In preclinical models, both
dietary fat reduction and
insulin-like growth factor I receptor (IGF-1R) blockade individually inhibit
prostate cancer xenograft growth. We hypothesized that a
low-fat diet combined with IGF-1R blockade would cause additive inhibition of
prostate cancer growth and offset possible untoward metabolic effects of IGF-1R blockade antibody
therapy. Fifty severe combined immunodeficient mice were injected with 22Rv1 cells subcutaneously. Ten days postinjection, the animals were randomized to four groups: (i) high-fat diet + saline (
HF); (ii) high-fat diet + IGF-1R blocking antibody,
ganitumab (HF/Ab); (iii)
low-fat diet + saline (LF); and (iv)
low-fat diet +
ganitumab (LF/Ab). After 19 days of treatment, the animals were euthanized, serum was collected, and
tumors were weighed.
Tumor Ki67, Akt and
extracellular signal-regulated kinase (ERK) activation, serum
insulin,
IGF-I and TNF-α were measured. In vitro,
ganitumab treatment inhibited growth and induced apoptosis in several
prostate cancer cell lines. In vivo,
tumor weights and volumes were unaffected by the different treatments. The LF/Ab
therapy significantly reduced proliferation (Ki67) and ERK activation in
tumors. The HF/Ab group had significantly higher serum
insulin levels than the HF group. However, LF/Ab combination significantly reduced serum
insulin back to normal levels as well as normalizing serum TNF-α level. Whereas the combination of
low-fat diet and IGF-1R blockade did not have additive inhibitory effects on
tumor weight, it led to reduced
tumor cell proliferation and a reduction in serum
insulin and TNF-α levels.