Characterization of SGN-CD123A, A Potent CD123-Directed Antibody-Drug Conjugate for Acute Myeloid Leukemia

Treatment choices for acute myelogenous leukemia (AML) patients resistant to conventional chemotherapies are limited and novel therapeutic agents are needed. IL3 receptor alpha (IL3Rα, or CD123) is expressed on the majority of AML blasts, and there is evidence that its expression is increased on leukemic relative to normal hematopoietic stem cells, which makes it an attractive target for antibody-based therapy. Here, we report the generation and preclinical characterization of SGN-CD123A, an antibody-drug conjugate using the pyrrolobenzodiazepine dimer (PBD) linker and a humanized CD123 antibody with engineered cysteines for site-specific conjugation. Mechanistically, SGN-CD123A induces activation of DNA damage response pathways, cell-cycle changes, and apoptosis in AML cells. In vitro, SGN-CD123A-mediated potent cytotoxicity of 11/12 CD123⁺ AML cell lines and 20/23 primary samples from AML patients, including those with unfavorable cytogenetic profiles or FLT3 mutations. In vivo, SGN-CD123A treatment led to AML eradication in a disseminated disease model, remission in a subcutaneous xenograft model, and significant growth delay in a multidrug resistance xenograft model. Moreover, SGN-CD123A also resulted in durable complete remission of a patient-derived xenograft AML model. When combined with a FLT3 inhibitor quizartinib, SGN-CD123A enhanced the activity of quizartinib against two FLT3-mutated xenograft models. Overall, these data demonstrate that SGN-CD123A is a potent antileukemic agent, supporting an ongoing trial to evaluate its safety and efficacy in AML patients (NCT02848248). Mol Cancer Ther; 17(2); 554-64. ©2017 AACR.

Diagnostic accuracy of confocal microscopy imaging vs. punch biopsy for diagnosing and subtyping basal cell carcinoma

Background

In vivo reflectance confocal microscopy (RCM) is a promising non‐invasive skin imaging technique that could facilitate early diagnosis of basal cell carcinoma (BCC) instead of routine punch biopsies. However, the clinical value and utility of RCM vs. a punch biopsy in diagnosing and subtyping BCC is unknown.

Objective

To assess diagnostic accuracy of RCM vs. punch biopsy for diagnosing and subtyping clinically suspected primary BCC.

Methods

A prospective, consecutive cohort of 100 patients with clinically suspected BCC were included at two tertiary hospitals in Amsterdam, the Netherlands, between 3 February 2015 and 2 October 2015. Patients were randomized between two test‐treatment pathways: diagnosing and subtyping using RCM imaging followed by direct surgical excision (RCM one‐stop‐shop) or planned excision based upon the histological diagnosis and subtype of punch biopsy (standard care). The primary outcome was the agreement between the index tests (RCM vs. punch biopsy) and reference standard (excision specimen) in correctly diagnosing BCC. The secondary outcome was the agreement between the index tests and reference standard in correctly identifying the most aggressive BCC subtypes.

Results

Sensitivity to detect BCC was similar for RCM and punch biopsy (100% vs. 93.94%), but a punch biopsy was more specific than RCM (79% vs. 38%). RCM expert evaluation for diagnosing BCC had a sensitivity of 100% and a specificity of 75%. The agreement between RCM and excision specimen in identifying the most aggressive BCC subtype ranged from 50% to 85% vs. 77% by a punch biopsy.

Conclusion

Reflectance confocal microscopy and punch biopsy have comparable diagnostic accuracy to diagnose and subtype BCC depending on RCM experience. Although experienced RCM users could accurately diagnose BCC at a distance, we found an important difference in subtyping BCC. Future RCM studies need to focus on diagnostic accuracy, reliability and specific criteria to improve BCC subtype differentiation.

Tumor-Associated Macrophages Can Contribute to Antitumor Activity through FcγR-Mediated Processing of Antibody-Drug Conjugates

The primary mechanism of antibody-drug conjugates (ADC) is targeted delivery of a cytotoxic payload to tumor cells via cancer-associated membrane receptors. However, the tumor microenvironment likely plays a role in ADC penetration, distribution, and processing and thus impacts the overall antitumor activity. Here, we report on the potential contribution of Fc-FcγR interactions between ADCs and tumor-associated macrophages (TAM) to the preclinical antitumor activities of ADCs. In the CD30⁺ L-428 Hodgkin lymphoma model, anti-CD30-vcMMAE and a non-binding control (hIgG-vcMMAE) demonstrated similar antitumor activity as well as similar payload release in the tumors. IHC analysis revealed L-428 tumors contained highly abundant TAMs, which were confirmed to bind ADCs by IHC and flow cytometry. The infiltration of TAMs was further found to correlate with the antitumor activity of the non-binding hIgG-vcMMAE in five additional xenograft models. hIgG1V1-vcMMAE, bearing a mutation in the Fc region which ablates Fc gamma receptor (FcγR) binding, lost antitumor activity in three TAM-high xenograft models, suggesting Fc-FcγR interactions modulate the TAM-ADC interaction. Our results suggest that TAMs can contribute to ADC processing through FcγR interaction in preclinical tumor models and may represent an important additional mechanism for drug release from ADCs. Correlative studies in clinical trials will further shed light on whether TAMs play a role in patients' response to ADC therapies. Mol Cancer Ther; 16(7); 1347-54. ©2017 AACR.

The dendritic cell high-affinity IgE receptor is overexpressed in both asthma and severe COPD

BACKGROUND

The reduction of asthma exacerbations following omalizumab treatment has been related to the suppression of the high-affinity IgE receptor (FcεRI) on plasmacytoid dendritic cells (DCs). However, the FcεRI expression on DCs in chronic obstructive pulmonary disease (COPD) is unknown.

OBJECTIVE

To compare FcεRI expression on DCs in COPD with patients with allergic asthma and healthy controls, and to relate the findings to clinical parameters, blood eosinophil concentrations and serum immunoglobin E (IgE) concentrations.

METHODS

Using four-colour flow cytometry, FcεRI expression on blood myeloid DCs and plasmacytoid DCs was analyzed in 64 patients with COPD, 20 patients with allergic asthma, 41 asymptomatic never smokers and 21 asymptomatic current smokers.

RESULTS

As compared with never smokers, current smokers displayed an increased expression of the FcεRI on myeloid and plasmacytoid DCs. In patients with COPD, the expression of the FcεRI on plasmacytoid DCs, but not myeloid DCs, increased from spirometric GOLD stage 2 to GOLD stage 4, and was correlated with several lung function parameters. Patients with severe COPD and patients with allergic asthma displayed a similar FcεRI overexpression on plasmacytoid DCs. In all groups, there was a positive correlation between total IgE serum concentrations and the FcεRI expression on plasmacytoid DCs.

CONCLUSIONS AND CLINICAL RELEVANCE

Severe COPD and allergic asthma are characterized by a similar overexpression of the high-affinity IgE receptor on plasmacytoid DCs. In view of the effect of anti-IgE on exacerbations in asthma, trials investigating the effect of anti-IgE on exacerbations in severe COPD appear to be warranted.

Anti-angiogenic effects of novel cyclin-dependent kinase inhibitors with a pyrazolo[4,3-d]pyrimidine scaffold

BACKGROUND AND PURPOSE

Cyclin-dependent kinase 5 (CDK5) has recently emerged as an attractive target in several tumour entities. Inhibition of CDK5 has been shown to have anti-angiogenic effects in vitro and in vivo. However, potent inhibitors of CDK5, which can be applied in vivo, are still scarce. We have recently developed a new series of 5-substituted 3-isopropyl-7-[4-(2-pyridyl)benzyl]amino-1(2)H-pyrazolo[4,3-d]pyrimidines that show a preference for inhibiting CDK5 and tested them in vitro and in vivo in a murine model of hepatocellular carcinoma.

EXPERIMENTAL APPROACH

All compounds were initially examined for effects on proliferation of HUVECs. The most potent compounds were then tested on migration, and one of them, LGR2674, was selected for assessing effects on nuclear fragmentation, cell cycle, cell viability and metabolic activity. Furthermore, LGR2674 was tested in a tube formation assay and in vivo in a murine model of hepatocellular carcinoma, induced by s.c. injection of HUH7 cells (measurement of in vivo toxicity, tumour vascularization, tumour cell proliferation and tumour size).

KEY RESULTS

LGR2674 showed an EC50 in the low nanomolar range in the proliferation and migration assays. Cytotoxic effects started at 50 nM, a concentration that did not influence the cell cycle. In vivo, LGR2674 was well tolerated and caused a clear reduction in vessel density in the tumours; also tumour cell proliferation was inhibited and tumour growth retarded.

CONCLUSIONS AND IMPLICATIONS

Pyrazolo[4,3-d]pyrimidine is a novel scaffold for the development of potent CDK inhibitors with in vivo potential. Such structures are good candidates for broadening our pharmacological arsenal against various tumours.

Abstract 2082: Fc-FcγR interaction impacts the clearance and antitumor activity of antibody-drug conjugates in NSG mice

Majority of preclinical efficacy studies for cancer therapeutics are performed on tumor models implanted in immune-deficient mouse strains, including athymic nude, severe combined immunodeficiency (SCID), or NOD-SCID/IL2Rgamma null (NSG) mice. To better understand the correlation between drug exposure and preclinical antitumor activity of biologics, we evaluated the pharmacokinetic (PK) profiles of antibodies and antibody-drug conjugates (ADC) in four strains of mice commonly used in cancer research, including BALB/c, athymic nude, SCID, and NSG. To our surprise, antibodies and ADCs had an abnormally short serum half-life in NSG mice, compared to other strains of mice.

We hypothesized that the fast clearance from plasma in NSG mice may reduce the overall exposure of xenografts to the ADCs, resulting in underestimation of antitumor activity. This was confirmed by comparing cAC10-vcMMAE in CD30+ Karpas-299 tumors implanted in either SCID mice or NSG mice. A single dose of 1 mg/kg cAC10-vcMMAE ADC resulted in complete remission of Karpas-299 tumors implanted in SCID mice (5/5). In contrast, the same treatment regimen had no effect on Karpas-299 tumors implanted in NSG mice (0/5). This observation suggests indeed the shortened exposure penalizes ADC efficacy in NSG models.

We then hypothesized that the fast clearance of ADCs from plasma in NSG mice could be mediated by Fc-FcγR interaction; compromising this interaction may improve the serum half-lives of antibodies and ADCs and thus enhance ADC-mediated antitumor effects in NSG mice. To test this, we utilized a mutant antibody with the amino acid substitutions of E233P:L234V:L235 in its Fc domain that result in significantly reduced FcγR binding (G1V1). These mutations restored the serum exposure in NSG mice to that level comparable to other strains of mice. As a result, treatment of 1 mg/kg cAC10G1V1-vcMMAE led to tumor remission in Karpas-299 tumors grown in NSG mice, correlating with extended exposure. In parallel, pretreatment with human IV immunoglobulin also enhanced ADC exposure and antitumor activity in the NSG mice.

In summary, these results suggest preclinical PK/PD assessment should be performed in the same strains of mice, especially when NSG xenograft models are used to evaluate activities. Moreover, reduced FcγR binding may enhance ADC exposure and allow a better assessment of therapeutic potential of biologics in NSG-based xenograft models.

Citation Format: Fu Li, Michelle Ulrich, Joshua Hunter, Lori Westendorf, Devra Olson, Cassie Baker Lee, Dennis Benjamin, Che-Leung Law. Fc-FcγR interaction impacts the clearance and antitumor activity of antibody-drug conjugates in NSG mice. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2082.

Abstract 2966: Preclinical combinations of the antibody-drug conjugate SGN-LIV1A with chemotherapies show increased activity

SGN-LIV1A is an antibody-drug conjugate (ADC) currently being evaluated in a phase 1 clinical trial for metastatic breast cancer. SGN-LIV1A consists of the microtubule disrupting agent, monomethyl auristatin E (MMAE), conjugated to the anti-LIV-1 humanized monoclonal antibody hLIV22. LIV-1, as a downstream target of STAT3, promotes the epithelial to mesenchymal transition that is important in the malignant progression to metastasis. We have previously shown that as a single agent, SGN-LIV1A displays target specific internalization and cytotoxic activity against a breast cancer cell line in vitro and also demonstrates antitumor activity in in vivo preclinical xenograft models with significant delay of tumor growth. We report here additive and synergistic effects when combining SGN-LIV1A with current chemotherapeutic modalities used in the treatment of metastatic breast cancer. Specifically, we show synergy between SGN-LIV1A in combination with either doxorubicin or Abraxane in MCF-7 breast cancer tumor model. In addition, we show additive effects when carboplatin or protein kinase inhibitors are dosed in combination with SGN-LIV1A in this tumor model. These findings support further evaluation and development of SGN-LIV1A in combination with standard of care chemotherapeutic agents for the treatment of breast cancer.

Citation Format: Fu Li, Martha Anderson, Joshua Hunter, Jaime Miyamoto, Michelle Ulrich, Ana Kostic, Che-Leung Law, Django Sussman. Preclinical combinations of the antibody-drug conjugate SGN-LIV1A with chemotherapies show increased activity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2966.

Interleukin-4 and interferon-γ orchestrate an epithelial polarization in the airways

Interferon-γ (IFN-γ) and interleukin-4 (IL-4) are key effector cytokines for the differentiation of T helper type 1 and 2 (Th1 and Th2) cells. Both cytokines induce fate-decisive transcription factors such as GATA3 and TBX21 that antagonize the polarized development of opposite phenotypes by direct regulation of each other's expression along with many other target genes. Although it is well established that mesenchymal cells directly respond to Th1 and Th2 cytokines, the nature of antagonistic differentiation programs in airway epithelial cells is only partially understood. In this study, primary normal human bronchial epithelial cells (NHBEs) were exposed to IL-4, IFN-γ, or both and genome-wide transcriptome analysis was performed. The study uncovers an antagonistic regulation pattern of IL-4 and IFN-γ in NHBEs, translating the Th1/Th2 antagonism directly in epithelial gene regulation. IL-4- and IFN-γ-induced transcription factor hubs form clusters, present in antagonistically and polarized gene regulation networks. Furthermore, the IL-4-dependent induction of IL-24 observed in rhinitis patients was downregulated by IFN-γ, and therefore IL-24 represents a potential biomarker of allergic inflammation and a Th2 polarized condition of the epithelium.