In vivo evaluation of battery-operated light-emitting diode-based photodynamic therapy efficacy using tumor volume and biomarker expression as endpoints

In low- to middle-income countries (LMICs), the rates of cancer occurrence and cancer-related mortality are increasing at paces that will exceed such rates in more developed countries.1 In a study of cancer-specific patterns and trends, Bray et al. predict an increase in cancer incidence from the 12.7 million new cases in 2008 to 22.2 million cases by 2030, and with the rapid socioeconomic transition of LMICs toward westernization, countries might see a reduction in infection-related cancers but an increase in reproductive, dietary, or hormonal related cancers.2 With the rise of cancer occurrence and cancer-related mortality, the GLOBOCAN initiative and several recent articles indicate the need for closing the disproportional gap between cancer incidence and mortality rates in developed countries and LMICs.3–5 Several countries have already taken the initiative to bridge this gap, and a Global Task Force has been created to increase the accessibility of cancer in LMICs.3 To solve this particular global cancer challenge, it is critical to develop cancer diagnostic and therapeutic techniques that are inexpensive and can be used in low-resource settings. Surgery, radiation, and chemotherapy are the mainstays of cancer management, yet they require major medical infrastructure and are costly for both the patient and the society. Therefore, there is a need for an alternative approach to these high-cost procedures. Photodynamic therapy (PDT) is one such option and has shown promise in treating several types of cancers that are prevalent in LMICs, such as oral, bladder, glioma, pancreatic, and esophageal cancers. PDT is a photochemistry-based modality that imparts light-mediated cytotoxicity to target tissues via excitation of a photosensitizer with light of a specific wavelength.6–8 The technique is clinically approved for the treatment of a number of carcinomas, and the mechanisms of action have been well studied.6,9 The two major components that need to be available for the successful implementation of PDT in LMICs are affordable photosensitizers and light sources. The prodrug δ-aminolevulinic acid (ALA), which preferentially converts to the photosensitizer protoporphyrin IX (PpIX) in tumors, can be stored at room temperature without specialty storage equipment. ALA can be easily administered to patients topically, as a cream, or orally, through ingestion in beverages, without sophisticated medical setups or highly trained healthcare professionals. Moreover, ALA is readily available in LMICs such as India (DUSA Pharmaceuticals, Inc., a subsidiary of Sun Pharmaceutical Industries Ltd., an India-based conglomerate). The second major component of PDT is the light source required to initiate photodynamic action.10 Often, light sources are expensive, bulky, and immobile. Moreover, current PDT light sources (e.g., lasers) typically require electricity for continuous operation, a feature not available in developing countries due to frequent electrical power failure. In recent years, there have been several attempts to replace lasers with light-emitting diode (LED)-based light sources to reduce cost and increase flexibility of use in sites outside major hospitals.11 In an effort to make PDT a viable treatment in LMICs and LMIC-like settings, here we evaluate a battery-powered LED light source which, in addition to providing reduced costs, could also be independent of plug-in electricity during treatment and be powered using precharged batteries. The specific goal of this pilot study was to explore the feasibility of a low-cost battery powered broadband LED-based light source for PDT in LMICs by comparing it to a standard monochromatic, relatively costly diode laser as the illumination device. We accomplished this goal by testing the two devices for ALA-PDT in vivo in a xenograft murine model of squamous cell carcinoma (SCC). Several frequently occurring cancers in the developing world, such as oral, cervical, and skin, are of SCC origin, and we view this proof-of-principle study as an early step toward implementing PDT in low resource settings to treat these SCCs and related cancers. While typical study endpoints of tumor volume or weight are extremely useful measures of treatment efficacy, they do not provide any insights into the mechanistic aspects and long-term outcomes of a given therapeutic modality. Instead, better quantitative measures and biomarkers are often considered to be better prognostic indicators. Here, we calculated areas of necrosis in PDT-treated tumors and also gauged the extent of PDT-induced hypoxia by immunofluorescence (IFC) staining for the biomarker carbonic anhydrase IX (CAIX) and established alterations in the microvessel density (MVD). These parameters have the potential to predict tumor treatment efficacy12–15 and provide mechanistic insights into the success or failure of the therapy, enabling early additional or secondary interventions in the future.