Design and Evaluation of ZD06519, a Novel Camptothecin Payload for Antibody Drug Conjugates

In recent years, the field of antibody drug conjugates (ADC) has seen a resurgence, largely driven by the clinical benefit observed in patients treated with ADCs incorporating camptothecin-based topoisomerase I inhibitor payloads. Herein, we present the development of a novel camptothecin ZD06519 (FD1), which has been specifically designed for its application as an ADC payload. A panel of camptothecin analogs with different substituents at the C-7 and C-10 positions of the camptothecin core was prepared and tested in vitro. Selected compounds spanning a range of potency and hydrophilicity were elaborated into drug-linkers, conjugated to trastuzumab, and evaluated in vitro and in vivo. ZD06519 was selected on the basis of its favorable properties as a free molecule and as an antibody conjugate, which include moderate free payload potency (∼1 nmol/L), low hydrophobicity, strong bystander activity, robust plasma stability, and high-monomeric ADC content. When conjugated to different antibodies using a clinically validated MC-GGFG-based linker, ZD06519 demonstrated impressive efficacy in multiple cell line-derived xenograft models and noteworthy tolerability in healthy mice, rats, and non-human primates.

Abstract 2641: ZW191, a novel FRa-targeting antibody drug conjugate bearing a topoisomerase 1 inhibitor payload

Background: Folate Receptor alpha (FRa) is a validated cell surface cancer target that is prevalently expressed in multiple cancers with high unmet need, including ovarian cancer and other gynecological cancers, while exhibiting minimal expression in normal tissues. Due to FRa’s favorable expression profile, multiple antibody-drug conjugates (ADCs) are being explored in this setting. Here we present the preclinical characterization of a new anti-FRa ADC, ZW191. ZW191 is an antibody drug conjugate (ADC) comprised of a humanized IgG1 antibody conjugated to a novel camptothecin-based topoisomerase 1 inhibitor payload, ZD06519, via a maleimidocaproyl (MC) anchor and a glycyl glycyl phenylalanyl glycine (GGFG)-aminomethyl (AM) cleavable linker at a drug-to-antibody ratio (DAR) of 8.

Materials and Methods: The novel antibody and drug-linker components of ZW191 were generated, characterized, and optimally integrated. The apparent binding affinity and cellular internalization of the ZW191 antibody, and the intracellular concentration of the released camptothecin payload, ZD06519, were determined in FRa-expressing cells. Additionally, the binding specificity of the ZW191 antibody was determined using a cell microarray technology to test for binding against over 6,000 full length proteins that are individually over-expressed in human cells. Tumor spheroid cancer cell cultures were utilized to determine the cytotoxicity of ZW191 and the ability of ZW191 to penetrate the layers of the three-dimensional (3D) spheroid. The bystander activity of ZW191 was assessed using antigen positive and negative co-culture experiments. The anti-tumor activity of ZW191 was evaluated in a panel of cell line-derived xenograft (CDX) and patient-derived xenograft (PDX) ovarian cancer models spanning a range of FRa expression. ZW191 was evaluated in toxicology and pharmacokinetic (PK) studies performed in rodents and non-human primates (NHP).

Results: The antibody component of ZW191 features a favorable binding profile with strong and exclusive binding to FRa, and drives superior tumor spheroid penetration, cellular internalization, and payload delivery compared to FRa targeted antibodies used in other ADCs. ZW191 demonstrates potent activity in FRa expressing 3D tumor spheroid cultures and effective bystander activity. In a panel of CDX and PDX models representing a range of FRa expression, ZW191 demonstrates compelling anti-tumor activity at exposures that are estimated to be readily achievable in the clinic. ZW191 was tolerated up to 200 mg/kg in a two-dose rat study and at 30 mg/kg in a two-dose NHP study, with favorable PK. The promising efficacy, tolerability, and PK supports the potential of ZW191 as a novel therapeutic agent that may help address unmet need in patients with high and low FRa-expressing cancers.

Citation Format: Sam Lawn, Andrea Hernandez Rojas, Raffaele Colombo, Dayananda Siddappa, Jodi Wong, Kaylee Wu, Vincent Fung, Dunja Urosev, Luying Yang, Jamie R. Rich, Stuart D. Barnscher. ZW191, a novel FRa-targeting antibody drug conjugate bearing a topoisomerase 1 inhibitor payload [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 2641.

Abstract 2935: ZW270, a conditionally masked IL-12 cytokine fusion protein displaying potent anti-tumor activity absent systemic toxicity

IL-12 is a pleiotropic cytokine that potently stimulates anti-tumor cytotoxic T and NK cell mediated immunity. Recombinant IL-12 reduces tumor growth in multiple mouse models, but its therapeutic application has been limited by severe toxicities. Protease dependent activation of therapeutics with high on-target, off-tumor toxicities may be used to localize activity to the tumor but achieving sufficient exposure of the activated therapeutic in the tumor microenvironment remains a challenge. We have previously shown our design strategy for masked, protease activated IL-12Fc that included optimization of blocking modules, fusion geometry, and linker design. Here we have further expanded our mechanistic evaluations by combining masked, protease activated IL-12Fc with attenuated potency engineering, and selected a lead candidate (ZW270) based on anti-tumor activity and non-human primate (NHP) tolerability.

The relative activity of masked and unmasked IL-12Fc variants comprising wild type (wt) or attenuated (att) IL-12 potency was evaluated in CD8 T cell activity assays. The wt IL-12Fc displayed comparable potency to recombinant IL-12 and up to 100x reduced potency when masked. Introduction of attenuating mutations to the p40 subunit reduced the potency of the IL-12Fc by up to 20x and addition of the protease cleavable mask further reduced the potency to up to 5000x compared to wt IL-12Fc. In a single dose NHP study, masked att IL-12Fc was well tolerated up to 31.8 mg/kg, while wt IL-12Fc demonstrated a maximum tolerated dose of below 1.3 mg/kg.

Despite the reduced potency of att IL-12Fc in vitro, in in vivo efficacy studies in a human PBMC engrafted xenograft model the masked att IL-12Fc was able to control tumor growth whereas masked wt IL-12Fc and wt IL-12Fc showed limited anti-tumor activity, suggesting the approach of masked, protease activated att IL-12Fc might be able to achieve a higher exposure of active cytokine in the tumor in comparison to the masked wt IL-12Fc and wt IL-12 comparator. To further investigate the potentially superior exposure response relationship of masked att IL-12Fc, we developed a quantitative systems pharmacology (QSP) model based on our experimental data and literature data. In this model the predicted ratio of IL-12-receptor occupancy by active IL-12Fc in the tumor vs. blood was 18x greater for masked att IL-12Fc than for wt IL-12Fc, whereas the ratio was under 10x greater for masked wt IL-12Fc vs. wt IL-12Fc.

In summary, the affinity attenuated, masked IL-12Fc lead ZW270 has potent and superior anti-tumor activity to wt IL-12Fc and masked wt IL-12Fc, and is well tolerated in NHPs to >30 mg/kg. Our data suggests that the combined strategy of masked, protease activated IL-12Fc and attenuated IL-12 potency has the potential to widen the therapeutic index and to have superior activity to masked, protease cleavable wt IL-12 and unmasked wt IL-12 fusions.

Citation Format: Maya C. Poffenberger, Jennifer L. Bishop, Ryan J. Blackler, Kevin G. Haworth, Steven Booth, Shalla Hanson, Jeff R. Proctor, I-Ting Shao, Nichole K. Escalante, Dayananda Siddappa, Joel Smith, Gursev Anmole, Saki Konomura, Nicholas A. Dawson, Sifa Arrafi, Desmond Lau, Gerry Rowse, Rupert H. Davies, Thomas Spreter von Kreudenstein. ZW270, a conditionally masked IL-12 cytokine fusion protein displaying potent anti-tumor activity absent systemic toxicity [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 2935.

Sustained ERK1/2 signaling is necessary for follicular rupture during ovulation in mice

Abolition of the LH-induced ERK1/2 pathway leads to dramatic changes in gene expression in granulosa cells, subsequently abrogating ovulation. Here we explored whether sustained ERK1/2 signaling beyond immediate-early hours of the LH surge is important for ovulation in mice. First, we examined the effect of inhibition of ERK1/2 activity at 4 h after hCG stimulation on ovulation in superovulated immature mice. Treatment with the ERK1/2 pathway inhibitor PD0325901 at 4 h post-hCG disrupted follicular rupture without altering cumulus expansion, oocyte meiotic maturation and luteinization. Profiling the expression pattern of genes of the RSK family of ERK1/2 signal mediators revealed that RSK3, but not other isoforms, was induced by hCG treatment. Further, RSK3-knockout mice were sub-fertile with reduced ovulation rate and smaller litter size compared to WT mice. Given that PD0325901 inhibits all mediators of ERK1/2 signaling, we chose to evaluate the gene expression underlying deficient follicular rupture in ERK1/2 inhibited mice. We found that inhibition of ERK1/2 signaling at 4 h post-hCG resulted in an imbalance in the expression of genes involved in extracellular matrix degradation and leukocyte infiltration necessary for follicular rupture. In conclusion, our data demonstrate that sustained ERK1/2 signaling during ovulation is not required for cumulus expansion, oocyte meiotic maturation and luteinization, but is required for follicular rupture.

Effect of the transient pharmacological inhibition of Mapk3/1 pathway on ovulation in mice

Mitogen-activated protein kinase 3/1 (Mapk3/1) pathway is critical for LH signal transduction during ovulation. However, the mechanisms remain incompletely understood. We hypothesized that Mapk pathway regulates ovulation through transcriptional regulation of ovulatory genes. To test this hypothesis we used immature mice superovulated with equine and human chorionic gonadotropins (eCG and hCG) and PD0325901, to inhibit hCG-induced Mapk3/1 activity. Mice received either the inhibitor PD0325901 (25 μg/g, i.p.) or vehicle at 2h before hCG stimulation. Administration of the inhibitor abolished Mapk3/1 phosphorylation in granulosa cells. While vehicle-treated mice ovulated normally, there were no ovulations in inhibitor-treated mice. First, we analyzed gene expression in granulosa cells at 0h, 1h and 4h post-hCG. There was expected hCG-driven increase in mRNA abundance of many ovulation-related genes including Ptgs2 in vehicle-treated granulosa cells, but not (P<0.05) in inhibitor-treated group. There was also reduced mRNA and protein abundance of the transcription factor, early growth response 1 (Egr1) in inhibitor-treated granulosa cells. We then used GRMO2 cell-line to test if Egr1 is recruited to promoter of Ptgs2 followed by chromatin immunoprecipitation with either Egr1 or control antibody. Enrichment of the promoter regions in immunoprecipitants of Egr1 antibody indicated that Egr1 binds to the Ptgs2 promoter. We then knocked down Egr1 expression in mouse primary granulosa cells using siRNA technology. Treatment with Egr1-siRNA inhibited Egr1 transcript accumulation, which was associated with reduced expression of Ptgs2 when compared to control-siRNA treated granulosa cells. These data demonstrate that transient inhibition of LH-stimulated MAPK3/1 activity abrogates ovulation in mice. We conclude that Mapk3/1 regulates ovulation, at least in part, through Egr1 and its target gene, Ptgs2 in granulosa cells of ovulating follicles in mice.

The fatty acid binding protein 6 gene (Fabp6) is expressed in murine granulosa cells and is involved in ovulatory response to superstimulation

The fatty acid binding protein 6 (Fabp6) is commonly regarded as a bile acid binding protein found in the distal portion of the small intestine and has been shown to be important in maintaining bile acid homeostasis. Previous studies have also reported the presence of Fabp6 in human, rat and fish ovaries, but the significance of Fabp6 in this organ is largely unknown. Therefore, we surveyed murine ovaries for Fabp6 gene expression and evaluated its role in ovarian function using mice with whole body Fabp6 deficiency. Here we show that the Fabp6 gene is expressed in granulosa and luteal cells of the mouse ovary. Treatment with gonadotropins stimulated Fabp6 gene expression in large antral follicles. The ovulation rate in response to superovulatory treatment in Fabp6-deficient mice was markedly decreased compared to wildtype (C57BL/6) mice. The results of this study suggest that expression of Fabp6 gene in granulosa cells serves an important and previously unrecognized function in fertility.

Mechanistic target of rapamycin (MTOR) signaling during ovulation in mice

A complex network of endocrine/paracrine signals regulates granulosa-cell function in ovarian follicles. Mechanistic target of rapamycin (MTOR) has recently emerged as a master intracellular integrator of extracellular signals and nutrient availability. The objectives of the present study were to characterize the expression pattern and kinase activity of MTOR during follicular and corpus luteum development, and to examine how inhibition of MTOR kinase activity affects preovulatory maturation of ovarian follicles. MTOR expression was constitutive throughout follicular and corpus luteum development. Gonadotropins induced MTOR kinase activity in the ovary, which was inhibited by rapamycin treatment (10 µg/g body weight, intraperitoneal injection). Inhibition of human chorionic gonadotropin (hCG)-induced MTOR activity during preovulatory follicle maturation did not change key events of ovulation. Granulosa cells of rapamycin-treated mice showed reduced MTOR kinase activity at 1 and 4 hr post-hCG and overexpression of hCG-induced ovulation genes at 4 hr post-hCG. Overexpression of these ovulatory genes was associated with hyper-activation of extracellular signal-regulated kinase 1/2 (ERK1/2), which occurred in response to inhibition of MTOR with rapamycin and suggested that MTOR may function as a negative regulator of the mitogen-activated protein kinase (MAPK) pathway. Indeed, simultaneous inhibition of MTOR and ERK1/2 activities during preovulatory follicle maturation caused anovulation. Inhibition of hCG-induced ERK1/2 activity alone suppressed MTOR kinase activity, indicating that MAPK pathway is upstream of MTOR. Thus, normal ovulation appears to be a result of complex interactions between MTOR and MAPK signaling pathways in granulosa cells of ovulating follicles in mice.

Role of leptin receptors in granulosa cells during ovulation

Leptin is an important hormone influencing reproductive function. However, the mechanisms underpinning the role of leptin in the regulation of reproduction remain to be completely deciphered. In this study, our objective is to understand the mechanisms regulating the expression of leptin receptor (Lepr) and its role in ovarian granulosa cells during ovulation. First, granulosa cells were collected from superovulated mice to profile mRNA expression of Lepr isoforms (LeprA and LeprB) throughout follicular development. Expression of LeprA and LeprB was dramatically induced in the granulosa cells of ovulating follicles at 4 h after human chorionic gonadotropin (hCG) treatment. Relative abundance of both mRNA and protein of CCAAT/enhancer-binding protein β (Cebpβ) increased in granulosa cells from 1 to 7 h post-hCG. Furthermore, chromatin immunoprecipitation assay confirmed the recruitment of Cebpβ to Lepr promoter. Thus, hCG-induced transcription of Lepr appears to be regulated by Cebpβ, which led us to hypothesise that Lepr may play a role during ovulation. To test this hypothesis, we used a recently developed pegylated superactive mouse leptin antagonist (PEG-SMLA) to inhibit Lepr signalling during ovulation. I.p. administration of PEG-SMLA (10 μg/g) to superovulated mice reduced ovulation rate by 65% compared with control treatment. Although the maturation stage of the ovulated oocytes remained unaltered, ovulation genes Ptgs2 and Has2 were downregulated in PEG-SMLA-treated mice compared with control mice. These results demonstrate that Lepr is dramatically induced in the granulosa cells of ovulating follicles and this induction of Lepr expression requires the transcription factor Cebpβ. Lepr plays a critical role in the process of ovulation by regulating, at least in part, the expression of the important genes involved in the preovulatory maturation of follicles.