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Abstract

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

While photodynamic therapy (PDT) has been recognized as a promising therapeutic modality for the treatment of various cancers and diseases, developments of effective photosensitizers are highly desired to improve the prospect for the use of PDT. In this study, we evaluated DH-II-24, a new photosensitizer, for antitumor PDT in vitro and in vivo. Loaded into human colorectal carcinoma cells (HCT116), DH-II-24 was primarily accumulated in mitochondria, lysosomes, and endoplasmic reticula. Administration of DH-II-24 followed by light exposure induced necrotic cell death in a dose-dependent manner, whereas DH-II-24 in the absence of light induced minimal cell death. In order to investigate the distribution and phamacokinetics of the photosensitizer in vivo, DH-II-24 was intravenously injected to female BALB/c nude mice. Fluorescence imaging in vivo showed that DH-II-24 was rapidly distributed across the entire body and then mostly eliminated at 24 h. Next, effectiveness of DH-II-24-mediated PDT was examined on colorectal carcinoma xenografts established subcutaneously in BALB/c nude mice. DH-II-24 (1 mg/kg, i.v. administration) followed by light exposure significantly suppressed growth of xenograft tumors, compared to light exposure or DH-II-24 alone. Histological examination revealed necrotic damage in PDT-treated tumors, concomitantly with severe damage of tumor vasculature. These results suggest that DH-II-24 is a potential photosensitizer of photodynamic therapy for cancer. (Cancer Sci 2009; 100: 2431–2436)

Photodynamic therapy (PDT) is emerging as a promising non-invasive treatment for cancer.(1–4) PDT involves an administration of a photosensitizer followed by illumination of tumor tissues with visible light of a suitable wavelength for excitation of the photosensitizer.(5,6) The activation of the photosensitizer leads to conversion of molecular oxygen to various highly reactive oxygen species (ROS), which kills tumor cells directly or damages the tumor-associated vasculature.(1,2,7) Tumor vascular damage subsequently deprives the oxygen and nutrients of tumor, resulting in tumor cell death.(2,4,8) In addition, PDT could have a significant stimulatory effect on the immune system.(1,8,9) These multifactorial mechanisms by which PDT mediates tumor destruction have been suggested to be beneficial for long-term tumor control.(7,9)

PDT has several advantages over other conventional cancer treatments.(4) Since it requires mere illumination of the tumor site, the treatment is relatively non-invasive.(4) PDT does not induce systemic immunosupression that causes a variety of infections.(8) PDT displays low systemic toxicity and relatively selective destruction of tumors, which is known to be in part due to preferential localization of photosensitizer within tumor.(2,10,11) Thus, PDT has been widely employed to various tumors directly approachable to illumination, such as esophageal carcinoma, head and neck tumors, bladder, prostate, nonmelanoma skin cancers, and actinic keratosis.(7,12–16) Compared with other therapies, PDT often produces a high cure rate and low recurrence rate.(6,16)

However, as every technique has its limits, the prospect of the use of PDT has been limited due to lack of effective photosensitizers.(6) For example, Photofrin, the most widely used photosensitizer in clinical PDT, has several weaknesses with clinical applications(2) including prolonged skin photosensitivity and absorption wavelength not optimal for tissue penetration.(4,6) Thus, a great deal of effort has been invested in the development of new photosensitizers that display preferential accumulation in the target tumor tissue, rapid clearance from the circulation system, minimal toxicity in the absence of light, and high molecular extinction coefficient.(4,6,7,17,18) Several second-generation photosensitizers have been shown to improve efficacy and decrease side effects, compared to first-generation photosensitizers, hematoporphyrin derivatives such as Photofrin.(4,6) In parallel with the development of new photosensitizers, DH-II-24 was recently developed and investigated in vitro.(19) DH-II-24-mediated PDT has been reported to produce intracellular ROS via elevation in intracellular calcium resulting in necrotic death of the human gastric adenocarcinoma cells.(19)

In this present study, we demonstrate, for the first time, that DH-II-24-mediated PDT effectively represses growth of xenograft tumors via necrotic cell death. DH-II-24 presents some characteristics of ideal photosensitizers such as a strong absorption band at relatively long wavelength (λmax = 666), low dark toxicity, significant cytotoxicity in the presence of light, and rapid clearance from the body. This study suggests that DH-II-24-based PDT is potentially a feasible and efficient approach for non-invasive treatment of cancer.

Materials and Methods

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

Chemicals and reagents.  Fetal bovine serum, penicillin/streptomycin solution, and Dulbecco’s Modified Eagle Medium (DMEM) were obtained from Invitrogen (Carlsbad, CA, USA). MitoTracker Green FM, LysoTracker Green DND-26, and 3,3′-dihexyloxacarbocyanine iodide (DiOC6[3]) were obtained from Invitrogen. Evans Blue and methylthiazolyldiphenyl-tetrazolium bromide (MTT) were obtained from Sigma (St. Louis, MO, USA). DH-II-24 [methyl-13b-(2-dimethylaminoethoxycarbonyl)-13b-demethoxycarbonyl-pheophorbide α] (Fig. 1A) was kindly provided by Professor Chang-Hee Lee (Department of Chemistry, Kangwon National University, Korea).

image

Figure 1.  Uptake and sub-cellular localization of DH-II-24. (A) Chemical structure of DH-II-24. (B) HCT116 human colon carcinoma cells, grown on round coverslips, were incubated with the indicated concentrations of DH-II-24 for 12 h, and the uptake of DH-II-24 was estimated at the single-cell level by confocal microscopy. Data are the means ± SD of intensities of 30 cells from three independent experiments. a.u., arbitrary unit. (C) The cells were loaded with 5 μg/mL DH-II-24 for 12 h and labeled with MitoTracker Green FM, LysoTracker Green DND-26, or 3,3′-dihexyloxacarbocyanine iodide (DiOC6[3]). The images were obtained by confocal microscopy. Bar, 10 μm.

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Animals and cell lines.  Pathogen-free female BALB/c nude mice, 6 weeks of age, with a body weight of 20–25 g were obtained from Charles River (Orient Bio, Seongnam, Korea). Animals were allowed to acclimatize for 1 week in the animal facility before any intervention was initiated. All experimental procedures were conducted in accordance with the guidelines of the Kangwon Institutional Animal Care and Use Ethics Committee. HCT116 human colon cancer cells (American Type Culture Collection) were maintained at 37°C in DMEM medium supplemented with 10% fetal bovine serum, 100 unit/mL penicillin, and 100 μg/mL streptomycin in a humidified 5% CO2 incubator.

Uptake and intracellular localization of DH-II-24.  To monitor uptake of DH-II-24, HCT116 cells were grown on coverslips and incubated with various concentration of DH-II-24 for 12 h in culture medium. The cells were fixed with 3.7% formaldehyde in phosphate buffered saline (PBS) for 30 min, washed with PBS, and observed with a confocal microscope (FV 300; Olympus, Tokyo, Japan). Approximately 30 cells were randomly selected from three independent experiments, and the fluorescence intensities were measured at a single cell level.

To localize DH-II-24, HCT116 cells were loaded with 5 μg/mL DH-II-24 for 12 h in culture medium, and then incubated with 200 nm MitoTracker Green FM for 30 min, 1 μm LysoTracker Green DND-26 for 10 min, and 200 nm DiOC6(3) for 20 min to label mitochondria, lysosome, and endoplasmic reticula, respectively. The stained live cells were washed in fresh culture medium and observed with the confocal microscope.

In vitro PDT.  HCT116 cells were grown in 24-well plates and incubated with 5 μg/mL of DH-II-24 in culture medium for 12 h. Cells in a plate were placed on the microscope stage at a distance of 5 cm from the condenser and exposed to red light (1.45 mW/cm2) for different durations. Red light was generated by filtering light from a built-in 100 W halogen lamp of the confocal microscope using a long-pass filter LP630 (Fiber Optic Korea, Cheonan, Korea).

Cell viability assay.  Cell viability was determined by the MTT reduction assay. Cells were incubated with 1 mg/mL MTT solution in culture medium for 4 h, and the resulting formazan precipitate was dissolved in 200 μL of isopropanol. Absorbance at 570 nm was measured with a microplate reader (Moleclular Devices, Sunnyvlae, CA, USA). Cell viability was expressed as a percentage of A570 value of untreated control cells.

FACS analysis.  After the PDT treatment in vitro, HCT116 cells were harvested and stained with annexin V and propidium iodide (PI) using a Annexin V-FITC apoptosis detection kit I (BD Biosciences Pharmingen, San Diego, CA, USA), according to the manufacturer’s instructions. Stained cells were analyzed with a FACScan with CELLQuest software (Becton Dickinson, San Jose, CA, USA). At least 10 000 events were collected for each sample. The analyses were performed at 3, 6, and 12 h after PDT.

In vivo optical imaging of mice. In vivo fluorescence imaging was performed with an IVIS200 animal imaging system (Xenogen, Alameda, CA, USA). A Cy5.5 filter set was used for acquiring fluorescence images of DH-II-24 in vivo. Identical illumination settings (lamp voltage, filters, f/stop, field of views, binning) were used for acquiring all images, and fluorescence emission was normalized to photons per second per centimeter squared per steradian (p/s/cm2/sr). Images were acquired and analyzed using Living Image 2.6 software (Xenogne, Alameda, CA, USA).

In vivo PDT.  A xenograft tumor model was created in 6-week-old female BALB/c nude mice by subcutaneous injection of HCT116 cells (5 × 106) in 200 μL of PBS. When a tumor grew to approximately 100 mm3 in size, mice were given intravenous injection (via tail vein) of DH-II-24 in PBS at a dose of 1 mg/kg. At 4 h after injection, the tumor was illuminated for 20 min at a dose of 154 J/cm2 by closely positioning the optical fiber tip (diameter, 13 mm) to the skin right above the tumor. A fiberoptic no-coherent illuminator (FOK-150W) in combination with a LP630 filter was used for the purpose. The controls were the following: DH-II-24 alone, the mice were i.v. injected with the photosensitizer and placed in a dark place without illumination; and light alone, tumors in PBS-injected mice were illuminated under standard conditions.

Assessment of tumor response.  Tumor growth was monitored every day for 20 days by measuring tumor volume with varnier calipers. Tumor volume was calculated by the modified ellipsoidal formula: (length × width × depth)/2.(20,21) Tumor response was also examined by vital staining, which was performed by i.v. injection (via tail vein) of 350 μL 1% Evans blue solution at 12 h after the PDT session. Animals were euthanized and sacrificed 6 h later to excise tumors. The excised tumors were grossly examined and recorded photographically. For further histological examination, the excised tumors were fixed in 3.7% formaldehyde in PBS, embedded in paraffin, and sectioned to obtain 5-μm thick sections. The sections were stained with hematoxylin–eosin, and examined under a light microscope.

Results

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

Uptake and subcellular localization of DH-II-24 in HCT116 cells.  In order to evaluate DH-II-24 as a potential photosensitizer for PDT, we first examined uptake of the photosensitizer in human colorectal carcinoma HCT116 cells. After HCT116 cells were incubated with various concentrations of DH-II-24 for 12 h, the uptake of DH-II-24 was estimated by measuring the intensity of the characteristic red fluorescence at the single cell level using confocal microscopy. As shown in Figure 1B, the cells were loaded with DH-II-24 in a dose-dependent manner, with a detectable uptake at 0.5 μg/mL, and uptake saturation was observed at 5 μg/mL. Next, we investigated subcellular localization of DH-II-24 using fluorescence probes for intracellular organelles. HCT116 cells were loaded with DH-II-24 and incubated with MitoTracker Green FM, LysoTracker Green DND-26, and DiOC6(3) to label mitochondria, lysosomes, and endoplasmic reticula, respectively. DH-II-24 colocalized with all three fluorescence probes, indicating that the photosensitizer accumulated in mitochondria, lysosome, and endoplasmic reticula (Fig. 1C).

PDT with DH-II-24 induced necrotic cell death.  To examine cell death induced by PDT with DH-II-24, HCT116 cells were loaded with 5 μg/mL DH-II-24 and exposed to red-light (>630 nm, 1.45 mW/cm2). DH-II-24-mediated PDT caused cell death in a light dose-dependent manner (Fig. 2A). In the absence of light, DH-II-24 treatment up to 2 μg/mL did not display any significant toxicity (data not shown), and 5 μg/mL DH-II-24 produced a minimal dark toxicity as indicated by a small percentage of cell death (Fig. 2). Without the photosensitizer, exposing HCT116 cells to red-light (>630 nm) did not affect cell survival at all (Fig. 2A). In order to examine the mode of cell death induced by DH-II-24-mediated PDT, we performed staining HCT116 cells with annexin V and PI as the markers for apoptosis and necrosis, respectively (see Materials and Methods). Vast majority of cells (>80%) died 3 h after the PDT treatment, mostly via necrosis as indicated by the PI-positive and annexin V-negative staining pattern (Fig. 2B). Later, cell death became even more pronounced (>90% at 12 h) as shown in Figure 2(B).

image

Figure 2.  Cell death by photodynamic therapy (PDT) with DH-II-24. (A) After being loaded with 5 μg/mL DH-II-24, HCT116 human colon carcinoma cells were illuminated for the duration indicated on x-axis. Twenty-four hours later, cell viability was determined by methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay (see Materials and Methods). Data, expressed as a percentage of the mean value of untreated control cells, are the means ± SD from three independent experiments. (B) Cells were loaded with DH-II-24 for 12 h, irradiated for 120 s, and incubated for the indicated times. Cells were stained with annexin V-fluorescein isothiocyanate (FITC) and propidium iodide (PI) and analyzed on a FACScan. Three main subpopulations, corresponding to viable cells (lower left quadrant), apoptotic cells stained with annexin V-FITC (lower right quadrant), and necrotic PI-stained cells (upper left quadrant), can be readily differentiated. The experiments were repeated three times and one representative figure is displayed.

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Pharmacokinetic studies.  Spatial distribution of DH-II-24 in mice was analyzed at 6, 12, 24, and 48 h after intravenous injection of 1 mg/kg DH-II-24 into mice. Serial fluorescence images of the whole mice were obtained using the In Vivo Imaging System (IVIS200; Xenogen, Alameda, CA, USA). As shown in Figure 3, DH-II-24 was rapidly distributed across the entire body at 6 h, maintained until 12 h, and then completely cleared within 48 h. The rapid distribution and clearance of DH-II-24 in mice would be beneficial to subdue adverse side effects of the photosensitizer.

image

Figure 3.  Phamacokinetics of DH-II-24. Mice were given i.v. injection of 1 mg/kg DH-II-24, and spatial distribution of DH-II-24 was monitored at the indicated post-injection time using the In Vivo Imaging System (IVIS200). Note the rapid distribution (at 6 h) and clearance (at 48 h) across the entire body.

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Antitumor effects of DH-II-24 PDT in vivo.  In order to examine effects of DH-II-24-mediated PDT on HCT116 tumors in vivo, PDT was performed on the xenograft tumor models established by implanting HCT116 cells subcutaneously. When tumors grew to approximately 100 mm3 in size, mice were given intravenous injection (via tail vein) of DH-II-24 at a dose of 1 mg/kg followed by illumination of red light (154 J/cm2). As shown in Figure 4, tumor volume increased about 10-fold for 20 days in control mice: the light alone (i.e. illuminated without DH-II-24 administration, = 8) and DH-II-24 alone (i.e. administrated with DH-II-24 and kept under the darkness, = 8) controls. In contrast, tumor growth was significantly suppressed for 20 days in the PDT-treated animals (= 9). DH-II-24-mediated PDT even decreased the tumor volume during the first week of the post-treatment. Little damage was observed in normal tissues surrounding the xenograft tumor, in particular, the skin (Fig. 4A). We then investigated anti-angiogenic effect of DH-II-24-mediated PDT in tumor tissues. Tumor-bearing mice in each group were sacrificed 20 days after the PDT session for macroscopic examination of tumor vasculature. As shown in Figure 5, tumor vasculature was far less developed in the PDT-treated tumors compared to the control tumors. To quantify the effect of PDT on tumor vasculature, we measured total blood vessel length of images in Figure 5 with Image Acquision and Analysis Software (Lab Works, UVP Inc., Upland, CA, USA), and the PDT decreased the total blood vessel length to 65% of the control tumors (= 3, < 0.005). Thus, tumor vascular damage by DH-II-24-mediated PDT might contribute in part to its antitumor effect demonstrated here in HCT116 xenograft tumor models, which was further supported by histological examination.

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Figure 4.  Inhibition of tumor growth by photodynamic therapy (PDT) with DH-II-24. Tumor-bearing mice were given intravenous injections of 1 mg/kg DH-II-24 and exposed to red light. (A) Tumor-bearing regions of the control (DH-II-24 only) and PDT-treated mice were photographed. (B) Tumor volumes were monitored every day for 20 days. Growth of xenograft tumors was significantly suppressed by DH-II-24-mediated PDT, compared to the light alone and DH-II-24 alone control groups. Data are means ± SD.

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image

Figure 5.  Antiangiogenic effect of photodynamic therapy (PDT) with DH-II-24. Mice were given intravenous injection of DH-II-24, and irradiated. At 20 days after PDT, the mice were sacrificed and photographed. Tumor vasculature is far less developed in the PDT-treated mouse compared to the DH-II-24 alone control.

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Histology.  Since DH-II-24-mediated PDT induced necrotic death in HCT116 cells, we examined necrotic tissue damage by DH-II-24-PDT in HCT116 xenograft tumor models by vital staining using Evans blue.(22) The tumors were illuminated with a fiberoptic no-coherent illuminator when their volume reached 400–500 mm3. Twelve hours after the PDT, the mice were given tail vein injections of 1% Evans Blue solution. Tumors were excised from the mice 6 h after the dye injection. Tumor tissues in the control (DH-II-24 alone and light alone) mice were evenly stained with Evans blue, whereas those of the PDT-treated mice were not (Fig. 6A), indicating that PDT induced necrotic tissue damage in the xenograft models. As indicated in Figure 6(A), the tumors were then cross-sectioned to examine necrotic tissue damage in the interior of tumors. Consistent with the observation of tumor surfaces, necrotic tissue damage was found in the interior of PDT-treated tumors, whereas the controls (DH-II-24 only and light only mice) were well stained with Evans blue. The excised tumors were processed to make thin sections and the sections were stained with hematoxylin–eosin. In the sections of PDT-treated tumor, necrotic cells were more frequently observed and intact blood vessels were far less frequently found, compared to the control sections (Fig. 6B). Thus, DH-II-24-mediated PDT induced necrotic cell death in tumor tissues and affected the tumor vasculature in HCT116 xenograft tumor models.

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Figure 6.  Histological examination of the HCT116 human colon carcinoma xenograft tumors. (A) At 12 h after photodynamic therapy (PDT), mice were administrated with 1% Evans blue and sacrificed to excise stained tumors (upper panels). Necrotic tumor tissue appeared almost white, which indicates massive necrotic tissue damage. Then, the tumors were cross-sectioned according to the indicated lines in the upper panels to examine the interiors of the tumors (lower panels). Bar, 5 mm. (B) For histological examination, excised tumors were fixed, sectioned, and stained with hematoxylin–eosin. The sections were examined under a light microscope and photographed. Tumor blood vessels were frequently observed in the control sections (arrows), which is absent in the section from the PDT-treated tumor. Bar, 200 μm.

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Discussion

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

While there is a great interest in the synthesis of new photosensitizers with improved PDT characteristics, chlorin derivatives are particularly strong under investigations in preclinical and clinical fluorescence diagnosis and PDT of tumors.(17,23) DH-II-24 was recently developed as a chlorin-based photosensitizer,(19) but is yet to be investigated for various applications. DH-II-24 is synthesized from methylpheophobide α methyl ester, and its absorption spectrum, measured in DMSO, has a major band at 666 nm.(19) DH-II-24 characterization was confirmed by 1H NMR spectrum, and the molecular weight was determined by fast atom bombardment mass spectrometry to be 664.30. In this study, we evaluated DH-II-24 as a photosensitizer for antitumor PDT in vitro as well as in vivo. In vitro, PDT with DH-II-24 (5 μg/mL) induced a necrotic cell death in a light dose-dependent manner. In colorectal carcinoma xenograft tumor models, DH-II-24-mediated PDT suppressed tumor growth with minimal damage to surrounding tissues, compared to the light alone or DH-II-24 alone control groups. In addition, in the PDT-treated animals, the suppression of tumor growth was accompanied by necrotic tumor destruction and vascular damage. Taken together, our results indicate that PDT with DH-II-24 could provide a minimally invasive therapeutic modality for clinical treatment of cancer.

In addition to the suppression effect of DH-II-24-mediated PDT on tumor growth, DH-II-24 displays some characteristics of the ideal photosensitizer. First, DH-II-24 has a strong absorption band at a relatively long wavelength (λmax = 666),(19) which is critical for efficient tissue penetration of light. Since the wavelength of light has been described as a primary factor determining the penetration of visible and near-infrared light in bovine muscle,(24) strong absorbance by light in 600–800 nm is typically desired for the ideal photosensitizer.(6) Second, DH-II-24 was rapidly distributed into the entire body of mice and completely cleared from the mice within 48 h, which would help reduce the adverse side effects of the photosensitizer. Third, PDT with DH-II-24 showed significant antitumor effect at a relatively low dosage (1 mg/kg). Several photosensitizers including Photofrin, pheophorbide α, ATX-S10Na(II), and disulfonated hydroxyaluminium phthlalocyanine have been typically used over 5 mg/kg in PDT for colorectal carcinoma xenografts.(22,25–27) Photofrin and pheophorbide α have been used at a dose of 30 mg/kg in HT29 tumor-bearing nude mice.(25) A dose of 18 mg/kg has been used for ATX-S10Na(II)-mediated PDT in Colon26 carcinoma-bearing mice.(27) Recently, other chlorin-based photosensitizers including chlorine e6 polyvinylpyrrolidone (5 mg/kg) and SN-38-loaded chlorine-core star block polymer (10 mg/kg) have been applied for PDT in human bladder cancer and colon cancer xenografts.(17,28) Furthermore, DH-II-24 was distributed across the entire body within 6 h and then rapidly cleared. In human umbilical vein endothelial cells, DH-II-24 showed a faster accumulation than DH-I-180-3, another chlorin-based photosensitizer synthesized from methylpheophobide α (data not shown), supporting rapid distribution of the photosensitizer. Fast clearance of DH-II-24 from mice might be explained by the chemical nature of the photosensitizer. DH-II-24 is hydrophobic in DMSO, but it can be partially protonated at physiological pH after being accumulated into cells. Thus, the antitumor effect of DH-II-24 at the relatively low dose implies its potency as a photosensitizer, although it is impossible to compare DH-II-24 with other photosensitizers based on previous studies with various differences in complex parameters from ours.

We observed PDT induce necrotic cell death with 5 μg/mL of DH-II-24 at a light dose of 1.74 J/cm2 in human colorectal HCT116 cells. Consistently, necrosis was also observed in damaged tumor tissues by DH-II-24 mediated-PDT. However, for several reasons, we do not negate the possibility that apoptotic death is induced by DH-II-24-mediated PDT in HCT116 cells. In human gastric adenocarcinoma (AGS) cells, we observed that apoptosis was caused by PDT with a relatively low dose (1 μg/mL) of DH-II-24 (data not shown), whereas necrosis was dominant at a high dose (5 μg/mL) of DH-II-24.(19) Although it remains to be examined in HCT116 cells, our observation in AGS cells is consistent with previous finding that the mode of cell death by PDT is controlled by the combination of photosensitizer concentration and illumination dose.(1) The mitochondrial localization of DH-II-24 in HCT116 cells also implies the involvement of apoptosis since sensitizers localized in mitochondria are likely to induce apoptosis.(29) Nonetheless, improvement of the antitumor effect of the treatment would be facilitated by better understanding how various parameters of the DH-II-24-mediated PDT protocol modulate the mode of cell death.

Three main mechanisms of PDT-mediated tumor destruction involve direct cellular damage, vascular damage, and immune reaction.(2,4,11) Although the relative contribution of each mechanism is not clear in our colorectal carcinoma xenograft study, the direct damage by DH-II-24-mediated PDT was clearly demonstrated in vitro. When vital staining with Evans blue(22) was performed to identify damaged tumor tissues, DH-II-24-mediated PDT was found to cause necrotic damage in colorectal carcinoma xenografts. Since severe damage to the tumor vasculature was frequently found in the xenografts treated by DH-II-24-mediated PDT, the suppression of tumor growth may be in part due to the vascular collapse and dissolution by the treatment.

This study demonstrates that DH-II-24-mediated PDT is able to induce cell death in the HCT116 xenograft tumor concomitant with severe damage of tumor vasculature. Based on the potential and characteristics of DH-II-24 presented in this study, we believe that it is worthwhile pursuing DH-II-24 as a photosensitizer for antitumor PDT strategies.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References

This work was supported in part by the Korea Science & Engineering Foundation through the Vascular System Research Center (R11-2001-090-00000-0), the Basic Research Program (2008-05943), and the Regional Research Universities Program. Young-Cheol Lim and Je-Ok Yoo were supported by the Brain Korea 21 Program. We would like to thank the Korea Basic Science Institute (Chuncheon Center) for help with in vivo imaging.

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  1. Top of page
  2. Abstract
  3. Materials and Methods
  4. Results
  5. Discussion
  6. Acknowledgments
  7. References
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