Progression to
androgen independence remains the main obstacle to improving survival and quality of life in patients with advanced
prostate cancer. Induction of differentiation may serve as a rational basis for prevention of progression to
androgen independence by modulating gene expression activated by
castration or upregulated during
androgen-independent progression. The objectives of this study were to characterize the in vitro effects of
sodium butyrate on human
prostate cancer cell growth, PSA gene expression, and differentiation in the LNCaP
tumor model and to determine whether
tumor progression in vivo is delayed by
isobutyramide, an orally bioavailable
butyrate analogue with a longer half-life. The effects of
isobutyramide on LNCaP
tumor growth and serum PSA levels in both intact and castrate male mice were compared to controls. At concentrations >1 mM,
butyrate induced dose-dependent changes towards a more differentiated phenotype, G1 cell cycle arrest, and an 80% decrease in LNCaP cell growth rates. PSA gene expression was increased threefold by
butyrate, indicative of differentiation-enhanced gene expression. The half-life of
isobutyramide in athymic mice was determined by gas chromatography to be 4 h. During a 4 week period in intact-placebo mice,
tumor volume and serum PSA increased 4.1- and 6.6-fold, respectively, compared to twofold and 2.7-fold increases in
tumor volume and serum PSA in intact-treated mice. During
a 7 week period in castrate-placebo mice,
tumor volume and serum PSA levels increased 2.4-fold and fourfold, respectively, compared to a 50% reduction in
tumor volume and a twofold increase in serum PSA above nadir levels in castrate mice treated with adjuvant
isobutyramide.
Isobutyramide treatment induced pronounced morphological changes in LNCaP
tumor cells, with loss of defined nucleoli and dispersion of
chromatin distribution. LNCaP
tumor PSA
mRNA levels actually increased threefold, indicative of differentiation-enhanced gene expression. This study demonstrates that
butyrate causes LNCaP cell cycle arrest and increased PSA gene expression, both indicative of differentiation. The combination of
castration and adjuvant
isobutyramide was synergistic in delaying
tumor progression. Decreased
tumor cell proliferation and increased PSA gene expression induced by
isobutyramide results in disconcordant changes in serum PSA and
tumor volume and reduces the utility of serum PSA as a marker of response to
therapy.