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Purpose: GSK461364 is an ATP-competitive inhibitor of polo-like kinase 1 (Plk1). A phase I study of two schedules of intravenous GSK461364 was conducted. Experimental Design: GSK461364 was administered in escalating doses to patients with solid malignancies by two schedules, either on days 1, 8, and 15 of 28-day cycles (schedule A) or on days 1, 2, 8, 9, 15, and 16 of 28-day cycles (schedule B). Assessments included pharmacokinetic and pharmacodynamic profiles, as well as marker expression studies in pretreatment tumor biopsies. Results: Forty patients received GSK461364: 23 patients in schedule A and 17 in schedule B. Dose-limiting toxicities (DLT) in schedule A at 300 mg (2 of 7 patients) and 225 mg (1 of 8 patients) cohorts included grade 4 neutropenia and/or grade 3–4 thrombocytopenia. In schedule B, DLTs of grade 4 pulmonary emboli and grade 4 neutropenia occurred at 7 or more days at 100 mg dose level. Venous thrombotic emboli (VTE) and myelosuppression were the most common grade 3–4, drug-related events. Pharmacokinetic data indicated that AUC (area under the curve) and Cmax (maximum concentration) were proportional across doses, with a half-life of 9 to 13 hours. Pharmacodynamic studies in circulating tumor cells revealed an increase in phosphorylated histone H3 (pHH3) following drug administration. A best response of prolonged stable disease of more than 16 weeks occurred in 6 (15%) patients, including 4 esophageal cancer patients. Those with prolonged stable disease had greater expression of Ki-67, pHH3, and Plk1 in archived tumor biopsies. Conclusions: The final recommended phase II dose for GSK461364 was 225 mg administered intravenously in schedule A. Because of the high incidence (20%) of VTE, for further clinical evaluation, GSK461364 should involve coadministration of prophylactic anticoagulation. Clin Cancer Res; 17(10); 3420–30. ©2011 AACR.

Purpose: GSK2126458 (GSK458) is a potent inhibitor of PI3K (α, β, γ, and δ), with preclinical studies demonstrating broad antitumor activity. We performed a first-in-human phase I study in patients with advanced solid tumors. Materials and Methods: Patients received oral GSK458 once or twice daily in a dose-escalation design to define the maximum tolerated dose (MTD). Expansion cohorts evaluated pharmacodynamics, pharmacokinetics, and clinical activity in histologically and molecularly defined cohorts. Results: One hundred and seventy patients received doses ranging from 0.1 to 3 mg once or twice daily. Dose-limiting toxicities (grade 3 diarrhea, n = 4; fatigue and rash, n = 1) occurred in 5 patients (n = 3 at 3 mg/day). The MTD was 2.5 mg/day (MTD with twice daily dosing undefined). The most common grade ≥3 treatment-related adverse events included diarrhea (8%) and skin rash (5%). Pharmacokinetic analyses demonstrated increased duration of drug exposure above target level with twice daily dosing. Fasting insulin and glucose levels increased with dose and exposure of GSK458. Durable objective responses (ORs) were observed across multiple tumor types (sarcoma, kidney, breast, endometrial, oropharyngeal, and bladder cancer). Responses were not associated with PIK3CA mutations (OR rate: 5% wild-type vs. 6% mutant). Conclusions: Although the MTD of GSK458 was 2.5 mg once daily, twice-daily dosing may increase duration of target inhibition. Fasting insulin and glucose levels served as pharmacodynamic markers of drug exposure. Select patients achieved durable responses; however, PIK3CA mutations were neither necessary nor predictive of response. Combination treatment strategies and novel biomarkers may be needed to optimally target PI3K. Clin Cancer Res; 22(8); 1932–9. ©2015 AACR.

Few therapeutic strategies exist for the treatment of metastatic tumor cells in the brain because the blood–brain barrier (BBB) limits drug access. Thus the identification of molecular targets and accompanying BBB permeable drugs will significantly benefit brain metastasis patients. Polo-like kinase 1 (Plk1) is an attractive molecular target because it is only expressed in dividing cells and its expression is upregulated in many tumors. Analysis of a publicly available database of human breast cancer metastases revealed Plk1 mRNA expression was significantly increased in brain metastases compared to systemic metastases (P = 0.0018). The selective Plk1 inhibitor, GSK461364A, showed substantial uptake in normal rodent brain. Using a breast cancer brain metastatic xenograft model (231-BR), we tested the efficacy of GSK461364A to prevent brain metastatic colonization. When treatment was started 3 days post-injection, GSK461364A at 50 mg/kg inhibited the development of large brain metastases 62% (P = 0.0001) and prolonged survival by 17%. GSK461364A sensitized tumor cells to radiation induced cell death in vitro. Previously, it was reported that mutations in p53 might render tumor cells more sensitive to Plk1 inhibition; however, p53 mutations are uncommon in breast cancer. In a cohort of 41 primary breast tumors and matched brain metastases, p53 immunostaining was increased in 61% of metastases; 44% of which were associated with primary tumors with low p53. The data suggest that p53 overexpression occurs frequently in brain metastases and may facilitate sensitivity to Plk1 inhibition. These data indicate Plk1 may be a new druggable target for the prevention of breast cancer brain metastases.

GSK923295 is an inhibitor of CENP-E, a key cellular protein important in the alignment of chromosomes during mitosis. This was a Phase I, open-label, first-time-in-human, dose-escalation study, to determine the maximum-tolerated dose (MTD), safety, and pharmacokinetics of GSK923295.Adult patients with previously treated solid tumors were enrolled in successive cohorts at GSK923295 doses ranging from 10 to 250 mg/m(2). GSK923295 was administered by a 1-h intravenous infusion, once weekly for three consecutive weeks, with treatment cycles repeated every 4 weeks.A total of 39 patients were enrolled. The MTD for GSK923295 was determined to be 190 mg/m(2). Observed dose-limiting toxicities (all grade 3) were as follows: fatigue (n = 2, 5%), increased AST (n = 1, 2.5%), hypokalemia (n = 1, 2.5%), and hypoxia (n = 1, 2.5%). Across all doses, fatigue was the most commonly reported drug-related adverse event (n = 13; 33%). Gastrointestinal toxicities of diarrhea (n = 12, 31%), nausea (n = 8, 21%), and vomiting (n = 7, 18%) were generally mild. Frequency of neutropenia was low (13%). There were two reports of neuropathy and no reports of mucositis or alopecia. GSK923295 exhibited dose-proportional pharmacokinetics from 10 to 250 mg/m(2) and did not accumulate upon weekly administration. The mean terminal elimination half-life of GSK923295 was 9-11 h. One patient with urothelial carcinoma experienced a durable partial response at the 250 mg/m(2) dose level.The novel CENP-E inhibitor, GSK923295, had dose-proportional pharmacokinetics and a low number of grade 3 or 4 adverse events. The observed incidence of myelosuppression and neuropathy was low. Further investigations may provide a more complete understanding of the potential for GSK923295 as an antiproliferative agent.

Polo-like kinases (Plk) function in mitosis and maintaining DNA integrity. There are four family members, of which Plk1 represents a target for anticancer therapy. Plk1 is only expressed in dividing cells with peak expression during G2/M. Plk1 functions in multiple steps of mitosis, and is overexpressed in many tumor types. Mitotic arrest and inhibition of proliferation, apoptosis, and tumor growth inhibition have been observed in preclinical studies using small interfering RNAs (siRNA) or small molecules that inhibit Plk1. Preclinical studies also show that Plk1 inhibitors may be active against tumors with RAS mutations and that tumor cells with mutations in TP53 are more sensitive to inhibition of Plk1. Several Plk inhibitors are in phase I or II clinical studies. As expected, hematologic toxicity is the primary dose-limiting toxicity. Some patients have achieved clinical response, although in some studies only at doses above the maximum tolerated dose defined in the study. Further evaluation is necessary to discern the clinical utility of Plk1 inhibitors. Clin Cancer Res; 16(2); 384–9

3018 Background: Phosphatidylinositol 3-kinase (PI3K) is critical to cancer cell growth, survival, and metabolism. GSK458 is an oral, potent inhibitor of PI3K (α, β, γ, δ), mTORC1, and mTORC2. Preclinically, GSK458 has demonstrated broad anti-tumor activity against solid tumors and hematologic malignancies in vitro and in vivo. Cell lines with common activating mutations of PIK3CA are particularly sensitive to GSK458. Methods: Adult patients (pts) with relapsed or refractory advanced solid tumors received GSK458 by mouth daily until disease progression or toxicity. Dose escalation used a modified accelerated titration scheme. Expansion cohorts further evaluated pharmacodynamics (PD), pharmacokinetics and clinical activity in specific target populations. Results: Preliminary data reveal that 78 pts (51% female) with mean age of 57 (25-85) yrs received ≥1 dose of GSK458. Doses ranged from 0.1 to 3 mg. Maximum tolerated dose was 2.5 mg daily. AUC and Cmax increased with dose. Across doses: median Tmax was 2 ...