Direct measurement of hypoxia in a xenograft multiple myeloma model by optical-resolution photoacoustic microscopy

Using photoacoustic microscopy (PAM), we evaluated non-invasively oxygenation and vascularization in vivo due to multiple myeloma (MM) progression. Mice injected with MM.1S-GFP were monitored with a fluorescence microscope for tumor progression. In vivo PAM of the cerebral bone marrow quantified the total oxygen saturation (sO(2)). At 28 days after the MM cell injection, the total sO(2) had decreased by half in the developing tumor regions, while in the non-tumor regions it had decreased by 20% compared with the value at one day post MM injection. The blood vessel density was reduced by 35% in the developing tumor regions, while in the non-tumor regions it was reduced by 8% compared with the value at one day post MM injection. Hence, PAM corroborated the development of hypoxia due to MM progression and demonstrated decreased vascularization surrounding the tumor areas.