News

STRO-001 – Publication Highlights

December 4, 2018

Pan Pacific Lymphoma, 2018

HIGH FREQUENCY OF CD74 EXPRESSION IN B-CELL NON-HODGKIN’S LYMPHOMA (NHL) AND TARGETING WITH STRO-001, A NOVEL ANTI-CD74 ANTIBODY DRUG CONJUGATE (ADC) WITH POTENT IN VITROCYTOTOXICTY AND IN VIVOANTI-TUMOR ACTIVITY

A Yu1, C Abrahams1, M Embry1, X Li1, S Zhao2, R Henningsen1, V DeAlmeida1, S Matheny1, T Kline1, A Yam1, R Stafford1, Y Natkunam2, T Hallam1, M Lupher1, A Molina1

1Sutro Biopharma, 2Stanford University Department of Pathology

Objective:

Generation and analysis of STRO-001, a novel, homogenous antibody drug conjugate (ADC) comprised of a human aglycosylated anti-CD74 IgG1 antibody (SP7219) with site-specific conjugation of a non-cleavable maytansinoid linker-warhead. CD74 is an attractive target for treatment of B cell malignancies.

Methods:

Tissue samples from the Department of Pathology at Stanford University were used to evaluate CD74 expression by biotinylated SP7219 via immunohistochemistry (IHC). The binding affinity of SP7219 to recombinant human CD74 ECD (extracellular domain) and cynomolgus monkey (cyno) CD74 ECD was measured using a Biacore T200. Flow cytometry was used for measuring CD74 expression in NHL cell lines. STRO-001 was used to determine the EC50and percent span of killing in NHL cell lines. The anti-tumor activity of STRO-001 in NHL xenografts in severe combined immune deficient (SCID) mice was examined.

Results:

Anti-CD74 antibody SP7219 binds to both human and cyno CD74 ECD with high affinity (KD=0.85nM for human, KD=2.4nM for cyno).CD74 expression was observed in 404/423 (96%) of all B cell lymphomas tested: 135/140 (96%) diffuse large B-cell lymphoma (DLBCL), 148/151 (98%) follicular lymphoma and 19/21 (90%) mantle cell lymphoma (MCL), 32/35 (91%) marginal zone lymphoma, 36/36 (100%) small lymphocytic lymphoma/chronic lymphocytic leukemia and 5/5 (100%) lymphoplasmacytic lymphoma samples. In vitrocytotoxicity assays show potent activity of STRO-001 in a diverse panel of B-cell tumor lines with EC50values ranging from 0.17-13 nM. STRO-001 exhibits dose-dependent tumor growth inhibition in rituximab-resistant germinal center B-cell-like (GCB)-DLBCL SU-DHL-6 xenografts. STRO-001+bendamustine/rituximab (BR) further improves tumor suppression in SU-DHL-6 xenografts compared to vehicle (p = 0.002) or BR alone (p = 0.02). In the activated B-cell (ABC)-DLBCL U2932 model, single doses of STRO-001 produce dose-dependent growth inhibition at 1 and 3 mg/kg and complete tumor regression at 10 mg/kg in 7/7 animals with no tumor re-growth up to > 90 days post-treatment.  Studies with an MCL model, Jeko-1, demonstrate robust STRO-001 anti-tumor activity compared to vehicle (p < 0.0001) starting at a single 3 mg/kg dose, with a single 10 mg/kg dose resulting in tumor regression for up to 64 days post treatment. STRO-001 treatment 14 days post tumor inoculation was used to evaluate disease progression in the disseminated Mino MCL model. Vehicle-treated animals developed advanced disease with median survival of 81 days. In contrast, all Mino xenografts treated with STRO-001 at 3 mg/kg or 10 mg/kg were alive and disease-free at sacrifice, 135 days post tumor inoculation.

Conclusions:

CD74 is expressed with high frequency and intensity in DLBCL, follicular lymphoma and MCL, supporting the investigation of novel biologics targeting this antigen.  STRO-001 demonstrates potent in vitrocytotoxicity in multiple NHL cell lines and anti-tumor activity in GCB-DLBCL, ABC-DLBCL and mantle cell lymphoma xenograft models, including prolongation of survival in the disseminated Mino MCL model and prevention of tumor regrowth in the U2932 ABC-DLBCL and Jeko-1 MCL subcutaneous models.  Clinical studies of this novel ADC for treatment of B-cell malignancies are ongoing.

 

ASCO 2018 Trials in Progress Poster

J Clin Oncol 36, 2018 (suppl; abstr TPS7586)

A phase 1 open-label, safety, pharmacokinetic, and preliminary efficacy study of STRO-001, an anti-CD74 antibody drug conjugate, in patients with advanced B-cell malignancies.

Amrita Y. Krishnan, Nina Shah, Alexander I. Spira, Jonathan L. Kaufman, Ruben Niesvizky, Nirav Niranjan Shah, John M. Burke, Leslie Popplewell, Thomas G. Martin, Julee Cheung, Shannon L. Matheny, John Paul Leonard, Arturo Molina; City of Hope, Duarte, CA; University of California, San Francisco, San Francisco, CA; Virginia Cancer Specialists, Fairfax, VA; Winship Cancer Institute of Emory University, Atlanta, GA; New York Presbyterian Hospital-Cornell Campus, New York, NY; Medical College of Wisconsin, Milwaukee, WI; Rocky Mountain Cancer Centers, Aurora, CO; University of California at San Francisco, San Francisco, CA; Sutro Biopharma, South San Francisco, CA; Sutro Biopharma, South San Francisco, CA; Weill Cornell Medical College, New York-Presbyterian Hospital, New York, NY

Background:

Sutro’s cell-free antibody production system was used to make STRO-001, a novel CD74 targeting antibody drug conjugate. CD74 is expressed on B cells throughout differentiation, and is an attractive target for treatment of B cell malignancies. STRO-001 demonstrates potent cytotoxicity in non-Hodgkin lymphoma (NHL) and multiple myeloma (MM) cell lines and anti-tumor activity in xenograft models. Toxicology studies demonstrate dose-dependent B-cell depletion and reversible hematologic toxicity when STRO-001 is administered at up to 10 mg/kg.

Methods:

This study is a first-in-human Phase 1, open-label, multicenter, dose escalation (Part 1) study with dose expansion (Part 2) to identify the maximum tolerated dose (MTD), recommended phase 2 doses (RP2D) and to evaluate the safety, tolerability, and preliminary anti-tumor activity of STRO-001 in adults with B-cell malignancies (MM and NHL) who are refractory to, or intolerant of, all therapy known to provide clinical benefit. STRO-001 is given to all patients on study via intravenous infusion on Day 1 and Day 15 of each cycle until disease progression. Dose limiting toxicities will be assessed in the first cycle (Days 1-28) of dose escalation. In Part 1, 2 cohorts (1 for MM and 1 for NHL) will enroll 30 patients each to determine the MTD and RP2D for expansion while Part 2 will enroll 4 cohorts based on disease subtypes (MM, diffuse large B cell, mantle cell and follicular lymphomas). Efficacy will be evaluated per MM-specific or NHL-specific criteria. Key inclusion criteria include relapsed or relapsed/refractory disease, adequate bone marrow and renal function, and ability to comply with treatment, testing and pharmacokinetic (PK) schedules. NHL patients must have at least one measurable lesion. Key exclusion criteria include leukemic manifestations of lymphoma, need for ongoing anti-coagulants or immunotherapy including systemic corticosteroids and a history of CNS involvement. Samples will be collected to assess the PK and immunogenicity. No formal statistical hypothesis testing will be conducted in this study. This study is currently open for enrollment in the US. Clinical trial information: NCT03424603

https://meetinglibrary.asco.org/record/165482/abstract

 

EHA, NHL, 2017

STRO-001, A NOVEL ANTI-CD74 ANTIBODY DRUG CONJUGATE (ADC) FOR TREATMENT OF B-CELL NON-HODGKIN’S LYMPHOMA (NHL)

Author(s): Abigail Yu, Cristina Abrahams, Millicent Embry, Xiaofan Li, Venita DeAlmeida, John Lee, Shannon Matheny, Toni Kline, Alice Yam, Ryan Stafford, Trevor Hallam, Mark Lupher, Arturo Molina

Background:

CD74 is a type II transmembrane glycoprotein involved in the formation and transport of MHC class II protein. CD74 is rapidly internalized and 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 comprised of a p-azido-methyl-phenylalanine (pAMF)-containing anti-CD74 aglycosylated human IgG1 antibody (SP7219) conjugated to a non-cleavable dibenzocyclooctyne (DBCO)-maytansinoid linker-warhead. Highly efficient site-specific conjugation enabled by Sutro’s cell-free antibody production and click chemistry produced a well-defined homogeneous ADC with a drug-antibody ratio (DAR) of 2. 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 a reference cytotoxic maytansine. Since 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, this novel ADC has potential for improved PK, safety and activity profiles.

Aims:

The aim of this study was to investigate the therapeutic potential of STRO-001 in non-Hodgkin’s lymphoma (NHL) cell lines and xenografts. A dose-escalating exploratory toxicology study was also conducted in cynomolgus monkeys.

Methods:

Biotinylated SP7219 was used for immunohistochemistry (IHC). DBCO-Alexa647-conjugated SP7219 and flow cytometry were used for detection and quantitation of CD74 expression on NHL cell lines and B-cells from normal human donors. STRO-001 was used to determine the EC50and percent span of killing in NHL cell lines. The anti-tumor activity of STRO-001 in SCID mice bearing NHL tumor cell xenografts was examined. STRO-001 was administered to cynomolgus monkeys in an exploratory dose-escalating study of repeat IV doses of 1, 3, 10 and 30 mg/kg on days 1 and 15.

Results:

Expression of CD74 in different lymphoma subtypes was evaluated by IHC on duplicate core (matched pair) biopsies. Medium to high CD74 expression in >70% of cells was observed in 86/100 diffuse large B-cell (DLBCL), 22/28 follicular lymphoma and 49/78 mantle cell lymphoma (MCL) samples. In vitrocytotoxicity assays show potent activity of STRO-001 in a diverse panel of B-cell tumor lines including 9 germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL), 3 activated B-cell (ABC) DLBCL, and 4 mantle cell lymphoma (MCL) cell lines with EC50values ranging from 0.17-13 nM. STRO-001 has only modest effects on naïve B-cells, but exhibits more potent cell killing in activated human B-cells that have upregulated CD74 expression (similar CD74 expression as SU-DHL-6 cell line). 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=0.4154). STRO-001 exhibits dose-dependent tumor growth inhibition in rituximab-resistant SU-DHL-6 xenografts starting at 2.5 mg/kg weekly x 3 doses. The standard of care 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). 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 a single 10 mg/kg dose resulting in tumor regression for up to 64 days post treatment. STRO-001 treatment 14 days post tumor inoculation was used to evaluate disease progression in Mino, a slow growing disseminated MCL xenograft model. Vehicle-treated animals developed advanced disease with palpable tumors and distended abdomens, with median survival of 81.3 days. In contrast, Mino xenografts treated with STRO-001 at 3 mg/kg or 10 mg/kg exhibited improved survival, with most animals healthy and disease free at the time of sacrifice 135 days post inoculation. STRO-001 demonstrated B-cell depletion in cynomolgus monkeys, confirming the intended pharmacodynamic effect. Myelosuppression was observed at the highest dose but there was no evidence of off-target toxicity.

Conclusion:

STRO-001 demonstrates potent in vitro cytotoxicity in NHL cell lines and anti-tumor activity in NHL xenograft models, including prolonged survival in the disseminated Mino MCL model. STRO-001 depletes B cells in a dose-dependent manner. Clinical studies of this novel ADC for treatment of B-cell malignancies are under development.

https://learningcenter.ehaweb.org/eha/2017/22nd/181149/arturo.molina.stro-001.a.novel.anti-cd74.antibody.drug.conjugate.%28adc%29.for.html

 

EHA, MM 2017

TARGETING CD74 IN MULTIPLE MYELOMA WITH A NOVEL ANTIBODY DRUG CONJUGATE (ADC), STRO-001

Author(s): Millicent Embry, Xiaofan Li, Venita DeAlmeida, Cristina Abrahams, Abigail Yu, Stellanie Krimm, Sarah Krueger, Shannon Matheny, Toni Kline, Alice Yam, Ryan Stafford, Trevor Hallam, Mark Lupher, Arturo Molina

Background:

CD74 is a transmembrane glycoprotein involved in MHC protein formation and transport. CD74 expression has been observed in up to 90% of B-cell malignancies, including multiple myeloma (MM), with minimal expression in normal tissues.  CD74 is rapidly internalized, making it an attractive target for ADCs.  STRO-001 is a novel ADC comprised of an aglycosylated anti-CD74 IgG1 human antibody (SP7219) conjugated covalently to the non-natural amino acid para-azido-methyl-L-phenylalanine (pAMF) with a non-cleavable dibenzocyclooctyne (DBCO)-maytansinoid linker-warhead.  Highly efficient site-specific conjugation enabled by novel cell-free antibody production and click chemistry results in a well-defined homogeneous ADC drug product with a drug-antibody ratio (DAR) of 2.

Aims:

The in vitro cytotoxicity and in vivo efficacy of STRO-001 was investigated in MM cell lines and xenografts. An exploratory toxicology study was conducted in a non-human primate model.

Methods:

DBCO-Alexa647-conjugated SP7219 staining and flow cytometry were used for detection and quantitation of CD74 expression on MM cell lines.  STRO-001 was used to determine the EC50 and percent span of killing in MM cell lines. The anti-tumor activity of STRO-001 was evaluated in the disseminated ARP-1 and MM.1S MM models.  In vivo bioluminescence imaging (BLI) for animals bearing MM.1s-luc cells was performed using an IVIS Spectrum. BLI images were collected 7, 14, 21, and 28 days post-tumor cell inoculation.  STRO-001 was administered to cynomolgus monkeys in an exploratory dose-escalating study of repeat IV doses of 1, 3, 10 and 30 mg/kg on days 1 and 15.

Results:

In vitro cytotoxicity assays show nanomolar potency of STRO-001 in five MM cell lines: MC/CAR (EC50 0.8 nM), ARD (EC50 6.5 nM), MM.1S (EC50 10-11 nM), U266B1 (EC50 8.5-9.3 nM), and ARP-1 (EC50 4.3-22 nM). CD74 cell surface expression is required for STRO-001 cytotoxic activity but expression level, as measured by antibody-binding capacity, does not correlate strongly with in vitro potency (R2=0.5837 for MM cell lines).  STRO-001 inhibits the growth of CD138+ plasma cells in bone marrow (BM) and formation of visceral tumors (p=0.002 for kidney; p<0.0001 for ovary) after 4 weekly doses of 3 mg/kg in the ARP-1 disseminated MM xenograft model. STRO-001 dosed at 3 mg/kg and 10 mg/kg weekly x 3 also eradicates malignant BM plasma cells by day 32 post-inoculation (p<0.0001) and prolongs survival in the MM.1S disseminated model. At termination of the study, 129 days post-inoculation, 100% of the STRO-001 treated animals survived and showed no evidence of disease with no CD138+ cells in their bone marrow, while mean survival of vehicle-treated control animals was 35 days with almost 50% of their bone marrow containing myeloma cells. BLI of luciferase-expressing MM.1S (MM.1S-luc) tumor cell lines enabled noninvasive quantitation of tumor burden. Single doses of 1, 3, and 10 mg/kg STRO-001 (administered on day 7 post-inoculation) resulted in eradication of myeloma by day 28 based on bioluminescence signal and quantification of CD138+ cells in bone marrow. In addition, STRO-001 produced a dose-dependent reduction in normal B-cells in cynomolgus monkeys, providing pharmacodynamic evidence of B-cell targeting.

Conclusion:

STRO-001 demonstrates potent in vitrocytotoxicity in MM cell lines and reduces tumor burden in MM xenograft models, including significant prolongation of survival in the MM.1S model.  Based on these encouraging observations, STRO-001 is advancing to the clinic for the treatment of CD74-expressing B-cell malignancies.

https://learningcenter.ehaweb.org/eha/2017/22nd/181615/arturo.molina.targeting.cd74.in.multiple.myeloma.with.a.novel.antibody.drug.html

 

ICML 2017

Hematological Oncology, 17 June, 2017 Volume35, IssueS2, p255-256.

STRO‐001, A NOVEL ANTI‐CD74 ANTIBODY DRUG CONJUGATE (ADC) FOR TREATMENT OF B‐CELL NON‐HODGKIN’S LYMPHOMAS (NHL)

  1. Molina, A. Yu, C. Abrahams, M. Embry, X. Li, V. DeAlmeida, J. Lee, S. Matheny, T. Kline, A. Yam, R. Stafford, T. Hallam, M. Lupher

Background: CD74 is a type II transmembrane glycoprotein involved in the formation and transport of MHC class II protein. CD74 is rapidly internalized and 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 comprised of a p-azido-methyl-phenylalanine (pAMF)-containing anti-CD74 aglycosylated human IgG1 antibody (SP7219) conjugated to a non-cleavable dibenzocyclooctyne (DBCO)-maytansinoid linker warhead. Highly efficient site-specific conjugation enabled by Sutro’s cell-free antibody production and click chemistry produced a well-defined homogeneous ADC with a drug-antibody ratio (DAR) of 2. 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 a reference cytotoxic maytansine. Since 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, this novel ADC has potential for improved PK, safety and activity profiles. Aims: The aim of this study was to investigate the therapeutic potential of STRO-001 in non-Hodgkin’s lymphoma (NHL) cell lines and xenografts. A dose-escalating exploratory toxicology study was also conducted in cynomolgus monkeys. Methods: Biotinylated SP7219 was used for immunohistochemistry (IHC). DBCO-Alexa647-conjugated SP7219 and flow cytometry were used for detection and quantitation of CD74 expression on NHL cell lines and B-cells from normal human donors. STRO-001 was used to determine the EC50 and percent span of killing in NHL cell lines. The anti-tumor activity of STRO-001 in SCID mice bearing NHL tumor cell xenografts was examined. STRO-001 was administered to cynomolgus monkeys in an exploratory dose-escalating study of repeat IV doses of 1, 3, 10 and 30 mg/kg on days 1 and 15. Results: Expression of CD74 in different lymphoma subtypes was evaluated by IHC on duplicate core (matched pair) biopsies. Medium to high CD74 expression in >70% of cells was observed in 86/100 diffuse large B-cell (DLBCL), 22/28 follicular lymphoma and 49/78 mantle cell lymphoma (MCL) samples. In vitro cytotoxicity assays show potent activity of STRO-001 in a diverse panel of B-cell tumor lines including 9 germinal center B-cell (GCB) diffuse large B-cell lymphoma (DLBCL), 3 activated B-cell (ABC) DLBCL, and 4 mantle cell lymphoma (MCL) cell lines with EC50 values ranging from 0.17-13 nM. STRO-001 has only modest effects on naïve B-cells, but exhibits more potent cell killing in activated human B-cells that have upregulated CD74 expression (similar CD74 expression as SU-DHL-6 cell line). 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=0.4154). STRO-001 exhibits dose-dependent tumor growth inhibition in rituximab-resistant SU-DHL-6 xenografts starting at 2.5 mg/kg weekly x 3 doses. The standard of care 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). 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 a single 10 mg/kg dose resulting in tumor regression for up to 64 days post treatment. STRO-001 treatment 14 days post tumor inoculation was used to evaluate disease progression in Mino, a slow growing disseminated MCL xenograft model. Vehicle-treated animals developed advanced disease with palpable tumors and distended abdomens, with median survival of 81.3 days. In contrast, Mino xenografts treated with STRO-001 at 3 mg/kg or 10 mg/kg exhibited improved survival, with most animals healthy and disease free at the time of sacrifice 135 days post inoculation. STRO-001 demonstrated B-cell depletion in cynomolgus monkeys, confirming the intended pharmacodynamic effect. Myelosuppression was observed at the highest dose but there was no evidence of off-target toxicity. Summary/Conclusion: STRO-001 demonstrates potent in vitro cytotoxicity in NHL cell lines and anti-tumor activity in NHL xenograft models, including prolonged survival in the disseminated Mino MCL model. STRO-001 depletes B cells in a dose dependent manner. Clinical studies of this novel ADC for treatment of B-cell malignancies are under development.

DOI   https://doi.org/10.1002/hon.2438_121

 

AACR, 2017 MM and NHL

Cancer Research, Volume 77, Issue 13 Supplement, pp. 67

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

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 and Arturo Molina

Abstract:

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.

DOI  https://doi.org/10.1158/1538-7445.AM2017-67

 

ASH, 2016 MM

Blood, vol.128 Issue 22 pg 4465, 2016.

Discovery and Preclinical Development of Novel CD74-Targeting Antibody-Drug Conjugates (ADCs) with Significant Activity in Multiple Myeloma (MM) Cell Lines and Xenograft Models.

Cristina Abrahams, Xiaofan Li, Abigail Yu, Stellanie Krimm, Jason Kahana, Rama Krishna Narla, Eric Schwartz, John Boylan, Heidi Hoffmann, Alexander Steiner, James Zawada, Heather Stephenson, Maureen Bruhns, Venita DeAlmeida, Shannon Matheny, Stuart Bussell, Adam Galan, Toni Kline, Nicki Vasquez, Alice Yam, Ryan Stafford, Henry Heinsohn, Aaron Sato, Arturo Molina, Trevor Hallam and Mark Lupher Jr.

Abstract:

CD74, also known as HLA-DR-associated invariant chain, is a type II transmembrane glycoprotein highly expressed in many B-cell malignancies. The limited expression of CD74 in normal tissues suggests it may be a suitable ADC target for these tumor types. Accordingly, we engineered an anti-CD74 human IgG1 antibody (SP7219) using novel Fab-based ribosome display methods. The selected Fabs were readily reformatted and directly screened as IgGs using Sutro’s unique high-throughput, cell-free protein synthesis platform, Xpress CFTM. We then developed novel, potent ADCs, SP7676 and SP7675 (STRO-001), comprised of our lead antibody (SP7219) conjugated to non-cleavable DBCO-maytansinoid linker-warheads with an average drug-antibody ratios (DAR) of 2. We used site-specific conjugation technology which results in a high degree of homogeneity characterized by the drug linker covalently binding to a single defined site. The sites for conjugation were selected based on highest cell killing activity and stablity in vitro and in vivo. Both ADCs demonstrate potent cell killing activity across multiple B-cell tumor lines in vitro, and anti-tumor activity in preclinical multiple myeloma xenograft models. In vitro cytotoxicity assays show nanomolar potency of STRO-001 in four MM cell lines: Mc/CAR (IC50 0.8 nM), MM.1S (IC50 10-11 nM), U266B1 (IC50 8.5 -9.3 nM), and ARP-1 (IC50 4.3-22 nM). CD74 cell surface expression is required for ADC anti-proliferative effect but the expression level does not seem to correlate with in vitro potency. SP7676 elicited a robust anti-tumor response in the ANBL-6 multiple myeloma xenograft model. Durable regressions were observed in all mice at ≥ 3 mg/kg, with equivalent efficacy (regression) at 3 mg/kg (every 3 days x5) and 10 mg/kg (every 3 days x5 or weekly x3). SP7676 also elicited a clear survival benefit in a disseminated multiple myeloma CAG xenograft model starting at 1mg/kg every 3 days x 5 doses. Similarly, both SP7676 and STRO-001 inhibited the formation of internal visceral tumors in the ARP-1 xenograft model after 3 weekly doses of 3 mg/kg. Evaluation of our lead candidate, STRO-001 in additional MM cell lines and primary patient samples is planned. The tolerability of STRO-001 in non-human primates is under evaluation. STRO-001 was administered to cynomolgous monkeys in an exploratory dose-escalating study up to 30 mg/kg x 2 doses on Day 1 and 15. STRO-001 reduces normal B-cell populations at ≥1 mg/kg after a single dose, providing pharmacodynamic evidence of B-cell targeting while other hematopoietic lineages are mostly affected only at the highest dose studied. Anticipated hematologic toxicities were readily reversible at 1, 3 and 10 mg/kg and target organs of interest were identified. Based on these encouraging data, STRO-001 is advancing to IND-enabling studies for the treatment of CD74 expressing multiple myeloma and other B-cell malignancies.

 

ASH, 2016 NHL

Blood, vol.128 Issue 22 pg 464, 2016.

Targeting CD74 with Novel Antibody Drug Conjugates (ADCs) for the Treatment of B-Cell Non-Hodgkin’s Lymphoma (NHL)

Xiaofan Li, Cristina Abrahams, Millicent Embry, Abigail Yu, Jason Kahana, Michael Brown, Rama Krishna Narla, Leo Barnes, Eric Schwartz, John Boylan, James Zawada, Heather Stephenson, Maureen Bruhns, Stuart Bussell, Alexander Steiner, Adam Galan, Toni Kline, Alice Yam, Ryan Stafford, Heidi Hoffmann, Shannon Matheny, Venita DeAlmeida, Nicki Vasquez, Henry Heinsohn, Aaron Sato, Arturo Molina, Trevor Hallam and Mark Lupher Jr.

Abstract:

CD74 is a type II transmembrane glycoprotein involved in the formation and transport of MHC class II protein. High expression of CD74 has been confirmed in follicular lymphoma, diffuse large B-cell lymphoma (DLBCL), chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) and other types of NHL with immunohistochemistry (IHC) using the LL1 antibody (Stein et al. Clin Cancer Res 2007). We employed site-specific conjugation technology to generate novel CD74-targeting ADCs, SP7676 and SP7675 (STRO-001) that exhibit a high degree of homogeneity characterized by the drug linker covalently binding to a single defined site. The human anti-CD74 IgG1 antibody (SP7219) used for ADCs SP7676 and STRO-001 was engineered using novel Fab-based ribosome display methods enabling selection from ~1012 different antibody variants. Hundreds of unique Fabs from this selection were converted to IgGs and expressed directly in Sutro’s proprietary cell-free protein synthesis platform, Xpress CFTM, for extensive screening. The top antibody lead derived from this screen is further tested to identify the best sites for conjugation of linker-warheads. Sutro’s SP7219 emerged as the top performing antibody and was conjugated to noncleavable DBCO-maytansinoid linker-warheads to form the ADCs SP7676 and STRO-001. Since conjugation sites were selected based on highest stability both in vitro and in vivo, these novel ADCs lose little drug moiety in circulation and have potential for improved PK, safety and activity profiles. In vitro cell proliferation/cytotoxicity assays show potent activity in 1) DLBCL (germinal center B-cell-like [GCB] and “double-hit”) lines: SU-DHL-4, IC50 – 1nM; SU-DHL-6, IC50 – 0.4 nM; WSU-NHL, IC50 – 1.6 nM; Pfeiffer, IC50 – .09 nM; NUDUL-1, IC50 – 0.4 nM; HT, IC50 – 0.7 nM; OCI-LY-19, IC50 – 0.7 nM; WSU-DLBCL2, IC50 – 0.3 nM; 2) mantle cell lymphoma (MCL) cell lines: Mino, IC50 – 0.4-0.7 nM; JVM-2, IC50 – 1.7-2.9 nM; Jeko-1, IC50 – 0.4 – 0.6 nM; 3) Ph+ acute lymphoblastic leukemia (ALL): SUP-B15, IC50 – 3.9-4.6 nM; and 4) CLL (EBV-transformed): JVM-13, IC50 – 3.0-3.4 nM. SP7676 elicited strong anti-tumor response in the OCI-LY-10 lymphoma xenograft model with 100% of animals achieving complete regression of tumors at 3mg/kg every 3 days x 5 doses and 10 mg/kg weekly x 3 doses. In the WSU-DLCL2 “double-hit” lymphoma xenograft model, administration of SP7676 (with re-dosing at time of re-growth) produced tumor regressions at 10 mg/kg every 3 days x 5 (6/8 mice tumor free, remaining 2 with small tumors) and 10 mg/kg weekly x 3 (tumor regression in most animals, 4/8 tumor free). Additionally, STRO-001 exhibits dose-dependent tumor growth inhibition in SUDHL-6 xenografts starting at 2.5 mg/kg weekly x 3 doses. Exploratory testing of our lead candidate, STRO-001 in cynomologous monkeys showed dose-dependent B-cell depletion at 1 – 30 mg/kg doses on Day 1 and 15, confirming the intended pharmacodynamic effect. Our preliminary data demonstrate that SP7676 and STRO-001 generate potent cell killing activity across multiple B-cell lymphoma/leukemia cell lines in vitro, and anti-tumor activity in preclinical B-cell NHL xenografts. Evaluation of STRO-001 in other cell lines and xenograft models and in combination studies is ongoing. GLP toxicology and other IND-enabling studies are planned.