Precision Biologics to Unveil In Vitro and In Vivo Efficacy of New ADC against human ovarian cancer at AACR Special Conference

BETHESDA, Md., Sept. 19, 2025  /PRNewswire/ -- Precision Biologics, Inc. reports that in vitro and in vivo efficacy of the novel ADC, using its anti-core 2 O-glycans anti-human carcinoma mAb PB-223 (PB-vcMMAE-5), against human ovarian cancer expressing truncated core 2 O-glycans will be presented in a poster at the American Association for Cancer Research (AACR) Special Conference in Cancer Research: Advances in Ovarian Cancer Research on September 20^th, 2025, Grand Hyatt Denver, Denver, Colorado, USA.

Poster title: In vitro and in vivo efficacy of the antibody-drug-conjugate (ADC) PB-vcMMAE-5 against human ovarian cancer expressing truncated core 2 O-glycans

The presentation of the poster will be made in person on the following date and location:

Saturday, September 20, 6:30 p.m. – 8:00 p.m.

Grand Hyatt Denver, Denver, Colorado, USA

Poster Section: B

Abstract Control Number: B068

BACKGROUND:

Ovarian cancers remain largely unresponsive to immune checkpoint inhibitors, in part due to their ability to suppress the cytotoxic activity of immune cells infiltrating the tumor microenvironment. One of the disrupted pathways in these cancers is O-glycosylation, a feature particularly associated with ovarian cancer progression, metastasis and poor prognosis. This underscores the urgent need for alternative therapeutic strategies.  We developed an ADC, designated PB-vcMMAE-5, composed of the following:  

• The mAb: We used PB-223, an innovative mAb developed through affinity maturation of mAb NEO-102 (Ensituximab), a chimeric human IgG1 mAb that targets truncated core 2 O-glycans, specifically expressed by cancer cells and not by healthy tissues. The binding affinity of PB-223 for its target was improved, compared to NEO-102, by optimizing its VH and VL sequences through Fast Screening for Expression Biophysical Properties and Affinity. PB-223 demonstrated a binding affinity (KD) at least 4-fold lower than NEO-102, indicating stronger tumor binding. PB-223 does not bind to normal tissues and it can be internalized into human cancer cell lines expressing its target.
  
  
• The payload: Monomethyl auristatin E (MMAE) was used as payload. MMAE is a potent antimitotic agent that inhibits cell division by blocking the polymerization of tubulin and is the most common ADC payload used to be linked to antibodies in clinical development for oncologic applications.
  
  
• The linker: mc-vc-PABc was used as a cleavable linker. PB-223 was conjugated to the linker-payload through a cysteine-based conjugation method.

STUDY PRESENTED AT AACR Special Conference in Cancer Research: Advances in Ovarian Cancer Research, 2025

After development of the ADC PB-vcMMAE-5, we evaluated its efficacy in vitro and in vivo

• In vitro efficacy: The in vitro cytotoxicity of PB-vc-MMAE-5 was tested in four human cancer cell lines: triple-negative breast cancer (HCC1937, MDA-MB-231), ER⁺/PR⁺/HER2⁺ breast cancer (BT474), and ovarian cancer (OV-90). Cells were treated with varying ADC concentrations for 5 days.
  This study shows that PB-vcMMAE-5 effectively killed all cell lines tested.
  At the highest concentration, the percentage of cell killing for PB-vcMMAE-5 was 52.72% in HCC1937 and 88.36% in MDA-MB-231.
  At the highest concentration, the percentage of cell killing for PB-vcMMAE-5 was 92.51% in OV-90 and 83.22% in BT474.
  In contrast, naked PB-223 mAb showed no killing in all cell lines tested
  
  
• In vivo safety: In a study presented in April 2025, at AACR Annual Meeting 2025, we showed that PB-vcMMAE-5 was well tolerated in rats. No sign of distress nor loss of body weight were observed after administration. In this study we confirm the same pattern in mice. NOD-SCID mice bearing OV-90 xenografts were treated with weekly doses of PBS, MMAE alone, or PB-vc-MMAE-5 (1, 3, 6, or 9 mg/kg) for five weeks. Animal body weight was monitored regularly, twice a week, as an indirect measure of toxicity. The ADC PB-vcMMAE-5 was well tolerated in mice. No sign of distress and loss of body weight were observed
  
  No significant hematological or pathological changes were detected in the liver, spleen, brain, or heart of mice treated with efficacious doses of the ADC compared with controls.
  
  
• In vivo efficacy: The efficacy of the ADC PB-vcMMAE-5 was assessed in OV-90 subcutaneous xenograft model established in NOD-SCID mice. The ADC PB-vcMMAE-5 was administered intravenously at doses 1, 3, 6 or 9 mg/kg, once per week for five weeks.
  
  On day 31 from first ADC infusion, most alive mice were sacrificed, and tumors were excised for histological analysis using Ki-67 staining to assess proliferating viable tumor cells. To further assess systemic toxicity and prolonged efficacy, three mice each from the 6 and 9 mg/kg groups were followed to day 45.
  
  Data presented in this study show that PB-vcMMAE-5 at 1 mg/kg did not significantly reduce tumor volume compared with PBS, whereas PB-vcMMAE-5 at 6 and 9 mg/kg induced robust reduction of tumor volume.
  
  In addition, analysis of tumor viability at day 45 (Ki67 H-score) showed no tumor activity in mice treated with PB-vcMMAE-5 at 9 mg/kg

Findings from this study showed that PB-vcMMAE-5 can kill human cancer cells expressing PB-223's target, is not toxic in vivo in mice and is highly effective in vivo at 9 mg/kg in NOD-SCID mice bearing human ovarian cancer. In addition, in a poster presented at AACR Annual Meeting 2025 we reported that PB-vcMMAE-5 is stable in human plasma.

All these data suggest that PB-vcMMAE-5 has promising potential as a therapeutic option for human ovarian tumors and for a range of human malignancies expressing core 2 O-glycans.

The PDF of the poster will be available starting from September 19^th, 2025, at the following link:

https://precision-biologics.com/wp-content/uploads/AACR-OVARIAN-2025-Final-9-12-25.pdf

SOURCE Precision Biologics