Efficacy of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a in photodynamic therapy of human esophageal squamous cancer cells

Abstract

The present study investigated the effects of 2-(1-hexyloxyethyl)-2-devinylpyro pheophorbide-a (HPPH)-mediated photodynamic therapy (PDT) on in vitro cell survival and in vivo tumor growth derived from human esophageal squamous cancer cells (Eca109). A cell counting kit 8 (CCK8) assay was used to assess the phototoxicity of HPPH-mediated PDT in cultured Eca109 cells. The inhibition of tumor growth was determined by the changes in the relative tumor volume (RTV) and tumor weight. The results revealed that HPPH, in the range of 0.005-1 μg/ml, exhibited no cytotoxicity in the Eca109 cells without light exposure and that the in vitro efficiency of HPPH-mediated PDT was higher compared with that of Photofrin^®-mediated PDT. The in vivo results indicated that graded doses of HPPH-mediated PDT significantly inhibited the xenograft tumor growth derived from the Eca109 cells in a dose-dependent manner. The inhibition efficacy of 0.6 and 1.0 mg/kg HPPH-mediated PDT was similar to that of 10 mg/kg Photofrin-mediated PDT. Furthermore, HPPH possessed a lower toxicity than Photofrin at the dose that achieved the same efficacy in mice bearing Eca109 subcutaneous tumors. The histopathological findings indicated that the tumor tissues in the photosensitizer (PS)-treated mice demonstrated varying degrees of necrosis. HPPH and Photofrin exhibited vascular cytotoxicity on the treated tumors. In conclusion, the present study demonstrated that the phototoxicity of HPPH-mediated PDT is higher than that of Photofrin-mediated PDT of the same dose. HPPH possessed lower toxicity than Photofrin at the dose that achieved the same efficacy. Therefore, HPPH may be a promising agent for treating human esophageal squamous cell cancer (ESCC).

Keywords: 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a photodynamic therapy; human esophageal squamous cell cancer.

Figure 1

Chemical structure of 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a (HPPH).

Figure 2

(A) Effects of the incubation time of drugs prior to light exposure. (B) Effect of times following light exposure on the phototoxicity of HPPH-mediated PDT. Data are presented as the mean ± SD (n=3). Statistically significant differences were calculated by Student’s t-test using SPSS 11.5 software and are indicated by ^*P<0.01. HPPH, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; PDT, photodynamic therapy.

Figure 3

Effect of the dose of the light exposure on the phototoxicity of HPPH-mediated PDT. Data are presented as the mean ± SD (n=3). HPPH, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; PDT, photodynamic therapy.

Figure 4

Efficacy of HPPH and Photofrin^®-mediated PDT in Eca109 cells. Data are presented as the mean ± SD (n=3). HPPH, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; PDT, photodynamic therapy.

Figure 5

The tumor weights of mice following HPPH- and Photofrin^®-mediated PDT. ^*P<0.05, vs. the HPPH vehicle group. HPPH, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; PDT, photodynamic therapy; NS, normal saline.

Figure 6

Edema surrounding the tumors at day 1 post-PDT. Mice bearing representative tumors were randomly selected from each group. (A) no edema, (B) slight edema, (C) moderate edema and (D) severe edema. PDT, photodynamic therapy.

Figure 7

Micrographs of 10-mm slices of xenografted tumors derived from Eca109 cells that were stained with hematoxylin-eosin (HE) and observed under (A, C and E) ×40 or (B, D and F) ×400 magnification using a light microscope. (A and B) PDT with HPPH vehicle or NS. (C and D) PDT with 0.15 or 0.3 mg/kg HPPH. (E and F) PDT with 0.6 or 1.0 mg/kg HPPH or 10 mg/kg Photofrin^®. Samples were selected at random from each group. Black arrows indicate tumor vessels. HPPH, 2-(1-hexyloxyethyl)-2-devinyl pyropheophorbide-a; PDT, photodynamic therapy; NS, normal saline.