Calistoga Pharmaceuticals Research Articles

CAL-101, An Oral p110δ Selective Phosphatidylinositol-3-Kinase (PI3K) Inhibitor for the Treatment of B Cell Malignancies Inhibits PI3K Signaling, Cellular Viability and Protective Signals of the Microenvironment.

Abstract 286It is well established that deregulation of the PI3K signaling pathway plays an important role in the etiology of human malignancies including those of hematologic origin. In 30–50% of solid tumors, oncogenic activation of the PI3K pathway is the result of gain-of-function mutations in the PI3K p110α isoform or due to the loss-of-function of the PTEN phosphatase that is responsible for PI3K downregulation. In B cell malignancies these mutations are rarely observed in spite of the fact that PI3K pathway activation is commonly observed and often essential for tumor cell growth and survival. In this case, PI3K pathway activation has been shown to result from constitutive B cell receptor (BCR) activation and/or from exposure to survival factors present in the microenvironment. The activation of the PI3K pathway by cell surface receptors is directly mediated by the Class I isoforms (α, β, δ, and γ), however, their relative contribution in B cell tumors is unknown. Interestingly, genetic and pharmacological approaches that specifically inactivate the p110δ isoform have demonstrated its important role in normal B cell signaling in response to multiple factors including antigen, CD40L, BAFF, SDF-1 and CXCR13 making it an attractive target for therapeutic intervention in B cell malignancies. CAL-101 is an oral p110δ specific inhibitor which is currently being evaluated in a phase I clinical trial for the treatment of patients with select hematologic malignancies. This compound is a novel potent p110δ inhibitor with an IC50 of 2.5 nM against purified p110δ and EC50 of 65 nM in p110δ-mediated basophil activation in whole blood. CAL-101 demonstrates 300-, 200-, and 40-fold selectivity over the other class I family members (α, β, and, γ respectively) and no activity against class II and III PI3K family members or other PI3K-related proteins including mTOR and DNA-PK. Furthermore, a kinome-wide screen failed to detect activity against any additional kinases. To investigate the potential role of p110δ in B cell hematologic tumors we screened a wide range of leukemia and lymphoma cell lines for constitutive PI3K pathway activation. The expression of p110δ was observed in >90% of these cell lines and in many cases was accompanied by constitutive Akt phosphorylation. In this context, CAL-101 was able to reduce p-Akt levels and block additional downstream effectors such as p-S6, and GSK-3β in cells that represent a range of tumor types including follicular lymphoma, acute lymphoblastic leukemia (ALL), diffuse large B-cell lymphoma, and mantle cell lymphoma (MCL). Furthermore, treatment with CAL-101 resulted in growth suppression and induction of apoptosis which was accompanied by PARP and caspase-3 cleavage. Growing evidence suggests that signals from the microenviroment are essential for the expansion, homing, and survival of malignant B cells, in addition to promoting resistance to conventional drug therapy. To investigate the potential role p110δ plays during B cell signaling via interactions with the microenvironment, we examined invoked stimulation of leukemia and lymphoma cell lines with CXCL12, CXCL13, BAFF, or BCR crosslinking in the presence or absence of CAL-101. Stimulation with either chemokines or growth factors resulted in the phosphorylation of Akt which was inhibited by CAL-101 in a dose dependent manner. Moreover, p110δ inhibition with CAL-101 inhibits the chemotaxis of ALL and MCL cell lines to CXCL12. These studies have now been extended to the analysis of primary patient B-ALL and MCL cells to further establish preclinical proof of concept for therapeutic application of CAL-101. In summary, CAL-101 is a potent and selective p110δ kinase inhibitor with broad anti-tumor activity against cancer cells of hematologic origin. Our results demonstrate that selective inhibition of p110δ with CAL-101 inhibits malignant B cell growth, survival, and migration. Furthermore, p110δ inhibition may enhance the effect of cytotoxic drugs or overcome cell mediated drug resistance by inhibiting the protective signals of the microenviroment, providing a rational for combination therapy. These data suggest that p110δ may play an important role in regulating signals between malignant B cells and their microenvironment thereby providing the preclinical rationale for clinical evaluation of CAL-101 alone or in combination with cytotoxics or biologics in patients with hematologic malignancies. Disclosures:Lannutti:Calistoga Pharmaceuticals: Employment. Meadows:Calistoga Pharmaceuticals: Employment. Kashishian:Calistoga Pharmaceuticals: Employment. Steiner:Calistoga Pharmaceuticals: Employment. Johnson:Calistoga Pharmaceuticals: Research Funding. Giese:Calistoga Pharmaceuticals: Employment.

Evidence of Clinical Activity in a Phase 1 Study of CAL-101, An Oral P110Δ Isoform-Selective Inhibitor of Phosphatidylinositol 3-Kinase, in Patients with Relapsed or Refractory B-Cell Malignancies.

Abstract 922 Introduction:The class I phosphatidylinositol 3-kinases (PI3Ks) regulate a variety of cellular functions relevant to oncogenesis, including metabolism, proliferation and survival. The PI3K p110Δ isoform is primarily expressed in cells of hematopoietic origin and plays a key role in normal B cell maturation and function. CAL-101 is an oral, potent inhibitor of PI3K p110Δ (IC50 of 2.5 nM against purified enzyme and EC50 of 65 nM in a whole blood basophil assay) with 40 to 300-fold selectivity compared to other PI3K isoforms. This selectivity may provide a better therapeutic index relative to pan-PI3K inhibitors. In vitro studies of 0.1 to 10 uM CAL-101 showed inhibition of AKT phosphorylation and/or apoptotic effects against primary chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML) cells and against a range of leukemia, lymphoma and multiple myeloma (MM) cell lines. Methods and Patients:A Phase 1 study was undertaken to evaluate the safety and clinical activity of CAL-101 in patients with select hematologic malignancies. During initial dose escalation, sequential cohorts of 3 patients with relapsed/refractory CLL or select B-cell non-Hodgkin's lymphoma (NHL) were enrolled to determine dose limiting toxicity (DLT). During subsequent cohort expansion, approximately 12 patients each with CLL, indolent NHL, aggressive NHL, and AML were to be enrolled. CAL-101 was administered orally twice daily (BID) continuously for 28 days per cycle. Clinical response was evaluated at the end of Cycles 1 and 2 and every 2 cycles thereafter. Results:To date, 43 patients have been enrolled and followed for at least 4 weeks, consisting of 17 patients with CLL, 9 patients with indolent NHL, 10 patients with aggressive NHL and 7 patients with AML. The demographic and disease characteristics were 33% female, mean age 65 (60% over age 65), 49% had refractory disease and the median number of prior regimens was 5. During dose escalation (n=12), 3 patients per cohort were administered dose levels of 50 mg, 100 mg, 200 mg or 350 mg BID. In cohort expansion 31 patients were enrolled to either 200 mg (n=17) or 350 mg (n=14) BID. The median duration of treatment at data cutoff was 3 cycles (range 1 to 10). Two patients discontinued early due to adverse events, one for acute on chronic renal failure and one for abnormal liver function tests (LFTs). DLTs were observed in 5 patients with increases in LFTs, which resolved following discontinuation of CAL-101 dosing. No patient had Grade 4 hematological toxicity. Serious infections were reported in 9 patients, with pneumonia being the most frequent. 41 patients were evaluable for clinical response. At data cutoff, the response rate in NHL was 10/18 (56%); all were partial responses (PR). Of the 9 patients with indolent NHL, 5 patients had PR and 2 patients had stable disease (SD) and remained on study. Of the 9 patients with aggressive NHL, 5 patients had PR (all with mantle cell lymphoma) and 1 patient had SD on study. Of the 17 patients with CLL, 6 patients had PR and 7 other patients had >50% reduction in lymphadenopathy and concurrent increase in peripheral blood lymphocytosis to >50% of baseline, suggesting compartmentalization shift of CLL cells. Lymphocytosis was maximal during the first 2 cycles and decreased thereafter. This effect of dislocating CLL cells from the tissue microenvironment suggests that CAL-101 treatment in combination with cytotoxic agents may be particularly active. Of the 6 patients with AML, no patient had responded and 2 patients remained on study. Clinical responses were observed in patients at all 4 dose levels administered. At data cutoff, the longest duration of response was 9 months in a patient with follicular lymphoma, which was longer than the response to any of the 6 prior regimens this patient received, including autologous hematopoietic stem cell transplant. Plasma exposure increased from 50 mg to 200 mg, without further change at 350 mg. At the 200 mg and 350 mg dose levels, mean peak and trough drug concentrations at the end of Cycle 1 were 5 uM and 1 uM, respectively. Enrollment in cohort expansion is continuing with the addition of patients with MM and updated data will be presented at the meeting. Conclusions:Interim results from the first Phase 1 study to evaluate an oral PI3K p110Δ inhibitor, CAL-101, show promising activity in patients with relapsed or refractory B-cell malignancies with acceptable toxicity. Disclosures:Byrd:Calistoga Pharmaceuticals, Inc: Consultant. Furman:Calistoga Pharmaceuticals, Inc: Consultant. Brown:Calistoga Pharmaceuticals, Inc: Consultant. Giese:Calistoga Pharmaceuticals, Inc: Employment, Ownership Interest. Yu:Calistoga Pharmaceuticals, Inc.: Employment, Ownership interest.

Comparison of Steady-State Imatinib (IM) Trough Levels, Clinical Response, and Safety Between Caucasian and Asian Patients with Chronic Lyeloid Leukemia in Chronic Phase (CML-CP) Treated with 400mg and 800mg Daily Doses of IM in the Tyrosine Kinase Inhibitor Optimization and Selectivity (TOPS) Study.

Abstract Abstract 1127 Poster Board I-149 Background In the TOPS study, IM trough levels (Cmin) were collected from different race groups, mainly Caucasian and Asian, but also Black and others. Inter-ethnic differences in the PK of a drug are known to be important factors accounting for inter-individual variation in drug responsiveness. This analysis reports the comparison between Caucasian and Asian CML patients (pts) treated at doses of 400 mg QD and 400 mg bid (800 mg daily) of IM Cmin on Day 29 of initial treatment, clinical response, safety and tolerability. Methods Steady state IM Cmin on Day 29 and clinical response and safety data obtained during the first 12 months (mos) of treatment were obtained from pts randomized 2:1 to 800 mg or 400 mg daily IM. The steady-state Cmin was defined as predose concentration collected approximately within ±3 hours of the scheduled dosing time on Day 29. The associations of race with the rates of major molecular response (MMR) and complete cytogenetic response (CCyR) were evaluated. Correlation of IM exposure with clinical response (MMR and CCyR) was assessed by grouping pts into quartiles based on their measured IM Cmin levels at Day 29. The safety endpoint for each pt was the presence or absence of an adverse event (AE) of grade 3 or higher in the first 12 mos from the first dose. Results IM Cmin levels were available from 229 pts in TOPS including 54 Caucasians, 18 Asians, and 14 Black and others at 400 mg (total 86) and 103 Caucasians, 29 Asians, and 11 Black and others at 800 mg (total 143). For the first 12 mos, the means of the average dose intensities for Asian (mean [range], 362 [267-400] in 400 mg and 666 [226-800] in 800 mg) were not significantly different from Caucasian (386 [204-597] in 400 mg and 666 [289-800] in 800 mg) (P=0.070 and P=0.995 for the 400 mg and 800 mg arms, respectively). Mean (± SD) of IM Cmin levels (ng/mL) with respect to race are shown in Table 1. IM Cmin was slightly over-proportional to dose and showed large interpatient variability (CV=42-60%) for both dose groups regardless of the race group. In the lower quartile Cmin group (Cmin<1290 ng/mL), the differences in CCyR and MMR rates between Asian and Caucasian pts were significant (P=0.031 and P=0.022 respectively), which was probably due to a higher rate of dose interruptions in the 1st 12 mos in Asian pts. A definitive conclusion cannot be drawn due to the small number of Asian pts. Occurrences of at least one grade 3 or 4 adverse event were found to be significantly higher in Asian pts (69% and 75% in the 1st 6 and 12 mos respectively) compared to Caucasian pts (53% and 57% in the 1st 6 and 12 mos respectively) (P=0.028 and P=0.008 respectively). Conclusion The results of this analysis from TOPS show that IM Cmin levels were similar between Caucasian and Asian CML pts in each treatment arm. There were no major differences in efficacy, as measured by MMR and CCyR rates by 12 mos, between Asian and Caucasian pts. There were no unexpected differences in patterns of AEs between Caucasian and Asian pts; however, occurrences of one or more grade 3 AEs were higher in Asian. Further analysis on a larger group of CML pts will be needed to evaluate the impact of AE rate differences between Caucasian and Asian pts. Disclosures Kim: Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; BMS: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Wyeth: Research Funding. Granvil:Novartis: Employment. Demirhan:Novartis: Employment. Reynolds:Novartis: Employment. Jin:Novartis: Employment. Wang:Novartis: Employment, Equity Ownership. Baccarani:Novartis Pharma: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Mayer Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau. Cortes-Franco:Novartis: Honoraria, Research Funding, Speakers Bureau; Wyeth: Honoraria, Research Funding, Speakers Bureau; BMS: Honoraria, Research Funding, Speakers Bureau. Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. Hughes:Bristol-Myers Squibb: Advisor, Honoraria, Research Funding; Novartis: Advisor, Honoraria, Research Funding. Guilhot:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria.

Steady-State Imatinib Trough Levels as Well as Dose Interruptions Are Associated with Clinical Response (CCyR and MMR) and Adverse Events (AEs) in Patients with Chronic Myeloid Leukemia (CML) Receiving IM as Frontline Therapy.

Abstract 2213Poster Board II-190 Background:Correlations between IM trough plasma levels (Cmin) and clinical response have been previously reported [Picard et al. Blood 2007; Larson et al. (IRIS) Blood 2008; Guilhot et al. (TOPS) ASH 2008]. This analysis correlates IM Cmin on Day 29 of initial treatment with complete cytogenetic response (CCyR) and major molecular responses (MMR) at 12 months and with cumulative Grade 3&4 toxicity over 12 months based on data pooled from 2 studies, IRIS (400 mg qd) and TOPS (400 mg bid (800 mg/daily) vs 400 mg qd), in newly diagnosed, previously untreated, Ph+ CML-CP. Methods:Steady-state Cmin was defined as predose blood level collected within ±3 hours of the scheduled dosing time on Day 29 without any dose interruptions within 5 days prior to PK sampling. The correlation between IM Cmin and CCyR and MMR at 12 months was studied by two approaches: 1) analysis of outcomes by quartile groups based on patients' IM Cmin levels; 2) logistic regression analysis with Cmin as a continuous variable plus Sokal risk scores and cumulative days with any dose interruptions during the initial 12 months. Safety parameters included Grade 3&4 AEs, as well as all frequently-occurring (>10%) AEs of any grade that occurred during the 12 months. Patients with missing covariates were excluded. Results:Steady-state IM Cmin trough levels were available in 526 patients: 319 in IRIS and 207 from TOPS. At the time of assessment most patients received either 400 mg or 800 mg; 8 patients received reduced doses (6 at 300 mg; 2 at 600 mg). The median IM Cmin [25-75% quartiles] for 400 mg in the pooled dataset was 943 ng/mL [688-1280 ng/mL], and that for 800 mg was 2910 ng/mL [2333-3900 ng/mL]. IM Cmin showed large inter-patient variability for both 400 mg and 800 mg dose groups (52.7% and 39.9%, respectively). Both CCyR and MMR rates at 12 months were significantly correlated with IM Cmin on Day 29. Besides Cmin on Day 29, Sokal risk scores and cumulative dose interruptions (due either to treatment-related toxicities or non-adherence) were significant covariates for 12 month CCyR and MMR. Patients with high Sokal scores (H) had lower CCyR and MMR rates than those with low Sokal scores (L), 64% (H), 69% (intermediate (I)), and 83% (L), respectively, for CCyR, and 37%, 48%, and 59%, respectively, for MMR. Response rates at 12 months were significantly lower for patients with cumulative dose interruptions > 28 days (in the first 12 months): 45% vs 76% for CCyR, and 27% vs 48% for MMR. Modeling predicts that at a Cmin level of 1000 ng/mL and assuming no or minimal dose interruptions, the CCyR at 12 months would be 85%, 78%, and 68% for L, I, and H Sokal risk patients, respectively, and for MMR 55%, 45% and 36%, respectively. If the Cmin were 2000 ng/mL, the CCyR at 12 months would be 93%, 89%, and 83% for L, I, and H Sokal risk patients, respectively, and for MMR 65%, 55% and 44%, respectively. The predicted CCyR and MMR would be lower if there were dose interruptions. Patients who had Grade 3&4 AEs over first 12 months period (n=136) had a higher IM Cmin on Day 29 (median [25-75% quartiles], 1985 [982-2943] ng/mL vs 1010 [728-1468] ng/mL, P<0.001), than those without (n=390) as well as longer cumulative dose interruptions (20 [8-41] days vs 0 [0-2] days, P<0.001), lower CCyR rate (66%; 77/117 vs 75%; 277/369, P=0.05), and lower MMR rate (37%; 49/131 vs 48%; 155/323, P=0.006). Most Grade 3&4 AEs were treatment-related hematologic AEs with median times to onset between 50-63 days. Regression analysis showed the correlation between hematologic Grade 3&4 AEs and IM Cmin level for the population (Figure). Among all-grade non-hematologic AEs, rash and vomiting were associated with higher IM Cmin levels. [Display omitted] Conclusion:IRIS+TOPS pooled data confirmed earlier findings that higher steady-state IM levels correlate with better CCyR and MMR responses but also with more Grade 3&4 treatment-related toxicities. Dose interruptions compromise CCyR and MMR rates at 12 months. IM Cmin levels provide additional information together with clinical response and tolerability to inform dose changes for individual patients. Disclosures:Larson:Novartis: Consultancy, Honoraria, Research Funding. Chia:Novartis: Employment. Granvil:Novartis: Employment. Guilhot:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria. Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. O'Brien:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Wyeth: Research Funding. Baccarani:Novartis Pharma: Consultancy, Honoraria, Research Funding, Speakers Bureau; Bristol-Mayer Squibb: Consultancy, Honoraria, Research Funding, Speakers Bureau. Hughes:Bristol-Myers Squibb: Advisor, Honoraria, Research Funding; Novartis: Advisor, Honoraria, Research Funding. Nedelman:Novartis: Employment, Equity Ownership. Wang:Novartis: Employment, Equity Ownership.

The Oncogenic Role of Tumor Suppressor Protein p27 in Ph+ Chronic Myeloid Leukemia.

Abstract 3276Poster Board III-1 Background:Several studies have indicated that BCR-ABL causes cell cycle defects by interfering with the cell cycle regulatory functions of p27, a Cyclin dependent kinase (Cdk) inhibitor and tumor suppressor. Studies in BCR-ABL positive cell lines have shown that BCR-ABL promotes proteasomal degradation of p27 in a pathway that involves the SCFSKP2 ubiquitin ligase, while cytoplasmic mislocalization has been described in primary CML cells. It has been suggested that the principal effect of this cytoplasmic mislocalization is to remove p27 from the nucleus, thereby relieving Cdks from p27 inhibition. However, recent studies have shown that a p27 mutant (p27CK-), that cannot bind to Cdks or Cyclins, actively contributes to oncogenesis. This raises the question as to whether cytoplasmic mislocalization of p27 in CML cells may in fact promote leukemogenesis rather than merely compromise Cdk inhibition. We therefore hypothesized that the net contribution of p27 in CML is to promote leukemogenesis due to the oncogenic activity of cytoplasmic p27. Experimental approach and results:We determined p27 localization in BCR-ABL positive cell lines and CD34+ progenitor cells from newly diagnosed chronic phase CML patients (N=7) and from CML patients in blast crisis (N=2) by immunoblotting of nuclear and cytoplasmic cellular fractions. We found that p27 is predominantly cytoplasmic in most CML cell lines and in CD34+ cells from 8/9 (89%) patient samples, including patients in blastic phase. Cytoplasmic localization of p27 in CD34+ cells from CML patients was also confirmed by immunofluorescence analysis. Further, we observed that inhibition of BCR-ABL kinase by imatinib, an Abl kinase inhibitor increased nuclear p27 in all cell lines tested and in 4/9 patient samples (3/7 chronic phase and 1/2 blastic phase samples). However, we did not observe a substantial change in the cytoplasmic p27 levels. Similar results were obtained in Ba/F3 and 32D murine hematopoietic cell lines expressing BCR-ABL when compared with the respective parental cells. Further, SKP2 was up-regulated in CD34+ cell from CML patients as compared to the normal patients consistent withSKP2 mediated down-regulation of nuclear p27. These data suggest that nuclear but not cytoplasmic p27 levels are predominantly regulated by BCR-ABL kinase activity. To test whether p27 is crucial for BCR-ABL-driven leukemia, we compared leukemogenesis between recipients of BCR-ABL transduced p27+/+ and p27-/- bone marrow. Mice transplanted with BCR-ABL infected p27-/- marrow had significantly longer median survival (70 days, range 48-150 days) compared to recipients of p27+/+ marrow (37 days, range 14-56 days) (p=0.0123). To exclude that this difference was related to the differences in homing and engraftment capabilities of p27+/+ and p27-/- bone marrow cells, we compared short term homing and long term engraftment of p27+/+ and p27-/- bone marrow cells transplanted into wild-type recipients and found no differences. These data suggest that the net contribution of p27 to BCR-ABL-mediated leukemogenesis is positive. Further, to investigate the contribution of nuclear p27 to leukemogenesis, we utilized marrow from p27S10A mice in the murine CML model. In p27S10A mice, p27 is nuclear to to abrogation of the phosphorylation site implicated in nuclear export. We injected BCR-ABL transduced bone marrow cells of p27S10A and p27+/+ mice into wild-type recipients and compared the disease progression. We observed that mice transplanted with BCR-ABL infected p27S10A marrow had significantly longer median survival (28 days, range 23-79 days) compared to the recipients of p27+/+ marrow (23 days, range 21-38 days) (p=0.0139). This data is consistent with nuclear tumor suppressor function of p27. Combined with the data above, this suggests that cytoplasmic p27 promotes BCR-ABL mediated leukemogenesis. Conclusions:Our data suggest that though nuclear p27 functions as a tumor suppressor, the net contribution of p27 in CML might be oncogenic due to an oncogenic role of the increased cytoplasmic p27. Restoring nuclear p27 or reducing cytoplasmic p27 may be therapeutically useful in malignancies with low nuclear and high cytoplasmic p27 expression. Disclosures:Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. Deininger:Genzyme: Research Funding; BMS: Consultancy; Novartis: Consultancy, Honoraria; Ariad : Research Funding.

Development of a Small-Molecule Inhibitor Screen to Rapidly Identify Key Signaling Pathways in Leukemogenesis.

Abstract 708Aberrantly activated tyrosine kinases and their associated signaling pathways are critical to leukemogenesis and primary acute myeloid leukemia (AML) cell viability. While aberrant kinase activation has been confirmed in a significant percentage of AML, constitutive phosphorylation of STAT5, a marker of tyrosine kinase activation, is present in the majority of AML samples indicating that as yet unidentified tyrosine kinases can be aberrantly activated and contribute to leukemogenesis. Efforts to identify activating tyrosine kinase mutations using high-throughput sequencing have identified low frequency mutations of uncertain functional significance. Because these studies failed to detect additional high-frequency kinase mutations, the identity and mechanism of tyrosine kinase activation may be unique in many AMLs. To avoid the imitations of high-throughput sequencing, we have developed a functional assay that can rapidly and simultaneously identify therapeutic targets while providing therapeutic options. Methods:To rapidly identify activated kinase pathways in individual, primary AML samples, we have developed a small-molecule inhibitor array which includes 90 small-molecule, cell-permeable inhibitor compounds including a core of 36 tyrosine kinase inhibitors that covers the majority of the tyrosine kinome. Many of the inhibitors are available for clinical use or are in clinical development. In this assay, inhibitors were placed in 96-well plates at four serial dilutions to allow IC50 calculations. Three days after adding primary AML cells to each well, we performed an MTS cell viability assay to evaluate the effect of each inhibitor on cell viability. Because most inhibitors affect multiple kinases, we compared target specificities of compounds that decrease primary AML cell viability with those that have no effect to identify potential targets. Results:In preliminary proof-of-principal experiments, we tested leukemia cell lines with known activating tyrosine kinase mutations and Ba/F3 cell lines expressing activated tyrosine kinases. Appropriate inhibitor sensitivity profiles were obtained in CMK cells which depend on a JAK3 A572V mutation for viability, MKPL-1 cells with an activating CSF1R translocation, and in a Ba/F3 line expressing JAK2 V617F. In addition to the primary target, downstream targets were frequently identified; MKPL-1 cells also showed sensitivity to phosphoinositol 3-kinase and NFKB inhibitors. Thus, not only primary targets but the downstream signaling pathways critical to leukemic cell viability can be highlighted using this assay. To date, we have analyzed approximately 150 primary leukemia and lymphoma samples. In some cases, targets could be identified by comparison of overlapping kinase specificities for compounds that decreased leukemic cell viability and subtraction of possible kinase targets inhibited by compounds that had no effect on viability. However, many cases exhibited complex, often unique, inhibitor sensitivity profiles that complicated target identification. Comparison with sensitivity profiles for known aberrantly activated kinases was useful when available. Accordingly, additional leukemia cell lines and Ba/F3 lines that depend on a single aberrantly activated tyrosine kinase for viability are being evaluated. Automated scripts that correlate the leukemic cell inhibitor sensitivity with the inhibitor target specificity are also in preparation. Conclusions:These preliminary data demonstrate that the small-molecule inhibitor functional assays can rapidly identify disease causing genes, provide insights into their mechanism of action, and suggest therapeutic options. The distinct patterns of tyrosine kinase sensitivity in these samples support the hypothesis that tyrosine kinases and related pathways contributing to leukemogenesis in each patient may be different and that targeted therapy will be most effective when administered on an individualized basis. Disclosures:Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding.

24 Months Update of the TOPS Study: a Phase III, Randomized, Open-Label Study of 400mg/d (SD-IM) Versus 800mg/d (HD-IM) of Imatinib Mesylate (IM) in Patients (Pts) with Newly Diagnosed, Previously Untreated Chronic Myeloid Leukemia in Chronic Phase (CML-CP).

24 Months Update of the TOPS Study: a Phase III, Randomized, Open-Label Study of 400mg/d (SD-IM) Versus 800mg/d (HD-IM) of Imatinib Mesylate (IM) in Patients (Pts) with Newly Diagnosed, Previously Untreated Chronic Myeloid Leukemia in Chronic Phase (CML-CP).

Tumor Necrosis Factor-Alpha (TNF) Expression Is Elevated in Myelo-Proliferative Neoplasms (MPN) and Modulated by Inhibition of JAK2 V617F.

Abstract 2917Poster Board II-893 BACKGROUND:Myeloproliferative neoplasms (MPN) are hematopoietic stem cell diseases encompassing chronic myeloid leukemia (CML), essential thrombocythemia (ET), idiopathic myelofibrosis (IMF), and polycythemia vera (PV). More than 95% of all patients with PV and some 50% of patients with ET and IMF have an activating mutation of JAK2 (JAK2 V617F). Tumor necrosis factor-alpha (TNF) is a pleiotropic cytokine produced by multiple cell types, including macrophages, NK, T and B cells. TNF plays a key regulatory role in immune and inflammatory responses. There is also evidence that TNF is involved in the regulation of erythropoiesis. We have previously reported that TNF levels are elevated in mice with retrovirally induced JAK2 V617F-positive PV-like MPN and that lack of TNF attenuates MPN in this model. APPROACH AND RESULTS:We studied the expression of TNF in white blood cells from PV patients (n=43) and normal controls (n=21), using qPCR. PV patients expressed on average 2.5-fold higher levels of TNF than controls (p<0.0004). Upon examination of a panel of human leukemia lines (n=8) we found the highest TNF expression in HEL cells, which are homozygous for JAK2 V617F, suggesting that JAK2 V617F may upregulate TNF expression. Consistent with this, we found 6.9-fold higher TNF expression in Ba/F3 cells constitutively co-expressing EPOR and JAK2 V617F compared to parental cells. Exposure of HEL cells or Ba/F3 EPOR JAK2 V617F cells to the JAK2 inhibitor CYT387 (2 μM) resulted in a time dependent 3.3 to 7.5-fold decrease of TNF mRNA as assessed by qPCR. By contrast, TNF mRNA expression was not found to be down-regulated by CYT387 in HL60 cells lacking mutated JAK2. CYT387 was also found to down-regulate TNF mRNA expression in MNC derived from MPN patients. To assess differential effects of TNF on normal versus MPN progenitor cells, we performed clonogenic assays of peripheral blood MNC from normal donors (n=4) and MNC from MPN patients (n=9) in the presence of graded concentrations of EPO (0, 0.05, 0.5 and 5 IU/mL) and TNF (1, 10, 100 ng/mL). Intermediate and high TNF (10, 100 ng/mL) caused a dose-dependent reduction of BFU-E and CFU-GM compared to controls. However, in all conditions colony survival in MPN samples was higher compared to normal controls. Low TNF (1 ng/mL) in cultures supported by EPO (0.5 or 5.0 IU/mL) increased BFU-E formation by MPN cells to 142% of controls, but reduced BFU-E formation by normal MNC to 65%. CONCLUSIONS:Our data indicate that JAK2 V617F upregulates TNF expression in cell lines and primary MPN cells. Compared to normal progenitor cells, MPN progenitor cells are less sensitive to or even stimulated by TNF. These data suggest that JAK2 V617F-induced TNF may contribute to MPN pathogenesis by conferring a growth advantage to MPN over normal cells. Disclosures:Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. Burns:Cytopia: Employment. Deininger:Genzyme: Research Funding; BMS: Consultancy; Novartis: Consultancy, Honoraria; Ariad : Research Funding.

RAPID siRNA Screen for Identification of Therapeutic Gene Targets in Patients with Hematologic Malignancies.

Abstract 3978Poster Board III-914A large percentage of cancer cases present without knowledge of the causative genetic events. Tyrosine kinases are frequently implicated in the pathogenesis of cancer, but identification of specific kinases as cancer targets has been a slow process. Inhibition of cancer-causing tyrosine kinases offers a promising avenue of therapy, however this strategy of targeted therapy will require a detailed understanding of the oncogenic targets in each cancer patient. Here, we present an RNAi-assisted protein target identification (RAPID) assay by which cells from leukemia patients are functionally screened with siRNA to determine tyrosine kinases that constitute amenable targets for therapeutic intervention. Combination of the RAPID screen with gene-specific therapeutic approaches promises to yield a powerful synthesis of methodologies by which cancer patients can be specifically treated on the basis of functionally diagnosed gene targets. MethodsTo detect gene targets necessary for viability of malignant cells, we screened primary cells from 150 patients with hematologic malignancies by electroporating siRNAs individually targeting each member of the tyrosine kinase gene family. Four days later, we measured cell viability and tabulated sensitivity to silencing of specific genes. Samples were also screened for sensitivity to small-molecule kinase inhibitors. The mechanism of oncogenesis was investigated for each positive result. ResultsIn total, we have identified 40 patient-specific gene targets in primary leukemia samples. We demonstrate that siRNA screening can identify known oncogenic lesions such as K-RasG13D and JAK2V617F in primary cells from leukemia patients. The RAPID screen has also directed us towards a novel insertional mutation in the thrombopoietin receptor, MPL (1886InsGG). Additionally, we have detected FLT3 sensitivity in patients with FLT3-ITD and loss of heterozygosity, although not in FLT3-ITD heterozygous patients. Agreement between siRNA-sensitive gene targets and small-molecule inhibitor sensitivity profiles has been high. The mechanism of oncogenesis and its relation to the gene target has been established in select other samples with abnormalities including gene overexpression and patient-specific mis-splicing events. ConclusionsWe demonstrate that RNAi functional screening can determine sensitivity to individual genes in cells obtained directly from cancer patients. Thus, this technique offers the potential to match targeted therapies with patients in a personalized manner. Application of these technologies will enable efficient discovery of the genetic etiology of cancer as well as a means for gene-specific therapeutic intervention. Disclosures:Deininger:Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; Calistoga: Research Funding; Genzyme: Research Funding. Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding.

Mutational Analysis of BCR-Abl From Subjects with Relapsed Ph+ALL Treated On the COG Protocol AALL0031: a Report From the Children's Oncology Group.

Abstract 2634Poster Board II-610 Background:Philadelphia chromosome positive Acute Lymphoblastic Leukemia (Ph+ALL) occurs in 2–5% of pediatric ALL and is associated with a poor prognosis. COG AALL0031 treated children with an intensified chemotherapy backbone plus imatinib. All subjects received imatinib at 340mg/m^2 daily. Exposure to imatinib progressively increased in each of five cohorts. Patients had a total imatinib exposure (before maintenance) of 42 days in cohort 1, 63 days in cohort 2, 84 days in cohort 3, 126 days in cohort 4, and 280 days in cohort 5. All groups received an additional 336 days of imatinib exposure in maintenance cycles 1 through 12 for approximately 2 years (with imatinb given on 21 day cycles for maintenance cycles 1 – 4, and a two-week on/two-week off schedule for maintenance cycles 5 - 12). Early results of this trial show encouraging outcome with a 3-year event free survival of 80±11% (95% CI 64 – 90%) for patients in cohort 5. In studies of adults with Ph+ALL treated with imatinib many patients recurred with imatinib resistant BCR-Abl mutations. To date, there are no data on the occurrence of BCR-Abl mutations in pediatric Ph+ALL. Patients and Methods:We performed nested PCR to identify BCR-Abl point mutations in nine samples obtained at bone marrow (BM) relapse from Ph+ALL subjects on AALL0031. Results:(Table 1) Three samples from cohort 1 that had no exposure to imatinib prior to relapse showed wild-type sequence. There were 5 of 6 samples that also showed wild-type sequence. One sample was from cohort 2 and 3 samples were from cohort 3. Each subject relapsed 1 to 2 years after diagnosis while receiving varying amounts of imatinib with continued intensive therapy. One subject recurred after stem cell transplant in first remission. One sample from cohort 4 recurred after the completion of chemotherapy and imatinib. One subject from cohort 5 carried the histidine 396 to proline (H396P) mutation. This mutation, which increases the imatinib IC50 by 10-fold, has been previously described to occur in adults with CML and Ph+ALL treated with imatinib. The subject from cohort 5 recurred 1 year after diagnosis on therapy with imatinib.#Cohorttime to relapseimatinib ExposureBCR-Abl1126 months0 (BMT)WT2110 months0WT31refractory0WT4212 months4 monthsWT5323 months10 monthsWT6319 months2 (BMT)WT7339 months15 monthsWT8445 months17 monthsWT9515 months12 monthsH396P Conclusions:Only 1 resistant mutation in BCR-Abl has been identified among nine children with Ph+ALL treated on AALL0031. Therefore, unlike results in the adults, resistant mutations do not appear to drive early recurrence in Ph+ALL. Further studies will be needed to identify whether BCR-Abl mutations are identified in subjects who develop a late relapse after treatment with AALL0031 or subsequent treatment studies. Disclosures:Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents & Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents & Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding. Schultz:novartis: Membership on an entity's Board of Directors or advisory committees.

International Randomized Study of Interferon Vs STI571 (IRIS) 8-Year Follow up: Sustained Survival and Low Risk for Progression or Events in Patients with Newly Diagnosed Chronic Myeloid Leukemia in Chronic Phase (CML-CP) Treated with Imatinib.

Abstract Abstract 1126 Poster Board I-148 Background The IRIS study demonstrated superior safety and efficacy of imatinib (IM) relative to interferon-αa + cytarabine. Based on results from this trial, IM is currently recommended as front-line therapy for CML-CP patients (pts). We report 8-yr follow-up of IRIS, evaluating long-term efficacy and safety of IM. Methods The 553 pts randomized to first-line IM were evaluated for cytogenetic and molecular responses, event-free survival (EFS), progression to accelerated-phase (AP) or blast crisis (BC), overall survival (OS), discontinuations, and frequency of serious adverse events (SAEs). EFS was defined as time until the first occurrence of any of the following: death from any cause, progression to AP/BC, loss of a complete hematologic response or major cytogenetic response, or an increasing white cell count to &gt; 20 × 109/L. Yearly progression rates were calculated using the life-table method considering available follow-up. Following study drug discontinuation, pts were followed for OS and stem cell transplant (SCT) information. Results At the 8-yr data cut-off, 304 (55%) pts remained on IM study treatment, and 45% had discontinued treatment due to adverse events (AEs)/safety (6%), unsatisfactory therapeutic outcome (16%), SCT (3%), death (3%) or other reasons (17% for withdrawal or lack of renewal of consent and miscellaneous). No new safety issues were identified in a long-term analysis of serious adverse events. Estimated EFS at 8 yr was 81% and freedom from progression to AP/BC was 92%. Estimated OS was 85% at 8 yr, and 93% when only CML-related deaths and those prior to SCT were considered. Three events occurred in yr 8: 1 progression to AP/BC and 2 deaths unrelated to CML (chronic obstructive pulmonary disease [1]; pneumonia aspiration [1]). The annual rates of progression to AP/BC in yr 4 to 8 after initiation of therapy were 0.9%, 0.5%, 0%, 0%, &amp; 0.4%, respectively. Only 15 (3%) pts who achieved complete cytogenetic response (CCyR) progressed to AP/BC, all but 1 within 2 yr of achieving CCyR. BCR-ABL transcript numbers were monitored sequentially in 98 pts. Among these, the rate of major molecular response (MMR, &lt; 0.1% BCR-ABL/control gene ratio on international scale) increased from 24% at 6 months (mo) and 39% at 12 mo to a best observed MMR rate of 86% with current follow-up. None of the pts with documented MMR at 12 mo progressed to AP/BC. To establish the relationship between early cytogenetic response (CyR) status and subsequent outcomes during 8 yr of IM treatment, we compared the cumulative incidence of achieving stable CCyR (defined as CCyR without subsequent event) vs the probability of an event (as described above but excluding CML-unrelated deaths) according to levels of CyR at 3, 6, 12, &amp; 18 mo (Table 1). Pts with minor to partial CyR (&gt; 0–65% Ph+ metaphases) at 3 mo and those with partial CyR (PCyR; &gt; 0–35% Ph+ metaphases) at 6 &amp; 12 mo were more likely to achieve a stable CCyR than have an event. Among pts with less than CCyR at 18 mo, the probability of an event was comparable to the probability of achieving stable CCyR. Conclusions CML-CP pts responding to IM had a low overall risk of progression to AP/BC. Most AP/BC events occurred early, with minimal risk after yr 3 and no evidence for an increase over time. Minor CyR at 3, PCyR at 6 and 12, and CCyR at 18 mo were associated with stable CCyR over the observation period. The safety profile of IM remains unchanged after 8 yr, with no previously unreported AEs identified over the past 36 mo. These data suggest that pts responding to IM are likely to maintain their responses on long-term therapy and confirm a favorable risk-benefit ratio in CML-CP pts. Disclosures Deininger: Novartis: Consultancy; Bristol-Myers Squibb: Consultancy; Calistoga: Research Funding; Genzyme: Research Funding. O'Brien:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Wyeth: Research Funding. Guilhot:Novartis: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria. Goldman:Novartis: Honoraria, Speakers Bureau; Bristol-Myers Squibb: Honoraria, Speakers Bureau. Hochhaus:Novartis: Research Funding. Hughes:Bristol-Myers Squibb: Advisor, Honoraria, Research Funding; Novartis: Advisor, Honoraria, Research Funding. Radich:Novartis: Consultancy, Honoraria, Research Funding. Hatfield:Novartis: Employment, Equity Ownership, Patents &amp; Royalties. Mone:Novartis: Employment. Filian:Novartis: Employment. Reynolds:Novartis: Employment. Gathmann:Novartis: Employment. Larson:Novartis: Consultancy, Honoraria, Research Funding. Druker:OHSU patent #843 - Mutate ABL Kinase Domains: Patents &amp; Royalties; MolecularMD: Equity Ownership; Roche: Consultancy; Cylene Pharmaceuticals: Consultancy; Calistoga Pharmaceuticals: Consultancy; Avalon Pharmaceuticals: Consultancy; Ambit Biosciences: Consultancy; Millipore via Dana-Farber Cancer Institute: Patents &amp; Royalties; Novartis, ARIAD, Bristol-Myers Squibb: Research Funding.