Anti-LGALS3BP antibody-drug conjugate treatment induces durable and potent antitumor response in a preclinical model of adenoid cystic carcinoma

OBJECTIVES

Adenoid cystic carcinoma (ACC) is a rare type of cancer that typically arises from glandular tissues, most commonly in the salivary glands. Although relatively rare, it represents a serious clinical issue as the management of the disease is highly complex being the only therapeutic options represented by invasive surgery and/or radiotherapy. In the present study, we have explored the potential of galectin-3 binding protein (LGALS3BP) as a novel target for antibody-drug conjugate (ADC) therapy in ACC.

MATERIALS AND METHODS

RNAseq was conducted on a panel of 10 ACC patient-derived xenografts (PDX)s tissues and 6 normal salivary glands to analyze LGALS3BP gene expression. Protein expression was assessed in ACC PDX and primary tumor tissues using immunohistochemistry. Anti-LGALS3BP ADC named 1959-sss/DM4, was tested in high LGALS3BP expressing ACC PDX model ST1502B.

RESULTS

RNAseq analysis revealed that LGALS3BP expression was highly expressed in ACC PDX tissues compared to normal salivary gland tissues. As evaluated by immunohistochemical analysis, LGALS3BP protein was found to be heterogeneously expressed in 10 ACC PDX and in tumor tissues derived from a cohort of 37 ACC patients. Further, treatment with 1959-sss/DM4 ADC led to durable tumor growth inhibition (TGI) in 100% of animals without observed toxicity.

CONCLUSIONS

Our study provides strong evidence that LGALS3BP is a promising therapeutic target for ACC, warranting further expedited preclinical and clinical investigation.

Spatial Immunoprofiling of Adenoid Cystic Carcinoma Reveals B7-H4 Is a Therapeutic Target for Aggressive Tumors

PURPOSE

Adenoid cystic carcinoma (ACC) is a heterogeneous malignancy, and no effective systemic therapy exists for metastatic disease. We previously described two prognostic ACC molecular subtypes with distinct therapeutic vulnerabilities, ACC-I and ACC-II. In this study, we explored the ACC tumor microenvironment (TME) using RNA-sequencing and spatial biology to identify potential therapeutic targets.

EXPERIMENTAL DESIGN

Tumor samples from 62 ACC patients with available RNA-sequencing data that had been collected as part of previous studies were stained with a panel of 28 validated metal-tagged antibodies. Imaging mass cytometry (IMC) was performed using the Fluidigm Helios CyTOF instrument and analyzed with Visiopharm software. The B7-H4 antibody-drug conjugate AZD8205 was tested in ACC patient-derived xenografts (PDX).

RESULTS

RNA deconvolution revealed that most ACCs are immunologically "cold," with approximately 30% being "hot." ACC-I tumors with a poor prognosis harbored a higher density of immune cells; however, spatial analysis by IMC revealed that ACC-I immune cells were significantly restricted to the stroma, characterizing an immune-excluded TME. ACC-I tumors overexpressed the immune checkpoint B7-H4, and the degree of immune exclusion was directly correlated with B7-H4 expression levels, an independent predictor of poor survival. Two ACC-I/B7-H4-high PDXs obtained 90% complete responses to a single dose of AZD8205, but none were observed with isotype-conjugated payload or in an ACC-II/B7-H4 low PDX.

CONCLUSIONS

Spatial analysis revealed that ACC subtypes have distinct TMEs, with enrichment of ACC-I immune cells that are restricted to the stroma. B7-H4 is highly expressed in poor-prognosis ACC-I subtype and is a potential therapeutic target.

Abstract LB084: AXL as a therapeutic target in adenoid cystic carcinoma: preclinical evaluation of AXL targeting antibody-drug conjugate (ADCT-601)

Background: Adenoid cystic carcinoma (ACC) is a rare cancer of salivary gland cancer with a significant unmet clinical need. Conventional systemic therapy has limited efficacy and there are currently no FDA approved drugs for these patients with metastatic disease. Advances in molecular profiling led identification of potential therapeutic targets, and previous studies with proteomic analysis identified AXL as a potential therapeutic target in ACC. AXL, a member of the TAM tyrosine kinase receptor family has been generally associated with poor prognosis, and its overexpression and activation is implicated in conferring resistance to conventional systemic therapies in solid tumors. ADCT-601 is an antibody drug conjugate targeting human AXL carrying novel pyrrolobenzodiazepine dimer cytotoxin as the payload.

Methods: The goal of this study is to determine the in vitro and in vivo anti-tumor activity of ADCT-601 in ACC cell lines and patient-derived xenograft (ACCX) models with varying AXL expression determined by Western blot. ADCT-601 treated cell lines in vitro were analyzed by MTT-based cytotoxic assay and immunoblotting, and anti-tumorigenicity was assessed in two ACCX models.

Results: ADCT-601 induced a potent dose-dependent cytotoxic effect in ACC cell lines, but its cytotoxic activity was attenuated after AXL knockdown. Biochemical data indicated that ADCT-601 treatment led to DNA damage and induction of apoptotic factors accompanied by phosphorylation of gamma-H2AX. In high AXL expressing ACCX6 model, a single dose of either 0.5 or 1.0 mg/kg ADCT-601 significantly suppressed tumor growth resulting 3/5 partial responders (PRs) at 1mg/kg and 2/5 PRs at 0.5 mg/kg, compared to the vehicle or isotype-ADC control treated mice (0/5 PR and 1/5 PR, respectively). ADCT-601 appears to eliminate tumor, as no evidence of recovery in tumor growth was observed during a 60-day period. In low AXL expressing ACCX9 model, ADCT-601 treatment (at either the 0.5 or 1.0 mg/kg dose) delayed tumor growth compared to isotype-ADC control, but did not lead to durable partial responses.

Conclusion: This study demonstrated that ADCT-601 induced a potent and specific in vitro and in-vivo anti-tumor activities in AXL expressing ACC models and suggests further development of ADCT-601 in biomarker driven clinical trials.

Citation Format: Joseph O. Humtsoe, Leilani Jones, Shorook Naara, Francesca Zammarchi, Nicole Spardy Burr, Patrick H. van Berkel, Patrick K. Ha, Hyunseok Kang. AXL as a therapeutic target in adenoid cystic carcinoma: preclinical evaluation of AXL targeting antibody-drug conjugate (ADCT-601) [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 LB084.

Abstract 177: Ex vivo 3D culture of adenoid cystic carcinoma PDX models recapitulate disease biomarkers and predict drug response

Adenoid cystic carcinoma (ACC) is a rare, glandular cancer whose incidence rate and limited 2D cell culture capability make it difficult to study primary patient samples. Although well characterized ACC patient-derived xenografts (PDX) have proven to be a useful model to study disease mechanisms and therapeutic sensitives, animal drug studies are relatively low throughput, costly, and take months to accomplish. Ex vivo 3D cell culture can provide a high-throughput, less costly, and significantly faster platform for these drug studies but are hampered by the rarity of tissue. To address this unmet need for models of rare tumor types we developed 3D spheroid (3D-XPDXs™) and microtumor (3D-XPDXmt™) models of ACC using PDX as the primary tissue source. ACC PDX cells readily formed spheroids in our 3D-XPDXs™ platform, remained viable for up to 14 days, and maintained disease-relevant biomarkers such as MYB and c-kit. 3D-XPDXmt™ represent a more complex model of ACC by incorporating extracellular matrix. ACC 3D-XPDXmt™ displayed tumor-like morphologies concordant with the parental tumors and exhibited MYB and c-kit biomarker expression for up to 56 days in culture. Drug response profiling (DRP) was performed using the 3D-XPDXs™ ACC model with KIYATEC’s validated KIYA-PREDICT™ DRP platform. The screening panel consisted of drugs and drug-like compounds currently in use or under investigation for use in ACC, including broad-spectrum chemotherapies and targeted agents. Individualized drug responses were noted for each model as they exhibited differential sensitivities to DNA-damaging agents, microtubule stabilizers, and c-kit targeting kinase inhibitors mirroring the diversity of clinical outcomes. KIYA-PREDICT™ also identified drugs and drug-like compounds that uniformly inhibited viability. This is significant because there is currently no standard of care drugs for ACC, as few, if any have demonstrated homogenous responses in test populations. Monensin has been shown to inhibit activity of the MYB transcription factor, making it an attractive candidate drug for the treatment of ACCs which have a high prevalence of MYB activating alterations. In our study, monensin was effective in all three models with IC50 concentrations in the low micromolar range. These results correlate well with immunohistochemical staining of MYB in ACC 3D-XPDXs™ and 3D-XPDXmt™. Taken together, this data represents a new ex vivo 3D cell culture platform for the study of ACC biology and potential therapies.

Citation Format: Melissa Millard, Teresa M. DesRochers, Michael J. Wick, Jeffrey Kaufman, Nicole Spardy Burr. Ex vivo 3D culture of adenoid cystic carcinoma PDX models recapitulate disease biomarkers and predict drug response [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 177.

Abstract 1138: PRMT5 inhibition downregulates MYB and NOTCH1 signaling, key molecular drivers of adenoid cystic carcinoma

Adenoid cystic carcinoma (ACC) is a rare cancer of secretory glands, characterized by slow and unpredictable growth, unrelenting relapse and high rates of metastasis. Poor response to chemotherapy and targeted drugs has resulted in there being no approved therapies to date, which contributes to poor prognosis with less than a 20% 5-year survival rate in patients with high-risk ACC. A vast majority of ACC tumors are known to have recurrent chromosomal translocation t(6;9) or t(8;9) resulting in MYB/MYBL1-NFIB fusions, and high levels of MYB protein expression. Furthermore, a subset of ACC tumors expresses NOTCH1 activating mutations (20-25%) and hyperactive NOTCH signaling in both primary and recurrent/metastatic tumors. A previous report has demonstrated that an inhibitor of PRMT5 (protein arginine methyltransferase) shows favorable responsiveness in patients with advanced ACC in a phase I clinical trial. Here, we investigate mechanistic aspects as to how PRMT5 inhibition potentially regulates the unique molecular drivers of ACC tumor growth. Due to a limited number of validated in vitro cellular models, we selected a group of head and neck cancer cell lines, including those originating from salivary gland, along with MYB and NOTCH1-driven leukemia models, to evaluate the effects of PRMT5 inhibition on MYB and NOTCH regulated genes. Treatment with PRT543, a potent and selective PRMT5 inhibitor, decreased expression of MYB and its associated downstream gene GATA3, as well as ACC-related genes such as SOX4 and POU3F2. Furthermore, PRT543 downregulated MYB signaling (MYB, FOXM1, NIK and SKI) as well as MYB alternative isoforms MYB-9A and MYB-10A in MYB expressing leukemia cells. Intriguingly, treatment with PRT543 also downregulated the transcription factor, HSF4, that is uniquely linked to regulation by N-terminal truncated MYB, a variant driven by an alternative promoter (TSS2) and reported as being active in ACC tumors. In addition to regulation of MYB, we also show that PRT543 downregulates NOTCH1 expression as well as multiple NOTCH1 target genes in leukemia cells which harbor a NOTCH1 active mutation. Given these results, we investigated the ability of PRT543 to inhibit the growth of ACC PDX tumor models in vivo and demonstrate that PRT543 significantly inhibits the growth of ACC PDX tumors in vivo. We confirmed that PRT543 downregulates levels of global symmetric dimethylarginine (sDMA, a substrate of PRMT5) in the treated tumors. Further studies with PRT543 in ex vivo and in vivo ACC models are ongoing. Collectively, these findings provide a strong molecular rationale for exploring PRT543 as a potential therapeutic option for ACC tumors. PRT543 is currently under evaluation in a Phase I clinical trial in patients with advanced solid tumors and hematological malignancies (NCT03886831).

Citation Format: Jack Carter, Koichi Ito, Venkat Thodima, Neha Bhagwat, Joseph Rager, Nicole Spardy Burr, Jeffrey Kaufman, Bruce Ruggeri, Peggy Scherle, Kris Vaddi. PRMT5 inhibition downregulates MYB and NOTCH1 signaling, key molecular drivers of adenoid cystic carcinoma [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 1138.

A phase II trial of all-trans retinoic acid (ATRA) in advanced adenoid cystic carcinoma

BACKGROUND

Effective therapies are lacking for recurrent, metastatic adenoid cystic carcinoma (R/M ACC) and preclinical models suggest retinoic acid agonists inhibit ACC growth. This phase II trial evaluated all-trans retinoic acid (ATRA) as a novel therapy for ACC.

METHODS

Patients with R/M ACC (any site) with clinical and/or radiographic progression ≤12 months prior to study entry were eligible. Cohort 1 (CH1) received ATRA 45 mg/m² split oral daily dosing on days 1-14 of a 28-day cycle; Cohort 2 (CH2) received the same dosing continuously. Primary endpoint was best overall response rate (CR + PR) (RECIST v1.1). Secondary endpoints: safety and progression-free survival (PFS). Exploratory analyses: ATRA impact on MYB expression and genomic predictors of response.

RESULTS

Eighteen patients enrolled. There were no responses, but 61% (11/18) had stable disease (SD) and 28% (5/18) progression as best response; 11% (2/18) unevaluable. Median duration of stability: 3.7 months (95%CI, 1.9-3.9). One patient (CH1) remains on drug with SD approaching 1 year. Half of those who received prior VEGFR therapy achieved SD (4/8). At median follow up of 7.9 months, median PFS was 3.2 months (95%CI, 1.8-3.9). N = 1 required dose adjustment; N = 1 came off drug for toxicity. There were no grade 3-4 adverse events. NOTCH1 and PI3K pathway alterations were most frequent. Low MYB protein expression was associated with longer duration of stability on ATRA (P < 0.01).

CONCLUSION(S)

While the trial did not meet its prespecified response endpoint, ATRA alone or in combination may be a low toxicity treatment for disease growth stabilization in R/M ACC.

Abstract 2146: Activity of entinostat alone and in combination with cisplatin in a panel of low passage adenoid cystic carcinoma patient-derived xenograft (PDX) models

Background: Adenoid Cystic Carcinoma (ACC) is a rare cancer of secretory glands, most typically occurring in the salivary glands. No approved standard of care exists for systemic therapy. To identify potentially useful therapies, we screened Food and Drug Administration (FDA)-approved and investigational therapies using a well characterized panel of low passage ACC PDX models. Based on these results, combination treatments were evaluated for additive or super-additive effects. In line with the clinical chemo resistance observed in ACC patients, we previously reported that ACC tumor models are insensitive to platinum therapies. Interestingly, histone deacetylase (HDAC) inhibitors have been shown to sensitize cancer cells to anti-cancer agents in vitro. Entinostat is an oral class 1 selective HDAC inhibitor in Phase 3 testing for ER+ breast cancer in combination with hormone therapy. To better understand the potential effects of entinostat in ACC, we evaluated this agent alone and in combination with cisplatin in ACC PDX tumor models.

Methods: Low passage ACC models were established in immune-deficient mice from primary or metastatic patient tissue and confirmed by histologic comparative analysis. Drug sensitivity studies evaluating entinostat, cisplatin and the combination were performed in three models, including ACCx5M1, ACCx6 and ACCx9. Study endpoints included tumor volume and time from treatment initiation with tumor growth inhibition, delay and regression reported at study completion.

Results: Entinostat, cisplatin and the combination were all well tolerated with minimum cycle-based weight loss. Cisplatin tested alone (3 mg/kg weekly) was similar to control in all models, while single agent entinostat (5 mg/kg daily) showed significant anti-tumor activity in the ACCx5M1 (p&lt;0.05) and ACCx9 (p&lt;0.0001) models. Combination of entinostat and cisplatin exerted significant anti-tumor activity versus control in ACCx5M1 (p&lt;0.01) and in ACCx9 versus control (p&lt;0.0001) or entinostat alone (p&lt;0.05). Sequence based and other characterization analysis is currently underway to correlate sensitivity and resistance between models.

Conclusion: Our studies identify entinostat as an agent of potential benefit in treating ACC and demonstrate that entinostat can induce low-dose cisplatin activity in the ACCx9 model, which harbors a mutation in the NOTCH1 gene that has been linked with chemo resistance and worse prognosis. Genomic and other characterization methods are currently underway to correlate sensitivity and resistance between models.

Citation Format: Amanda Mangold, Melissa Rundle, Nicole Spardy Burr, Alyssa Moriarty, Priscila Goncalves, Rogerio Castilho, Peter Ordentlich, Jeffrey Kaufman, Kyriakos Papadopoulos, Michael J. Wick. Activity of entinostat alone and in combination with cisplatin in a panel of low passage adenoid cystic carcinoma patient-derived xenograft (PDX) models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2146.