Different mechanisms for resistance to trastuzumab versus lapatinib in HER2- positive breast cancers - role of estrogen receptor and HER2 reactivation

Abstract

IntroductionThe human epidermal growth factor receptor 2 (HER2)-targeted therapies trastuzumab (T) and lapatinib (L) show high efficacy in patients with HER2-positive breast cancer, but resistance is prevalent. Here we investigate resistance mechanisms to each drug alone, or to their combination using a large panel of HER2-positive cell lines made resistant to these drugs.MethodsResponse to L + T treatment was characterized in a panel of 13 HER2-positive cell lines to identify lines that were de novo resistant. Acquired resistant lines were then established by long-term exposure to increasing drug concentrations. Levels and activity of HER2 and estrogen receptor (ER) pathways were determined by qRT-PCR, immunohistochemistry, and immunoblotting assays. Cell growth, proliferation, and apoptosis in parental cells and resistant derivatives were assessed in response to inhibition of HER or ER pathways, either pharmacologically (L, T, L + T, or fulvestrant) or by using siRNAs. Efficacy of combined endocrine and anti-HER2 therapies was studied in vivo using UACC-812 xenografts.ResultsER or its downstream products increased in four out of the five ER+/HER2+ lines, and was evident in one of the two intrinsically resistant lines. In UACC-812 and BT474 parental and resistant derivatives, HER2 inhibition by T reactivated HER network activity to promote resistance. T-resistant lines remained sensitive to HER2 inhibition by either L or HER2 siRNA. With more complete HER2 blockade, resistance to L-containing regimens required the activation of a redundant survival pathway, ER, which was up-regulated and promoted survival via various Bcl2 family members. These L- and L + T-resistant lines were responsive to fulvestrant and to ER siRNA. However, after prolonged treatment with L, but not L + T, BT474 cells switched from depending on ER as a survival pathway, to relying again on the HER network (increased HER2, HER3, and receptor ligands) to overcome L's effects. The combination of endocrine and L + T HER2-targeted therapies achieved complete tumor regression and prevented development of resistance in UACC-812 xenografts.ConclusionsCombined L + T treatment provides a more complete and stable inhibition of the HER network. With sustained HER2 inhibition, ER functions as a key escape/survival pathway in ER-positive/HER2-positive cells. Complete blockade of the HER network, together with ER inhibition, may provide optimal therapy in selected patients.

Dual mTOR Kinase Inhibitor MLN0128 Sensitizes HR+/HER2+ Breast Cancer Patient-Derived Xenografts to Trastuzumab or Fulvestrant

“…The molecular mechanisms of acquired and de novo resistance to anti-HER2 agents vary in different biological contexts. Several studies reveal that ERa signaling is augmented in the presence of anti-HER2 agents (9,10). Notably, cancer cell lines resistant to anti-HER2 agents are often sensitive to the pure antiestrogen fulvestrant.…”

“…To overcome this barrier, the ATP-competitive dual mTOR kinase inhibitors, such as MLN0128, are developed to simultaneously target both mTORC1 and mTORC2 (20). Presently, there are a few HR þ /HER2 þ breast cancer cell lines available for preclinical research (9), which are limits in understanding the clinical features of patient tumors. Instead, PDXs mimicking the features from the tumors of origin can offer a realistic solution (21).…”

Progesterone impairs Herceptin effect on breast cancer cells

“…HER2 overexpression has been linked with resistance to endocrine therapies both in vitro and in vivo (10). Consistently, there are studies showing that ER activity can function as an escape pathway for ER + /HER2 + cells exposed to anti-HER2 treatment (18). The role of PG/PR in the process of resistance to anti-HER2 therapies remains elusive.…”

Lapatinib, trastuzumab or the combination added to neoadjuvant chemotherapy for breast cancer

“…The study systematically (Konecny et al, 2006). In addition, more thorough and more comprehensive anti-HER2 therapy seems to reduce the resistance of HER2 (Wang et al, 2011). That trastuzumab, lapatinib double anti-HER2 drugs cure HER2-positive metastatic breast cancer, which have been confirmed in clinical therapy (Blackwell et al, 2012).…”