Background

Nasopharyngeal Carcinoma (NPC) is one of the top ten cancers with the annual incidence of over 800 new cases in Hong Kong. Chemo-radiotherapy is the conventional treatment for NPC yet failure of therapies is found to be associated with the advanced staging, distant recurrence and multi-drug resistance properties. Photodynamic Therapy (PDT) is one of the alternative therapeutic approaches proved to be effective on NPC. In this study, multicellular tumor spheroid models established were used to evaluate the effect of PDT.

Methods

To evaluate the effect of a photosensitizer, FosPeg®, multicellular tumor spheroids were generated with multi-cellular layer (MCL) and multi-cellular spheroid (MCS) models using NPC/C666-1 cells. 1 x 10⁵ cells were cultured in 96 well plate for 2D, 3D MCL (agarose basement) and MCS (hanging drop) models. PDT efficacy were revealed via phototoxicity assay (MTT assay) and photobleaching analysis. Photobleaching effect after laser activation was evaluated using fluorescence microscopy and ImageJ software. The photobleaching effect was evaluated and presented as the percentage of photobleaching.

Results

Multicellular tumor spheroids were obtained in day 3 in both models. The drug was incubated for 24 hours in both 2D and 3D spheroids models. FosPeg^® PDT was effective in all NPC cell culture models with no dark toxicity identified. As expected, FosPeg^® PDT was more effective on 2D model than 3D models. LD₂₅ and LD₅₀ were obtained at 0.001 μg/mL and 0.0025 μg/mL of FosPeg^® in 2D model and at 0.1 μg/mL and 1 μg/mL of FosPeg^® in both MCL and MCS models. This finding was echoed with the photobleaching analysis that FosPeg^® was photobleached after laser activation in a time dependent manner, with 19.9%, 18.1% and 17.8% of photobleaching obtained at 10 minutes post PDT in 2D, MCL and MCS models respectively.

Conclusions

FosPeg^® PDT was more effective in 2D model than 3D multicellular tumor spheroids models. Further investigation is needed on PDT mediated cellular changes using multicellular tumor spheroids models.

Acknowledgement: The work described here was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (project no.: 2015-00-74-RGC150201).

Clinical trial identification

NIL

Legal entity responsible for the study

None

Funding

Research Grants Council of Hong Kong Special Administrative Region

Disclosure

All authors have declared no conflicts of interest.