Prostate cancer (PC) is an aggressive cancer that can progress rapidly and eventually become castrate-resistant prostate cancer (CRPC). Stage IV metastatic castrate-resistant prostate cancer (mCRPC) is an incurable late-stage cancer type with a low 5-year overall survival rate. Targeted therapeutics such as antibody-drug conjugates (ADCs) based on high-affinity monoclonal antibodies and potent drugs conjugated via smart linkers are being developed for PC management. Conjugating further with in vitro or in vivo imaging agents, ADCs can be used as antibody-theranostic conjugates (ATCs) for diagnostic and image-guided drug delivery. In this study, we have developed a novel ATC for PSMA (+) PC therapy utilizing (a) anti-PSMA 5D3 mAb, (b) Aurora A kinase inhibitor, MLN8237, and (c) for the first time using tetrazine (Tz) and trans-cyclooctene (TCO) click chemistry-based conjugation linker (CC linker) in ADC development. The resulting 5D3(CC-MLN8237)3.2 was labeled with suitable fluorophores for in vitro and in vivo imaging. The products were characterized by SDS-PAGE, MALDI-TOF, and DLS and evaluated in vitro by optical imaging, flow cytometry, and WST-8 assay for cytotoxicity in PSMA (+/-) cells. Therapeutic efficacy was determined in human PC xenograft mouse models following a designed treatment schedule. After the treatment study animals were euthanized, and toxicological studies, complete blood count (CBC), blood clinical chemistry analysis, and H&E staining of vital organs were conducted to determine side effects and systemic toxicities. The IC50 values of 5D3(CC-MLN8237)3.2-AF488 in PSMA (+) PC3-PIP and PMSA (-) PC3-Flu cells are 8.17 nM and 161.9 nM, respectively. Pure MLN8237 shows 736.9 nM and 873.4 nM IC50 values for PC3-PIP and PC3-Flu cells, respectively. In vivo study in human xenograft mouse models confirmed high therapeutic efficacy of 5D3(CC-MLN8237)3.2-CF750 with significant control of PSMA (+) tumor growth with minimal systemic toxicity in the treated group compared to PSMA (-) treated and untreated groups. Approximately 70% of PSMA (+) PC3-PIP tumors did not exceed the threshold of the tumor size in the surrogate Kaplan-Meyer analysis. The novel ATC successfully controlled the growth of PSMA (+) tumors in preclinical settings with minimal systemic toxicities. The therapeutic efficacy and favorable safety profile of novel 5D3(CC-MLN8237)3.2 ATC demonstrates their potential use as a theranostic against aggressive PC.

• Keywords
• Aurora A kinase inhibition, MLN8237, PSMA -prostate-specific membrane antigen, antibody-theranostic conjugates, image-guided drug delivery, prostate cancer, targeted therapy, theranostics,
• Publication type
• Journal Article MeSH

Prostate-Specific Membrane Antigen (PSMA) is an established biomarker for the imaging and experimental therapy of prostate cancer (PCa), as it is strongly upregulated in high-grade primary, androgen-independent, and metastatic lesions. Here, we report on the development and functional characterization of recombinant single-chain Fv (scFv) and Fab fragments derived from the 5D3 PSMA-specific monoclonal antibody (mAb). These fragments were engineered, heterologously expressed in insect S2 cells, and purified to homogeneity with yields up to 20 mg/L. In vitro assays including ELISA, immunofluorescence and flow cytometry, revealed that the fragments retain the nanomolar affinity and single target specificity of the parent 5D3 antibody. Importantly, using a murine xenograft model of PCa, we verified the suitability of fluorescently labeled fragments for in vivo imaging of PSMA-positive tumors and compared their pharmacokinetics and tissue distribution to the parent mAb. Collectively, our data provide an experimental basis for the further development of 5D3 recombinant fragments for future clinical use.

• Keywords
• NAALADase, antibody fragment, glutamate carboxypeptidase II, in vivo imaging, monoclonal antibody, prostate cancer, prostate-specific membrane antigen,
• MeSH
• Antigens, Surface immunology   MeSH
• Cell Line MeSH
• PC-3 Cells MeSH
• Fluorescence MeSH
• Glutamate Carboxypeptidase II immunology   MeSH
• Insecta MeSH
• Single-Chain Antibodies immunology   MeSH
• Humans MeSH
• Antibodies, Monoclonal immunology   MeSH
• Mice, Nude MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Prostatic Neoplasms immunology   MeSH
• Recombinant Proteins immunology   MeSH
• Xenograft Model Antitumor Assays methods   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Antigens, Surface MeSH
• FOLH1 protein, human MeSH Browser
• Glutamate Carboxypeptidase II MeSH
• Single-Chain Antibodies MeSH
• Antibodies, Monoclonal MeSH
• Recombinant Proteins MeSH

Prostate cancer (PC) is a potentially high-risk disease and the most common cancer in American men. It is a leading cause of cancer-related deaths in men in the US, second only to lung and bronchus cancer. Advanced and metastatic PC is initially treated with androgen deprivation therapy (ADT), but nearly all cases eventually progress to castrate-resistant prostate cancer (CRPC). CRPC is incurable in the metastatic stage but can be slowed by some conventional chemotherapeutics and second-generation ADT, such as enzalutamide and abiraterone. Therefore, novel therapeutic strategies are urgently needed. Prostate-specific membrane antigen (PSMA) is overexpressed in almost all aggressive PCs. PSMA is widely used as a target for PC imaging and drug delivery. Anti-PSMA monoclonal antibodies (mAbs) have been developed as bioligands for diagnostic imaging and targeted PC therapy. However, these mAbs are successfully used in PC imaging and only a few have gone beyond phase-I for targeted therapy. The 5D3 mAb is a novel, high-affinity, and fast-internalizing anti-PSMA antibody. Importantly, 5D3 mAb demonstrates a unique pattern of cellular localization to the centrosome after internalization in PSMA(+) PC3-PIP cells. These characteristics make 5D3 mAb an ideal bioligand to deliver tubulin inhibitors, such as mertansine, to the cell centrosome, leading to mitotic arrest and elimination of dividing PC cells. We have successfully developed a 5D3 mAb- and mertansine (DM1)-based antibody-drug conjugate (ADC) and evaluated it in vitro for binding affinity, internalization, and cytotoxicity. The in vivo therapeutic efficacy of 5D3-DM1 ADC was evaluated in PSMA(+) PC3-PIP and PSMA(-) PC3-Flu mouse models of human PC. This therapeutic study has revealed that this new anti-PSMA ADC can successfully control the growth of PSMA(+) tumors without inducing systemic toxicity.

• Keywords
• 5D3 antibody, MCC linker, anti-PSMA antibody, antibody-drug conjugates (ADC), drug delivery, mertansine (DM1), prostate cancer, prostate-specific membrane antigen (PSMA), targeted therapy,
• MeSH
• Androstenes pharmacology   MeSH
• Androgen Antagonists pharmacology   MeSH
• Antigens, Surface metabolism   MeSH
• Benzamides pharmacology   MeSH
• PC-3 Cells MeSH
• Centrosome metabolism   MeSH
• Phenylthiohydantoin pharmacology   MeSH
• Glutamate Carboxypeptidase II metabolism   MeSH
• Immunoconjugates pharmacology   MeSH
• Humans MeSH
• Tubulin Modulators pharmacology   MeSH
• Antibodies, Monoclonal pharmacology   MeSH
• Mice, Nude MeSH
• Mice MeSH
• Cell Line, Tumor MeSH
• Prostatic Neoplasms, Castration-Resistant drug therapy   metabolism   MeSH
• Nitriles pharmacology   MeSH
• Xenograft Model Antitumor Assays MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, U.S. Gov't, Non-P.H.S. MeSH
• Names of Substances
• abiraterone MeSH Browser
• Androstenes MeSH
• Androgen Antagonists MeSH
• Antigens, Surface MeSH
• Benzamides MeSH
• enzalutamide MeSH Browser
• Phenylthiohydantoin MeSH
• FOLH1 protein, human MeSH Browser
• Glutamate Carboxypeptidase II MeSH
• Immunoconjugates MeSH
• Tubulin Modulators MeSH
• Antibodies, Monoclonal MeSH
• Nitriles MeSH