Anti-CD45 PBD-based antibody-drug conjugates are effective targeted conditioning agents for gene therapy and stem cell transplant

Stem cell gene therapy and hematopoietic stem cell transplantation (SCT) require conditioning to ablate the recipient's hematopoietic stem cells (HSCs) and create a niche for gene-corrected/donor HSCs. Conventional conditioning agents are non-specific, leading to off-target toxicities and resulting in significant morbidity and mortality. We developed tissue-specific anti-human CD45 antibody-drug conjugates (ADCs), using rat IgG2b anti-human CD45 antibody clones YTH24.5 and YTH54.12, conjugated to cytotoxic pyrrolobenzodiazepine (PBD) dimer payloads with cleavable (SG3249) or non-cleavable (SG3376) linkers. In vitro, these ADCs internalized to lysosomes for drug release, resulting in potent and specific killing of human CD45+ cells. In humanized NSG mice, the ADCs completely ablated human HSCs without toxicity to non-hematopoietic tissues, enabling successful engraftment of gene-modified autologous and allogeneic human HSCs. The ADCs also delayed leukemia onset and improved survival in CD45+ tumor models. These data provide proof of concept that conditioning with anti-human CD45-PBD ADCs allows engraftment of donor/gene-corrected HSCs with minimal toxicity to non-hematopoietic tissues. Our anti-CD45-PBDs or similar agents could potentially shift the paradigm in transplantation medicine that intensive chemo/radiotherapy is required for HSC engraftment after gene therapy and allogeneic SCT. Targeted conditioning both improve the safety and minimize late effects of these procedures, which would greatly increase their applicability.

In relapsed or refractory diffuse large B-cell lymphoma, CD19 expression by immunohistochemistry alone is not a predictor of response to loncastuximab tesirine

CD19-targeting treatments have shown promise in relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL). Loncastuximab tesirine (loncastuximab tesirine-lpyl [Lonca]) is a CD19-targeting antibody-drug conjugate indicated for R/R DLBCL after at least two systemic treatments. CD19 expression was evaluated in patients receiving Lonca in the LOTIS-2 clinical trial with available tissue samples obtained after last systemic therapy/before Lonca treatment. Lonca cytotoxicity was evaluated in a panel of six lymphoma cell lines with various CD19 expression levels. Quantitative systems pharmacology (QSP) modelling was used to predict Lonca responses. Lonca responses were seen in patients across all CD19 expression levels, including patients with low/no detectable CD19 expression and H-scores at baseline. Similarly, Lonca induced cytotoxicity in cell lines with different levels of CD19 expression, including one with very low expression. QSP modelling predicted that CD19 expression by immunohistochemistry alone does not predict Lonca response, whereas inclusion of CD19 surface density improved response prediction. Virtual patients responded to Lonca with estimated CD19 as low as 1000 molecules/cell of CD19, normally below the immunohistochemistry detection level. We found Lonca is an effective treatment for R/R DLBCL regardless of CD19 expression by immunohistochemistry. These results provide the basis for future studies addressing CD19-targeted agent sequencing.

Abstract 2638: Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers

Prostate-specific membrane antigen (PSMA) is a membrane-bound glutamate carboxypeptidase that is highly expressed in nearly all prostate cancers with the highest expression in metastatic castration-resistant prostate cancer. Moreover, PSMA is expressed in the neovasculature that supplies most non-prostatic solid tumors, including carcinomas of the lung, colon, breast, kidney, liver, and pancreas. ADCT-212 is an antibody-drug conjugate composed of the human IgG1 antibody 2A10 directed against human PSMA, site-specifically conjugated using GlycoConnectTM technology to PL1801, which contains HydraspaceTM, a valine-alanine cleavable linker and the pyrrolobenzodiazepine (PBD) dimer warhead SG2000 (drug-antibody ratio of ~1.8). The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity of ADCT-212 in human cancer cell lines and xenograft models and to determine its tolerability and pharmacokinetic (PK) in the rat. In vitro, ADCT-212 demonstrated potent cytotoxicity in a panel of PSMA-positive prostate cancer cell lines, whereas its activity was greatly reduced in PSMA-negative cell lines. ADCT-212 was efficiently internalized by PSMA-expressing LNCaP cells. Trafficking to the lysosomes started as early as 30 minutes and peaked at 1-2 hours post treatment. In line with the mechanism of action of the PBD dimer, ADCT-212 produced DNA interstrand cross-links (ICLs) that peaked by 12 hours and persisted for up to 36 hours post-treatment. In contrast, the peak of DNA ICLs formation for SG2000, the PBD dimer warhead alone, was observed immediately after 2-hour incubation, while a non-targeted PBD-ADC did not yield any appreciable DNA ICLs. Moreover, ADCT-212 showed indirect bystander killing activity in PSMA-negative PC3 cells incubated with conditioned medium from ADCT-212-treated LNCaP cells. In vivo, ADCT-212 showed strong antitumor activity against CWR22Rv1 and LNCaP prostate cancer xenograft models. In the CWR22Rv1 model, a tumor with heterogeneous PSMA expression, ADCT-212 achieved dose-dependent antitumor activity when administered as single dose at 2, 4 or 6 mg/kg, which resulted in increased survival compared to the control animals. In the LNCaP model, a single dose of ADCT-212 at 5 or 10 mg/kg resulted in strong and specific antitumor activity. Conversely, in the PSMA-negative PC3 xenograft model, ADCT-212 did not show anti-tumor activity compared to the controls, highlighting its target-mediated antitumor activity. ADCT-212 was tolerated as a single 20 mg/kg dose in male rats, with exposure data being indicative of a linear PK profile with a half-life of approximately 12 days. In conclusion, ADCT-212 demonstrated potent and specific in vitro and in vivo anti-tumor activity while it was stable and well tolerated in the rat, warranting further development of ADCT-212 into the clinic.

Citation Format: Francesca Zammarchi, Karin Havenith, Lolke de Haan, Ian Kirby, Narinder Janghra, Veronica Gil, Pedro Alves, Kristina Zaitseva, Meghann Kerr, Ben Leatherdale, Afroze Patel, Marie Thoelke, Shiran Huang, John A Hartley, Patrick H van Berkel. Preclinical development of ADCT-212, a PSMA-targeted antibody-drug conjugate employing the pyrrolobenzodiazepine dimer SG2000 for PSMA-expressing cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2638.

Abstract 1604: Preclinical development of ADCT-211, a novel pyrrolobenzodiazepine dimer-based antibody-drug conjugate targeting solid tumors expressing IL13RA2

Interleukin 13 receptor subunit alpha 2 (IL13RA2) is one of the two major receptors for the cytokine interleukin 13 (IL-13). While IL13RA1 has low affinity for IL-13 and it is expressed ubiquitously in humans, IL13RA2 has high binding affinity to IL-13 and its expression in normal tissues is mainly restricted to the testes. IL13RA2 was initially regarded as a decoy receptor because it has a short cytoplasmic tail with no known signaling motifs, and its binding to IL-13 does not lead to activation of the JAK/STAT6 pathway. However, recent studies demonstrated that IL-13-mediated IL13RA2 signaling occurs via STAT6-independent pathways. IL13RA2 is reported to be expressed at a high frequency in glioblastoma multiforme (GBM) as well as in other solid tumors including melanoma, renal cell carcinoma and adrenocortical carcinoma and is correlated with poor prognosis. ADCT-211 is an antibody-drug conjugate composed of HuCl47, a humanized IgG1 antibody directed against human IL13RA2, site-specifically conjugated using GlycoConnectTM technology to PL1801, which contains HydraspaceTM, a valine-alanine cleavable linker and the PBD dimer cytotoxin SG2000 (drug to antibody ratio ~ 1.8). The purpose of this study was to characterize the in vitro and in vivo anti-tumor activity of ADCT-211 in human cancer cell lines and xenograft models, to determine its safety, tolerability and pharmacokinetic (PK) in the rat and to measure IL13RA2 expression by immunohistochemistry (IHC) in human tumor specimens. HuCl47 showed specific binding to recombinant IL13RA2, while it did not bind to IL13RA1. In vitro, ADCT-211 had highly potent and targeted cytotoxicity against various IL13RA2-expressing solid cancer cell lines. In vivo, a single dose of ADCT-211 at 10 mg/kg was able to completely eradicate tumors in the subcutaneous (sc) A375 human melanoma xenograft model and resulted in 8/8 tumor-free survivors (TFS) at the end of the study on day 57. In the sc U251 human glioblastoma xenograft model, a single dose of ADCT-211 at 3.75 mg/kg showed potent and durable antitumor activity and it resulted in 5/10 partial responders and 5/10 complete responders, 2 of which were TFS at the end of the study on day 51. In an MTD study in male rats, ADCT-211 was stable and tolerated up to 24 mg/kg single dose, with exposure data being indicative of a linear PK profile with a half-life of 12-19 days. Expression of membranous IL13RA2 was confirmed by IHC in a panel of primary and refractory GBM samples and malignant melanoma, highlighting them as potential indications for the clinical development of ADCT-211. In conclusion, ADCT-211 demonstrated potent and specific in vitro and in vivo anti-tumor activity and it was stable and well tolerated in the rat, warranting further development of ADCT-211 into the clinic in IL13RA2-expressing cancers.

Citation Format: Francesca Zammarchi, Karin Havenith, Ben Leatherdale, Britanny Roberts, Lara Montolio, Afroze Patel, Narinder Janghra, Pedro Alves, Kristina Zaitseva, Cecile Oblette, Ian Kirby, Lolke de Haan, Patrick H van Berkel. Preclinical development of ADCT-211, a novel pyrrolobenzodiazepine dimer-based antibody-drug conjugate targeting solid tumors expressing IL13RA2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1604.

Population pharmacokinetics analysis of camidanlumab tesirine in patients with relapsed or refractory Hodgkin lymphoma and non-Hodgkin lymphoma

PURPOSE

The objective of this analysis was to develop a population pharmacokinetic (PPK) model to characterize camidanlumab tesirine (Cami) pharmacokinetics based on the phase 1 study in relapsed/refractory lymphoma (NCT02432235).

METHODS

An initial PPK model was developed based on a two-compartment model with parallel linear and nonlinear elimination pathways. Pharmacokinetic parameters were evaluated for correlation with potential demographic covariates; significant covariates were retained in the final model.

RESULTS

In the final PPK model, baseline weight effects were included on clearance (CL), intercompartmental clearance (Q), and the volumes of distribution in the central (V₁) and peripheral (V₂) compartments. The baseline soluble CD25 (sCD25) effect was included on CL and maximum velocity of saturable clearance (V_max); sex effect was included on CL and V₁; and ethnicity effect was included on deconjugation clearance (CL_dec). For a typical patient, CL and CL_dec were 0.516 and 0.21 L/day, respectively (tAb elimination half-life: 18.72 days); V₁ and V₂ were 4.41 and 2.67 L, respectively; V_max was 0.49 mg/day; the Michaelis-Menten constant (K_m) was 0.409 µg/mL; and the first-order rate for decrease of V_max (K_DES) was 0.0197/day. Cami exposure was higher for patients with low baseline sCD25, higher body weight, and females.

CONCLUSIONS

The final model described the observed data well, estimates of PK parameters were obtained, and covariates with significant effects on Cami exposure were identified. Altogether, this final PPK model provides a robust basis for analysis of Cami exposure-response relationships and further supports identification of the optimal Cami dosing schedule for patients with relapsed/refractory lymphoma.

Abstract 4151: Effect of camidanlumab tesirine (Cami) as monotherapy and in combination with pembrolizumab (PEM) on the immune cell profile in patients with selected advanced solid tumors

Background: Cami, an investigational anti-CD25, pyrrolobenzodiazepine-based antibody drug conjugate, imparts cytotoxicity on CD25+ regulatory T cells (Tregs), leading to immunomodulatory effects (eg, modifying effector T cell [Teff]:Treg intratumoral balance).

Objective: Describe the pharmacokinetics (PK) and circulating immune cell profile of Cami monotherapy and in combination with PEM in patients with advanced solid tumors.

Methods: In the dose-escalation phase 1b trial of Cami (NCT03621982) in patients with advanced solid tumors after failure of recommended therapies, we investigated Cami monotherapy (n=44; doses: 20, 30, 45, 60, 80, 100, 125, and 150 µg/kg every 3 weeks [Q3W]) and Cami combination therapy (n=12; doses: 30, 45, and 60 µg/kg with PEM 200 mg Q3W). Serum conjugated antibody (cAb) and total antibody (tAb) were quantified by a validated chemoimmunoluminescence assay. Soluble CD25 was quantified by a qualified enzyme-linked immunoassay. Circulating immune cell absolute counts were assessed by flow cytometry for Tregs (FoxP3+CD25+CD127low) as a fraction of absolute CD4+ cells, Teff (CD8+), and Teff:Treg. Statistical analyses were performed using a linear mixed-effects model (maximum likelihood) for the biomarker effects model with cAb area under the curve (AUC) during cycle 1, therapy (monotherapy vs combination), and treatment cycle as fixed effects and log AUC slope with intercept by subject or visit day as random effects.

Results: PK analysis found Cmax and AUC of cAb and tAb increased during cycles 1 and 2 with Cami monotherapy and combination therapy across the range of doses. Variability of AUCinf for cAb in cycle 1 appeared modest to marked across discrete dose groups (CV=14.7-98.1%). The clearance of cAb ranged from 1.34 to 3.52 L/day in cycle 1 with no apparent differences between monotherapy and combination therapy. Biomarker modeling demonstrated that cAb AUC and cycle were associated with a significant Tregs depletion and a significant positive effect on Teff:Treg ratio but with no relevant effect on Teff. Within cycle, treatment-related modulation of Teff and Tregs was observed for all doses and conditions. Soluble CD25 appears to be significantly positively affected by cycle 2 treatment.

Conclusions: PK exposure of Cami was dose-related with varying degrees of interpatient variability. Circulating Tregs were significantly decreased and Teff:Treg was significantly increased by Cami exposure, demonstrating the intended immunomodulatory effect of Cami in circulation and suggesting that a combination approach with Cami could address an immune-resistance mechanism. Future analyses will consider discrete PEM effect, correlates to tumor biopsy expression and response, and combined Cami+PEM effect in tumor biopsies. Funding: ADC Therapeutics; medical writing: CiTRUS Health Group.

Citation Format: Igor Puzanov, Christopher T. Chen, Patricia LoRusso, Kyriakos P. Papadopoulos, Shivaani Kummar, Erika Hamilton, Yvan LeBruchec, Karin Havenith, Serafino Pantano, Marie Toukam, Jens Wuerthner, Joseph Boni. Effect of camidanlumab tesirine (Cami) as monotherapy and in combination with pembrolizumab (PEM) on the immune cell profile in patients with selected advanced solid tumors [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 4151.

Camidanlumab tesirine in patients with relapsed or refractory lymphoma: a phase 1, open-label, multicentre, dose-escalation, dose-expansion study

BACKGROUND

Novel approaches are required to improve outcomes in relapsed or refractory classical Hodgkin lymphoma and non-Hodgkin lymphoma. We aimed to evaluate camidanlumab tesirine, an anti-CD25 antibody-drug conjugate, in this patient population.

METHODS

This was a phase 1, dose-escalation (part 1), dose-expansion (part 2), multicentre trial done in 12 hospital sites (seven in the USA and five in the UK). Adults (≥18 years old) with pathologically confirmed relapsed or refractory classical Hodgkin lymphoma or non-Hodgkin lymphoma, an Eastern Cooperative Oncology Group performance status 0-2, who had no therapies available to them with established clinical benefit for their disease stage were enrolled. Camidanlumab tesirine was administered intravenously (3-150 μg/kg) once every 3 weeks. Primary objectives were to assess dose-limiting toxicity, determine maximum tolerated dose and recommended expansion dose(s), and assess safety of camidanlumab tesirine. Safety was assessed in all treated patients; antitumour activity was assessed in patients with one or more valid baseline and post-baseline disease assessment and in those who had disease progression or died after first study-drug dose. This trial was registered with ClinicalTrials.gov, NCT02432235.

FINDINGS

Between Oct 5, 2015, and Jun 30, 2019, 133 patients were enrolled (77 [58%] had classical Hodgkin lymphoma and 56 (42%) had non-Hodgkin lymphoma). Median follow-up was 9·2 months (IQR 4·2-14·3). Eight dose-limiting toxicities were reported in five (6%) of 86 patients who were evaluable; the maximum tolerated dose was not reached. The recommended doses for expansion were 30 μg/kg and 45 μg/kg for patients with classical Hodgkin lymphoma and 80 μg/kg for patients with T-cell non-Hodgkin lymphomas. No recommended doses for expansion were defined for B-cell non-Hodgkin lymphomas. Grade 3 or worse treatment-emergent adverse events (reported by ≥10% of the 133 patients) included increased γ-glutamyltransferase (20 [15%] patients), maculopapular rash (16 [12%]), and anaemia (15 [11%]); 74 (56%) patients had serious treatment-emergent adverse events, most commonly pyrexia (16 [12%]). One (1%) fatal treatment-emergent adverse event and two (2%) deaths outside the reporting period were considered at least possibly study-drug related. Antitumoural activity was seen in classical Hodgkin and non-Hodgkin lymphomas; notably in all patients with classical Hodgkin lymphoma, the overall response was 71% (95% CI 60-81).

INTERPRETATION

These results warrant evaluation of camidanlumab tesirine as a potential treatment option for relapsed or refractory lymphoma, particularly in patients with classical Hodgkin lymphoma.

FUNDING

ADC Therapeutics.

A phase 1b, open-label, dose-escalation study to evaluate camidanlumab tesirine (Cami) as monotherapy in patients (pts) with advanced solid tumors

2556

Background: Depletion of tumor-infiltrating CD25+ regulatory T cells (Tregs), which inhibit tumor-specific immune responses, could contribute to tumor eradication. Cami (ADCT-301), an anti-CD25, pyrrolobenzodiazepine-based antibody-drug conjugate, targets CD25+ Tregs. A mouse surrogate has shown potent antitumor activity in solid tumor models. Here we report preliminary data from the monotherapy arm of a phase 1b trial of Cami in pts with selected advanced solid tumors. Methods: The monotherapy dose-escalation part of this open-label study enrolled pts (aged ≥18 years) with selected advanced solid tumors and no suitable existing therapy. The primary objective was to characterize safety and tolerability, and to identify the recommended phase 2 dose of Cami monotherapy. Secondary and exploratory objectives included evaluation of preliminary antitumor activity, pharmacokinetics (PK), pharmacodynamics (PD), and immunogenicity. Pts received Cami every 3 weeks (1 cycle) with dose escalation per a 3+3 design. Disease control rate (DCR) was assessed (complete and partial responses [CR, PR] and stable disease). Results: At data cut-off (Dec 17, 2020), 44 pts were enrolled, with primary tumor types (stage IVA/B: 27 pts; 61.4%) of colorectal (15 pts; 34.1%), pancreatic (14 pts; 31.8%), head and neck, ovarian/fallopian tube, and renal cell carcinoma (all 3 pts; 6.8%), non-small cell lung cancer (2 pts; 4.5%), gastric, esophageal/GEJ, melanoma, and triple-negative breast cancer (each 1 pt; 2.3%). Median (range) age was 60.5 (33–82) years; median (range) number of prior systemic therapies was 4 (1–9). Pts received a median (range) of 2 (1–6) Cami cycles at doses of 20–150 µg/kg. Median (range) treatment duration was 22 (1–178) days. No dose-limiting toxicities were reported. The maximum tolerated dose (MTD) was not reached. All-grade treatment-emergent adverse events (TEAEs) in ≥20% pts were nausea (18 pts; 40.9%), decreased appetite and fatigue (each 16 pts; 36.4%), constipation (13 pts; 29.5%), abdominal pain (11 pts; 25%), and rash (10 pts; 22.7%). The only Grade ≥3 TEAE in ≥10% pts was anemia (5 pts; 11.4%). Grade 3 autoimmune AEs (colitis, immune-mediated AE, systemic inflammatory response syndrome) and neurologic AEs (dysphagia and asthenia, but not GBS) were reported in 3 (6.8%) and 2 (4.5%) pts, respectively. 1 (2.3%) Cami-related TEAE led to treatment withdrawal; no Cami-related TEAEs were fatal. DCR was 25% (95% CI: 11.1, 34.7); 11/44 pts attained stable disease. No pts had CR or PR. Conclusions: Dose escalation of Cami monotherapy is complete. The safety profile is encouraging and MTD was not reached. PK/PD data will be presented. 150 µg/kg is the highest dose investigated for single-agent Cami and the highest to be investigated combined with pembrolizumab in selected advanced solid tumors in the current protocol. Funding: ADC Therapeutics SA NCT03621982. Clinical trial information: NCT03621982.

CD25-targeted antibody-drug conjugate depletes regulatory T cells and eliminates established syngeneic tumors via antitumor immunity

Background

Regulatory T cells (T_regs) contribute to an immunosuppressive tumor microenvironment. They play an important role in the establishment and progression of tumors with high T_regs infiltration and present a major obstacle to tumor eradication by immunotherapies. Numerous strategies have been attempted to deplete or block T_regs, although their success has been limited.

Methods

A CD25-targeted, pyrrolobenzodiazepine (PBD) dimer-based antibody–drug conjugate (ADC) was investigated for its ability to deplete T_regs and induce antitumor immunity. Antitumor activity of CD25-ADC either alone or in combination with an anti-programmed cell death protein 1 (PD-1) antibody was evaluated in CD25-negative syngeneic models that exhibit tumor infiltration of CD25-expressing T_regs, and its pharmacodynamics and pharmacokinetics were assessed.

Results

Single low doses of CD25-ADC resulted in potent and durable antitumor activity in established syngeneic solid tumor models and the combination of a suboptimal dose was synergistic with PD-1 blockade. Tumor eradication by the CD25-targeted ADC was CD8+ T cell-dependent and CD25-ADC induced protective immunity. Importantly, while CD25-ADC mediated a significant and sustained intratumoral T_regs depletion, accompanied by a concomitant increase in the number of activated and proliferating tumor-infiltrating CD8+ T effector cells, systemic T_regs depletion was transient, alleviating concerns of potential autoimmune side effects.

Conclusions

This study shows that a PBD dimer-based, CD25-targeted ADC is able to deplete T_regs and eradicate established tumors via antitumor immunity. This represents a novel approach to efficiently deplete T_regs via a very potent DNA damaging toxin known to induce immunogenic cell death. Moreover, this study provides proof of concept for a completely new application of ADCs as immunotherapeutic agents, as the main mode of action relies on the ADC directly targeting immune cells, rather than tumor cells. These strong preclinical data warrant the clinical evaluation of camidanlumab tesirine (ADCT-301), a PBD-based ADC targeting human CD25, either alone or in combination with checkpoint inhibitors in solid tumors with known T_regs infiltration. A phase I trial (NCT03621982) of camidanlumab tesirine in patients with selected advanced solid tumors is ongoing.

Abstract 234: Pre-clinical characterization of 3A4-PL1601, a novel pyrrolobenzodiazepine (PBD) dimer-based antibody-drug conjugate (ADC) directed against KAAG1-expressing malignancies

Kidney-associated antigen 1 (KAAG1) is an 84 amino acid protein encoded by the reverse strand of a housekeeping gene called DCDC2 which was identified from a cDNA library derived from a histocompatibility leukocyte antigen-B7 renal carcinoma cell line as an antigenic peptide presented to cytotoxic T lymphocytes. More recently, KAAG1 has been identified by a sensitive subtractive cloning technology called STAR as a novel tumor-associated antigen expressed in a high percentage of ovarian tumors and triple-negative breast cancers (TNBCs), while it has restricted normal tissue expression. 3A4 is a humanized antibody raised against human KAAG1, which binds to KAAG1 expressed on the surface of cancer cells, rapidly internalizes and co-localizes with LAMP-1, a lysosomal marker. Altogether, KAAG1 represents an attractive target for an antibody-drug conjugate (ADC) approach based on its high and selective expression in various malignancies and its restricted expression in healthy tissues. 3A4-PL1601 is an ADC composed of the 3A4 antibody, site-specifically conjugated using GlycoConnectTM technology to PL1601, which contains HydraspaceTM, a valine-alanine cleavable linker and the PBD dimer cytotoxin SG3199. The purpose of this study was to characterize the in vitro and in vivoanti-tumor activity of 3A4-PL1601 in human cancer cell lines and xenografts models and to determine its safety and tolerability in the cynomolgus monkey. In vitro, the 3A4-PL1601 demonstrated potent cytotoxicity in a panel of human cancer cell lines of different origin and levels of KAAG1, while its potency was strongly reduced in KAAG1-negative cell lines. In vivo, 3A4-PL1601 showed potent and specific anti-tumor activity in the TNBC-derived MDA-MB-231 xenograft compared to the vehicle- and isotype control ADC-treated mice. A single dose of 3A4-PL1601 at 0.6 mg/kg resulted in 4/8 partial responders (PR) and 3/8 complete responders, two of which were tumor-free survivors at the end of the study on day 59, while none of the mice treated with the vehicle or the isotype-control ADC showed any activity. Moreover, 3A4-PL1601 showed potent and dose-dependent anti-tumor activity in the KAAG1-expressing, human renal cell carcinoma-derived SN12C xenograft when tested as single dose at 0.3, 0.6 or 1 mg/kg. At the highest dose tested, 3A4-PL1601 resulted in sustained tumor growth control and 2/8 PRs at the end of the study on day 60. 3A4-PL1601 was stable, well tolerated (MTD at least 0.8 mg/kg) and showed a favorable pharmacokinetic profile (t1/2 ~ 6 days) in the cynomolgus monkey (cross-reactive species). In conclusion, 3A4-PL1601 demonstrated potent and specific in vitro and in vivo anti-tumor activity in KAAG1-expressing cancer-derived models and it was stable and well tolerated in cynomolgus monkey, warranting further development of this ADC into the clinic.

Citation Format: Francesca Zammarchi, Francois Bertelli, Karin Havenith, Ian Kirby, Simon Chivers, Patrick H. van Berkel. Pre-clinical characterization of 3A4-PL1601, a novel pyrrolobenzodiazepine (PBD) dimer-based antibody-drug conjugate (ADC) directed against KAAG1-expressing malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 234.

Abstract A004: MEDI3726 (ADCT-401), a novel antibody-drug conjugate targeting PSMA, has potent in vivo antitumor activity in prostate cancer patient-derived xenograft models

Prostate specific membrane antigen (PSMA), a type II membrane glycoprotein, is highly expressed in nearly all prostate cancers, with the highest expression in metastatic castration-resistant prostate cancer (mCRPC). The prevalence, increased surface expression in prostate tumors, and constitutive internalization make PSMA an attractive target for an antibody-drug conjugate (ADC) approach in anticancer treatment of patients with mCRPC.

MEDI3726 (previously known as ADCT-401) is an ADC consisting of an engineered version of anti-PSMA antibody J591, site-specifically conjugated with DNA cross-linking pyrrolobenzodiazepine (PBD) dimer SG3249 for targeting prostatic cancer cells. Using prostate cancer cell line models, we have previously shown that MEDI3726 specifically binds to the extracellular domain of PSMA and, once internalized, releases the PBD dimer to cross link DNA and achieve potent in vitro and in vivo cytotoxicity.

Here we investigated the in vivo activity of MEDI3726 in a series of LuCaP prostate cancer patient-derived xenograft (PDX) models. The selected LuCaP models had varying PSMA expression and heterogeneous genetic and phenotypic backgrounds. In agreement with the earlier cell line xenograft data, dose-dependent antitumor activity was observed in PSMA-positive PDX models with durable tumor regressions in models with high PSMA expression. In the PSMA-negative LuCaP 35CR PDX model, MEDI3726 did not have significant antitumor activity, thus highlighting target-mediated in vivo activity. Increased phosphorylation of histone H2AX was observed in xenografts dosed with MEDI3726, confirming DNA damage induced by interstrand cross-linking PBD dimer as the mechanism of antitumor activity of MEDI3726.

In summary, MEDI3726 demonstrated potent and specific in vivo antitumor activity, concurrent with DNA damage, in clinically relevant prostate cancer PDX models. MEDI3726 is being evaluated in phase 1 clinical trial as an anticancer treatment in patients with metastatic castrate-resistant prostate cancer (NCT02991911).

Citation Format: Song Cho, Francesca Zammarchi, Noel R. Monks, Kapil Vashisht, Ravinder Tammali, Kevin Schifferli, Patrick Strout, Wanda King, Karma Dacosta, Ryan Fleming, David G. Williams, Karin Havenith, Mary Jane Masson Hinrichs, Simon Chivers, Nazzareno Dimasi, Phil W. Howard, John A. Hartley, Steve Coats, Ronald Herbst, Patrick H. van Berkel, David A. Tice. MEDI3726 (ADCT-401), a novel antibody-drug conjugate targeting PSMA, has potent in vivo antitumor activity in prostate cancer patient-derived xenograft models [abstract]. In: Proceedings of the AACR Special Conference: Prostate Cancer: Advances in Basic, Translational, and Clinical Research; 2017 Dec 2-5; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(16 Suppl):Abstract nr A004.

Abstract 3111A: ADCT-401/MEDI3726, a novel pyrrolobenzodiazepine (PBD)-based antibody-drug conjugate (ADC) targeting PSMA-expressing prostate cancers

Prostate-specific membrane antigen (PSMA) is an attractive target for an ADC approach as it is over-expressed by virtually all prostate cancers and its expression is highest in poorly-differentiated, metastatic and castration-resistant cases. PSMA has limited expression in non-prostatic tissues, it is not secreted or cleaved by PSMA-expressing cells, and it is constitutively internalized, a process that may be accelerated by specific antibody binding. ADCT-401/MEDI3726 is an ADC composed of a monoclonal antibody (J591), directed against human PSMA, site-specifically conjugated (drug-to-antibody ratio of 1.8) to a highly cytotoxic DNA cross-linking PBD dimer with a valine-alanine dipeptide linker. In vitro, ADCT-401/MEDI3726 demonstrated potent and specific cytotoxicity in a panel of PSMA-expressing prostate cancer cell lines, whereas its activity was greatly reduced in PSMA-negative cell lines. In vivo, ADCT-401/MEDI3726 showed strong antitumor activity against CWR22Rv1 and LNCaP human-derived prostate cancer xenograft models. In the CWR22Rv1 model, a tumor with low, heterogeneous PSMA expression, ADCT-401/MEDI3726 achieved dose-dependent antitumor activity when administered as single dose at either 0.33 or 1 mg/kg, which resulted in significant increase in survival compared to the vehicle-treated animals. Moreover, a single dose of ADCT-401/MEDI3726 showed remarkable superior antitumor activity compared to multiple doses of another PSMA-targeted ADC stochastically conjugated to the auristatin payload vcMMAE with a DAR of ~4. In the LNCaP model, ADCT-401/MEDI3726 resulted in dose-dependent antitumor activity when dosed once at 0.11, 0.33 or 1 mg/kg. In the PSMA-negative prostate cancer-derived PC3 xenograft model, ADCT-401/MEDI3726 and an isotope-control ADC showed limited tumor growth inhibition highlighting target-mediated antitumor activity. ADCT-401/MEDI3726 demonstrated potent and specific in vitro and in vivo antitumor activity in prostate cancer-derived models of differing levels of PSMA and this warrants further development of this ADC into the clinic.

Citation Format: Francesca Zammarchi, Simon Chivers, Karin Havenith, David G. Williams, Lauren Adams, Maria Mellinas-Gomez, Simon Corbett, Peter Tyrer, Francois D'Hooge, Song Cho, Nazzareno Dimasi, Mary Jane Hinrichs, Phil W. Howard, John A. Hartley, Patrick H. van Berkel. ADCT-401/MEDI3726, a novel pyrrolobenzodiazepine (PBD)-based antibody-drug conjugate (ADC) targeting PSMA-expressing prostate cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3111A. doi:10.1158/1538-7445.AM2017-3111A

Abstract 637: Preclinical activity of hLL2-PBD, a novel anti-CD22 antibody-pyrrolobenzodiazepine (PBD) conjugate in models of non-Hodgkin lymphoma

CD22 is a type I transmembrane sialoglycoprotein, which expression is restricted to the B-cell lineage. CD22 is also found highly expressed on most malignant mature B cells, including follicular non-Hodgkin lymphoma (NHL), marginal zone lymphoma (MZL), mantle cell lymphoma (MCL), diffuse large B-cell lymphoma (DLBCL), small lymphocytic lymphoma (SLL) and chronic lymphocytic leukemia (CLL).

The differential and favorable expression profile of CD22 in normal and tumor tissues, together with its rapid internalization upon binding with a ligand or antibody, make CD22 an attractive target for an antibody drug conjugate (ADC) mediated treatment of B-cell malignancies. hLL2-PBD is an ADC composed of the humanized monoclonal antibody epratuzumab (hLL2) against human CD22 stochastically conjugated via a valine-alanine cleavable, maleimide linker to a PBD dimer. PBD dimers represent a novel class of payloads, which bind in the DNA minor groove and form highly cytotoxic DNA interstrand cross-links. The average drug to antibody ratio (DAR) of hLL2-PBD is 2.

In vitro, hLL2-PBD showed potent and specific cytotoxicity, as assessed by the MTS assay, in the CD22-positive human Burkitt's lymphoma-derived cell lines Ramos and Daudi and the human diffuse large B-cell lymphoma-derived cell line WSU-DLCL2.

In vivo, hLL2-PBD demonstrated potent anti-tumor efficacy in subcutaneously (s.c.) implanted Daudi and Ramos xenograft models. In the Daudi model, hLL2-PBD, administered as a single dose at either 0.1 or 0.3 mg/kg, achieved dose-dependent anti-tumor activity, resulting in significant increase in survival. At 0.3 mg/kg, hLL2-PBD induced complete tumor regression in all treated animals. In the Ramos xenograft model, a single dose of 1 mg/kg of hLL2-PBD achieved strong tumor regression. Moreover, hLL2-PBD achieved a superior anti-tumor activity compared to Hu10F4-vcMMAE, a CD22-targeting ADC with the auristatin payload vcMMAE and a DAR of 4 (Genentech Inc.), when tested at 1 mg/kg, single dose. Pharmacokinetic (PK) analysis of hLL2-PBD in CB.17 SCID mice showed a favorable PK profile, with a half-life of approximately 12 days.

In conclusion, these data demonstrate the potent in vitro and in vivo anti-tumor activity of hLL2-PBD against CD22-positive hematological tumors and warrant further development of this ADC into the clinic.

Citation Format: Francesca Zammarchi, David Williams, Karin Havenith, Francois D'Hooge, Philip W. Howard, John A. Hartley, Patrick van Berkel. Preclinical activity of hLL2-PBD, a novel anti-CD22 antibody-pyrrolobenzodiazepine (PBD) conjugate in models of non-Hodgkin lymphoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 637. doi:10.1158/1538-7445.AM2015-637

Features of macrophage differentiation induced by p19INK4d, a specific inhibitor of cyclin D-dependent kinases

The mitogen-dependent induction of cyclin D-dependent kinase activity is required for cells to enter the DNA synthetic (S) phase of their division cycle. Immature 32Dcl3 myeloid cells (32D) proliferating in the presence of interleukin-3 (IL-3) normally express cyclins D2 and D3, which assemble into binary holoenzyme complexes with their catalytic subunits, CDK4 and CDK6. When 32D cells are switched to medium containing granulocyte colony-stimulating factor (G-CSF) instead of IL-3, D-type cyclins are degraded and, in the absence of their associated kinase activity, the cells arrest in the first gap phase (G1) of the cell cycle and differentiate to neutrophils. We derived 32D cells in which the expression of p19INK4d, a specific polypeptide inhibitor of CDK4 and CDK6, is regulated by the heavy metal-inducible sheep metallothionein promoter. Induction of p19INK4d in response to zinc prolonged cell survival in the absence of growth factor treatment. When maintained in medium containing both IL-3 and zinc, these cells lost cyclin D-dependent kinase activity, underwent G1 phase arrest, and acquired certain morphologic, antigenic, and functional properties of mononuclear phagocytes. Cells induced to express p19INK4d did not synthesize receptors for macrophage colony-stimulating factor (M-CSF/CSF-1) and reverted to an immature myeloid phenotype when shifted back into medium containing IL-3 alone. These cells exhibited accelerated differentiation to neutrophils in response to G-CSF but also gave rise to macrophage-like cells when maintained in medium containing both G-CSF and zinc. Therefore, the acquisition of macrophage properties in response to zinc treatment neither depended upon IL-3 nor upon G1 phase arrest per se and instead reflects some ability of p19INK4d, and presumably cyclin D-dependent kinases, to affect myeloid differentiation.

A subset of splenic macrophages process and present native antigen to naive antigen-specific CD4+ T-cells from mice transgenic for an alpha beta T-cell receptor

The progeny of individual macrophage precursors from mouse spleen were examined for their ability to constitutively process and present native pigeon cytochrome c or a peptide fragment of this antigen to naive CD4+ T-cells from mice transgenic for a V alpha 11/V beta 3 TCR that recognizes an epitope in the antigen fragment. The results show that constitutive Ag processing and presentation is a stable characteristic restricted to the progeny of approximately 20% of splenic macrophage precursors. This property does not appear to be randomly acquired, but to reflect the ability of certain macrophages to produce IL-12.