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Photodynamic therapy using a second generation photosensitizer, Talaporfin
Photodiagnosis and Photodynamic Therapy (2007) 4, 269—274
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/pdpdt
Photodynamic therapy using a second generation photosensitizer, Talaporfin Kazuya Kondo MD, PhD a,∗, Takanori Miyoshi a, Haruhiko Fujino a, Hiromitsu Takizawa a, Satoshi Imai b, Naoki Kobayashi c, Koichiro Kenzaki a, Shoji Sakiyama a, Akira Tangoku a a
Department of Oncological and Regenerative Surgery, Institute of Health Biosciences, University of Tokushima Graduate School, Kuramoto-cho, Tokushima 770-8503 Japan b Meiji Seika Kaisha, Ltd., Tokyo, Japan c Nippon Koden Corporation, Tokyo, Japan Available online 3 August 2007
KEYWORDS Talaporfin; Photodynamic therapy; Pulse oximeter; Lung cancer
Summary Background: Photodynamic therapy (PDT) using Talaporfin is an attractive treatment for centraltype early lung cancer. It was noted that some patients had altered levels of arterial oxygen saturation as indicated by pulse oximeter (SpO2 ) and arterial oxygen saturation levels in blood gas analysis (SaO2 ) during PDT. The present experiments were designed to provide an explanation for these findings. Methods: The influence of Talaporfin on SpO2 using in vitro and in vivo experiments, and clinically, was examined. Results: Our in vitro and in vivo experiments showed a linear relationship between Talaporfin concentration in the plasma and the SpO2 level (R = 0.9957 and 0.9837). The apparent SpO2 level decreased according to the increase of Talaporfin concentration in the plasma. In two patients with PDT, SpO2 levels at 4—6 h and 24 h after Talaporfin administration were 93% and 97%, respectively. Conclusions: Talaporfin raised blood absorbance at 660 nm with a pulse oximeter. It appeared that the presence of the drug falsely decreased the level of SpO2 since SpO2 did not actually change. © 2007 Elsevier B.V. All rights reserved.
Introduction Photodynamic therapy (PDT) utilizes photosensitizing agents that are selectively retained within tumor cells. The agents
∗
Corresponding author. Tel.: +81 88 633 7143; fax: +81 88 633 7144. E-mail address: [email protected] (K. Kondo).
remain inactive until being exposed to light of the proper wavelength. When activated by light, these compounds generate toxic oxygen species that promote tumor necrosis [1]. In Japan, PDT is frequently used for early lung cancer of the central airway, although it is often used for advanced lung cancer with airway obstruction in Europe and the USA [2—5]. A prospective phase II study on PDT with Photofrin for centrally located early stage lung cancer in Japan demonstrated excellent PDT efficacy (CR rate: 84.8%, recurrence rate: 10.0%) [6]. The Japanese government approved the
1572-1000/$ — see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.pdpdt.2007.06.001
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use of this modality for centrally located early stage lung cancer in 1994 and it is now the first-choice modality in Japan. However, its use is not widespread because of the very expensive and large laser equipment required (excimer dye laser) and the length of hospital stay required to prevent skin photosensitization [1,7]; therefore, there is great interest in the synthesis of new photosensitizers for PDT. Talaporfin (mono-L-aspartyl chlorin e6; Meiji Seika Kaisha, Ltd.) is a second generation photosensitizer, and has a major absorption peak at 664 nm. The characteristics of this compound include a low degree of skin photosensitivity and both a direct antitumor activity and vascular obstruction effect, which is similar to Photofrin [8]. A prospective phase II study on PDT with Talaporfin for centrally located early stage lung cancer demonstrated excellent PDT efficacy (CR rate: 85.7%) and skin photosensitivity mostly disappeared within 2 weeks [9]. Thus, PDT for early lung cancer by Talaporfin is expected to become popular as a noninvasive therapy. PDT was performed with Talaporfin for six patients with centrally located early stage lung cancer. It was noticed that some patients had differences between the arterial oxygen saturation level using a pulse oximeter (SpO2 ) and using a blood gas analysis (SaO2 ) during PDT. A pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin using a 660 nm (red) and 940 nm (infrared) lightemitting diode (LED) [10]. Talaporfin is excited by 664 nm LED light. It was considered that the 660 nm red LED light of the pulse oximeter excited Talaporfin, and that Talaporfin increased blood absorbance at 660 nm, affecting the SpO2 by pulse oximeter. In order to confirm this speculation, the influence of Talaporfin on SpO2 by pulse oximeter was examined using in vitro and in vivo experiments, and clinically.
Material and methods
Influence of Talaporfin on SpO2 by pulse oximeter in an in vitro experiment The optical absorption of pig plasma was measured with or without Talaporfin using a UV-3000 spectrophotometer (Shimadzu Corp., Kyoto, Japan). The relationship between optical absorption and wavelength is shown in Fig. 1. Pig plasma with 10 g/mL Talaporfin showed a peak wavelength of 664 nm. Fifty milligrams of Talaporfin was dissolved in 5 mL saline (concentration 10 mg/mL). Talaporfin 100 g (10 L) was added to pig plasma (10 mL) to made a Talaporfin solution of 10 g/mL. The optical absorption of the pig plasma was measured at various wavelengths, with or without Talaporfin, using a UV-3000 spectrophotometer (Shimadzu Corp., Kyoto, Japan) (Fig. 1). In order to determine whether the presence of Talaporfin created false readings of SpO2 in pulse oximetry in an in vitro experiment, a Waseda mock circulatory system was used, which simulates blood circulation in tissue. The Waseda mock circulatory system was constructed with an artificial heart, compliance chambers of the arteries and veins, an artificial lung, and a pulsation cell through which the optical properties of the flowing blood were investigated [11]. In the pulsation flow cell, the thickness of the blood layer changed in proportion to the pulsatile pressure. 1.7 L of pig whole blood (Hb = 15.5 g/dL) were added to the Waseda mock circulatory system. Blood pressure was set at 120/90 mmHg (Sys/Dia) and the heart rate was 60 beats/min. To measure the light transmitted through the blood, a pulse oximeter probe, TL-341P (Nihon Kohden Corp., Tokyo, Japan) was attached to the light source and a photo detector to the pulsation flow cell. The pulse oximeter, DDG-3300 (Nihon Kohden Corp., Tokyo, Japan) calculated the SpO2 level using absorption ratios of 660 nm and 940 nm (A660 /A940 ). The Talaporfin concentration in the pig plasma was changed and SpO2 measured using a pulse oximeter, DDG-3300. Hundred percent of O2 gas was supplied to the artificial lung to maintain a blood SaO2 level of 100%.
Photosensitizer Talaporfin (talaporfin sodium, Laserphyrin® , formerly called mono-L-aspartyl chlorin e6, Meiji Seika Kaisha, Ltd., Tokyo, Japan) is an effective photosensitizer possessing high chemical purity and a major absorption band at 664 nm [8].
Figure 1 664 nm.
Influence of Talaporfin on SpO2 by pulse oximeter in an in vivo experiment Three healthy anesthetized pigs of mixed breed (Hampshire, Yorkshire and Swedish native breed) with a mean weight of 40 kg were investigated. The protocols of all ani-
Optical absorption and wavelength of pig plasma with or without Talaporfin. Talaporfin has a major absorption band at
PDT using Talaporfin mal experiments were approved by the Institutional Animal Care and Use Committee of the University of Tokushima Graduate School, and performed according to their guidelines. Before being transported to the laboratory, the pigs were premedicated with 2 mg of azaperon per kg of body weight, administered by intramuscular (IM) injection. Anesthesia was induced with 0.05 mg of atropine and 10 mg of ketamine per kg of body weight IM. A bolus injection of 1 mg/kg body of isozol was administered intravenously. The animals were placed in the supine position on a heating pad and intubated with a cuffed endotracheal tube, with an inner diameter of 6.0 mm. Anesthesia was maintained by the inhalation of 2% isofuran in 1000 mL of Rehydrex with glucose. All pigs received mechanical ventilation (Evita 4; Dr¨ ager Medical; L¨ ubeck, Germany) in volume-controlled (intermittent positive-pressure ventilation) mode. Ventilator settings were the fraction of inspired oxygen of 0.4 and a PEEP of 3 cm H2 O. The tidal volume was set to 14 mL/kg. The respiratory rate was adjusted to achieve a stable end-tidal CO2 of 5.5 kPa. A pulse oximeter (OLV-3100, Nihon Kohden Corp., Tokyo, Japan) was attached to a pig earlobe and the SpO2 level was confirmed to be more than 98%. After administrating Talaporfin (10 mg/kg body weight) to pigs intravenously, SpO2 levels were measured with the pulse oximeter, SaO2 by blood gas analysis, and the plasma concentration of Talaporfin at 10, 20, 30, 40, 55 and 110 min after administration.
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Figure 2 SpO2 level and Talaporfin concentration in pig plasma using a pulse oximeter in the Waseda mock circulatory system. Talaporfin concentration in plasma and the SaO2 level showed a linear relation (R = 0.9957).
pulse oximeter and SaO2 from blood gas pre-PDT and 5 or 24 h post-PDT to examine the influence of Talaporfin on SpO2 by pulse oximetry. Informed consent was obtained from each patient.
Results Measurement of Talaporfin concentration in pig plasma Ten milliliters of pig blood was centrifuged and separated into blood cells and plasma. A hundred microliters of pig plasma was mixed with 100 L of 50 mM HEPES Buffer with 0.4% EDTA (pH 7.4) and 700 L of 125 ng/mL Fluoranthene (internal control solution). This mixture was vigorously shaken for 3 min and the phases were then separated by centrifugation at 4 ◦ C (10000 rpm for 10 min). The upper phase was removed and analyzed using HPLC: LC-10A (Shimadzu Corp., Kyoto, Japan) and a fluorescence detector: RF-10AXL (Shimadzu Corp., Kyoto, Japan).
Influence of Talaporfin on SpO2 by pulse oximeter in the clinic Three patients with early lung cancer of the central airway underwent PDT using Talaporfin in our hospital. All patients were male, and their median age was 65.2 years old. The histological type was squamous cell carcinoma. One vial of Talaporfin, containing 100 mg, was dissolved in 4 mL of physiological saline, and the defined dose (40 mg/m2 ) was slowly injected intravenously. At 4 h after administration, a 664 nm laser beam was used to irradiate the tumor site endoscopically using a diode laser (PD laser, Matsushita Electric Industrial Co., Ltd., Kadoma, Japan; power density: 150 mW/cm2 ; energy level: 100 J/cm2 ). The output power and wavelength of the laser were determined before and after irradiation using an optical power meter and an optical spectrum analyzer in order to confirm the performance of the laser apparatus. SpO2 was measured by
Influence of Talaporfin on SpO2 by pulse oximeter in the in vitro experiment Talaporfin in the plasma was measured at five concentrations between 0 g/mL and 20.8 g/mL, and SpO2 was measured using a pulse oximeter with the Waseda mock circulatory system that simulates blood circulation in tissue. The relationship between the Talaporfin concentration in plasma and the SpO2 level by the pulse oximeter is shown in Fig. 2, and was linear (R = 0.9957). The SpO2 level was apparently decreasing, according to the increase of the Talaporfin concentration in the plasma, which therefore underestimates the value of SpO2 as determined by the apparatus.
Influence of Talaporfin on SpO2 by pulse oximeter in the in vivo experiment After administering Talaporfin (10 mg/kg body weight) to three pigs intravenously, SpO2 was measured with a pulse oximeter, SaO2 from blood gas, and the plasma concentration of Talaporfin at 10, 20, 30, 40, 55 and 110 min after administration. The hemoglobin of pigs was about 7.0 g/dL. The relationship between the plasma concentration of Talaporfin and the time after the administration of Talaporfin in one pig is shown in Fig. 3. The serum concentration of Talaporfin decreased with time. The relationship between the serum concentration of Talaporfin and the SpO2 level is shown in Fig. 4 (n = 3). The plasma concentration of Talaporfin and the SpO2 level showed a linear relation (R = 0.9837). The indicated SpO2 level decreased with the
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K. Kondo et al. before administration (98% in Patient D, 94% in Patient E, or 96.7% (SaO2 by blood gas analysis) in Patient F).
Discussion
Figure 3 Serum concentration of Talaporfin and the time after administrating Talaporfin in a pig. Serum concentration of Talaporfin decreased with time.
increase of Talaporfin concentration in the plasma. The increase of the Talaporfin concentration in the plasma therefore underestimates the value of SpO2 .
Influence of Talaporfin on SpO2 by pulse oximeter in the clinic Three patients (A—C) with early lung cancer of the central airway were injected with Talaporfin (40 mg/m2 ) intravenously and underwent laser irradiation 4 h after administration in our hospital. SpO2 by pulse oximeter and SaO2 by blood gas analysis pre-PDT and 5 or 24 h post-PDT are shown in Table 1. In Patients A and B, SpO2 by pulse oximeter before the administration of Talaporfin was 97%, whereas it was 93% at 5 h after administration and 97% at 24 h after administration. On the other hand, SaO2 by blood gas analysis pre-PDT and 5 or 24 h post-PDT was almost constant (97.3—98.8%). SaO2 by blood gas analysis 5 h after administration in Patient C was not more than 97% because of his severe COPD. Table 1 also shows the SpO2 by pulse oximeter before and after the administration of Talaporfin in patients (D—F) in other hospitals. It was indicated that SpO2 levels after the administration of Talaporfin (90% in Patient D, 88% and 92% in Patient E, 87% and 94% in Patient F) were lower than
Figure 4 Plasma concentration of Talaporfin and SpO2 level. The plasma concentration of Talaporfin and the SpO2 level showed a linear relation (R = 0.9837).
Two large clinical studies on PDT with Photofrin for early stage lung cancer in Japan demonstrated that the rate of CR was about 80% for early stage lung cancer of the central type [9,12]. In Japan, PDT is the first-choice modality for centrally located early stage lung cancer; however, PDT using Photofrin had some problems: (1) the drug and laser equipment are very expensive, (2) the laser equipment is particularly large, (3) patients treated with PDT frequently suffer from skin photosensitization. Dougherty and Marcus reported that 20—40% of patients treated with PDT had some type of phototoxic response [1]. PDT using a second generation photosensitizer, Talaporfin, and a PD laser is a very attractive method which can overcome some disadvantages of PDT using Photofrin. Talaporfin has shown the same antitumor efficacy as Photofrin and is rapidly cleared from the skin. A skin photosensitivity test in a rat tumor model demonstrated that the photosensitivity of Photofrin continued until 14 days after administration, and that the photosensitivity of Talaporfin disappeared after the 2nd day [8]. A phase II clinical study of PDT using Talaporfin in Japan reported that the frequency of grade 1 skin photosensitivity was 10.0% (4/40), and that grade 2—4 skin photosensitivity or skin photosensitization was zero. Talaporfin showed very low skin photosensitivity compared with Photofrin (grade 1 skin photosensitization: 28.8%, grade 2: 1.9%) [9]. Moreover, PD laser equipment is compact, easy to handle, almost maintenance free and inexpensive. PDT using Talaporfin and a PD laser is widely employed. Twenty-one patients with lung cancer of the central airway were treated by PDT using Photofrin, and six patients with lung cancer by PDT using Talaporfin. It was noticed that some patients had altered levels of SpO2 by pulse oximeter and SaO2 by blood gas analysis during PDT using Talaporfin; however, this has not been experienced using Photofrin. Talaporfin has a major absorption band at 664 nm, while Photofrin has a band at 630 nm. The mathematical model for computing arterial oxygen saturation by pulse oximeter (SpO2 ) is based on the ratio of optical density in the tissues at red and infrared wavebands (Fig. 5) [13]. The pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin with 660 nm (red) and 910—940 nm (infrared) LEDs (Nippon Koden Corporation, Tokyo, Japan; red: 660 nm; infrared: 940 nm, Nellcor Corporation; red: 660 nm; infrared: 920 nm, Masimo Corporation; red: 660 nm; infrared 910 nm) [10,14]. Although the wavelength in the infrared region slightly differs in several companies, the wavelength in the red region is constant. It was considered that the 660 nm red LED light of the pulse oximeter affected Talaporfin, which raised blood absorbance at 660 nm and reduced the SpO2 by pulse oximeter. The pulse oximeter has emerged as an easily applied, noninvasive and continuous monitor of SpO2 in patients with respiratory failure and in the perioperative period. Previous studies have already demonstrated that intravenously administered dyes, such as patent blue, indigo carmine and
PDT using Talaporfin Table 1
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SpO2 of the pulse oximeter before and after the administration of Talaporfin in the patients
Talaporfin administration
O2 therapy (L/min)
SpO2 by pulse oximeter (%)
SpO2 by blood gas analysis (%)
PaO2 by blood gas analysis (mmHg)
Patient A Before 6 h after 24 h after
0 2 2
97 93 97
97.3 98.4 98.8
94.9 116.6 135.3
Patient B Before 1 h after 5 h after 24 h after
0 0 0 0
97 95 93 97
97.5 98.1 97.4 98.2
89.5 96 84.8 100.2
Patient C Before 5 h after 24 h after
0 2 2
92 94 99
93.6 93.4 97.5
69.1 66.1 94.9
Patient D Before 4 h after
0 2
98 90
— —
— —
Patient E Before Soon after 4 h after
0 0 0
94 88 92
— — —
— — —
Patient F Before 4 h after 9 h after
3 3 3
97 87 94
— — —
— — —
methylene blue can cause sudden decreases in the pulse oximeter [15,16]. This study is the first to demonstrate that a photosensitizer for PDT influences the SpO2 level by pulse oximeter.
Figure 5 Best estimate of the spectrum of Hb and HbO2 from a variety of sources by Scott Prahl. The pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin using 660 nm (red) and 910—940 nm (infrared) LEDs.
First, the in vitro experiment using the Waseda mock circulatory system demonstrated that the Talaporfin concentration in the plasma and SpO2 level showed a linear relation (R = 0.9957). Second, the in vivo experiment using pigs also demonstrated that the relationship between the plasma concentration of Talaporfin and the SpO2 level was linear (R = 0.9837). Fig. 6 shows the Talaporfin concentration in the plasma of humans after the administration of 1 mg/kg body weight Talaporfin [8]. Talaporfin concentration in plasma was about 23 g/mL from 2 to 6 h after administration, whereas it was about 12 g/mL at 24 h after administration, and decreased with time. The in vitro experiment showed that SpO2 levels at 20 and 10 g/mL Talaporfin concentration in the plasma were 91% and 95.5%, respectively. The in vivo experiment showed that SpO2 levels at 20 and 10 g/mL Talaporfin concentration in the plasma were 93% and 96%, respectively. The clinical data in our hospital showed that SpO2 levels in patients without severe COPD 4—6 h and 24 h after Talaporfin administration were 93% and 97%, although the SaO2 level by blood gas analysis was constant. Data from the clinic and experiments in this study demonstrated that the 660 nm red LED light of the pulse oximeter affected Talaporfin, and that Talaporfin raises blood absorbance at 660 nm and decreases the SpO2 by pulse oximeter. In PDT for central-type early lung cancer, most patients were heavy smokers and had various respiratory disorders. PDT for lung cancer was primarily performed with a
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K. Kondo et al. University of Tsukuba, Shinji Sasada, MD, Department of Thoracic Malignancy, Osaka Prefectural Medical Center for Respiratory and Allergic Disease, Masashi Uomoto MD, PhD, Department of Thoracic Surgery, Matsuyama Shimin Hospital for the provision of clinical data (SpO2 by pulse oximeter before and after the administration of Talaporfin in patients with lung cancer).
References
Figure 6 Talaporfin concentration in the plasma of humans after the administration of 1 mg/kg body weight of Talaporfin. Talaporfin concentration in the plasma was about 23 g/mL from 2 to 6 h after administration. Talaporfin concentration in the plasma 24 h after administration was about 12 g/mL.
flexible bronchoscope under local anesthesia, accompanied by coughing, which deteriorates the respiratory condition. Monitoring patients’ respiratory state using a pulse oximeter during and after PDT is indispensable. In the 0—24 h after Talaporfin administration (1 mg/kg body weight), the SpO2 level by pulse oximeter can decrease to 90%. The decrease of the SpO2 level just after administration was the greatest, and then increased according to the decrease of the Talaporfin concentration in the plasma. If physicians need to know the true SpO2 level during this period, they should perform blood gas analysis. From 24 h after administration, the decrease by Talaporfin of the SpO2 level by pulse oximeter was clinically not a problem. If physicians understand the influence of Talaporfin on the SpO2 level by pulse oximeter, they can perform appropriate respiratory care using a pulse oximeter for patients that undergo PDT with Talaporfin. In conclusion, this method will likely become the standard modality of PDT for central-type early lung cancer; however, this study demonstrated that the 660 nm red LED of the pulse oximeter affected Talaporfin. It appears that the presence of the drug falsely decreased the level of SpO2 . Several dyes such as Talaporfin, patent blue, indigo carmine and methylene blue have been widely used in diagnostic and therapeutic procedures, and improvement of the pulse oximeter, which can measure the absorbance of two wavelengths of light that are not influenced by dyes, is expected in the future.
Acknowledgments We thank Shigemi Ishikawa, MD, Department of Chest Surgery, Graduate School of Comprehensive Human Science,
[1] Dougherty TJ, Marcus SL. Photodynamic therapy. Eur J Cancer 1992;28A:1734—42. [2] Kato H, Okunaka T, Shimatani H. Photodynamic therapy for early stage bronchogenic carcinoma. J Clin Laser Med Surg 1996;14:235—8. [3] McCaugham J, Williams T. Photodynamic therapy for endobronchial malignant disease. A prospective fourteen years study. J Thorac Cardiovasc Surg 1997;114:940—7. [4] Moghissi K, Dixon K, Stringer M, Freeman T, Thorpe A, Brown S. The place of bronchoscopic photodynamic therapy in advanced unresectable lung cancer: experience of 100 cases. Eur J Cardiothorac Surg 1999;15:1—6. [5] Ost D. Photodynamic therapy in lung cancer. Oncology (Huntingt) 2000;14:379—86. [6] Furuse K, Fukuoka M, Kato H, et al. A prospective phase II study on photodynamic therapy with Photofrin II for centrally located early-stage lung cancer. J Clin Oncol 1993;11:1852— 7. [7] Marcus SL. Clinical photodynamic therapy: the continuing evolution. In: Henderson BW, Dougherty TJ, editors. Photodynamic therapy, basic principles and clinical applications. New York: Dekker; 1992. p. 219—68. [8] Saito K, Shibasaki S, Kurosawa T. Kagakuryouhou no ryouiki (in Japanese) 2004;20:1571—1576. [9] Kato H, Furukawa K, Sato M, et al. Phase II clinical study of photodynamic therapy using mono-L-aspartyl chlorin e6 and diode laser for early superficial squamous cell carcinoma of the lung. Lung Cancer 2003;42:103—11. [10] Aoyagi T. Pulse oximetry. Jpn Soc Resp Japan 1992;11:560— 7. [11] Suzaki H, Kobayashi N, Kubota H, et al. Relation between hematocrit and optical density in pulse oximetry: in vitro study with Waseda mock circulatory system. In: Proceeding of 27th Annual International Conference of the IEEE Engineering and Biology Society (EMBC’05). 2005. p. 251— 4. [12] Kato H. Study on photodynamic therapy by laser. Annual report of the Cancer Research Ministry of Health and Welfare. National Cancer Center (in Japanese), 1988, p. 255— 261. [13] Scott Prahl. http://omlc.ogi.edu/spectra/hemoglobin/index. html. [14] Farber NE, McNeely J, Rosner D. Skin burn associated with pulse oximetry during perioperative photodynamic therapy. Aneshesiology 1996;84:983—5. [15] Saito S, Fukura H, Shimada H, Fujita T. Prolonged interference of blue dye ‘‘patent blue’’ with pulse oximetry readings. Acta Anaesthesiol Scand 1995;39:268—9. [16] Scheller MS, Unger RJ, Kelner MJ. Effects of intravenously administered dyes on pulse oximetry readings. Aneshesiology 1986;65:550—2.
available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/pdpdt
Photodynamic therapy using a second generation photosensitizer, Talaporfin Kazuya Kondo MD, PhD a,∗, Takanori Miyoshi a, Haruhiko Fujino a, Hiromitsu Takizawa a, Satoshi Imai b, Naoki Kobayashi c, Koichiro Kenzaki a, Shoji Sakiyama a, Akira Tangoku a a
Department of Oncological and Regenerative Surgery, Institute of Health Biosciences, University of Tokushima Graduate School, Kuramoto-cho, Tokushima 770-8503 Japan b Meiji Seika Kaisha, Ltd., Tokyo, Japan c Nippon Koden Corporation, Tokyo, Japan Available online 3 August 2007
KEYWORDS Talaporfin; Photodynamic therapy; Pulse oximeter; Lung cancer
Summary Background: Photodynamic therapy (PDT) using Talaporfin is an attractive treatment for centraltype early lung cancer. It was noted that some patients had altered levels of arterial oxygen saturation as indicated by pulse oximeter (SpO2 ) and arterial oxygen saturation levels in blood gas analysis (SaO2 ) during PDT. The present experiments were designed to provide an explanation for these findings. Methods: The influence of Talaporfin on SpO2 using in vitro and in vivo experiments, and clinically, was examined. Results: Our in vitro and in vivo experiments showed a linear relationship between Talaporfin concentration in the plasma and the SpO2 level (R = 0.9957 and 0.9837). The apparent SpO2 level decreased according to the increase of Talaporfin concentration in the plasma. In two patients with PDT, SpO2 levels at 4—6 h and 24 h after Talaporfin administration were 93% and 97%, respectively. Conclusions: Talaporfin raised blood absorbance at 660 nm with a pulse oximeter. It appeared that the presence of the drug falsely decreased the level of SpO2 since SpO2 did not actually change. © 2007 Elsevier B.V. All rights reserved.
Introduction Photodynamic therapy (PDT) utilizes photosensitizing agents that are selectively retained within tumor cells. The agents
∗
Corresponding author. Tel.: +81 88 633 7143; fax: +81 88 633 7144. E-mail address: [email protected] (K. Kondo).
remain inactive until being exposed to light of the proper wavelength. When activated by light, these compounds generate toxic oxygen species that promote tumor necrosis [1]. In Japan, PDT is frequently used for early lung cancer of the central airway, although it is often used for advanced lung cancer with airway obstruction in Europe and the USA [2—5]. A prospective phase II study on PDT with Photofrin for centrally located early stage lung cancer in Japan demonstrated excellent PDT efficacy (CR rate: 84.8%, recurrence rate: 10.0%) [6]. The Japanese government approved the
1572-1000/$ — see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.pdpdt.2007.06.001
270
K. Kondo et al.
use of this modality for centrally located early stage lung cancer in 1994 and it is now the first-choice modality in Japan. However, its use is not widespread because of the very expensive and large laser equipment required (excimer dye laser) and the length of hospital stay required to prevent skin photosensitization [1,7]; therefore, there is great interest in the synthesis of new photosensitizers for PDT. Talaporfin (mono-L-aspartyl chlorin e6; Meiji Seika Kaisha, Ltd.) is a second generation photosensitizer, and has a major absorption peak at 664 nm. The characteristics of this compound include a low degree of skin photosensitivity and both a direct antitumor activity and vascular obstruction effect, which is similar to Photofrin [8]. A prospective phase II study on PDT with Talaporfin for centrally located early stage lung cancer demonstrated excellent PDT efficacy (CR rate: 85.7%) and skin photosensitivity mostly disappeared within 2 weeks [9]. Thus, PDT for early lung cancer by Talaporfin is expected to become popular as a noninvasive therapy. PDT was performed with Talaporfin for six patients with centrally located early stage lung cancer. It was noticed that some patients had differences between the arterial oxygen saturation level using a pulse oximeter (SpO2 ) and using a blood gas analysis (SaO2 ) during PDT. A pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin using a 660 nm (red) and 940 nm (infrared) lightemitting diode (LED) [10]. Talaporfin is excited by 664 nm LED light. It was considered that the 660 nm red LED light of the pulse oximeter excited Talaporfin, and that Talaporfin increased blood absorbance at 660 nm, affecting the SpO2 by pulse oximeter. In order to confirm this speculation, the influence of Talaporfin on SpO2 by pulse oximeter was examined using in vitro and in vivo experiments, and clinically.
Material and methods
Influence of Talaporfin on SpO2 by pulse oximeter in an in vitro experiment The optical absorption of pig plasma was measured with or without Talaporfin using a UV-3000 spectrophotometer (Shimadzu Corp., Kyoto, Japan). The relationship between optical absorption and wavelength is shown in Fig. 1. Pig plasma with 10 g/mL Talaporfin showed a peak wavelength of 664 nm. Fifty milligrams of Talaporfin was dissolved in 5 mL saline (concentration 10 mg/mL). Talaporfin 100 g (10 L) was added to pig plasma (10 mL) to made a Talaporfin solution of 10 g/mL. The optical absorption of the pig plasma was measured at various wavelengths, with or without Talaporfin, using a UV-3000 spectrophotometer (Shimadzu Corp., Kyoto, Japan) (Fig. 1). In order to determine whether the presence of Talaporfin created false readings of SpO2 in pulse oximetry in an in vitro experiment, a Waseda mock circulatory system was used, which simulates blood circulation in tissue. The Waseda mock circulatory system was constructed with an artificial heart, compliance chambers of the arteries and veins, an artificial lung, and a pulsation cell through which the optical properties of the flowing blood were investigated [11]. In the pulsation flow cell, the thickness of the blood layer changed in proportion to the pulsatile pressure. 1.7 L of pig whole blood (Hb = 15.5 g/dL) were added to the Waseda mock circulatory system. Blood pressure was set at 120/90 mmHg (Sys/Dia) and the heart rate was 60 beats/min. To measure the light transmitted through the blood, a pulse oximeter probe, TL-341P (Nihon Kohden Corp., Tokyo, Japan) was attached to the light source and a photo detector to the pulsation flow cell. The pulse oximeter, DDG-3300 (Nihon Kohden Corp., Tokyo, Japan) calculated the SpO2 level using absorption ratios of 660 nm and 940 nm (A660 /A940 ). The Talaporfin concentration in the pig plasma was changed and SpO2 measured using a pulse oximeter, DDG-3300. Hundred percent of O2 gas was supplied to the artificial lung to maintain a blood SaO2 level of 100%.
Photosensitizer Talaporfin (talaporfin sodium, Laserphyrin® , formerly called mono-L-aspartyl chlorin e6, Meiji Seika Kaisha, Ltd., Tokyo, Japan) is an effective photosensitizer possessing high chemical purity and a major absorption band at 664 nm [8].
Figure 1 664 nm.
Influence of Talaporfin on SpO2 by pulse oximeter in an in vivo experiment Three healthy anesthetized pigs of mixed breed (Hampshire, Yorkshire and Swedish native breed) with a mean weight of 40 kg were investigated. The protocols of all ani-
Optical absorption and wavelength of pig plasma with or without Talaporfin. Talaporfin has a major absorption band at
PDT using Talaporfin mal experiments were approved by the Institutional Animal Care and Use Committee of the University of Tokushima Graduate School, and performed according to their guidelines. Before being transported to the laboratory, the pigs were premedicated with 2 mg of azaperon per kg of body weight, administered by intramuscular (IM) injection. Anesthesia was induced with 0.05 mg of atropine and 10 mg of ketamine per kg of body weight IM. A bolus injection of 1 mg/kg body of isozol was administered intravenously. The animals were placed in the supine position on a heating pad and intubated with a cuffed endotracheal tube, with an inner diameter of 6.0 mm. Anesthesia was maintained by the inhalation of 2% isofuran in 1000 mL of Rehydrex with glucose. All pigs received mechanical ventilation (Evita 4; Dr¨ ager Medical; L¨ ubeck, Germany) in volume-controlled (intermittent positive-pressure ventilation) mode. Ventilator settings were the fraction of inspired oxygen of 0.4 and a PEEP of 3 cm H2 O. The tidal volume was set to 14 mL/kg. The respiratory rate was adjusted to achieve a stable end-tidal CO2 of 5.5 kPa. A pulse oximeter (OLV-3100, Nihon Kohden Corp., Tokyo, Japan) was attached to a pig earlobe and the SpO2 level was confirmed to be more than 98%. After administrating Talaporfin (10 mg/kg body weight) to pigs intravenously, SpO2 levels were measured with the pulse oximeter, SaO2 by blood gas analysis, and the plasma concentration of Talaporfin at 10, 20, 30, 40, 55 and 110 min after administration.
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Figure 2 SpO2 level and Talaporfin concentration in pig plasma using a pulse oximeter in the Waseda mock circulatory system. Talaporfin concentration in plasma and the SaO2 level showed a linear relation (R = 0.9957).
pulse oximeter and SaO2 from blood gas pre-PDT and 5 or 24 h post-PDT to examine the influence of Talaporfin on SpO2 by pulse oximetry. Informed consent was obtained from each patient.
Results Measurement of Talaporfin concentration in pig plasma Ten milliliters of pig blood was centrifuged and separated into blood cells and plasma. A hundred microliters of pig plasma was mixed with 100 L of 50 mM HEPES Buffer with 0.4% EDTA (pH 7.4) and 700 L of 125 ng/mL Fluoranthene (internal control solution). This mixture was vigorously shaken for 3 min and the phases were then separated by centrifugation at 4 ◦ C (10000 rpm for 10 min). The upper phase was removed and analyzed using HPLC: LC-10A (Shimadzu Corp., Kyoto, Japan) and a fluorescence detector: RF-10AXL (Shimadzu Corp., Kyoto, Japan).
Influence of Talaporfin on SpO2 by pulse oximeter in the clinic Three patients with early lung cancer of the central airway underwent PDT using Talaporfin in our hospital. All patients were male, and their median age was 65.2 years old. The histological type was squamous cell carcinoma. One vial of Talaporfin, containing 100 mg, was dissolved in 4 mL of physiological saline, and the defined dose (40 mg/m2 ) was slowly injected intravenously. At 4 h after administration, a 664 nm laser beam was used to irradiate the tumor site endoscopically using a diode laser (PD laser, Matsushita Electric Industrial Co., Ltd., Kadoma, Japan; power density: 150 mW/cm2 ; energy level: 100 J/cm2 ). The output power and wavelength of the laser were determined before and after irradiation using an optical power meter and an optical spectrum analyzer in order to confirm the performance of the laser apparatus. SpO2 was measured by
Influence of Talaporfin on SpO2 by pulse oximeter in the in vitro experiment Talaporfin in the plasma was measured at five concentrations between 0 g/mL and 20.8 g/mL, and SpO2 was measured using a pulse oximeter with the Waseda mock circulatory system that simulates blood circulation in tissue. The relationship between the Talaporfin concentration in plasma and the SpO2 level by the pulse oximeter is shown in Fig. 2, and was linear (R = 0.9957). The SpO2 level was apparently decreasing, according to the increase of the Talaporfin concentration in the plasma, which therefore underestimates the value of SpO2 as determined by the apparatus.
Influence of Talaporfin on SpO2 by pulse oximeter in the in vivo experiment After administering Talaporfin (10 mg/kg body weight) to three pigs intravenously, SpO2 was measured with a pulse oximeter, SaO2 from blood gas, and the plasma concentration of Talaporfin at 10, 20, 30, 40, 55 and 110 min after administration. The hemoglobin of pigs was about 7.0 g/dL. The relationship between the plasma concentration of Talaporfin and the time after the administration of Talaporfin in one pig is shown in Fig. 3. The serum concentration of Talaporfin decreased with time. The relationship between the serum concentration of Talaporfin and the SpO2 level is shown in Fig. 4 (n = 3). The plasma concentration of Talaporfin and the SpO2 level showed a linear relation (R = 0.9837). The indicated SpO2 level decreased with the
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K. Kondo et al. before administration (98% in Patient D, 94% in Patient E, or 96.7% (SaO2 by blood gas analysis) in Patient F).
Discussion
Figure 3 Serum concentration of Talaporfin and the time after administrating Talaporfin in a pig. Serum concentration of Talaporfin decreased with time.
increase of Talaporfin concentration in the plasma. The increase of the Talaporfin concentration in the plasma therefore underestimates the value of SpO2 .
Influence of Talaporfin on SpO2 by pulse oximeter in the clinic Three patients (A—C) with early lung cancer of the central airway were injected with Talaporfin (40 mg/m2 ) intravenously and underwent laser irradiation 4 h after administration in our hospital. SpO2 by pulse oximeter and SaO2 by blood gas analysis pre-PDT and 5 or 24 h post-PDT are shown in Table 1. In Patients A and B, SpO2 by pulse oximeter before the administration of Talaporfin was 97%, whereas it was 93% at 5 h after administration and 97% at 24 h after administration. On the other hand, SaO2 by blood gas analysis pre-PDT and 5 or 24 h post-PDT was almost constant (97.3—98.8%). SaO2 by blood gas analysis 5 h after administration in Patient C was not more than 97% because of his severe COPD. Table 1 also shows the SpO2 by pulse oximeter before and after the administration of Talaporfin in patients (D—F) in other hospitals. It was indicated that SpO2 levels after the administration of Talaporfin (90% in Patient D, 88% and 92% in Patient E, 87% and 94% in Patient F) were lower than
Figure 4 Plasma concentration of Talaporfin and SpO2 level. The plasma concentration of Talaporfin and the SpO2 level showed a linear relation (R = 0.9837).
Two large clinical studies on PDT with Photofrin for early stage lung cancer in Japan demonstrated that the rate of CR was about 80% for early stage lung cancer of the central type [9,12]. In Japan, PDT is the first-choice modality for centrally located early stage lung cancer; however, PDT using Photofrin had some problems: (1) the drug and laser equipment are very expensive, (2) the laser equipment is particularly large, (3) patients treated with PDT frequently suffer from skin photosensitization. Dougherty and Marcus reported that 20—40% of patients treated with PDT had some type of phototoxic response [1]. PDT using a second generation photosensitizer, Talaporfin, and a PD laser is a very attractive method which can overcome some disadvantages of PDT using Photofrin. Talaporfin has shown the same antitumor efficacy as Photofrin and is rapidly cleared from the skin. A skin photosensitivity test in a rat tumor model demonstrated that the photosensitivity of Photofrin continued until 14 days after administration, and that the photosensitivity of Talaporfin disappeared after the 2nd day [8]. A phase II clinical study of PDT using Talaporfin in Japan reported that the frequency of grade 1 skin photosensitivity was 10.0% (4/40), and that grade 2—4 skin photosensitivity or skin photosensitization was zero. Talaporfin showed very low skin photosensitivity compared with Photofrin (grade 1 skin photosensitization: 28.8%, grade 2: 1.9%) [9]. Moreover, PD laser equipment is compact, easy to handle, almost maintenance free and inexpensive. PDT using Talaporfin and a PD laser is widely employed. Twenty-one patients with lung cancer of the central airway were treated by PDT using Photofrin, and six patients with lung cancer by PDT using Talaporfin. It was noticed that some patients had altered levels of SpO2 by pulse oximeter and SaO2 by blood gas analysis during PDT using Talaporfin; however, this has not been experienced using Photofrin. Talaporfin has a major absorption band at 664 nm, while Photofrin has a band at 630 nm. The mathematical model for computing arterial oxygen saturation by pulse oximeter (SpO2 ) is based on the ratio of optical density in the tissues at red and infrared wavebands (Fig. 5) [13]. The pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin with 660 nm (red) and 910—940 nm (infrared) LEDs (Nippon Koden Corporation, Tokyo, Japan; red: 660 nm; infrared: 940 nm, Nellcor Corporation; red: 660 nm; infrared: 920 nm, Masimo Corporation; red: 660 nm; infrared 910 nm) [10,14]. Although the wavelength in the infrared region slightly differs in several companies, the wavelength in the red region is constant. It was considered that the 660 nm red LED light of the pulse oximeter affected Talaporfin, which raised blood absorbance at 660 nm and reduced the SpO2 by pulse oximeter. The pulse oximeter has emerged as an easily applied, noninvasive and continuous monitor of SpO2 in patients with respiratory failure and in the perioperative period. Previous studies have already demonstrated that intravenously administered dyes, such as patent blue, indigo carmine and
PDT using Talaporfin Table 1
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SpO2 of the pulse oximeter before and after the administration of Talaporfin in the patients
Talaporfin administration
O2 therapy (L/min)
SpO2 by pulse oximeter (%)
SpO2 by blood gas analysis (%)
PaO2 by blood gas analysis (mmHg)
Patient A Before 6 h after 24 h after
0 2 2
97 93 97
97.3 98.4 98.8
94.9 116.6 135.3
Patient B Before 1 h after 5 h after 24 h after
0 0 0 0
97 95 93 97
97.5 98.1 97.4 98.2
89.5 96 84.8 100.2
Patient C Before 5 h after 24 h after
0 2 2
92 94 99
93.6 93.4 97.5
69.1 66.1 94.9
Patient D Before 4 h after
0 2
98 90
— —
— —
Patient E Before Soon after 4 h after
0 0 0
94 88 92
— — —
— — —
Patient F Before 4 h after 9 h after
3 3 3
97 87 94
— — —
— — —
methylene blue can cause sudden decreases in the pulse oximeter [15,16]. This study is the first to demonstrate that a photosensitizer for PDT influences the SpO2 level by pulse oximeter.
Figure 5 Best estimate of the spectrum of Hb and HbO2 from a variety of sources by Scott Prahl. The pulse oximeter can measure the amounts of oxyhemoglobin and reduced hemoglobin using 660 nm (red) and 910—940 nm (infrared) LEDs.
First, the in vitro experiment using the Waseda mock circulatory system demonstrated that the Talaporfin concentration in the plasma and SpO2 level showed a linear relation (R = 0.9957). Second, the in vivo experiment using pigs also demonstrated that the relationship between the plasma concentration of Talaporfin and the SpO2 level was linear (R = 0.9837). Fig. 6 shows the Talaporfin concentration in the plasma of humans after the administration of 1 mg/kg body weight Talaporfin [8]. Talaporfin concentration in plasma was about 23 g/mL from 2 to 6 h after administration, whereas it was about 12 g/mL at 24 h after administration, and decreased with time. The in vitro experiment showed that SpO2 levels at 20 and 10 g/mL Talaporfin concentration in the plasma were 91% and 95.5%, respectively. The in vivo experiment showed that SpO2 levels at 20 and 10 g/mL Talaporfin concentration in the plasma were 93% and 96%, respectively. The clinical data in our hospital showed that SpO2 levels in patients without severe COPD 4—6 h and 24 h after Talaporfin administration were 93% and 97%, although the SaO2 level by blood gas analysis was constant. Data from the clinic and experiments in this study demonstrated that the 660 nm red LED light of the pulse oximeter affected Talaporfin, and that Talaporfin raises blood absorbance at 660 nm and decreases the SpO2 by pulse oximeter. In PDT for central-type early lung cancer, most patients were heavy smokers and had various respiratory disorders. PDT for lung cancer was primarily performed with a
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K. Kondo et al. University of Tsukuba, Shinji Sasada, MD, Department of Thoracic Malignancy, Osaka Prefectural Medical Center for Respiratory and Allergic Disease, Masashi Uomoto MD, PhD, Department of Thoracic Surgery, Matsuyama Shimin Hospital for the provision of clinical data (SpO2 by pulse oximeter before and after the administration of Talaporfin in patients with lung cancer).
References
Figure 6 Talaporfin concentration in the plasma of humans after the administration of 1 mg/kg body weight of Talaporfin. Talaporfin concentration in the plasma was about 23 g/mL from 2 to 6 h after administration. Talaporfin concentration in the plasma 24 h after administration was about 12 g/mL.
flexible bronchoscope under local anesthesia, accompanied by coughing, which deteriorates the respiratory condition. Monitoring patients’ respiratory state using a pulse oximeter during and after PDT is indispensable. In the 0—24 h after Talaporfin administration (1 mg/kg body weight), the SpO2 level by pulse oximeter can decrease to 90%. The decrease of the SpO2 level just after administration was the greatest, and then increased according to the decrease of the Talaporfin concentration in the plasma. If physicians need to know the true SpO2 level during this period, they should perform blood gas analysis. From 24 h after administration, the decrease by Talaporfin of the SpO2 level by pulse oximeter was clinically not a problem. If physicians understand the influence of Talaporfin on the SpO2 level by pulse oximeter, they can perform appropriate respiratory care using a pulse oximeter for patients that undergo PDT with Talaporfin. In conclusion, this method will likely become the standard modality of PDT for central-type early lung cancer; however, this study demonstrated that the 660 nm red LED of the pulse oximeter affected Talaporfin. It appears that the presence of the drug falsely decreased the level of SpO2 . Several dyes such as Talaporfin, patent blue, indigo carmine and methylene blue have been widely used in diagnostic and therapeutic procedures, and improvement of the pulse oximeter, which can measure the absorbance of two wavelengths of light that are not influenced by dyes, is expected in the future.
Acknowledgments We thank Shigemi Ishikawa, MD, Department of Chest Surgery, Graduate School of Comprehensive Human Science,
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