Chk1 inhibition after replicative stress activates a double strand break response mediated by ATM and DNA-dependent protein kinase

Checkpoint kinase 1 (Chk1) regulates cell cycle checkpoints and DNA damage repair in response to genotoxic stress. Inhibition of Chk1 is an emerging strategy for potentiating the cytotoxicity of chemotherapeutic drugs. Here, we demonstrate that AZD7762, an ATP -competitive Chk1/2 inhibitor induces gammaH2AX in gemcitabine-treated cells by altering both dynamics and stability of replication forks, allowing the firing of suppressed replication origins as measured by DNA fiber combing and causing a dramatic increase in DNA breaks as measured by comet assay. Furthermore, we identify ATM and DNA-PK, rather than ATR, as the kinases mediating gammaH2AX induction, suggesting AZD7762 converts stalled forks into double strand breaks (DSBs). Consistent with DSB formation upon fork collapse, cells deficient in DSB repair by lack of BRCA2, XRCC3 or DNA-PK were selectively more sensitive to combined AZD7762 and gemcitabine. Checkpoint abrogation by AZD7762 also caused premature mitosis in gemcitabine-treated cells arrested in G(1)/early S-phase. Prevention of premature mitotic entry via Cdk1 siRNA knockdown suppressed apoptosis. These results demonstrate that chemosensitization of gemcitabine by Chk1 inhibition results from at least three cellular events, namely, activation of origin firing, destabilization of stalled replication forks and entry of cells with damaged DNA into lethal mitosis. Additionally, the current study indicates that the combination of Chk1 inhibitor and gemcitabine may be particularly effective in targeting tumors with specific DNA repair defects.

A phase I clinical trial of FOLFIRI in combination with the pan-cyclin-dependent kinase (CDK) inhibitor flavopiridol

BACKGROUND

The cyclin-dependent kinase inhibitor flavopiridol increases irinotecan- and fluorouracil-induced apoptosis. We conducted a phase I trial of FOLFIRI + flavopiridol in patients with advanced solid tumors.

DESIGN

FOLFIRI + flavopiridol were administered every 2 weeks. Based on sequence-dependent inhibition, flavopiridol was given 3 h after irinotecan but before 5-FU. Two maximum tolerated doses were determined, one with flavopiridol administered over 1 h, and one with flavopiridol split as a 30-min bolus followed by a 4-h infusion.

RESULTS

A total of 74 patients were enrolled and 63 were evaluable. The MTD with FOLFIRI was flavopiridol 80 mg/m(2) over 1 h or 35 mg/m(2) bolus + 35 mg/m(2) over 4 h. Dose-limiting toxicities were diarrhea, fatigue, neutropenia, and neuropathy. Clinical activity included 2 partial responses in small bowel cancer and bladder cancer and 1 complete response in mucosal melanoma. Stable disease was seen in 22 patients. Pharmacokinetic studies showed increasing C(max) with increasing flavopiridol dose. Clinical benefit was correlated with the presence of wild-type p53. Of 25 patients with colorectal cancer, 11 had as best response SD for >3 m (median 6 m, range 4.2-15.4 m), despite failing ≥1 irinotecan-containing regimen.

CONCLUSIONS

Treatment with flavopiridol and FOLFIRI is a safe and effective regimen. Concentrations of flavopiridol that enhance the effects of FOLFIRI can be achieved. Clinical activity is encouraging and includes prolonged stable disease in patients with irinotecan-refractory colorectal cancer.

Regional chemotherapy for unresectable primary liver cancer: results of a phase II clinical trial and assessment of DCE-MRI as a biomarker of survival

BACKGROUND

This study reports the results of hepatic arterial infusion (HAI) with floxuridine (FUDR) and dexamethasone (dex) in patients with unresectable intrahepatic cholangiocarcinoma (ICC) or hepatocellular carcinoma (HCC) and investigates dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) assessment of tumor vascularity as a biomarker of outcome.

PATIENTS AND METHODS

Thirty-four unresectable patients (26 ICC and eight HCC) were treated with HAI FUDR/dex. Radiologic dynamic and pharmacokinetic parameters related to tumor perfusion were analyzed and correlated with response and survival.

RESULTS

Partial responses were seen in 16 patients (47.1%); time to progression and response duration were 7.4 and 11.9 months, respectively. Median follow-up and median survival were 35 and 29.5 months, respectively; 2-year survival was 67%. DCE-MRI data showed that patients with pretreatment integrated area under the concentration curve of gadolinium contrast over 180 s (AUC 180) >34.2 mM.s had a longer median survival than those with AUC 180 <34 mM.s (35.1 versus 19.1 months, P = 0.002). Decreased volume transfer exchange between the vascular space and extracellular extravascular space (-DeltaK(trans)) and the corresponding rate constant (-Deltak(ep)) on the first post-treatment scan both predicted survival.

CONCLUSIONS

In patients with unresectable primary liver cancer, HAI therapy can be effective and safe. Pretreatment and early post-treatment changes in tumor perfusion characteristics may predict treatment outcome.

Analysis of survival with modified docetaxel, cisplatin, fluorouracil (mDCF), and bevacizumab (BEV) in patients with metastatic gastroesophageal (GE) adenocarcinoma: Results of a phase II clinical trial

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Background: Metastatic GE cancer is an aggressive disease with poor patient (pt) outcomes. Despite response rates of 30–60% to combination chemotherapy, response duration is usually 4–6 mo and 24-mo survival is 5–10%. The addition of BEV to chemotherapy has improved survival in several solid tumors, and has demonstrated encouraging activity in GE cancer (Shah et al, JCO 2006). We report mature tolerability and efficacy results of mDCF+BEV in GE cancer, with an emphasis on prolonged pt survival. Methods: Previously untreated metastatic GE pts with adequate end organ function received BEV 10mg/kg, Docetaxel 40mg/m2, FU 400mg/m2, Leucovorin 400mg/m2 on day 1, FU 1000 mg/m2/day x 2 days IVCI, and Cisplatin 40mg/m2 on day 3. Treatment is repeated every 14 days without prophylactic growth factor support. The primary objective is to improve 6-month progression free survival (PFS) from 43% (historical DCF control) to 63% with the addition of BEV. Target accrual is 44 evaluable pts, with 10% type I & II error. Secondary objectives include tolerability, response rates (RECIST), median PFS, 12-mo survival, and overall survival (OS). Results: Pt enrollment has completed: median age 57(range 29–74), median KPS 80% (70–100), M:F 32:12, gastric/GEJ/esophagus 22:17:5. In 39 patients with measurable disease we observed 26 confirmed partial responses (67%, 95% CI 50%- 81%), and 12 (31%) stable disease. Six-month PFS is 79% (95% CI 68%-93%), the median PFS is 12 mo (95% CI: 8.8–16). At median follow up of 12.3 mo, median OS is 16.2 mo (95%CI 11.4-infinitiy). 12- and 18-mo OS is 63% (95%CI 44–77%) and 46% (95%CI 27–63%), respectively. Minimal chemotherapy related grade 3–4 adverse events were observed: fatigue (20%), dehydration (13%), mucositis (9%), nausea/vomiting (7%), febrile neutropenia (4%). BEV related adverse event was perforation (n=1) and bleeding (n=1). 31% developed grade 3–4 venous thromboembolism, of which 93% were asymptomatic. No grade 3–4 hypertension, proteinuria or arterial thrombosis was observed. Conclusions: mDCF+BEV appears tolerable and has notable long term pt outcomes: 6-mo PFS is 79% (surpassing our efficacy endpoint), median OS 16.2 mo, and 18-mo OS 46%.

No significant financial relationships to disclose.

A phase II study of flavopiridol (Alvocidib) in combination with docetaxel in refractory, metastatic pancreatic cancer

BACKGROUND/AIMS

Pancreatic adenocarcinoma (PC) harbors frequent alterations in p16, resulting in cell cycle dysregulation. A phase I study of docetaxel and flavopiridol, a pan-cyclin-dependent kinase inhibitor, demonstrated encouraging clinical activity in PC. This phase II study was designed to further define the efficacy and toxicity of this regimen in patients with previously treated PC.

METHODS

Patients with gemcitabine-refractory, metastatic PC were treated with docetaxel 35 mg/m(2) followed by flavopiridol 80 mg/m(2) on days 1, 8, and 15 of a 28-day cycle. Tumor measurements were performed every two cycles. A Simon two-stage design was used to evaluate the primary endpoint of response.

RESULTS

Ten patients were enrolled, and 9 were evaluable for response. No objective responses were observed; however, 3 patients (33%) achieved transient stable disease, with one of these patients achieving a 20% reduction in tumor size. Median survival was 4.2 months, with no patients alive at the time of analysis. Adverse events were significant, with 7 patients (78%) requiring >or=1 dose reduction for transaminitis (11%), grade 4 neutropenia (33%), grade 3 fatigue (44%), and grade 3 diarrhea (22%).

CONCLUSIONS

The combination of flavopiridol and docetaxel has minimal activity and significant toxicity in this patient population. These results reflect the challenges of treating patients with PC in a second-line setting where the risk/benefit equation is tightly balanced.

Pharmacokinetics (PK) of split-dose flavopiridol (F) administered with CPT-11 (CPT) and cisplatin (Cis)

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Background: F, a cyclin-dependent kinase inhibitor, induces tumor lysis in CLL when administered as a 30 mg/m2 loading dose over 0.5h followed by a 30 mg/m2 maintenance dose over 4h (hybrid F; Byrd et al, Blood 2006). F given as a 1h bolus (bolus F) demonstrates promising clinical activity when combined with CPT in solid tumors (Shah et al, CCR 2005). Data suggest that F concentrations of 2–3 μM are required to enhance the effects of CPT in solid tumors (Motwani et al, CCR 2001), but controversy exists over the optimal F schedule for chemotherapy potentiation. Methods: We are conducting a phase I trial of CPT/Cis→F, with F administered on both a bolus F and hybrid F schedule. After identifying the maximum tolerated dose (MTD) of bolus F (CPT/Cis→F 50mg/m2), the hybrid F schedule was examined. The F loading dose was escalated from 20→30mg/m2 and the F maintenance dose escalated from 20→50mg/m2. Plasma samples were obtained from patients (pts) treated with bolus F at the MTD and with hybrid F at all dose levels. To better assess F PK interaction with CPT/Cis, F was given before CPT/Cis on cycle 2 only. Results: Complete PK data are available from 6 pts treated at the bolus F MTD (50 mg/m2) and on 20 pts treated with hybrid F (20→20 mg/m2, 25→25 mg/m2 and 30→30 mg/m2) for cycles 1 and 2. Both bolus F and hybrid F PK are consistent with data previously reported. Although cycle 1 AUCs are similar for bolus F 50 mg/m2 and hybrid F 30→30 mg/m2 (10.47±4.97 vs 10.75±15.14 μM/h, p=NS), the Cmax achieved with bolus F 50 mg/m2 is significantly greater than that achieved with hybrid F 30→30 mg/m2 (2.31±0.65 vs 1.21±0.35 μM, p<0.02). No significant PK differences occurred between cycles 1 and 2. Toxicity was not associated with F Cmax. With CPT/Cis→bolus F, the PR rate was 10/29 (35%) vs 3/33 (9%) with CPT/Cis→hybrid F. Conclusions: The Cmax achieved with bolus F is greater than that achieved with hybrid F, with no increase in toxicity. Additionally, the Cmax achieved with hybrid F does not exceed the 2 μM plasma concentration required for potentiation of chemotherapy-induced apoptosis. The greater number of responses achieved with bolus F suggests that bolus F may be more efficacious than hybrid F when used in combination with CPT for the treatment of solid tumors. (Supported by R01-CA67819)

No significant financial relationships to disclose.

Multicenter phase II study of irinotecan, cisplatin, and bevacizumab in patients with metastatic gastric or gastroesophageal junction adenocarcinoma

PURPOSE

Bevacizumab improves survival in several solid tumor malignancies when combined with chemotherapy. We evaluated the efficacy and safety of the addition of bevacizumab to chemotherapy in the treatment of gastric and gastroesophageal junction (GEJ) adenocarcinoma.

PATIENTS AND METHODS

Forty-seven patients with metastatic or unresectable gastric/GEJ adenocarcinoma were treated with bevacizumab 15 mg/kg on day 1, irinotecan 65 mg/m2, and cisplatin 30 mg/m2 on days 1 and 8, every 21 days. The primary end point was to demonstrate a 50% improvement in time to progression over historical values. Secondary end points included safety, response, and survival.

RESULTS

Patient characteristics were as follows: median age 59 years (range, 25 to 75); Karnofsky performance status 90% (70% to 100%); male:female, 34:13; and gastric/GEJ, 24:23. With a median follow-up of 12.2 months, median time to progression was 8.3 months (95% CI, 5.5 to 9.9 months). In 34 patients with measurable disease, the overall response rate was 65% (95% CI, 46% to 80%). Median survival was 12.3 months (95% CI, 11.3 to 17.2 months). We observed no increase in chemotherapy related toxicity. Possible bevacizumab-related toxicity included a 28% incidence of grade 3 hypertension, two patients with a gastric perforation and one patient with a near perforation (6%), and one patient with a myocardial infarction (2%). Grade 3 to 4 thromboembolic events occurred in 25% of patients. Although the primary tumor was unresected in 40 patients, we observed only one patient with a significant upper gastrointestinal bleed.

CONCLUSION

Bevacizumab can be safely given with chemotherapy even with primary gastric and GEJ tumors in place. The response rate, time to disease progression (TTP), and overall survival are encouraging, with TTP improved over historical controls by 75%. Further development of bevacizumab in gastric and GEJ cancers is warranted.

Aurora Kinases: New Targets for Cancer Therapy

The Aurora kinase family is a collection of highly related serine/threonine kinases that functions as a key regulator of mitosis. In mammalian cells, Aurora has evolved into three related kinases known as Aurora-A, Aurora-B, and Aurora-C. These kinases are overexpressed in a number of human cancers, and transfection studies have established Aurora-A as a bone fide oncogene. Because Aurora overexpression is associated with malignancy, these kinases have been targeted for cancer therapy. This article reviews the multiple functions of Aurora kinase in the regulation of mitosis and the mitotic checkpoint, the role of abnormal Aurora kinase activity in the development of cancer, the putative mechanisms of Aurora kinase inhibition and its antitumor effects, the development of the first generation of Aurora kinase inhibitors, and prospects for the future of Aurora kinase inhibition in the treatment of cancer.

Final results of a multicenter phase II study of irinotecan (CPT), cisplatin (CIS), and bevacizumab (BEV) in patients with metastatic gastric or gastroesophageal (GEJ) adenocarcinoma (NCI #6447)

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Background: BEV improves survival in several solid tumors when combined with chemotherapy. CPT/CIS is active in gastric and GEJ cancers with a median time to progression(TTP) of 4.2 months, response rate(RR) of 30%, and median survival of ∼7 months (Pozzo Ann Onc 2004). Anti-angiogenic therapy for upper GI cancers is of concern due to a potential increased risk of perforation or GI bleed. We evaluated the efficacy and safety of the combination of CPT, CIS, and BEV in the treatment of gastric and GEJ cancers. Methods: 47 patients with previously untreated metastatic gastric or GEJ adenocarcinomas were treated with BEV 15mg/kg day 1, CPT 65mg/m2 and CIS 30mg/m2 days 1 and 8, every 21 days. The primary endpoint was TTP, with 90% power to demonstrate a 50% improvement in TTP (eg. from 5 to 7.5 months) over historical control. Safety, response, and survival were secondary endpoints. Results: Patient characteristics: median age 59 (range 25–75), KPS 90% (70%-100%), Male 34, Gastric/GEJ 27:20. With a median follow up of 9.0 months, median TTP is 9.9 months (95%CI: 6.5–11.8 months). In 33 patients with measurable disease, the RR (partial + complete) is 66.7% (95%CI: 51–83%). Median survival is 12.6 months (95%CI: 10.1–17.1 months). We observed no change in expected CPT/CIS related toxicity: eg. grade 3/4 neutropenia (29%), nausea/vomiting (10%), and diarrhea (13%). Possible BEV related toxicity includes 2 gastric perforations, 1 grade 3 peri-rectal fistula, 2 cardiac events(1 ischemia, 1 reduced ejection fraction), and 10 patients with grade 3/4 hypertension. Although the primary tumor was unresected in 35 patients, we observed only 1 patient with an upper GI bleed. Grade 3/4 thromboembolic events occurred in 25%. Conclusions: The combination of CPT/CIS/BEV is active in gastric and GEJ cancers. The toxicity profile is acceptable. The primary endpoint of improving TTP was exceeded by 100% with median TTP 9.9 months. Despite the majority of patients having their primary tumor unresected, GI bleeding was not significant. The thromboembolic and perforation rates with CPT/CIS are similar with or without BEV (Shah et al JCO 2005). Further development of BEV in gastric and GEJ cancers is clearly warranted.

[Table: see text]

Cetuximab shows activity in colorectal cancer patients with tumors that do not express the epidermal growth factor receptor by immunohistochemistry

PURPOSE

To establish evidence of activity, or lack thereof, of cetuximab-based therapy in patients with refractory colorectal cancer with tumors that do not demonstrate epidermal growth factor receptor (EGFR) expression by immunohistochemistry (IHC).

PATIENTS AND METHODS

Pharmacy computer records were reviewed to identify all patients who received cetuximab at Memorial Sloan-Kettering Cancer Center in a nonstudy setting during the first 3 months of cetuximab's commercial availability. Medical records of these patients were then reviewed to identify colorectal cancer patients who had experienced failure with a prior irinotecan-based regimen and who had a pathology report indicating an EGFR-negative tumor by IHC. Pathology slides from these patients were reviewed by a reference pathologist to confirm EGFR negativity, and computed tomography scans during cetuximab-based therapy were reviewed by a reference radiologist. Response rates were reported using WHO criteria.

RESULTS

Sixteen chemotherapy-refractory, EGFR-negative colorectal cancer patients who received cetuximab in a nonstudy setting were identified. Fourteen of these patients received cetuximab plus irinotecan, and two received cetuximab monotherapy. In the 16 patients, four major objective responses were seen (response rate, 25%; 95% CI, 4% to 46%).

CONCLUSION

Colorectal cancer patients with EGFR-negative tumors have the potential to respond to cetuximab-based therapies. EGFR analysis by current IHC techniques does not seem to have predictive value, and selection or exclusion of patients for cetuximab therapy on the basis of currently available EGFR IHC does not seem warranted.

Endocytosis in identified rat corticotrophs

1. We used the patch-clamp technique, in conjunction with membrane capacitance measurement, fluorescence measurement of intracellular calcium concentration ([Ca(2+)](i)), and flash photolysis of caged Ca(2+) to study exo- and endocytosis in identified rat corticotrophs. 2. Exocytosis stimulated by depolarization pulses was typically followed by a 'slow' endocytosis that retrieved the membrane with a time constant of approximately 6 s. The efficiency (the endocytosis/exocytosis amplitude ratio) of 'slow' endocytosis was approximately 1.2 at [Ca(2+)](i) < 3 microM and increased to approximately 1.6 at [Ca(2+)](i) > 3 microM. 3. Whole-cell dialysis through a patch pipette did not affect the kinetics and the efficiency of 'slow' endocytosis, but the amplitude of exocytosis was reduced. 4. 'Slow' endocytosis did not require sustained [Ca(2+)](i) elevation and its kinetics was only weakly [Ca(2+)](i) dependent. Our results suggest that 'slow' endocytosis involves a Ca(2+) sensor with a high Ca(2+) affinity (approximately 500 nM). 5. At high [Ca(2+)](i) (> 10 microM), the 'slow' endocytosis was frequently preceded by a 'fast' endocytosis that comprised multiple steps of rapid decrease in membrane capacitance. 6. Neither calmodulin nor calcineurin appeared to be the Ca(2+) sensor for endocytosis because the two forms of endocytosis were not affected by the calmodulin inhibitor calmidazolium (500 microM) or the calcineurin inhibitors cyclosporin A (1 microM) and calcineurin autoinhibitory peptide (1 mg ml(-1)). Ba(2+), a poor activator of calmodulin, could support both forms of endocytosis but slowed the kinetics of 'slow' endocytosis approximately 2-fold. 7. Non-hydrolysable analogues of GTP (GDP-beta-S) and ATP (ATP-gamma-S) also failed to inhibit either form of endocytosis, indicating that neither GTP nor ATP was essential for endocytosis. 8. We suggest that the high Ca(2+) affinity of 'slow' endocytosis may be important for maintaining continuous cycles of exocytosis-endocytosis during sustained adrenocorticotropin secretion in corticotrophs.

Voltage-gated Ca2+ channels and intracellular Ca2+ release regulate exocytosis in identified rat corticotrophs

1. The patch clamp technique was used in conjunction with a fluorescent Ca2+ indicator (indo-1, or indo-1FF) to measure simultaneously cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis (changes in membrane capacitance) in single, identified rat corticotrophs. 2. Exocytosis could be stimulated by extracellular Ca2+ entry (via voltage-gated Ca2+ channels). A train of depolarizations could exhaust the pool of readily releasable granules and the pool replenished with a time constant of 42 s (at 22-25 C). 3. Recordings from cells with 0.5 mM intracellular cAMP showed that the amplitude of the depolarization-triggered exocytosis, the Ca2+ sensitivity of exocytosis, as well as the rate of replenishment of the readily releasable pool, were similar to the controls. 4. Exocytosis could also be stimulated by intracellular Ca2+ release from the inositol 1,4, 5-trisphosphate (IP3)-sensitive store (via flash photolysis of caged IP3). At comparable [Ca2+]i, extracellular Ca2+ entry and intracellular Ca2+ release had similar efficacy in triggering exocytosis. 5. The rate of exocytosis triggered via depolarization or intracellular Ca2+ release was much faster than that triggered via uniform elevation of [Ca2+]i (Ca2+ dialysis or flash photolysis of caged Ca2+). 6. The above findings suggest that both intracellular Ca2+ release and voltage-gated extracellular Ca2+ entry generate a spatial Ca2+ gradient, such that the local [Ca2+] near the exocytic sites was approximately 3-fold higher than the mean cytosolic [Ca2+]. However, neither cAMP nor the spatial Ca2+ gradient generated during depolarization could account for the high efficacy of corticotropin-releasing hormone (CRH) in stimulating adrenocorticotropic hormone (ACTH) secretion from corticotrophs.

Stimulation of Ca(2+)-independent exocytosis in rat pituitary gonadotrophs by G-protein

We employed the whole-cell recording technique in conjunction with fluorometry to measure cytosolic Ca(2+) concentration ([Ca(2+)](i)) and exocytosis (capacitance measurement) in single, identified rat gonadotrophs. Direct activation of G-protein (via intracellular dialysis of non-hydrolysable analogues of GTP, but not of GDP) triggered a slow rise in capacitance even in the presence of a fast intracellular Ca(2+) chelator. The broad-spectrum kinase inhibitors H7 and staurosporine did not prevent this Ca(2+)-independent exocytosis, ruling out the involvement of the cAMP and PKC pathways. AlF(4)(-), a potent stimulator of heterotrimeric G-proteins, failed to stimulate any exocytosis when the intracellular Ca(2+) store was depleted, implicating the involvement of AlF(4)(-)-insensitive G-protein(s). Maximal stimulation of Ca(2+)-independent exocytosis by GTP analogues did not reduce the number of readily releasable granules that were available subsequently for Ca(2+)-dependent release. The last finding raises the possibility that the G-protein-stimulated Ca(2+)-independent exocytosis may regulate a pool of granules that is distinct from the Ca(2+)-dependent pool.

Tissue-specific expression of functional isoforms of mouse folypoly-gamma-glutamae synthetase: a basis for targeting folate antimetabolites

Folates and folate antimetabolites are metabolically trapped in mammalian cells as polyglutamates, a process catalyzed by folylpoly-gamma-glutamate synthetase (FPGS). Using 5'-rapid amplification of cDNA ends, RNase protection assays, transfection of cDNAs into FPGS-deficient cells, and kinetic analysis of recombinant enzymes expressed in insect cells, it was determined that the species of active FPGS in mouse liver and kidney was different from that in mouse tumor cells, bone marrow, and intestine. The NH2-terminal peptide of hepatic enzyme contained 18 amino acids not found in enzyme from dividing tissues, and the specificity of the two isoforms for antifolates also differed, suggesting different architecture of the active sites. In most tissues, the expression of one isozyme or the other was an all-or-nothing event. The exclusive use of one of two alternative sets of initial coding exons in different tissues underlies this phenomenon, suggesting the design of antifolates specific for activation by individual FPGS isoforms and hence tissue-selective targeting of antifolate therapy for cancer, arthritis, or psoriasis.