Also, visit HSP90 Central for details on AACR presentations related to ASTX's heat shock protein 90 inhibitor AT13387.
Abstract Number: 4077
Chemosensitizing effects of the novel, small molecule DNA methylation inhibitor SGI-110 in ovarian cancer
Deoxycytosine methylation of CpG islands in promoter regions of tumor suppressor genes (TSGs) plays a prominent role in the development and progression of drug-resistant epithelial ovarian cancer (OC). We previously demonstrated in a phase I/II trial that the DNA methylation inhibitor decitabine alters DNA methylation and restores platinum sensitivity in platinum-resistant OC patients, resulting in significant clinical activity. SGI-110 (Astex Pharmaceuticals) is a DNA hypomethylating agent with demonstrated activity in restoring silenced TSG expression in cancer cells by reversal of DNA methylation. As a decitabine-deoxyguanosine dinucleotide, SGI-110 has been shown to be less prone to deamination by cytidine deaminase and could have advantages over decitabine, such as better stability, less toxicity and a more convenient and less frequent SQ administration. We examined SGI-110 for its ability to inhibit OC cell proliferation and to demethylate and induce TSGs in vitro and in vivo. A 48 hour pretreatment with SGI-110 resensitized drug-resistant ovarian cancer cell lines to cisplatin (3-fold reduction in IC50 of cisplatin). In A2780 platinum sensitive OC cells, SGI-110 pre-treatment for 5 days reduced cisplatin IC50 by >2-fold. Prolonged (7 days) SGI-110 treatment reduced by 2-fold the number of ALDH1+ cells in SKOV3 and A2780 cells, suggesting an effect on the stem cell population, potentially involved in drug resistance. SGI-110 induced significant demethylation of TSGs ras-associated domain family 1A (RASSF1A) and human MutL homologue-1 (MLH1) and the differentiation-associated gene HOXA10; furthermore, RASSF1A, MLH1 and HOXA10 gene reexpression was also observed after 48 hour SGI-110 treatment. SGI-110 prevented TGF-β induced epithelial to mesenchymal transition of OC cells, as measured morphologically and by quantification of E-cadherin, Zeb1, Slug and miR200c expression levels. SGI-110 suppressed E-cadherin promoter methylation induced by TGF-β. We then examined the in vivo tolerability and efficacy of SGI-110, singly and in combination with cisplatin, in nude athymic mice. Mice were injected qd or bi-weekly with SGI-110 (sc) and/or cisplatin (ip) and body weights were measured twice weekly. In the qd regimen, SGI-110 2 mg/kg plus 4 mg/kg cisplatin was tolerated. The 10 mg/kg bi-weekly dose of SGI-110 was tolerated, either alone or in combination with 2 mg/kg cisplatin (5mg/kg SGI-110 plus 4 mg/kg cisplatin was similarly tolerated). SGI-110 induced significant global hypomethylation, as determined by pyrosequencing analysis of LINE1 demethylation in peripheral blood mononuclear cells. We are currently assessing the activity of SGI-110 in combination with cisplatin to retard the growth of platinum resistant human ovarian cancer xenografts. In summary, SGI-110 combined with platinum is a promising clinical combination for the therapy of ovarian cancer.
Abstract Number: 4076
SGI-110, a novel subcutaneous (SQ) second generation DNA hypomethylating agent achieves improved pharmacodynamics (PD), safety and pharmacokinetics (PK) in comparison to IV decitabine in a non-human primate in vivo study
SGI-110, is a novel second generation DNA methylation inhibitor that is currently in Phase I/II clinical study for treatment of myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). SGI-110 is a dinucleotide of DAC and deoxyguanosine designed to be more stable than decitabine to deamination by cytidine deaminase, thus offering a promising alternative to current hypomethylating agents approved in MDS.
We report here the results of a preclinical study in which safety, PK, and PD of different dosing regimens of SGI-110 SQ were compared to the clinical dose and regimen of DAC IV in 4 groups of male cynomolgus monkeys (n=4). The treatment groups consisted of: 1) Control group of DAC IV 1-h infusion at a dose equivalent to the clinically approved regimen of 20 mg/m2 x 5 (1.7 mg/kg daily x5); 2) 1.7 mg/kg SGI-110 SQ daily x 5 (molar equivalent to 42% of the clinical DAC dose); 3) 3.0 mg/kg SGI-110 SQ daily x 5 ( molar equivalent to 75% of the clinical DAC dose); and 4) 3.0 mg/kg of SGI-110 SQ once weekly x3 (molar equivalent to 44% of the total clinical DAC dose). DAC and SGI-110 plasma levels were measured and monkeys were monitored for 28 days for hematological changes, and global DNA methylation (LINE-1).
Reversible hematological changes included a reduction in leukocytes, red blood cells (RBCs), and neutrophil counts with the nadir counts generally occurring between D8 and D14 and recovery occurring D21 to D28. The DAC-treated group showed the greatest reduction and slowest recovery compared to all SGI-110 treated groups. Changes in methylation patterns of LINE-1 and miRNA-29b were evaluated in DNA extracted from monkey blood as PD markers of biological efficacy after treatment with SGI-110 or DAC. All groups achieved a decrease in LINE-1 methylation of approximately 15-20% from baseline between Day 8 and 21 with remethylation back to baseline levels by day 28. Both SGI-110 SQ dailyx5 regimens achieved slightly more hypomethylation than DAC IV on days 8 (group 3) and 11 (group 2). Overall, the magnitude and duration of the decrease in DNA methylation at lower molar equivalent doses of SQ SGI-110 were similar to or better than DAC IV. SGI-110 appeared to convert to DAC resulting in similar exposure window compared to IV DAC. The dose-adjusted plasma DAC exposures, on molar equivalence basis, were somewhat lower compared to the DAC group. The Cmax ranged 52-163 vs 215-525(DAC) ng/mL, while dose-adjusted AUCs were 21.6-51.6 vs 98.6-221(DAC) ng*hr/mL.
In conclusion, these preclinical studies showed that SQ SGI-110 may represent a more convenient and tolerable option for delivering DAC where either the weeklyx3 or dailyx5 regimens at a lower dose achieved DNA hypomethylating effects that were similar to or better than seen with DAC IV and with less myelosuppressive effects.
Abstract Number: 928
The novel clinical candidate AT13148 is an oral multi-AGC kinase inhibitor with potent pharmacodynamic and antitumor activity and demonstrates a mechanism of action distinct from AKT inhibitors
The AGC kinase AKT is a key component of the phosphatidylinositol 3-kinase (PI3K) pathway, which is frequently deregulated in cancer, making AKT a target of major therapeutic interest. However, PI3K signaling through both AKT-dependent and AKT-independent mechanisms involving other AGC kinases, such as p70S6K, PKA, SGK and ROCK, is important in a range of cancers. Hence, the pharmacological inhibition of these multiple AGC kinases may increase response rates and minimize clinical resistance compared with targeting AKT alone.
The clinical drug candidate AT13148 is a multi-AGC kinase, ATP-competitive inhibitor, identified utilizing high-throughput X-ray crystallography and fragment-based lead discovery techniques. Screening of this oral small molecule against a panel of kinases at 10μM revealed >80% inhibition of the structurally related AGC kinases AKT, PKA, ROCK2, p70S6K, MSK, RSK1/2, and SGK. We demonstrate that AT13148 has antiproliferative activity in a range of in vitro models harboring relevant genetic abnormalities, including PTEN, KRAS, PIK3CA and HER2 aberrations. AT13148 caused substantial blockade of AKT, p70S6K, PKA, ROCK and SGK substrate phosphorylation and induction of apoptosis in both a concentration and time-dependent manner in cancer cells with clinically relevant genetic defects both in vitro and in vivo. Antitumor efficacy in HER2-positive, PIK3CA-mutant BT474 breast, PTEN-deficient PC3 human prostate cancer and PTEN-deficient MES-SA uterine tumor xenografts was demonstrated. We show for the first time that induction of AKT phosphorylation at serine 473 by AT13148, as reported for other ATP competitive inhibitors of AKT, is not a therapeutically relevant reactivation step for this compound.
We used gene expression microarray studies to characterize the underlying molecular mechanisms of action of AT13148 and the selective AKT inhibitor CCT128930, and observed the induction of upstream regulators including insulin receptor substrate-2 and PIK3IP1 due to compensatory feedback loops, consistent with blockade of AKT signaling. These studies also showed that AT13148 and CCT128930 have distinct molecular effects in cancer cells: AT13148 had a predominant effect on apoptosis genes and caused a greater apoptotic phenotype, while CCT128930 modulated genes in the network regulating cell cycle. This finding emphasizes the functional differences of AT13148 as a multi-AGC kinase inhibitor in contrast to a more AKT-selective inhibitor.
In view of the potential mechanistic advantages detailed above, and the potent antitumor activity observed at well tolerated doses against established human tumor xenografts with clinically relevant genetic drivers, the clinical utility of such an AGC kinase inhibitor strategy will now be assessed in a first-in-human Phase I trial of AT13148.