Abstract 1763: Gastric cancer antibody fragment drug-conjugates (FDCs): Succeeding in solid tumors where ADCs fail

Antibody Drug Conjugates (ADCs) are failing due to 3 critical limitations: Low potency, ineffective solid-tumor penetration and poor tolerability. The industry is full of approaches where full-length Immunoglobulins have been engineered to carry defined numbers of payloads with higher-loadings of less potent payloads appearing to be well-tolerated. However, antibody fragments (e.g. single-chain Fcs-scFvs), which have many advantages including rapid tumor penetration, faster clearance, inexpensive manufacture, have been technologically challenging to apply in oncology. Our novel approach enables scFvs to have a high Drug:Antibody loading ratio (DAR) whilst retaining effective binding and other favorable biophysical properties, leading to a new product class tailored for solid tumors. Antikor has two FDC products in development for solid tumors, notably gastric: anti-HER2 FDC (ANT-043) and a second target (ANT-045) which will be disclosed during this presentation. ANT-043 has pM potencies in a range of HER2-expressing cell-lines, including trastuzumab-resistant models, excellent tumor ablation effects in breast, ovarian and gastric cancer xenograft models and superior tolerability compared to an ADC in rat toxicology studies at a dose of 1mg/kg/weekly. Quantitative payload tumor uptake and fluorescent immuno-histological studies demonstrate superior solid tumor penetration across the entire tumor and diffusion from blood vessels. In collaboration with our partners, Essex Biotechnology, Antikor is taking ANT-043 into IND-enabling studies for clinical development. ANT-045, which emerged from Antikor’s proprietary FDC ‘discovery engine’, is progressing towards IND-filing and updated data will illustrate how ANT-045 could have a broader patient benefit in gastro-intestinal cancers. ANT-045 has excellent in vitro cell-kill potency (pM IC50s) and excellent stability and superior in vivo tumor cure efficacy, compared to a leading clinical stage benchmark ADC. This presentation will focus on Antikor’s FDC discovery platform (stable high-DAR scFv-display libraries, tailored linker-payloads and design features) that has the potential to generate first-in-class products for difficult to treat solid tumors for patient benefit and promising to succeed where ADCs have failed to deliver.

Citation Format: Mahendra P. Deonarain, Gokhan Yahioglu, Ioanna Stamati, Bryan Edwards, Soraya Diez-Posada, Isabel Perez-Castro, Anja Pomowski, Laura Bouche, Ashleigh Stewart, Monika Maciuszek, Sam Ness, Malcolm Ngiam, Quinn Xue. Gastric cancer antibody fragment drug-conjugates (FDCs): Succeeding in solid tumors where ADCs fail [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1763.

Clinical application of extended half-life factor VIII in children with severe haemophilia A

INTRODUCTION

Only few studies have presented results from real-world clinical use of Extended Half-Life (EHL) products in children with haemophilia (CWH).

AIM

To retrospectively examine real-life experience with EHL factor VIII products use in CWH A, comparing with clinical experience from standard half-life products (SHL).

METHODS

A retrospective review of medical records of CWH A who have been prescribed EHL factor concentrates was conducted. All before/after comparisons were performed with the Wilcoxon matched-pairs signed-ranks test.

RESULTS

Twenty-three children with severe haemophilia A were enrolled in the study (3-6 years old: n = 4, 7-12 years old: n = 7 and 13-18 years old: n = 12). Median length of time that patients were treated with EHL products was 78 weeks. Median dosing interval was significantly lengthened from 2.3 to 3.5 days after switching from SHL to EHL concentrates. Mean trough FVIII levels were significantly increased from 2.3% to 4.1% after treatment with EHL products. Also, CWH A had a reduction of mean annual bleeding rate (ABR) and mean annual joint bleeding rate (AJBR) from 1 and .8 to .3 and .2, respectively, following treatment with EHL concentrates (ABR: p = .02, AJBR: p = .05). However, after switching to factor EHL, actual FVIII consumption, including bleeds, was significantly increased from 94 IU/kg/week to 118 IU/kg/week in CWH A. There was no inhibitor development.

CONCLUSION

This study demonstrates the successful transition of 23 CWH A from SHL to EHL factor concentrates.

Abstract 909: Antibody fragment drug-conjugates (FDCs)-application of ANT-043 and ANT-045 in solid tumors

Despite the recent resurgence, Antibody Drug Conjugates (ADCs) are failing to address challenging cancer indications due to 3 critical limitations: Low potency, ineffective solid-tumour penetration and poor tolerability. The industry is well-served by approaches where full-length Immunoglobulins are designed to carry defined numbers of payloads. However, antibody fragments (e.g. single-chain Fvs-scFvs), which have many advantages including rapid tumour penetration, faster clearance, inexpensive manufacture, have been technologically challenging to apply in oncology. Our novel approach enables scFvs to have a high Drug:Antibody loading ratio (DAR) whilst retaining effective binding and other favourable biophysical properties, leading to a new product class tailored for solid tumours. Antikor has two ‘first-in-class' FDC products in development for solid tumours: anti-HER2 FDC (ANT-043) a follow-up product against a second target (ANT-045) which will be disclosed during this presentation. ANT-043 has demonstrated excellent tumour ablation effects in breast, ovarian and gastric cancer xenograft models and superior tolerability compared to an ADC. Quantitative payload tumour uptake by mass spectrometry and fluorescent immuno-histological studies demonstrate superior solid tumour penetration across the entire tumour and diffusion from blood vessels and rapid kinetic uptake. In collaboration with our partners, Essex Biotechnology, ANT-043 is moving into IND-enabling studies for clinical development. Our new flagship product, ANT-045, which emerged from our proprietary FDC ‘discovery engine', is progressing well and new data will illustrate how ANT-045 could have a broader patient benefit in gastro-intestinal cancers. Like ANT-043, ANT-045 has potent in vitro cell-kill properties, excellent stability and drug-like features and illustrates how linker-payload design is critical for the tailoring properties of this emerging format of ADC. This presentation will focus on ANT-045's remarkable development and show that this FDC demonstrates superior efficacy and tolerability compared to an ADC when equated on an equi-mass, equi-molar and equi-payload basis. ANT-045 could be used to switch ‘immunologically-cold' tumour ‘hot' to benefit from checkpoint inhibitor therapy and data will be presented to support this concept.

Citation Format: Mahendra P. Deonarain, Gokhan Yahioglu, Ioanna Stamati, Bryan Edwards, Soraya Diez-Posada, Anja Pomowski, Ashleigh Stewart, Isabel Perez-Castro, Laura Bouche, Triin Jurgenson, Monika Maciuszek, Sam Ness, Malcolm Ngiam, Quinn Xue. Antibody fragment drug-conjugates (FDCs)-application of ANT-043 and ANT-045 in solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 909.

Using antibody directed phototherapy to target oesophageal adenocarcinoma with heterogeneous HER2 expression

Early oesophageal adenocarcinoma (OA) and pre-neoplastic dysplasia may be treated with endoscopic resection and ablative techniques such as photodynamic therapy (PDT). Though effective, discrete areas of disease may be missed leading to recurrence. PDT further suffers from the side effects of off-target photosensitivity. A tumour specific and light targeted therapeutic agent with optimised pharmacokinetics could be used to destroy residual cancerous cells left behind after resection. A small molecule antibody-photosensitizer conjugate was developed targeting human epidermal growth factor receptor 2 (HER2). This was tested in an in vivo mouse model of human OA using a xenograft flank model with clinically relevant low level HER2 expression and heterogeneity. In vitro we demonstrate selective binding of the conjugate to tumour versus normal tissue. Light dependent cytotoxicity of the phototherapy agent in vitro was observed. In an in vivo OA mouse xenograft model the phototherapy agent had desirable pharmacokinetic properties for tumour uptake and blood clearance time. PDT treatment caused tumour growth arrest in all the tumours despite the tumours having a clinically defined low/negative HER2 expression level. This new phototherapy agent shows therapeutic potential for treatment of both HER2 positive and borderline/negative OA.

Small-Format Drug Conjugates: A Viable Alternative to ADCs for Solid Tumours?

Antibody-Drug Conjugates (ADCs) have been through multiple cycles of technological innovation since the concept was first practically demonstrated ~40 years ago. Current technology is focusing on large, whole immunoglobulin formats (of which there are approaching 100 in clinical development), many with site-specifically conjugated payloads numbering 2 or 4. Despite the success of trastuzumab-emtansine in breast cancer, ADCs have generally failed to have an impact in solid tumours, leading many to explore alternative, smaller formats which have better penetrating properties as well as more rapid pharmacokinetics (PK). This review describes research and development progress over the last ~10 years obtained from the primary literature or conferences covering over a dozen different smaller format-drug conjugates from 80 kDa to around 1 kDa in total size. In general, these agents are potent in vitro, particularly more recent ones incorporating ultra-potent payloads such as auristatins or maytansinoids, but this potency profile changes when testing in vivo due to the more rapid clearance. Strategies to manipulate the PK properties, whilst retaining the more effective tumour penetrating properties could at last make small-format drug conjugates viable alternative therapeutics to the more established ADCs.

A HER2 selective theranostic agent for surgical resection guidance and photodynamic therapy

In many cancers early intervention involves surgical resection of small localised tumour masses. Inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. This work describes production of a HER2 targeting antibody Fab fragment dual conjugated to achieve both real time near-infrared fluorescent imaging and photodynamic therapy. The use of fluorescence emission from a NIR-dye could be used to guide resection of tumour bulk, for example during endoscopic diagnosis for oesophago-gastric adenocarcinoma, this would then be followed by activation of the photodynamic therapeutic agent to destroy untreated localised areas of cancer infiltration and tumour infiltrated lymph nodes. This theranostic agent was prepared from the Fab fragment of trastuzumab initially by functional disulfide re-bridging and site-specific click reaction of a NIR-dye. This was followed by further reaction with a novel pre-activated form of the photosensitiser chlorin e6 with the exposed fragments' lysine residues. Specific binding of the theranostic agent was observed in vitro with a HER2 positive cell line and cellular near-infrared fluorescence was observed with flow cytometry. Specific photo-activity of the conjugates when exposed to laser light was observed with HER2 positive but not HER2 negative cell lines in vitro, this selectivity was not seen with the unconjugated drug. This theranostic agent demonstrates that two different photo-active functions can be coupled to the same antibody fragment with little interference to their independent activities.

Development of Photodynamic Antimicrobial Chemotherapy (PACT) for Clostridium difficile

BACKGROUND

Clostridium difficile is the leading cause of antibiotic-associated diarrhoea and pseudo membranous colitis in the developed world. The aim of this study was to explore whether Photodynamic Antimicrobial Chemotherapy (PACT) could be used as a novel approach to treating C. difficile infections.

METHODS

PACT utilises the ability of light-activated photosensitisers (PS) to produce reactive oxygen species (ROS) such as free radical species and singlet oxygen, which are lethal to cells. We screened thirteen PS against C. difficile planktonic cells, biofilm and germinating spores in vitro, and cytotoxicity of effective compounds was tested on the colorectal adenocarcinoma cell-line HT-29.

RESULTS

Three PS were able to kill 99.9% of bacteria in both aerobic and anaerobic conditions, both in the planktonic state and in a biofilm, after exposure to red laser light (0.2 J/cm2) without harming model colon cells. The applicability of PACT to eradicate C. difficile germinative spores indirectly was also shown, by first inducing germination with the bile salt taurocholate, followed by PACT.

CONCLUSION

This innovative and simple approach offers the prospect of a new antimicrobial therapy using light to treat C. difficile infection of the colon.

Emerging formats for next-generation antibody drug conjugates

INTRODUCTION

Antibody drug conjugates now make up a significant fraction of biopharma's oncology pipeline due to great advances in the understanding of the three key components and how they should be optimised together. With this clinical success comes innovation to produce new enabling technologies that can deliver more effective antibody-drug conjugates (ADCs) with a larger therapeutic index.

AREAS COVERED

There are many reviews that discuss the various strategies for ADCs design but the last 5 years or so have witnessed the emergence of a number of different antibody formats compete with the standard whole immunoglobulin. Using published research, patent applications and conference disclosures, the authors review the many antibody and antibody-like formats, discussing innovations in protein engineering and how these new formats impact on the conjugation strategy and ultimately the performance. The alternative chemistries that are now available offer new linkages, stability profiles, drug:antibody ratio, pharmacokinetics and efficacy. The different sizes being considered promise to address issues, such as tumour penetration, circulatory half-life and side-effects.

EXPERT OPINION

ADCs are at the beginning of the next stage in their evolution and as these newer formats are developed and examined in the clinic, we will discover if the predicted features have a clinical benefit. From the commercial activity, it is envisaged that smaller or fragment-based ADCs will expand oncological applications.

Novel photosensitisers derived from pyropheophorbide-a: uptake by cells and photodynamic efficiency in vitro

Photodynamic Therapy (PDT) is a minimally invasive procedure used for treating a range of neoplastic diseases, which utilises combined action of light and a PDT drug called a photosensitiser. The efficiency of this treatment depends crucially on the properties of the photosensitiser used, namely on its efficient uptake by cells or by the surrounding vasculature, intracellular localisation, minimal dark toxicity and substantial phototoxicity. In this report we compare the spectroscopic properties, cell uptake and in vitro phototoxicity of two novel hydrophilic photosensitisers derived from pyropheophorbide-a (PPa). Both new photosensitisers have the potential to form bioconjugates with antibody fragments for targeted PDT. We find that the photophysical properties of both new photosensitisers are favourable compared to the parent PPa, including enhanced absorption in the red spectral region and substantial singlet oxygen quantum yields. Both molecules show efficient cellular uptake, but display a different intracellular localisation. Both new photosensitisers exhibit no significant dark-toxicity at concentrations of up to 100 microM. The phototoxicity of the two photosensitisers is strikingly different, with one derivative being 13 times more efficient than the parent PPa and another derivative being 18 times less efficient in SKOV3 ovarian cancer cells. We investigate the reasons behind such drastic differences in phototoxicity using confocal fluorescence microscopy and conclude that intracellular localisation is a crucial factor in the photodynamic efficiency of pheophorbide derivatives. These studies highlight the underlying factors behind creating more potent photosensitisers through synthetic manipulation.

Fluorescence characterisation of multiply-loaded anti-HER2 single chain Fv-photosensitizer conjugates suitable for photodynamic therapy

We report the synthesis, spectroscopic properties and intracellular imaging of recombinant antibody single chain fragment (scFv) conjugates with photosensitizers used for photodynamic therapy of cancer (PDT). Two widely-studied photosensitizers have been selected: preclinical pyropheophorbide-a (PPa) and verteporfin (VP), which has been clinically approved for the treatment of acute macular degeneration (Visudyne). Pyropheophorbide-a and verteporfin have been conjugated to an anti-HER2 scFv containing on average ten photosensitizer molecules per scFv with a small contribution (<or=20%) from non-covalently bound molecules. Confocal fluorescence microscopy demonstrates good cellular uptake of PPa conjugate with the HER2-positive cell line, SKOV-3, while negligible cell uptake is demonstrated for the HER2-negative cell line, KB. For the VP conjugate, increased rate of cellular uptake and prolonged retention in SKOV-3 cells is observed compared to free photosensitizer. In clinical applications this could provide increased potency and desired selectivity towards malignant tissue, leaving surrounding healthy tissue unharmed and reducing skin photosensitivity. The present study highlights the usefulness of photosensitizer immunoconjugates with scFvs for targeted PDT.