The class I phosphatidylinositol 3' kinase (PI3K) plays a major role in proliferation and survival in a wide variety of human cancers. A key factor in successful development of drugs targeting this ...pathway is likely to be the identification of responsive patient populations with predictive diagnostic biomarkers. This study sought to identify candidate biomarkers of response to the selective PI3K inhibitor GDC-0941.
We used a large panel of breast cancer cell lines and in vivo xenograft models to identify candidate predictive biomarkers for a selective inhibitor of class I PI3K that is currently in clinical development. The approach involved pharmacogenomic profiling as well as analysis of gene expression data sets from cells profiled at baseline or after GDC-0941 treatment.
We found that models harboring mutations in PIK3CA, amplification of human epidermal growth factor receptor 2, or dual alterations in two pathway components were exquisitely sensitive to the antitumor effects of GDC-0941. We found that several models that do not harbor these alterations also showed sensitivity, suggesting a need for additional diagnostic markers. Gene expression studies identified a collection of genes whose expression was associated with in vitro sensitivity to GDC-0941, and expression of a subset of these genes was found to be intimately linked to signaling through the pathway.
Pathway focused biomarkers and the gene expression signature described in this study may have utility in the identification of patients likely to benefit from therapy with a selective PI3K inhibitor.
Docetaxel is a front-line standard-of-care chemotherapeutic drug for the treatment of breast cancer. Phosphoinositide 3-kinases (PI3K) are lipid kinases that regulate breast tumor cell growth, ...migration, and survival. The current study was intended to determine whether GDC-0941, an orally bioavailable class I selective PI3K inhibitor, enhances the antitumor activity of docetaxel in human breast cancer models in vitro and in vivo.
A panel of 25 breast tumor cell lines representing HER2+, luminal, and basal subtypes were treated with GDC-0941, docetaxel, or the combination of both drugs and assayed for cellular viability, modulation of PI3K pathway markers, and apoptosis induction. Drug combination effects on cellular viability were also assessed in nontransformed MCF10A human mammary epithelial cells. Human xenografts of breast cancer cell lines and patient-derived tumors were used to assess efficacy of GDC-0941 and docetaxel in vivo.
Combination of GDC-0941 and docetaxel decreased the cellular viability of breast tumor cell lines in vitro but to variable degrees of drug synergy. Compared with nontransformed MCF10A cells, the addition of both drugs resulted in stronger synergistic effects in a subset of tumor cell lines that were not predicted by breast cancer subtype. In xenograft models, GDC-0941 enhanced the antitumor activity of docetaxel with maximum combination efficacy observed within 1 hour of administering both drugs. GDC-0941 increased the rate of apoptosis in cells arrested in mitosis upon cotreatment with docetaxel.
GDC-0941 augments the efficacy of docetaxel by increasing drug-induced apoptosis in breast cancer models.
The PTEN/PI3K pathway is commonly mutated in cancer and therefore represents an attractive target for therapeutic intervention. To investigate the primary phenotypes mediated by increased pathway ...signaling in a clean, patient-relevant context, an activating PIK3CA mutation (H1047R) was knocked-in to an endogenous allele of the MCF10A non-tumorigenic human breast epithelial cell line. Introduction of an endogenously mutated PIK3CA allele resulted in a marked epithelial-mesenchymal transition (EMT) and invasive phenotype, compared to isogenic wild-type cells. The invasive phenotype was linked to enhanced PIP(3) production via a S6K-IRS positive feedback mechanism. Moreover, potent and selective inhibitors of PI3K were highly effective in reversing this phenotype, which is optimally revealed in 3-dimensional cell culture. In contrast, inhibition of Akt or mTOR exacerbated the invasive phenotype. Our results suggest that invasion is a core phenotype mediated by increased PTEN/PI3K pathway activity and that therapeutic agents targeting different nodes of the PI3K pathway may have dramatic differences in their ability to reverse or promote cancer metastasis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Estrogen receptor-positive (ER+) breast cancers frequently remain dependent on ER signaling even after acquiring resistance to endocrine agents, prompting the development of optimized ER antagonists. ...Fulvestrant is unique among approved ER therapeutics due to its capacity for full ER antagonism, thought to be achieved through ER degradation. The clinical potential of fulvestrant is limited by poor physicochemical features, spurring attempts to generate ER degraders with improved drug-like properties. We show that optimization of ER degradation does not guarantee full ER antagonism in breast cancer cells; ER “degraders” exhibit a spectrum of transcriptional activities and anti-proliferative potential. Mechanistically, we find that fulvestrant-like antagonists suppress ER transcriptional activity not by ER elimination, but by markedly slowing the intra-nuclear mobility of ER. Increased ER turnover occurs as a consequence of ER immobilization. These findings provide proof-of-concept that small molecule perturbation of transcription factor mobility may enable therapeutic targeting of this challenging target class.
Display omitted
•Drug candidates optimized for ER degradation can weakly activate ER in cancer cells•“ER degraders” trigger interaction of ER with DNA at canonical binding sites•Impact on chromatin accessibility distinguishes ER antagonists from weak activators•Dramatic slowing of ER mobility drives ER antagonism, and precedes ER turnover
Ligands that limit estrogen receptor mobility exhibit superior anti-proliferative capacity compared to those aimed solely at promoting ER degradation, pointing to a distinct approach for developing treatments for ER+ breast cancer.
Abstract
Approximately 65% of breast cancers are estrogen receptor alpha (ERα)-positive and depend on ERα signaling for growth. Clinical data indicate that ERα-positive breast cancers have a better ...prognosis when another hormone receptor, the progesterone receptor (PR), is coexpressed. Recent studies show that in the presence of its ligand progesterone, PR redirects ERα chromatin binding and transcriptional activity, thereby impacting prognosis and therapeutic response.
To further examine PR function, we knocked out the PGR gene in the ERα-positive breast cancer cell lines MCF-7 and T47D using CRISPR-mediated gene editing. Knockout clones from each model were analyzed for ER- and PR-mediated transcriptional activity and gene expression profile, as well as response to selective estrogen receptor degraders (SERDs).
The T47D cell line expresses high levels of PR in the presence or absence of estrogen, and stimulation with progesterone induces robust PR phosphorylation and modulation of PR target gene expression. Furthermore, progesterone attenuates estradiol-induced cell proliferation in a dose-dependent manner. Knockout of PR in this model abrogates the ability of progesterone to induce gene expression changes or attenuate estradiol-induced cell proliferation. In contrast, the MCF-7 cell line expresses low basal levels of PR, and is refractory to stimulation with progesterone. Interestingly, in estrogenic growth media, knockout of PR in this model results in basal gene expression changes that resemble a gene signature associated with tamoxifen resistance. Consistent with these findings, knockout of PR reduces the response to SERDs in a 5-day cell proliferation assay. ChIP-seq and RNA-seq analyses are ongoing to examine how loss of PR impacts ERα chromatin binding and transcriptional output.
Citation Format: Amy Young, Jane Guan, Anneleen Daemen, Lori Friedman, Kui Lin. Progesterone receptor signaling in estrogen receptor-positive breast cancer abstract. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B36.
Abstract
Aromatase inhibitors (AIs), the Estrogen Receptor (ER) modulator tamoxifen and the full ER antagonist fulvestrant each target ER signaling and constitute the backbone of standard of care for ...ER+ breast cancer. The growing appreciation of liabilities associated with each of these modalities, which may limit their clinical potential, has triggered a wave of activity around next-generation ER therapeutics, and there are currently more than 10 new molecular entities targeting ER being evaluated in Phase 1 clinical trials. In addition to a collection of ER-targeted therapeutics either approved or under evaluation, the emergence of CDK4/6 inhibitors as combination partners has meaningfully contributed to the oncologist’s tool box for the treatment of breast cancer, while also adding complexity to the treatment landscape.
Although direct ER antagonists are expected to be superior to AIs in patients with tumors expressing constitutively activating ER mutations (e.g. ER.Y537S), it is currently unclear if a subset of ER wildtype patients may likewise derive superior benefit from direct ER targeting. It is also unclear which ER+ tumors require CDK4/6 inhibitor/ER antagonist combinations for maximal anti-tumor activity, versus those where single-agent ER antagonist treatment may achieve full cell cycle control. To address these key questions, we used a panel of 22 ER+ cell lines to evaluate the relative anti-proliferative and cytotoxic effects of estrogen (E2) withdrawal (modeling AIs), ER modulation, and full ER inhibition, as single agents and in combination with the CDK4/6 inhibitor Palbociclib. We find a number of cell lines in which direct ER antagonism is superior to E2 withdrawal and is associated with E2-independent ER signaling not attributable to ER mutations. The impact of E2 withdrawal on cell cycle control and proliferation is significantly enhanced by concurrent CDK4/6 inhibition, in line with clinical observations, however, direct ER antagonism in combination with CDK4/6 inhibition remains most efficacious.
We are integrating our cell response data with detailed molecular analyses and transcriptional profiling to 1) identify cellular contexts, beyond ER mutations, where direct ER antagonism is superior to targeting E2 synthesis, 2) identify tumors where full cell cycle control and anti-tumor efficacy is achievable through single-agent ER targeting, and 3) better understand the basis for the co-operativity of endocrine suppression with CDK4/6 inhibition. Deconvolution of the ER+ breast cancer response to distinct modes of ER signaling inhibition alone and in combination with CDK4/6 inhibitors has the potential to guide clinical decision-making for personalized patient care.
Citation Format: Wei Zhou, Jane Guan, Georgia Hatzivassiliou, Anneleen Daemen, Marc Hafner, Ciara Metcalfe. Leveraging an expanding tool box for ER+ breast cancer: exploring breast cancer dependencies to support optimal therapeutic strategies abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1004.
Alterations of the phosphoinositide-3 kinase (PI3K)/Akt signaling pathway occur broadly in cancer via multiple mechanisms including mutation of the PIK3CA gene, loss or mutation of phosphatase and ...tensin homolog (PTEN), and deregulation of mammalian target of rapamycin (mTOR) complexes. The dysregulation of this pathway has been implicated in tumor initiation, cell growth and survival, invasion and angiogenesis, thus, PI3K and mTOR are promising therapeutic targets for cancer. We discovered GDC-0980, a selective, potent, orally bioavailable inhibitor of Class I PI3 kinase and mTOR kinase (TORC1/2) with excellent pharmacokinetic and pharmaceutical properties. GDC-0980 potently inhibits signal transduction downstream of both PI3K and mTOR, as measured by pharmacodynamic (PD) biomarkers, thereby acting upon two key pathway nodes to produce the strongest attainable inhibition of signaling in the pathway. Correspondingly, GDC-0980 was potent across a broad panel of cancer cell lines, with the greatest potency in breast, prostate, and lung cancers and less activity in melanoma and pancreatic cancers, consistent with KRAS and BRAF acting as resistance markers. Treatment of cancer cell lines with GDC-0980 resulted in G1 cell-cycle arrest, and in contrast to mTOR inhibitors, GDC-0980 induced apoptosis in certain cancer cell lines, including those with direct pathway activation via PI3K and PTEN. Low doses of GDC-0980 potently inhibited tumor growth in xenograft models including those with activated PI3K, loss of LKB1 or PTEN, and elicited an exposure-related decrease in PD biomarkers. These preclinical data show that GDC-0980 is a potent and effective dual PI3K/mTOR inhibitor with promise for the clinic.
is one of the most frequently mutated oncogenes; the p110a protein it encodes plays a central role in tumor cell proliferation. Small-molecule inhibitors targeting the PI3K p110a catalytic subunit ...have entered clinical trials, with early-phase GDC-0077 studies showing antitumor activity and a manageable safety profile in patients with
-mutant breast cancer. However, preclinical studies have shown that PI3K pathway inhibition releases negative feedback and activates receptor tyrosine kinase signaling, reengaging the pathway and attenuating drug activity. Here we discover that GDC-0077 and taselisib more potently inhibit mutant PI3K pathway signaling and cell viability through unique HER2-dependent mutant p110a degradation. Both are more effective than other PI3K inhibitors at maintaining prolonged pathway suppression. This study establishes a new strategy for identifying inhibitors that specifically target mutant tumors by selective degradation of the mutant oncoprotein and provide a strong rationale for pursuing PI3Kα degraders in patients with HER2-positive breast cancer. SIGNIFICANCE: The PI3K inhibitors GDC-0077 and taselisib have a unique mechanism of action; both inhibitors lead to degradation of mutant p110a protein. The inhibitors that have the ability to trigger specific degradation of mutant p110a without significant change in wild-type p110a protein may result in improved therapeutic index in
-mutant tumors.
.
.
Abstract
Introduction: The phosphoinositide-3 kinase (PI3K)/Akt signaling pathway is deregulated in a wide variety of cancers. Somatic activating mutations and amplifications in PI3K are common in ...multiple cancers including breast, colon, and lung cancer. PTEN, a phosphatase that converts PIP3 to PIP2 and thus has an opposing function to PI3K, is a commonly mutated tumor suppressor in multiple cancers including prostate and glioblastoma. Alterations of this pathway have been implicated in tumor initiation, progression, survival, angiogenesis, and metastasis. PI3K/Akt pathway activation has also been implicated in therapeutic resistance. Thus PI3K is considered to be a promising therapeutic target for cancer.
Summary of Results: Medicinal chemistry efforts resulted in the discovery of GDC-0980, a selective, orally bioavailable inhibitor of PI3 Kinase and mTOR kinase with promising pharmacokinetic and pharmaceutical properties. Here we report the first pre-clinical profile of GDC-0980. This compound is a potent ATP-competitive Class I PI3 kinase inhibitor with an IC50 of 4.8 nM against the PI3K p110apha subunit, 26.8 nM p110beta, 6.7 nM p110delta, 13.8 nM p110gamma, and an mTOR Kiapp of 17.3 nM. GDC-0980 demonstrates selectivity against a large panel of protein kinases as well as selectivity over PIK family kinases including Class II, Class III, and DNA-PK. GDC-0980 inhibits the PI3K signaling pathway in vitro causing a reversible G1 cell cycle arrest, and apoptosis induction in a subset of tumor cell lines. Levels of signaling pathway markers such as phosphorylated AKT (pAKT), PRAS40 (pPRAS40), and S6 (pS6) are rapidly and dramatically reduced following exposure of cells to GDC-0980. Oral dosing of GDC-0980 potently inhibits tumor growth in xenograft models including those mutated in PI3K and PTEN, and elicits an exposure-related concomitant decrease in PD biomarkers.
Conclusion: These preclinical data provide compelling evidence in support of GDC-0980 as a clinical candidate, and Phase I studies are ongoing.
Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C201.
PDF
