STRO-002 is a novel homogeneous folate receptor alpha (FolRα) targeting antibody–drug conjugate (... more STRO-002 is a novel homogeneous folate receptor alpha (FolRα) targeting antibody–drug conjugate (ADC) currently being investigated in the clinic as a treatment for ovarian and endometrial cancers. Here, we describe the discovery, optimization, and antitumor properties of STRO-002. STRO-002 was generated by conjugation of a novel cleavable 3-aminophenyl hemiasterlin linker-warhead (SC239) to the nonnatural amino acid para-azidomethyl-L-phenylalanine incorporated at specific positions within a high affinity anti-FolRα antibody using Sutro's XpressCF+, which resulted in a homogeneous ADC with a drug–antibody ratio (DAR) of 4. STRO-002 binds to FolRα with high affinity, internalizes rapidly into target positive cells, and releases the tubulin-targeting cytotoxin 3-aminophenyl hemiasterlin (SC209). SC209 has reduced potential for drug efflux via P-glycoprotein 1 drug pump compared with other tubulin-targeting payloads. While STRO-002 lacks nonspecific cytotoxicity toward FolRα-negative cell lines, bystander killing of target negative cells was observed when cocultured with target positive cells. STRO-002 is stable in circulation with no change in DAR for up to 21 days and has a half-life of 6.4 days in mice. A single dose of STRO-002 induced significant tumor growth inhibition in FolRα-expressing xenograft models and patient-derived xenograft models. In addition, combination treatment with carboplatin or Avastin further increased STRO-002 efficacy in xenograft models. The potent and specific preclinical efficacy of STRO-002 supports clinical development of STRO-002 for treating patients with FolRα-expressing cancers, including ovarian, endometrial, and non–small cell lung cancer. Phase I dose escalation for STRO-002 is in progress in ovarian cancer and endometrial cancer patients (NCT03748186 and NCT05200364).
An approach is described for the simultaneous identification and quantitation of oxidant-sensitiv... more An approach is described for the simultaneous identification and quantitation of oxidant-sensitive cysteine thiols in a complex protein mixture using a thiol-specific, acid-cleavable isotope-coded affinity tag (ICAT) reagent (Applied Biosystems, USA). The approach is based on the fact that only free cysteine thiols are susceptible to labeling by the iodoacetamide-based ICAT, and that mass spectrometry can be used to quantitate the relative labeling of free thiols. Applying this approach, we have identified cysteine thiols of proteins in a rabbit heart membrane fraction that are sensitive to a high concentration of hydrogen peroxide. Previously known and some novel proteins with oxidant-sensitive cysteines were identified. Of the many protein thiols labeled by the ICAT, only relatively few were oxidized more than 50% despite the high concentration of oxidant used, indicating that oxidant-sensitive thiols are relatively rare, and denoting their specificity and potential functional relevance.
Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein ... more Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein that is widely expressed in serous and epithelial ovarian cancer, endometrial adenocarcinoma, non-small cell lung cancer and triple negative breast cancer. In contrast, FolRα expression is highly restricted on normal tissues, making it a highly promising target for cancer therapy using antibody drug conjugates (ADCs). We have designed a novel, FolRα-targeting ADC, STRO-002, with potent cytotoxic activity on FolRα expressing tumors in vitro and in vivo, including in cells with low expression levels (~0.2 million copies/cell) of FolRα. STRO-002 contains the anti-FolRa human IgG1 antibody (SP8166) conjugated to a proprietary cleavable drug-linker (SC239). SC239 contains a tubulin-targeting 3-aminophenyl hemiasterlin warhead, SC209, which has potent cytotoxic activity and is a weak substrate for efflux pumps. SP8166 was discovered and optimized using a Fab ribosome display selection and screening platform based on Sutro's Xpress CF+TM system. Four non-natural amino acid p-azidomethyl phenylalanine (pAMF) residues are incorporated into SP8166 at two defined sites on each heavy chain. These sites were selected based on optimal stability and activity in vitro and in vivo. The SC239 drug-linker is conjugated via a cleavable valine citrulline p-aminobenzyl carbamate linker functionalized with dibenzocyclooctyne (DBCO). The rapid and selective reaction of DBCO and pAMF results in a well-defined, homogeneous ADC with a drug-antibody ratio (DAR) of ~4. STRO-002 has potent cytotoxic activity (0.1-3 nM) on multiple FolRα-positive ovarian cancer cell lines in vitro and demonstrates strong anti-tumor response in KB, Igrov1 and OvCAR3 xenograft models in vivo. On Igrov1 xenografts, STRO-002 exhibits dose-dependent tumor growth inhibition starting at a single dose as low as 2.5 mg/kg. Evaluation of in vivo activity of STRO-002 in additional xenograft and PDX models, as well as in combination studies with chemotherapeutic agents is ongoing. Data from exploratory safety studies of STRO-002 in cynomolgus monkey and SC209 (active catabolite) in rats show a favorable safety profile. Our data suggests that STRO-002 is a promising clinical candidate for ovarian cancer, including tumors with low expression levels of FolRα, and IND enabling studies are currently being conducted. Citation Format: Xiaofan Li, Cristina Abrahams, Sihong Zhou, Stellanie Krimm, Robert Henningsen, Heather Stephenson, Jeffrey Hanson, Mary Rose Masikat, Krishna Bajjuri, Tyler Heibeck, Cuong Tran, Gang Yin, James Zawada, Ganapathy Sarma, Joy Chen, Maureen Bruhns, Willy Solis, Alexander Steiner, Adam Galan, Toni Kline, Ryan Stafford, Alice Yam, Venita I. De Almeida, Mark Lupher, Trevor Hallam. Discovery and activity of STRO-002, a novel ADC targeting folate receptor alpha for ovarian and endometrial 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 1782.
Antibody-drug conjugates (ADCs) are a targeted chemotherapeutic currently at the cutting edge of ... more Antibody-drug conjugates (ADCs) are a targeted chemotherapeutic currently at the cutting edge of oncology medicine. These hybrid molecules consist of a tumor antigen-specific antibody coupled to a chemotherapeutic small molecule. Through targeted delivery of potent cytotoxins, ADCs exhibit improved therapeutic index and enhanced efficacy relative to traditional chemotherapies and monoclonal antibody therapies. The currently FDA-approved ADCs, Kadcyla (Immunogen/Roche) and Adcetris (Seattle Genetics), are produced by conjugation to surface-exposed lysines, or partial disulfide reduction and conjugation to free cysteines, respectively. These stochastic modes of conjugation lead to heterogeneous drug products with varied numbers of drugs conjugated across several possible sites. As a consequence, the field has limited understanding of the relationships between the site and extent of drug loading and ADC attributes such as efficacy, safety, pharmacokinetics, and immunogenicity. A robust platform for rapid production of ADCs with defined and uniform sites of drug conjugation would enable such studies. We have established a cell-free protein expression system for production of antibody drug conjugates through site-specific incorporation of the optimized non-natural amino acid, para-azidomethyl-l-phenylalanine (pAMF). By using our cell-free protein synthesis platform to directly screen a library of aaRS variants, we have discovered a novel variant of the Methanococcus jannaschii tyrosyl tRNA synthetase (TyrRS), with a high activity and specificity toward pAMF. We demonstrate that site-specific incorporation of pAMF facilitates near complete conjugation of a DBCO-PEG-monomethyl auristatin (DBCO-PEG-MMAF) drug to the tumor-specific, Her2-binding IgG Trastuzumab using strain-promoted azide-alkyne cycloaddition (SPAAC) copper-free click chemistry. The resultant ADCs proved highly potent in in vitro cell cytotoxicity assays.
An efficient on-line digestion system that reduces the number of sample manipulation steps has be... more An efficient on-line digestion system that reduces the number of sample manipulation steps has been demonstrated for high throughput proteomics. By incorporating a pressurized sample loop into a liquid chromatography-based separation system, both sample and enzyme (eg, ...
OBJECTIVES: Folate receptor alpha (FolRα) is a cell-surface glycoprotein, highly expressed in ova... more OBJECTIVES: Folate receptor alpha (FolRα) is a cell-surface glycoprotein, highly expressed in ovarian and endometrial adenocarcinoma, and thus a promising target for cancer therapy using antibody drug conjugates (ADCs). Most ADCs currently in development are generated by random attachment of the cytotoxic payload to the antibody and result in a heterogeneous mixture, comprised of many different forms that are likely to vary in stability and activity, and therefore may be suboptimal therapeutic agents. We have employed an E. coli cell-free expression system (XpressCFTM) and site-specific conjugation technology, to generate STRO-002, a novel homogenous FolRα-targeting ADC. STRO-002 was optimized by selection of the antibody, drug-linker, conjugation site and drug-antibody ratio (DAR) that conferred the best pharmacological properties. We have conducted preclinical studies to evaluate the stability of STRO-002 and characterize the pharmacological properties of the cytotoxic metabolite ...
Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein ... more Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein that is widely expressed in serous and epithelial ovarian cancer, endometrial adenocarcinoma, non-small cell lung cancer and triple negative breast cancer. In contrast, FolRα expression is highly restricted on normal tissues, making it a highly promising target for cancer therapy using antibody drug conjugates (ADCs). We have designed a novel, FolRα-targeting ADC, STRO-002, with potent cytotoxic activity on FolRα expressing tumors in vitro and in vivo, including in cells with low expression levels (~0.2 million copies/cell) of FolRα. STRO-002 contains the anti-FolRa human IgG1 antibody (SP8166) conjugated to a proprietary cleavable drug-linker (SC239). SC239 contains a tubulin-targeting 3-aminophenyl hemiasterlin warhead, SC209, which has potent cytotoxic activity and is a weak substrate for efflux pumps. SP8166 was discovered and optimized using a Fab ribosome display selection and scre...
STRO-002 is a novel homogeneous folate receptor alpha (FolRα) targeting antibody–drug conjugate (... more STRO-002 is a novel homogeneous folate receptor alpha (FolRα) targeting antibody–drug conjugate (ADC) currently being investigated in the clinic as a treatment for ovarian and endometrial cancers. Here, we describe the discovery, optimization, and antitumor properties of STRO-002. STRO-002 was generated by conjugation of a novel cleavable 3-aminophenyl hemiasterlin linker-warhead (SC239) to the nonnatural amino acid para-azidomethyl-L-phenylalanine incorporated at specific positions within a high affinity anti-FolRα antibody using Sutro's XpressCF+, which resulted in a homogeneous ADC with a drug–antibody ratio (DAR) of 4. STRO-002 binds to FolRα with high affinity, internalizes rapidly into target positive cells, and releases the tubulin-targeting cytotoxin 3-aminophenyl hemiasterlin (SC209). SC209 has reduced potential for drug efflux via P-glycoprotein 1 drug pump compared with other tubulin-targeting payloads. While STRO-002 lacks nonspecific cytotoxicity toward FolRα-negative cell lines, bystander killing of target negative cells was observed when cocultured with target positive cells. STRO-002 is stable in circulation with no change in DAR for up to 21 days and has a half-life of 6.4 days in mice. A single dose of STRO-002 induced significant tumor growth inhibition in FolRα-expressing xenograft models and patient-derived xenograft models. In addition, combination treatment with carboplatin or Avastin further increased STRO-002 efficacy in xenograft models. The potent and specific preclinical efficacy of STRO-002 supports clinical development of STRO-002 for treating patients with FolRα-expressing cancers, including ovarian, endometrial, and non–small cell lung cancer. Phase I dose escalation for STRO-002 is in progress in ovarian cancer and endometrial cancer patients (NCT03748186 and NCT05200364).
An approach is described for the simultaneous identification and quantitation of oxidant-sensitiv... more An approach is described for the simultaneous identification and quantitation of oxidant-sensitive cysteine thiols in a complex protein mixture using a thiol-specific, acid-cleavable isotope-coded affinity tag (ICAT) reagent (Applied Biosystems, USA). The approach is based on the fact that only free cysteine thiols are susceptible to labeling by the iodoacetamide-based ICAT, and that mass spectrometry can be used to quantitate the relative labeling of free thiols. Applying this approach, we have identified cysteine thiols of proteins in a rabbit heart membrane fraction that are sensitive to a high concentration of hydrogen peroxide. Previously known and some novel proteins with oxidant-sensitive cysteines were identified. Of the many protein thiols labeled by the ICAT, only relatively few were oxidized more than 50% despite the high concentration of oxidant used, indicating that oxidant-sensitive thiols are relatively rare, and denoting their specificity and potential functional relevance.
Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein ... more Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein that is widely expressed in serous and epithelial ovarian cancer, endometrial adenocarcinoma, non-small cell lung cancer and triple negative breast cancer. In contrast, FolRα expression is highly restricted on normal tissues, making it a highly promising target for cancer therapy using antibody drug conjugates (ADCs). We have designed a novel, FolRα-targeting ADC, STRO-002, with potent cytotoxic activity on FolRα expressing tumors in vitro and in vivo, including in cells with low expression levels (~0.2 million copies/cell) of FolRα. STRO-002 contains the anti-FolRa human IgG1 antibody (SP8166) conjugated to a proprietary cleavable drug-linker (SC239). SC239 contains a tubulin-targeting 3-aminophenyl hemiasterlin warhead, SC209, which has potent cytotoxic activity and is a weak substrate for efflux pumps. SP8166 was discovered and optimized using a Fab ribosome display selection and screening platform based on Sutro's Xpress CF+TM system. Four non-natural amino acid p-azidomethyl phenylalanine (pAMF) residues are incorporated into SP8166 at two defined sites on each heavy chain. These sites were selected based on optimal stability and activity in vitro and in vivo. The SC239 drug-linker is conjugated via a cleavable valine citrulline p-aminobenzyl carbamate linker functionalized with dibenzocyclooctyne (DBCO). The rapid and selective reaction of DBCO and pAMF results in a well-defined, homogeneous ADC with a drug-antibody ratio (DAR) of ~4. STRO-002 has potent cytotoxic activity (0.1-3 nM) on multiple FolRα-positive ovarian cancer cell lines in vitro and demonstrates strong anti-tumor response in KB, Igrov1 and OvCAR3 xenograft models in vivo. On Igrov1 xenografts, STRO-002 exhibits dose-dependent tumor growth inhibition starting at a single dose as low as 2.5 mg/kg. Evaluation of in vivo activity of STRO-002 in additional xenograft and PDX models, as well as in combination studies with chemotherapeutic agents is ongoing. Data from exploratory safety studies of STRO-002 in cynomolgus monkey and SC209 (active catabolite) in rats show a favorable safety profile. Our data suggests that STRO-002 is a promising clinical candidate for ovarian cancer, including tumors with low expression levels of FolRα, and IND enabling studies are currently being conducted. Citation Format: Xiaofan Li, Cristina Abrahams, Sihong Zhou, Stellanie Krimm, Robert Henningsen, Heather Stephenson, Jeffrey Hanson, Mary Rose Masikat, Krishna Bajjuri, Tyler Heibeck, Cuong Tran, Gang Yin, James Zawada, Ganapathy Sarma, Joy Chen, Maureen Bruhns, Willy Solis, Alexander Steiner, Adam Galan, Toni Kline, Ryan Stafford, Alice Yam, Venita I. De Almeida, Mark Lupher, Trevor Hallam. Discovery and activity of STRO-002, a novel ADC targeting folate receptor alpha for ovarian and endometrial 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 1782.
Antibody-drug conjugates (ADCs) are a targeted chemotherapeutic currently at the cutting edge of ... more Antibody-drug conjugates (ADCs) are a targeted chemotherapeutic currently at the cutting edge of oncology medicine. These hybrid molecules consist of a tumor antigen-specific antibody coupled to a chemotherapeutic small molecule. Through targeted delivery of potent cytotoxins, ADCs exhibit improved therapeutic index and enhanced efficacy relative to traditional chemotherapies and monoclonal antibody therapies. The currently FDA-approved ADCs, Kadcyla (Immunogen/Roche) and Adcetris (Seattle Genetics), are produced by conjugation to surface-exposed lysines, or partial disulfide reduction and conjugation to free cysteines, respectively. These stochastic modes of conjugation lead to heterogeneous drug products with varied numbers of drugs conjugated across several possible sites. As a consequence, the field has limited understanding of the relationships between the site and extent of drug loading and ADC attributes such as efficacy, safety, pharmacokinetics, and immunogenicity. A robust platform for rapid production of ADCs with defined and uniform sites of drug conjugation would enable such studies. We have established a cell-free protein expression system for production of antibody drug conjugates through site-specific incorporation of the optimized non-natural amino acid, para-azidomethyl-l-phenylalanine (pAMF). By using our cell-free protein synthesis platform to directly screen a library of aaRS variants, we have discovered a novel variant of the Methanococcus jannaschii tyrosyl tRNA synthetase (TyrRS), with a high activity and specificity toward pAMF. We demonstrate that site-specific incorporation of pAMF facilitates near complete conjugation of a DBCO-PEG-monomethyl auristatin (DBCO-PEG-MMAF) drug to the tumor-specific, Her2-binding IgG Trastuzumab using strain-promoted azide-alkyne cycloaddition (SPAAC) copper-free click chemistry. The resultant ADCs proved highly potent in in vitro cell cytotoxicity assays.
An efficient on-line digestion system that reduces the number of sample manipulation steps has be... more An efficient on-line digestion system that reduces the number of sample manipulation steps has been demonstrated for high throughput proteomics. By incorporating a pressurized sample loop into a liquid chromatography-based separation system, both sample and enzyme (eg, ...
OBJECTIVES: Folate receptor alpha (FolRα) is a cell-surface glycoprotein, highly expressed in ova... more OBJECTIVES: Folate receptor alpha (FolRα) is a cell-surface glycoprotein, highly expressed in ovarian and endometrial adenocarcinoma, and thus a promising target for cancer therapy using antibody drug conjugates (ADCs). Most ADCs currently in development are generated by random attachment of the cytotoxic payload to the antibody and result in a heterogeneous mixture, comprised of many different forms that are likely to vary in stability and activity, and therefore may be suboptimal therapeutic agents. We have employed an E. coli cell-free expression system (XpressCFTM) and site-specific conjugation technology, to generate STRO-002, a novel homogenous FolRα-targeting ADC. STRO-002 was optimized by selection of the antibody, drug-linker, conjugation site and drug-antibody ratio (DAR) that conferred the best pharmacological properties. We have conducted preclinical studies to evaluate the stability of STRO-002 and characterize the pharmacological properties of the cytotoxic metabolite ...
Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein ... more Folate receptor alpha (FolRα) is a glycosylphosphatidylinositol linked cell-surface glycoprotein that is widely expressed in serous and epithelial ovarian cancer, endometrial adenocarcinoma, non-small cell lung cancer and triple negative breast cancer. In contrast, FolRα expression is highly restricted on normal tissues, making it a highly promising target for cancer therapy using antibody drug conjugates (ADCs). We have designed a novel, FolRα-targeting ADC, STRO-002, with potent cytotoxic activity on FolRα expressing tumors in vitro and in vivo, including in cells with low expression levels (~0.2 million copies/cell) of FolRα. STRO-002 contains the anti-FolRa human IgG1 antibody (SP8166) conjugated to a proprietary cleavable drug-linker (SC239). SC239 contains a tubulin-targeting 3-aminophenyl hemiasterlin warhead, SC209, which has potent cytotoxic activity and is a weak substrate for efflux pumps. SP8166 was discovered and optimized using a Fab ribosome display selection and scre...
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