Targeting CD74 in B-cell non-Hodgkin lymphoma with the antibody-drug conjugate STRO-001

Overexpression of CD74, a type II transmembrane glycoprotein involved in MHC class II antigen presentation, has been reported in many B-cell non-Hodgkin lymphomas (NHLs) and in multiple myeloma (MM). STRO-001 is a site-specific, predominantly single-species antibody-drug conjugate (ADC) that targets CD74 and has demonstrated efficacy in xenograft models of MM and tolerability in non-human primates. Here we report results of preclinical studies designed to elucidate the potential role of STRO-001 in B-cell NHL. STRO-001 displayed nanomolar and sub-nanomolar cytotoxicity in 88% (15/17) of cancer cell lines tested. STRO-001 showed potent cytotoxicity on proliferating B cells while limited cytotoxicity was observed on naïve human B cells. A linear dose-response relationship was demonstrated in vivo for DLBCL models SU-DHL-6 and U2932. Tumor regression was induced at doses less than 5 mg/kg, while maximal activity with complete cures were observed starting at 10 mg/kg. In MCL Mino and Jeko-1 xenografts, STRO-001 starting at 3 mg/kg significantly prolonged survival or induced tumor regression, respectively, leading to tumor eradication in both models. In summary, high CD74 expression levels in tumors, nanomolar cellular potency, and significant anti-tumor in DLBCL and MCL xenograft models support the ongoing clinical study of STRO-001 in patients with B-cell NHL.

Abstract CT125: STRO-002-GM1, a first in human, phase 1 study of STRO-002, an anti-folate receptor alpha (FRα) antibody drug conjugate (ADC), in patients with advanced platinum-resistant/refractory epithelial ovarian cancer (OC), including fallopian tube or primary peritoneal cancers

Introduction: FRα is overexpressed in 80% of OC with minimal expression in normal tissues. STRO-002 is a novel FRα-targeting ADC designed to circumvent limitations of current ADCs. STRO-002 was generated with a cell-free antibody production system (XpressCF™) and site-specific conjugation (XpressCF+™) platform. STRO-002 has a DAR of 4 and contains the tubulin-targeting 3-aminophenyl hemiasterlin warhead SC209, a potent cytotoxin that is rapidly cleared and a weak substrate for P-gp efflux pumps. STRO-002 demonstrated potent cytotoxic activity in multiple FRα-positive tumor cell lines and significant efficacy in OC xenograft models. Herein we report the results of our dose escalation study of STRO-002 in patients (pts) with OC. Methods: STRO-002-GM1 is a Phase I, open-label, multicenter, dose escalation study with dose expansion to identify the maximum tolerated dose (MTD), and recommended Phase II dose (RP2D) in pts with advanced, platinum resistant or refractory OC. There is no patient selection based on FRα expression. STRO-002 is given IV on Day 1 of each 21-day cycle (C) until disease progression. Ocular exams are performed at baseline and every other cycle. No prophylactic corticosteroid eye drops are used. Results: 20 pts have been dosed & 18 pts have completed at least 1 cycle of STRO-002 at 7 dose levels: 0.5, 1.0, 1.8, 2.9, 4.3, 5.2 and 6.0 mg/kg. Median age is 60.5 (r, 48-70). Median ECOG status is 0 (r, 0-1). Median # of prior therapies is 6 (r, 2-10). 55% of pts have prior PARP inhibitors, 85% have prior bevacizumab. Median # of STRO-002 cycles is 3 (r, 1-15). One DLT of grade 3 neuropathy was reported at the 6.0 mg/kg dose level. Two patients have experienced grade 4 neutropenia, an expected and reversible side effect of STRO-002 treatment. 92% of AEs are grade 1 or 2. The most common TEAEs in ≥ 30 % of pts includes fatigue, nausea, decreased appetite and dizziness. No ocular findings have been observed. Emerging PK profile: after 1 hour infusion, total antibody concentrations declined in a log-linear manner with a 22-84 h half-life, dose-exposure relationship appeared linear without accumulation after repeat administration. Six pts have discontinued due to disease progression. 14 pts remain on treatment and dose escalation is ongoing. One patient has achieved a confirmed partial response (PR); 2 patients have confirmed stable disease (cSD) at C5, 2 pts have cSD at C7 and 1 pt has cSD at C13; 3 patients have achieved a confirmed CA-125 response. Conclusions: STRO-002 is the first hemiasterlin-containing ADC generated with cell-free protein synthesis technology to be tested in pts with solid tumors. The preliminary safety profile and evidence of efficacy and clinical benefit in the first 20 OC pts treated with STRO-002 is encouraging, particularly in this heavily pre-treated, platinum resistant/refractory patient population. No ocular toxicity signals have been observed. MTD has not been reached. Updated results and the recommended phase 2 dose will be presented. This study is registered with clinicaltrials.gov identifier NCT03748186.

Citation Format: R. Wendel Naumann, Denise Uyar, John W. Moroney, Fadi S. Braiteh, Russell J. Schilder, John P. Diaz, Erika Hamilton, Sami Diab, Lainie P. Martin, David M. O'Malley, Richard T. Penson, Clifford DiLea, Michael Palumbo, Venita DeAlmeida, Shannon Matheny, Arturo Molina. STRO-002-GM1, a first in human, phase 1 study of STRO-002, an anti-folate receptor alpha (FRα) antibody drug conjugate (ADC), in patients with advanced platinum-resistant/refractory epithelial ovarian cancer (OC), including fallopian tube or primary peritoneal cancers [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT125.

Targeting CD74 in multiple myeloma with the novel, site-specific antibody-drug conjugate STRO-001

STRO-001 is a site-specific, predominantly single-species, fully human, aglycosylated anti-CD74 antibody-drug conjugate incorporating a non-cleavable linker-maytansinoid warhead with a drug-antibody ratio of 2 which was produced by a novel cell-free antibody synthesis platform. We examined the potential pharmacodynamics and anti-tumor effects of STRO-001 in multiple myeloma (MM). CD74 expression was assessed in MM cell lines and primary bone marrow (BM) MM biopsies. CD74 mRNA was detectable in CD138+ enriched plasma cells from 100% (892/892) of patients with newly diagnosed MM. Immunohistochemistry confirmed CD74 expression in 35/36 BM biopsies from patients with newly diagnosed and relapsed/refractory MM. Cytotoxicity assays demonstrated nanomolar STRO-001 potency in 4/6 MM cell lines. In ARP-1 and MM.1S tumor-bearing mice, repeat STRO-001 dosing provided significant antitumor activity with eradication of malignant hCD138+ BM plasma cells and prolonged survival. In a luciferase-expressing MM.1S xenograft model, dose-dependent STRO-001 efficacy was confirmed using bioluminescent imaging and BM tumor burden quantification. Consistent with the intended pharmacodynamic effect, STRO-001 induced dose-responsive, reversible B-cell and monocyte depletion in cynomolgus monkeys, up to a maximum tolerated 10 mg/kg, with no evidence of off-target toxicity. Collectively, these data suggest that STRO-001 is a promising therapeutic agent for the treatment of MM.

Abstract 742: Nonclinical safety evaluation of STRO-001, a site-specific anti-CD74 antibody-drug conjugate for the potential treatment of B-cell malignancies

Antibody-drug conjugates (ADCs) constitute an expanding class of therapeutic molecules in preclinical and clinical development for multiple oncology indications. These antibody-based therapeutics are designed to selectively deliver cytotoxic payloads to tumor targets to improve efficacy and minimize toxicity. Cluster of differentiation 74 (CD74), a membrane-bound glycoprotein, is an antigen amenable ADC targeting because of its low expression in normal tissues and over expression in B-cell malignancies (multiple myeloma and non-Hodgkin's Lymphoma). STRO-001, a well-defined, homogenous, and site-specific ADC, is comprised of maytansinoid cytotoxic drugs conjugated to an anti-CD74 aglycosylated antibody (SP7219) through a noncleavable linker at two engineered non-natural amino acids. In an in vitro immunological activation assay, STRO-001 did not elicit cytokine production when incubated with human PBMCs for 48 hours, suggesting a low risk for immunological response in cancer patients. In a tissue cross-reactivity study with human tissues, STRO-001-specific membranous staining was detected primarily in lymphoid organs and lymphocytic infiltrates in multiple non-lymphoid tissues. In an exploratory nonclinical safety study in cynomolgus monkeys, a pharmacologically relevant model for toxicity testing, STRO-001 was tolerated at 1, 3, and 10 mg/kg, but not at 30 mg/kg, when intravenously administered on days 1 and 15 followed by a 4-week observation period. Dose-dependent and transient decreases in B-cells and monocytes were observed at tolerated doses (on-target pharmacology), with no effects on NK/T-cells. At tolerated doses, the main findings included reversible toxicities to hematopoietic and lymphoid tissues that correlated with cytopenias. Hematopoietic toxicity is considered antigen-independent, clinically manageable, and consistent with that of other ADCs with similar payloads. Toxicokinetic analysis confirmed drug exposures (total antibody, ADC, and a prominent linker-maytansine catabolite) with evidence of non-linearity suggesting target-dependent clearance. In summary, STRO-001 ADC has a favorable nonclinical safety profile and Phase I study of STRO-001 in patients with B-cell malignancies is planned.

Citation Format: Willy Solis, Venita De Almeida, Abigail Yu, Maureen Bruhns, James Zawada, Adam Galan, Shannon Matheny, Arturo Molina, Trevor Hallam, Mark Lupher. Nonclinical safety evaluation of STRO-001, a site-specific anti-CD74 antibody-drug conjugate for the potential treatment of B-cell malignancies [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 742.

Abstract 67: Characterization and preclinical development of STRO-001, a novel CD74-targeting antibody-drug conjugate (ADC) for the treatment of B-cell malignancies

CD74 is a type II transmembrane glycoprotein involved in the formation and transport of MHC class II protein. CD74 is highly expressed in many B-cell malignancies with limited expression in normal tissues (Stein R. et al., CCR 2007). STRO-001 is a novel CD74-targeting ADC containing an anti-CD74 aglycosylated human IgG1 antibody (SP7219) conjugated to a non-cleavable dibenzocyclooctyne (DBCO)-maytansinoid linker-warhead. SP7219 was discovered from a Fab ribosome display library based on Sutro’s Xpress CFTM technology. Highly efficient site-specific conjugation enabled by our cell-free antibody production and click chemistry results in a well-defined homogeneous ADC drug product with a drug-antibody ratio (DAR) of 2. Conjugation sites were selected based on highest stability both in vitro and in vivo, thereby limiting loss of drug moiety from STRO-001 in circulation. Due to its limited cell permeability, the major catabolite released by STRO-001 has 1000X lower cell killing activity on CD74 positive and negative cells compared to the reference cytotoxic maytansine. In vitro cytotoxicity assays show potent activity of STRO-001 in a diverse panel of B-cell tumor lines including 4 multiple myeloma (MM), 9 germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL), 3 activated B-cell (ABC) DLBCL, and 3 mantle cell lymphoma (MCL) cell lines with IC50 ranging from 0.17-20 nM. CD74 cell surface expression is required for STRO-001 cytotoxic activity but expression level, as measured by antibody-binding capacity, does not correlate with in vitro potency (R2=0.4640). STRO-001 inhibits the formation of visceral tumors (p<0.004) and prevents growth of CD138+ plasma cells in bone marrow (BM) after 4 weekly doses of 3 mg/kg in the ARP-1 disseminated MM xenograft model. STRO-001 dosed at 3 mg/kg weekly x 3 also eradicates malignant BM plasma cells (p<0.0001) and prolongs survival in the MM.1S disseminated model (100% animals alive at >90 days). STRO-001 exhibits dose-dependent tumor growth inhibition in SU-DHL-6 xenografts starting at 2.5 mg/kg weekly x 3 doses. The combination of bendamustine/rituximab (BR) + STRO-001 further improves tumor suppression in SU-DHL-6 xenografts compared to vehicle (p = 0.002) or BR alone (p = 0.02). Preliminary studies with a MCL xenograft model, Jeko-1, demonstrate potent anti-tumor activity compared to vehicle (p<0.0001) starting at a single STRO-001 dose of 3 mg/kg, with ongoing tumor stasis up to 21 days after treatment. STRO-001 reduces normal B-cells in cynomologous monkeys, providing pharmacodynamic evidence of B-cell targeting. Based on these encouraging observations, STRO-001 is advancing to IND-enabling studies for the treatment of CD74-expressing B-cell malignancies.

Citation Format: Cristina Abrahams, Xiaofan Li, Venita DeAlmeida, Millicent Embry, Abigail Yu, Stellanie Krim, Heidi Hoffmann, James Zawada, Maureen Bruhns, Shannon Matheny, Stuart Bussell, Toni Kline, Alice Yam, Ryan Stafford, Trevor Hallam, Mark Lupher, Arturo Molina. Characterization and preclinical development of STRO-001, a novel CD74-targeting antibody-drug conjugate (ADC) for the treatment of B-cell malignancies [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 67. doi:10.1158/1538-7445.AM2017-67

A Highly Sensitive and Quantitative Test Platform for Detection of NSCLC EGFR Mutations in Urine and Plasma

INTRODUCTION

In approximately 60% of patients with NSCLC who are receiving EGFR tyrosine kinase inhibitors, resistance develops through the acquisition of EGFR T790M mutation. We aimed to demonstrate that a highly sensitive and quantitative next-generation sequencing analysis of EGFR mutations from urine and plasma specimens is feasible.

METHODS

Short footprint mutation enrichment next-generation sequencing assays were used to interrogate EGFR activating mutations and the T790M resistance mutation in urine or plasma specimens from patients enrolled in TIGER-X (NCT01526928), a phase 1/2 clinical study of rociletinib in previously treated patients with EGFR mutant-positive advanced NSCLC.

RESULTS

Of 63 patients, 60 had evaluable tissue specimens. When the tissue result was used as a reference, the sensitivity of EGFR mutation detection in urine was 72% (34 of 47 specimens) for T790M, 75% (12 of 16) for L858R, and 67% (28 of 42) for exon 19 deletions. With specimens that met a recommended volume of 90 to 100 mL, the sensitivity was 93% (13 of 14 specimens) for T790M, 80% (four of five) for L858R, and 83% (10 of 12) for exon 19 deletions. A comparable sensitivity of EGFR mutation detection was observed in plasma: 93% (38 of 41 specimens) for T790M, 100% (17 of 17) for L858R, and 87% (34 of 39) for exon 19 deletions. Together, urine and plasma testing identified 12 additional T790M-positive cases that were either undetectable or inadequate by tissue test. In nine patients monitored while receiving treatment with rociletinib, a rapid decrease in urine T790M levels was observed by day 21.

CONCLUSIONS

DNA derived from NSCLC tumors can be detected with high sensitivity in urine and plasma, enabling diagnostic detection and monitoring of therapeutic response from these noninvasive "liquid biopsy" samples.

Assessment of EGFR Mutation Status in Matched Plasma and Tumor Tissue of NSCLC Patients from a Phase I Study of Rociletinib (CO-1686)

PURPOSE

The evaluation of plasma testing for the EGFR resistance mutation T790M in NSCLC patients has not been broadly explored. We investigated the detection of EGFR activating and T790M mutations in matched tumor tissue and plasma, mostly from patients with acquired resistance to first-generation EGFR inhibitors.

EXPERIMENTAL DESIGN

Samples were obtained from two studies, an observational study and a phase I trial of rociletinib, a mutant-selective inhibitor of EGFR that targets both activating mutations and T790M. Plasma testing was performed with the cobas EGFR plasma test and BEAMing.

RESULTS

The positive percent agreement (PPA) between cobas plasma and tumor results was 73% (55/75) for activating mutations and 64% (21/33) for T790M. The PPA between BEAMing plasma and tumor results was 82% (49/60) for activating mutations and 73% (33/45) for T790M. Presence of extrathoracic (M1b) versus intrathoracic (M1a/M0) disease was found to be strongly associated with ability to identify EGFR mutations in plasma (P < 0.001). Rociletinib objective response rates (ORR) were 52% [95% confidence interval (CI), 31 - 74%] for cobas tumor T790M-positive and 44% (95% CI, 25 - 63%) for BEAMing plasma T790M-positive patients. A drop in plasma-mutant EGFR levels to ≤10 molecules/mL was seen by day 21 of treatment in 7 of 8 patients with documented partial response.

CONCLUSIONS

These findings suggest the cobas and BEAMing plasma tests can be useful tools for noninvasive assessment and monitoring of the T790M resistance mutation in NSCLC, and could complement tumor testing by identifying T790M mutations missed because of tumor heterogeneity or biopsy inadequacy. Clin Cancer Res; 22(10); 2386-95. ©2016 AACR.

Abstract A31: Assessment of EGFR mutations in matched urine, plasma and tumor tissue in NSCLC patients treated with rociletinib (CO-1686)

Background: The acquisition of suitable tumor tissue is a challenge for a significant fraction of late-stage NSCLC patients who require EGFR testing to inform choice of therapy. An alternative for these patients could be the assessment of EGFR mutations in circulating tumor DNA (ctDNA). In this study, we examined the detection of EGFR T790M mutation in ctDNA from urine, assessed urine sample requirements, and compared the results with contemporaneously matched tumor tissue and plasma in TIGER-X (NCT01526928), a Phase 1/2 clinical study of rociletinib in previously treated mutant EGFR patients with advanced NSCLC. Rociletinib is an oral, potent, small-molecule irreversible tyrosine kinase inhibitor that selectively targets mutant forms of EGFR, including T790M, L858R and Del(19), while sparing wild-type EGFR.

Methods: 63 Stage IIIB/IV NSCLC patients enrolled in either Phase 1 or 2 components of TIGER-X and representing all therapeutic dose groups consented to optional urine collection. Maximum sample volumes were 100 mL for urine and 2 mL for plasma. To maximize assay sensitivity in urine, samples containing the recommended sample volume of ≥90 mL (≥ 90% of maximum in this study) were evaluated; all samples received were processed to assess this recommendation. Urinary and plasma ctDNA were tested for mutations by the same EGFR assays using a sensitive and quantitative short footprint assay method that employs a mutation enrichment step followed by next generation sequencing.

Results: Urine volumes ranged from 8-100 mL with a median DNA yield of 313 ng (N = 63). The median DNA yield was 299 ng for urine specimens with volume &lt;90 mL (N = 44) and 392 ng for specimens with the previously recommended volume of ≥90 mL (N = 19). 45/63 patients (71%) were positive for T790M by urine in comparison to 47/63 (75%) by central lab testing of tissue. Using tissue as the reference, the positive percent agreement (PPA) between urine and tumor T790M test results was 93% (13/14) using urine samples with volumes ≥90 mL and 73% (34/47) when the urine volume was &lt;90 mL. The PPA between plasma and tissue T790M test results was 80% (42/51). Overall, there were 13 cases that were tumor T790M+/urine T790M-, and 7 cases that were urine T790M+/tumor T790M-. Six urine T790M+/tumor T790M- cases were also T790M+ in plasma. Two additional urine T790M+ cases could not be analyzed by the tumor test due to insufficient material. Serially matched urine and plasma assessments were performed on a subset of patients (N = 15). In most cases, the urine and plasma serial profiles mirrored one another. A rapid drop in urine and plasma mutant EGFR levels was seen in almost all patients who experienced clinical benefit from rociletinib.

Conclusions: The analysis of ctDNA from urine identified a similar proportion of T790M+ patients as tissue-based testing with highest PPA amongst patients with urine volumes ≥90 mL. Discordant samples between urine and tissue that were not identified by the tumor test may be explained by tumor heterogeneity and/or inadequate biopsy. EGFR mutation detection from urine increases with urine volume and DNA yields and should be considered as a viable approach, particularly when tumor tissue is not available. Lastly, monitoring urine ctDNA T790M mutations longitudinally with baseline and post-therapy sampling could be clinically useful to determine benefit from therapy.

Citation Format: Shirish Gadgeel, Chris Karlovich, Vlada Melnikova, Lecia V. Sequist, D. Ross Camidge, Heather Wakelee, Maurice Perol, Geoffrey R. Oxnard, Karena Kosco, Cecile Rose T. Vibat, Elaina Mann, Shannon Matheny, Lindsey Rolfe, Mitch Raponi, Mark G. Erlander, Karen Reckamp. Assessment of EGFR mutations in matched urine, plasma and tumor tissue in NSCLC patients treated with rociletinib (CO-1686). [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 A31.

Abstract 927: Pretreatment and serial plasma assessments of EGFR mutations in NSCLC patients treated with rociletinib (CO-1686)

Background:

EGFR mutation testing is required to identify patients who may respond to TKI therapy. However, tumor biopsies from NSCLC patients can pose challenges for molecular analyses due to inadequate sample material, the inability to biopsy patients due to poor health status or inaccessible lesions, and tumor heterogeneity. We examined the detection of EGFR mutations in circulating cell-free DNA (cfDNA) from plasma and the concordance of EGFR mutation status with contemporaneously matched tumor tissue in TIGER-X, a Phase 1/2 clinical study of rociletinib (CO-1686) in previously treated advanced NSCLC patients harboring EGFR mutations in their tumors. Rociletinib is an oral, potent, small-molecule irreversible tyrosine kinase inhibitor that selectively targets mutant forms of EGFR, including T790M, L858R and Del(19), while sparing wild-type EGFR.

Methods:

Pretreatment matched tumor tissue and plasma from 139 Stage IIIB/IV NSCLC patients enrolled in TIGER-X were evaluated for EGFR status. Tumor tissue was processed as FFPE and tested by allele-specific PCR. Plasma was tested as a two mL aliquot using BEAMing, a quantitative and sensitive detection technology based on digital PCR.

Results:

Using tissue as the reference, the positive percent agreement between tumor and BEAMing plasma test results was 86% (102/119) for activating mutations and 77% (78/101) for T790M. Four plasma samples of the 23 tumor T790M+/plasma T790M- cases were also tested by three independent plasma testing platforms with claimed analytical sensitivities of &lt;10 molecules/mL. All four plasma cases were T790M- by each test method. Of the 139 patients evaluated, there were 14 cases that were tumor T790M-/plasma T790M+. Seven of these were retested by a second plasma test platform, and five were confirmed as positive. The remaining two were near the limit of detection by BEAMing. Nine tumor samples from the plasma T790M+ cases could not be analyzed due to insufficient material. Clinical characteristics positively associated with the ability to identify EGFR mutations in plasma included M1b disease and higher tumor burden. Serial plasma assessments were performed on a subset of patients. A drop in plasma mutant EGFR levels to ≤10 molecules/mL was seen by Day 21 of treatment in 7 of 8 patients assessed who eventually experienced a PR. Re-emergence of the EGFR activating mutation in plasma, consistent with development of acquired resistance to rociletinib, was observed as early as 12 weeks prior to clinical progression by RECIST.

Conclusions:

The BEAMing plasma test identified EGFR mutations detected in tumor with high sensitivity. In addition, plasma testing identified T790M+ patients that were determined T790M- by the tumor test, which may be in part explained by tumor heterogeneity and/or inadequate biopsy. These findings demonstrate that BEAMing can be a useful tool for the non-invasive assessment of EGFR mutations in NSCLC.

Citation Format: Jonathan W. Goldman, Chris Karlovich, Elaina Mann, Lindsey Rolfe, Shannon Matheny, Darrin Despain, Philipp Angenendt, Claudia Stamm, Heather A. Wakelee, Jean-Charles Soria, Benjamin Solomon, D. R. Camidge, Rafal Dziadziuszko, Leora Horn, Shirish Gadgeel, Mitch Raponi, Andrew R. Allen, Lecia V. Sequist. Pretreatment and serial plasma assessments of EGFR mutations in NSCLC patients treated with rociletinib (CO-1686). [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 927. doi:10.1158/1538-7445.AM2015-927

BAI1 regulates spatial learning and synaptic plasticity in the hippocampus

Synaptic plasticity is the ability of synapses to modulate the strength of neuronal connections; however, the molecular factors that regulate this feature are incompletely understood. Here, we demonstrated that mice lacking brain-specific angiogenesis inhibitor 1 (BAI1) have severe deficits in hippocampus-dependent spatial learning and memory that are accompanied by enhanced long-term potentiation (LTP), impaired long-term depression (LTD), and a thinning of the postsynaptic density (PSD) at hippocampal synapses. We showed that compared with WT animals, mice lacking Bai1 exhibit reduced protein levels of the canonical PSD component PSD-95 in the brain, which stems from protein destabilization. We determined that BAI1 prevents PSD-95 polyubiquitination and degradation through an interaction with murine double minute 2 (MDM2), the E3 ubiquitin ligase that regulates PSD-95 stability. Restoration of PSD-95 expression in hippocampal neurons in BAI1-deficient mice by viral gene therapy was sufficient to compensate for Bai1 loss and rescued deficits in synaptic plasticity. Together, our results reveal that interaction of BAI1 with MDM2 in the brain modulates PSD-95 levels and thereby regulates synaptic plasticity. Moreover, these results suggest that targeting this pathway has therapeutic potential for a variety of neurological disorders.

Response to androgen signaling (AS)-directed therapy after treatment with abiraterone acetate (AA) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC): Post hoc analysis of study COU-AA-302

21

Background: In study COU-AA-302 of men with mCRPC and no prior chemotherapy, AA plus prednisone (hereafter AA) significantly increased radiographic progression-free survival. There is limited information about response to subsequent AS-directed therapies following AA. In this post hoc analysis of pts who received AA during study COU-AA-302, we evaluated clinical response to subsequent AA or enzalutamide (ENZ). Methods: In COU-AA-302, 546 pts were randomized and received AA. Subsequent response and discontinuation data from 88 pts receiving AS-directed therapy after study were collected retrospectively, source verified, and entered into the database. Median time to prostate-specific antigen (PSA) progression with 95% confidence intervals was estimated using the Kaplan-Meier method. Results: As of May 2013, following AA on study, 55 pts received subsequent AA and 33 received subsequent ENZ. 69% (38/55) of pts in the AA then AA group and 67% (22/33) pts in the AA then ENZ group received intervening chemotherapy. Baseline patient characteristics were similar across both groups and to the overall COU-AA-302 population. Median (range) exposure to subsequent therapy was 4 (1-20) months for AA and 5 (1-12) months for ENZ. Response to subsequent AA or ENZ is summarized in the Table. Conclusions: In this post hoc analysis, pts previously treated with AA experienced modest clinical response on subsequent treatment with either AA or ENZ. These data support further studies of subsequent AS-targeted drugs following treatment with AA for mCRPC. Clinical trial information: NCT00887198. [Table: see text]

Relationship of baseline PSA and degree of PSA decline to radiographic progression-free survival (rPFS) in patients with chemotherapy-naive metastatic castration-resistant prostate cancer (mCRPC): Results from COU-AA-302

5010

Background: Abiraterone acetate (AA), an androgen biosynthesis inhibitor, prolongs overall survival (OS) in mCRPC patients and is approved for use in this population. The relationship of PSA kinetics to rPFS was evaluated in an exploratory analysis of patients from COU-AA-302, a randomized phase III study of AA in chemotherapy-naive mCRPC patients. Methods: 1,088 patients were randomized 1:1 to AA (1 g) + prednisone (P) (5 mg BID) or P alone. rPFS and OS were co-primary endpoints. rPFS was defined as time to first occurrence of bone scan progression by PCWG2 criteria, progression by CT/MRI by modified RECIST 1.0 criteria, or death from any cause; PSA changes were not a factor in determining rPFS. Quartiles of baseline PSA and % PSA decrease from baseline to nadir were analyzed. Stratified Cox regression models were used with factors for treatment, PSA outcomes, and baseline covariates performed at 55% of OS events. Results: 54/546 patients (10%) in AA + P arm achieved undetectable PSA vs 14/542 patients (3%) in the P arm; at median follow-up of 27.1 mos, radiographic progression was observed in 28% (AA + P) vs 50% of patients (P). There was a consistent trend of decreasing hazard of progression with decreasing baseline PSA and increasing % PSA decline (Table). Treatment effect of AA + P vs P with decreasing baseline PSA or % PSA decline remained significant (p=0.001) after adjusting for other factors (PSA, LDH, alk phos, hemoglobin, bone metastasis) in the model. Conclusions: rPFS was positively associated with the magnitude of PSA decline and inversely associated with baseline PSA. These effects remained after correcting for covariates. In all analyses, treatment with AA led to rPFS outcomes superior to P. Clinical trial information: NCT00887198. [Table: see text]

Randomized double-blind, comparative study of abiraterone acetate (AA) plus low-dose prednisone (P) plus androgen deprivation therapy (ADT) versus ADT alone in newly diagnosed, high-risk, metastatic hormone-naive prostate cancer (mHNPC)

TPS5097

Background: Patients (pts) who initially present with metastatic prostate cancer (MPC) (up to 30% of men in Europe; 4% in US) typically progress to metastatic castration-resistant prostate cancer (mCRPC) with a poor prognosis. Prognostic factors impacting survival include high PSA concentration, high Gleason score, high volume of metastatic disease, and bone symptoms. AA decreases testosterone via CYP17 inhibition and is approved for treatment of mCRPC before and after docetaxel-based chemotherapy. Two recent reports (J Clin Oncol. 2012: 30 [suppl. abstr 4521 and 4556]) showed that AA + P in addition to ADT (LHRH agonist) in the neoadjuvant setting led to higher rates of undetectable PSA and complete pathologic response (cPR) or near-cPR in pts undergoing prostatectomy for high risk-localized prostate cancer than with ADT alone, suggesting a potential role for inhibiting extragonadal androgen synthesis prior to emergence of castration-resistance. Because of its benefit in mCRPC, as well as early activity in high risk-localized prostate cancer, AA is being evaluated in high risk mHNPC. Methods: Approximately 1,270 men with newly diagnosed (within 3 months of randomization) high risk mHNPC with at least 2 of 3 high risk factors (≥ 3 bone lesions, presence of visceral metastases or Gleason score ≥ 8) are being randomized to AA 1000 mg + P 5 mg daily + ADT or ADT alone. Pts are stratified by presence of visceral disease and ECOG PS (0-1 vs 2). Distant metastatic disease must be documented by positive bone scan or CT/MRI. ADT or orchiectomy within 3 mos of randomization is allowed. Continued use of anti-androgens after randomization is not allowed on study. The primary endpoint is overall survival. Secondary endpoints include radiographic PFS, time to next skeletal-related event, PSA progression, and subsequent therapy. Two interim analyses and a final analysis are planned. 300 sites from 36 countries will participate. As of February 4, 2013, one patient has entered screening. Clinical trial information: NCT01715285.

Ambulatory diagnoses-cluster statistics of patient visits at a clinic in the Amazon Region of Ecuador

INTRODUCTION

Mondana Clinic is a small rural clinic located in the Napo river region of the Amazon basin in Ecuador. Since its opening in 1997 the clinic has grown to be the primary health care facility for approximately 3000 individuals.

METHODS

A retrospective study was performed tabulating the ambulatory diagnosis, age, sex, and domicile of patients over a 9 month period in 1999.

RESULTS

During the study period there were 765 patient visits that resulted in at least one diagnosis. Of the patient visits, 175 (22.8%) resulted in multiple diagnoses. Women accounted for 58% of the patient visits, which is similar to the 60% of ambulatory patient visits made in the USA by women. The age distribution showed 66% of patients were under 25 years of age. When comparing diagnoses of males with females, several differences were noted. As expected, urinary tract infections were approximately four-fold more common in females than in males. Gastritis and headaches were also more common reasons for patient visits in the female population than in the male. Conversely, lacerations, abrasions, and contusions ranked higher in the male than in the female population for patient visits.

CONCLUSION

This study is the first to provide public health information for this region that will prove useful to the health professionals and funding agencies working in the region. Furthermore, it provides a baseline for comparison with other regions in Ecuador and South America in general, as well as comparisons with data-rich countries such as the USA.

The problem of emesis during oral glucose-electrolytes therapy given from the onset of severe cholera

In an attempt to obviate the need for intravenous fluids by preventing dehydration, 57 adult volunteers who experienced induced clinical cholera during a vaccine development programme were treated from the onset of diarrhoea with oral glucose-electrolytes therapy. 44 individuals with mild to moderately profuse diarrhoea (less than 8 L. total volume) were maintained in normal water and electrolyte balance with oral therapy alone. 13 individuals with severe diarrhoea (greater than 8 L. total volume) could not be maintained in balance with oral therapy alone, due chiefly to emesis during the first day of illness. Emesis occurred in the absence of significant dehydration or acidosis. Since emesis precludes effective early oral therapy in severe cases, domiciliary oral therapy is unlikely to eliminate cholera mortality. Rural diarrhoea treatment centres using oral therapy with limited amounts of intravenous fluids when needed, could reduce case fatality from cholera and related diarrhoeas virtually to zero with least expense.