Combination therapies of photochemical internalization (PCI) and moderate hyperthermia (MHT) were investigated in an in vitro system consisting of human and rat glioma spheroids. PCI using the amphiphilic photosensitizer, AlPcS2a and two anti cancer agents BLM or 5-FU were used. Spheroids were irradiated with λ = 670 nm laser light in an incubator at temperatures ranging from 37 to 44°C. For each temperature investigated, spheroids were divided into 4 groups: control, drug-only, photodynamic therapy (PDT), and PCI. PDT and PCI spheroids were exposed to radiant exposures ranging from 0.3 to 2.5 J cm(-2) using an irradiance of 5 mW cm(-2). Toxicity was evaluated from spheroid growth kinetics. The combination of PCI and MHT resulted in significant increases in BLM efficacy at 44°C for both cell line derived spheroids compared to controls at 37°C over the range of radiant exposures examined. 5-FU PCI was ineffective for the human cell line at both 37 and 44°C.

Background

Macrophage (Ma) vectorization of chemotherapeutic drugs has the advantage for cancer therapy in that it can actively target and maintain an elevated concentration of drugs at the tumor site, preventing their spread into healthy tissue. A potential drawback is the inability to deliver a sufficient number of drug-loaded Ma into the tumor, thus limiting the amount of active drug delivered. This study examined the ability of photochemical internalization (PCI) to enhance the efficacy of released drug by Ma transport.

Methods

Tumor spheroids consisting of either F98 rat glioma cells or F98 cells combined with a subpopulation of empty or doxorubicin (DOX)-loaded mouse Ma (RAW264.7) were used as in vitro tumor models. PCI was performed with the photosensitizer AlPcS_2a and laser irradiation at 670 nm.

Results

RAW264.7 Ma pulsed with DOX released the majority of the incorporated DOX within two hours of incubation. PCI significantly increased the toxicity of DOX either as pure drug or derived from monolayers of DOX-loaded Ma. Significant growth inhibition of hybrid spheroids was also observed with PCI even at subpopulations of DOX-loaded Ma as low as 11% of the total initial hybrid spheroid cell number.

Conclusion

Results show that RAW264.7 Ma, pulsed with DOX, could effectively incorporate and release DOX. PCI significantly increased the ability of both free and Ma-released DOX to inhibit the growth of tumor spheroids in vitro. The growth of F98 + DOX loaded Ma hybrid spheroids were synergistically reduced by PCI, compared to either photodynamic therapy or released DOX acting alone.