Background: Indium (III) phthalocyanine (InPc) was encapsulated into nanoparticles (NP) of PEGylated poly (D,L-lactide-co-glycolide) (PLGA-PEG) to improve the photobiological activity of the photosensitizer. The efficacy of NP loaded with InPc and their cellular uptake was investigated with MCF-7 cells, and compared with the free InPc. Methods: NP were prepared by the method of emulsion/evaporation. The emulsion was washed and centrifuged and lyophilized. The lyophilized particles were characterized via scanning electron microscopy. The evaluation of the cell suspensions viability incubated with InPc free and encapsulated and subsequently irradiated with a 665 nm laser diode was performed at different concentrations of InPc (1.8-7.5 mol/L), incubation times (1-2h) and laser power (10-100mW) by MTT assay. The internalization of the InPc free and encapsulated cells was assessed via confocal microscopy. Measurement of absorbance spectra and fluorescence of free and encapsulated InPc were monitored during irradiation assessment photodegradation to the photosensitizer. The generation of singlet oxygen was monitored by electron paramagnetic resonance spectroscopy.

Findings: The influence of photosensitizer (PS) concentration (1.8-7.5 mol/L), incubation time (1-2h), and laser power (10-100mW) were studied on the photodynamic effect caused by the encapsulated and the free InPc. NP with a size distribution ranging from 61 to 243 and with InPc entrapment efficiency of 72±6% were used in the experiments. Only the photodynamic effect of encapsulated InPc was dependent on PS concentration and laser power. The InPc loaded NP were more efficient in reducing MCF-7 cell viability than the free PS. For a light dose of 7.5 J/cm2 and laser power of 100 mW, the effectiveness of encapsulated InPc to reduce the viability was 34±3 % while for free InPc was 60±7 %. Confocal microscopy showed that InPc-loaded NP, as well as free InPc, were found throughout the cytosol. The NP aggregates and the aggregates of free PS were found in the cell periphery and outside of the cell. The NP aggregates were generated due to the particles concentration used in the experiment because of the small loading of the InPc while the low solubility of InPc caused the formation of aggregates of free PS in the culture medium. The participation of singlet oxygen in the photocytotoxic effect of InPc-loaded NP was corroborated by electron paramagnetic resonance experiments, and the encapsulation of photosensitizers reduced the photobleaching of InPc. Interpretation: The InPc encapsulated was more effective in reducing the MCF-7 viability compared to InPc free due to increased internalization of InPc encapsulated in tumor cells due to the aggregate state of the InPc free hampering the generation of singlet oxygen.

Note: This abstract was not presented at the meeting.

Citation Format: Carlos Augusto Zanoni Souto, Klesia Pirola Madeira, Leticia Rangel, André Romero da Silva. Nanoparticles loaded with indium (III) phthalocyanine are more effective in promoting cell proliferation inhibition on MCF-7 breast cancer cells when compared to free InPc. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5396. doi:10.1158/1538-7445.AM2014-5396