Renal toxicity of the anticancer drug fostriecin

Safety, Tolerability, and Preliminary Activity of LB-100, an Inhibitor of Protein Phosphatase 2A, in Patients with Relapsed Solid Tumors: An Open-Label, Dose Escalation, First-in-Human, Phase I Trial

Purpose: To determine the MTD and to assess the safety, tolerability, and potential activity of LB-100, a first-in-class small-molecule inhibitor of protein phosphatase 2A (PP2A) in adult patients with progressive solid tumors.Experimental Design: LB-100 was administered intravenously daily for 3 days in 21-day cycles in a 3 + 3 dose escalation design.Results: There were 29 patient entries over 7 dose escalations. One patient stopped treatment after one dose because of an acute infection and was reenrolled after recovery; each course was analyzed as a separate patient entry. Two patients had dose-limiting toxicity (reversible increases in serum creatinine or calculated serum creatinine clearance) at the 3.1 mg/m² level. Probable or possible study drug-related grade 3 adverse events occurred in 6 (20.7%) patients [anemia (n = 2), decreased creatinine clearance, dyspnea, hyponatremia, and lymphopenia]. Ten (50%) of 20 response-evaluable patients had stable disease for four or more cycles. One patient with pancreatic adenocarcinoma had a partial response noted after 10 cycles, which was maintained for five additional cycles. The other patients achieving stable disease had one of the following: fibrosarcoma, chondrosarcoma, thymoma, atypical carcinoid of lung, or ovarian, testicular, breast (n = 2), and prostate cancer. The recommended phase II dose of LB-100 is 2.33 mg/m² daily for 3 days every 3 weeks.Conclusions: The safety, tolerability, preliminary evidence of antitumor activity, and novel mechanism of action of LB-100 support its continued development alone and in combination with other therapies. Clin Cancer Res; 23(13); 3277-84. ©2016 AACR.

Synthesis and anticancer activity of a series of norcantharidin analogues

Cantharidin (1) and norcantharidin (2) display high levels of anticancer activity against a broad range of tumour cell lines. Synthetic manipulation of norcantharidin yields (3S,3aR,4S,7R,7aS)-3-hydroxyhexahydro-4,7-epoxyisobenzofuran-1(3H)-one (3), which also displays a high level of anticancer activity against tumour cells but interestingly, shows selectivity towards HT29 (colon; GI(50) = 14 μM) and SJ-G2 (glioblastoma; GI(50) = 15 μM) cell lines. Substitution at the hydroxyl group of the cyclic lactone within (3) produces a diasteromeric pair of products that have no difference in cytotoxicity over the cell lines tested. Incorporation of an isopropyl tail at this position (16) produced the most promising compound of this series to date, with strong selectivity towards HT29 (colon; GI(50) = 19 μM) and SJ-G2 (glioblastoma; GI(50) = 21 μM) cell lines but completely void of any activity against the remaining tumour cell lines (GI(50) > 100 μM), as per the parent molecule. We also discovered that the introduction of a terminal phosphate moiety (28) at the same position produced a different trend in cytotoxicity with strong activity in BE2-C (neuroblastoma; GI(50) = 9 μM) cells; suggestive of an alternate mode of action.

Phase I and pharmacokinetic study of fostriecin given as an intravenous bolus daily for five consecutive days

Fostriecin (CI-920) is a potent inhibitor of protein phosphatase 2A (PP2A) and protein phosphatase 4(PP4) found to have anticancer activity in preclinical testing. A phase I study was conducted to evaluate the maximum-tolerated dose (MTD), toxicity profile, and pharmacokinetics (PK) of this drug. Forty-six patients were treated with escalating doses of fostriecin (2-47 mg/m2) administered as a daily bolus infusion for five consecutive days. PK studies were performed at different time points following administration of fostriecin. Dose-limiting toxicities included: elevation of creatinine, bilirubin, and hepatic transaminases; nausea, anorexia, lethargy, and hypotension. PK studies were compatible with a two-compartment model. Regression analysis revealed a significant relationship between dose and clearance; however, the r2 value was only 0.168 indicating a low predictive value for the model. No significant difference was seen in PK parameters with repeated dosing during the same cycle. Although no tumor responses were seen, 16 patients had stable disease with a median duration response of 2.6 months. The study was closed before reaching MTD due to problems with the supply of fostriecin from the National Cancer Institute of the United States (NCI US). New methods for synthesizing fostriecin have recently been described and therefore further development of this unique anticancer agent may be warranted.

Protein phosphatase 2A enhances activation of human immunodeficiency virus type 1 by phorbol myristate acetate

The viral replication rate in patients infected with human immunodeficiency virus type 1 (HIV-1) is controlled in part by regulation of the transcription of viral genes. The rate of transcription is determined by a complex interplay between cellular and viral proteins and the promoter elements found in the long terminal repeats. Protein phosphatase 2A (PP2A) is a phosphoprotein that plays important roles in the regulation of signal transduction and cell growth. In this report, we demonstrate that overexpression of the catalytic subunit of protein phosphatase 2A (PP2Ac) increases the basal activity of the HIV-1 promoter and, especially, enhances the promoter's response to the protein kinase C (PKC) activator 12-O-tetradecanoyl phorbol-13-acetate (PMA). Additionally, ectopic PP2Ac enhances activation of HIV-1 provirus by PMA. Okadaic acid, a potent inhibitor of PP2A, markedly reduces both HIV-1 enhancer and proviral activation. Fostriecin, a PP2A inhibitor which has been used as an antineoplastic agent in clinical trials, is also able to inhibit PMA-stimulated HIV-1 proviral activation. These observations demonstrate a role for the important cellular phosphatase PP2A in HIV-1 transcription and replication and also suggest that PKC can potentiate the activity of PP2A. PP2A is a potential target for therapeutic intervention in patients infected with HIV-1.

Anticancer activity and protein phosphatase 1 and 2A inhibition of a new generation of cantharidin analogues

Cantharidin (Spanish Fly) is a natural toxin and an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A), which have key roles in cell cycle progression. We have synthesised two series of demethylated cantharidin analogues, one displaying an open-ring lactone configuration in solution (Novo-1 to Novo-5) similar to cantharidin, the other showing a closed-ring lactone configuration (Novo-6 to Novo-10). In the present study, these ten agents were screened for in vitro PP1 and PP2A inhibition and cellular cytotoxicity in nine cancer cell lines of haematopoietic (L1210, HL60), ovarian (A2780, ADDP), osteo (143B), and colon (HCT116, HT29, WiDr, SW480) origin and one normal colon cell line (CCD-018). The open-ring series (IC50, PPI=2.0-4.8 microM, PP2A=0.2-0.5 microM) maintained the PP2A selectivity of cantharidin (IC50, PPI=1.8 microM, PP2A=0.2 microM), although some were less potent. The closed-ring series (IC50, PPI=12.5->1000 microM, PP2A=5->1000 microM) were considerably less potent inhibitors, confirming the need of ring opening for inhibition. The cytotoxicity (IC50, 72 h, MTT assay) of cantharidin ranged from 6-15 microM, while the new analogues ranged from 14 to >1000 microM. Cytotoxicity of the agents did not consistently parallel the in vitro potency of protein phosphatase inhibition. A number of analogues showed colon cancer selectivity, particularly Novo-6, where the cytotoxicity ranged from 14-88 microM in the colon cancer cells and 275-680 microM in all other cell lines including normal colon cells. The reason for this selectivity was not apparent and may involve additional intracellular targets. Cell cycle analysis showed cantharidin to enhance cell cycle progression as evident from an increased S-phase population and enhanced DNA synthesis, culminating in G2/M arrest and apoptosis. With Novo-1 and Novo-6, the cell cycle changes paralleled the cytotoxicity responses, with the predominant effect of G2/M cell cycle arrest followed by cell death. In conclusion, we have synthesised new anticancer agents that show selective cytotoxicity in colon cancer cells while remaining inactive in normal colon cells, and which mediate their effects via the G2/M phase of the cell cycle.

Anticancer activity and protein phosphatase 1 and 2A inhibition of a new generation of cantharidin analogues

Cantharidin (Spanish Fly) is a natural toxin and an inhibitor of protein phosphatases 1 (PP1) and 2A (PP2A), which have key roles in cell cycle progression. We have synthesised two series of demethylated cantharidin analogues, one displaying an open-ring lactone configuration in solution (Novo-1 to Novo-5) similar to cantharidin, the other showing a closed-ring lactone configuration (Novo-6 to Novo-10). In the present study, these ten agents were screened for in vitro PP1 and PP2A inhibition and cellular cytotoxicity in nine cancer cell lines of haematopoietic (L1210, HL60), ovarian (A2780, ADDP), osteo (143B), and colon (HCT116, HT29, WiDr, SW480) origin and one normal colon cell line (CCD-018). The open-ring series (IC50, PPI=2.0-4.8 microM, PP2A=0.2-0.5 microM) maintained the PP2A selectivity of cantharidin (IC50, PPI=1.8 microM, PP2A=0.2 microM), although some were less potent. The closed-ring series (IC50, PPI=12.5->1000 microM, PP2A=5->1000 microM) were considerably less potent inhibitors, confirming the need of ring opening for inhibition. The cytotoxicity (IC50, 72 h, MTT assay) of cantharidin ranged from 6-15 microM, while the new analogues ranged from 14 to >1000 microM. Cytotoxicity of the agents did not consistently parallel the in vitro potency of protein phosphatase inhibition. A number of analogues showed colon cancer selectivity, particularly Novo-6, where the cytotoxicity ranged from 14-88 microM in the colon cancer cells and 275-680 microM in all other cell lines including normal colon cells. The reason for this selectivity was not apparent and may involve additional intracellular targets. Cell cycle analysis showed cantharidin to enhance cell cycle progression as evident from an increased S-phase population and enhanced DNA synthesis, culminating in G2/M arrest and apoptosis. With Novo-1 and Novo-6, the cell cycle changes paralleled the cytotoxicity responses, with the predominant effect of G2/M cell cycle arrest followed by cell death. In conclusion, we have synthesised new anticancer agents that show selective cytotoxicity in colon cancer cells while remaining inactive in normal colon cells, and which mediate their effects via the G2/M phase of the cell cycle.

Phase I and pharmacokinetic study of the topoisomerase II catalytic inhibitor fostriecin

We conducted a phase I and pharmacokinetic study of the topoisomerase II catalytic inhibitor fostriecin. Fostriecin was administered intravenously over 60 min on days 1-5 at 4-week intervals. Dose was escalated from 2 mg m(-2) day(-1) to 20 mg m(-2) day(-1) in 20 patients. Drug pharmacokinetics was analysed with high performance liquid chromatography with UV-detection. Plasma collected during drug administration was tested in vitro for growth inhibition of a teniposide-resistant small-cell lung cancer (SCLC) cell line. The predominant toxicities were elevated liver transaminases (maximum common toxicity criteria (CTC) grade 4) and serum creatinine (maximum CTC grade 2). These showed only a limited increase with increasing doses, often recovered during drug administration and were fully reversible. Duration of elevated alanine-amino transferase (ALT) was dose-limiting in one patient at 20 mg m(-2). Other frequent toxicities were grade 1-2 nausea/vomiting, fever and mild fatigue. Mean fostriecin plasma half-life was 0.36 h (initial; 95% CI, 0-0.76 h) and 1.51 h (terminal; 95% CI, 0.41-2.61 h). A metabolite, most probably dephosphorylated fostriecin, was detected in plasma and urine. No tumour responses were observed, but the plasma concentrations reached in the patients were insufficient to induce significant growth inhibition in vitro. The maximum tolerated dose (MTD) has not been reached, because drug supply was stopped at the 20 mg m(-2) dose level. However, further escalation seems possible and is warranted to achieve potentially effective drug levels. Fostriecin has a short plasma half-life and longer duration of infusion should be considered.