Cryosurgery is a minimally invasive
cancer treatment using cryogenic temperatures. Intraoperative monitoring of iceball growth is an advantage of the treatment. However, whereas the iceball can be easily visualized, destruction within the iceball is incomplete and the means to monitor the "kill zone" are urgently needed. Recently, we have shown the ability of
tumor necrosis factor-alpha (
TNF-alpha) to enhance destruction within an iceball. To avoid systemic toxicity, we delivered
TNF-alpha selectively to the
tumor by a
gold nanoparticle of 30-nm diameter (CYT-6091) tagged with
TNF-alpha and
thiol-derivatized
polyethylene glycol. Using a dorsal skin fold chamber (DSFC) in a nude mouse, both normal skin and human prostate
carcinoma (LNCaP Pro 5) were pretreated with soluble
TNF-alpha (topically or i.v.) or
CYT-6091 (i.v.) and frozen after 4 h. The cryolesion was assessed after 3 days by comparing histologic
necrosis with perfusion defects. Hind limb
tumors were also treated by visibly encompassing the
tumor with an iceball and assessing gross changes over time. A 5-mug dose of soluble
TNF-alpha or
CYT-6091 increased the temperature threshold of
necrosis in the
tumor in the DSFC from -14.0 +/- 1.6 degrees C (n = 6) to 0.9 +/- 1.5 degrees C (n = 6) and -1.5 +/- 3.7 degrees C (n = 6), respectively. In hind limb
tumors, the same dose resulted in significant
tumor shrinkage and remission in 2 of 8 (for soluble
TNF-alpha) and in 3 of 8 (for CYT-6091). The nanoparticle alone group without
TNF-alpha increased the temperature threshold of
necrosis to -7.0 +/- 2.3 degrees C in the
tumor in the DSFC and more shrinkage of the
tumor in the hind limb when compared with cryo alone treatment. Systemic toxicity was noted in all soluble
TNF-alpha groups but none with
CYT-6091. These results suggest that it is possible to destroy all of a
tumor within an iceball by preincubation with
TNF-alpha and systemic toxicity can be avoided by
CYT-6091.