Judith A. Fox

Mechanism of action of SNS-032, a novel cyclin-dependent kinase inhibitor, in chronic lymphocytic leukemia

Inhibitors of cyclin-dependent kinases (Cdks) have been reported to have activities in chronic lymphocytic leukemia cells by inhibiting Cdk7 and Cdk9, which control transcription. Here we studied the novel Cdk inhibitor SNS-032, which exhibits potent and selective inhibitory activity against Cdk2, Cdk7, and Cdk9. We hypothesized that transient inhibition of transcription by SNS-032 would decrease antiapoptotic proteins, resulting in cell death. SNS-032 effectively killed chronic lymphocytic leukemia cells in vitro regardless of prognostic indicators and treatment history. This was associated with inhibition of phosphorylation of RNA polymerase II and inhibition of RNA synthesis. Consistent with the intrinsic turnover rates of their transcripts and proteins, antiapoptotic proteins, such as Mcl-1 and X-linked inhibitor of apoptosis protein (XIAP), were rapidly reduced on exposure to SNS-032, whereas Bcl-2 protein was not affected. The initial decrease of Mcl-1 protein was the result of transcriptional inhibition rather than cleavage by caspase. Compared with flavopiridol and roscovitine, SNS-032 was more potent, both in inhibition of RNA synthesis and at induction of apoptosis. SNS-032 activity was readily reversible; removal of SNS-032 reactivated RNA polymerase II, which led to resynthesis of Mcl-1 and cell survival. Thus, these data support the clinical development of SNS-032 in diseases that require short-lived oncoproteins for survival.

Voreloxin Is an Anticancer Quinolone Derivative that Intercalates DNA and Poisons Topoisomerase II

Background Topoisomerase II is critical for DNA replication, transcription and chromosome segregation and is a well validated target of anti-neoplastic drugs including the anthracyclines and epipodophyllotoxins. However, these drugs are limited by common tumor resistance mechanisms and side-effect profiles. Novel topoisomerase II-targeting agents may benefit patients who prove resistant to currently available topoisomerase II-targeting drugs or encounter unacceptable toxicities. Voreloxin is an anticancer quinolone derivative, a chemical scaffold not used previously for cancer treatment. Voreloxin is completing Phase 2 clinical trials in acute myeloid leukemia and platinum-resistant ovarian cancer. This study defined voreloxins anticancer mechanism of action as a critical component of rational clinical development informed by translational research. Methods/Principal Findings Biochemical and cell-based studies established that voreloxin intercalates DNA and poisons topoisomerase II, causing DNA double-strand breaks, G2 arrest, and apoptosis. Voreloxin is differentiated both structurally and mechanistically from other topoisomerase II poisons currently in use as chemotherapeutics. In cell-based studies, voreloxin poisoned topoisomerase II and caused dose-dependent, site-selective DNA fragmentation analogous to that of quinolone antibacterials in prokaryotes; in contrast etoposide, the nonintercalating epipodophyllotoxin topoisomerase II poison, caused extensive DNA fragmentation. Etoposides activity was highly dependent on topoisomerase II while voreloxin and the intercalating anthracycline topoisomerase II poison, doxorubicin, had comparable dependence on this enzyme for inducing G2 arrest. Mechanistic interrogation with voreloxin analogs revealed that intercalation is required for voreloxins activity; a nonintercalating analog did not inhibit proliferation or induce G2 arrest, while an analog with enhanced intercalation was 9.5-fold more potent. Conclusions/Significance As a first-in-class anticancer quinolone derivative, voreloxin is a toposiomerase II-targeting agent with a unique mechanistic signature. A detailed understanding of voreloxins molecular mechanism, in combination with its evolving clinical profile, may advance our understanding of structure-activity relationships to develop safer and more effective topoisomerase II-targeted therapies for the treatment of cancer.

Vosaroxin plus cytarabine versus placebo plus cytarabine in patients with first relapsed or refractory acute myeloid leukaemia (VALOR): a randomised, controlled, double-blind, multinational, phase 3 study.

BACKGROUND Safe and effective treatments are urgently needed for patients with relapsed or refractory acute myeloid leukaemia. We investigated the efficacy and safety of vosaroxin, a first-in-class anticancer quinolone derivative, plus cytarabine in patients with relapsed or refractory acute myeloid leukaemia. METHODS This phase 3, double-blind, placebo-controlled trial was undertaken at 101 international sites. Eligible patients with acute myeloid leukaemia were aged 18 years of age or older and had refractory disease or were in first relapse after one or two cycles of previous induction chemotherapy, including at least one cycle of anthracycline (or anthracenedione) plus cytarabine. Patients were randomly assigned 1:1 to vosaroxin (90 mg/m(2) intravenously on days 1 and 4 in a first cycle; 70 mg/m(2) in subsequent cycles) plus cytarabine (1 g/m(2) intravenously on days 1-5) or placebo plus cytarabine through a central interactive voice system with a permuted block procedure stratified by disease status, age, and geographical location. All participants were masked to treatment assignment. The primary efficacy endpoint was overall survival and the primary safety endpoint was 30-day and 60-day all-cause mortality. Efficacy analyses were done by intention to treat; safety analyses included all treated patients. This study is registered with ClinicalTrials.gov, number NCT01191801. FINDINGS Between Dec 17, 2010, and Sept 25, 2013, 711 patients were randomly assigned to vosaroxin plus cytarabine (n=356) or placebo plus cytarabine (n=355). At the final analysis, median overall survival was 7·5 months (95% CI 6·4-8·5) in the vosaroxin plus cytarabine group and 6·1 months (5·2-7·1) in the placebo plus cytarabine group (hazard ratio 0·87, 95% CI 0·73-1·02; unstratified log-rank p=0·061; stratified p=0·024). A higher proportion of patients achieved complete remission in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group (107 [30%] of 356 patients vs 58 [16%] of 355 patients, p<0·0001). Early mortality was similar between treatment groups (30-day: 28 [8%] of 355 patients in the vosaroxin plus cytarabine group vs 23 [7%] of 350 in the placebo plus cytarabine group; 60-day: 70 [20%] vs 68 [19%]). Treatment-related deaths occurred at any time in 20 (6%) of 355 patients given vosaroxin plus cytarabine and in eight (2%) of 350 patients given placebo plus cytarabine. Treatment-related serious adverse events occurred in 116 (33%) and 58 (17%) patients in each group, respectively. Grade 3 or worse adverse events that were more frequent in the vosaroxin plus cytarabine group than in the placebo plus cytarabine group included febrile neutropenia (167 [47%] vs 117 [33%]), neutropenia (66 [19%] vs 49 [14%]), stomatitis (54 [15%] vs 10 [3%]), hypokalaemia (52 [15%] vs 21 [6%]), bacteraemia (43 [12%] vs 16 [5%]), sepsis (42 [12%] vs 18 [5%]), and pneumonia (39 [11%] vs 26 [7%]). INTERPRETATION Although there was no significant difference in the primary endpoint between groups, the prespecified secondary analysis stratified by randomisation factors suggests that the addition of vosaroxin to cytarabine might be of clinical benefit to some patients with relapsed or refractory acute myeloid leukaemia. FUNDING Sunesis Pharmaceuticals.

A phase Ib study of vosaroxin, an anticancer quinolone derivative, in patients with relapsed or refractory acute leukemia

This study of vosaroxin evaluated dose-limiting toxicity (DLT), maximum-tolerated dose (MTD), pharmacokinetics (PK), clinical activity and pharmacodynamics in relapsed/refractory leukemia. Dosing was weekly (days 1, 8 and 15) or twice weekly (days 1, 4, 8 and 11). Seventy-three treated patients had a median age of 65 years, 85% had acute myeloid leukemia and 78% had refractory disease. Weekly schedule: 42 patients received 18–90 mg/m2; MTD was 72 mg/m2. Twice-weekly schedule: 31 patients received 9–50 mg/m2; MTD was 40 mg/m2. DLT was stomatitis; primary non-hematologic toxicity was reversible gastrointestinal symptoms and febrile neutropenia. Thirty-day all-cause mortality was 11%. Five patients had complete or incomplete remissions; median duration was 3.1 months. A morphologic leukemia-free state (bone marrow blast reduction to <5%) occurred in 11 additional patients. Antileukemic activity was associated with total dose or weekly time above 1 μmol/l plasma vosaroxin concentration (P<0.05). Vosaroxin exposure was dose proportional over 9–90 mg/m2. The average terminal half-life was ∼25 h and clearance was non-renal. No induction or inhibition of vosaroxin metabolism was evident. Vosaroxin-induced DNA damage was detected as increased intracellular γH2AX. Vosaroxin had an acceptable safety profile, linear PK and encouraging clinical activity in relapsed/refractory leukemia.

A phase 1b/2 study of vosaroxin in combination with cytarabine in patients with relapsed or refractory acute myeloid leukemia

Vosaroxin is a first-in-class anticancer quinolone derivative that intercalates DNA and inhibits topoisomerase II. This study assessed the safety and tolerability of vosaroxin plus cytarabine in patients with relapsed/refractory acute myeloid leukemia. Escalating vosaroxin doses (10-minute infusion; 10–90 mg/m2; days 1, 4) were given in combination with cytarabine on one of two schedules: schedule A (24-hour continuous intravenous infusion, 400 mg/m2/day, days 1–5) or schedule B (2-hour intravenous infusion, 1 g/m2/day, days 1–5). Following dose escalation, enrollment was expanded at the maximum tolerated dose. Of 110 patients enrolled, 108 received treatment. The maximum tolerated dose of vosaroxin was 80 mg/m2 for schedule A (dose-limiting toxicities: grade 3 bowel obstruction and stomatitis) and was not reached for schedule B (recommended phase 2 dose: 90 mg/m2). In the efficacy population (all patients in first relapse or with primary refractory disease treated with vosaroxin 80–90 mg/m2; n=69), the complete remission rate was 25% and the complete remission/complete remission with incomplete blood count recovery rate was 28%. The 30-day all-cause mortality rate was 2.5% among all patients treated at a dose of 80–90 mg/m2. Based upon these results, a phase 3 trial of vosaroxin plus cytarabine was initiated in patients with relapsed/refractory acute myeloid leukemia.

REVEAL-1, a phase 2 dose regimen optimization study of vosaroxin in older poor-risk patients with previously untreated acute myeloid leukaemia.

This phase 2 study (N = 116) evaluated single‐agent vosaroxin, a first‐in‐class anticancer quinolone derivative, in patients ≥60 years of age with previously untreated unfavourable prognosis acute myeloid leukaemia. Dose regimen optimization was explored in sequential cohorts (A: 72 mg/m2 d 1, 8, 15; B: 72 mg/m2 d 1, 8; C: 72 mg/m2 or 90 mg/m2 d 1, 4). The primary endpoint was combined complete remission rate (complete remission [CR] plus CR with incomplete platelet recovery [CRp]). Common (>20%) grade ≥3 adverse events were thrombocytopenia, febrile neutropenia, anaemia, neutropenia, sepsis, pneumonia, stomatitis and hypokalaemia. Overall CR and CR/CRp rates were 29% and 32%; median overall survival (OS) was 7·0 months; 1‐year OS was 34%. Schedule C (72 mg/m2) had the most favourable safety and efficacy profile, with faster haematological recovery (median 27 d) and lowest incidence of aggregate sepsis (24%) and 30‐d (7%) and 60‐d (17%) all‐cause mortality; at this dose and schedule, CR and CR/CRp rates were 31% and 35%, median OS was 7·7 months and 1‐year OS was 38%. Overall, vosaroxin resulted in low early mortality and an encouraging response rate; vosaroxin 72 mg/m2 d 1, 4 is recommended for further study in this population. Registered at www.clinicaltrials.gov: #NCT00607997.

Abstract C186: SNS-062 is a potent noncovalent BTK inhibitor with comparable activity against wild type BTK and BTK with an acquired resistance mutation

Background and purpose: BTK mediates B-cell receptor signaling and was validated as a target by the BTK inhibitor ibrutinib in several B-cell malignancies, including mantle cell lymphoma and chronic lymphocytic leukemia (CLL). However, patients may have or acquire resistance. Resistance mechanisms include mutation of the cysteine in the BTK active site that ibrutinib requires for covalent binding (C481). We identified and characterized SNS-062, a potent, noncovalent BTK inhibitor with activity towards BTK harboring resistance mutations that also inhibits ITK and may provide enhanced anti-tumor immune responses. SNS-062 shows restricted kinase selectivity and nonclinical pharmacology, pharmacokinetics (PK) and toxicology profiles distinct from ibrutinib and merits clinical investigation. Methods and Results: In in vitro kinase binding assays, SNS-062 bound to 9 kinases with Kd Citation Format: Minke E. Binnerts, Kevin L. Otipoby, Brian T. Hopkins, Tonika Bohnert, Stig Hansen, Gene Jamieson, Pamela A. Howland, Eric H. Bjerkholt, Deborah A. Thomas, Judith A. Fox, Adam R. Craig. SNS-062 is a potent noncovalent BTK inhibitor with comparable activity against wild type BTK and BTK with an acquired resistance mutation. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C186.

Abstract 1207: SNS-062 demonstrates efficacy in chronic lymphocytic leukemia in vitro and inhibits C481S mutated Bruton tyrosine kinase

Introduction: In order to address the issue of acquired resistance to ibrutinib, we sought to characterize the Bruton agammaglobulinemia tyrosine kinase (BTK) inhibitor SNS-062 in preclinical models of chronic lymphocytic leukemia (CLL). Methods: Primary CLL B cells were isolated from the whole blood of consented patients by ficoll density centrifugation and Rosette-Sep negative selection. Annexin V and propidium iodide flow cytometry was used to measure patient CLL cell viability and 7-AAD was used to measure viability in stromal co-culture. CD40 and CD86 expression was evaluated via flow cytometry subsequent to sustained 3.2uM CpG stimulation. BCR signaling in primary CLL cells was investigated by immunoblot following 1 hour treatment and following 1 hour or 24 hours of incubation with SNS-062 in XLA cell lines. ITK inhibition was investigated via immunoblot after stimulation with anti-CD3 and anti-CD28 and incubation with SNS-062 for 1 hour. SNS-062 was used at a concentration of 1uM in preclinical studies unless otherwise noted. Measurement of kinase activity in human recombinant WT BTK or C481S BTK was performed in a FRET kinase assay. Results: Immunoblots of BTK and ERK phosphorylation of XLA cells transfected with WT or C481S BTK demonstrated that SNS-062 inhibition is comparable to that of ibrutinib in WT BTK and greater than that of ibrutinib in C481S BTK. Using a recombinant kinase assay, we found the IC50 of SNS-062 against WT BTK to be 4.6nM and C481S BTK to be 1.1nM, suggesting that SNS-062 retains activity against the mutated BTK variant. Additionally, SNS-062 was found to be six times more potent than ibrutinib and greater than 640 times more potent than acalabrutinib against C481S BTK. SNS-062 demonstrates dose-dependent inhibition of BTK in primary patient CLL cells comparable to ibrutinib via immunoblot for BTK phosphorylation. The viability of primary patient cells treated with 0.1uM, 1.0uM, and 10.0uM SNS-062 for 48 hours was measured to be 96.7%, 96.1%, and 88.1%, respectively, that of the untreated condition. At 48 hours, SNS-062 decreased viability of primary CLL cells in the presence of HS5 stromal protection by 5.5%. SNS-062 was found to decrease CpG induced CD40 and CD86 expression by 8.7% and 15.7%, respectively. Using an in vitro kinase assay, SNS-062 inhibited ITK with an IC50 value of 24nM. An immunoblot of anti-CD3/CD28 stimulated Jurkat cells revealed that SNS-062 decreased the phosphorylation of ERK, implying inhibition of ITK. Conclusion: Unlike ibrutinib, SNS-062 inhibits BTK signaling in the presence of the C481S mutation and may address acquired resistance to covalent BTK inhibitors. SNS-062 decreases B cell activation markers, viability, and stromal cell protection in primary patient CLL cells and was shown to inhibit ITK, suggesting support of T cell mediated antitumor activities. These data support further investigation of this molecule and advancement into clinical trials. Citation Format: Catherine A. Fabian, Sean D. Reiff, Daphne Guinn, Linda Neuman, Judith A. Fox, Wendy Wilson, John C. Byrd, Jennifer A. Woyach, Amy J. Johnson. SNS-062 demonstrates efficacy in chronic lymphocytic leukemia in vitro and inhibits C481S mutated Bruton tyrosine kinase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1207. doi:10.1158/1538-7445.AM2017-1207

Abstract C198: PDK1 inhibitors SNS-229 and SNS-510 cause pathway modulation, apoptosis and tumor regression in hematologic cancer models in addition to solid tumors

Background and purpose: Phosphatidyl-inositol (PI) dependent kinase 1, PDK1, is a master kinase that activates kinases important in cell growth and survival including members of the AKT, PKC, RSK and SGK families. PDK1 can interact with its substrates through PI-dependent (PH-mediated) or PI-independent (PIF-mediated) mechanisms. Here we report characterization of two potent PDK1 kinase inhibitors, SNS-229 and SNS-510, that block both PI-dependent and PI-independent substrate phosphorylation and have broad anti-tumor activity in hematologic cancers. Methods and results: SNS-229 and SNS-510 belong to a series of novel PDK1 inhibitors that bind the inactive conformation of PDK1 as determined by X-ray crystallography. The compounds bind deep in the adaptive pocket, distorting the N-terminal domain and perturbing the PIF-pocket, thereby affecting PI-independent substrate binding. SNS-510 was evaluated in more than 20 cell lines derived from hematologic cancers including AML, MM, DLBCL, and MCL and showed strong anti-proliferative activity with EC50s ranging from 3 nM to 900 nM, with particularly strong activity observed in the AML cell lines Molm-13 and MV4-11 (EC50 3 and 7 nM), the DLBCL cell line U-2932 (EC50 56 nM) and the MM cell lines U-266 and RPMI-8226 (EC50 130 and 163 nM). Anti-proliferative activity correlated with pathway modulation as assessed by inhibition of phosphorylation of PDK1, RSK, and AKT. Interestingly, inhibition of PDK1 phosphorylation was time-dependent showing 2 to 5-fold more inhibition after 24 hours than at 4 hours. In addition, SNS-510 produced substantial apoptosis after 24 hours. SNS-510 was compared to the PDK1 inhibitor GSK2334470, showing comparable biochemical potency. However, SNS-510 was 10 to 30 fold more potent at inhibiting PDK1 and RSK phosphorylation in all cell lines tested. SNS-510 was at least 10-fold more potent than GSK2334470 in 72 hour viability assays. In mice, SNS-229 and SNS-510 showed good oral bioavailability (%F>40%) with a Tmax of 4 to 8 hours and prolonged exposure. Pathway modulation was evaluated in vivo in a MV4-11 xenograft mouse model. Potent, dose-dependent pathway modulation was observed at 4 and 24 hours after a single oral dose of SNS-229 and SNS-510 (1 to 25 mg/kg). After 21- day dosing in MV4-11 xenografts, both SNS-229 and SNS-510 showed dose-related efficacy with > 95% tumor growth inhibition and partial regression (>50% tumor shrinkage) in 70% and 100% of animals at the highest dose. Conclusion: With this class of PDK1 inhibitors, we have previously reported strong tumor growth inhibition (66%-95%) in gastric, lung, pancreatic and colorectal cancer xenograft models. Here we report a PK/PD (pathway modulation) relationship that correlates with profound tumor growth inhibition in hematologic cancers. Thus, targeting the inactive conformation of PDK1 and inhibiting PI-independent substrate binding has broad potential for the treatment of solid and hematologic cancers. Citation Format: Stig Hansen, Johan Enquist, Jeff Iwig, Minke E. Binnerts, Gene Jamieson, Judith A. Fox, Adam R. Craig. PDK1 inhibitors SNS-229 and SNS-510 cause pathway modulation, apoptosis and tumor regression in hematologic cancer models in addition to solid tumors. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr C198.

Abstract C222: Voreloxin is synergistic in in vitro combination with cytarabine and additive in combination with azacitidine, decitabine, and clofarabine

Voreloxin is a first‐in‐class anticancer quinolone derivative that intercalates DNA and poisons topoisomerase II (Stockett et al. and Hawtin et al., AACR 2008). This leads to replication‐dependent, site‐selective DNA double strand breaks (DSB) targeting G/C‐rich sequences that are characteristic sites of quinolone‐induced DNA cleavage (Noble et al., 2003; Richter et al., 2007; Stockett et al., AACR 2008). A consequence of this DNA damage is G2 arrest, and cell death by apoptosis. Voreloxin is under clinical investigation in acute myeloid leukemia (AML) and ovarian cancer. Clinical responses have been observed in these indications (Lancet et al., ASCO 2009; Maris et al., ASCO 2009; McGuire et al., SGO 2008), as well as in NSCLC and SCLC (Burris et al., ECCO 2007). The current analysis was performed in support of a Phase 1b/2 clinical study (SPO‐0012) of voreloxin in combination with cytarabine in relapsed or refractory AML, and to investigate the feasibility for combining voreloxin with other agents currently in clinical use for the treatment of AML. The cytotoxicity of of voreloxin in combination with cytarabine was evaluated in 3 acute leukemic cell lines (HL‐60 acute promyelocytic (APL), MV4‐11 Flt‐3 ITD positive AML and CCRF‐CEM acute lymphoblastic leukemia (ALL)). The cytotoxicity of voreloxin in combination with the nucleoside analog hypomethylating agents azacitidine, decitabine (pyrimidine analogs), and clofarabine (purine analog) was also studied in the HL‐60 APL cell line. Cytotoxicity was assessed by proliferation inhibition. The combined activity of voreloxin and cytarabine was evaluated using the combination index (CI) analysis method, in which each drug is serially diluted based on either 10X or 1X single agent IC50 values. The combination was synergistic in the AML cell lines MV4‐11 and HL‐60, as demonstrated by a leftward shift in the voreloxin IC50 curves and calculated CI less than 0.85. In the ALL cell line CCRF‐CEM, an additive increase in cytotoxicity was observed with CI of ≤ 0.99. Voreloxin in combination with azacitidine, decitabine or clofarabine was evaluated after simultaneous or sequential addition of the drugs. The combinations were analyzed by: 1) serial‐dilution of voreloxin combined with a fixed dose (IC10) of the second compound, and 2) fixed dose (IC10) of voreloxin combined with a serial dilution of the second compound. No significant change in activity was observed when compared with the single‐agent activity of each compound. Sequential dosing of the agents did not alter the cytotoxicity of the reagents in combination. These data support the ongoing phase 1b/2 clinical study of voreloxin in combination with cytarabine in relapsed or refractory AML and demonstrate the feasibility for combining voreloxin with other DNA damaging agents currently in clinical use for the treatment of AML. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C222.