Selective Kinesin Spindle Protein Inhibitor Research Articles

Coupling Kinesin Spindle Protein and Aurora B Inhibition with Apoptosis Induction Enhances Oral Cancer Cell Killing.

Many proteins regulating mitosis have emerged as targets for cancer therapy, including the kinesin spindle protein (KSP) and Aurora kinase B (AurB). KSP is crucial for proper spindle pole separation during mitosis, while AurB plays roles in chromosome segregation and cytokinesis. Agents targeting KSP and AurB selectively affect dividing cells and have shown significant activity in vitro. However, these drugs, despite advancing to clinical trials, often yield unsatisfactory outcomes as monotherapy, likely due to variable responses driven by cyclin B degradation and apoptosis signal accumulation networks. Accumulated data suggest that combining emerging antimitotics with various cytostatic drugs can enhance tumor-killing effects compared to monotherapy. Here, we investigated the impact of inhibiting anti-apoptotic signals with the BH3-mimetic Navitoclax in oral cancer cells treated with the selective KSP inhibitor, Ispinesib, or AurB inhibitor, Barasertib, aiming to potentiate cell death. The combination of BH3-mimetics with both KSP and AurB inhibitors synergistically induced substantial cell death, primarily through apoptosis. A mechanistic analysis underlying this synergistic activity, undertaken by live-cell imaging, is presented. Our data underscore the importance of combining BH3-mimetics with antimitotics in clinical trials to maximize their effectiveness.

Kinesin spindle protein inhibitor SB743921 induces mitotic arrest and apoptosis and overcomes imatinib resistance of chronic myeloid leukemia cells

Inhibition of the cell mitotic pathway may provide a novel means for therapeutic intervention in chronic myeloid leukemia (CML). Kinesin spindle protein (KSP), a microtubule-associated motor protein which is essential for cell cycle progression, is overexpressed in bcr–abl+ CML cells. Retrovirus mediated bcr–abl transduction increases KSP expression in cord blood CD34 + cells. SB743921 is a selective KSP inhibitor which is being investigated in ongoing clinical trials for treatment of myeloma, leukemia and solid tumors. Treatment of CML cells with SB743921 resulted in reduced proliferation and colony forming cell (CFC) formation ability. SB743921 also actively blocked cell cycle progression, leading to apoptosis in both primary CML cells and cell lines. KSP inhibition sensitized CML cells to imatinib-induced apoptosis. Importantly, SB743921 inhibited the proliferation of various CML cells including T315I mutation-harboring cells. Furthermore, we demonstrated that SB743921 treatment suppressed ERK and AKT activity in CML cells. These data indicate that SB743921 may become a novel treatment agent for patients with CML.

ARRY-520 Combined With Pomalidomide Displays Enhanced Anti-Tumor Activity In Preclinical Models Of Multiple Myeloma

Inhibitors of Kinesin Spindle Protein (KSP), a mitosis-specific motor protein, represent a novel class of targeted anti-cancer therapies that have demonstrated clinical activity in hematological cancers. Inhibition of KSP results in the formation of aberrant monopolar spindles, mitotic arrest, and rapid apoptosis through degradation of the survival protein Mcl-1. The majority of KSP-inhibitor sensitive cells are proliferating hematopoietic cells which are dependent on Mcl-1 for survival. ARRY-520, a highly selective KSP inhibitor, is currently in Phase 2 clinical studies in patients with relapsed and refractory multiple myeloma. To date, ARRY-520 has demonstrated a well-tolerated safety profile and clinical activity both alone and in combination with bortezomib, dexamethasone, or carfilzomib in heavily pretreated patients. Updated clinical data will be disclosed at this meeting in separate abstracts. While prior preclinical studies have shown that ARRY-520 is additive or synergistic when combined with bortezomib in several in vivo models of multiple myeloma, the combinability of ARRY-520 with other myeloma standards of care, such as immunomodulatory drugs (IMiD), has not been thoroughly investigated. In the present studies, we have evaluated the combination utility of ARRY-520 and pomalidomide, an IMiD recently approved by the FDA, in preclinical models of multiple myeloma. Our findings show that the combination of ARRY-520 (12.5 mg/kg, IP, D1, 2) with pomalidomide (10 mg/kg, IP, QD) is significantly more active than either monotherapy alone in several in vivo models of multiple myeloma. In particular, complete responses and cures were observed in two models. In the RPMI-8226 model, a 100% cure rate was observed with the combination regimen as compared to a 0% cure rate for either monotherapy (cure is defined as no palpable tumor 100 days from study initiation). Likewise, in the JJN3 model a 100% complete response rate was observed with the combination regimen versus a 0% complete response rate for either monotherapy (complete response is defined as no palpable tumor for 2 consecutive tumor measurements). Notably, similar combination efficacy was also observed in the RPMI-8226 model at full and significantly reduced doses of both ARRY-520 and pomalidomide, supporting a synergistic interaction between these drugs. Characterization of the mechanism underlying the anti-tumor activity of this combination is currently being explored. The combination regimen was well tolerated causing no significant enhancement of body weight loss (not exceeding 10% for any group). Additionally, hematology analysis showed that the combination regimen caused no significant increase in thrombocytopenia or leukopenia. Consistent with clinical findings, both single agent ARRY-520 and pomalidomide caused neutropenia while the combination of these drugs moderately enhanced these effects. Pharmacokinetic studies confirmed that administration of pomalidomide with ARRY-520 does not alter the exposure of either compound, suggesting that the mechanism of enhanced anti-tumor activity is dependent upon pharmacodynamic rather than pharmacokinetic effects. Taken together, these findings show that the novel combination of ARRY-520 and pomalidomide is a well-tolerated and synergistic preclinical regimen that warrants investigation in future clinical trials in patients with multiple myeloma. Disclosures:Humphries:Array BioPharma: Employment. Anderson:Array BioPharma: Employment. Williams:Array BioPharma: Employment. Rieger:Array BioPharma: Employment. Tunquist:Array BioPharma: Employment. Walker:Array BioPharma: Employment.

A Phase I/II Trial of the KSP Inhibitor ARRY-520 In Relapsed/Refractory Multiple Myeloma

A Phase I/II Trial of the KSP Inhibitor ARRY-520 In Relapsed/Refractory Multiple Myeloma

Phase I trial of ARRY-520 in relapsed/refractory multiple myeloma (RR MM).

8132 Background: Kinesin Spindle Protein (KSP) is required for cell cycle progression through mitosis. ARRY-520 is a potent, selective inhibitor of KSP, arresting cells in mitosis with subsequent o...

A Phase I-II Trial of Ispinesib, a Kinesin Spindle Protein Inhibitor, Dosed Every Two Weeks as First Line Chemotherapy for Advanced Locally Recurrent or Metastatic Breast Cancer.

Abstract Background: Kinesin Spindle Protein (KSP) is a mitotic kinesin essential for cell cycle progression. Ispinesib, a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and subsequent cell death. When dosed on a q21d schedule, the maximum tolerated dose (MTD) was18 mg/m2 and neutropenia was the dose-limiting toxicity (DLT), with nadir at 7-10 d and recovery by d15. Activity was observed in a Phase II trial of ispinesib dosed at 18 mg/m2 q21d in patients (pts) with locally-advanced (LA) or metastatic breast cancer (MBC) after anthracycline and taxane failure (response rate 4/45 [9%]). This trial evaluates safety and efficacy of ispinesib as 1st line chemotherapy (CT) in LA or MBC given on d1 and d15 q28d, which may increase dose density.Methods: This is a multicenter Phase I-II trial. In Phase I, DLT and MTD of ispinesib given d1 and d15 q28d will be determined. Eligibility criteria: LA or MBC; no prior CT except neoadjuvant or adjuvant and ≥ 1 year elapsed since CT; no CNS or leptomeningeal metastases; ECOG 0-1. This is a standard 3+3 dose escalation trial design, starting at 10 mg/m2 and escalating based on tolerability in Cycle (cy) 1. Pharmacokinetic data are collected on d1 and d15 of Cy 1. Phase II of this trial will evaluate efficacy (response rate by RECIST) of ispinesib at the MTD.Results: Phase I of the trial is ongoing. To date, 16 pts were treated at 3 dose levels: 10 (1 cy, n=1; 3 cy, n=1; 6 cy, n=1), 12 (≤1063 cy, n=4; 6 cy, n=1; 10 cy, n=1) and 14 mg/m2 (≤3 cy, n=4; 4 cy, n=2; 12+ cy, n=1). Mean age was 50 yr. 9 pts were Stage IV, 7 Stage IIIB/C; 11 were chemo-naïve; 5 had prior anthracycline and/or taxane; 4 were HER2+ and 5 ER-, PR-, HER2-. The most frequent toxicity was neutropenia: 88% of pts in Cy 1; grade 3/4 in 75%; duration ≤5d; no febrile neutropenia. Diarrhea was reported in 25% and nausea in 19%; all grade 1/2. There was no neuropathy or alopecia. Increased ALT, AST and alkaline phosphatase were reported in 56%, 31% and 19% of pts, respectively. At the 14 mg/m2 dose level, 2/7 pts had DLTs of transient grade 3 AST and ALT increases after Cy 1 d15 dosing; both without increases upon retreatment; 1 pt had liver metastases; neither pt had significant increases in alkaline phosphatase or bilirubin. The 12 mg/m2 cohort was expanded to 6 pts without DLT. There was no cumulative toxicity with continued dosing. 3 pts had partial response, after 1 (n=1) and 4 (n=2) cy, respectively; 1 confirmed by RECIST with duration of 24 weeks; 4 pts had stable disease ≥4 mo.Conclusions: Ispinesib appears to be well tolerated on a q14d dosing schedule at doses tested to date. A dose-density equal to that given in the prior Phase II trial (0.86 mg/m2/d) was tolerated with the q14d schedule with preliminary evidence of efficacy. Further exploration of the 14 mg/m2 dose level and above, as warranted by safety and tolerability, is planned. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 6103.

A Phase I/II Trial of the Kinesin Spindle Protein (KSP) Inhibitor SB-743921 Dosed Q14D without and with Prophylactic G-CSF in Non-Hodgkin (NHL) or Hodgkin Lymphoma (HL).

Abstract 1673Poster Board I-699 BackgroundKSP is a mitotic kinesin essential for cell cycle progression. SB-743921, a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and cell death. In the first-in-humans (FIH) trial, the maximum tolerated dose (MTD) was 4 mg/m2 q21d. Since neutropenia was the major dose-limiting toxicity (DLT), with recovery by ∼d15, a q14d schedule without (-GCSF) and with prophylactic G-CSF (+GCSF) is being explored. MethodsIn Phase I of this Phase I/II trial, DLT and MTD of SB-921 given on d1 and d15 q28d (-GCSF) and (+GCSF) were determined. Eligible patients (pts) had relapsed or refractory HL or NHL, aggressive (a) or indolent (i), had at least 1 prior chemotherapy (CT) regimen, and had relapsed after or were not candidates for stem cell transplant. This was a standard 3+3 dose escalation trial design, starting at 2 mg/m2 and escalating by 1 mg/m2. Once DLT (-GCSF) was identified, (+GCSF) dosing started at the (-GCSF) MTD, escalating until (+GCSF) DLT was identified. MTD was defined as one dose level below maximum administered dose (MAD). Response was assessed with IWG criteria (2007). Results39 pts were treated (-GCSF) at 6 dose levels (2-7 mg/m2). Five pts had DLT: 1/3 at 4 (grade 3 hepatic enzyme elevation; found retrospectively); 2/10 at 6 (both sepsis with neutropenia), and 2/7 DLT-evaluable at 7 (both grade 4 neutropenia lasting >5d) mg/m2. MTD (-GCSF) was 6 mg/m2. 17 pts were treated with SB-743921 (+GCSF) at 6 (n=4), 7 (n=3), 8 (n=3) and 9 (n=7) mg/m2, with 1 DLT of neutropenia lasting >5d at 9 mg/m2. For all 56 pts treated at these dose levels, mean age was 51 yr; 54% were male; 39% HL, 30% aNHL, and 30% iNHL; 79% had ≥3 prior CT regimens. The most frequent grade 3/4 toxicity in Cycle 1 was neutropenia: 47% at ≥MTD (-GCSF) and 41% (+GCSF). Other grade 3/4 AEs (all cohorts combined, Cycle 1) were: thrombocytopenia 14% and anemia 5%; other grade 3/4 AEs were <5%. Nausea and diarrhea occurred in 13-14% of pts, all grade 1/2. There was no neuropathy or alopecia >grade 1. Seven pts were treated at 10 mg/m2 (+GCSF): 2 were not DLT-evaluable; 2/5 DLT-evaluable pts had DLT of grade 4 thrombocytopenia. The SB-743921 (+GCSF) MAD was 10 mg/m2 and the MTD was 9 mg/m2. There were 4 partial responses (PR), 3 in HL (1 at 6; 1 at 8; and 1 at 9 mg/m2) and 1 in marginal zone NHL (at 9 mg/m2); duration of response was 8-28+ weeks. One pt with diffuse large B cell NHL remains on study with stable disease for >17 months. ConclusionsThe MTD of SB-743921 on a q14d schedule (-GCSF) was 6 mg/m2 and (+GCSF) was 9 mg/m2. These dose densities (0.43 and 0.64 mg/m2/d) are >2- and 3-fold higher, respectively, than in the FIH trial with a q21d schedule (0.19 mg/m2/d). SB-743921 is well tolerated with minimal toxicity other than hematologic. Activity has been observed in heavily pre-treated HL and NHL, with 4 PRs at doses ≥6 mg/m2. SB-743921 warrants further investigation in lymphoma. DisclosuresChen:Cytokinetics: Employment. Saikali:Cytokinetics: Employment. Seroogy:Cytokinetics: Employment. Escandon:Cytokinetics: Employment. Wolff:Cytokinetics: Employment. Conlan:Cytokinetics: Employment.

A Phase 1 Dose-Escalation Study of the Novel KSP Inhibitor ARRY-520 in Advanced Leukemias.

Abstract 2047Poster Board II-24 Introduction:The mitotic kinesin spindle protein (KSP) is required for the assembly of a normal bipolar spindle and cell cycle progression through mitosis. ARRY-520 is a potent, selective inhibitor of KSP that arrests cells in mitosis forming an abnormal monopolar spindle with subsequent onset of apoptosis. ARRY 520 has shown potent activity in preclinical models of hematological malignancies which support clinical investigation of this novel targeted antimitotic therapy in patients with leukemias. ARRY-520 was evaluated in a Phase 1 trial, administered as an intravenous (IV) infusion on Day 1 or on Days 1, 3 and 5 in patients with advanced/refractory leukemias. Objectives:The primary objectives of this study were to establish the safety and the maximum tolerated dose (MTD) of ARRY-520 when given as a 1-hour infusion in either a single dose or on a Days 1, 3 and 5 divided-dose schedule per cycle. Secondary objectives were to characterize the pharmacokinetics (PK) of ARRY-520 when given on these schedules, to assess evidence of preliminary clinical activity, and to explore potential biomarkers of KSP inhibition. Methods:ARRY-520 was administered as a 1-hour IV infusion as a single dose per cycle or on a divided dose schedule, in a “3 + 3” Phase 1 design. PK analyses for ARRY-520 were performed on plasma samples collected during Cycle 1 and Cycle 2. Results:A total of 33 patients with acute myelogenous leukemia (AML) and with a median age of 66 years (range 21-88 yrs) were enrolled: 15 in the single-dose schedule (dose levels 2.5, 3.75, 4.5 and 5.6 mg/m2) and 18 in the divided dose schedule (dose levels 0.8, 1.2, 1.5 and 1.8 mg/m2/day). All but one patient had disease refractory to and/or relapsed from prior therapy with a median of 4 prior regimens (range 0-7). The MTD was 4.5 mg/m2 for the single-dose schedule with the dose-limiting toxicity (DLT) of Grade 3 mucositis and was 1.5 mg/m2/day (cumulative dose per cycle of 4.5 mg/m2) for the divided dose schedule, with DLTs of Grade 3 mucositis, hand-foot syndrome and hyperbilirubinemia. ARRY-520 was well tolerated at the MTD and doses below. At the MTD, Grades 3 or 4 reversible drug-related leukopenia were observed in 4/8 evaluable patients (Grade 0 or 1 WBC at baseline) with a median nadir occurring on Day 7. In both schedules ARRY-520 showed promising signs of clinical activity as measured by significant decreases in leukemic blasts in both the peripheral blood and bone marrow. Four of 33 patients (12%) showed at least 50% reduction in bone marrow blasts and 12/33 patients (36%) showed > 1 log reduction in blasts in the peripheral blood. Preliminary plasma PK analyses revealed increasing ARRY-520 concentrations with increasing dose, a mean terminal t1/2 of ∼90 hours, with clearance values ranging from 1.6 to 8.0 L/hr. Conclusions:ARRY-520 showed promising signs of clinical activity and has been well tolerated in both schedules investigated in patients with AML. The most prominent DLTs were mucositis and hand-foot syndrome. The MTD was determined to be the same total dose per cycle for the single-dose and the divided-dose schedule. Data including the safety, PK, pharmacodynamics and preliminary activity of ARRY 520 from this study will be presented. Disclosures:Bethelmie-Bryan:Array BioPharma: Employment. Rush:Array BioPharma: Employment. Freeman:Array BioPharma: Employment. Simmons:Array BioPharma: Employment. Ptaszynski:Array BioPharma: Employment.

A phase I/II trial of the kinesin spindle protein (KSP) inhibitor SB-743921 dosed q14d without and with prophylactic G-CSF in non-Hodgkin lymphoma (NHL) or Hodgkin lymphoma (HL)

8578 Background: KSP is a mitotic kinesin essential for cell cycle progression. SB-743921 (SB-921), a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and cell death. In the first-in-humans (FIH) trial, the MTD was 4 mg/m2 q21d. Since neutropenia was the major DLT, with recovery by ∼d15, a q14d schedule without (-GCSF) and with prophylactic G-CSF (+GCSF) is being explored. Methods: In phase I of this phase I/II trial, DLT and MTD of SB-921 given on d1 and d15 q28d (-GCSF) and (+GCSF) will be determined. Eligible patients (pts) have relapsed or refractory HL or NHL, aggressive (a) or indolent (i), have had at least 1 prior chemotherapy (CT) regimen, and have relapsed after or were not candidates for stem cell transplant. This is a standard 3+3 dose escalation trial design, starting at 2 mg/m2 and escalating by 1 mg/m2. Once DLT (-GCSF) is identified, (+GCSF) dosing starts at the (-GCSF) MTD, escalating until (+GCSF) DLT is identified. Results: 39 pts were treated (-GCSF) at 6 dose levels (2–7 mg/m2). 5 pts had DLT: 1/3 at 4 (grade 3 hepatic enzymes; found retrospectively); 2/10 at 6 (both sepsis with neutropenia), and 2/7 at 7 (both grade 4 neutropenia lasting &gt;5d) mg/m2. MTD (-GCSF) was 6 mg/m2. 12 pts were treated with SB-921 (+GCSF) at 6 (n=4), 7 (n=3), 8 (n=3) and 9 (n=2) mg/m2, with 1 DLT of neutropenia at 9 mg/m2. Expansion of the 9 mg/m2 (+GCSF) cohort to n=6 is ongoing. For all 51 pts treated to date, mean age was 52 yr; 53% were male; 39% HL, 33% aNHL, and 28% iNHL; 76% had ≥3 prior CT regimens. The most frequent grade 3/4 toxicity was neutropenia: 58% at ≥MTD (-GCSF) and 42% (+GCSF). Other grade 3/4 events were uncommon. There was no neuropathy or alopecia &gt;grade 1. There were 2 partial responses (PR), both in elderly pts with HL with ≥2 prior CT regimens, 1 at 6 (-GCSF) and 1 at 8 (+GCSF) mg/m2, ongoing at Cycle 4+. Conclusions: The MTD of SB-921 (-GCSF) on a q14d schedule was 6 mg/m2. This dose density (0.43 mg/m2/d) is &gt;2-fold higher than in the FIH trial with a q21d schedule (0.19 mg/m2/d). Dose escalation (+GCSF) is continuing. SB-921 is well tolerated with minimal toxicity other than hematologic. Activity has been observed in HL, with 2 PRs at doses ≥6 mg/m2. [Table: see text]

A phase I/II trial of ispinesib, a kinesin spindle protein (KSP) inhibitor, dosed q14d in patients with advanced breast cancer previously untreated with chemotherapy for metastatic disease or recurrence

1077 Background: KSP is a mitotic kinesin essential for cell cycle progression. Ispinesib, a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and subsequent cell death. On a q21d schedule, the MTD was 18 mg/m2. In a phase II trial of ispinesib dosed at 18 mg/m2 q21d in patients (pts) with advanced breast cancer after anthracycline and taxane failure, the response rate was 4/45 (9%). This trial evaluates ispinesib given on d1 and d15 q28d, thus increasing dose density. Methods: In phase I of this phase I/II trial, DLT and MTD of ispinesib given d1 and d15 q28d will be determined. Eligibility criteria: advanced breast cancer; no prior chemotherapy (CT) except neoadjuvant or adjuvant and ≥ 1 yr elapsed since CT; no CNS metastases; ECOG 0–1. This is a standard 3+3 dose escalation trial design, starting at 10 mg/m2 and escalating based on tolerability in cycle (cy) 1. Pharmacokinetic data are collected in cy 1. Results: Phase I of the trial is ongoing. 16 pts were treated at 3 dose levels: 10 (n = 3), 12 (n = 6), and 14 mg/m2 (n = 7). 9 pts were stage IV; 11 were chemo-naïve; 5 had prior anthracycline and/or taxane; 4 were HER-2+ and 5 ER-, PR-, HER-2-. The most frequent toxicity was neutropenia. 88% of pts in cy 1 (grade 3/4 in 75%; no febrile neutropenia). Mild GI toxicity occurred in &lt;37.5% of pts. There was no neuropathy or alopecia. At the 14 mg/m2 dose level, 2/7 pts had DLTs of transient grade 3 AST and ALT increases after cy 1 d15 dosing; both without increases upon retreatment; 1 in a pt with liver metastases; neither pt had significant increases in alkaline phosphatase or bilirubin. The 12 mg/m2 cohort was expanded to 6 pts without DLT. 3 pts had partial response (after 1 [n = 1] and 4 [n = 2] cy, respectively); 1 confirmed and ongoing after 8+ cy; 4 pts had stable disease ≥4 mo. Conclusions: Ispinesib appears to be well tolerated on a q14d dosing schedule at doses tested to date. A dose-density equal to that given in the prior phase II trial (0.86 mg/m2/d) was tolerated with the q14d schedule with preliminary evidence of efficacy. Further exploration of the 14 mg/m2 dose level is planned. [Table: see text]

A Phase I/II Trial of the Kinesin Spindle Protein (KSP) Inhibitor SB- 743921 Administered on Days 1 and 15 Every 28 Days without and with Prophylactic G-CSF in Non-Hodgkin or Hodgkin Lymphoma.

Background: KSP is a mitotic kinesin essential for cell cycle progression. SB-743921 (SB-921), a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and cell death. Since neurons lack a mitotic spindle, neurotoxicty, common with anti-tubulins, is not expected. In the first-in-humans (FIH) trial, the maximum tolerated dose (MTD) was 4 mg/m2 q21 days (d), a dose density of 0.2 mg/m2/d. Since neutropenia was the major dose-limiting toxicity (DLT), with nadir at ~d8 and recovery by ~d15, a q14d schedule without (−GCSF) and with prophylactic G-CSF (+GCSF) is being explored in this trial.Methods: In Phase I of this Phase I/II trial, the MTD of SB-921 (−GCSF) and (+GCSF) will be determined. In Phase II, efficacy and safety of the MTD will be further explored. Eligible patients (pts) have relapsed or refractory Hodgkin (HL) or non-Hodgkin (NHL) lymphoma, aggressive (a) or indolent (i), have had at least 1 prior chemotherapy (CT) regimen, and have relapsed after or were not candidates for autologous stem cell transplant. SB-921 is given to cohorts of 3 on d1/d15 q28d, starting at 2 mg/m2 and escalating by 1 mg/m2. Cohorts expand to 6 if 1/3 pts have DLT. Once DLT (−GCSF) is identified, (+GCSF) dosing begins at the (−GCSF) MTD, escalating in 1 mg/m2 increments until (+GCSF) DLT is identified.Results: The (−GCSF) cohort included 39 pts treated at 6 dose levels (2–7 mg/m2) of SB-921. DLT was reported in 4 pts: 2/10 at 6 mg/m2 (both neutropenia with sepsis) and 2/7 at 7 mg/m2 (both Grade 4 neutropenia lasting >5d). MTD (−GCSF) was 6 mg/m2. Ten pts have been treated with SB-921 (+GCSF) at 6 (n=4), 7 (n=3) and 8 (n=3) mg/m2, with no DLT. Enrollment at 9 mg/m2 is ongoing. Among the first 39 pts treated with SB-921 (−GCSF), mean age was 47 yr, 49% were male, histology was 46% HL, 28% aNHL, and 26% iNHL, 67% had ≥3 prior CT regimens. The most common Grade 3/4 adverse event (AE) was neutropenia (42% of pts treated at or above MTD). Other Grade 3/4 AEs were uncommon. No neuropathy or alopecia >Grade 1 was reported. Demographics and AEs in the (+GCSF) cohort are similar with less Grade 3/4 neutropenia. Two partial responses (PRs) have been reported, both in elderly pts with HL, 1 at 6 mg/m2 (−GCSF) after 2 cycles and 1 at 8 mg/m2 (+GCSF) after 2 cycles.Conclusions: The MTD of SB-921 (−GCSF) on a d1/d15 q28d schedule was 6 mg/m2 (dose density = 0.42 mg/m2/d). The current MTD (+GCSF) is ≥8 mg/m2 and dose escalation is continuing. This dose density (0.57 mg/m2/d) is nearly 3-fold higher than observed in the FIH trial with a q21d schedule (0.2 mg/m2/d). SB-921 is well tolerated with few Grade 3/4 AEs other than hematologic. Activity has been observed in HL, with 2 PRs at doses ≥ the (−GCSF) MTD.

Conformation-Dependent Ligand Regulation of ATP Hydrolysis by Human KSP: Activation of Basal Hydrolysis and Inhibition of Microtubule-Stimulated Hydrolysis by a Single, Small Molecule Modulator

Human kinesin spindle protein (KSP)/hsEg5, a member of the kinesin-5 family, is essential for mitotic spindle assembly in dividing human cells and is required for cell cycle progression through mitosis. Inhibition of the ATPase activity of KSP leads to cell cycle arrest during mitosis and subsequent cell death. Ispinesib (SB-715992), a potent and selective inhibitor of KSP, is currently in phase II clinical trials for the treatment of multiple tumor types. Mutations that attenuate Ispinesib binding to KSP in vitro have been identified, highlighting the need for inhibitors that target different binding sites and inhibit KSP activity by novel mechanisms. We report here a small-molecule modulator, KSPA-1, that activates KSP-catalyzed ATP hydrolysis in the absence of microtubules yet inhibits microtubule-stimulated ATP hydrolysis by KSP. KSPA-1 inhibits cell proliferation and induces monopolar-spindle formation in tumor cells. Results from kinetic analyses, microtubule (MT) binding competition assays, and hydrogen/deuterium-exchange studies show that KSPA-1 does not compete directly for microtubule binding. Rather, this compound acts by driving a conformational change in the KSP motor domain and disrupts productive ATP turnover stimulated by MT. These findings provide a novel mechanism for targeting KSP and perhaps other mitotic kinesins.

A phase I-II open-label trial of ispinesib on an alternate dosing schedule in chemotherapy-naive patients with locally advanced or metastatic breast cancer (MBC)

1143 Background: Kinesin spindle protein (KSP) is a mitotic kinesin essential for cell cycle progression. Ispinesib, a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and subsequent cell death. In the first-in-humans trial, the maximum tolerated dose (MTD) was 18 mg/m2 q21 days (d). Neutropenia, the dose-limiting toxicity (DLT), reached nadir at 7–10 d and recovered fully by d15. Other toxicities ≥ grade 3 were uncommon and unrelated to dose. A prior phase II trial evaluating ispinesib at 18 mg/m2 q21d in patients (pts) with locally advanced or MBC which recurred or progressed after treatment with anthracyclines and taxanes identified partial responses (RECIST) in 4 of 45 evaluable pts in this heavily pre-treated population. Ispinesib was also well tolerated in this trial; neutropenia again reached nadir at 7–10 d and recovered by d15 with no cumulative effect, suggesting ispinesib may be given on d1 and d15 q28d, thus increasing dose density (and possibly efficacy) while maintaining favorable tolerability. Methods: Phase I of this trial determines the DLT and MTD of ispinesib given d1 and d15 q28d as 1st-line therapy for locally advanced (Stage IIIB) or MBC (Stage IV). Pts are either chemotherapy-naïve or ≥ 1 year has elapsed since adjuvant or neoadjuvant treatment with anthracycline-based chemotherapy. Ispinesib is given to cohorts of 3 pts on d1 and d15 q28d, starting at 10 mg/m2 and escalates based on tolerability. A cohort expands to 6 pts if 1/3 pts have a DLT. Phase II of this trial evaluates the potential efficacy of ispinesib at the phase I MTD in pts with locally advanced or MBC who have had no prior chemotherapy. The primary endpoint is response rate by RECIST. Results and Conclusions: Enrollment initiated with ispinesib at 10 mg/m2 given d1 and d15 q28d. Data from phase I (DLT, MTD, and potential efficacy) will be presented. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Cytokinetics

A phase I-II trial of the kinesin spindle protein (KSP) inhibitor SB-743921 on days 1 and 15 every 28 days in non-Hodgkin or Hodgkin lymphoma

8539 Background: KSP is a mitotic kinesin essential for cell cycle progression. SB-743921 (SB-921), a selective KSP inhibitor, blocks mitotic spindle assembly with cell cycle arrest in mitosis and cell death. In the first-in-humans (FIH) trial, the maximum tolerated dose (MTD) was 4 mg/m2 q21 days (d), i.e., 0.2 mg/m2/d. Neutropenia was the major dose-limiting toxicity (DLT). Methods: Phase I of this trial determines the MTD of SB-921 without prophylactic GCSF (pGCSF) in patients (pts) with Non-Hodgkin (NHL) or Hodgkin Lymphoma (HL). Eligible pts with relapsed or refractory lymphoma had at least 1 prior chemotherapy regimen, and had relapsed after or were not candidates for autologous stem cell transplant. SB-921 is given to cohorts of 3 on d1/d15 q28d, starting at 2 mg/m2 and escalating by 1 mg/m2. Cohorts expand to 6 if 1/3 pts have a DLT. Results: To date, 32 pts have received ≤ 7 mg/m2 of SB-921; 14 had HL; 18 had NHL (9 indolent, 9 aggressive). Thirty-one pts had ≥ 2 prior chemotherapy regimens (14 had ≥ 5). Cycle 1 neutropenia ≥ grade 3 occurred in 7 pts. Two DLTs at 6 mg/m2 occurred with ≥ grade 3 neutropenia; one was noted after escalation to 7 mg/m2, a dose tolerated through cycle 1 without DLT by 3 pts. Cycle 1 drug-related non-hematologic toxicities ≥ grade 3 were infection (1), dehydration (1) and dyspnea (1). A HL pt had a partial response (PR) for 4 cycles at 6 mg/m2; a NHL pt begun at 3 mg/m2 and escalated to 5 mg/m2 had stable disease for 13 cycles. Conclusions: SB-921 is well tolerated without pGCSF at < 6 mg/m2 and possibly at ≥ 7 mg/m2 given d1/d15 q28d, an increase from the MTD of 4 mg/m2 q21d in the FIH trial (possibly ≥ 0.5 vs. 0.2 mg/m2/d). The 6 mg/m2 cohort was expanded and may allow re-escalation to > 7 mg/m2. A HL pt had a PR at 6 mg/m2. If the MTD without pGCSF is neutropenia, the MTD will next be determined with pGCSF. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Expert Testimony Other Remuneration Cytokinetics

A Phase I-II Study To Determine the Safety, Pharmacokinetics and Potential Efficacy of the Kinesin Spindle Protein (KSP) Inhibitor SB-743921 on Days 1 and 15 of a 28 Day Schedule in Patients with Non-Hodgkin's or Hodgkin's Lymphoma.

Background: KSP is required for mitotic spindle bipolarity and cell cycle progression. SB-743921 (SB-921) is a selective KSP inhibitor blocking assembly of the mitotic spindle, causing cell cycle arrest in mitosis and subsequent cell death. Neutropenia was the dose-limiting toxicity (DLT) in the first-in-human study of SB-921 and the maximum tolerated dose (MTD) was 4 mg/m2 when given on a Q21 day dosing schedule.Methods: Data from the Phase I portion of this study determining the safety, pharmacokinetics and MTD of SB-921 without prophylactic GCSF in patients (pts) with Non-Hodgkin's Lymphoma (NHL) or Hodgkin's Disease (HD) are reported. Pts with relapsed or refractory lymphoma were eligible if they had received at least 1 prior chemotherapy regimen, had relapsed after high-dose therapy with autologous stem cell transplant (ASCT), or were not candidates for ASCT. SB-921 was given in cohorts of 3–6 pts as a 1 hour IV infusion on day 1 and 15 of a Q28 day dosing schedule (cycle). Dosing began at 2 mg/m2 and escalated in 1 mg/m2 increments. Pts without DLT not completing Cycle 1 were replaced. Cohort expansion to 6 pts occurred if 1/3 pts experienced a DLT, defined as any drug-related non-hematologic toxicity ≥ grade 3 or grade 4 neutropenia ≥ 5 days or neutropenic fever/sepsis.Results: Twenty four pts were treated to date, with the highest dose studied being 6 mg/m2. Twenty three patients had > 2 prior regimens and 10 had > 5 prior regimens. The median age was 48 yrs (24–78); Of the 24 patients receiving one dose, 9 pts had HD and 15 had NHL (7 indolent, 8 aggressive); 14 were female, 21 were Caucasian and 3 were African-American. The median number of cycles was 2 (1–9). Two septic DLTs were reported at 6 mg/m2 associated with grade 4 neutropenia. Overall, dose related grade 3 (3 pts) and grade 4 (3 pts) neutropenia was reported in 6 patients. Grade 4 neutropenia resolved in all pts in < 5 days. There was 1 grade 3 and no grade 4 anemia. Two pts had grade 3 thrombocytopenia. Two pts had lymphopenia, 1 grade 3 and the other grade 4. There was 1 report of grade 3 nausea and vomiting but most other non-hematologic adverse events were grade 1–2. There was 1 report each of grade 1 neuropathy and alopecia. A 78 yr old woman with HD in second relapse (after receiving ABVD and ICE) had a partial response at 6 mg/m2 and a 24 year old with small cleaved cell, follicular lymphoma (progressed after R-CHOP chemotherapy, R-ICE and APSCT) initially treated at 3 mg/m2 (subsequently escalated to 5 mg/m2) had stable disease for 9 cycles.Conclusions: These data suggest that SB-921 was well tolerated without prophylactic GCSF in doses < 6 mg/m2 in this Phase I study. The septic DLTs were associated with neutropenia of < 5 days. The cohort at 5 mg/m2 has been expanded and pending data review, dose escalation will continue. A partial response was seen in a patient with refractory HD at 6 mg/m2. Future directions of the study are to try and mitigate the DLT of neutropenia with concurrent growth factor support.

A phase I-II study to assess the safety, pharmacokinetics, and potential efficacy of intravenous SB-743921 on days 1 and 15 of a 28-day cycle in patients with non-Hodgkin lymphoma

18516 Background: Kinesin spindle protein (KSP) is required for mitotic spindle bipolarity and cell cycle progression. SB-743921 (SB- 921), a selective KSP inhibitor, blocks mitotic spindle assembly, causing cell cycle arrest in mitosis and subsequent cell death. Neutropenia was the dose-limiting toxicity (DLT) in the first-in-humans study of SB-921 given Q21 days. Methods: Cohort 1 of the Phase I portion of a study determining the safety, pharmacokinetics and MTD of SB-921 without prophylactic GCSF in patients (pts) with Non-Hodgkin’s Lymphoma (NHL) or Hodgkin’s Disease is reported. Pts with relapsed or refractory disease were eligible if they had received at least one prior chemotherapy regimen, had failed high-dose therapy with autologous stem cell transplant (ASCT), or were not candidates for ASCT. SB-921 is given to dose-escalating cohorts of 3 pts as a 1 hr IV infusion, Q14 days. Dosing began at 2 mg/m2 and escalated in 1 mg/m2 increments after 3 pts tolerated 1 cycle. Pts without dose-limiting toxicity (DLT) not completing Cycle 1 are replaced. Cohort expansion to 6 pts occurs if 1/3 pts experiences DLT, defined as any drug-related toxicity = grade 3 or drug-related grade 4 hematologic toxicity. Results: Cohort 1 (2 mg/m2) enrolled 6 NHL pts (5 indolent, 1 aggressive). 4 were female; median age = 59 (52–73); 5 Caucasian, 1 African-American; median no. of cycles = 2 (1–6). 5/6 pts were evaluable; 1 dropped out before dosing. The most common Grade 1–2 AEs, in decreasing order, were fatigue, dysgeusia, paresthesia, leukopenia, and diarrhea. Grade 3 AEs of note were 1 each of hemolytic anemia, leukopenia, thrombocytopenia and dyspnea; 1 Grade 4 anemia was reported. Conclusions: SB-921 was well tolerated without prophylactic GCSF in Cohort 1 of the Phase I portion of this study, which continues to dose-escalate. If neutropenia is the DLT, dose escalation will continue with prophylactic GCSF. No significant financial relationships to disclose.

A phase II, open-label study of ispinesib (SB-715992) in patients with platinum/taxane refractory or resistant relapsed ovarian cancer

5562 Background: Kinesin spindle protein (KSP) is required for mitotic spindle bipolarity and cell cycle progression. Ispinesib (ISP), a selective KSP inhibitor, blocks assembly of the mitotic spindle leading to cell cycle arrest and cell death. Methods: This was a phase II study to determine the effectiveness of ISP in patients (pts) with platinum/taxane resistant or refractory ovarian cancer. Pts with progression during, or recurrence &lt; 6 months after prior platinum/taxane therapy, ECOG status 0–2, and CA-125 &gt; 40 U/ml were eligible. ISP was given as a 1 hr IV infusion of 18 mg/m2 Q 21 days. A 2-stage Green-Dahlberg design was employed. In Stage I, 20 evaluable pts were enrolled. If there were no CA-125 responses (Rustin criteria), the study was to be stopped. If &gt; 1 CA-125 responses were seen, 15 more pts were to be enrolled in Stage 2. Overall response was defined by pts who achieved both CA-125 and RECIST criteria. Results: 22 pts with carboplatin/taxane resistant (9) or refractory disease (13) were enrolled: median age = 63 (43–80); 21 were Caucasian; median no. of cycles = 2 (1 - &gt;16). All pts were evaluable for CA-125 assessment. The best CA-125 response was SD in 10 pts (45%); 12 pts had PD (55%). The best radiographic response was a confirmed PR lasting &gt; 30 weeks in one pt who also met CA-125 progression criteria (5%); 5 pts (26%) had SD; and 13 pts (68%) had PD. The most common AEs, in decreasing order, were neutropenia, fatigue, anemia, leukopenia, thrombocytopenia, diarrhea, nausea, vomiting, and decreased appetite. The most frequent Gr 3/4 AE was neutropenia. Conclusions: This study was terminated after Stage I as the CA-125 response criterion to progress to Stage II was not met. One confirmed radiographic partial response was observed. ISP was well tolerated with an acceptable safety profile. No significant financial relationships to disclose.

Phase I study to determine tolerability and pharmacokinetics (PK) of SB-743921, a novel kinesin spindle protein (KSP) inhibitor

2000 Background: SB-743921, a potent and selective inhibitor of KSP (Ki =100 pM; &gt;40,000-fold selectivity vs other kinesins), causes mitotic arrest, potent inhibition of tumor cell proliferation, and demonstrates activity in a broad range of human tumor xenografts. Methods: A phase I study was conducted to determine the maximum tolerated dose (MTD) and PK profile of SB-743921 when administered IV over 60 minutes every 21 (Q 21) days (d). Results: 44 patients (pts) (M/F 19/25), median age 61.5 yrs (range 32–80, with solid tumors were treated at doses of 2 (n=2), 4 (n=27), 5 (n=6), 6 (n=3), and 8 (n=6) mg/m2 (median cycles 2, range 1–10, total cycles 101). Frequent tumor types included colorectal (n=11), ovarian (n=5), NSCLC (n=5), esophageal (n=4), and pancreatic (n=4). Dose-limiting toxicities (DLTs) at 8 mg/m2 consisted of (max CTC grade/pt) prolonged grade (gr) 4 neutropenia (n=2), gr 3 elevated ALT/AST (n=1), and gr 3 elevated bilirubin (n=1). DLTs at 6 mg/m2 were gr 3 hyponatremia (n=1) and prolonged gr 4 neutropenia (n=1). DLTs at 5 mg/m2 were limited to febrile neutropenia (n=2). The 4 mg/m2 dose level was determined as the phase II dose. Toxicities at 4 mg/m2 included gr 1 fatigue (n=8) and neutropenia [gr 1 (n=4), gr 2 (n=7), gr 3 (n=3), gr 4 (n=2)]. Neutropenia nadir was day 6–8 with recovery to gr ≤2 by day 15. Gr 3 non-hematologic toxicities at 4 mg/m2 included gr 3 ALT (n=1), gr 3 AST (n=2), gr 3 hyperbilirubinemia (n=1), gr 3 hypophosphatemia (n=1), and gr 3 alkaline phosphatase elevation (n=1). Median PK values in cycle 1 at 4 mg/m2 were: Cmax 473 ng/ml, AUC0-∞ 5207 ng.hr/ml, and t½ 36 hr. AUC0-∞ and Cmax were proportional to dose. No consistent correlation was observed between DLTs and PK parameters. Stable disease for ≥ 4 cycles (range 4–11) was observed in 6 pts (4 pts at 4 mg/m2; 1 pt at 6 mg/m2; 1 pt at 8 mg/m2). A pt with cholangiocarcinoma had evidence of radiographic tumor regression (post cycle 10) and a &gt;50% decrease in her CA 19–9. Conclusions: The recommended phase II dose of SB-743921 on the Q 21 day schedule is 4 mg/m2. The observed toxicities at the recommended phase II dose are manageable and reversible. The onset and duration of neutropenia is predictable. [Table: see text]

Phase I study to determine tolerability and pharmacokinetics (PK) of SB-743921, a novel kinesin spindle protein (KSP) inhibitor

2010 Background: The mitotic kinesin KSP, plays an exclusive and essential role in assembly and function of the mitotic spindle. It is expressed in proliferating tumor cells, but is not expressed in terminally differentiated neurons. Targeting KSP may lead to the development of novel anti-mitotic drugs that lack neurotoxicity associated with anti-tubulin agents. SB-743921, the second KSP inhibitor to be evaluated in clinical trials, is a potent and selective inhibitor of KSP with a Ki of 100 pM and > 40,000-fold selectivity versus other kinesins. In pre-clinical studies, SB-743921 caused mitotic arrest and potent inhibition of tumor cell proliferation. SB-743921 was active in a broad range of human tumor xenografts. In some models, doses well below the maximum tolerated dose (MTD) of SB-743921 produced tumor regressions and cures. Methods: We initiated a phase I study to determine the MTD, tolerability, and PK profile of SB-743921 administered, IV over 60-minutes every 21 (Q 21) days (d). Interim Results: Eleven patients (pts) (M/F 6/5), median age 62 yrs (range 32- 73), with solid tumors were treated at doses of 2 - 8 mg/m2. Common tumor types included NSCLC (n=2), HCC (n=2), and CRC (n=2). Prolonged (≥5 d) Grade (Gr) 4 neutropenia was observed in 1 pt at 8 mg/m2 leading to an expanded cohort of 6 pts. Three further pts experienced a DLT in this cohort: prolonged Gr 4 neutropenia (n=2), Gr 3 elevated ALT/AST (n=1), and Gr 3 elevated bilirubin (n=1). The most common toxicities (all Gr 1) observed during this study included headaches (n=3), chills (n=3), nausea (n=3), myalgias (n=2), and injection site reactions (n=2). Gr 3 toxicities included neutropenia (n=1), acute abdominal pain (n=1), ileus (n=1), and fatigue (n=1). Median PK values in cycle 1 at 8 mg/m2 were as follows: Cmax 803.6 ng/ml, AUC0-∞ 10350.7 ng.hr/ml, and t½ 30.3 hr. Increases in AUC0-∞ and Cmax were dose-related. Conclusion: This is the first study of SB-743921 in humans. The MTD was exceeded at 8 mg/m2 Q 21 days due to prolonged neutropenia and hepatic lab abnormalities. Further dose exploration will continue at 6 mg/m2 to determine a MTD. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration GlaxoSmithKline GlaxoSmithKline Amgen, GlaxoSmithKline, Kosan, Pfizer, Roche, sanofi-aventis

Phase I trial of novel kinesin spindle protein (KSP) inhibitor SB-715992 IV days 1, 8, 15 q 28 days

2004 Background: The mitotic kinesin KSP plays an exclusive and essential role in assembly and function of the mitotic spindle. KSP represents a novel target for development of therapeutics against cancer. SB-715992 is a unique and selective inhibitor of KSP, that is preferentially overexpressed in malignant cells, functions exclusively in mitosis, and is not expressed in terminally differentiated neurons. In pre-clinical studies in a broad range of human tumor xenografts, doses of SB-715992 below the MTD produced tumor regression and cures. Methods: The current study determines the safety, MTD, and PK profile of SB-715992 administered over 1-hour on days 1, 8, 15 q 28 days. Results: 27 patients (pts) (M/F 15/12) with solid tumors were treated at doses of 1 to 8 mg/m2. Median age was 53 years (range 29–78). Common tumor types included CRC (5), RCC (4), breast (4), and lung (3). 2 pts developed DLT at 8 mg/m2 consisting of Grade (Gr) 3 neutropenia, resulting in the inability to administer the d 15 dose. The 7 mg/m2 dose level was expanded as a potential recommended phase II dose. No Gr 3 or 4 toxicities have been observed at this dose level. At dose levels < 4 mg/m2 drug-related Gr 2 constipation (n=1) and Gr 2 anemia (n=1) were observed. At dose levels ≥ 4 mg/m2, Gr 2 neutropenia (n=2), Gr 3 neutropenia (n=1), Gr 2 anemia (n=1), Gr 3 anemia (n=1), and Gr 3 transaminitis (n=1) have been noted. Increases in AUC0-∞ and Cmax are dose-related without accumulation following multiple doses. SD was observed for 3–4 cycles in 3 pts with RCC, SCCHN, and CRC. For the 7 mg/m2 dose level in Cycle 1, Day 1and 15 median PK values (n=6) were Cmax = 349 and 218 ng/mL; AUC0-∞ = 2965 and 1994 ng.h/mL; t1/2 = 37 and 22 hrs; CL = 5196 and 7546 mL/hr; and Vss = 235 and 240 L. Conclusion: SB-715992 administered on days 1, 8, 15 q 28 days at 7 mg/m2 is the MTD and is recommended for phase II investigations. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration GlaxoSmithKline GlaxoSmithKline GlaxoSmithKline