Avigdor Scherz

Monitoring photodynamic therapy of solid tumors online by BOLD-contrast MRI

Antivascular photodynamic therapy (PDT) of tumors with palladium-bacteriopheophorbide (TOOKAD) relies on in situ photosensitization of the circulating drug by local generation of cytotoxic reactive oxygen species, which leads to rapid vascular occlusion, stasis, necrosis and tumor eradication. Intravascular production of reactive oxygen species is associated with photoconsumption of O2 and consequent evolution of paramagnetic deoxyhemoglobin. In this study we evaluate the use of blood oxygenation level–dependent (BOLD) contrast magnetic resonance imaging (MRI) for real-time monitoring of PDT efficacy. Using a solid tumor model, we show that TOOKAD-PDT generates appreciable attenuation (25–40%) of the magnetic resonance signal, solely at the illuminated tumor site. This phenomenon is independent of, though augmented by, ensuing changes in blood flow. These results were validated by immunohistochemistry and intravital microscopy. The concept of photosensitized BOLD-contrast MRI may have intraoperative applications in interactive guidance and monitoring of antivascular cancer therapy, PDT treatment of macular degeneration, interventional cardiology and possibly other biomedical disciplines.

Photodynamic therapy with Pd-Bacteriopheophorbide (TOOKAD): successful in vivo treatment of human prostatic small cell carcinoma xenografts.

Small cell carcinoma of the prostate (SCCP), although relatively rare, is the most aggressive variant of prostate cancer, currently with no successful treatment. It was therefore tempting to evaluate the response of this violent malignancy and its bone lesions to Pd‐Bacteriopheophorbide (TOOKAD)‐based photodynamic therapy (PDT), already proven by us to efficiently eradicate other aggressive non‐epithelial solid tumors. TOOKAD is a novel bacteriochlorophyll‐derived, second‐generation photosensitizer recently, developed by us for the treatment of bulky tumors. This photosensitizer is endowed with strong light absorbance (ϵ0 ∼ 105 mol−1 cm−1) in the near infrared region (λ=763nm), allowing deep tissue penetration. The TOOKAD‐PDT protocol targets the tumor vasculature leading to inflammation, hypoxia, necrosis and tumor eradication. The sensitizer clears rapidly from the circulation within a few hours and does not accumulate in tissues, which is compatible with the treatment of localized tumor and isolated metastases. Briefly, male CD1‐nude mice were grafted with the human SCCP (WISH‐PC2) in 3 relevant anatomic locations: subcutaneous (representing tumor mass), intraosseous (representing bone metastases) and orthotopically within the murine prostate microenvironment. The PDT protocol consisted of i.v. administration of TOOKAD (4 mg/kg), followed by immediate illumination (650–800 nm) from a xenon light source or a diode laser emitting at 770 nm. Controls included untreated animals or animals treated with light or TOOKAD alone. Tumor volume, human plasma chromogranin A levels, animal well being and survival were used as end points. In addition, histopathology and immunohistochemistry were used to define the tumor response. Subcutaneous tumors exhibited complete healing within 28–40 days, reaching an overall long‐term cure rate of 69%, followed for 90 days after PDT. Intratibial WISH‐PC2 lesions responded with complete tumor elimination in 50% of the treated mice at 70–90 days after PDT as documented histologically. The response of the orthotopic model was also analyzed histologically with similar results. The study with this model suggests that TOOKAD‐based PDT can reach large tumors and is a feasible, efficient and well‐tolerated approach for minimally invasive treatment of local and disseminated SCCP.

Stimuli responsive materials : new avenues toward smart organic devices

“Smart” patternable polymer-based materials that can be designed from various molecular building blocks show great potential, as they may be used in many fields, including nanotechnology, biochemistry, organic and physical chemistry, and materials science. The focus of this highlight will be on the basic design characteristics of practical Stimuli Responsive Materials (SRMs), the wide range of potential applications and the challenges to be accomplished in this rapidly expanding area. In particular, recent developments are described which are related to two of the many fundamental aspects of stimuli triggered responses: those that are photo-triggered and those that are solvent triggered. These selected state-of-the-art examples demonstrate the large scope and diversity in terms of activation mechanism, response time and property control.

Vascular-targeted photodynamic therapy (padoporfin, WST09) for recurrent prostate cancer after failure of external beam radiotherapy: a study of escalating light doses

To report on the efficacy of TOOKAD® (WST 09; NegmaLerads, Magny‐Les‐Hameaux, France) vascular‐targeted photodynamic therapy (VTP) as a method of whole‐prostate ablation in patients with recurrent localized prostate cancer after the failure of external beam radiotherapy (EBRT).

Preclinical Studies in Normal Canine Prostate of a Novel Palladium-Bacteriopheophorbide (WST09) Photosensitizer for Photodynamic Therapy of Prostate Cancer¶

Abstract Photodynamic therapy (PDT) uses light to activate a photosensitizer to achieve localized tumor control. In this study, PDT mediated by a second-generation photosensitizer, palladium-bacteriopheophorbide WST09 (Tookad) was investigated as an alternative therapy for prostate cancer. Normal canine prostate was used as the animal model. PDT was performed by irradiating the surgically exposed prostate superficially or interstitially at 763 nm to different total fluences (100 or 200 J/cm2; 50, 100 or 200 J/cm) at 5 or 15 min after intravenous administration of the drug (2 mg/kg). Areas on the bladder and colon were also irradiated. The local light fluence rate and temperature were monitored by interstitial probes in the prostate. All animals recovered well, without urethral complications. During the 1 week to 3 month posttreatment period, the prostates were harvested for histopathological examination. The PDT-induced lesions showed uniform hemorrhagic necrosis and atrophy, were well delineated from the adjacent normal tissue and increased linearly in diameter with the logarithm of the delivered light fluence. A maximum PDT-induced lesion size of over 3 cm diameter could be achieved with a single interstitial treatment. There was no damage to the bladder or rectum caused by scattered light from the prostate. The bladder and rectum were also directly irradiated with PDT. At 80 J/cm2, a full-depth necrosis was observed but resulted in no perforation. At 40 J/cm2, PDT produced minimal damage to the bladder or rectum. On the basis of optical dosimetry, we have estimated that 20 J/cm2 is the fluence required to produce prostatic necrosis. Thus, the normal structure adjacent to the prostate can be safely preserved with careful dosimetry. At therapeutic PDT levels, there was no structural or functional urethral damage even when the urethra was within the treated region. Hence, Tookad-PDT appears to be a promising candidate for prostate ablation in patients with recurrent, or possibly even primary, prostate cancer.

WST11, A Novel Water-soluble Bacteriochlorophyll Derivative; Cellular Uptake, Pharmacokinetics, Biodistribution and Vascular-targeted Photodynamic Activity Using Melanoma Tumors as a Model¶

Abstract WST11 is a novel negatively charged water-soluble palladium-bacteriochlorophyll derivative that was developed for vascular-targeted photodynamic therapy (VTP) in our laboratory. The in vitro results suggest that WST11 cellular uptake, clearance and phototoxicity are mediated by serum albumin trafficking. In vivo, WST11 was found to clear rapidly from the circulation (t1/2 = 1.65 min) after intravenous bolus injection in the mouse, whereas a longer clearance time (t1/2 = 7.5 min) was noted in rats after 20 min of infusion. The biodistribution of WST11 in mouse tissues indicates hepatic clearance (t1/2 = 20 min), with minor (kidney, lung and spleen) or no intermediary accumulation in other tissues. As soon as 1 h after injection, WST11 had nearly cleared from the body of the mouse, except for a temporal accumulation in the lungs from which it cleared within 40 min. On the basis of these results, we set the VTP protocol for a short illumination period (5 min), delivered immediately after WST11 injection. On subjecting M2R melanoma xenografts to WST11-VTP, we achieved 100% tumor flattening at all doses and a 70% cure with 9 mg/kg and a light exposure dose of 100 mW/cm2. These results provide direct evidence that WST11 is an effective agent for VTP and provide guidelines for further development of new candidates.

Local photodynamic therapy (PDT) of rat C6 glioma xenografts with Pd-bacteriopheophorbide leads to decreased metastases and increase of animal cure compared with surgery

Photodynamic therapy (PDT), locally applied to solid C6 rat glioma tumors in the foot of CD1 nude mice, eradicated the primary tumor and also decreased the rate of groin and lung metastases. Pd‐Bacteriopheophorbide (Pd‐Bpheid), a novel photosensitizer synthesized in our laboratory, was used in our study. The primary lesion in the hind leg was treated by an i.v. injection of 5 mg/kg of Pd‐Bpheid and immediate illumination (650–800 nm, 360 J/cm2). This protocol and the surgical amputation of the leg were compared for local and metastasis responses. Following PDT, hemorrhage, inflammation with tumor necrosis and flattening were observed and histologically verified in the photodynamically treated tumor. Whereas local tumor control rates were up to 64% following PDT, in surgically treated animals, local tumor control was absolute. The rates of metastases in the groin and the lungs were at least 12‐fold lower in the photodynamically treated animals compared with untreated or surgery‐treated groups. The overall cure rates after PDT or surgery were 36% and 6%, respectively, at 8 weeks. These findings suggest that local PDT with Pd‐Bpheid, which acts primarily on the tumor vasculature, efficiently eradicates the solid C6 tumors. In addition, the local PDT of the primary lesion has beneficial therapeutic effects on remote C6 metastasis, which is not obtained with surgery. It is therefore suggested, that although surgery is highly efficient for the immediate removal of the primary tumor, it lacks such systemic, therapeutic effects on distant metastases. Pd‐Bpheid‐PDT may thus offer a potentially superior curative therapy for C6 glioma tumors in the limb by eradicating the target tumor and by reducing the rate of metastasis in the groin and lung, possibly due to innate immunity.

TOOKAD® Soluble vascular‐targeted photodynamic (VTP) therapy: determination of optimal treatment conditions and assessment of effects in patients with localised prostate cancer

To evaluate the optimal treatment conditions and effects of TOOKAD® Soluble vascular‐targeted photodynamic (VTP) therapy in patients with localised prostate cancer. To evaluate the safety and quality of life after TOOKAD® Soluble VTP treatment in patients with localised prostate cancer.

Antivascular Treatment of Solid Melanoma Tumors with Bacteriochlorophyll–serine-based Photodynamic Therapy¶

We describe here a strategy for photodynamic eradication of solid melanoma tumors that is based on photoinduced vascular destruction. The suggested protocol relies on synchronizing illumination with maximal circulating drug concentration in the tumor vasculature attained within the first minute after administrating the sensitizer. This differs from conventional photodynamic therapy (PDT) of tumors where illumination coincides with a maximal concentration differential of sensitizer in favor of the tumor, relative to the normal surrounding tissue. This time window is often achieved after a delay (3–48 h) following sensitizer administration. We used a novel photosensitizer, bacteriochlorophyll–serine (Bchl–Ser), which is water soluble, highly toxic upon illumination in the near‐infrared (λmax 765–780 nm) and clears from the circulation in less than 24 h. Nude CD1 mice bearing malignant M2R melanotic melanoma xenografts (76–212 mm3) received a single complete treatment session. Massive vascular damage was already apparent 1 h after treatment. Changes in vascular permeability were observed in vivo using contrast‐enhanced magnetic resonance imaging (MRI), with the contrast reagent Gd‐DTPA, by shortening spin–spin relaxation time because of hemorrhage formation and by determination of vascular macromolecular leakage. Twenty‐four hours after treatment a complete arrest of vascular perfusion was observed by Gd‐DTPA–enhanced MRI. Histopathology performed at the same time confirmed primary vascular damage with occlusive thrombi, hemorrhage and tumor necrosis. The success rate of cure of over 80% with Bchl–Ser indicates the benefits of the short and effective treatment protocol. Combining the sensitizer administration and illumination steps into one treatment session (30 min) suggests a clear advantage for future PDT of solid tumors.

Photocatalytic Generation of Oxygen Radicals by the Water-Soluble Bacteriochlorophyll Derivative WST11, Noncovalently Bound to Serum Albumin

Light-induced radical generation is the hallmark of fundamental processes and many applications including photosynthesis and photodynamic therapy (PDT). In this manuscript, we present two novel observations made upon monitoring light-induced generation of reactive oxygen species (ROS) in aqueous solutions by WST11, a water-soluble derivative of the photosynthetic pigment Bacteriochlorophyll a (Bchl). Using a host of complementary experimental techniques including time-resolved spectroscopy at the subpicosecond to the millisecond range, ESR spectroscopy, electrochemistry, spectroelectrochemistry, oximetry, and protein mass spectroscopy, we first show that in aqueous solutions WST11 generates only superoxide (O(2)(-*)) and hydroxyl (OH*) radicals with no detectable traces of singlet oxygen. Second, we show that WST11 makes a noncovalent complex with human serum albumin (HSA) and that this complex functions as a photocatalytic oxidoreductase at biologically relevant concentrations enabling approximately 15 cycles of electron transfer from the associated HSA protein to molecular oxygen in the solution. These findings rule out the paradigm that porphyrin and chlorophyll based PDT is mainly mediated by formation of singlet oxygen, particularly in vascular targeted photodynamic therapy (VTP) with sensitizers that undergo photoactivation during circulation in the plasma, like [Pd]-Bacteriopheophorbide (WST09, Tookad). At the same time, our findings open the way for new design paradigms of novel sensitizers, since O(2)(-*) and OH* radicals are well-recognized precursors of important pathophysiological processes that can be activated for achieving tumor eradication. Moreover, the finding that promiscuous protein scaffolds become sinks for holes and electrons when holding light-activated pigments provides a new insight to the evolution and action mechanism of natural light activated oxidoreductases (such as photosynthetic reaction centers) and new guidelines for the preparation of synthetic-light converting machineries.