Characterization of the mechanism of action of the pan class I PI3K inhibitor NVP-BKM120 across a broad range of concentrations.

The pan-phosphoinositide 3-kinase (PI3K) inhibitor BKM120 was found, at high concentrations, to cause cell death in various cellular systems, irrespective of their level of PI3K addiction. Transcriptional and biochemical profiling studies were used to identify the origin of these unexpected and apparently PI3K-independent effects. At 5- to 10-fold, the concentration needed to half-maximally inhibit PI3K signaling. BKM120 treatment caused changes in expression of mitotic genes and the induction of a robust G(2)-M arrest. Tubulin polymerization assays and nuclear magnetic resonance-binding studies revealed that BKM120 inhibited microtubule dynamics upon direct binding to tubulin. To assess the contribution of this off-target activity vis-à-vis the antitumor activity of BKM120 in PI3K-dependent tumors, we used a mechanistic PI3K-α-dependent model. We observed that, in vivo, daily treatment of mice with doses of BKM120 up to 40 mg/kg led to tumor regressions with no increase in the mitotic index. Thus, strong antitumor activity can be achieved in PI3K-dependent models at exposures that are below those necessary to engage the off-target activity. In comparison, the clinical data indicate that it is unlikely that BKM120 will achieve exposures sufficient to significantly engage the off-target activity at tolerated doses and schedules. However, in preclinical settings, the consequences of the off-target activity start to manifest themselves at concentrations above 1 µmol/L in vitro and doses above 50 mg/kg in efficacy studies using subcutaneous tumor-bearing mice. Hence, careful concentration and dose range selection is required to ensure that any observation can be correctly attributed to BKM120 inhibition of PI3K.

Patupilone (epothilone B, EPO906) inhibits growth and metastasis of experimental prostate tumors in vivo.

BACKGROUND: Microtubule agents appear promising for the treatment of prostate cancer. Patupilone (epothilone B), a highly potent non-taxane microtubule stabilizing agent, was evaluated in models of androgen-independent prostate cancer. METHODS: Patupilone was administered to athymic mice bearing human prostate cancer xenografts (subcutaneous DU 145 and PC-3M, orthotopic PC-3M). RESULTS: One 4 mg/kg patupilone administration produced transient regression of DU 145 tumors, while two weekly administrations of 2.5 mg/kg produced stable disease followed by protracted regression, however with more pronounced body weight loss. Taxol (15 mg/kg every other day) weakly inhibited tumor growth, but with less body weight loss. Patupilone (5 mg/kg) produced protracted growth inhibition of subcutaneous PC-3M tumors, with transient body weight loss. In mice with orthotopic PC-3M tumors, 4 or 5 mg/kg/week patupilone impaired primary tumor growth, abrogated metastases and enhanced survival, with only transient body weight loss. CONCLUSIONS: These data suggest that patupilone holds promise for prostate cancer treatment.