Activity In Multiple Xenograft Models Research Articles

SGN-B7H4V, an investigational vedotin ADC directed to the immune checkpoint ligand B7-H4, shows promising activity in preclinical models

BackgroundSGN-B7H4V is a novel investigational vedotin antibody–drug conjugate (ADC) comprising a B7-H4-directed human monoclonal antibody conjugated to the cytotoxic payload monomethyl auristatin E (MMAE) via a protease-cleavable maleimidocaproyl valine citrulline...

Abstract 3941: TNG908 is an MTAPnull-selective PRMT5 inhibitor that drives tumor regressions in MTAP-deleted xenograft models across multiple histologies

Abstract TNG908 is an investigational PRMT5 inhibitor with a novel MTA-cooperative binding mechanism designed to leverage the synthetic lethal interaction between PRMT5 inhibition and MTAP deletion. MTAP deletion occurs in 10-15% of all human cancer representing multiple histologies. MTA is a negative regulator of PRMT5 that accumulates as a result of MTAP deletion. TNG908 selectively binds the PRMT5-MTA complex driving selective inhibition of PRMT5 in MTAP-null cancers, which is postulated to create a large therapeutic index relative to PRMT5 inhibitors currently in clinical development. TNG908 is 15X selective for MTAPnull cell lines over isogenic MTAPWT cell lines, and has marked selectivity for MTAP-deleted cancer cell lines independent of lineage in a large, diverse cell line panel. In vitro mechanistic studies confirm that MTAPnull-selective PRMT5 inhibitors can selectively target MTAPnull cancer cells in either an admixture of MTAPnull and MTAPWT cells, or with intracellular MTA accumulation 2-5X relative to basal levels in MTAPWT cells. Oral administration of TNG908 drives dose-dependent, MTAPnull-selective antitumor activity in multiple xenograft models, including tumor regressions in models representing non-small cell lung cancer (adenocarcinoma and squamous), cholangiocarcinoma, urothelial carcinoma, and others. Preclinical studies suggest clinical combinations that leverage PRMT5 biology and/or concurrent oncogenic driver mutations, such as KRASG12C. In summary, TNG908 is a novel, potent PRMT5 inhibitor with excellent drug-like properties and strong preclinical activity in multiple xenograft models that has the potential for histology-agnostic clinical development in MTAP-deleted solid tumors. Citation Format: Kimberly J. Briggs, Kevin M. Cottrell, Matthew R. Tonini, Erik W. Wilker, Lina Gu, Charles B. Davis, Minjie Zhang, Doug Whittington, Deepali Gotur, Matthew J. Goldstein, Heather DiBenedetto, Marc S. Rudoltz, Alan Huang, John P. Maxwell. TNG908 is an MTAPnull-selective PRMT5 inhibitor that drives tumor regressions in MTAP-deleted xenograft models across multiple histologies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3941.

Abstract 1533: IMGC936, a first-in-class ADAM9-targeting antibody-drug conjugate, demonstrates promising anti-tumor activity

Abstract Dysregulation of ADAM9, a member of the ADAM (a disintegrin and metalloproteinase) family of proteases, has been implicated in tumor progression and metastasis, as well as pathological neovascularization. ADAM9 overexpression correlates with poor prognosis in multiple cancers. We have shown that ADAM9 is overexpressed in multiple solid tumor indications and that anti-ADAM9 antibodies are efficiently internalized and degraded by tumor cell lines making ADAM9 an attractive target for antibody-drug conjugate (ADC) development. Here, we describe IMGC936, the first ADAM9-targeting ADC to enter preclinical development. IMGC936 is comprised of a high-affinity humanized antibody site-specifically conjugated to DM21, a next-generation linker-payload that combines a maytansinoid microtubule-disrupting payload with a stable peptide linker at a drug-antibody ratio of two. To maximize the potential for IMGC936 activity, the M252Y/S254T/T256E (YTE) mutation was introduced into the CH2 domain of the antibody to increase in vivo plasma half-life and exposure. In vitro studies demonstrated targeted cytotoxicity of IMGC936 across a panel of ADAM9-positve tumor cell lines with activity at least 2 logs greater than a non-targeting conjugate. Consistent with the in vitroactivity, an anti-ADAM9-DM21 conjugate displayed compelling anti-tumor activity in multiple xenograft models representing non-small cell lung, gastric and colorectal cancers. For example, in the EBC-1 non-small cell lung cancer subcutaneous xenograft model with only moderate ADAM9 expression (H-score of 130), anti-ADAM9-DM21 not only induced tumor growth delay but produced complete and durable remissions in 6/6 mice following a single intravenous dose of 8.6 mg Ab/kg (100 ug DM21/kg). IMGC936 demonstrated a favorable pharmacokinetic profile with good conjugate stability in non-human primates. Importantly, IMGC936 was well-tolerated following repeat dosing in cynomolgus monkeys with no ADAM9 target-related toxicities identified at doses exceeding the levels required for anti-tumor activity in murine xenograft models. Based on the totality of the preclinical data, IMGC936 represents a promising therapeutic candidate to target a wide range of ADAM9-expressing tumors. Citation Format: Stuart Hicks, Deryk Loo, Kerstin Sinkevicius, Juniper Scribner, Bhaswati Barat, Nicholas Yoder, Christopher Espelin, Marian Themeles, Francine Chen, Jacquelynn Lucas, Jennifer Brown, Bahar Matin, Megan Fuller, Jenny Lee, Paulin Salomon, Juliet Costoplus, Sadiqa Yancey, Gundo Diedrich, Sergey Gorlatov, Thomas Son, Michael Chiechi, Pam Li, Michael Spliedt, Valentina Ciccarone, Jeff Hooley, Nadia Gantt, James Tamura, Kerry Donahue, Paul Moore, Syd Johnson, Thomas Chittenden, Richard Gregory, Ezio Bonvini. IMGC936, a first-in-class ADAM9-targeting antibody-drug conjugate, demonstrates promising anti-tumor activity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1533.

Abstract P6-20-03: Tumor epichaperome expression using 124I PU-H71 PET (PU-PET) as a biomarker of response for PU-H71 plus nab-paclitaxel in HER2 negative (HER2-) metastatic breast cancer (MBC)

Abstract Background: The epichaperome is a new cancer target required for tumor survival (Joshi et al. Nature Reviews Cancer 2018). PU-H71 is a synthetic, purine scaffold epichaperome inhibitor that binds to the ATP-binding site of HSP90 specifically when HSP90 is integrated into the epichaperome (Rodina et al. Nature 2016). It has demonstrated antitumor activity in multiple xenograft models. Furthermore, sequential administration of nab-paclitaxel and PU-H71 in TNBC xenograft models augmented epichaperome levels, and in turn resulted in super-synergistic drug action with ablation of xenografted tumors and cures in mice. Methods: This is an open label phase1b study of PU-H71 + nab-paclitaxel in pts with HER2- MBC. Pts received nab-paclitaxel at a standard dose of 260mg/m2 IV Q 3weeks. PU-H71 was administered IV 6 hrs (+/-1 hr) post nab-paclitaxel Q3weeks in 2 escalating dose levels (225mg/m2 and 300 mg/m2). All pts underwent FDG PET/CT every 6 weeks. Additionally, patients had the option to enroll on a separate diagnostic PU-PET protocol to measure epichaperome expression prior to initiating treatment on the phase 1b study, wherein they received a single dose of up to 11mci of 124I-PU-H71 IV and underwent imaging at 3-4hrs and 20-24 hrs. Primary objective was to establish the MTD/RP2D of this regimen. Secondary objectives were to assess PK of PU-H71 + nab-paclitaxel and clinical efficacy. Exploratory analysis included correlation of epichaperome expression at baseline using PU-PET with tumor response. Results: 12 patients (5 ER+/HER2- ; 7 TNBC) were enrolled (6 at 225mg/m2 of PU-H71 and 6 at 300mg/m2). Median Age: 54 yrs (range: 37-71). Median ECOG: 0. Median lines of therapy in the metastatic setting: 6 (range 1-11) including prior taxanes in 75% of pts. Most common toxicities included diarrhea G1 58%; G2 7%, G3 7%) that was easily managed with anti-diarrheal agents, G1 fatigue (25%), G1/2 peripheral neuropathy (17%), G1 hyperglycemia (67%), G1 increases in alk phos (58%), AST (50%) and ALT (42%). Hematological toxicities included G3 leukopenia (42%), G3/4 neutropenia (67%), G3 anemia (50%) and G2 thrombocytopenia (17%). There were no DLTs. 33% (4/12) had PR, 58% (7/12) achieved SD with only 1 PD at the time of first scan; 5 pts are currently ongoing including 2 TNBC pts with PR who have been on therapy > 7 months. PK data will be presented. 8/12 patients also underwent PU-PET at baseline. A higher tumor to muscle SUV ratio at 24 hrs on PU-PET predicted response and increased PU-H71 retention on PU-PET at 24 hrs correlated with a longer duration of response. Conclusion: The RP2D of PU-H71 was 300mg/m2 with 260mg/m2 of nab-paclitaxel administered IV every 3 weeks. The regimen is well tolerated with promising clinical activity in this heavily pre-treated cohort. Tumor epichaperome expression at baseline using PU-PET has the potential to serve as a predictive biomarker of response. A Phase 2 trial of this combination along with baseline PU-PET is currently planned. Citation Format: Jhaveri K, Dunphy M, Wang R, Comen E, Fornier M, Moynahan ME, Bromberg J, Ma W, Patil S, Taldone T, Rodina A, Sterlin V, Khoshi S, Lewis J, Norton L, Chiosis G, Modi S. Tumor epichaperome expression using 124I PU-H71 PET (PU-PET) as a biomarker of response for PU-H71 plus nab-paclitaxel in HER2 negative (HER2-) metastatic breast cancer (MBC) [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P6-20-03.

Abstract 3961: Role for neuropilin1 in mode of action of chlorotoxin

Abstract Chlorotoxin is an established tumor targeting peptide that naturally occurs in scorpion venom. 131I-labelled chlorotoxin assessed in early phase human glioma clinical trials achieved promising results. A peptide drug conjugate (PDC) composed of chlorotoxin peptide linked to a cytotoxic payload (cryptophycin analog) was used as a tool to probe the tumor targeting mechanism of chlorotoxin. The PDC proved efficacious, yet differential sensitivity was observed in multiple human tumor models. Previously described chlorotoxin targets did not align with observed PDC activity; therefore, studies to further elucidate its mechanism were undertaken. PDC treatment of distinct xenograft models led to a wide range of antitumor activity even though similar levels of active metabolite were present in tumor lysates; thus it was hypothesized that a role for chlorotoxin in uptake may be relevant. We identified that the endocytic receptor Neuropilin1 (NRP1) binds to chlorotoxin peptide fragments following proteolytic digestion in vitro. NRP1 binding was selective for peptides with a free C-terminal arginine, while native chlorotoxin which has an amidated C-terminal arginine did not bind. Recovery of chlorotoxin from ex vivo tumor lysate revealed its metabolism to a carboxylated C-terminal arginine version of the peptide, capable of binding to NRP1. These data suggest that chlorotoxin acts as a cryptic peptide incapable of binding to NRP1 systemically and only when metabolized in the tumor microenvironment is NRP1 binding revealed. The expression level of human NRP1 in tumors correlated to the PDC antitumor activity in multiple xenograft models; a wider therapeutic window was observed when NRP1 was highly expressed. Reduction of NRP1 levels in vivo through administration of NRP1 blocking antibodies or by NRP1 knockout in tumor cells blunted PDC antitumor activity while not affecting activity of the cytotoxic payload alone. Reduced PDC antitumor activity correlated with significantly lower levels of active metabolite detected in NRP1-deficient tumors. Together, our findings suggest that chlorotoxin metabolized in the tumor microenvironment binds NRP1 on tumor cells to increase uptake of active metabolite into cells, resulting in enhanced antitumor activity. The identification of NRP1 as an uptake mechanism for chlorotoxin will enable selection of tumors for treatment with chlorotoxin-based therapeutics. Citation Format: Donna Kolber-Simonds, Jiayi Wu, Utpal Majumder, Daniel Custar, Danyang Li, Hong Du, Maarten H. Postema, Thomas Noland, Andrew Hart, George Lai, Sean Eckley, Vaishali Dixit, Karen Tendyke, Kenichi Nomoto, Mary Woodall-Jappe, Sharon McGonigle. Role for neuropilin1 in mode of action of chlorotoxin [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3961.

Abstract 3073: Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931

Abstract Cell division cycle 7 (CDC7) is a serine/threonine kinase, which plays important roles in initiation of DNA replication by phosphorylating MCM2. Kinase activity of CDC7 is controlled by its binding protein DBF4 in a cell-cycle dependent manner. Here we developed a potent CDC7 inhibitor TAK-931 (IC50< 0.3 nM) as a cancer therapeutic drug candidate, which exhibits a time-dependent ATP-competitive kinetics to its ATP-binding pocket. The selectivity studies using the 308 kinases revealed >120-fold selectivity of TAK-931 for CDC7 kinase inhibition compared to other kinase inhibitions. Treatment with TAK-931 suppressed the cellular MCM2 phosphorylation at Ser40, resulting in a delayed S phase progression, checkpoint activation, apoptosis, and potent growth suppression in various cancer cell lines. Furthermore, oral administration of TAK-931 as a single agent caused a significant antitumor activity in multiple xenograft models which include both cell line-based xenografts and patient-derived xenograft (PDX) models. These results demonstrate that TAK-931 is a highly potent and selective inhibitor of CDC7 kinase, and causes a potent antiproliferation both in vitro and in vivo studies using various cancer cells. Next, to identify potential predictive biomarkers to guide patient-selection strategies, in vitro cell panel screening of TAK-931 using was tested for its ability to antiproliferation in 246 cell lines, which includes both solid and hematological cancer cells. TAK-931 inhibited proliferation of multiple cancer cell lines, with mean concentration producing a half-maximal response (EC50) values ranging from 29.1 nM to > 30 μM (median = 554.5 nM). While the wide range of TAK-931 antiproliferative spectrum was observed, neither doubling speed nor CDC7 expression profile did predict tTAK-931 sensitivity in cancer cell lines. A correlative study of the tumor genetic mutations in relation to antiproliferative activity that KRAS mutant cancer cells were more sensitive to TAK-931 compared to KRAS non-mutant cell lines (p<0.05). We also confirmed this KRAS-associated antiproliferative effect of TAK-931 in the SW48 isogenic cell lines of KRAS mutations (G12V, G13D). The ectopic expressions of G12V- and G13D-KRAS mutations increased the TAK-931 sensitivity compared to the KRAS-wild parental SW48 cell line. Given that KRAS mutations are frequently detected in clinical pancreatic tumors, we next conducted in vivo efficacy studies using pancreatic PDX models. Consistent to our hypothesis from in vitro studies, KRAS-mutant pancreatic PDX tumors were more sensitive to TAK-931 than the KRAS-wild pancreatic tumors; all KRAS-mutant pancreatic PDX models we tested exhibited >60% TGI. Our findings suggest that the KRAS-mutant pancreatic tumors could be the potential candidate for the TAK-931 target indication. Citation Format: Kenichi Iwai, Tadahiro Nambu, Osamu Kurasawa, Noriko Uchiyama, Ryo Dairiki, Yukiko Yamamoto, Satoru Nishizawa, Mengkun Zhang, Yuko Ishii, Huifeng Niu, Akihiro Ohashi. Potential predictive biomarkers of clinical responses for a novel CDC7-selective inhibitor TAK-931 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3073. doi:10.1158/1538-7445.AM2017-3073

Abstract B100: ASN003, a unique B-RAF inhibitor with additional selective activity against PI3K and mTOR kinases, shows strong antitumor activity in multiple xenograft models

Abstract Various genes in RAS-RAF and PI3K pathways are frequently mutated in a wide variety of solid tumors. Concurrent double mutations are also observed quite often in a broad range of tumor types. Combined inhibition of both pathways has been shown to impart greater efficacy in multiple tumor models in animals. In order to simultaneously block these pathways, we have discovered and characterized several molecules showing dual inhibition of the RAS-RAF and PI3K pathways. ASN003 has been identified as a lead compound with potent and highly selective inhibitory activity against B-RAF, PI3K and mTOR kinases (low nM IC50). Within the PI3K family, ASN003 has high selectivity for inhibition of PI3Kα and PI3Kδ over PI3Kβ. In cell-based mechanistic studies, ASN003 did not increase phospho-ERK levels in the KRAS mutant cell line HCT116 and thus may not cause paradoxical activation of RAS/MAPK pathway in tumors. Consistent with its dual inhibition profile, ASN003 showed strong antiproliferative activity in cell lines with B-RAF and PI3K pathway mutations as well as vemurafenib (B-RAF inhibitor)-resistant cell lines. ASN003 suppressed the phosphorylation of downstream targets of B-RAF, PI3K and mTOR in pharmacodynamic studies in multiple tumor models, indicating appropriate target engagement. In in vivo efficacy studies, ASN003 showed regression in a B-RAFV600E mutant A375 xenograft model and also caused significant tumor growth inhibition in RKO and A2058 tumor models, which harbor mutations in PIK3CA or PTEN genes, respectively, in addition to the B-RAF V600E mutation. Dual targeting of the B-RAF and PI3K pathways with ASN003 has the potential to treat and/or prevent the acquired resistance to selective B-RAF inhibitors, and may also treat a broader patient population and provide greater efficacy and survival benefit than selective B-RAF inhibitors or selective PI3K pathway inhibitors alone. Due to the lack of paradoxical activation, treatment with ASN003 may not cause skin toxicities seen with pure B-RAF inhibitors. ASN003 is currently in preclinical development and is expected to enter Phase I/II clinical trials by early 2016. Citation Format: Scott K. Thompson, Mahaboobi Jaleel, Vijay Kumar Nyavanandi, Murali Ramachandra, Hosahalli Subramanya, Aravind Basavaraju, Vaibhav Sihorkar, Roger A. Smith, Niranjan Rao, Sandeep Gupta, Sanjeeva P. Reddy. ASN003, a unique B-RAF inhibitor with additional selective activity against PI3K and mTOR kinases, shows strong antitumor activity in multiple xenograft models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B100.

Abstract DDT02-02: BAY 1143572: A first-in-class, highly selective, potent and orally available inhibitor of PTEFb/CDK9 currently in Phase I, inhibits MYC and shows convincing anti-tumor activity in multiple xenograft models by the induction of apoptosis

Abstract PTEFb/CDK9 mediated transcription of short-lived anti-apoptotic survival proteins like MYC, a key oncogene in multiple tumors, plays a critical role in cancer cell growth and survival. In addition, these survival proteins exhibit important functions in the development of resistance to chemotherapy. In contrast to pan-CDK inhibitors which are currently evaluated in Phase I and II clinical trials, to our knowledge PTEFb selective inhibitors have not been explored for clinical utility. We report for the first time the preclinical profile and structure of BAY 1143572, a novel selective PTEFb/CDK9 inhibitor currently being investigated in a Phase I clinical trial. BAY 1143572 had potent and highly selective PTEFb-kinase inhibitory activity in the low nanomolar range against PTEFb/CDK9 and an at least 50-fold selectivity against other CDKs in enzymatic assays. Furthermore, BAY 1143572 showed a favorable selectivity against a panel of non-CDK kinases in vitro. The potent enzymatic activity on PTEFb translated into broad antiproliferative activity against a panel of tumor cell lines with sub-micromolar IC-50 values. In line with the proposed mode of action, a concentration-dependent inhibition of the phosphorylation of the RNA polymerase II and downstream reduction of MYC mRNA and protein levels was observed in vitro. This inhibition was accompanied by an induction of apoptosis in cellular assays. BAY 1143572 also showed single agent in vivo efficacy at tolerated doses in various xenograft tumor models in mice and rats upon once daily oral administration. Potent anti-tumor activity characterized with partial or even complete remissions could be documented in models showing different MYC gene alterations like amplifications and translocations. Treatment with BAY 1143572 resulted in a transient inhibition of intratumoral MYC mRNA and protein levels and an induction of apoptosis in these models. The inhibition of MYC mRNA was also observed in blood cells of BAY 1143572-treated rats indicating the potential clinical utility of MYC in blood cells as a pharmacodynamic marker in clinical development. The in vivo efficacy of BAY 1143572 was significantly enhanced in combination with several chemotherapeutics in different solid tumor models. These pharmacology data provided the rationale for the initiation of clinical development of BAY 1143572 in advanced cancer patients (NCT01938638). In conclusion, our data provide preclinical proof of concept for BAY 1143572 as a potent and highly selective inhibitor of PTEFb/CDK9 with first-in-class potential. Further clinical evaluation of BAY 1143572 for the treatment of cancers dependent on the transcription of the key oncogene MYC and other short-lived survival proteins is warranted. Citation Format: Arne Scholz, Ulrich Luecking, Gerhard Siemeister, Philip Lienau, Ulf Boemer, Peter Ellinghaus, Annette O. Walter, Ray Valencia, Stuart Ince, Franz von Nussbaum, Dominik Mumberg, Michael Brands, Karl Ziegelbauer. BAY 1143572: A first-in-class, highly selective, potent and orally available inhibitor of PTEFb/CDK9 currently in Phase I, inhibits MYC and shows convincing anti-tumor activity in multiple xenograft models by the induction of apoptosis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr DDT02-02. doi:10.1158/1538-7445.AM2015-DDT02-02

Abstract 2541: Preclinical results of SGN-CD19A in combination with R-ICE or R-CHOP in non-Hodgkin lymphoma models

Abstract SGN-CD19A is an antibody drug conjugate (ADC) that recognizes CD19, a B-cell specific marker expressed in B-cell malignancies including non-Hodgkin lymphoma (NHL). SGN-CD19A is currently in a phase I clinical trial for adult patients with relapsed refractory B-cell NHL (CT.gov NCT01786135) in which it has shown evidence of single-agent activity (1). This ADC binds CD19, internalizes, and releases cys-mcMMAF, which ultimately induces apoptosis in targeted cells (2). Lymphoma tumor xenografts treated with SGN-CD19A show growth delay in a dose dependent manner. Here we show that SGN-CD19A in combination with standard of care [rituximab/ifosfamide/carboplatin/etoposide (R-ICE), rituximab/cyclophosphamide/doxorubicin/vincristine/prednisone (R-CHOP), or components] exceeds the activity of SGN-CD19A alone and results in impressive anti-tumor activity in multiple xenograft models. It was notable that in some xenograft models, SGN-CD19A + R-CHOP or SGN-CD19A + R-ICE yielded activity that was similar to SGN-CD19A plus rituximab alone. This strong interaction between rituximab and SGN-CD19A was modeled in vitro. SGN-CD19A synergized with rituximab, in the absence of cross-linking, to cause decreased cell viability in NHL cell lines. These data suggest that cell autonomous signaling contributes to the unique interaction between rituximab and SGN-CD19A. Our in vivo and in vitro data support R-CHOP, R-ICE, or rituximab as viable combination therapies for NHL patients with SGN-CD19A. 1) Uma Borate et al. A first-in-human phase 1 study of the antibody-drug conjugate SGN-CD19A in relapsed or refractory B-lineage acute leukemia and highly aggressive lymphoma. Blood 2013 122:1437 2) Che-Leung Law et al. Preclinical characterization of an auristatin-based anti-CD19 drug conjugate, SGN-19A. Abstract number 625. In: Proceedings of the 102th Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Citation Format: Heather A. Van Epps, Kerry Klussman, Martha Anderson, Weiping Zeng, Devra Olson, Maureen Ryan, Tina Albertson, Che-Leung Law. Preclinical results of SGN-CD19A in combination with R-ICE or R-CHOP in non-Hodgkin lymphoma models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2541. doi:10.1158/1538-7445.AM2015-2541

Abstract DDT02-02: Identification of LY3009120 as a pan inhibitor of Raf isoforms and dimers with minimal paradoxical activation and activities against BRaf or Ras mutant tumor cells

Abstract Mutations in KRas, NRas, BRaf and NF-1 that activate the Ras and mitogen-activated protein kinase (MAPK) pathway are among the most common oncogenic drivers in many cancers, including melanoma, lung, colorectal, and pancreatic cancer. Two BRaf selective inhibitors, vemurafenib and dabrafenib, have been approved for the treatment of melanoma patients harboring the BRaf V600E/K mutation. However, both compounds have been reported to promote paradoxical MAPK pathway activation in BRaf wild-type cells through induction of active Raf dimers. Therefore, they are believed to be contraindicated for treatment of cancers with BRaf wild type background. In this study, we have identified and characterized a pyrido-pyrimidine derivative inhibitor of all three Raf isoforms. A whole-cell mass spectrum-based analysis revealed that LY3009120 binds to ARaf, BRaf and CRaf isoforms with similar affinity in cells with activating mutations of BRaf or KRas, while vemurafenib or dabrafenib have little or modest CRaf activity. Additionally, LY3009120 induces BRaf-CRaf heterodimerization, but inhibits the phosphorylation of downstream MEK and ERK, indicating that it effectively inhibits the kinase activity of BRaf-CRaf heterodimer. Due to its activity against the three Raf isoforms and dimer, LY3009120 induces minimal paradoxical pathway activation in NRas or KRas mutant cells. These unique pharmacological properties of LY3009120 further distinguish it from selective BRaf inhibitors by its physiologically-relevant activities against tumor cells with NRas or KRas mutations. LY3009120 inhibits MEK phosphorylation and cell proliferation in vitro, and exhibits anti-tumor activity in multiple xenograft models carrying mutations in BRaf, NRas or KRas. LY3009120 is also active against melanoma cells with acquired resistance to vemurafenib or dabrafenib in the setting of MAPK reactivation and cyclin D1 upregulation caused by RTK/Ras activation, BRaf splice variants, or NRas Q61K mutation. Collectively, our findings identify LY3009120 as a potentially best-in-class inhibitor of three Raf isoforms and Raf dimer, with activity against tumor cells with BRaf, NRas or KRas mutations, as well as melanoma cells with acquired resistance to current BRaf therapies. These unique features support investigation of LY3009120 in clinical studies. Citation Format: Sheng-Bin Peng, James Henry, Michael Kaufman, Wei-Ping Lu, Bryan D. Smith, Subha Vogeti, Scott Wise, Youyan Zhang, Robert Van Horn, Xiaoyi Zhang, Tinggui Yin, Vipin Yadav, Lysiane Huber, Lisa Kays, Jennie Walgren, Denis McCann, Phenil Patel, Sean Buchanan, Ilaria Conti, James J. Starling, Daniel L. Flynn. Identification of LY3009120 as a pan inhibitor of Raf isoforms and dimers with minimal paradoxical activation and activities against BRaf or Ras mutant tumor cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr DDT02-02. doi:10.1158/1538-7445.AM2014-DDT02-02

456P - Multicenter, Dose-Escalation Study of the Investigational Drug Tak-733, An Oral Mek inhibitor, in Patients (PTS) with Advanced Solid Tumors: Preliminary Phase 1 Results

ABSTRACT Background TAK-733 is an investigational, orally available, selective, non-ATP-competitive, allosteric inhibitor of MEK1/2 shown to have anti-tumor activity in multiple xenograft models. In this first-in-human ph 1 study (NCT00948467), we evaluated safety, pharmacokinetics (PK), pharmacodynamics (PD), maximum tolerated dose (MTD) and efficacy of TAK-733 in pts with advanced solid tumors. Methods Pts aged ≥18 y, with ECOG PS 0–2 and radiographically or clinically evaluable tumors were eligible. Pts received TAK-733 QD on d 1–21 in 28-d cycles; doses escalated in a modified 3 + 3 design based on dose-limiting toxicities (DLTs) in cycle 1 to determine MTD. Plasma and blood samples for PK and PD analysis were collected pre-dose on d 1, 8, 15 and 21 and post-dose d 1 and 21 in cycle 1. Results As of March 16, 2012, 44 pts median age 58 (range 24 - 75) and 50% male, received TAK-733 (dose mg, [n]: 0.2, [1]; 0.4, [1]; 0.8, [2]; 1.6, [2]; 3.2, [4]; 4.4, [4]; 6, [4]; 8.4, [9]; 11.8, [8]; 16, [9]). 2 pts had DLTs (11.8 and 16.0 mg; both Grade 3 acneiform rash); MTD has not been reached. Pts received a median of 2 cycles (range 1-11, 6 pts ≥6 cycles). Safety and PK data are shown in the table. Maximum inhibition (Emax) of ERK phosphorylationin peripheral blood lymphocytes ranged from 21-95% (TAK-733; 0.2-16 mg QD), median Emax were 63%, 78%, and 92% at 8.4, 11.8, and 16 mg, respectively. In 32 evaluable pts, 1 pt (16 mg dose) with melanoma (BRAF L597R) had partial response confirmed at cycle 6 (RECIST v1.1) and is still on treatment at cycle 8; 12 pts had a best response of stable disease. Conclusions These preliminary data indicate that TAK-733 is generally well tolerated and pharmacodynamically active with signs of anti-tumor activity in pts with advanced non-hematologic malignancies. Dose escalation is continuing to determine the MTD. AEs, NCI-CTCAE v4.0 N = 44 Drug-related AE, n (%) 37 (84) ≥15% Dermatitis acneiform 19 (43) Diarrhoea 8 (18) Grade ≥3 drug-related AE, n (%) 7 (16) ≥5% Dermatitis acneiform 2 (5) Creatine phosphokinase evaluation 2 (5) PK data N = 41 Tmax, h 3 T1/2, h 53 Disclosure P.M. LoRusso: Consultancy or advisory board (Millennium Pharmaceuticals Inc.), Research Funding (Millennium Pharmaceuticals Inc.). A. Ribas: Consultancy or advisory board (Millennium Pharmaceuticals Inc.), Honoraria (Millennium Pharmaceuticals Inc.). J.A. Sosman: Consultancy or advisory board (Millennium Pharmaceuticals Inc.), Honoraria (Millennium Pharmaceuticals Inc.). B. Chmielowski: Consultancy within past 2 years (GSK, Genentech, Prometheus, CytRx, Morphotek). Membership on Board of Directors, Speakers Bureau, Advisory Committee (BMS, Genentech, Prometheus). P. Lipman: Employment (Millennium Pharmaceuticals Inc.). X. Zhou: Employment (Millennium Pharmaceuticals Inc.). V. Bozon: Employment (Millennium Pharmaceuticals Inc.). All other authors have declared no conflicts of interest.

Abstract 2797: AMG 511, a potent and selective class I PI3K inhibitor, demonstrates anti-tumor activity in multiple xenograft models

Abstract Background: Constitutive activation of the phosphoinositide 3-kinases (PI3K) signaling pathway is a frequent event in many cancers and results in increased cell growth and survival. Therefore, PI3K is an attractive target for oncology. This study evaluated the correlation between the pharmacokinetics (PK) and pharmacodynamics (PD) of AMG 511, a potent and selective class I PI3K inhibitor, and anti-tumor activity in preclinical models of human cancer which harbor mutations in the PI3K pathway. Method: To determine the PD, PK, and efficacy relationship of AMG 511, U87 MG (PTEN null), HCT-116 (PI3K & KRAS mutant), or BT474 (PI3K mutant, HER2 amplified) tumor bearing mice were treated with up to 10 mpk AMG 511 daily by oral gavage. For tumor PD time course and dose response studies, AKT phosphorylation (pAKT) was measured using an electrochemiluminescence detection assay after a single-dose of AMG 511 in U87 MG tumor bearing mice. To determine in vivo efficacy, mice bearing established U87 MG, HCT-116, or BT474 tumors were treated daily and measured 2x/week. The mechanism of action of AMG 511 was determined by examining effects on cell proliferation (BrdU incorporation) and apoptosis (caspase staining) using a combination of immunohistochemistry and flow cytometry analyses of ex-vivo U87 MG xenograft tumors following treatment with AMG 511. Results: Inhibition of pAKT in U87 MG tumor tissue was associated with increased plasma concentration of AMG 511 after a single dose (EC50=59 ng/mL). Treatment with 0.3, 1, and 3 mpk AMG 511 inhibited pAKT in tumor tissue by 39, 81, and 92 %, respectively. Treatment with 10 mpk AMG 511 significantly inhibited pAKT up to 16 hrs (p<0.01). A dose-dependent inhibition of xenograft growth was observed with AMG 511 versus vehicle control in multiple tumor xenograft models with PI3K pathway mutations (p<0.03). Flow cytometry analysis demonstrated that AMG 511 treatment resulted in a dose-dependent decrease of BrdU incorporation in tumor and CD31 positive endothelial cells at peak and trough plasma levels (p<0.05). Immunohistochemical analysis confirmed that AMG 511 treatment induced tumor cell apoptosis as measured by caspase staining in U87 MG tumor samples. Conclusion: AMG 511 is a potent pan-PI3K inhibitor, which has significant anti-tumor activity in human tumor xenograft models which harbor PI3K pathway mutations. Tumor growth inhibition is the result of an increase in AMG 511 exposure, a reduction in PI3K signaling, an inhibition of tumor cell and endothelial cell proliferation and an induction of tumor cell apoptosis. These data together provide evidence for the potential clinical investigation of AMG 511 in patients whose tumors harbor mutations in the PI3K pathway. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2797. doi:1538-7445.AM2012-2797

Abstract LB-393: The cancer metabolism inhibitor MPC-9528 induces tumor regression in xenograft models with multiple dosing schedules by causing rapid and sustained reduction in tumor NAD

Abstract Introduction: MPC-9528 is a potent, selective, orally bioavailable inhibitor of nicotinamide phosphoribosyltransferase (Nampt), which catalyzes the rate-limiting step for NAD biosynthesis from nicotinamide. Inhibition of Nampt by MPC-9528 results in cell death as a consequence of NAD depletion and inhibition of ATP synthesis. MPC-9528 is a potent tumoricidal agent of cancer cell lines of diverse origin and shows anti-tumor activity in multiple xenograft models. Here we explore the determinants of efficacy in xenograft models by comparing the effects of MPC-9528 oral dosing schedules in terms of both tumor NAD depletion and survival. Methods: HT1080 human fibrosarcoma cells were implanted subcutaneously into athymic mice (nu/nu) for tumor studies. Dosing was initiated when median tumor volume was >100 mm3. MPC-9528 was dosed orally, either once weekly, once daily, or twice daily, for a total of two or three weeks. For pharmacodynamic (PD) studies, animals were dosed with MPC-9528 and tumors were collected at various times post-dosing for NAD determination by LC-MS/MS. Results: MPC-9528 (75 mg/kg) dosed once weekly for three weeks in a HT1080 xenograft model resulted in 75% tumor regression on study Day 23, 8 days after the last dose. The ED50 for anti-tumor activity with this schedule was 44 mg/kg and doses at or below 35 mg/kg showed no anti-tumor activity. All doses were equally well-tolerated with <10% change in median body weight. In the same model, MPC-9528 dosed once daily at 10 mg/kg or twice daily at 3 mg/kg for 14 days showed 91% and 92% tumor regression, respectively, by the end of dosing on study Day 15. Two animals in each of the MPC-9528 dose groups showed complete tumor regression. MPC-9528 (4 mg/kg) dosed twice daily resulted in complete tumor regression in 9 out of 10 animals. The plasma concentration versus time profiles of MPC-9528 dosed at 3, 10 or 75 mg/kg indicated that anti-tumor activity was not dependent on maximal concentration of the compound in blood or the total absorbed dose but rather on maintenance of compound concentration above a threshold efficacious concentration. PD studies revealed a rapid and sustained reduction of NAD in tumors from mice dosed with MPC-9528 and that the magnitude and kinetics of NAD change depended on the dose and schedule. Conclusions: MPC-9528 administration results in regression of tumors when plasma concentrations of compound are maintained above a threshold. MPC-9528 shows comparable efficacy when given intermittently, on a weekly schedule, or continuously on a once, or twice daily schedule. This unique attribute of MPC-9528 reflects its mechanism of action as a cell metabolism inhibitor that functions by inhibiting NAD synthesis in tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-393. doi:10.1158/1538-7445.AM2011-LB-393

Abstract 3573: A small molecule PLK1 inhibitor, MLN0905, yields broad anti-tumor activity in human xenograft tumor models, and synergizes with taxane therapy

Abstract PLK1 is a serine/threonine mitotic kinase that plays a key role in mitotic cell cycle progression, and its over-expression has been linked to poor patient prognosis. We have discovered a potent and selective small molecule inhibitor of PLK1, MLN0905, which reduces cell viability and inhibits cell proliferation in a broad range of human tumor cells. We explored the pharmacokinetic, pharmacodynamic, and anti-tumor properties on MLN0905 in human xenograft models grown in rodents. MLN0905 rapidly and extensively distributed to xenograft tumor with a high tumor-to-plasma exposure ratio. In human xenograft tumor tissue, MLN0905 modulates the pharmacodynamic biomarker phospho-Histone H3 (in a dose dependent fashion), enabling us to track pathway modulation in vivo. MLN0905 demonstrated robust anti-tumor activity (partial and complete responses) in a variety of solid and hematological human xenograft models, including cancers derived from colon (HCT-116, HT29), NSCLC (Calu-6), Ovarian (SKOV3), and Lymphoma (OCI-LY19, OCI-LY10, and the primary lymphoma PHTX-22L). Significant anti-tumor activity was observed when dosing on either a continuous (daily) or intermittent schedule, underscoring the dosing flexibility with this compound. In the SKOV3 and Calu-6 xenograft models, MLN0905 yielded a synergistic anti-tumor response when combined with the standard of care therapy Taxane. This is the first report of a PLK1 inhibitor synergizing with taxane therapy in vivo. In summary, our findings indicate MLN0905 has good drug-like pharmacokinetic properties, modulates the biomarker phospho-Histone H3, and yields significant anti-tumor activity in multiple xenograft models. These preclinical data support further evaluating MLN0905 as a novel anti-cancer agent. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3573. doi:10.1158/1538-7445.AM2011-3573

Phase Ib study of PTC299, a novel oral inhibitor of tumor VEGF expression, in patients with advanced cancer.

3041 Background: PTC299 is a novel, oral investigational drug designed to inhibit tumor expression of VEGF and other angiogenic cytokines. PTC299–administered alone or in combination with taxanes–has shown antitumor activity in multiple xenograft models of human cancers. Methods: A phase Ib study comprised 3 stages, each using a classic 3+3 design. In stage 1, monotherapy was given 4 weeks on and 2 weeks off using body-weight-adjusted BID dosing. In stage 2, monotherapy was given continuously with unit BID or TID dosing. In stage 3, PTC299 was given with docetaxel, 75 mg/m2. Treatment was given until disease progression. Safety, PK, and activity were assessed. Results: The study enrolled 27 subjects (9 males, 18 females) with median [range] age 59 [31-75] years, ECOG PS 0 (n=16) or 1 (n=11), 13 tumor types, and median [range] of prior therapies of 3 [0-8] to receive PTC299 in stage 1 (n=12), stage 2 (n=6), or stage 3 (n=9). Median [range] of time on treatment has been 10 [3-61+] weeks. No MTD was observed through the highest dose levels: stage 1, 1.2 mg/kg BID; stage 2, 120 mg TID; and stage 3, 100 mg TID. Adverse events were infrequent, usually grade 1, and not generally considered PTC299-related. No hypertension was observed. PTC299 PK were generally dose proportional, with rapid appearance of drug in plasma, Tmax of ∼4 hours, and an effective t1/2 of ∼12 hours. From day 1 to day 28 (stage 1) or day 42 (stage 2), PTC299 showed a ∼2-fold accumulation when dosed continuously. Trough plasma concentrations exceeded values associated with maximal preclinical antitumor activity. Decreases in circulating angiogenic VEGF and inflammatory cytokines (IL-6) were seen. Patients with thyroid cancer (n=2), chondrosarcoma (n=1), and head and neck cancers (n=3) remain on study with stable disease for 14+, 2.8+, 8+, 5.6+, 3.7+, and 2.6+ months respectively. Patients with other advanced cancers (n=5) completed the study with stable disease for 3.5-12 months. Conclusions: PTC299 monotherapy or combination therapy with docetaxel is generally well tolerated, achieves target plasma concentrations, and shows evidence of pharmacodynamic and clinical activity. Author Disclosure Employment or Leadership Position Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration PTC Therapeutics PTC Therapeutics

Abstract B146: XL388: A novel, selective, orally bioavailable mTORC1 and mTORC2 inhibitor that demonstrates pharmacodynamic and antitumor activity in multiple human cancer xenograft models

Abstract Background: The mTOR kinase exists in at least two distinct kinase complexes, mTORC1 and mTORC2 which collectively regulate cell growth, proliferation, survival, autophagy, and angiogenesis. Derivatives of the macrolide antibiotic rapamycin have shown encouraging clinical activity as cancer therapeutics; however, these molecules only partially inhibit mTORC1 and mTORC2 activity. Here we provide the first pre-clinical description of XL388, a selective and orally bioavailable small-molecule ATP-competitive inhibitor of mTORC1 and mTORC2 that demonstrates pharmacodynamic and anti-tumor activity in multiple human cancer xenograft models. Methods: The in vitro inhibition of mTORC1 and mTORC2 by XL388 was assayed using purified, recombinant mTOR/G L/raptor kinase and mTORC2 immunoprecipitated from cells, respectively. mTORC1 and mTORC2 substrate phosphorylation and pharmacodynamic activity were measured by phosphospecific immunoblot of lysates prepared from XL388-treated cancer cells or from xenograft tumor lysates prepared from XL388-treated animals. Cancer cell viability was determined by measuring cellular ATP concentrations or the disruption of cell membrane integrity. Synergy of XL388 with chemotherapeutics was measured by the combination index (CI) method as established by Chou and Talalay (1984). XL388 in vivo efficacy and pharmacodynamic studies were performed in nude mice bearing human tumor xenografts and dosed orally with XL388. Results and Conclusions: XL388 inhibits mTORC1 and mTORC2 in vitro with IC50 values of 8 nM and 166 nM, respectively. In MCF-7 cells, XL388 blocks mTORC1 phosphorylation of p70S6K (T389) with an IC50 value of 94 nM and blocks mTORC2 phosphorylation of AKT (S473) with an IC50 value of 350 nM. In vitro, XL388 inhibits the viability of solid and hematopoietic tumor cell lines when assayed as a single agent. XL388 also synergizes with chemotherapeutics in cell-based assays to block cell viability. When dosed orally once daily in mice, XL388 shows robust anti-tumor activity in multiple xenograft models including > 100% tumor growth inhibition in the MCF-7 xenograft model. Taken together, these data indicate that XL388 may have broad utility in cancer therapy both as a single agent and in combination with chemotherapeutics. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B146.

Abstract A103: Preliminary results of a phase 1 study of FP-1039 (FGFR1:Fc), a novel antagonist of multiple fibroblast growth factor (FGF) ligands, in patients with advanced malignancies

Abstract Background: The human fibroblast growth factor (FGF) axis is a complex system comprised of 22 ligands that bind to various combinations of 4 distinct cell surface receptors (FGFR1-4). FGFs have been demonstrated to be involved in tumor growth promotion, tumor angiogenesis, and in tumor stem cell maintenance. FP-1039 acts as a potent ligand “trap” that sequesters multiple FGF family ligands, neutralizing their ability to bind to and activate multiple FGF receptors. FP-1039 has anti-tumor activity in multiple xenograft models both as a single agent and in combination with other anticancer agents. Study Design: We report preliminary results of a first-in-human study of FP-1039 as a single agent in patients with advanced solid malignancies. Objectives were to characterize the safety, pharmacokinetics (PK), and immunogeneicity profiles of FP-1039. Characterization of preliminary anti-tumor activity and pharmacodynamic biomarkers were exploratory objectives. Subjects received 4 once-weekly intravenous doses of FP-1039, followed by a two week observation period. In the absence of either unacceptable toxicity or progressive disease, patients were eligible to receive additional weekly doses of FP-1039. Results: To date, a total of 15 subjects have received FP-1039 at doses ranging from 0.5–1.0 mg/kg. FP-1039 was generally well tolerated at doses of 0.5 and 0.75 mg/kg. A single dose limiting toxicity (DLT) was seen at 0.75 mg/kg and two at 1 mg/kg. The DLTs were clinically distinct, no consistent pattern related to drug exposure could be discerned and confounding factors were present. Further dose exploration is ongoing. PK analysis revealed a linear, dose-dependent increase in drug exposure in the plasma compartment typical of a large protein. Cohort mean terminal half-lives ranged from 63 to 102 hours, and appeared to be similar on Day 1 and Day 22. There was accumulation after 4 weekly doses of FP-1039. Transient, weak anti-drug antibody responses were seen in 4 of 12 subjects (33%) which were not associated with changes in PK or clinical sequelae. Free plasma FGF2 levels were assessed prior to initial dosing and at multiple subsequent timepoints. All subjects had elevated FGF2 levels prior to FP-1039 treatment compared to published levels in normal individuals. Preliminary analysis demonstrated a decrease in plasma levels of free FGF2 following FP-1039 treatment at all doses. Ten subjects completed the treatment period while 5 did not due to adverse events or rapidly progressive disease. By RECIST criteria, 6 subjects had stable disease. In one of these, a subject with castration-resistant prostate cancer and progressive disease despite docetaxel treatment, a reduction in FDG PET SUV on 2- and 6-week scans and a 20% decrease in tumor size by CT scan were demonstrated. Conclusions: FP-1039 appears to be well tolerated at doses of 0.5–0.75 mg/kg, and exploration of higher doses is in progress. Preliminary PK and target engagement data (reduction in FGF2) support a weekly or longer dosing interval. Preliminary single agent activity is promising. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):A103.

A phase I study of XL281, a selective oral RAF kinase inhibitor, in patients (Pts) with advanced solid tumors

3513 Background: XL281 is a potent and selective inhibitor of wild type and mutant RAF kinases showing anti-tumor activity in multiple xenograft models. Mutations in KRAS or BRAF can activate the RAF/MEK/ERK pathway in human tumors and may promote sensitivity to RAF kinase inhibitors. Methods: Pts were enrolled in successive cohorts of XL281 orally once daily on a 28-day cycle. Tumor response was assessed per RECIST every 8 wks. Plasma pharmacokinetic and pharmacodynamic samples were collected. The maximum tolerated dose (MTD) was expanded to 10 pts each with colorectal (CRC), melanoma, papillary thyroid (PTC) and NSCLC. Pre- and post-dose tumor and surrogate tissues were obtained. Biomarker and genotype analyses of pathway genes were performed. Results: The dose escalation phase is complete; 30 pts were treated with XL281. DLTs of fatigue, nausea, vomiting, and diarrhea were observed at the MAD (225 mg). The MTD is 150 mg. The most common related AEs included Grade 1/2, fatigue (48%), diarrhea (35%), nausea (35%), vomiting (35%) and anorexia (30%). Three pts had related AEs ≥G3: hypokalemia, nausea, and vomiting. One pt with an ocular melanoma demonstrated a cPR of 4 mos duration. Twelve pts had SD (3 -17+ mos), including 2 with I131-refractory PTC harboring BRAF V600E mutations (15+ and 17+ mos). Nine of these pts had decreases in target lesions (5–29%), including a pt with KRAS mutant CRC on study for 20 wks with marked symptomatic improvement. At the MTD, paired biopsies from 4 pts (3 melanoma, 1 NSCLC) show an average 72 % decrease in pMEK, 68 % decrease in pERK, 24 % decrease in Ki67 (proliferation) and 64 % increase in TUNEL (apoptosis). Three of 6 evaluable pts in the MTD cohort show SD at first assessment, including 1 melanoma pt with a NRAS Q61R mutation who showed a 20% decrease in target lesions. Conclusions: XL281 was generally well tolerated and the MTD was established at 150 mg. One cPR occurred in an ocular melanoma subject, and clinical benefit (PR or SD) occurred in 43% (13/30) of pts in the dose-escalation phase. XL281 demonstrates biological activity by modulation of the RAF pathway in tumor and surrogate tissue, with decreases in cell proliferation and increases in apoptosis. [Table: see text]