A Two-Component Assay for Hypoxia Incorporating Long-Term Nitroreduction and Short-Term DNA-Damage Allows Differentiation of the Three Hypoxia Sub-types

Paired 18F-Fluorodeoxyglucose (18F-FDG), and 64Cu-Copper(II)-diacetyl-bis(N(4)-methylthiosemicarbazone) (64Cu-ATSM) PET Scans in Dogs with Spontaneous Tumors and Evaluation for Hypoxia-Directed Therapy

Hypoxia is associated with neoplastic tissue, protecting cancer cells from death by irradiation and chemotherapy. Identification of hypoxic volume of tumors could optimize patient selection for hypoxia-directed medical, immunological, and radiation therapies. Clostridium novyi-NT (CNV-NT) is an oncolytic bacterium derived from attenuated wild-type Clostridium novyi spores, which germinates exclusively in the anaerobic core of tumors with low-oxygen content. The hypothesis was that 64Cu-ATSM would localize to regions of hypoxia, and that greater hypoxic volume would result in greater germination of Clostridium novyi-NT (CNV-NT). Tumor-bearing companion dogs were recruited to a veterinary clinical trial. Dogs received a CT scan, 18F-FDG PET scan (74 MBq) and 64Cu-ATSM PET scan (74 MBq). Scan regions of interest were defined as the highest 20% of counts/voxel for each PET scan, and regions with voxels overlapping between the two scans. Maximum standardized uptake value (MaxSUV) and threshold volume were calculated. Direct oximetry was performed in select tumors. Tumor types evaluated included nerve sheath tumor (10), apocrine carcinoma (1), melanoma (3) and oral sarcoma (6). MaxSUVATSM ranged from 0.3-6.6. Measured oxygen tension ranged from 0.05-89.9 mmHg. Inverse of MaxSUVATSM had a linear relationship with oxygen tension (R2 = 0.53, P = 0.0048). Hypoxia <8 mmHg was associated with an SUVATSM > 1.0. Hypoxic volume ranged from 0 to 100% of gross tumor volume (GTV) and MaxSUVATSM was positively correlated with hypoxic volume (R = 0.674; P = 0.0001), but not GTV (P = 0.182). Tumor hypoxic volume was heterogeneous in location and distribution. 64Cu-ATSM-avid regions were associated with differential CT attenuation. Hypoxic volume did not predict CNV-NT germination. 64Cu-ATSM PET scanning predicts hypoxia patterns within spontaneously occurring tumors of dogs as measured by direct oxymetry. Total tumor volume does not accurately predict degree or proportion of tumor hypoxia.

Comparison of phosphorescent agents for noninvasive sensing of tumor oxygenation via Cherenkov-excited luminescence imaging

Cherenkov emission generated in tissue during radiotherapy can be harnessed for the imaging biochemistry of tissue microenvironments. Cherenkov-excited luminescence scanned imaging (CELSI) provides a way to optically and noninvasively map oxygen-related signals, which is known to correlate to outcomes in radiotherapy. Four candidate phosphorescent reagents PtG4, MM2, Ir(btb)2  (  acac  )  , and MitoID were studied for oxygen sensing, testing in a progressive series of (a) in solution, (b) in vitro, and (c) in subcutaneous tumors. In each test, the signal strength and response to oxygen were assessed by phosphorescence intensity and decay lifetime measurement. MM2 showed the most robust response to oxygen changes in solution, followed by PtG4, Ir(btb)2  (  acac  )  , and MitoID. However, in PANC-1 cells, their oxygen responses differed with Ir(btb)2  (  acac  )   exhibiting the largest phosphorescent intensity change in response to changes in oxygenation, followed by PtG4, MM2, and MitoID. In vivo, it was only possible to utilize Ir(btb)2  (  acac  )   and PtG4, with each being used at nanomole levels, to determine signal strength, lifetime, and pO2. Oxygen sensing with CELSI during radiotherapy is feasible and can estimate values from 1 mm regions of tissue when used in the configuration of this study. PtG4 was the most amenable to in vivo sensing on the timescale of external beam LINAC x-rays.