Transcriptional gene expression profiles indicate response of breast cancer cell lines to aminoflavone prodrug.

Abstract

Abstract Abstract #2153 Aminoflavone Prodrug (AFP464; NSC 710464) is a novel anticancer agent under phase I clinical investigation in the US and Europe. The drug is a ligand of the aryl hydrocarbon receptor (AhR). It exhibits differential in vitro cytotoxic activity in breast cancer cell lines with inhibitory 50% (IC50) concentrations ranging from 0.01-30µM. AFP464 plasma levels that can safely be reached in patients are ∼1µM. In sensitive cells, AFP464 induces AhR–mediated cytochrome P450 (CYP)-dependent xenobiotic response and cell death. In resistant cells, the CYP system is not induced. For upcoming phase II trials in breast cancer, it is therefore critical to study markers of sensitivity of breast cancer cells to AFP464.
 To determine parameters of response to AFP464, we have selected a panel of 11 breast cancer cell lines which represent the biological heterogeneity of primary breast cancers and for which distinct transcriptional profiles are known. They comprised luminal (MCF-7, MCF7TAM1, MCF7/Her2-18, T47D, SKBR3) and basal-like gene expression profiles; the latter were further subdivided into basal A (BT20, MDA-MB-468, HCC1937) and basal B (MDA-MB-231, Hs578T, MX-1) gene clusters. The basal B subgroup reflects the clinical ''triple-negative'' tumor type. We found that all luminal and basal A type breast cancer cells irrespective of resistance to anti-hormone therapies (e.g. tamoxifen refractory MCF7TAM1 cells) were exquisitely sensitive to AFP464 with IC50s between 0.01 and 0.025µM, whereas cell lines with a basal B gene cluster were resistant. Drug concentrations needed to inhibit basal B cell growth to 50% (25-30µM) may not be achieved in patients. Thus, we reasoned that in triple-negative breast cancers, combination treatments will be needed and that agents modifying gene transcription, such as the histone deacetylase inhibitor vorinostat, might be suitable combination partners. To test this hypothesis, we performed combination experiments using the fixed IC50 ratio method and treated MDA-MB-231 and Hs578T cells for 24, 48 and 72 hrs with vorinostat followed by AFP464 for a total for 5 days. We found that AFP464 and vorinostat can act synergistic; in Hs578T cells, combination indices (CI) of <0.3 were seen after pretreatment with vorinostat for 24 hrs; in MDA-MB-231 cells, CIs indicating synergism (<1) were observed after 48 and 72 hrs of exposure to vorinostat. Moreover, real time PCR assessing the induction of CYP1A1 and CYP1B1 in vorinostat and AFP464 treated MDA-MB-231 cells revealed that AhR-dependent xenobiotic response was restored.
 Together, our data indicate the usefulness of gene expression profiling in selecting patients for AFP464 treatment. While single agent therapy might present an option for hormone refractory luminal, and basal A type patient populations, breast cancer patients with basal B-like tumors will require combination therapies e.g. with vorinostat. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 2153.