Christina N. Carrigan

A novel anti-CD37 antibody-drug conjugate with multiple anti-tumor mechanisms for the treatment of B-cell malignancies

CD37 has gathered renewed interest as a therapeutic target in non-Hodgkin lymphoma (NHL) and chronic lymphocytic leukemia (CLL); however, CD37-directed antibody-drug conjugates (ADCs) have not been explored. Here, we identified a novel anti-CD37 antibody, K7153A, with potent in vitro activity against B-cell lines through multiple mechanisms including apoptosis induction, antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and complement-dependent cytotoxicity. The antibody was conjugated to the maytansinoid, DM1, a potent antimicrotubule agent, via the thioether linker, N-succinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate (SMCC), and the resulting ADC, IMGN529, retained the intrinsic antibody activities and showed enhanced cytotoxic activity from targeted payload delivery. In lymphoma cell lines, IMGN529 induced G2/M cell cycle arrest after internalization and lysosomal processing to lysine-N(ε)-SMCC-DM1 as the sole intracellular maytansinoid metabolite. IMGN529 was highly active against subcutaneous B-cell tumor xenografts in severe combined immunodeficient mice with comparable or better activity than rituximab, a combination of cyclophosphamide, vincristine, and prednisone, or bendamustine. In human blood cells, CD37 is expressed in B cells at similar levels as CD20, and IMGN529 resulted in potent and specific depletion of normal and CLL B cells. These results support evaluation of the CD37-targeted ADC, IMGN529, in clinical trials in patients with B-cell malignancies including NHL and CLL.

Lorvotuzumab mertansine, a CD56-targeting antibody-drug conjugate with potent antitumor activity against small cell lung cancer in human xenograft models

Lorvotuzumab mertansine (LM) is an antibody-drug conjugate composed of a humanized anti-CD56 antibody, lorvotuzumab, linked via a cleavable disulfide linker to the tubulin-binding maytansinoid DM1. CD56 is expressed on most small cell lung cancers (SCLC), providing a promising therapeutic target for treatment of this aggressive cancer, which has a poor five-year survival rate of only 5–10%. We performed immunohistochemical staining on SCLC tumor microarrays, which confirmed that CD56 is expressed at high levels on most (~74%) SCLC tumors. Conjugation of lorvotuzumab with DM1 did not alter its specific binding to cells and LM demonstrated potent target-dependent cytotoxicity against CD56-positive SCLC cells in vitro. The anti-tumor activity of LM was evaluated against SCLC xenograft models in mice, both as monotherapy and in combination with platinum/etoposide and paclitaxel/carboplatin. Dose-dependent and antigen-specific anti-tumor activity of LM monotherapy was demonstrated at doses as low as 3 mg/kg. LM was highly active in combination with standard-of-care platinum/etoposide therapies, even in relatively resistant xenograft models. LM demonstrated outstanding anti-tumor activity in combination with carboplatin/etoposide, with superior activity over chemotherapy alone when LM was used in combinations at significantly reduced doses (6-fold below the minimally efficacious dose for LM monotherapy). The combination of LM with carboplatin/paclitaxel was also highly active. This study provides the rationale for clinical evaluation of LM as a promising novel targeted therapy for SCLC, both as monotherapy and in combination with chemotherapy.

Abstract 1760: Preclinical evaluation of IMGN853, an anti-FOLR1 antibody-maytansinoid conjugate, as a potential therapeutic for ovarian cancer

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL IMGN853 (M9346A-sulfo-SPDB-DM4) is an antibody drug-conjugate consisting of the cytotoxic maytansinoid, DM4, covalently linked to the humanized monoclonal antibody M9346A, which selectively binds to folate receptor 1 (FOLR1). FOLR1 is over-expressed on ovarian cancers (38 of 67 tumor samples positive for FOLR1 ∼ 57%) suggesting that ovarian cancer may be a primary indication for clinical development of IMGN853. FOLR1 expression was evaluated on a panel of ovarian cancer xenografts and human ovarian tumors using a calibrated immunohistochemical (IHC) staining method on formalin-fixed paraffin-embedded sections. The FOLR1 expression levels and patterns in three ovarian adenocarcinoma xenografts, OVCAR-3, IGROV-1 and OV-90, were consistent with those observed in FOLR1-positive patient ovarian tumor samples. The anti-tumor activity of IMGN853 was evaluated in the three FOLR1-positive ovarian xenograft models identified. CB.17 SCID mice bearing established subcutaneous xenograft tumors (approximately 100 mm3) were treated with a single intravenous injection of IMGN853 at 1.2, 2.5 and 5.0 mg/kg (based on antibody concentration). IMGN853 was active in all three models evaluated. In OVCAR-3 xenografts, the minimally efficacious dose (MED) of IMGN853 was 1.2 mg/kg. The higher dose levels were highly active, resulting in complete regressions (CR) in 4/6 and 6/6 mice in the 2.5 and 5.0 mg/kg treatment groups, respectively. Treatment with IMGN853 resulted in strong anti-tumor activity in both IGROV-1 and OV-90 xenograft models, with a MED of 2.5 mg/kg, single injection. The strong anti-tumor activity of IMGN853 against ovarian xenograft tumors with FOLR1 expression levels comparable to patient tumors suggests that IMGN853 may be a promising candidate for clinical development in ovarian cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1760. doi:10.1158/1538-7445.AM2011-1760

Abstract 5483: Preclinical evaluation of IMGN289, an anti-EGFR antibody-maytansinoid conjugate for the treatment of squamous cell carcinoma of the head and neck.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Squamous cell carcinoma of the head and neck (SCCHN) include cancers that affect the squamous epithelium of the mouth, larynx, nasal passages, sinuses and pharynx. The epidermal growth factor receptor (EGFR) has emerged as an important antigen for novel targeted therapies in SCCHN, where EGFR overexpression correlates with aggressive disease, resistance to standard therapies and a poor prognosis. EGFR expression was evaluated on a panel of SCCHN xenografts and primary SCCHN tumors using a calibrated immunohistochemical (IHC) staining method on formalin-fixed paraffin-embedded sections. The results demonstrated that 83 of 85 (98%) SCCHN tumors stained positive for EGFR and, of the 83 positive tumors, 80 (96%) had high EGFR expression, confirming that EGFR represents an attractive therapeutic target for SCCHN. IMGN289 is an antibody-“drug” conjugate (ADC) consisting of the humanized monoclonal antibody, J2898A, which selectively binds to EGFR, linked to the potent cytotoxic maytansinoid, DM1, via a SMCC thioether linker. The cytotoxic activity of IMGN289 was evaluated against a panel of SCCHN cell lines in vitro. IMGN289 was active in 9 of 13 cell lines assayed, including 5 of 8 that were resistant to cetuximab. Cytotoxic activity was observed against cell lines originating from multiple anatomic sites including the pharynx, oral cavity, larynx and tongue. The anti-tumor activity of IMGN289 was evaluated in EGFR-positive SCCHN xenograft models with expression levels comparable to patient tumors. Immunodeficient mice bearing established subcutaneous xenograft tumors were treated with a single intravenous injection of IMGN289 at 1, 2.5 or 5.0 mg/kg (based on antibody concentration). A group of mice dosed with the J2898A antibody at 5 mg/kg was included in the study. In the FaDu xenograft model, IMGN289 was active with a minimally efficacious dose (MED) of 1 mg/kg, highly active at 2.5, and at 5 mg/kg 5/6 partial regressions (PR) and 2/6 complete regressions (CR) were observed. Conjugation of DM1 to J2898A achieved greater anti-tumor activity than J2898A, which was active in the study but without regressions. In the HSC-2 xenograft model, IMGN289 was also highly active, with a MED of 2.5 mg/kg and tumor regression at 5 mg/kg with 6/6 PR and 4/6 CR. Once again, the activity of IMGN289 was more robust than naked J2898A antibody, which was active with 2/6 PR and 1/6 CR. The strong anti-tumor activity of IMGN289 against SCCHN xenograft tumors with EGFR expression levels comparable to patient tumors suggests that IMGN289 may be a promising compound for the treatment of SCCHN. Citation Format: Jose F. Ponte, Yulius Y. Setiady, Ling Dong, Anna Skaletskaya, Christina N. Carrigan, Alfred Anderson-Villaluz, Robert J. Lutz, Jan Pinkas. Preclinical evaluation of IMGN289, an anti-EGFR antibody-maytansinoid conjugate for the treatment of squamous cell carcinoma of the head and neck. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5483. doi:10.1158/1538-7445.AM2013-5483

Abstract 5467: IMGN289, an EGFR-targeting antibody-maytansinoid conjugate with potent activity against non-small cell lung cancer (NSCLC) regardless of dependency on EGFR pathway.

NSCLC accounts for approximately 85% of all lung cancers. Based on tumor histology, NSCLC can be subdivided into adenocarcinoma (AC), squamous cell carcinoma (SCC), and large cell carcinoma (LCC), which account for 40%, 25-30% and 10-15% of NSCLC cases, respectively. In a fraction of AC cases, driver oncogenes have been identified that enable effective treatment with targeted therapies. For most NSCLC cases, however, etiology is still unknown and effective targeted therapies have yet to be achieved. Additionally, even cancers that initially respond to targeted therapies eventually develop resistance, creating the need for other therapeutic approaches. EGFR is one of the best characterized driver oncogenes in NSCLC and also is frequently expressed at high levels in this indication. In house immunohistochemical analysis found EGFR to be highly expressed in 23.8% of AC (n = 21), 60% of SCC (n = 10) and 50% of LCC (n = 8), confirming published data that EGFR represents an attractive therapeutic target for NSCLC. As a novel approach to targeting EGFR-expressing tumors, we have developed IMGN289, an antibody-“drug” conjugate (ADC) consisting of the J2898A antibody (Ab), which selectively binds to EGFR and inhibits EGFR-driven tumor cell growth, conjugated to the maytansinoid DM1, a potent anti-microtubule agent, via the SMCC thioether linker. IMGN289 showed significantly enhanced cytotoxic activity, relative to cetuximab or unconjugated J2898A, against a panel of NSCLC cell lines dependent on EGFR signaling. In vitro, anti-EGFR Abs typically inhibit less than 70% of tumor cell growth at 30 nM concentration, whereas IMGN289 exposure approached 100% inhibition at a significantly lower concentration. Enhanced potency of IMGN289 against EGFR-dependent tumors was demonstrated in vivo in the H292 xenograft tumor model, where the minimally effective doses of IMGN289 and its J2898A Ab were 1 and 3 mg/kg, respectively. In addition, IMGN289 was effective against EGFR-expressing NSCLC cells that are not dependent on EGFR signaling and therefore resistant to anti-EGFR Abs. For example, IMGN289 was active against H226 and H1703 mesenchymal cell lines in vitro and H1703 xenograft tumor in vivo, while neither cetuximab nor J2898A alone was active. IMGN289 was also active against EGFR mutant HCC827 cell lines that have acquired resistance to EGFR tyrosine kinase inhibitors through T790M EGFR mutation or MET gene amplification. Thus, EGFR-targeting IMGN289 achieves a distinct anti-tumor mechanism that is independent of EGFR pathway inhibition. In summary, IMGN289 is highly active against EGFR-positive NSCLC cells regardless of dependency on the EGFR pathway and represents a promising therapeutic candidate for NSCLC. Citation Format: Thomas D. Chittenden, Yulius Y. Setiady, Peter U. Park, Jose F. Ponte, Ling Dong, Anna Skaletskaya, Christina N. Carrigan, Alfred A. Villaluz, Jan Pinkas, Robert J. Lutz, John M. Lambert. IMGN289, an EGFR-targeting antibody-maytansinoid conjugate with potent activity against non-small cell lung cancer (NSCLC) regardless of dependency on EGFR pathway. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5467. doi:10.1158/1538-7445.AM2013-5467

Abstract 4564: huHER3-8, a novel humanized anti-HER3 antibody that inhibits exogeneous ligand-independent proliferation of tumor cells

HER3 (ErbB3) is a member of the human epidermal growth factor receptor (HER) tyrosine kinase family that includes EGFR and HER2, two well-known targets for oncology therapy. Kinase signaling of the HER family is initiated by ligand binding that induces receptor homodimerization or heterodimerization and transphosphorylation of the intracellular domain. In this regards, HER3 is unique among the HER kinase family members. Despite being able to bind ligand, HER3 does not possess a catalytically active kinase domain. To turn on the signaling pathway, HER3 needs to form a heterodimer with another HER family member. However, this does not make HER3 inferior with respect to HER pathway signaling, since dimerization of HER3 with HER2 elicits one of the most powerful oncogenic signals. Similar to EGFR and HER2, HER3 expression and activity have been linked to the pathogenesis of various cancers including breast, ovarian and melanoma, and has been associated with resistance to several cancer therapies. The significance of HER3 in cancer pathogenesis prompted us to develop HER3 antagonistic antibodies. A large number of HER3 antibodies were generated by immunizing mice with HER3 expressing cell lines, and screened for the ability to bind human and monkey HER3. Additionally, since HER3 and activated HER3 (phospho-HER3) were detected in the majority of primary as well as metastatic breast cancer tissues by immunohistochemistry staining, antibodies were screened for their ability to inhibit the HER3 ligand-induced proliferation as well as the basal proliferation of breast cancer cell lines. Three HER3 antibodies, HER3-3, HER3-8 and HER3-10, were exceptionally potent in inhibiting the basal proliferation of four breast cancer cell lines that constitutively express phospho-HER3, where other HER3 antibodies (i.e. U1-59 and MM-121) had little or no activity. In SKBR3 cells, these HER3 antibodies inhibited cell proliferation, comparable to the activity of trastuzumab although the HER3 expression level was thirty-fold lower than the HER2 level. All three HER3 antibodies recognized overlapping epitopes. However, only HER3-8 and HER3-10 antibodies strongly competed for the binding of HER3 ligand and inhibited HER2-HER3 dimerization. These HER3 antibodies were also very potent in inhibiting ligand-induced HER3 signaling and tumor cell proliferation. Because of its best overall activities, HER3-8 was humanized by variable domain resurfacing technology. Humanized HER3-8 retained all of the biological properties and activities of muHER3-8. In conclusion, we have generated a novel humanized HER3 antibody, huHER3-8 that is not only active in inhibiting exogenous ligand-induced HER3 signaling and tumor cell growth, but also effective in inhibiting the basal proliferation of HER3-positive tumor cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4564. doi:10.1158/1538-7445.AM2011-4564

Abstract 3503: A method for quantifying soluble folate receptor 1 in IMGN853 0401 clinical trial patients.

IMGN853, an antibody-“drug” conjugate (ADC), consists of a human folate receptor 1 (FOLR1)-binding monoclonal antibody, M9346A, conjugated to the maytansinoid, DM4, via the cleavable sulfo-SPDB linker. A phase I clinical study has been initiated to identify the maximum tolerated dose, safety, pharmacokinetics (PK), and preliminary efficacy of IMGN853 in patients with FOLR1-positive tumors, including ovarian cancer, non-small cell lung cancer, and other epithelial malignancies. The levels of soluble FOLR1 antigen (sFOLR1) in plasma may vary depending on factors such as tumor antigen expression level, tumor type, and disease stage, and may affect the PK of IMGN853and response to treatment. Previously reported studies describing the detection of sFOLR1 in patient samples are limited and not quantitative. The aim of this study was to develop a sandwich ELISA to quantify levels of sFOLR1 present in plasma samples from cancer patients for use as a potential biomarker of IMGN853 PK and/or clinical response. A panel of murine anti-FOLR1 antibodies was generated at ImmunoGen by standard hybridoma technology. Two clones were chosen for use as capture (FR1-9) and detector (FR1-13) antibodies in the ELISA due to their high affinity and ability to bind to FOLR1 even in the presence of IMGN853 or the FOLR1 ligand, folate. The extracellular domain of FOLR1 fused to murine IgG2a Fc region (FOLR1-Fc) was used as a reference standard. A sandwich ELISA was developed using FR1-9 antibody to capture sFOLR1 from patient plasma, and bound sFOLR1 was detected using biotinylated FR1-13 antibody and streptavidin-HRP with TMB as the substrate. The ELISA was used to quantify sFOLR1 in ovarian carcinoma patient plasma using a reference standard curve generated with FOLR1-Fc antigen. A robust sandwich ELISA was developed to quantify sFOLR1 in patient plasma. The quantitation range of the assay was determined to be 0.2 to 90 nanomolar. Coated plates stored frozen from 0-14 days and protein reagents freeze-thawed over two cycles gave repeatable results. The ELISA was able to detect sFOLR1 in 5 of 10 ovarian cancer patient plasma samples, where the levels of detectable sFOLR1 ranged from 0.7-31 nM. This ELISA is considered suitable to quantify levels of sFOLR1 in patients enrolled in the phase 1 trial over the course of IMGN853 treatment, and resulting data will be assessed for correlations with IMGN853 PK and with clinical response. Citation Format: Nathan Testa, Laura Bartle, Olga Ab, Judy Cheng, Gillian Payne, Robert J. Lutz, Ben Wolf, Christina Carrigan. A method for quantifying soluble folate receptor 1 in IMGN853 0401 clinical trial patients. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3503. doi:10.1158/1538-7445.AM2013-3503

Abstract 2513: Evaluation of CD37 expression by calibrated IHC identifies non-Hodgkin's lymphoma as a therapeutic target for IMGN529, an anti-CD37-maytansinoid conjugate

Background: CD37 is a B-cell surface antigen reported to be widely expressed on malignant B cells in patients with non-Hodgkin9s lymphoma (NHL) and chronic lymphocytic leukemia (CLL). Expression of CD37 in normal tissues is mainly restricted to B cells in blood and lymphoid tissues. This suggests that CD37 may be an attractive target for development of a therapeutic antibody drug conjugate (ADC). The antibody maytansinoid conjugate, IMGN529 consists of a CD37-binding monoclonal antibody, K7153A, with the DM1 maytansinoid cytotoxic agent attached via an SMCC linker. IMGN529 has demonstrated potent in vitro and in vivo anti-tumor activities supporting its development as a treatment for CD37-expressing lymphomas and CLL. Objective: The objectives of this study were to assess the potential utility of IMGN529 for treatment of lymphoma patients by: (1) determining the extent of CD37 expression in NHL tissue samples relative to CD20, a well-validated target for antibody-directed therapies against B-cell malignancies; (2) identifying xenograft models with similar CD37 expression as seen in NHL patient samples; and (3) evaluating IMGN529 efficacy in these xenograft models. Methods: CD37 expression in human lymphoma cell lines was determined by quantitative flow cytometry. Cell pellet controls were prepared from human lymphoma cell lines that represented a range of CD37 expression to establish a calibrated IHC method. Using this IHC method, CD37 and CD20 expression levels were evaluated on a panel of FFPE biopsy samples from patients with NHL and from NHL-derived tumor xenograft models. For all stained biopsy samples, the extent and intensity of immunostaining was evaluated and antigen expression levels were estimated by comparing to the quantified cell pellet controls. In vivo efficacy was evaluated in subcutaneous xenograft models in SCID mice. Results: Biopsy samples from patients with B-cell NHL including subtypes such as follicular lymphoma, diffuse large B-cell lymphoma, Burkitt9s lymphoma, and mantle cell lymphoma showed similar prevalence for CD37 and CD20. Most biopsy samples from patients with NHL showed strong and uniform expression levels of the CD37 antigen. As expected, no positive CD37 staining was seen in multiple myeloma and T-cell lymphoma biopsies. IMGN529 was highly active at a single dose of 10 mg/kg in tumor xenografts with CD37 expression levels similar to NHL patient samples. Conclusion: CD37 is expressed widely in B-cell lymphomas, including all major subtypes, which confirms CD37 as target for development of a therapeutic antibody drug conjugate. The CD37-targeting ADC, IMGN529, shows strong in vivo efficacy in lymphoma xenograft models with comparable CD37 expression levels as seen in lymphoma patients. Together these data support the development of IMGN529 for treatment of NHL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2513. doi:1538-7445.AM2012-2513

Abstract 3617: Evaluation of folate receptor 1 (FOLR1) expression by calibrated immunohistochemistry identifies candidate tumor subtypes for targeting by IMGN853, an anti-FOLR1-maytansinoid conjugate

Background: The folate receptor α (FOLR1) is a GPI-linked glycoprotein reported to be highly expressed in cancers including ovarian, renal, brain, lung, and breast carcinomas, while having restricted distribution in normal tissues, including kidney and lung. This expression profile suggests that FOLR1 may be an attractive target for development of a therapeutic antibody-drug conjugate. The antibody maytansinoid conjugate (AMC), IMGN853, consists of a FOLR1-binding monoclonal antibody, M9346A, conjugated to the maytansinoid, DM4, attached via the cleavable sulfo-SPDB linker. IMGN853 exhibited potent anti-tumor activity in preclinical studies, supporting its development as a treatment for FOLR1-expressing cancers. Objective: The aim of the study was to identify potential patient populations for treatment with IMGN853 by determining the level, cellular distribution, and incidence of FOLR1 expression in carcinomas. Methods: A calibrated immunohistochemical (IHC) staining method was developed for assessing FOLR1 expression in formalin-fixed paraffin-embedded (FFPE) tissues. Staining conditions were established wherein the intensity of FOLR1 membrane staining observed in tumor tissues could be related to FFPE cell pellet controls, prepared from human tumor cell lines expressing known levels of FOLR1 (quantified by flow cytometry). This calibrated IHC staining method was applied to FOLR1-positive controls and a panel of tumor tissues including ovarian, renal, brain, lung, and breast carcinomas. The extent, pattern, and intensity of immunostaining were evaluated for each tissue, and the level of FOLR1 expression was estimated using comparison to the cell pellet controls. Results: Biopsy samples from patients with ovarian cancer and non-small cell lung adenocarcinoma or bronchiolalveolar carcinomas of the lung express significant levels of membrane-associated FOLR1. Expression in these indications was frequently observed exhibiting high, homogeneous, and cell membrane-localized patterns – properties considered favorable for AMC-targeting. In particular, a high percentage of the most common subtypes of ovarian cancer, serous (79%) and endometrioid (70%), expressed high (> 260,000 antigen sites per cell) and homogeneous levels of FOLR1. Likewise, a high percentage of the non-small cell lung adenocarcinoma (54%) and bronchioloalveolar carcinoma (100%) subtypes also expressed high (> 260,000 antigens per cell) levels. In contrast, FOLR1 expression in most non-small cell lung squamous carcinomas was undetectable. These findings support the development of IMGN853 for treatment of ovarian carcinomas and NSCL adenocarcinoma and bronchiolalveolar carcinomas, and provide a potential approach for assessing FOLR1 expression in patient tumors during clinical development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3617. doi:10.1158/1538-7445.AM2011-3617

Abstract 5335: The antigen target of IMGN901, CD56, is expressed at significant levels in merkel cell carcinoma (MCC)

Background: IMGN901 consists of a CD56-binding monoclonal antibody, huN901, with a maytansinoid agent, DM1, attached via a stable disulfide linker, SPP. The CD56 antigen, also known as neural cell adhesion molecule (NCAM), is present in a number of malignancies including Merkel cell carcinoma (MCC), small cell lung carcinoma and other neuroendocrine tumors, ovarian cancers and multiple myeloma. Once bound to CD56, IMGN901 is internalized into a cancer cell and its DM1 is released to cause cell death via inhibition of tubulin polymerization. IMGN901 is currently in Phase I testing for the treatment of CD56-positive multiple myeloma and CD56-positive solid tumors. Six patients with MCC have received IMGN901, used as a single agent, in one of the Phase I trials underway. Clinical benefit was observed in 3 of these 6 patients: one complete response (CR), one partial response (PR) and one stable disease (SD). Objective: The goal of this study was to assess the potential utility of IMGN901 as a treatment for MCC by identifying the range of CD56 antigen expression levels in MCC. Methods: A calibrated immunohistochemical (IHC) staining method for CD56 was developed. CD56 staining conditions were established where 4 formalin fixed paraffin embedded (FFPE) MCC samples showed differential staining. FFPE cell pellet controls prepared from human tumor cell lines were next identified which showed CD56 staining in the same range as the MCC samples. The CD56 antigen level for each tumor cell line was subsequently quantified by flow cytometry. The calibrated IHC staining method was then applied to positive cell pellet controls and an extended panel of MCC tissues. For each resulting tissue section, the extent and intensity of immunostaining was evaluated and the CD56 expression level was estimated by comparing to the cell pellet controls. Results: The majority of samples from the MCC panel exhibited heterogeneous or homogeneous staining with significant levels of CD56 expression. Tissues from primary biopsy sites and from metastases showed comparable levels of CD56 expression. To date, biopsy samples have been acquired from 3 of the 6 MCC patients who have received IMGN901 (two IMGN901 non-responders and one responder) and these all showed high and homogeneous levels of CD56 expression. Conclusion: This IHC study indicates that the majority of MCC patient tissues express significant levels of CD56, supporting the development of the CD56-targeting compound, IMGN901, for this indication. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5335.