Stefania Bellone

Preclinical Activity of Datopotamab Deruxtecan (Dato-DXd), an Antibody–Drug Conjugate Targeting TROP2, in Poorly Differentiated Endometrial Carcinomas

Abstract Datopotamab deruxtecan (Dato-DXd) is a novel antibody–drug conjugate (ADC) targeting trophoblast antigen-2 (TROP2), a cell surface glycoprotein highly expressed in many epithelial tumors, to deliver DXd, a potent topoisomerase I inhibitor. We evaluated TROP2 expression in primary endometrial cancer cell lines and the activity of Dato-DXd against endometrial cancer cell lines with different TROP2 expression in vitro and in vivo. TROP2 expression was assessed in nine primary tumor cell lines by flow cytometry. Cell viability after exposure to Dato-DXd was evaluated using flow cytometry–based assays to calculate the IC50. Bystander effect assay assessed the viability of TROP2-negative cells when cocultured with high TROP2-expressing cells. Fluorescent anti–phosphorylated histone H2AX antibody was used to demonstrate double-strand DNA breaks. Antibody-dependent cell cytotoxicity was tested in vitro using 4-hour chromium release assays. In vivo activity of Dato-DXd was evaluated against TROP2-positive endometrial cancer xenografts. A total of 78% (seven of nine) of the primary endometrial cancer cell lines expressed TROP2. Endometrial cancer cell lines expressing TROP2 were significantly more sensitive to Dato-DXd compared with control ADC. Dato-DXd–exposed, TROP2-positive endometrial cancer demonstrated increased double-strand DNA breaks compared with non-binding conjugate exposure. Dato-DXd mediated antibody-dependent cell cytotoxicity against TROP2-positive cell lines and induced significant bystander killing of TROP2-negative tumors when admixed with TROP2-positive tumors. In vivo, injection of Dato-DXd was well tolerated and demonstrated impressive tumor growth inhibition against chemotherapy-resistant poorly differentiated endometrial cancer xenografts (P < 0.0001). In conclusion, Dato-DXd is a novel ADC with remarkable preclinical activity against poorly differentiated endometrial cancer cell lines overexpressing TROP2. Clinical trials with Dato-DXd in patients with recurrent endometrial cancer are warranted. Significance: Targeted treatment of aggressive forms of endometrial cancer using the biomarker TROP2 is a significant opportunity for the development of treatments when patients are resistant to other lines of treatment. Here, we present data showing preclinical evidence of effectiveness of this biomarker-targeted therapy in endometrial cancer.

Folate receptor alpha as a successful biomarker in the treatment of low-grade serous ovarian cancer patients using preclinical and clinical models

Low-grade serous ovarian cancer is a rare epithelial ovarian cancer subtype characterized by high resistance to chemotherapy. Development of novel, effective, targeted treatments for recurrent low-grade serous ovarian cancer remains an unmet medical need. We evaluated FOLR1 expression in a cohort of low-grade serous ovarian cancer patients and the preclinical and clinical activity of mirvetuximab soravtansine, an antibody-drug conjugate targeting FOLR1, in vivo in a patient-derived xenograft model and in a heavily pretreated low-grade serous ovarian cancer patient progressing after chemotherapy, aromatase inhibitor, and MEK inhibitor treatment. FOLR1 expression was evaluated in 27 low-grade serous ovarian cancer patients using immunohistochemistry. The efficacy of mirvetuximab soravtansine was assessed in vivo in a low-grade serous ovarian cancer patient-derived xenograft model in severe combined immunodeficient mice, as well as in a patient harboring a recurrent low-grade serous ovarian cancer resistant to standard treatment modalities. FOLR1 expression was detected in all 27 (100%) low-grade serous ovarian cancer cases, with 21 of 27 (78%) of the samples demonstrating 2+/3+ in ≥75% of tumor cells. In vivo studies in mice demonstrated that mirvetuximab soravtansine inhibited tumor growth and prolonged survival in a low-grade serous ovarian cancer patient-derived xenograft model derived from a patient progressing after chemotherapy/aromatase inhibitor/MEK inhibitor. Clinical evidence further supported the therapeutic activity of mirvetuximab soravtansine in a FOLR1-positive low-grade serous ovarian cancer patient, as indicated by a prolonged partial response after 8 months of treatment. FOLR1 is overexpressed in a large percentage of low-grade serous ovarian cancers. Mirvetuximab soravtansine may represent a novel treatment option for low-grade serous ovarian cancer patients progressing after standard treatment modalities. Clinical trials with mirvetuximab soravtansine in FOLR1-positive low-grade serous ovarian cancers are warranted.

Distinct Mechanisms of Mismatch-Repair Deficiency Delineate Two Modes of Response to Anti–PD-1 Immunotherapy in Endometrial Carcinoma

Abstract Mismatch repair–deficient (MMRd) cancers have varied responses to immune-checkpoint blockade (ICB). We conducted a phase II clinical trial of the PD-1 inhibitor pembrolizumab in 24 patients with MMRd endometrial cancer (NCT02899793). Patients with mutational MMRd tumors (6 patients) had higher response rates and longer survival than those with epigenetic MMRd tumors (18 patients). Mutation burden was higher in tumors with mutational MMRd compared with epigenetic MMRd; however, within each category of MMRd, mutation burden was not correlated with ICB response. Pretreatment JAK1 mutations were not associated with primary resistance to pembrolizumab. Longitudinal single-cell RNA-seq of circulating immune cells revealed contrasting modes of antitumor immunity for mutational versus epigenetic MMRd cancers. Whereas effector CD8+ T cells correlated with regression of mutational MMRd tumors, activated CD16+ NK cells were associated with ICB-responsive epigenetic MMRd tumors. These data highlight the interplay between tumor-intrinsic and tumor-extrinsic factors that influence ICB response. Significance: The molecular mechanism of MMRd is associated with response to anti–PD-1 immunotherapy in endometrial carcinoma. Tumors with epigenetic MMRd or mutational MMRd are correlated with NK cell or CD8+ T cell–driven immunity, respectively. Classifying tumors by the mechanism of MMRd may inform clinical decision-making regarding cancer immunotherapy. This article is highlighted in the In This Issue feature, p. 247

Preclinical Efficacy of the Estrogen Receptor Degrader Fulvestrant in Combination with RAF/MEK Clamp Avutometinib and FAK Inhibitor in a Low-Grade Serous Ovarian Cancer Animal Model with Acquired Resistance to Chemotherapy and Aromatase Inhibitor

Low-grade-serous ovarian carcinomas (LGSOC) are rare tumors characterized by a high recurrence rate and limited treatment options. Most LGSOC are estrogen receptor (ER)-positive and demonstrate alterations in the RAS/MAPK pathway. Avutometinib is a dual RAF/MEK clamp, whereas defactinib and VS-4718 are focal adhesion kinase (FAK) inhibitors. Fulvestrant is an ER antagonist/degrader. We assessed the preclinical efficacy of fulvestrant, avutometinib + VS-4718 (FAKi), and the triple combination in a chemotherapy/aromatase inhibitor-resistant LGSOC patient-derived tumor xenograft (PDX) model. Tissue obtained from a LGSOC patient wild-type for KRAS/NRAS/BRAF mutations in progression after chemotherapy/anastrozole was transplanted into female CB17/lcrHsd-Prkdc/SCID mice (PDX-OVA(K)250). The animals were treated with either saline/control, fulvestrant, avutometinib/FAKi, or the triple combination of avutometinib/FAKi/fulvestrant. Avutometinib and FAKi were given five-days on and two-days off through oral gavage. Fulvestrant was administered subcutaneously weekly. Mechanistic studies were performed ex vivo using Western blot assays. Animals treated with the triple combination demonstrated stronger tumor growth inhibition compared to all the other experimental groups including control/saline (p < 0.001), single-agent fulvestrant (p = 0.04 from day eight and onwards), and avutometinib/FAKi (p = 0.02 from day 18). Median survival for mice treated with saline/control was 29 days while mice in all other experimental groups were alive at day 60 (p < 0.0001). Treatment was well tolerated across all experimental treatments. By Western blot, exposure of OVA(K)250 to the triple combination demonstrated a decrease in phosphorylated MEK (p-MEK) and p-ERK levels. The addition of fulvestrant to avutometinib/FAKi is well tolerated in vivo and enhances the antitumor activity of avutometinib/FAKi in a LGSOC-PDX model with acquired resistance to chemotherapy/aromatase inhibitors. These results support the clinical evaluation of avutometinib/defactinib in combination with fulvestrant or an aromatase inhibitor in patients with recurrent LGSOC.

Preclinical Activity of Datopotamab Deruxtecan, an Antibody–Drug Conjugate Targeting Trophoblast Cell-Surface Antigen 2, in Uterine Serous Carcinoma

Abstract Uterine serous carcinoma (USC) is a rare subset of endometrial cancer with a poor prognosis and high recurrence rate. Datopotamab deruxtecan (Dato-DXd) is a novel antibody–drug conjugate (ADC). The objective of this study was to evaluate the preclinical activity of Dato-DXd in USC in vitro against primary USC cell lines with various trophoblast cell-surface antigen 2 (TROP2) expression and in vivo in TROP2-overexpressing cell line–derived mice xenografts. USC primary tumor cell lines were treated with Dato-DXd and a control ADC (CTL ADC) to evaluate cell viability following exposure. Antibody-dependent cell-mediated cytotoxicity against TROP2-overexpressing and -nonexpressing cell lines was evaluated using a 4-hour chromium release assay. USC xenografts in mice were treated with Dato-DXd, CTL ADC, datopotamab, and vehicle to assess the in vivo effects via retro-orbital Dato-DXd administration. We found USC cell lines with TROP2 overexpression to be significantly more sensitive to killing induced by Dato-DXd compared with CTL ADC in vitro (e.g., IC50: 0.11 µmol/L vs. 30.07 µmol/L, P = 0.0074 and 0.11 µmol/L vs. 48.95 µmol/L, P = 0.0127, respectively). Dato-DXd induced antibody-dependent cell-mediated cytotoxicity in the presence of peripheral blood lymphocytes from healthy donors. TROP2-nonexpressing cell lines demonstrated minimal killing by Dato-DXd; however, when admixed with TROP2-overexpressing cells, a significant bystander effect was appreciated. In vivo, mice xenografts overexpressing TROP2 treated with Dato-DXd demonstrated tumor growth suppression and longer overall survival compared with CTL ADC–treated xenografts. These data demonstrate Dato-DXd to be highly active against TROP2-overexpressing USC in vitro and in vivo. Our preclinical activity results warrant future clinical trials for patients with advanced or recurrent USC. Significance: Targeted treatment of USC using the biomarker TROP2 represents a significant opportunity for further treatment options for patients already resistant to other lines of treatment. In this study, we present data showing preclinical evidence of effectiveness of this biomarker-targeted therapy in USC.

Randomized Phase II Trial of Imiquimod with or without 9-Valent HPV Vaccine versus Observation in Patients with High-grade Pre-neoplastic Cervical Lesions (NCT02864147)

Abstract Purpose: We report the results of a randomized phase II trial of imiquimod, a topical immune-response modulator versus imiquimod plus a 9-valent human papillomavirus (HPV) vaccine (9vHPV) versus clinical surveillance in cervical intraepithelial neoplasia (CIN2/3) patients. Patients and Methods: We randomly allocated 133 patients with untreated CIN2/3 in equal proportions to a 4-month treatment with self-applied vaginal suppositories containing imiquimod (Arm B) or imiquimod plus a 9vHPV (Arm C) versus clinical surveillance (Arm A). The main outcome was efficacy, defined as histologic regression to CIN1 or less. Secondary outcomes were HPV clearance and tolerability. Exploratory objectives included the comparison of cervical CD4/CD8 T-cell infiltration at baseline, mid-study, and posttreatment by flow cytometry among study arms. Results: Of the 114 evaluable patients 77% and 23% harbored CIN2 and CIN3, respectively. Regression to CIN1 or less was observed in 95% of patients in the imiquimod group (Arm B) compared with 79% in the control/surveillance (Arm A); P = 0.043 and 84% in the imiquimod+9vHPV group (Arm C; P = 0.384 vs. Arm A). Neither of the treatment-arm differences from Arm A reached the prespecified α = 0.025 significance level. No significant differences were noted in the secondary outcome of rate of HPV clearance. The number of tissue-resident memory CD4/CD8 T cells in cytobrush samples demonstrated a >5-fold increase in Arm B/imiquimod when compared with Arm A/surveillance (P < 0.01). In contrast, there was no significant difference in T-cell responses among participants in Arm C when compared with Arm A. Imiquimod treatment was well tolerated. Conclusions: Although imiquimod induced a higher regression to CIN1 or less and significant increases in CD4/CD8 T cells infiltrating the cervix, it did not meet its prespecified statistical outcome for efficacy. A higher regression rate than expected was observed in the surveillance arm of this prospective trial. Future clinical trials with imiquimod targeting CIN3 patients are warranted.