Abstract LB-296: Discovery and development of MEDI7247, a novel Pyrrolobenzodiazepine (PBD)-based antibody drug conjugate targeting ASCT2, for treating hematological and solid cancers

The sodium dependent neutral amino acid transporter, ASCT2/SLC1A5 is frequently overexpressed in cancer to sustain “glutamine addiction” of cancer cells and to meet their increased demand for energy and nutrients. High expression of ASCT2 is often associated with poor disease prognosis. Immuno-histochemistry (IHC) data from 600+ tumor samples suggest ASCT2 expression in hematologic and solid cancers, including MM, AML, and DLBCL (≥ 95% positive in respective tumor samples), as well as squamous cell carcinoma of the head and neck (SCCHN), non-small cell lung cancer (NSCLC), small cell lung cancer (SCLC), prostate, pancreatic, and colorectal cancer (66% to 95% positivity in respective tumors). Broad expression across various cancers and restricted expression in normal tissues warrant ASCT2 as an attractive candidate for an antibody drug conjugate. MEDI7247 is a novel investigational antibody-drug conjugate (ADC) comprising an anti-ASCT2 human monoclonal antibody site-specifically conjugated to pyrrolobenzodiazepine (PBD) dimer via a protease-cleavable linker, with a drug to antibody ratio (DAR) of 2. MEDI7247 specifically binds to cell surface ASCT2 while exhibiting no affinity to the other members of the family, including ASCT1. Following binding, MEDI7247 is internalized and trafficked to the lysosomes to subsequently release the PBD warhead. PBD enters the nucleus where it induces DNA damage and results in tumor cell death. MEDI7247 shows potent in vitro cytotoxicity in several human cancer cell lines expressing variable levels of ASCT2. Dose dependent in vivo efficacy of MEDI7247 was determined in solid tumor xenografts and disseminated hematological malignancy models. MEDI7247 is cross-reactive with cynomolgous monkey ASCT2 and shows similar binding and killing with cyno ASCT2 expressing cells. MEDI7247 demonstrated acceptable safety profile in toxicity studies with non-human primates to support first in human trials. Based on its combined efficacy and safety, MEDI7247 is in clinical development for the treatment of ASCT2 positive cancers.

Citation Format: Nabendu Pore, M Jack Borrok, Marlon Rebellato, MaryJane Hinrichs, Kevin P. Schifferli, Noel R. Monks, Ravinder Tammali, Ronald Herbst, Steven R. Coats, David A. Tice. Discovery and development of MEDI7247, a novel Pyrrolobenzodiazepine (PBD)-based antibody drug conjugate targeting ASCT2, for treating hematological and solid cancers [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 LB-296.

Abstract 759: Preclinical evaluation of a GFRA1 targeted antibody-drug conjugate in breast cancer

Despite recent advances in treatment, breast cancer remains the second-most common cause of cancer death among American women. A greater understanding of the molecular characteristics of individual tumors could ultimately lead to improved treatment options, particularly for subsets of breast cancer patients with unmet needs. Using an unbiased genomics approach to identify membrane-localized tumor associated antigens (TAAs), we have identified a novel breast cancer TAA that can potentially be exploited through antibody-drug conjugate (ADC) therapy. Here, we describe the development of a GFRA1-targeted ADC that demonstrates activity in GFRA1-positive cell lines and PDX tumor models. Work in non-Good Laboratory Practice (GLP) rat toxicology models revealed acceptable toxicity profiles and supports further evaluation of GFRA1-PBD in GFRA1-positive tumors.

Citation Format: Emily E. Bosco, Ronald J. Christie, Rosa Carrasco, Darrin Sabol, Jiping Zha, Karma DaCosta, Lee Brown, Sandrina Phipps, Qun Du, Binyam Bezabeh, Shannon Breen, Cui Chen, Molly Reed, MaryJane Hinrichs, Haihong Zhong, Zhan Xiao, Rakesh Dixit, Ronald Herbst, David A. Tice. Preclinical evaluation of a GFRA1 targeted antibody-drug conjugate in breast cancer [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 759.

Preclinical evaluation of a GFRA1 targeted antibody-drug conjugate in breast cancer

Despite recent advances in treatment, breast cancer remains the second-most common cause of cancer death among American women. A greater understanding of the molecular characteristics of breast tumors could ultimately lead to improved tumor-targeted treatment options, particularly for subsets of breast cancer patients with unmet needs. Using an unbiased genomics approach to uncover membrane-localized tumor-associated antigens (TAAs), we have identified glial cell line derived neurotrophic factor (GDNF) family receptor α 1 (GFRA1) as a breast cancer TAA. Immunohistochemistry (IHC) revealed that GFRA1 displays a limited normal tissue expression profile coupled with overexpression in specific breast cancer subsets. The cell surface localization as determined by fluorescence-activated cell sorting (FACS) and the rapid internalization kinetics of GFRA1 makes it an ideal target for therapeutic exploitation as an antibody-drug conjugate (ADC). Here, we describe the development of a pyrrolobenzodiazepine (PBD)-armed, GFRA1-targeted ADC that demonstrates cytotoxicity in GFRA1-positive cell lines and patient-derived xenograft (PDX) models. The safety profile of the rat cross-reactive GFRA1-PBD was assessed in a rat toxicology study to find transient cellularity reductions in the bone marrow and peripheral blood, consistent with known off-target effects of PBD ADC's. These studies reveal no evidence of on-target toxicity and support further evaluation of GFRA1-PBD in GFRA1-positive tumors.

Clinical performance of a specific algorithm to reconfirm self-terminating ventricular arrhythmias in current implantable cardioverter-defibrillators

Inappropriate shock therapy is a frequent problem in patients with implantable cardioverter-defibrillators (ICDs), caused mostly by supraventricular rhythms. Self-terminating ventricular arrhythmias (STVAs), however, may also lead to inappropriate shock discharges even in ICDs with abortive shock capabilities. The aim of this study was to evaluate the clinical performance of a specific ventricular tachycardia/ventricular fibrillation (VT/VF) reconfirmation algorithm implemented in current ICD devices from Medtronic to prevent inappropriate shock discharges due to STVAs. A total of 161 STVA episodes were documented in 59 of 150 patients (39%) within a mean follow-up of 30 +/- 20 months and resulted in 25 inappropriate shock discharges in 15 of 150 patients (10%) despite activation of the reconfirmation algorithm. The first synchronization interval of the algorithm was met in 92% of STVA episodes with and even 38% of STVA episodes without shock delivery. A reduced incidence of inappropriate shocks due to STVAs was found with tachycardia/fibrillation detection intervals (TDI/FDI) programmed to shorter cycle lengths < or =280 ms or the use of the first 2 cycles after the end of charging to be considered for reconfirmation only. Thus, inappropriate shocks due to STVAs still occur in 10% of patients with ICDs despite activation of a specific VT/VF reconfirmation algorithm, and are mainly caused by meeting the first synchronization interval that therefore should be shortened in cycle length. Moreover, to reduce the likelihood of inappropriate shocks, the VF reconfirmation algorithm should be optimized by basing the synchronization intervals exclusively on the FDI with short cycle lengths or using the first 2 cycles for reconfirmation only.

Genetic imbalances in precursor lesions of endometrial cancer detected by comparative genomic hybridization

Endometrial hyperplasia is regarded as a precursor lesion of endometrioid adenocarcinomas of the endometrium. The genetic events involved in the multistep process from normal endometrial glandular tissue to invasive endometrial carcinomas are primarily unknown. We chose endometrial hyperplasia as a model for identifying chromosomal aberrations occurring during carcinogenesis. Comparative genomic hybridization (CGH) was performed on 47 formalin-fixed, paraffin-embedded specimens of endometrial hyperplasia using the microdissection technique to increase the number of tumor cells in the samples and reduce contamination from normal cells. CGH analysis revealed that 24 out of 47 (51%) samples had detectable chromosomal imbalances, whereas 23 (49%) were in a genetically balanced state. The incidence of aberrant CGH profiles tended to parallel dysplasia grade, ranging from 22% aberrant profiles in simple hyperplasia to 67% in complex hyperplasia with atypia. The most frequent imbalances were 1p, 16p, and 20q underrepresentations and 4q overrepresentations. Copy number changes in 1p were more frequent in atypical complex hyperplasia than in complex lesions without atypical cells or simple lesions (42% versus 20% and 0%). Our results show that endometrial hyperplasia reveals recurrent chromosomal imbalances which tend to increase with the presence of atypical cells. The most frequent aberrations in endometrial cancer, 1q and 8q overrepresentations, are not present or are rare in its precursor lesions. This analysis provides evidence that tumorigenesis proceeds through the accumulation of a series of genetic alterations and suggests a stepwise mode of tumorigenesis.

Functional characterization of an extremely thermophilic ATPase in membranes of the crenarchaeon Acidianus ambivalens

A plasma membrane-bound adenosine triphosphatase with specific activities up to 0.2 micromol min(-1) (mg protein)(-1) at 80 degrees C was detected in the thermoacidophilic crenarchaeon Acidianus ambivalens (DSM 3772). The enzymatic activity exhibited a broad pH-optimum in the neutral range with two suboptima at pH 5.5 and 7.0, respectively. Sulfite activation resulted in only one pH optimum at 6.25. In the presence of the divalent cations Mg2+ and Mn2+ the ATPase activity was maximal. Remarkably, the hydrolytic rates of GTP and ITP were substantially higher than for ATP. ADP and pyrophosphate were only hydrolyzed with small rates, whereas AMP was not hydrolyzed at all. Both activities could be weakly inhibited by the classical F-type ATPase inhibitor N,N'-dicyclohexylcarbodiimide, whereas azide had no influence at all. The classical inhibitor of V-type ATPases, nitrate, also exerted a small inhibitory effect. The strongly specific V-type ATPase inhibitor concanamycin A, however, showed no effect at all. The P-type ATPase inhibitor vanadate had no inhibitory effect on the ATPase activity at pH 7.0, whereas a remarkable inhibition at high concentrations could be observed for the activity at pH 5.5. Arrhenius plots for both membrane bound ATPase activities were linear up to 95 degrees C, reflecting the enormous thermostability of the enzyme.

Detection of myocardial injury during transvenous implantation of automatic cardioverter-defibrillators

OBJECTIVES

The present study was designed to assess the extent of myocardial injury in patients undergoing transvenous implantation of an automatic implantable cardioverter-defibrillator (ICD) using cardiac troponin I (cTNI), which is a highly specific marker of structural cardiac injury.

BACKGROUND

During ICD implantation, repetitive induction and termination of ventricular fibrillation (VF) via endocardial direct current shocks is required to demonstrate the correct function of the device. Transthoracic electrical shocks can cause myocardial cell injury.

METHODS

Measurements of total creatine kinase (CK), CK-MB, myoglobin, cardiac troponin T (cTNT) and cTNI were obtained before and after ICD implantation in 49 consecutive patients. Blood samples were drawn before and 2, 4, 8, and 24 h after implantation.

RESULTS

Elevations of CK, CK-MB, myoglobin, cTNT and cTNI above cut-off level were found in 25%, 6%, 76%, 37% and 14% of patients, respectively, with peak cTNI concentrations ranging from 1.7 to 5.5 ng/ml. Cumulative defibrillation energy (DFE), mean DFE, cumulative VF time, number of shocks as well as prior myocardial infarction (MI) were found to be significantly related to a rise of cTNI. Mean DFE > or = 18 J and a recent MI were identified as strong risk factors for cTNI rise.

CONCLUSIONS

During transvenous ICD implantation myocardial injury as assessed by cTNI rise occurs in about 14% of the patients. Peak cTNI concentrations are only minimally elevated reflecting subtle myocardial cell damage. Patients with a recent MI and a mean DFE > or = 18 J seem to be prone to cTNI rise.

[The results of strontium-90 contact therapy to prevent the recurrence of pterygium]

AIM

Aim of the study was the evaluation of the role of adjuvant radiation therapy in the prevention of recurrence after excision.

PATIENTS AND METHODS

Between July 1, 1985 and April 1, 1993, 64 patients (43 male, 21 female) were referred to radiation therapy after excision of a nasal pterygium. Radiation therapy was done with a strontium-90 eye applicator and a total dose of 30 Gy, fractionated in 6 fractions of 5 Gy each, 3 times a week. Forty-nine patients were treated primarily, 15 patients underwent radiation therapy for the first time in case of recurrent pterygium after multiple re-excisions. All patients had a following of 1 to 9 years with a median of 5.5 years.

RESULTS

In 8 of 64 irradiated patients recurrent pterygium was detected (12.5%). Differentiated into the 2 groups 4 of the primarily treated patients had recurrent pterygium (8.16%), the other 4 were in the group with multiple former re-excisions (26.7%). With regard to the initiation of the irradiation after surgery pterygium did not recur in any of the primarily treated patients who were irradiated in between 3 days after surgery. In contrary 3 of 7 primarily treated patients (42.9%) who started radiation therapy between 7 and 10 days after surgery had recurrent pterygium. For the patients with primarily recurrent pterygium no dependence of the initiation of radiation therapy after surgery could be detected.

CONCLUSIONS

Adjuvant radiation therapy after excision of pterygium lowers the rate of recurrence from about 40% to 12.5%, in a primarily adjuvant situation to 8.16%. In these patients radiation therapy should be initiated within 3 days after surgery. Patients with primarily recurrent pterygium have an elevated risk of recurrence independently of the initiation of radiation therapy.

Results of adjuvant radiation therapy after surgical excision of pterygium

The aim of the present study was the evaluation of the role of adjuvant radiation therapy in the prevention of recurrence after excision. Between July 1, 1985, and April 1, 1993, 64 patients (43 men, 21 women) were referred for radiation therapy after excision of a nasal pterygium. All patients were followed for 1-9 years (median 5.5 years). Radiation therapy was done with a strontium 90 eye applicator at a total dose of 30 Gy fractionated into six fractions of 5 Gy each. In all, 49 patients were treated after their first excision and 15 patients had undergone multiple prior excisions. In 8 of 64 irradiated patients, recurrent pterygium was detected (12.5%); 4 recurrences developed after first excision and adjuvant radiation therapy (8.16%) and the other 4, following multiple former reexcisions and radiotherapy (26.7%). Pterygium did not recur in any of the primarily treated patients who were irradiated within 3 days of surgery. In contrast, 3 of 7 accordingly treated patients (42.9%) who started radiation therapy at between 7 and 10 days after surgery developed recurrent pterygium. Adjuvant radiation therapy after excision of pterygium lowers the overall rate of recurrence to 12.5%. In an adjuvant situation after first excision, radiation therapy should be initiated within 3 days of surgery, the result being freedom from recurrence.