Ligand-dependent activation of the hedgehog (Hh) signalling pathway has been associated with tumorigenesis in a number of human tissues. Here we show that, although previous reports have described a ...cell-autonomous role for Hh signalling in these tumours, Hh ligands fail to activate signalling in tumour epithelial cells. In contrast, our data support ligand-dependent activation of the Hh pathway in the stromal microenvironment. Specific inhibition of Hh signalling using small molecule inhibitors, a neutralizing anti-Hh antibody or genetic deletion of smoothened (Smo) in the mouse stroma results in growth inhibition in xenograft tumour models. Taken together, these studies demonstrate a paracrine requirement for Hh ligand signalling in the tumorigenesis of Hh-expressing cancers and have important implications for the development of Hh pathway antagonists in cancer.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Glioblastoma multiforme (GBM) is the most common primary brain tumor in adults. Limited treatment options have only marginally impacted patient survival over the past decades. The phophatidylinositol ...3-kinase (PI3K) pathway, frequently altered in GBM, represents a potential target for the treatment of this glioma. 5-(6,6-Dimethyl-4-morpholino-8,9-dihydro-6H-1,4oxazino4,3-epurin-2-yl)pyrimidin-2-amine (GDC-0084) is a PI3K inhibitor that was specifically optimized to cross the blood-brain barrier. The goals of our studies were to characterize the brain distribution, pharmacodynamic (PD) effect, and efficacy of GDC-0084 in orthotopic xenograft models of GBM. GDC-0084 was tested in vitro to assess its sensitivity to the efflux transporters P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) and in vivo in mice to evaluate its effects on the PI3K pathway in intact brain. Mice bearing U87 or GS2 intracranial tumors were treated with GDC-0084 to assess its brain distribution by matrix-assisted laser desorption ionization (MALDI) imaging and measure its PD effects and efficacy in GBM orthotopic models. Studies in transfected cells indicated that GDC-0084 was not a substrate of P-gp or BCRP. GDC-0084 markedly inhibited the PI3K pathway in mouse brain, causing up to 90% suppression of the pAkt signal. MALDI imaging showed GDC-0084 distributed evenly in brain and intracranial U87 and GS2 tumors. GDC-0084 achieved significant tumor growth inhibition of 70% and 40% against the U87 and GS2 orthotopic models, respectively. GDC-0084 distribution throughout the brain and intracranial tumors led to potent inhibition of the PI3K pathway. Its efficacy in orthotopic models of GBM suggests that it could be effective in the treatment of GBM. GDC-0084 is currently in phase I clinical trials.
Abstract
PI3K inhibitors have shown promise for the treatment of anti-estrogen-resistant breast cancers. Current PI3K inhibitor treatment regimens incompletely and transiently inhibit the pathway in ...carcinomas, and are accompanied by adverse effects in patients. We found that different periods of PI3K inhibition (12, 24, 36 h) potentiated anti-estrogen-induced apoptosis and inhibition of proliferation to similar extents in cultured ER+ cells. We thus hypothesized that short-term, complete inhibition of PI3K will have a greater anti-tumor effect and reduced systemic toxicity than chronic, partial inhibition.
Pharmacokinetic analysis of the orally available pan-PI3K inhibitor GDC-0941 at low (100 mg/kg) and high (800 mg/kg) doses in mice revealed that plasma levels peaked after 15-30 min. (18.6 uM and 20.7 uM, respectively), and decreased to a plateau phase after 1 h that was maintained for 8 h with low dose (6.8-10.7 uM) and 23 h with high dose (7.9-15 uM). We performed MCF-7 tumor pharmacokinetic analyses with low and high doses, and with 2 low doses administered 12 hours apart. Tumor GDC-0941 levels peaked after 9 h (1.6 uM with low-dose; 16.9 uM with high-dose). The second low dose increased tumor drug concentrations to 3.2 uM at 9 h after the second dose, compared to 1.6 uM at 9 h after the first dose. After 48 h, tumor drug concentrations decreased to 0 uM with low dose, and to 4.5 uM with high dose.
Mice bearing MCF-7 tumors were treated with fulvestrant (5 mg/wk). Three days later, GDC-0941 was administered to assess pharmacodynamic effects. Phospho-AKT and -S6 levels (markers of PI3K and mTORC1 activities, respectively) were maximally suppressed after 1 h and 3 h of high- and low-dose treatments, respectively, returned to baseline within 16 h after low-dose treatment, and remained suppressed for 36 h following high-dose treatment. PARP cleavage (marker of apoptosis) occurred within 1 h and 3 h of high- and low-dose treatments, and increased over time. Re-treatment of mice with low-dose GDC-0941 after 12 h induced continued inhibition of PI3K and mTORC1 for 9-12 h, suggesting that BID low-dose treatment may be sufficient to continually inhibit PI3K. Comparison of high-dose and low-dose BID tumors showed that these treatments induced similar amounts of PI3K inhibition and PARP cleavage at 21-24 h.
Mice bearing MCF-7 or fulvestrant-resistant T47D/FR tumors were treated with vehicle, fulvestrant, GDC-0941 (100 mg/kg QD 5 d/wk; 100 mg/kg BID 3 d/wk, 800 mg/kg QW), or combinations of fulvestrant and GDC-0941. Drug combinations induced tumor regression, fulvestrant did not affect tumor growth, high-dose GDC-0941 QW slowed tumor growth, and low-dose GDC-0941 QD or BID appreciably inhibited tumor growth. However, there was no significant difference among doses and schedules of GDC-0941 in the context of a fulvestrant backbone in either tumor model. These data suggest that transient/metronomic (QD, BID) and chronic/infrequent (QW) PI3K inhibition may provide similar anti-tumor efficacy in combination with an anti-estrogen. However, these tumor growth data conflict with cell fate data indicating that high-dose GDC-0941 induced much more apoptosis than low-dose GDC-0941. Ongoing studies will reveal how different schedules of PI3K inhibition shape tumor biology.
Citation Format: Wei Yang, Jennifer R Bean, Lloye Dillon, Laurent Salphati, Jodie Pang, Xiaolin Zhang, Michelle Nannini Pepe, Todd W Miller. Understanding pharmacodynamics and consequences of PI3K inhibition in ER+ breast tumors abstract. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-20-03.
Abstract
Background: The PI3K/AKT pathway is frequently activated in cancer by multiple mechanisms including PI3K activating mutations, PTEN loss, RTK activation, and other means. GDC-0068 is a ...potent, highly selective, ATP-competitive pan-AKT inhibitor that is currently in Phase 1a and Phase 1b clinical development. Here, we describe the cell line screening efforts and xenograft studies that provide rationale for a predictive biomarker strategy both for single agent studies and combinations with chemotherapeutic agents. Methods: Cell line screening using GDC-0068 as a single agent and in combination with other agents provided a means of identifying predictive markers across various indications and drug combinations. Single agent screens were performed with GDC-0068 in 9 prostate, 54 breast, and 18 ovarian cell lines. We evaluated combination activity of GDC-0068 with docetaxel, doxorubicin, rapamycin and MEK inhibitor in a panel of 24 cell lines and combination activity of GDC-0068 with 5FU/Cisplatin (Folfox) in a panel of 11 gastric and 15 head and neck cancer cell lines. We also evaluated both single agent activity and combination activity in select xenograft models. Results: Single agent screens identified PTEN loss, PIK3CA activating mutations, and RTK activation (HER2 in breast) as key predictive markers in breast, ovarian and prostate cell lines. Similarly, in prostate cancer xenograft models, the highest tumor growth inhibition was seen in models with PI3K pathway activation, e.g. via PTEN loss. In the GDC-0068 combination studies, MEK inhibitors provided the most significant synergy across different targeted and chemotherapy agents tested (rapamycin, docetaxel, doxurubicin). In combination with 5FU/Cisplatin, we observed additive effects in gastric and head and neck cell lines and this response was best observed in cell lines with pathway activation: PTEN loss, PI3K mutations or amplifications, and/or high pAKT. The in vitro results were recapitulated in vivo with the combination of GDC-0068 with either docetaxel or carboplatin enhancing the antitumor efficacy compared to either single agent alone in multiple tumor xenograft models. All combinations were well tolerated as assessed by animal body weights and mortalities. Conclusions: Across various indications, PTEN loss or PI3K pathway activation via PIK3CA activating mutations are strong predictive biomarkers of GDC-0068 activity either as a single agent or in combination studies and provide a strong diagnostic hypothesis for evaluation in the clinic. Based on these results and others, GDC-0068 is currently being tested for single agent activity in a diagnostically selected Phase 1a expansion cohort in breast and prostate cancer, and in multiple combination Phase Ib trials.
Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 966. doi:1538-7445.AM2012-966
PDF
