Effect of selumetinib on the growth of anastrozole-resistant tumors

Abstract

Despite significant improvement in the treatment outcome of hormone responsive postmenopausal breast cancer, some patients eventually acquire resistance to aromatase inhibitors (AIs). Using our MCF-7Ca xenograft model, we observed that although AIs such as anastrozole initially inhibit tumor growth effectively, tumors eventually began to grow. Our previous data show that anastrozole-resistant tumors upregulate growth factor receptor pathways as they adapt to grow in the low estrogen environment. Therefore, in the current study, we investigated the effect of inhibiting the growth factor receptor pathways with a MEK-1/2 inhibitor selumetinib (AZD6244, ARRY-142866). We treated the mice with anastrozole-resistant tumors with selumetinib alone or in combination with anastrozole. MCF-7Ca cells were inoculated sc into ovariectomized athymic nude mice supplemented throughout the experiment with androstenedione (100 μg/day), the substrate for aromatase conversion to estrogen. Once the tumors reached a measurable size (~300 mm(3)), the mice were treated with anastrozole (200 μg/day), supplemented with androstenedione (Δ(4)A). The tumors in the anastrozole group doubled in volume after 6 weeks, at which time the animals were regrouped to receive the following treatments: (i) anastrozole, (ii) anastrozole withdrawal (Δ(4)A alone), (iii) selumetinib (25 mg/kg/d, bid, po), and (iv) selumetinib + anastrozole, (n = 10 mice/group). The treatments were given for 6 weeks (till week 12) and then the mice were euthanized, the tumors were collected and analyzed. The tumors of mice treated with selumetinib + anastrozole had significantly lower growth rates than those treated with single agents (p = 0.008). Western blot analysis of the tumors showed that treatment with anastrozole resulted in upregulation of proteins in the growth factor receptor cascade such as p-mTOR, pAkt, pMEK, and pMAPK. This was accompanied by downregulation of ERα protein, consistent with previous findings. The treatment of mice with selumetinib resulted in downregulation of activated MAPK, along with p-mTOR, which likely resulted in upregulation of ERα. Our results suggest that inhibition of the growth factor receptor pathway with selumetinib can reverse anastrozole resistance.

Treatment with aromatase inhibitors stimulates the expression of epidermal growth factor receptor-1 and neuregulin 1 in ER positive/HER-2/neu non-amplified primary breast cancers

“…Thus, combinatorial treatment blocking both ER and growth factor signaling pathways has been suggested to be the most effective inhibition of proliferation in ER positive breast cancer cells [12,16,51,53,54]. In line with this, treatment with the MAPK/ERK kinase inhibitor, selumetinib reversed the AI resistance in mice exhibiting anastrozole resistant tumors [55]. Adding the dual EGFR/HER-1 / HER-2/neu inhibitor lapatinib to the AI inhibitor letrozole improved the progression free survival (PFS) in patients with ER positive/HER-2/neu amplified tumors, whereas no effects were observed in the ER positive/HER-2/neu non-amplified subgroup [56].…”

Stimulus-dependent differences in signalling regulate epithelial-mesenchymal plasticity and change the effects of drugs in breast cancer cell lines

“…The lack of frequent mutations within the core Ras-Raf-MEK axis, but the potential for cross-talk with a plethora of pathways intrinsic to breast cancer progression, may mean that the potential of MEK blockade lies in treatment combinations to overcome resistance. This is borne out by pre-clinical studies which have shown MEK inhibition has the potential to enhance sensitivity of breast cancer xenografts to HER2 blockade [ 105 ] and anti-estrogen treatment [ 106 ]. Furthermore, studies with breast cancer cell lines have shown that MEK inhibition also increases sensitivity to EGFR blockade [ 107 ], and reversed the effects of IGF-1R overexpression in promoting proliferation [ 108 ].…”

Histone deacetylase inhibitor entinostat in combination with a retinoid downregulates HER2 and reduces the tumor initiating cell population in aromatase inhibitor-resistant breast cancer

“…As demonstrated previously, ectopic overexpression of HER2 in human breast cancer cells correlates with increases in TIC characteristics, including mammosphere formation, expression of the breast cancer resistance protein (BCRP), and side population (SP)-positive cells [5]. AI-resistant cell lines, including LTLT-Ca and Ac1ANAR (anastrozole resistant, [6]), have increased HER2 expression when compared to their parental controls, which is accompanied by increased expression of TIC characteristics [5,7]. Furthermore, lapatinib treatment reduced SP and mammosphere formation [7] in LTLT-Ca cells.…”

“…LTLT-Ca were generated from MCF7-Ca as previously described [2] and were maintained in phenol red-free modified IMEM supplemented with 5 % CDT-FBS, 1 % P/S, 750 lg/mL G418 and 1 lM letrozole. Ac-1 cells (MCF-7 cells stably transfected with aromatase gene in our laboratory) were used to develop the Ac1ANAR cell line as described previously [6]. Ac1ANAR were maintained in IMEM containing 5 % CDT-FBS, 1 % P/S, 800 lg/mL G418 and 2 lM anastrozole.…”

“…We have used letrozoleresistant LTLT-Ca and anastrozole-resistant Ac1ANAR for our studies. Both cell lines demonstrate a downregulation of ERa and upregulation of HER2 protein expression [2,6], as well as increased TIC characteristics [5,7] when compared to their AI-sensitive parental cell lines. LTLT-Ca and Ac1ANAR were treated with ATRA, ENT, or the combination for 96 h and expression of HER2 was assessed via western blot.…”