Abstract
e13522 Background: Our in vitro and in vivo studies showed that single agent valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, is effective in a subset of breast cancers. Whether VPA is effective as a single agent and what the optimal dosing would be are unknown. Methods: In an ongoing IRB-approved, window-of-opportunity study testing a genomic predictor of sensitivity to VPA (NCT01007695), we performed biopsies and DCE-MRI on women before and after seven days of escalating doses of VPA on untreated women with breast adenocarcinoma with an intact breast tumor. Within patient dose-escalation was done with a goal dose of 50 mg/kg. Proliferation was assessed with MIB-1 immunohistochemistry. Only correlative secondary endpoints are presented here. Results: Sixteen women have completed treatment and are evaluable. Total and free VPA levels on the last day of treatment averaged 136 µg/ml (range 15-242) and 30 µg/ml (range 1-90), respectively. Proliferation rate by MIB-1 decreased by and average of -7.25% (range +4% to -45%, p=0.04). The change in proliferation did not correlated with VPA levels, although only one of four women with VPA levels less than 100 µg/ml had a decrease in proliferation, compared to five of twelve women with VPA levels greater than 100 µg/ml. Four women had MIB-1 decreases of 10% or greater. Two women have had post-treatment biopsies with fibrosis similar to that seen with chemotherapy treatment effect. DCE-MRI parameters, including ktrans, vp, and kep, did not change significantly with VPA treatment or correlate with VPA levels. Conclusions: VPA as a single agent can reduce proliferation in a subset of women with breast cancers. Higher VPA levels are needed than those achieved at standard dose levels, but VPA levels by themselves do not predict effect. Other monitoring parameters, such as peripheral blood histone acetylation changes, or other predictors of benefit are needed. Clinical trial information: NCT01007695.
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