Responsiveness to PI3K and MEK Inhibitors in Breast Cancer. Use of a 3D Culture System to Study Pathways Related to Hormone Independence in Mice

Abstract

BackgroundA significant proportion of breast cancer patients face failure of endocrine therapy due to the acquisition of endocrine resistance. We have explored mechanisms involved in such disease progression by using a mouse breast cancer model that is induced by medroxyprogesterone acetate (MPA). These tumors transit through different stages of hormone sensitivity. However, when cells from tumor variants were seeded on plastic, all were stimulated by progestins and inhibited by antiprogestins such as RU486. Furthermore, cells from a RU486-resistant tumor variant recovered antiprogestin sensitivity.HypothesisA three-dimensional (3D) culture system, by maintaining differential cellular organization that is typical of each tumor variant, may allow for the maintenance of particular hormone responses and thus be appropriate for the study of the effects of specific inhibitors of signaling pathways associated with disease progression.MethodWe compared the behavior of tumors growing in vivo and cancer cells ex vivo (in 3D Matrigel). In this system, we evaluated the effects of kinase inhibitors and hormone antagonists on tumor growth.Principal FindingsLY294002, a PI3K/AKT pathway inhibitor, decreased both tumor growth in vivo and cell survival in Matrigel in MPA-independent tumors with higher AKT activity. Induction of cell death by anti-hormones such as ICI182780 and ZK230211 was more effective in MPA-dependent tumors with lower AKT activity. Inhibition of MEK with PD98059 did not affect tumor growth in any tested variant. Finally, while Matrigel reproduced differential responsiveness of MPA-dependent and -independent breast cancer cells, it was not sufficient to preserve antiprogestin resistance of RU486-resistant tumors.ConclusionWe demonstrated that the PI3K/AKT pathway is relevant for MPA-independent tumor growth. Three-dimensional cultures were useful to test the effects of kinase inhibitors on breast cancer growth and highlight the need for in vivo models to validate experimental tools used for selective therapeutic targeting.

Ligand-free estrogen receptor activity complements IGF1R to induce the proliferation of the MCF-7 breast cancer cells

“…The fact that chemical inhibitors of PI3K block the mitogenic signaling in breast cancer cells has been reported earlier [9,23]. This is also illustrated by the effect of LY 294002 on the expression of cyclin A (Figure 4, upper panel).…”

MPA-induced gene expression and stromal and parenchymal gene expression profiles in luminal murine mammary carcinomas with different hormonal requirements

“…5). PTEN is a negative regulator of Akt activity, and the higher expression of this gene in C4-HD tumors is in agreement with recent work by our group showing that C4-HI tumors exhibit elevated activation of Akt compared with that in C4-HD tumors [36]. To study the expression of MMP9 and MMP13 proteins, we used IF experiments.…”

Mitogen-Activated Protein Kinase Signal Transduction in Solid Tumors

“…For example, cell proliferation inhibitor Emodin is justly proved to function in a MAPK way, targeting at ERα (Jia-Qi et al, 2014). But endocrine therapy targeting at ER or HER don't receive much effect as imaged, now, researches have showed that the ERK is closely connected to hormone resistance by the oncogenic RAS-MEK-ERK pathway (Polo et al, 2010). So, specific inhibitors of ERK kinase (MEK) should be of help.…”