Richard A. Miller

Texaphyrins : New drugs with diverse clinical applications in radiation and photodynamic therapy

The texaphyrins are quintessential metal-coordinating expanded porphyrins. They constitute a new series of synthetic porphyrin analogues that show promise as drugs for use in a range of medical therapies. Currently, two different water-solubilized lanthanide(III) texaphyrin complexes, namely the gadolinium(III) and lutetium(III) derivatives 1 and 2 (Gd-Tex and Lu-Tex, respectively), are being tested clinically. The first of these, XCYTRIN, is in a pivotal Phase III clinical trial as a potential enhancer of radiation therapy for patients with metastatic cancers to the brain receiving whole brain radiation therapy. The second, in various formulations, is being tested as a photosensitizer for use in: (i) the photodynamic treatment of recurrent breast cancer (LUTRIN; Phase II clinical trials complete), (ii) photoangioplastic reduction of atherosclerosis involving peripheral arteries (ANTRIN; now in Phase II testing), and (iii) light-based treatment of age-related macular degeneration (OPTRIN; currently in Phase I clinical trials), a vision-threatening disease of the retina. Taken in concert, these two metallotexaphyrins provide a powerful new class of experimental drugs whose diverse potential utility is abetted by a combination of well-optimized physical features, favorable tissue biolocalization characteristics, and novel mechanisms of action. Interestingly, these mechanisms may alter conventional wisdom regarding mechanisms of radiation therapy and the pathophysiology of atherosclerosis.

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

PURPOSEnMotexafin 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.nnnPATIENTS AND METHODSnMotexafin 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.nnnRESULTSnTwenty-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 gadoliniums tumor selectivity was established with MRI.nnnCONCLUSIONn(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.

Multicenter Phase Ib/II Trial of the Radiation Enhancer Motexafin Gadolinium in Patients With Brain Metastases

PURPOSEnMotexafin gadolinium is a magnetic resonance imaging (MRI)--detectable redox active drug that localizes selectively in tumor cells and enhances the effect of radiation therapy. This phase Ib/II trial of motexafin gadolinium, administered concurrently with 30 Gy in 10 fractions whole-brain radiation therapy (WBRT), was conducted to determine maximum-tolerated dose (MTD), dose-limiting toxicity, pharmacokinetics, and biolocalization in patients with brain metastases. Additional endpoints were radiologic response rate and survival.nnnPATIENTS AND METHODSnMotexafin gadolinium was administered before each radiation treatment in this open-label, multicenter, international trial. In phase Ib, drug dose was escalated until the MTD was exceeded. In phase II, drug was evaluated in a narrow dose range.nnnRESULTSnIn phase Ib, the motexafin gadolinium dose was escalated in 39 patients (0.3 mg/kg to 8.4 mg/kg). In phase II, 22 patients received 5 mg/kg to 6.3 mg/kg motexafin gadolinium. Ten once-daily treatments were well tolerated. The MTD was 6.3 mg/kg, with dose-limiting reversible liver toxicity. Motexafin gadoliniums tumor selectivity was established using MRI. The radiologic response rate was 72% in phase II. Median survival was 4.7 months for all patients, 5.4 months for recursive partitioning analysis (RPA) class 2 patients, and 3.8 months for RPA class 3 patients. One-year actuarial survival for all patients was 25%.nnnCONCLUSIONnMotexafin gadolinium was well tolerated at doses up to 6.3 mg/kg, was selectively accumulated in tumors, and, when combined with WBRT of 30 Gy in 10 fractions, was associated with a high radiologic response rate.

Motexafin gadolinium combined with prompt whole brain radiotherapy prolongs time to neurologic progression in non-small-cell lung cancer patients with brain metastases: results of a phase III trial.

PURPOSEnTo determine the efficacy of motexafin gadolinium (MGd) in combination with whole brain radiotherapy (WBRT) for the treatment of brain metastases from non-small-cell lung cancer.nnnMETHODS AND MATERIALSnIn an international, randomized, Phase III study, patients with brain metastases from non-small-cell lung cancer were randomized to WBRT with or without MGd. The primary endpoint was the interval to neurologic progression, determined by a centralized Events Review Committee who was unaware of the treatment the patients had received.nnnRESULTSnOf 554 patients, 275 were randomized to WBRT and 279 to WBRT+MGd. Treatment with MGd was well tolerated, and 92% of the intended doses were administered. The most common MGd-related Grade 3+ adverse events included liver function abnormalities (5.5%), asthenia (4.0%), and hypertension (4%). MGd improved the interval to neurologic progression compared with WBRT alone (15 vs. 10 months; p = 0.12, hazard ratio [HR] = 0.78) and the interval to neurocognitive progression (p = 0.057, HR = 0.78). The WBRT patients required more salvage brain surgery or radiosurgery than did the WBRT+MGd patients (54 vs. 25 salvage procedures, p < 0.001). A statistically significant interaction between the geographic region and MGd treatment effect (which was in the prespecified analysis plan) and between treatment delay and MGd treatment effect was found. In North American patients, where treatment was more prompt, a statistically significant prolongation of the interval to neurologic progression, from 8.8 months for WBRT to 24.2 months for WBRT+MGd (p = 0.004, HR = 0.53), and the interval to neurocognitive progression (p = 0.06, HR = 0.73) were observed.nnnCONCLUSIONnIn the intent-to-treat analysis, MGd exhibited a favorable trend in neurologic outcomes. MGd significantly prolonged the interval to neurologic progression in non-small-cell lung cancer patients with brain metastases receiving prompt WBRT. The toxicity was acceptable.

REDOX CYCLING BY MOTEXAFIN GADOLINIUM ENHANCES CELLULAR RESPONSE TO IONIZING RADIATION BY FORMING REACTIVE OXYGEN SPECIES

PURPOSEnTo examine the mechanism of radiation enhancement by motexafin gadolinium (Gd-Tex) in vitro.nnnMETHODS AND MATERIALSnOxidation of ascorbate and NADPH by Gd-Tex was evaluated in a neutral buffer. Growth inhibition of human uterine cancer cell line MES-SA was measured using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) dye. Clonogenic assays were used to measure radiation response in MES-SA, A549 human lung carcinoma, E89, a CHO cell line variant deficient in glucose-6-phosphate dehydrogenase activity, and murine lymphoma cell lines LYAR and LYAS.nnnRESULTSnGd-Tex catalyzed the oxidation of NADPH and ascorbate under aerobic conditions, forming hydrogen peroxide. Decreased viability was observed in MES-SA cells incubated with Gd-Tex in media containing NADPH or ascorbate. Gd-Tex and ascorbate increased fluorescence in dichlorofluorescin acetate-treated cultures. Synergistic effects on the aerobic radiation response in MES-SA and A549 were seen using Gd-Tex in combination with L-buthionine-(S,R)-sulfoximine (BSO). Incubation with Gd-Tex in the presence of ascorbate increased the aerobic radiation response of E89 and the apoptosis-sensitive B-cell line (LYAS).nnnCONCLUSIONSnGd-Tex sensitizes cells to ionizing radiation by increasing oxidative stress as a consequence of futile redox cycling. Optimization of the concentration of ascorbate (or other reducing species) may be required when evaluating Gd-Tex activity in vitro.

Motexafin Gadolinium and Zinc Induce Oxidative Stress Responses and Apoptosis in B-Cell Lymphoma Lines

There is an emerging appreciation of the importance of zinc in regulating cancer cell growth and proliferation. Recently, we showed that the anticancer agent motexafin gadolinium (MGd) disrupted zinc metabolism in A549 lung cancer cells, leading, in the presence of exogenous zinc, to cell death. Here, we report the effect of MGd and exogenous zinc on intracellular levels of free zinc, oxidative stress, proliferation, and cell death in exponential phase human B-cell lymphoma and other hematologic cell lines. We find that increased levels of oxidative stress and intracellular free zinc precede and correlate with cell cycle arrest and apoptosis. To better understand the molecular basis of these cellular responses, gene expression profiling analyses were conducted on Ramos cell cultures treated with MGd and/or zinc acetate. Cultures treated with MGd or zinc acetate alone elicited transcriptional responses characterized by induction of metal response element-binding transcription factor-1 (MTF-1)-regulated and hypoxia-inducible transcription factor-1 (HIF-1)-regulated genes. Cultures cotreated with MGd and zinc acetate displayed further increases in the levels of MTF-1- and HIF-1-regulated transcripts as well as additional transcripts regulated by NF-E2-related transcription factor 2. These data provide insights into the molecular changes that accompany the disruption of intracellular zinc homeostasis and support a role for MGd in treatment of B-cell hematologic malignancies.

Lutetium texaphyrin (Lu-Tex): A potential new agent for ocular fundus angiography and photodynamic therapy

PURPOSEnTo investigate the suitability of lutetium texaphyrin (lu-tex) as a fluorescence imaging agent in the delineation of retinal vascular and choroidal vascular diseases. The utilization of an efficient fluorescent molecule that is also a photosensitizer represents a unique opportunity to couple diagnosis and therapy.nnnMETHODSnFundus fluorescence angiography comparing lu-tex (motexafin lutetium, Optrin, Pharmacyclics Inc, Sunnyvale, California) with the conventional angiographic dyes, sodium fluorescein, and indocynanine green (ICG), was performed on the eyes of normal and laser-injured New Zealand white rabbits. Plasma pharmacokinetic data and plasma protein binding were assessed in addition to light microscopy of the retina in both imaged and laser-injured eyes.nnnRESULTSnNormal retinal and choroidal vasculature was well delineated by lu-tex angiography. Experimentally induced choroidal and retinal vascular lesions were enhanced by lu-tex and demonstrated different staining patterns than fluorescein or ICG, particularly at the margins of the lesions. Lu-tex cleared rapidly from the plasma, with 39.7% bound to the high-density lipoprotein (HDL) fraction while 15.8% was bound to the low-density lipoprotein (LDL) fraction. No evidence of retinal toxicity after dye administration was observed by either ophthalmoscopy and fundus photography or by light microscopy.nnnCONCLUSIONnLu-tex angiography is a potentially valuable method for retinal vascular and choroidal vascular evaluation, and it has advantages over fluorescein and ICG angiography. The same agent could conceivably be used for both the identification of abnormal vasculature and subsequent photodynamic treatment.

Biomedical applications of lanthanide (III) texaphyrins Lutetium(III) texaphyrins as potential photodynamic therapy photosensitizers

Abstract The texaphyrins are a novel class of pentadentate, porphyrin-like aromatic macrocyclic ligands that form kinetically stable complexes with essentially all cations of the trivalent lanthanide series. This ability, combined with certain features inherent to the texaphyrin skeleton, gives rise to species that are of potential interest in a range of medical applications including diagnosis and therapy. In this paper, the biomedical utility of one particular metallotexaphyrin derivative, namely the lutetium(III) complex PCI-0123 (1), is highlighted. This system generates singlet oxygen in 11% quantum yield in water (20–30% in organic solvents) and is an effective sensitizer for photodynamic cancer therapy as judged from animal model studies. It is currently in Phase I human clinical trials.

Motexafin gadolinium reacts with ascorbate to produce reactive oxygen species

Motexafin gadolinium (MGd) oxidizes ascorbate, in neutral buffer and in cell culture, forming reactive oxygen species and a coordination polymer with oxalate.

Selective uptake of texaphyrins in atheromatous plaque

Texaphyrins are water soluble porphyrinoids which selectively localize in atheromatous plaque. The paramagnetic gadolinium texaphyrin is an excellent contrast agent which enables plaque detection by MRI. The diamagnetic lutetium texaphyrin, using fluorescence methods, was also shown to label atheromatous plaque. The chemical environment of bound lutetium texaphyrin within plaque was determined by fluorescence emission spectra to be predominantly lipophilic. The texaphyrin was found to bind to the lower density lipoproteins in the atherosclerotic-induced animals. Lutetium texaphyrin is an excellent candidate for photoatherolytic therapy.