Transdermal administration of melatonin coupled to cryopass laser treatment as noninvasive therapy for prostate cancer

Abstract

Melatonin, a pineal gland hormone, exerts oncostatic activity in several types of human cancer, including prostate, the most common neoplasia and the third most frequent cause of male cancer death in the developed world. The growth of androgen-sensitive LNCaP prostate cancer cells in mice is inhibited by 3 mg/kg/week melatonin (0.09 mg/mouse/week) delivered by i.p. injections, which is equivalent to a dose of 210 mg/week in humans. The aim of this study is to test an alternative noninvasive delivery route based on transdermal administration of melatonin onto the tumor area followed by cryopass-laser treatment. Two groups of immunodepressed mice were studied, one (n = 10) subjected to 18 cryopass-laser therapy sessions and one (n = 10) subjected to the same treatment without melatonin. These groups were compared with mice treated with i.p.-administered melatonin or vehicle with the same time schedule. We found that cryopass-laser treatment is as efficient as i.p. injections in reducing the growth of LNCaP tumor cells, affecting plasma melatonin and redox balance. Furthermore, both delivery routes share the same effects on the involved biochemical pathway driven by hypoxia-inducible factor 1α. However, cryopass-laser, as used in the present experimental setup, is less efficient than i.p delivery route in increasing the melatonin content and Nrf2 expression in the tumor mass. We conclude that cryopass-laser treatment may have impact for melatonin-based therapy of prostate cancer, by delivering drugs transdermally without causing pain and targeting directly on the site of interest, thereby potentially making long-term treatments more sustainable.

Keywords: Melatonin; anticancer activity; cryopass-laser therapy; drug delivery; experimental prostate cancer; transdermal administration.

Figure 1.

Experimental flowchart. Human prostate cancer cells (LNCaP) were cultured and resuspended in ice-cold Matrigel (1:1) at a final concentration of 3x106/0.1 ml. Mice were inoculated in each flank with LNCaP and subjected to cryopass-laser treatment (with 4 mg/kg melatonin or vehicle) three times/week, for 6 weeks, for a total of 18 treatments. At the end of the experimental time, tumors and blood were collected for the biochemical analysis.

Figure 2.

Body weight and tumor volume changes. (A) Time course of body weight of mice treated with melatonin or vehicle. (B) Time course of tumor volume in mice treated with melatonin or vehicle. Tumor volume was calculated as length x width x height x 0.5236 by a caliper. (C) Tumor volume at day 42. Data are expressed as the ratio (tumor volume)/(body weight) to compensate different rates of body growth in the experimental groups. Data are expressed as mean ± SEM, *p < .05 for treatment factor (Two-way ANOVA).

Figure 3.

Plasma measurements. (A) Melatonin content in plasma at day 42 of mice treated with melatonin or vehicle. (B) Oxidant capacity in plasma determined measuring Reactive Oxygen Metabolites (ROMs) and expressed as H₂O₂ equivalents. (C) Plasma antioxidant capacity expressed as Trolox equivalents. Data are expressed as mean ± SEM, *p < .05 for treatment factor (two-way ANOVA).

Figure 4.

Measurements in tumor mass. (A) Melatonin content in tumor of mice treated with melatonin or vehicle, determined by competitive enzyme immunoassay as described in the Methods section. (B) Expression of Nrf2 protein measured by Western Blot. The intensity of Nrf2 bands were quantified and expressed as ratio with the intensity of β-actin bands. (C) Representative microphotographs of HIF-1α marked by immunofluorescence of all the experimental groups considered. The bars represent 50 μm. (D) Quantification of the HIF-1α signal measured as the sum of green pixels intensities exclusively in the tumor area, without considering the inflammatory infiltrate area. (E) Expression of the HIF-1α protein measured by Western Blot. The intensity of HIF-1α bands were quantified and expressed as ratio with the intensity of β-actin bands. Data are expressed as mean ± SEM, *p < .05 for treatment factor (Two-way ANOVA) and ^$p < .05 for delivery route factor.