Effects of Motexafin gadolinium on tumor metabolism and radiation sensitivity

Inhibition of the thioredoxin system for radiosensitization therapy of cancer

Radiotherapy (RT) stands as a cornerstone in the clinical armamentarium against various cancers due to its proven efficacy. However, the intrinsic radiation resistance exhibited by cancer cells, coupled with the adverse effects of RT on normal tissues, often compromises its therapeutic potential and leads to unwanted side effects. This comprehensive review aims to consolidate our understanding of how radiosensitizers inhibit the thioredoxin (Trx) system in cellular contexts. Notable radiosensitizers, including gold nanoparticles (GNPs), gold triethylphosphine cyanide ([Au(SCN) (PEt3)]), auranofin, ceria nanoparticles (CONPs), curcumin and its derivatives, piperlongamide, indolequinone derivatives, micheliolide, motexafin gadolinium, and ethane selenide selenidazole derivatives (SeDs), are meticulously elucidated in terms of their applications in radiotherapy. In this review, the sensitization mechanisms and the current research progress of these radiosensitizers are discussed in detail, with the overall aim of providing valuable insights for the judicious application of Trx system inhibitors in the field of cancer radiosensitization therapy.

Targeting antioxidant enzymes as a radiosensitizing strategy

Radiotherapy represents a major anti-cancer modality and effectively kills cancer cells through generation of reactive oxygen species (ROS). However, cancer cells are commonly characterized by increased activity of ROS-scavenging enzymes in adaptation to intrinsic oxidative stress, leading to radioresistance. Abrogation of this defense network by pharmacological ROS insults therefore is shown to improve radioresponse in preclinical models; some of them are then tested in clinical trials. In this review, we address (1) the importance of ROS in radioresponse, (2) the main systems regulating redox homeostasis with a special focus on their prognostic effect and predictive role in radiotherapy, and (3) the potential radiosensitizers acting through inhibition of antioxidant enzymes.

Efficacy and safety of antitumor agents plus radiotherapy compared with radiotherapy alone for brain metastases from lung cancer

The present study aimed to investigate the efficacy and safety of different therapeutic regimens for brain metastases (BMs) from lung cancer (LC). A total of 13 controlled trials (1,783 cases) involving chemotherapy, tyrosine kinase inhibitors or endostatin plus radiotherapy (combination group) vs. radiotherapy alone group were identified from PubMed. Compared with the radiotherapy alone group, the combination group resulted in a significant benefit for objective response rate (ORR) [risk ratio (RR), 1.38; 95% confidence interval (CI), 1.19–1.60; P<0.0001], notably prolonged the time to central nervous system progression [CNS-TTP; hazard ratio (HR), 0.71; 95% CI, 0.57–0.90; P=0.004] and progression-free survival (PFS; HR, 0.60; 95% CI, 0.44–0.83; P=0.002); however, failed in prolonging the overall survival (OS; HR, 0.80; 95% CI, 0.61–1.05; P=0.11) with a higher overall severe adverse events (AEs, Grade ≥3; RR, 2.57; 95% CI, 1.24–5.35; P=0.01). Notably, subgroup analysis demonstrated that targeted therapy plus radiotherapy possessed a superior OS compared with radiotherapy alone (HR, 0.58; 95% CI, 0.37–0.90; P=0.01) with mild non-hematological toxicity and without severe hematotoxicity. The present study demonstrated that targeted agents plus radiotherapy possessed desirable effects with mild adverse events. Secondary to best, chemoradiotherapy is an alternative option for patients without suitable molecular targets.

Gliomas: Motexafin Gadolinium-enhanced Molecular MR Imaging and Optical Imaging for Potential Intraoperative Delineation of Tumor Margins

PURPOSE

To investigate the possibility of using motexafin gadolinium (MGd)-enhanced molecular magnetic resonance (MR) imaging and optical imaging to identify the true margins of gliomas.

MATERIALS AND METHODS

The animal protocol was approved by the institutional animal care and use committee. Thirty-six Sprague-Dawley rats with gliomas were randomized into six groups of six rats. Five groups were euthanized 15, 30, 60, 120, and 240 minutes after intravenous administration of 6 mg/kg of MGd, while one group received only saline solution as a control group. After craniotomy, optical imaging and T1-weighted MR imaging were performed to identify the tumor margins. One-way analysis of variance was used to compare optical photon intensity and MR imaging signal-to-noise ratios. Histologic analysis was performed to confirm the intracellular uptake of MGd by tumor cells and to correlate the tumor margins delineated on both optical and MR images.

RESULTS

Both optical imaging and T1-weighted MR imaging showed tumor margins. The highest optical photon intensity (2.6 × 10(8) photons per second per mm(2) ± 2.3 × 10(7); analysis of variance, P < .001) and MR signal-to-noise ratio (77.61 ± 2.52; analysis of variance, P = .006) were reached at 15-30 minutes after administration of MGd, with continued tumor visibility at 2-4 hours. Examination with confocal microscopy allowed confirmation that the fluorescence of optical images and MR imaging T1 enhancement exclusively originated from MGd that accumulated in the cytoplasm of tumor cells.

CONCLUSION

MGd-enhanced optical and MR imaging can allow determination of glioma tumor margins at the optimal time of 15-120 minutes after administration of MGd. Clinical application of these results may allow complete removal of gliomas in a hybrid surgical setting in which intraoperative optical and MR imaging are available.

Motexafin-gadolinium and involved field radiation therapy for intrinsic pontine glioma of childhood: a children's oncology group phase 2 study

PURPOSE

To evaluate the effects on 1-year event-free survival (EFS) and overall survival (OS) of combining motexafin and gadolinium (MGd), a potent radiosensitizer, with daily fractionated radiation therapy in children with newly diagnosed intrinsic pontine gliomas.

METHODS AND MATERIALS

Patients with newly diagnosed intrinsic pontine glioma were treated with MGd daily for 5 consecutive days each week, for a total of 30 doses. Patients received a 5- to 10-min intravenous bolus of MGd, 4.4 mg/kg/day, given 2 to 5 h prior to standard dose irradiation. Radiation therapy was administered at a daily dose of 1.8 Gy for 30 treatments over 6 weeks. The total dose was 54 Gy.

RESULTS

Sixty eligible children received MGd daily, concurrent with 6 weeks of radiation therapy. The estimated 1-year EFS was 18%±5%, and the estimated 1-year OS was 53%±6.5%. The most common grade 3 to 4 toxicities were lymphopenia, transient elevation of liver transaminases, and hypertension.

CONCLUSIONS

Compared to historical controls, the addition of MGd to a standard 6-week course of radiation did not improve the survival of pediatric patients with newly diagnosed intrinsic pontine gliomas.

Multicenter phase II trial of Motexafin gadolinium and pemetrexed for second-line treatment in patients with non-small cell lung cancer

BACKGROUND

Motexafin gadolinium (MGd) disrupts redox-dependent pathways by inhibiting oxidative stress-related proteins leading to apoptosis. MGd selectively targets tumor cells, disrupting energy metabolism and repair mechanisms, rendering cells more prone to apoptosis. Preclinical studies with MGd and pemetrexed show significant tumor growth delay in lung cancer cell lines.

METHODS

Patients with non-small cell lung cancer, Eastern Cooperative Oncology Group performance status 0 to 1, who had received one previous platinum containing regimen and normal organ function were treated with MGd 15 mg/kg and pemetrexed 500 mg/m q21days. Patients were allowed to receive more than one regimen if the initial treatment was in the adjuvant or curative setting and administered >12 months earlier. The primary end point was to demonstrate a 40% rate of 6-month progression free survival (PFS).

RESULTS

Seventy-two patients (30 women, 42 men), performance status 0/1 (30/42), and a median age of 63 years were enrolled. Most patients (96%) were current or former smokers. All histologic types were represented (squamous/adenocarcinoma/other: 28%, 42%, 31%). Number of prior regimens: 1: 69%; 2: 26%, and >2: 4%. Median number of cycles administered was (range) 2 (1-12).

TOXICITY

grade 3/4 neutropenia was noted in 8.3% with febrile neutropenia in 1.4%, thrombocytopenia in 8.3%, fatigue in 9.7%, and pneumonia in 11.1%. There were no complete responses, 8.1% had partial response, 56.5% had stable disease, and 35.5% had progressive disease as their best response. Twenty-three percent of patients were progression free at 6 months and the median PFS was 2.6 months with an overall survival of 8.1 months.

CONCLUSIONS

The combination of MGd and pemetrexed was well tolerated with toxicity similar to that of pemetrexed alone. However, the study did not achieve its end point of 40% 6-month PFS. The response rate, PFS, and overall survival did not seem markedly different than prior phase II and phase III studies of pemetrexed alone. Consequently, there are no further plans for development of this combination.

Six degrees of separation: the oxygen effect in the development of radiosensitizers

The popular theory six degrees of separation is used in this review as an analogy to relate all radiosensitization to oxygen. As the prime mover of all radiosensitizers, the pervasive influence of oxygen has consciously or unconsciously influenced the direction of research and development and provided the benchmark against which all other compounds and approaches are measured. It is the aim of this review to develop the six degrees of separation from oxygen analogy as a unifying framework for conceptually organizing the field and for giving context to its varied subspecializations and theories. Under such a framework, it would become possible for one area to consider questions and problems found in other areas of radiosensitization, using a common analogy, that would allow for further development and unification of this multifaceted discipline. In this review, approaches to the development of radiosensitizers and the current state of research in this field are discussed, including promising new agents in various stages of clinical development.

Safety and feasibility of motexafin gadolinium administration with whole brain radiation therapy and stereotactic radiosurgery boost in the treatment of ≤ 6 brain metastases: a multi-institutional phase II trial

To determine the safety, tolerability, and report on secondary efficacy endpoints of motexafin gadolinium (MGd) in combination with whole-brain radiotherapy (WBRT) and stereotactic radiosurgery (SRS) for patients with ≤ 6 brain metastases. We conducted an international study of WBRT (37.5 Gy in 15 fractions) and SRS (15-21 Gy) with the addition of MGd (5 mg/kg preceding each fraction beginning week 2). The primary endpoint was to evaluate the rate of irreversible grade 3 or any grade ≥ 4 neurotoxicity and establish feasibility in preparation for a phase III trial. Sixty-five patients were enrolled from 14 institutions, of which 45 (69%) received SRS with MGd as intended and were available for evaluation. Grade ≥ 3 neurotoxicity attributable to radiation therapy within 3 months of SRS was seen in 2 patients (4.4%), including generalized weakness and radionecrosis requiring surgical management. Immediately following the course of MGd plus WBRT, new brain metastases were detected in 11 patients (24.4%) at the time of the SRS treatment planning MRI. The actuarial incidence of neurologic progression at 6 months and 1 year was 17 and 20%, respectively. The median investigator-determined neurologic progression free survival and overall survival times were 8 (95% CI: 5-14) and 9 months (95% CI: 6-not reached), respectively. We observed a low rate of neurotoxicity, demonstrating that the addition of MGd does not increase the incidence or severity of neurologic complications from WBRT with SRS boost.

Ascorbate and endocytosed Motexafin gadolinium induce lysosomal rupture

Motexafin gadolinium (MGd) sensitizes malignant cells to ionizing radiation, although the underlying mechanisms for uptake and sensitization are both unclear. Here we show that MGd is endocytosed by the clathrin-dependent pathway with ensuing lysosomal membrane permeabilization, most likely via formation of reactive oxygen species involving redox-active metabolites, such as ascorbate. We propose that subsequent apoptosis is a synergistic effect of irradiation and high MGd concentrations in malignant cells due to their pronounced endocytic activity. The results provide novel insights into the mode of action of this promising anti-cancer drug, which is currently under clinical trials.

The novel expanded porphyrin, motexafin gadolinium, combined with [90Y]ibritumomab tiuxetan for relapsed/refractory non-Hodgkin's lymphoma: preclinical findings and results of a phase I trial

PURPOSE

Therapeutic strategies to enhance the efficacy of radioimmunotherapy have not been explored. Motexafin gadolinium is a novel anticancer agent that targets redox-dependent pathways and enhances sensitivity of tumor cells to ionizing radiation.

EXPERIMENTAL DESIGN

We did preclinical studies examining motexafin gadolinium combined with rituximab and/or radiation in lymphoma cells. We subsequently completed a phase I clinical trial combining escalating doses of motexafin gadolinium concurrently with standard [(90)Y]ibritumomab tiuxetan for patients with relapsed/refractory non-Hodgkin's lymphoma.

RESULTS

In HF1 lymphoma cells, motexafin gadolinium and rituximab resulted in synergistic cytotoxicity (combination index, 0.757) through a mitochondrial-mediated caspase-dependent pathway, whereas cell death in Ramos and SUDHL4 cells was additive. Motexafin gadolinium/rituximab combined with radiation (1-3 Gy) resulted in additive apoptosis. Twenty-eight of 30 patients were evaluable on the phase I clinical trial. Median age was 65 years (47-87 years), and histologies were marginal-zone (n = 1), mantle-cell (n = 3), diffuse large cell (n = 6), and follicular lymphoma (n = 18). Of all patients, 86% were rituximab refractory. Therapy was well tolerated, and no dose-limiting toxicity was seen. Overall response rate was 57% [complete remission (CR), 43%], with median time-to-treatment failure of 10 months (1-48+ months) and median duration-of-response of 17 months. Of note, all responses were documented at 4 weeks. Furthermore, in rituximab-refractory follicular lymphoma (n = 14), overall response rate was 86% (CR, 64%), with a median time-to-treatment failure of 14 months (2-48+ months).

CONCLUSIONS

This represents the first report of a novel agent to be combined safely concurrently with radioimmunotherapy. Furthermore, tumor responses with [(90)Y]ibritumomab tiuxetan/motexafin gadolinium were prompt with a high rate of CRs, especially in rituximab-refractory follicular lymphoma.

On the path to seeking novel radiosensitizers

Radiation therapy is a highly effective cancer treatment modality, and extensive investigations have been undertaken over the years to augment its efficacy in the clinic. This review summarizes the current understanding of the biologic bases underpinning many of the clinically used radiosensitizers. In addition, this review illustrates how the advent of innovative, high-throughput technologies with integration of different disciplines could be harnessed for an expeditious discovery process for novel radiosensitizers, providing an exciting future for such pursuits in radiation biology and oncology.

Motexafin gadolinium for the treatment of metastatic renal cell carcinoma: phase II study results

BACKGROUND

Thioredoxin reductase (Trx) has been implicated in activation of hypoxia-inducible factor-1alpha, which is overexpressed in > 85% of renal cell carcinomas (RCCs). We evaluated the safety and efficacy of motexafin gadolinium (MGd), a Trx inhibitor, as a single-agent therapy for metastatic RCC.

PATIENTS AND METHODS

Patients with metastatic RCC were infused daily with MGd 5 mg/kg on days 1-5 and days 15-19 of each 28-day cycle. Patients were evaluated for response on days 21-28 of every third cycle. Those with tumor response or stable disease (SD) continued treatment for < or = 12 cycles. Twenty-five patients with confirmed metastatic RCC were enrolled. All were evaluable for toxicity, and 20 were evaluable for response.

RESULTS

While no clinical responses were observed, 8 patients had SD after 3 treatment cycles, as did 4 after 6 cycles. Median overall survival was 10.1 months, and median progression- free survival was 2.7 months. The most common treatment-related toxicities were grade 1/2 pain, nausea, skin discoloration, fatigue, blisters, and headache. The most common grade 3 toxicity was hypophosphatemia, observed in 5 patients. MGd was reasonably tolerated, and disease stabilization was observed in several patients with metastatic RCC.

CONCLUSION

These results show promise for the use of MGd in combination with other molecularly targeted therapies in previously treated patients with metastatic RCC. However, further investigation of MGd alone for metastatic RCC is not recommended.

CHAINED LIGHTNING

RADIOSURGERY IS FUNDAMENTALLY the harnessing of energy and delivering it to a focal target for a therapeutic effect. The evolution of radiosurgical technology and practice has served toward refining methodologies for better conformal energy delivery. In the past, this has resulted in developing strategies for improved beam generation and delivery. Ultimately, however, our current instrumentation and treatment modalities may be approaching a practical limit with regard to further optimizing energy containment.

In looking forward, several strategies are emerging to circumvent these limitations and improve conformal radiosurgery. Refinement of imaging techniques through functional imaging and nanoprobes for cancer detection may benefit lesion localization and targeting. Methods for enhancing the biological effect while reducing radiation-induced changes are being examined through dose fractionation schedules. Radiosensitizers and photosensitizers are being investigated as agents for modulating the biological response of tissues to radiation and alternative energy forms. Discovery of new energy modalities is being pursued through development of microplanar beams, free electron lasers, and high-intensity focused ultrasound. The exploration of these future possibilities will provide the tools for radiosurgical treatment of a broader spectrum of diseases for the next generation.

Results of the phase I dose-escalating study of motexafin gadolinium with standard radiotherapy in patients with glioblastoma multiforme

PURPOSE

Motexafin gadolinium (MGd) is a putative radiation enhancer initially evaluated in patients with brain metastases. This Phase I trial studied the safety and tolerability of a 2-6-week course (10-22 doses) of MGd with radiotherapy for glioblastoma multiforme.

METHODS AND MATERIALS

A total of 33 glioblastoma multiforme patients received one of seven MGd regimens starting at 10 doses of 4 mg/kg/d MGd and escalating to 22 doses of 5.3 mg/kg/d MGd (5 or 10 daily doses then three times per week). The National Cancer Institute Cancer Therapy Evaluation Program toxicity and stopping rules were applied.

RESULTS

The maximal tolerated dose was 5.0 mg/kg/d MGd (5 d/wk for 2 weeks, then three times per week) for 22 doses. The dose-limiting toxicity was reversible transaminase elevation. Adverse reactions included rash/pruritus (45%), chills/fever (30%), and self-limiting vesiculobullous rash of the thumb and fingers (42%). The median survival of 17.6 months prompted a case-matched analysis. In the case-matched analysis, the MGd patients had a median survival of 16.1 months (n = 31) compared with the matched Radiation Therapy Oncology Group database patients with a median survival of 11.8 months (hazard ratio, 0.43; 95% confidence interval, 0.20-0.94).

CONCLUSION

The maximal tolerated dose of MGd with radiotherapy for glioblastoma multiforme in this study was 5 mg/kg/d for 22 doses (daily for 2 weeks, then three times weekly). The baseline survival calculations suggest progression to Phase II trials is appropriate, with the addition of MGd to radiotherapy with concurrent and adjuvant temozolomide.

Noninvasive and nondestructive optical spectroscopic measurement of motexafin gadolinium in mouse tissues: comparison to high-performance liquid chromatography

Efficient design of anti-cancer treatments involving radiation- and photo-sensitizing therapeutics requires knowledge of tissue-specific drug concentrations. This study investigates the use of the optical pharmacokinetic system (OPS) to measure concentrations of the anti-cancer agent motexafin gadolinium (MGd) in mouse tissues noninvasively and nondestructively using elastic-scattering spectroscopy. The magnitude of MGd absorbance was quantitated by integration of the MGd peak absorbance area, and MGd concentrations were estimated by comparison with standard curves that were validated by high performance liquid chromatography (HPLC). In tissue-simulating phantoms in vitro, MGd peak absorbance area correlated with MGd concentration. Female C.B-17 SCID mice, bearing subcutaneous MDA-MB-231 human breast cancer xenografts, were dosed with 23 mg/kg MGd i.v. At specific times between 5 min and 24h after dosing, noninvasive OPS measurements were made on skin overlaying the subcutaneous tumor and skin on the opposite flank in vivo, and following exsanguination, nondestructive measurements were made on tumor, skin, and internal tissues in situ. OPS measurements on tissues in vivo detected MGd present in both tissue and blood perfusing the tissue. Both the OPS and the HPLC detected selective localization of MGd in malignant tissues compared with surrounding non-malignant tissues, and neither technique detected MGd in brain tissue. Comparison of MGd concentrations measured by HPLC and OPS is complicated by mismatch between measured tissue volumes, heterogeneous spatial distribution of MGd in tissues, and blood-localized MGd at early time points. Tumor-specific MGd concentrations measured by HPLC correlated with those measured by OPS in vivo and in situ. Best fit lines to the concentration estimates (forced through zero) had slopes of 0.900 and 1.185, respectively; however, the variability was significant (r(2)=0.477 and 0.269). The clinical utility of the OPS to quantitate MGd concentrations remains to be validated.

Chemical radiosensitizers for use in radiotherapy

Radiosensitizers are intended to enhance tumour cell killing while having much less effect on normal tissues. Some drugs target different physiological characteristics of the tumour, particularly hypoxia associated with radioresistance. Oxygen is the definitive hypoxic cell radiosensitizer, the large differential radiosensitivity of oxic vs hypoxic cells being an attractive factor. The combination of nicotinamide to reduce acute hypoxia with normobaric carbogen breathing is showing clinical promise. 'Electron-affinic' chemicals that react with DNA free radicals have the potential for universal activity to combat hypoxia-associated radioresistance; a nitroimidazole, nimorazole, is clinically effective at tolerable doses. Hypoxia-specific cytotoxins, such as tirapazamine, are valuable adjuncts to radiotherapy. Nitric oxide is a potent hypoxic cell radiosensitizer; variations in endogenous levels might have prognostic significance, and routes to deliver nitric oxide specifically to tumours are being developed. In principle, many drugs can be delivered selectively to hypoxic tumours using either reductase enzymes or radiation-produced free radicals to activate drug release from electron-affinic prodrugs. A redox-active agent based on a gadolinium chelate is being evaluated clinically. Pyrimidines substituted with bromine or iodine are incorporated into DNA and enhance free radical damage; fluoropyrimidines act by different mechanisms. A wide variety of drugs that influence the nature or repair of DNA damage are being evaluated in conjunction with radiation; it is often difficult to define the mechanisms underlying chemoradiation regimens. Drugs being evaluated include topoisomerase inhibitors (e.g. camptothecin, topotecan), and the hypoxia-activated anthraquinone AQ4N; alkylating agents include temozolomide. Drugs involved in DNA repair pathways being investigated include the potent poly(ADP ribose)polymerase inhibitor, AG14,361. Proteins involved in cell signalling, such as the Ras family, are attractive targets linked to radioresistance, as are epidermal growth factor receptors and linked kinases (drugs including vandetanib [ZD6,474], cetuximab and gefitinib), and cyclooxygenase-2 (celecoxib). The suppression of radioprotective thiols seems to offer more potential with alkylating agents than with radiotherapy, although it remains a strategy worthy of exploration.

Motexafin gadolinium: A novel redox active drug for cancer therapy

Motexafin gadolinium (MGd, Xcytrin) is an aromatic macrocycle that has a strong affinity for electrons, i.e., it is easily reduced. In the presence of oxygen, MGd accepts electrons from various cellular reducing metabolites and forms superoxide and other reactive oxygen species (ROS) by redox cycling. The reaction with NADPH is dramatically accelerated by various oxido-reductases including thioredoxin reductase. In vitro studies with various cancer cell lines have shown an increase in ROS and intracellular free zinc in cells treated with MGd. MGd increases cytotoxicity of ionizing radiation and various chemotherapy agents and may be directly cytotoxic to tumor cells under certain conditions. MGd selectively localizes in tumors, perhaps due to their metabolic perturbations. MGd treatment in murine models enhances tumor response to radiation and chemotherapy agents. In controlled, randomized clinical trials, combining MGd treatment with ionizing radiation improves time to neurologic progression in lung cancer patients with brain metastases. The molecular target for MGd appears to be thioredoxin reductase which, when inhibited, results in cellular redox stress, cytotoxicity and an increase in tumor responsiveness to a variety of treatments.

Motexafin gadolinium modulates levels of phosphorylated Akt and synergizes with inhibitors of Akt phosphorylation

Motexafin gadolinium (MGd, Xcytrin) is a tumor-selective expanded porphyrin that targets oxidative stress-related proteins. MGd treatment of the follicular lymphoma-derived cell line HF-1 resulted in growth suppression and apoptosis whereas MGd treatment of the Burkitt's lymphoma-derived cell line Ramos resulted in growth suppression but not apoptosis. Because phosphorylation status of Akt/protein kinase B is regulated by oxidative stress, we monitored total and phosphorylated Akt (pAkt) in MGd-treated HF-1 and Ramos cells. Levels of pAkt increased within 30 minutes after MGd treatment of HF-1 but after 4 hours began to show a progressive decline to below baseline levels before cells underwent apoptosis. In MGd-treated Ramos cells, pAkt increased approximately 2-fold within 4 hours and remained persistently elevated. Because pAkt activates survival pathways, we determined if MGd-induced cell death could be enhanced by inhibiting phosphorylation of Akt. The addition of specific inhibitors of Akt phosphorylation (Akt inhibitor 1 or SH-5) reduced pAkt levels in MGd-treated HF-1 and Ramos cells and synergistically enhanced MGd-induced cell death. MGd was also evaluated in combination with celecoxib, an inhibitor of Akt phosphorylation, or docetaxel, a microtubule inhibitor that can decrease Akt phosphorylation. The combination of MGd/celecoxib or MGd/docetaxel resulted in decreased Akt phosphorylation and in synergistic cytotoxicity compared with either agent alone. These data point to a potential protective role for pAkt in MGd-induced apoptosis and suggest that MGd activity may be enhanced by combining it with agents that inhibit Akt phosphorylation.

State of the art chemotherapeutic management of pediatric brain tumors

CNS tumors are the most common solid tumor of childhood. This article will review current treatments for pediatric brain tumors; low-grade gliomas, high-grade gliomas, medulloblastomas and ependymomas. It will also highlight the treatments that are used for brain tumors in very young children and in children with recurrent brain tumors. The management of recurrent pediatric brain tumors unresponsive to standard therapy will be discussed. The agents used in this setting are mainly biological modifiers, which attempt to provide molecularly targeted therapy. Future directions of therapy for pediatric brain tumors are described. Future treatment paradigms will need to consider examining the use of multiple biological modifiers. Similarly, these agents will need to be examined in combination with cytotoxic chemotherapy. Finally, the future direction of pediatric neuro-oncology and the focus of the field as it battles pediatric brain tumors is discussed.

MRI measurement of the uptake and retention of motexafin gadolinium in glioblastoma multiforme and uninvolved normal human brain

PURPOSE

Motexafin gadolinium (MGd) is an investigational pharmaceutical with radiation enhancing properties. Magnetic Resonance Imaging (MRI) was used to measure brain and tumor MGd levels to evaluate (1) the degree to which MGd passes through the intact blood brain barrier, and (2) the retention of MGd in tumor in patients with glioblastoma multiforme (GBM).

METHODS AND MATERIALS

MRI studies were performed on GBM patients who participated in a phase I clinical trial in which MGd was given during standard fractionated radiation therapy. MGd was administered daily (Monday to Friday) for five or 10 doses as a loading regimen, followed by three times per week dosing as a maintenance schedule. T1-weighted MRI was performed at intervals throughout the course of the MGd administration and radiation therapy in the 33 participating patients. Eleven patients had pre- and post-MGd scans, allowing for study of MGd's normal blood brain barrier penetration. Twenty-two patients had adequate residual tumor for measurements to evaluate MGd retention in tumor during the course of MGd and radiation administration.

RESULTS AND CONCLUSIONS

The studies of uninvolved brain tissue support the conclusion that MGd does not cross the intact blood brain barrier in detectable quantities. The tumor study showed MGd uptake during loading and maintenance without measurably significant fall off on non-dosage days during the maintenance dosing. Although the number of cases is small, the 10-day loading regimen showed greater drug loading and retention compared with the 5 days loading regimen.

Population pharmacokinetics and bioavailability of motexafin gadolinium (Xcytrin®) in CD1 mice following intravenous and intraperitoneal injection

Motexafin gadolinium (Xcytrin) is an expanded porphyrin macrocyclic compound under development for the treatment of several types of cancer. Currently clinical trials and non-clinical pharmacology and toxicology studies are ongoing. The goals of this open label, four arm, non-crossover bioavailability study were to explore motexafin gadolinium pharmacokinetics, determine the i.p. bioavailability, and define a pharmacokinetic model suitable for descriptive and predictive use. Mice received one or seven daily i.v. or i.p. injections (40 mg/kg) then blood samples were collected and analyzed. Plasma concentration data were modelled using population pharmacokinetic methods and a two compartment model was the most appropriate model. The stability and predictive performance of the model were evaluated using bootstrap procedures. The accuracy of the predicted concentrations was 8.3%. Motexafin gadolinium was rapidly cleared from the plasma and although T(1/2beta) was 12.9 h there was no accumulation following seven doses. The i.p. bioavailability was 87.4% and higher plasma concentrations were sustainable for a longer period with i.p. dosing. V(c) was larger than the blood volume and the tissue compartment volume was 38% of V(c), suggesting motexafin gadolinium was not widely distributed into less well perfused tissues. The pharmacokinetic profile in this study was similar to that in oncology patients administered multiple doses of motexafin gadolinium. The unbiased model yields reliable parameter estimates and insight into the pharmacokinetics of motexafin gadolinium in mice, is suitable for both descriptive and predictive purposes, and is a valuable tool in the planning, analysis, and interpretation of pharmacology and toxicology studies in mice.

The treatment of high grade gliomas and diffuse intrinsic pontine tumors of childhood and adolescence: a historical - and futuristic - perspective

Pediatric high grade gliomas represent a heterogeneous group of tumors with poor prognoses despite the use of multimodal treatment. Very little progress has been made over the past decades in identifying efficacious therapeutic modalities against both high grade gliomas and diffuse brainstem gliomas in children. The degree of surgical resection is the most important clinical prognostic factor for children with high grade gliomas, and a complete resection should be attempted whenever feasible. The role of radiation therapy in the treatment of older children with high grade gliomas and diffuse brain stem gliomas is undisputed; however the benefit of using radiation for patients less than 6 years of age (with high grade gliomas) might be questionable. Despite the absence of solid evidence to support its use, chemotherapy is routinely used against these tumors. Currently temozolomide is being investigated due to its activity in adult trials and based on preliminary data regarding recurrent disease. A small subgroup of patients can be successfully treated with high dose chemotherapy followed by autologous stem cell rescue. Early trials using this modality in the past had been associated with high morbidity and mortality. High dose chemotherapy with autologous stem cell rescue in selected patients with minimal residual disease, angiogenesis inhibitors, radiosensitizers and other biological modifiers are being currently investigated in phase I/II trials.

Motexafin gadolinium, a tumor-selective drug targeting thioredoxin reductase and ribonucleotide reductase

Motexafin gadolinium (MGd) is a chemotherapeutic drug that selectively targets tumor cells and mediates redox reactions generating reactive oxygen species. Thioredoxin (Trx), NADPH, and thioredoxin reductase (TrxR) of the cytosol/nucleus or mitochondria are major thiol-dependent reductases with many functions in cell growth, defense against oxidative stress, and apoptosis. Mammalian TrxRs are selenocysteine-containing flavoenzymes; MGd was an NADPH-oxidizing substrate for human or rat TrxR1 with a Km value of 8.65 microM (kcat/Km of 4.86 x 10(4) M(-1) s(-1)). The reaction involved redox cycling of MGd by oxygen producing superoxide and hydrogen peroxide. MGd acted as a non-competitive inhibitor (IC50 of 6 microM) for rat TrxR. In contrast, direct reaction between MGd and reduced human Trx was negligible. The corresponding reaction with reduced Escherichia coli Trx was also negligible, but MGd was a better substrate (kcat/Km of 2.23 x 10(5) M(-1) s(-1)) for TrxR from E. coli and a strong inhibitor of Trx-dependent protein disulfide reduction. Ribonucleotide reductase (RNR), a 1:1 complex of the non-identical R1- and R2-subunits, catalyzes the essential de novo synthesis of deoxyribonucleotides for DNA synthesis using electrons from Trx and TrxR. MGd inhibited recombinant mouse RNR activity with either 3 microM reduced human Trx (IC50 2 microM) or 4 mM dithiothreitol (IC50 6 microM) as electron donors. Our results demonstrate MGd-induced enzymatic generation of reactive oxygen species by TrxR plus a powerful inhibition of RNR. This may explain the effects of the drug on cancer cells, which often overproduce TrxR and have induced RNR for replication and repair.

Radiation sensitization with redox modulators: A promising approach

PURPOSE

Radiation therapy plays a critical role in the local and regional control of malignant tumors. Its efficacy, however, is limited by a number of factors, including toxicity, tumor hypoxia, and tumor genetics. Recent attempts to enhance the efficacy of radiation therapy have focused on biologic agents that modulate reduction/oxidation reactions within tumor cells.

METHODS AND MATERIALS

We review five promising redox modulators that are in development. Tirapazamine and AQ4N are known as "hypoxic cell sensitizers" and are toxic in areas of low oxygen tension. RSR13 facilitates delivery of oxygen to tumor cells, thereby rendering them more sensitive to radiation. Motexafin gadolinium, with a porphyrin-like structure, selectively accumulates in tumor cells and thereby enhances radiation-induced DNA damage. HIF-1 inhibitors target a transcription factor that regulates hypoxia-related events and cell survival.

RESULTS

Our review of each agent included a thorough search of published preclinical and clinical data, including that presented in abstracts and posters at international meetings. Our objectives were not to identify a superior mechanism or drug, but rather to summarize the available safety and efficacy data.

CONCLUSION

Clearly, there is an unmet need for safer agents that augment the efficacy of radiation therapy. This review highlights five promising redox modulators that are in development. None has yet been approved by the Food and Drug Administration. These drugs were selected for discussion because they exemplify the current investigative landscape of radiosensitizers and are indicative of future directions in this area. These radiation sensitizers have the potential to succeed where others have failed, by locally increasing the radiosensitivity of tumor cells without enhancing that of surrounding normal tissues.

Redox-sensitive signaling factors as a novel molecular targets for cancer therapy

Tumor cells undergoing proliferation, de-differentiation and progression depend on a complex set of respiratory pathways to generate the necessary energy. The metabolites from these pathways produce significant oxidative stress and must be buffered to prevent permanent cell damage and cell death. It is now clear that, in order to cope with and defend against the detrimental effects of oxidative stress, a series of redox-sensitive, pro-survival signaling pathways and factors regulate a complex intracellular redox buffering network. This review develops the hypothesis that tumor cells use these redox-sensitive, pro-survival signaling pathways and factors - up-regulated due to increased tumor cell respiration - to evade the damaging and cytotoxic effects of specific anticancer agents. It further suggests that redox-sensitive, signaling factors may be potential novel targets for drug discovery.

Motexafin gadolinium induces mitochondriallymediated caspase-dependent apoptosis

Motexafin gadolinium (MGd, Xcytrin) is a tumor-localizing redox mediator that catalyzes the oxidation of intracellular reducing molecules including NADPH, ascorbate, protein and non-protein thiols, generating reactive oxygen species (ROS). MGd localizes to tumors and cooperates with radiation and chemotherapy to kill tumor cells in tissue culture and animal models. In this report, we demonstrate that MGd triggers the mitochondrial apoptotic pathway in the HF-1 lymphoma cell line as determined by loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, activation of caspase-9 prior to caspase-8, cleavage of PARP and annexin V binding. There was minimal effect on MGd-induced apoptosis by the caspase inhibitor z-VAD-fmk, even though caspase-3 activity (as measured by DEVD-cleavage) was completely inhibited. However, MGd-induced apoptosis was reduced to baseline levels by the more potent caspase inhibitor Q-VD-OPh, demonstrating that MGd-induced apoptosis is indeed caspase-dependent. Apoptosis induced by dexamethasone, doxorubicin and etoposide (mediated through the mitochondrial pathway) was also more sensitive to inhibition by Q-VD-OPh than z-VAD-fmk. Our results demonstrating differential sensitivity of drug-induced apoptosis to caspase inhibitors suggest that the term "caspase-independent apoptosis" cannot be solely defined as apoptosis that is not inhibited by z-VAD-fmk as has been utilized in some published studies.

Current Management of Brain Metastases, With a Focus on Systemic Options

Brain metastases are an important sequelae of many types of cancer, most commonly lung cancer. Current treatment options include whole-brain radiation therapy (WBRT), surgical resection, stereotactic radiosurgery, and chemotherapy. Corticosteroids and antiepileptic medications are commonly used for palliation of mass effect and seizures, respectively. The overall median survival is only 4 months after WBRT. Combined-modality strategies of WBRT with either chemotherapy or novel anticancer agents are under clinical investigation. Promising results have been obtained with several experimental agents and confirmatory phase III trials are underway. Although improvement in overall survival has not been seen universally, reduction in death due to progression of brain metastases and prolongation of the time to neurologic and neurocognitive progression have been reported in selected series. On the basis of these findings, it might be possible to identify new agents that may enhance the efficacy of WBRT.

Metabolic signatures associated with a NAD synthesis inhibitor-induced tumor apoptosis identified by 1H-decoupled-31P magnetic resonance spectroscopy

PURPOSE

Attempts to selectively initiate tumor cell death through inducible apoptotic pathways are increasingly being exploited as a potential anticancer strategy. Inhibition of NAD+ synthesis by a novel agent FK866 has been recently reported to induce apoptosis in human leukemia, hepatocarcinoma cells in vitro, and various types of tumor xenografts in vivo. In the present study, we used 1H-decoupled phosphorus (31P) magnetic resonance spectroscopy (MRS) to examine the metabolic changes associated with FK866 induced tumor cell death in a mouse mammary carcinoma.

EXPERIMENTAL DESIGN

Induction of apoptosis in FK866-treated tumors was confirmed by histology and cytofluorometric analysis. FK866-induced changes in mammary carcinoma tumor metabolism in vivo were investigated using 1H-decoupled 31P MRS. To discern further the changes in metabolic profiles of tumors observed in vivo, high-resolution in vitro 1H-decoupled 31P MRS studies were carried out with perchloric acid extracts of mammary carcinoma tumors excised after similar treatments. In addition, the effects of FK866 on mammary carcinoma tumor growth and radiation sensitivity were studied.

RESULTS

Treatment with FK866 induced a tumor growth delay and enhanced radiation sensitivity in mammary carcinoma tumors that was associated with significant increases in the 31P MR signal in the phosphomonoester region and a decrease in NAD+ levels, pH, and bioenergetic status. The 31P MRS of perchloric acid extracts of treated tumors identified the large unresolved signal in the phosphomonoester region as the resultant of resonances originating from intermediates of tumor glycolysis and guanylate synthesis in addition to alterations in pyridine nucleotide pools and phospholipid metabolism.

CONCLUSION

The present results suggest that FK866 interferes with multiple biochemical pathways that contribute to the increased cell death (apoptosis) and subsequent radiation sensitivity observed in the mammary carcinoma that could be serially monitored by 31P MRS.

Motexafin gadolinium induces oxidative stress and apoptosis in hematologic malignancies

Redox mechanisms have been shown to be important in malignant cell survival and are a system that may be modified for the treatment of hematologic malignancies. Motexafin gadolinium (MGd) is a synthetic expanded porphyrin that selectively accumulates in tumor cells and oxidizes various intracellular metabolites, including ascorbate, nicotinamide adenine dinucleotide phosphate, glutathione, and protein thiols, to generate reactive oxygen species in a process known as futile redox cycling. The rationale for its use in hematologic malignancies is that, like naturally occurring porphyrins, it tends to concentrate selectively in cancer cells, and it has a novel mechanism of action of inducing redox stress and triggering apoptosis in a broad range of malignancies. MGd induces apoptosis in B-cell non-Hodgkin's lymphoma, chronic lymphocytic leukemia, and highly resistant myeloma cell lines. Furthermore, MGd is additive or synergistic with ionizing radiation, several chemotherapy agents, and rituximab in vitro and in vivo tumor models. Through gene expression profiling, various stress-related genes are upregulated in response to MGd, including genes encoding metallothioneins, heat shock proteins, and heme oxygenase. Preliminary results from clinical trials with MGd in hematopoietic malignancies have shown that it is well tolerated, with minimal hematologic side effects in both; it has single agent activity in very heavily pretreated chronic lymphocytic leukemia /small lymphocytic lymphoma patients, and it has induced prompt complete remissions in combination with 90Yttrium-ibritumomab (Y-90 Zevalin; Biogen Idec Inc., Cambridge, MA) for relapsed non-Hodgkin's lymphoma in the first two cohorts of patients enrolled. Various clinical trials studying MGd as a single agent and in combination with radiation and/or chemotherapy for the treatment of hematologic malignancies are ongoing.

Effects of motexafin gadolinium on DNA damage and X-ray-induced DNA damage repair, as assessed by the Comet assay

PURPOSE

To investigate the effects of motexafin gadolinium (MGd) on the levels of reactive oxygen species (ROS), glutathione (GSH), and DNA damage in EMT6 mouse mammary carcinoma cells. The ability of MGd to alter radiosensitivity and to inhibit DNA damage repair after X-ray irradiation was also evaluated.

METHODS AND MATERIALS

Reactive oxygen species and GSH levels were assessed by 2,7-dichlorofluorescein fluorescence flow cytometry and the Tietze method, respectively. Cellular radiosensitivity was assessed by clonogenic assays. Deoxyribonucleic acid damage and DNA damage repair were assessed in plateau-phase EMT6 cells by the Comet assay and clonogenic assays.

RESULTS

Cells treated with 100 mumol/L MGd plus equimolar ascorbic acid (AA) had significantly increased levels of ROS and a 58.9% +/- 3.4% decrease in GSH levels, relative to controls. Motexafin gadolinium plus AA treatment increased the hypoxic, but not the aerobic, radiosensitivity of EMT6 cells. There were increased levels of single-strand breaks in cells treated with 100 mumol/L MGd plus equimolar AA, as evidenced by changes in the alkaline tail moment (MGd + AA, 6 h: 14.7 +/- 1.8; control: 2.8 +/- 0.9). The level of single-strand breaks was dependent on the length of treatment. Motexafin gadolinium plus AA did not increase double-strand breaks. The repair of single-strand breaks at 2 h, but not at 4 h and 6 h, after irradiation was altered significantly in cells treated with MGd plus AA (MGd + AA, 2 h: 15.8 +/- 3.4; control: 5.8 +/- 0.6). Motexafin gadolinium did not alter the repair of double-strand breaks at any time after irradiation with 10 Gy.

CONCLUSIONS

Motexafin gadolinium plus AA generated ROS, which in turn altered GSH homeostasis and induced DNA strand breaks. The MGd plus AA-mediated alteration of GSH levels increased the hypoxic, but not aerobic, radiosensitivity of EMT6 cells. Motexafin gadolinium altered the kinetics of single-strand break repair soon after irradiation but did not inhibit potentially lethal damage repair in EMT6 cells.

Motexafin gadolinium generates reactive oxygen species and induces apoptosis in sensitive and highly resistant multiple myeloma cells

Motexafin gadolinium (MGd), an expanded porphyrin, is a tumor-selective redox-mediator that reacts with many intracellular reducing metabolites. Because redox mechanisms mediate apoptosis in multiple myeloma, we hypothesized that disruption of redox balance by MGd would result in cellular cytotoxicity in myeloma. We examined the effects of MGd on cellular cytotoxicity, apoptosis, reactive oxygen species (ROS) production, and intracellular drug uptake in dexamethasone-sensitive (C2E3), dexamethasone-resistant (1-310 and 1-414) chemotherapy-sensitive (8226-RPMI) and highly chemotherapy-resistant (DOX-10V) myeloma cells. We found complete inhibition of proliferation and cytotoxicity in each sensitive and resistant cell line with 24-hour exposure to clinically relevant concentrations of 50 μM MGd and 50 to 100 μM ascorbate, which was required for the effect. The mechanism of cytotoxicity was related to induction of apoptosis as demonstrated by alteration in mitochondrial membrane potential and elevated annexin V expression. This was accompanied by depletion of intracellular glutathione and increased ROS production. Moreover, catalase substantially abrogated MGd-induced cell death. Using fluorescence microscopy and flow cytometry, we found intracellular uptake of MGd and intracellular ROS production. MGd also induced apoptosis in fresh malignant cells from patients with multiple myeloma. These studies provide a rationale for clinical investigation of this novel redox-mediating agent in patients with multiple myeloma and related disorders.

Motexafin gadolinium: a redox-active tumor selective agent for the treatment of cancer

PURPOSE OF REVIEW

Redox regulation has been shown to be an important component of malignant cell survival and is a system that may be pharmacologically manipulated for the treatment of cancer. Motexafin gadolinium is a member of a class of rationally designed porphyrin-like molecules called texaphyrins. The rationale for its use in cancer therapy is that, like naturally occurring porphyrins, it tends to concentrate selectively in cancer cells and it has a novel mechanism of action as it induces redox stress, triggering apoptosis in a broad range of cancers.

RECENT FINDINGS

In vitro studies have shown that motexafin gadolinium is synergistic with radiation and varied chemotherapeutic agents. A phase III international study has shown that the onset of neurologic progression is significantly delayed in patients with brain metastases from lung cancer treated with whole-brain radiation and motexafin gadolinium (compared with radiation alone). Recent preclinical data have shown that motexafin gadolinium alone is cytotoxic to cancers such as multiple myeloma, non-Hodgkin lymphoma, and chronic lymphocytic leukemia through redox and apoptotic pathways. Multiple clinical trials examining motexafin gadolinium as a single agent and in combination with radiation and/or chemotherapy for the treatment of solid and hematopoietic tumors are underway.

SUMMARY

Motexafin gadolinium is a novel tumor-targeted agent that disrupts redox balance in cancer cells by futile redox cycling. Motexafin gadolinium is currently in numerous hematology/oncology clinical trials for use as a single agent and in combination with chemotherapy and/or radiation therapy.

The emerging role of reactive oxygen species in cancer therapy

The generation of reactive oxygen species (ROS) can be exploited therapeutically in the treatment of cancer. One of the first drugs to be developed that generates ROS was procarbazine. It is oxidised readily in an oxic environment to its azo derivative, generating ROS. Forty years ago, Berneis reported a synergistic effect in DNA degradation when procarbazine was combined with radiation; this was confirmed in preclinical in vivo modes. Early uncontrolled clinical trials suggested an enhancement of the radiation effect with procarbazine, but two randomised trials failed to confirm this. The role of ROS in cancer treatments and in the development of resistance to chemotherapy is now better understood. The possibility of exploiting ROS as a cancer treatment is re-emerging as a promising therapeutic option with the development of agents such as buthionine sulfoximine and motexafin gadolinium.

Effects of texaphyrins on the oxygenation of EMT6 mouse mammary tumors

PURPOSE

To investigate the effects of texaphyrins on the oxygenation of EMT6 mouse mammary tumors in Balb/c Rw mice. Texaphyrins are synthetic, porphyrin-like molecules capable of stably coordinating lanthanide and nonlanthanide metals. Metallotexaphyrin compounds containing gadolinium (MGd), lutetium (MLu), europium (Eu-Tex), dysprosium (Dy-Tex), and manganese (Mn-Tex) were evaluated.

METHODS

Tumor oxygenation was measured using an Eppendorf pO2 histograph when tumors, implanted intradermally in the rear dorsum, reached 150-200 mm3. Oxygen measurements were also made in the leg muscle of tumor-bearing mice, to determine whether changes in oxygenation occurred in nontumor tissue.

RESULTS

Motexafin gadolinium (Xcytrin, MGd) seems to be an effective modulator of tumor oxygen tension. The mean of the median tumor pO2 6 hours after injection of MGd was 8.0 +/- 2.4 mm Hg. The control value was 1.5 +/- 0.4 mm Hg. The oxygen levels within EMT6 tumors were shifted significantly toward higher oxygen tensions 6-8 hours after i.v. injection of 40 micromol/kg MGd, thereby reducing the percentage of severely hypoxic readings (MGd, 6 hours: 44.6 +/- 4.3% <2.5 mm Hg;

CONTROL

69.4 +/- 3.0% <2.5 mm Hg). There was no significant change in the oxygenation of the leg muscle after MGd treatment. Eu-Tex and Mn-Tex increased the tumor oxygenation to a much lesser degree than MGd. MLu, Dy-Tex, and the vehicle (a 5% mannitol solution) did not modulate tumor oxygenation.

CONCLUSIONS

MGd is an effective modulator of tumor oxygenation. The central metal composition of texaphyrin compounds is an important determinant of the effect of the texaphyrins on tumor oxygenation.

Neurocognitive function and progression in patients with brain metastases treated with whole-brain radiation and motexafin gadolinium: results of a randomized phase III trial

PURPOSE

To report the neurocognitive findings in a phase III randomized trial evaluating survival and neurologic and neurocognitive function in patients with brain metastases from solid tumors receiving whole-brain radiation therapy (WBRT) with or without motexafin gadolinium (MGd).

PATIENTS AND METHODS

Patients were randomly assigned to receive WBRT 30 Gy in 10 fractions with or without MGd 5 mg/kg/d. Monthly neurocognitive testing for memory, executive function, and fine motor skill was performed.

RESULTS

Four hundred one patients were enrolled (251 with non-small-cell lung cancer, 75 with breast cancer, and 75 with other cancers); 90.5% patients had impairment of one or more neurocognitive tests at baseline. Neurocognitive test scores of memory, fine motor speed, executive function, and global neurocognitive impairment at baseline were correlated with brain tumor volume and predictive of survival. There was no statistically significant difference between treatment arms in time to neurocognitive progression. Patients with lung cancer (but not other types of cancer) who were treated with MGd tended to have improved memory and executive function (P =.062) and improved neurologic function as assessed by a blinded events review committee (P =.048).

CONCLUSION

Neurocognitive tests are a relatively sensitive measure of brain functioning; a combination of tumor prognostic variables and brain function assessments seems to predict survival better than tumor variables alone. Although the addition of MGd to WBRT did not produce a significant overall improvement between treatment arms, MGd may improve memory and executive function and prolong time to neurocognitive and neurologic progression in patients with brain metastases from lung cancer.

Response to motexafin gadolinium and ionizing radiation of experimental rat prostate and lung tumors

PURPOSE

To investigate the responses of two experimental rat tumors to single and fractionated X-ray doses whether or not combined with Motexafin gadolinium (MGd), and the distribution of MGd in R3327-MATLyLu (MLL) tumors using MRI.

METHODS

L44 lung tumor in BN rats and MLL prostate tumor in Copenhagen rats were grown subcutaneously. MGd at concentrations of 8.7 to 25.1 micro mol/kg was administered 2 h before or just before treatments with single and fractionated X-ray doses. Tumor volume growth delay was the endpoint used. The two-dimensional distribution of the MGd concentration in time was analyzed simultaneously in slices through the center of MLL tumors using MRI. Directly after the MRI experiments, tumor sections were stained for cytoplasm, nuclei, and microvessel endothelium.

RESULTS

MGd at different concentrations administered a few minutes or 2 h before X-ray doses produced no radiation enhancement in the two tumor models. The MGd concentration as determined by MRI was maximal 5 min after injection and decreased slowly thereafter. In a representative section at the center of the MLL tumor, the microvessel density is nearly homogeneous and correlates with a nearly homogeneous MGd distribution. Hardly any MGd is taken up in underlying muscle tissue.

CONCLUSION

No radiosensitization was observed for the different irradiation regimens. The distribution of MGd is nearly homogeneous in the MLL tumor and hardly any MGd is taken up in underlying muscles. Our negative results on radiosensitivity in our two tumor models raise questions about the efficacy of MGd as a general radiosensitizing agent.

Motexafin gadolinium: a possible new radiosensitiser

Motexafin gadolinium (MGd, PCI-0120, Xcytrin, a metallotexaphyrin developed by Pharmacyclics, is a redox active drug that selectively targets tumour cells with a potential action as a radiosensitiser. In vitro and in vivo models showed radiation enhancement when radiation followed MGd administration. Phase I and II clinical studies showed that MGd was well-tolerated with a maximum-tolerated dose set at 6.3 mg/kg. Acute side effects of discolouration of the sclera, skin and urine are reversible. The clinical efficacy was determined in an international Phase III trial for brain metastases with a significant difference in time to neurological progression for lung cancer brain metastases in favour of MGd and whole brain radiation versus whole brain radiation only. For the treatment of glioblastoma multiforme, promising results are found in a Phase I trial with a median survival of 17.3 months. Further investigation of the combination of MGd and radiotherapy will be worthwhile.

Survival and neurologic outcomes in a randomized trial of motexafin gadolinium and whole-brain radiation therapy in brain metastases

PURPOSE

This phase III randomized trial evaluated survival as well as neurologic and neurocognitive function in patients with brain metastases from solid tumors receiving whole-brain radiation therapy (WBRT) with or without motexafin gadolinium (MGd).

PATIENTS AND METHODS

Patients were randomly assigned to 30 Gy of WBRT +/- 5 mg/kg/d MGd. Survival and time to neurologic progression determined by a blinded events review committee (ERC) were coprimary end points. Standardized investigator neurologic assessment and neurocognitive testing were evaluated.

RESULTS

Four hundred one (251 non-small-cell lung cancer) patients were enrolled. There was no significant difference by treatment arm in survival (median, 5.2 months for MGd v 4.9 months for WBRT; P =.48) or time to neurologic progression (median, 9.5 months for MGd v 8.3 months for WBRT; P =.95). Treatment with MGd improved time to neurologic progression in patients with lung cancer (median, not reached for MGd v 7.4 months for WBRT; P =.048, unadjusted). By investigator, MGd improved time to neurologic progression in all patients (median, 4.3 months for MGd v 3.8 months for WBRT; P =.018) and in lung cancer patients (median, 5.5 months for MGd v 3.7 months for WBRT; P =.025). MGd improved neurocognitive function in lung cancer patients.

CONCLUSION

The overall results did not demonstrate significant differences by treatment arm for survival and ERC time to neurologic progression. Investigator neurologic assessments demonstrated an MGd treatment benefit in all patients. In lung cancer patients, ERC- and investigator-determined time to neurologic progression demonstrated an MGd treatment benefit. MGd may improve time to neurologic and neurocognitive progression in lung cancer.

Preliminary studies of the effects of gadolinium texaphyrin on the growth and radiosensitivity of EMT6 cells in vitro

PURPOSE

To investigate the effects of gadolinium texaphyrin (GdTx) on the growth and radiation response of cells in vitro, in a limited set of experiments designed to examine some areas of controversy concerning the effects of this compound.

METHODS AND MATERIALS

Exponentially growing cultures of EMT6 mouse mammary tumor cells, grown in Dulbecco's Modified Eagle's Medium with 10% dialyzed fetal bovine serum, were treated with GdTx either prepared from powder or obtained as a solution similar to that used clinically, in either the presence or absence of equimolar ascorbic acid. Cell viability was measured using a clonogenic assay.

RESULTS

Treatment with GdTx in the presence of ascorbic acid dramatically altered the growth, appearance, and behavior of the cells; treatment with GdTx in the absence of ascorbic acid had only minimal effects. The effects of the powdered drug and the solution were similar. GdTx used with equimolar ascorbic acid altered the radiation dose-response curves of cells irradiated under aerobic and hypoxic conditions; no significant changes were observed without ascorbic acid.

CONCLUSIONS

The details of the protocols used in experiments examining the effects of GdTx have major effects on the outcomes. Our results suggest that differences in the protocols used by different groups in past studies with GdTx probably were important in producing the disparate results reported previously.

Lead-in phase to randomized trial of motexafin gadolinium and whole-brain radiation for patients with brain metastases: centralized assessment of magnetic resonance imaging, neurocognitive, and neurologic end points

PURPOSE

Motexafin gadolinium is a redox mediator that selectively targets tumor cells, is detectable by magnetic resonance imaging (MRI), and enhances the effect of radiation therapy. This lead-in phase to a randomized trial served to evaluate radiologic, neurocognitive, and neurologic progression end points and to evaluate the safety and radiologic response of motexafin gadolinium administered concurrently with 30 Gy in 10-fraction whole-brain radiation therapy for the treatment of brain metastases.

PATIENTS AND METHODS

Motexafin gadolinium (5.0 mg/kg/d for 10 days) was administered before each radiation treatment in this prospective international trial. Patients were evaluated by MRI, neurologic examinations, and neurocognitive tests. Prospective criteria and centralized review procedures were established for radiologic, neurocognitive, and neurologic progression end points.

RESULTS

Twenty-five patients with brain metastases from lung (52%) and breast (24%) cancer, recursive partitioning analysis class 2 (96%), and an average of 11 brain metastases were enrolled. Neurocognitive function was highly impaired at presentation. Motexafin gadolinium was well tolerated. Freedom from neurologic progression was 77% at 1 year. Median survival was 5.0 months. In 29% of patients, the cause of death was brain metastasis progression. The radiologic response rate was 68%. Motexafin gadolinium's tumor selectivity was established with MRI.

CONCLUSION

(1) Centralized neurologic progression scoring that incorporated neurocognitive tests was implemented successfully. (2) Motexafin gadolinium was well tolerated. (3) Local control, measured by radiologic response rate, neurologic progression, and death caused by progression of brain metastasis, seemed to be improved compared with historical results. A randomized phase III trial using these methods for evaluation of efficacy has just been completed.