be an answer to the question, how well the energy dependence of in vitro survival data supports the potential for photon-activated Auger electron therapy with IUdR in cancer radiotherapy.

Dependence of cell survival on iododeoxyuridine concentration in 35-keV photon-activated Auger electron radiotherapy

PURPOSE

To measure and compare Chinese hamster ovary cell survival curves using monochromatic 35-keV photons and 4-MV x-rays as a function of concentration of the radiosensitizer iododeoxyuridine (IUdR).

METHODS AND MATERIALS

IUdR was incorporated into Chinese hamster ovary cell DNA at 16.6 ± 1.9%, 12.0 ± 1.4%, and 9.2 ± 1.3% thymidine replacement. Cells were irradiated from 1 to 8 Gy with 35-keV synchrotron-generated photons and conventional radiotherapy 4-MV x-rays. The effects of the radiation were measured via clonogenic survival assays. Surviving fraction was plotted vs. dose and fit to a linear quadratic model. Sensitization enhancement ratios (SER(10)) were calculated as the ratio of doses required to achieve 10% surviving fraction for cells without and with DNA-incorporated IUdR.

RESULTS

At 4 MV, SER(10) values were 2.6 ± 0.1, 2.2 ± 0.1, and 1.5 ± 0.1 for 16.6%, 12.0%, and 9.2% thymidine replacement, respectively. At 35 keV, SER(10) values were 4.1 ± 0.2, 3.0 ± 0.1, and 2.0 ± 0.1, respectively, which yielded SER(10) ratios (35 keV:4 MV) of 1.6 ± 0.1, 1.4 ± 0.1, and 1.3 ± 0.1, respectively.

CONCLUSIONS

SER(10) increases monotonically with percent thymidine replacement by IUdR for both modalities. As compared to 4-MV x-rays, 35-keV photons produce enhanced SER(10) values whose ratios are linear with percent thymidine replacement and assumed to be due to Auger electrons contributing to enhanced dose to DNA. Although this Auger effectiveness factor is less than the radiosensitization factor of IUdR, both could be important for the clinical efficacy of IUdR radiotherapy.

Simultaneous alteration of de novo and salvage pathway to the deoxynucleoside triphosphate pool by (E)-2'-deoxy-(fluoromethylene)cytidine (FMdC) and zidovudine (AZT) results in increased radiosensitivity in vitro

To test whether a thymidine analog zidovudine (=AZT), is able to modify the radiosensitizing effects of (E)-2'-Deoxy-(fluoromethylene)cytidine (FMdC). A human colon cancer cell line Widr was exposed for 48 hours prior to irradiation to FMdC. Zidovudine was added at various concentrations immediately before irradiation. We measured cell survival and the effect of FMdC, AZT and FMdC + AZT on deoxynucleotide triphosphate pool. FMdC results in a significant increase of radiosensitivity. The enhancement ratios (ER =surviving fraction irradiated cells/surviving fraction drug treated and irradiated cells), obtained by FMdC or AZT alone are significantly increased by the combination of both compounds. Adding FMdC to AZT yields enhancement ratios ranging from 1.25 to 2.26. FMdC reduces dATP significantly, with a corresponding increase of TTP, dCTP and dGTP. This increase of TTP, dCTP and dGTP is abolished with the addition of AZT. Adding AZT to FMdC results in a significant increase of the radiosensitizing effect of FMdC. This combination appears to reduce the reactive enhancement of TTP, dCTP and dGTP induced by FMdC while it does not affect the inhibitory effect on dATP.

Enhanced Prospects for Drug Delivery and Brain Targeting by the Choroid Plexus–CSF Route

The choroid plexus (CP), i.e., the blood-cerebrospinal fluid barrier (BCSFB) interface, is an epithelial boundary exploitable for drug delivery to brain. Agents transported from blood to lateral ventricles are convected by CSF volume transmission (bulk flow) to many periventricular targets. These include the caudate, hippocampus, specialized circumventricular organs, hypothalamus, and the downstream pia-glia and arachnoid membranes. The CSF circulatory system normally provides micronutrients, neurotrophins, hormones, neuropeptides, and growth factors extensively to neuronal networks. Therefore, drugs directed to CSF can modulate a variety of endocrine, immunologic, and behavioral phenomema; and can help to restore brain interstitial and cellular homeostasis disrupted by disease and trauma. This review integrates information from animal models that demonstrates marked physiologic effects of substances introduced into the ventricular system. It also recapitulates how pharmacologic agents administered into the CSF system prevent disease or enhance the brain's ability to recover from chemical and physical insults. In regard to drug distribution in the CNS, the BCSFB interaction with the blood-brain barrier is discussed. With a view toward translational CSF pharmacotherapy, there are several promising innovations in progress: bone marrow cell infusions, CP encapsulation and transplants, neural stem cell augmentation, phage display of peptide ligands for CP epithelium, CSF gene transfer, regulation of leukocyte and cytokine trafficking at the BCSFB, and the purification of neurotoxic CSF in degenerative states. The progressively increasing pharmacological significance of the CP-CSF nexus is analyzed in light of treating AIDS, multiple sclerosis, stroke, hydrocephalus, and Alzheimer's disease.

Polyamines in brain tumor therapy

In the search for ways to augment current brain tumor therapies many have sought to exploit the fact that adult brain tissue is virtually lacking in cell division. This endorses a special appeal to therapeutic approaches which target the dependence on cell division for brain tumor growth. Polyamines play an essential role in the proliferation of mammalian cells and depletion results in inhibition of growth. As a result, there are investigations into the feasibility of controlling tumor growth by targeting the enzymes in polyamine metabolism with specific enzyme inhibitors. DFMO, an inhibitor of putrescine synthesis, is a cytostatic agent which in combination with tritiated radioemitters or cytotoxic agents such as, MGBG or BCNU is an effective antitumor agent, but the effectiveness of DFMO in vivo is reduced by tumor cell uptake of polyamines released into the circulation by normal cells and from gut flora or dietary sources. However, DFMO therapy combined with elimination of exogenous polyamines inhibits tumor growth but also results in body weight loss, reduced protein synthesis and evidence of toxicity. Furthermore, tumor growth recurs upon termination of treatment. In contrast, competitive polyamine analogs function in the homeostatic regulation of polyamine synthesis but fail to fulfill the requirements for growth and they continue to inhibit tumor growth for several weeks after cessation of treatment. Analogs are now in clinical trials. However, their action may be highly specific and differ from one cell type to another. We suggest that the effectiveness of polyamine based therapy would be enhanced by two approaches: local delivery by intracerebral microdialysis and tumor cell killing by internal radioemitters such as tritiated putrescine or tritiated thymidine which are taken up in increased amounts by polyamine depleted tumor cells. The growth inhibition by polyamine depletion prevents the dilution of the radioactive putrescine and thymidine. The overload of radioactivity kills the growth inhibited cells so that growth cannot recur when treatment terminates.

Effect of D,L-alpha-difluoromethylornithine (DFMO) enhanced [3H]putrescine uptake on 9L tumor cell growth and colony forming efficiency

PURPOSE

This study explored the possible use of D,L- alpha-difluoromethylornithine (DFMO) to enhance the uptake of [3H] putrescine in order to selectively kill brain tumor cells.

METHODS AND MATERIALS

Gliosarcoma cells (9L) were grown for 4 or 20 day periods in monolayer cultures with or without [3H] putrescine and/or DFMO. Cells in culture incubated for 20 days were replated at 4-day intervals. Cells were counted on a Coulter Electronic Particle Counter and percent viability was determined by eosin dye exclusion. Survival of cells with proliferative capacity was assayed by their colony. Forming ability and surviving fraction was calculated. The radioactive counts due to [3H] putrescine were measured in 9L cells and in medium and expressed as cpm/100 cells or cpm/ml, respectively.

RESULTS

As previously reported (15), DFMO treatment resulted in termination of cell proliferation that was reversible by the addition of exogenous putrescine. Specifically, after 4 days in culture, cell counts in groups exposed to 10 mM DFMO were 55% of those in control groups and addition of 3 mM putrescine reversed the DFMO effects. Uptake of [3H] putrescine into untreated cells increased in proportion to the amount of exogenous putrescine present during 4 days of culture (range 0.01 nmol to 100 nmol) and the presence of DFMO in the medium enhanced the uptake 9 fold throughout these ranges. At activities greater than 100 cpm/100 cells the cell count was reduced to 23 to 48% of control after 4 days in culture. Extending the treatment to 20 days of incubation increased the killing of 9L cells. During the 20-day incubation, control cells increased from 5 x 10(5) to 13 x 10(12) of which 90% were colony forming cells. Treatment with either 25 microCi [3H] putrescine or 1 mM DFMO for 4 days followed by removal of these agents and incubation for an additional 16 days for a total of 20 days resulted in 31 x 10(8) or 18 x 10(7) colony forming cells, respectively. Combining [3H] putrescine and DFMO treatments during the first 4 days of the 20 day incubation reduced the colony forming cells to 21 x 10(5) (surviving fraction to 67%). When the DFMO treatment was present during the entire 20 days, it became cytotoxic since the colony forming cells were reduced to 35 x 10(3) (surviving fraction was 17%). The combination of the 4-day [3H putrescine and the 20 day DFMO treatments resulted in only 1200 surviving colony forming cells (surviving fraction was only 2%).

CONCLUSION

DFMO treatment of 9L cells for 20 days resulted in increased uptake of [3H] putrescine, a 10(10) fold inhibition of colony forming cells and extensive 9L cell killing relative to untreated controls.