Potential for a novel manganese porphyrin compound as adjuvant canine lymphoma therapy.

PURPOSE: Manganese porphyrins are redox-active drugs and superoxide dismutase mimics, which have been shown to chemosensitize lymphoma, a cancer which frequently occurs in dogs. This study aimed to identify critical information regarding the pharmacokinetics and toxicity of Mn(III) meso-tetrakis (N-n-butoxyetylpyridium-2-yl) porphyrin, (MnTnBuOE-2-PyP5+, MnBuOE) in dogs as a prelude to a clinical trial in canine lymphoma patients. METHODS: A single-dose pharmacokinetic (PK) study in normal dogs was performed to determine the plasma half-life (t 1/2) of MnBuOE. A dose reduction study was performed to establish the maximum tolerated dose (MTD) of MnBuOE. The safety and PK of a multi-dosing protocol was assessed. RESULTS: Peak plasma drug concentration occurred 30 min post-injection. The t 1/2 was defined as 7 h. MnBuOE induced an anaphylactic reaction and prolonged tachycardia. The MTD was defined as 0.25 mg/kg. The dogs were given MTD 3×/week for 2-3 weeks. The highest recorded tissue drug levels were in the lymph nodes (4-6 µM), followed by kidney and liver (2.5, 2.0 uM, respectively). CONCLUSIONS: We obtained critical information regarding the PK and toxicity of MnBuOE in dogs. The acute drug reaction and tachycardia post-injection have not been described in other species and may be specific to canines. The high tissue drug levels in lymph nodes have not been previously reported. MnBuOE accumulation in lymph nodes has important implications for the utility of adjuvant MnBuOE to treat lymphoma. With MnBuOE lymph node accumulation, reduction in the dose and/or administration frequency could be possible, leading to reduced toxicity.

[Is the determination of the defibrillation threshold in patients with an implantable cardioverter-defibrillator still required?]. / Wird die Bestimmung der Defibrillationsschwelle bei Patienten mit implantierbarem Kardioverter/Defibrillator noch benötigt?

BACKGROUND: Intraoperative testing of implantable cardioverter-defibrillators (ICDs) is time consuming and associated with risks. In the present study, we elucidated whether the initial implantation of an ICD with high energy output makes intraoperative defibrillation threshold testing (DFTT) unnecessary even though antiarrhythmic (AA) therapy is needed in the future. METHODS: A total of 111 patients (94 men, 17 women) receiving an ICD with subsequent AA therapy (mexiletine, amiodarone, sotalol, flecainide) were analyzed retrospectively. DFT was performed during ICD implantation and after AA drug therapy. In a second step, DFT results from the study cohort were analyzed for implantation of virtual ICDs with either low (≤ 30 J, LOD), intermediate (34 J, IOD), or high energy output (36 J, HOD). RESULTS: In the study cohort, all patients reached the safety margin (SM) of 10 J between DFT and maximal shock energy of the ICD. After loading of AA agents, 6 patients (12%) with a LOD, 3 patients (11%) with an IOD, and 3 (13%) patients with a HOD failed the 10 J SM. Using virtual ICDs, 6 (5.5%) patients with a LOD, 1 patient (1%) with an IOD, and no patients with a HOD would have failed the 10 J SM. After loading of AA agents, 18 patients (16%) with a virtual LOD, 12 patients (10.8%) with an IOD, and still 9 patients (8%) with a HOD would have failed the 10 J SM. CONCLUSION: Our results demonstrate that the 10 J SM would have been achieved intraoperatively in all patients with virtual HOD ICDs. Thus, determination of the DFT during implantation does not seem to be obligatory. However, in patients receiving AA agents, DFT testing is still required.

Enhanced tumour uptake of radiolabelled antibodies by hyperthermia: Part I: Timing of injection relative to hyperthermia.

Improving drug and macromolecular delivery of anti-cancer agents to tumours results in greater efficacy without increased toxicity. The current study was undertaken to assess the effects of the timing of injection of tumour specific and non-specific monoclonal antibodies (mAbs) relative to a hyperthermia treatment on tumour and normal tissue uptake. Using a local hyperthermia protocol of 45 min at 43 degrees C, uptake in tumour and normal tissues was measured at 1, 4, 12, 24, 48 and 72 h after injection. An anti-tenascin chimeric mAb, ch81C6, served as the specific mAb in a D-54 MG glioma xenograft mouse model. The chimeric mAb chTPS3.2 served as the control. A five-to-eight-fold increase in uptake of the tumour-targeted mAb was achieved in the heated tumours when compared with the non-heated tumours at 1 h. Differences in absolute tumour uptake of the specific mAb between the mice injected prior to hyperthermia and mice injected post-hyperthermia were seen only at 1 and 12 h. The median uptakes in the tumours of mice injected pre-heat were 25%ID/g at 1 h and 43.5%ID/g at 12 h, while in the animals injected post-hyperthermia the median uptakes were 45.5%ID/g and 80.2%ID/g, respectively. Blood levels of both the specific and non-specific mAbs were consistently higher over the initial 12 h period in the mice injected post-hyperthermia. Normal tissue uptake was also increased at most time points in the mice injected post-hyperthermia. The clinical importance of the differences in specific mAb uptake in tumour detected statistically at 1 and 12 h is questionable, given the highly variable nature of mAb uptake in vivo. Tumour targeting mAbs administered in combination with heat may be injected either prior to or immediately following hyperthermia treatment, with the expectation that levels of uptake in tumour will be relatively equivalent. Absolute normal tissue levels will be higher in patients receiving the mAb post-hyperthermia.

Enhanced tumour uptake of radiolabelled antibodies by hyperthermia. Part II: Application of the thermal equivalency equation.

Clinical application of local hyperthermia as a means for modulating drug and macro-molecular tumour uptake have been slow to develop, due in part to the difficulty in designing and comparing heating protocols. The thermal isodose formula developed by Sapareto and Dewey is used in cytotoxicity and radiosensitization hyperthermia protocols to compare different time/temperature combinations; however, its relevance to other end-points has not been evaluated. The current study was undertaken to determine whether heating protocols of different time and temperature, but predicted to be thermally equivalent by this formula, had similar effects on the tumour and normal tissue distribution of radiolabelled tumour-specific (anti-tenascin 81C6) and non-specific (anti-dansyl TPS3.2) monoclonal antibodies (mAbs). Two thermally equivalent heating protocols, 4 h at 41.8 degrees C and 45 min at 43 degrees C, were compared in mice with subcutaneous D54 MG human glioma xenografts. A 4-fold increase in xenograft localization of 81C6 mAb was achieved relative to that in non-heated control groups with both heating protocols. Both hyperthermia protocols also resulted in improved tumour:normal tissue ratios. However, differences in absolute tumour and normal tissue uptake were seen, suggesting that the thermal isodose formula has limited usefulness in the design and comparison of hyperthermia protocols for enhancing the tumour uptake of radiolabelled mAbs.

The effects of local hyperthermia on the catabolism of a radioiodinated chimeric monoclonal antibody.

Local hyperthermia has been shown to increase the tumor uptake and tumor:normal tissue ratios of radiolabeled monoclonal antibodies (mAbs) in athymic mouse xenograft models. The current study was undertaken to determine whether this behavior was related in part to alterations in mAb catabolism by local hyperthermia. Human/mouse chimeric 81C6 mAb reactive with tenascin and a nonspecific control mAb were labeled with 125I using Iodo-Gen and given to separate groups of athymic mice bearing s.c. D-54 MG human glioma xenografts. Half of the animals were then subjected to 4-h tumor-localized hyperthermia at 41.8 degrees C, a protocol previously shown to enhance the specific tumor uptake of the mAb in this xenograft model. The tumor, serum, liver, kidney, and urine were collected from heated as well as control animals 4 and 24 h after injection of the mAb and analyzed by SDS-PAGE and trichloroacetic acid precipitation. At 24 h, a significantly higher percentage of 81C6 was present as intact mAb in the tumors harvested from heated animals compared with those from controls. Unexpectedly, intact mAb was found in the urine of mice immediately after hyperthermia, but not in unheated control animals. We conclude that local hyperthermia decreases the catabolism of the mAb in the tumor and increases the urinary excretion of the mAb through a transient increase in glomerular permeability.

Cytotoxicity of alpha-particle-emitting astatine-211-labelled antibody in tumour spheroids: no effect of hyperthermia.

The high linear energy transfer, alpha-particle-emitting radionuclide astatine-211 (211At) is of interest for certain therapeutic applications; however, because of the 55- to 70-microm path length of its alpha-particles, achieving homogeneous tracer distribution is critical. Hyperthermia may enhance the therapeutic efficacy of alpha-particle endoradiotherapy if it can improve tracer distribution. In this study, we have investigated whether hyperthermia increased the cytotoxicity of an 211At-labelled monoclonal antibody (MAb) in tumour spheroids with a radius (approximately 100 microm) greater than the range of 211At alpha-particles. Hyperthermia for 1 h at 42 degrees C was used because this treatment itself resulted in no regrowth delay. Radiolabelled chimeric MAb 81C6 reactive with the extracellular matrix antigen tenascin was added to spheroids grown from the D-247 MG human glioma cell line at activity concentrations ranging from 0.125 to 250 kBq ml(-1). A significant regrowth delay was observed at 125 and 250 kBq ml(-1) in both hyperthermia-treated and untreated spheroids. For groups receiving hyperthermia, no increase in cytotoxicity was seen compared with normothermic controls at any activity concentration. These results and those from autoradiographs indicate that hyperthermia at 42 degrees C for 1 h had no significant effect on the uptake or distribution of this antitenascin MAb in D-247 MG spheroids.

A local hyperthermia treatment which enhances antibody uptake in a glioma xenograft model does not affect tumour interstitial fluid pressure.

Solid tumours have an elevated interstitial fluid pressure (IFP) due to the lack of normal lymphatics, increased permeability of tumour vasculature and an expanding cell population within a potentially limited space. This elevated IFP has been proposed to be an important barrier to the delivery of drugs and marcromolecules. We have demonstrated that local hyperthermia (4 h, 41.8 degrees C) is capable of significantly enhancing the uptake of radiolabelled monoclonal antibodies (mAbs) in D-54 MG glioma xenografts grown subcutaneously in athymic mice. To determine if this increased uptake was attributable to alterations in the tumour IFP, pressure measurements using the wick-in-needle technique were made in tumours after hyperthermia treatment. These pressure measurements were taken at various time points from 4 to 90 h following the initiation of the hyperthermia and compared with pressures taken concurrently in untreated tumours. In addition, pressures were measured following a 2 h, 41.8 degrees C hyperthermia treatment, a protocol which does not result in elevated uptake of radiolabeled mAbs. No significant differences were seen at any time point in IFP measured in the tumours receiving either hyperthermia treatment when compared with untreated tumours. Thus, we conclude that the mechanism by which this hyperthermia regimen enhances mAb uptake in this human glioma xenograft model is not due to alternations in tumour IFP.

Local hyperthermia improves uptake of a chimeric monoclonal antibody in a subcutaneous xenograft model.

This study was undertaken to determine the effect of local hyperthermia on the tissue distribution of a chimeric human/mouse IgG2 monoclonal antibody, 81C6, reactive with the extracellular matrix protein tenascin, which is expressed at high levels in gliomas, carcinomas of the breast and prostate, and other neoplasms. The D-54 MG s.c. glioma xenograft was treated with hyperthermia by immersion of the tumor-bearing leg in a circulating water bath. By 4 h after injection (immediately after heating), administration of chimeric 125I-labeled 81C6 (ch81C6) concomitantly with a 4-h local hyperthermia treatment at 41.8 degreesC resulted in an increase in tumor uptake of monoclonal antibody from a median of 12% of injected dose/g of tumor in normothermic mice to 42% of injected dose/g in mice receiving local hyperthermia. The increased level of uptake persisted in the heated tumors over the first 48 h and at 96 h. Additionally, heating increased the tumor:blood ratio of ch81C6 more than 7-fold at 4 h postinjection. The rate of uptake was also dramatically improved, with 60 and 90% of the maximum level of uptake achieved by 4 and 24 h, respectively, in the hyperthermia-treated mice, whereas the normothermic mice reached only 31 and 69% of their maximum uptake at those time points. In summary, local hyperthermia enhanced the absolute level and the rate of tumor uptake as well as tumor:normal tissue ratios for ch81C6. This approach may facilitate the clinical application of radionuclides with shorter half-lives, such as 211At, for the therapy of solid malignancies.

The effects of clinically relevant hyperthermic temperatures on the kinetic binding parameters of a monoclonal antibody.

Hyperthermia is a therapeutic modality under investigation for its ability to increase absolute levels of tumor uptake of radiolabeled monoclonal antibodies (MAbs). We have investigated whether hyperthermia may affect the binding parameters of MAbs. The effects of clinically relevant levels of hyperthermia on the kinetic binding parameters were investigated for 81C6, an antibody undergoing Phase I/II clinical trials for the treatment of brain tumors and neoplastic meningitis. No obvious effects of temperature in either the association or dissociation rate constants, nor in the equilibrium constants, were apparent between 37 degrees and 45 degrees C. The improved binding stability of the bivalent form of the MAb was apparent when compared with its monovalent Fab fragment.

Laparoscopic implantation of temporary electrodes for bladder stimulation in dogs.

Five female mongrel dogs were used in an acute animal experiment. Under general anesthesia two monopolar wire electrodes armed with needles on either side were implanted into the bladder wall, the leads of both electrodes were then pulled through the abdominal wall. Filling of the bladder and intravesical pressure measurement were achieved through a suprapublic percutaneous cystostomy. Electrostimulation was carried out using the XEJ-2 experimental electroejaculator (biphasic pulses, pulse width 2.5 msec, approximately 70 mAmp, 50 Hz). The pressure changes within the bladder following electrostimulation were recorded, the effect of stimulation was observed endoscopically. Electrostimulation of the bladder wall resulted in micturition in all cases, showing an initial pressure peak at the commencement of electrostimulation followed by a decrease after onset of evacuation. We believe that laparoscopic implantation of temporary wire electrodes followed by percutaneous electrostimulation may open up new possibilities for bladder rehabilitation as well as for diagnostic investigations into the contractile capabilities of the bladder.

Effect of whole body hyperthermia on carboplatin disposition and toxicity in dogs.

Fifty dogs with refractory or disseminated spontaneous tumours were evaluated in two independent phase I studies using either carboplatin (CBDCA) alone or CBDCA plus whole body hyperthermia (WBH). CBDCA was administered as a 30 min infusion at the onset of the plateau phase of WBH in dogs receiving combined treatment. Serum samples were collected and drug disposition was determined in both treatment groups. The dose-effect relationship was mathematically described with a logistic regression model developed from categorical toxicity data accumulated throughout the first two treatment courses in all dogs. The maximum tolerated dose (MTD) was defined as that dose which resulted in a 50% probability of achieving moderate or severe toxicity. The only toxicities observed were neutropenia and thrombocytopenia, which were dose-dependent. The nadir occurred between 7 and 14 days following treatment. A significant decrease in the area under the serum CBDCA versus time curve for dogs undergoing WBH was consistent with increased tissue binding of the drug as well as increased urinary eliminations. Serum AUC values determined following the first course of treatment were predictive of subsequent toxicity in both treatment groups. The MTD (95%CI) for CBDCA and CBDCA/WBH were estimated to be 318(44) and 239(51) mg/M2 respectively (p = 0.08). A randomized phase II evaluation should be initiated to determine if a therapeutic gain can be achieved using combined CBDCA and WBH. Further refinement of the CBDCA dose in such a trial should be based on both pharmacokinetic parameters and normal tissue response.

Quantitative estimation of the thermal dose-modifying factor for cis-diamminedichloroplatinum (CDDP) in tumour-bearing dogs.

A statistical method for estimating clinical toxicity was used to determine a theoretical isoeffect dose-modifying factor for dogs with disseminated or refractory neoplasia treated with cis-diammine dichloroplatinum (II) plus whole-body hyperthermia or CDDP alone. CDDP was administered every 3 weeks with vigorous saline hydration to 54 dogs (CDDP alone n = 21, CDDP/WBH n = 33) that were eligible for entry into this non-randomized study. CDDP was administered during the plateau phase of WBH in dogs receiving combined therapy. Acute toxicity included myelosuppression (CDDP n = 7; CDDP/WBH n = 5), nephrotoxicity (CDDP n = 1, CDDP/WBH n = 1) and respiratory distress (CDDP/WBH n = 2). Eight dogs experienced chronic renal dysfunction as a result of CDDP (n = 2) or CDDP/WBH (n = 6). A theoretical thermal dose-modifying factor was determined for both acute and cumulative toxicity by comparing the maximum tolerated dose of each treatment group. The maximum tolerated dose (MTD) of CDDP +/- WBH was defined as that dose producing a 50% incidence of moderate acute toxicity or acute plus mild chronic toxicity as estimated from logistic regression analysis of the toxicity data. The MTD (+/- .standard error) of CDDP/WBH for acute toxicity only was 54.6 (4.3) mg/M2 and for CDDP alone the MTD was 73.6 (40) mg/M2. Thus, the isoeffect dose-modifying factor for acute toxicity was 1.35 (0.12). The MTD (SE) of CDDP/WBH for cumulative toxicity (acute plus chronic toxicity) was 46.4 (2.7) mg/M2 and for CDDP alone waas 70.0 (2.9) mg/M2. The isoeffect dose-modifying factor for total cumulative toxicity was 1.5 (0.1).(ABSTRACT TRUNCATED AT 250 WORDS)