Photochemical internalization of CD133-targeting immunotoxins efficiently depletes sarcoma cells with stem-like properties and reduces tumorigenicity

Background

The normal stem cell marker CD133 is also a putative marker of cancer stem cells (CSCs) in different types of cancers. Hence, a major challenge when targeting CD133-expressing CSCs is to prevent depletion of the normal stem cell pool. We hypothesized that the site-specific and light-controlled drug delivery method photochemical internalization (PCI) may have the potential to enhance selectivity and endosomal escape of CD133-targeting immunotoxins in stem-like sarcoma cells.

Methods

We have used a sarcoma model, SW872 cells isolated from xenografts harboring CSCs within a ~ 2% CD133^high subpopulation to investigate the potential of PCI of CD133-targeting toxin as a novel strategy to kill CSCs. Model immunotoxins were generated by binding the ribosome-inactivating protein toxin saporin to each of the monoclonal antibodies CD133/1 (AC133) or CD133/2 (293C), specific for individual CD133-epitopes. Cellular targeting, intracellular co-localization with the PCI photosensitizer, disulfonated meso-tetraphenylchlorin (TPCS_2a), and cytotoxic efficacy of PCI of the CD133-targeting toxins were evaluated.

Results

PCI of CD133–saporin efficiently targets CD133-expressing SW872 and HT1080 sarcoma cells and results in loss of cell viability. Following sub-toxic treatment, surviving SW872 cells, depleted of the CD133-expressing population, display reduced proliferative capacity and attenuated CSC properties, such as reduced colony-forming ability and tumorigenicity.

Conclusion

Here we present a proof-of-concept study, where PCI enables light-triggered delivery of CD133-targeting antibody-drug conjugates, resulting in decreased sarcoma tumor-initiating capacity.

General significance

PCI of CD133-targeting toxins may be used as a minimal invasive strategy in the treatment of sarcomas, and potentially as a therapeutic for other solid tumors expressing CD133.