Antitumor Activity In HER2 Research Articles

CNS efficacy of trastuzumab deruxtecan in metastatic breast cancer: A single-institution, real-world analysis.

e13117 Background: Trastuzumab deruxtecan (T-DXd) is an antibody-drug conjugate that revolutionized the management of patients with HER2+ (HER2 FISH+, IHC 3+) and HER2low (HER2 FISH-, IHC 1+/2+) metastatic breast cancer (MBC). Studies have shown that T-DXd may induce antitumor activity in HER2+ MBC with brain metastases (BM). However, data is limited on the central nervous system (CNS) efficacy of T-DXd in HER2low disease. The only report thus far is from the HER2low cohorts in the DEBBRAH study with 12 patients showing an intracranial overall response rate (ORR-IC) of 50% and progression free survival (PFS) of 5.7 months. Here, we provide a real-world, retrospective analysis of the CNS efficacy of T-DXd in HER2+, HER2low, and HER2null MBC with BM. Methods: This is a single institution, retrospective analysis of patients with MBC with BM who received T-DXd between January 2020 and November 2023. Patients with HER2+, HER2low, or HER2null MBC and BM, treated or untreated at the time of T-DXd initiation, were included. All patients had baseline brain magnetic resonance imaging before T-DXd initiation. Efficacy analyses were performed using the RECIST 1.1 criteria to CNS target lesions by investigator assessment. ORR-IC and intracranial clinical benefit rate (CBR-IC) were reported. CNS PFS, defined as time until CNS progression or death of any cause, and overall survival (OS) were also evaluated. Results: 29 patients were included in the study: 10 (35%) had HER2+, 16 (55%) had HER2low, and 3 (10%) had HER2null disease. The patients had ECOG performance status ranging from 0 to 3, and received a median of 3 prior lines of therapy (range 1-8). At baseline, 3 patients (10%) had untreated BM, 6 (21%) had prior surgery, and 23 (79%) had prior radiation. 28 (97%) had concurrent extra-cranial metastases. Best CNS response and duration of response are listed in the table below. ORR-IC was 10% overall and 6% in HER2low group. CBR-IC was 58% overall and 50% in HER2low group. Median OS in all patients was 65 weeks. Median CNS PFS was not statistically different in the overall group (24 weeks) compared to the HER2low group (21 weeks) with p=0.4661 via log rank test. Conclusions: This is the first real-world study reporting the CNS efficacy of T-DXd in patients with MBC across HER2 expression levels. The CNS efficacy of T-DXd in our institutional experience was similar in HER2+ and HER2low MBC, and was much lower than previously reported in prospective clinical trials. Performance status, extent of prior treatment, and systemic disease burden likely contributed to this difference. Larger cohort and prospective studies on patients with HER2low MBC with BM are warranted. [Table: see text]

P-26 HERIZON-GEA-01: A phase 3 study of zanidatamab in combination with chemotherapy with or without tislelizumab in first-line human epidermal growth factor receptor 2 positive (HER2+) advanced/metastatic gastroesophageal adenocarcinoma (GEA)

Gastroesophageal adenocarcinomas (GEAs), including gastric, esophageal, and gastroesophageal junction (GEJ) adenocarcinomas, are common cancers with high morbidity and mortality. In approximately 25% of GEA cases, HER2 is overexpressed/amplified. Patients with advanced/metastatic HER2+ GEA are typically treated with trastuzumab, a HER2-targeted therapy, plus chemotherapy in the first-line setting. Preliminary data suggests that the addition of an immune checkpoint inhibitor to the treatment regimen may further improve patient outcomes. Zanidatamab is a novel, bispecific HER2-targeting monoclonal antibody (mAb) that binds to two non-overlapping extracellular domains (ECD4 and ECD2) on HER2. This bispecific binding forms HER2 clusters and induces greater internalization and downregulation of cell surface HER2 compared to trastuzumab (as observed in preclinical studies). Zanidatamab also causes growth signal reduction and triggers immune-mediated antitumor activity through antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). Early studies have shown that zanidatamab has a manageable safety profile with encouraging antitumor activity in HER2+ GEA, when used both as a monotherapy and in combination with chemotherapy in later-line treatment. In the first-line setting in a phase 2 study, zanidatamab plus chemotherapy demonstrated a confirmed objective response rate (ORR) of 75%, median duration of response (DOR) of 16.4 months, and median progression-free survival (PFS) of 12.0 months. Separately, the anti-programmed cell death-1 (PD1) mAb tislelizumab has demonstrated a manageable safety profile and clinical activity in multiple cancers, including gastric and GEJ adenocarcinoma. The combination of zanidatamab with chemotherapy plus tislelizumab is being studied in an ongoing phase 1b/2 study and has recently completed accrual. HERIZON-GEA-01 (NCT05152147; EudraCT#: 2021-000296-36), is a global, randomized, open-label, active-comparator, phase 3 study that will further investigate the efficacy and safety of zanidatamab in combination with chemotherapy with or without tislelizumab as first-line treatment for patients with advanced/metastatic HER2+ GEA. Key eligibility criteria include: age ≥ 18 years, untreated, unresectable locally advanced/metastatic GEA that is HER2+ (IHC3+ or IHC2+/ISH+) per central testing, ECOG PS of 0 or 1, and adequate organ function, including LVEF > 50%. Enrolled patients will be assigned randomly (1:1:1) to either: trastuzumab (6 mg/kg IV Q3W) plus chemotherapy; zanidatamab (1800 mg IV [patient 2 IV Q3W and capecitabine 1000 mg/m2 oral BID on days 1–15) or FP (cisplatin 80 mg/m2 IV Q3W and 5-fluorouracil 800 mg/m2 continuous IV on days 1–5). The primary endpoints of the study are PFS per RECIST v1.1 assessed by blinded independent central review (BICR), and overall survival. Secondary endpoints include: BICR-assessed confirmed ORR and DOR; investigator-assessed PFS, ORR, and DOR; incidence and severity of AEs; and changes in health-related quality of life (HRQoL). 714 patients are planned to be enrolled from ∼300 sites in 30+ countries across North America (not including the US), South America, Europe, Africa, Asia, and Oceania. The study is currently recruiting patients. NCT05152147; EudraCT#: 2021-000296-36. Sponsor.

Abstract 74: Co-targeting BCL-xL and HER2 high expression to overcome apoptosis blockade in gastric cancer

Abstract Background: Gastric cancer is one of the most prevalent cancers in the East Asia population. The five-year survival rate is approximately 20% globally. The analysis of gene expression data suggests that anti-apoptotic protein BCL-xL may be the oncogenic driver in gastric cancer as its expression levels are much higher than BCL-2 (Pan Cancer Atlas). In this study, we investigated if a clinical stage BCL-2/BCL-xL dual inhibitor APG-1252 would elicit therapeutic activity and associated mechanisms using a panel of gastric cancer patient-derived xenograft (PDX) models. Additionally, we explored if the combination with HER2 inhibition could enhance the antitumor activity in HER2+ gastric cancer models. Methods and Experiments: Eighteen PDX models of gastric cancer that bore high levels of BCL-xL expression (BCL-xLhigh) based on the gene expression profiles were selected for a mouse trial (n=2) with a dosage regimen of APG-1252 (100 mg/kg, BIW, IV) for three weeks. In a combination study (n=5), APG-1252 (50 mg/kg, BIW, IV) and lapatinib (100 mg/kg, QD, PO) were concurrently administered for three weeks. An advanced ELISA (MSD) and Western blot analysis were performed to detect BCL-xL complex and the protein level, respectively, in tumor samples. Results: APG-1252 treatment resulted in tumor growth inhibition (TGI greater than 50%) in four PDXs (20%), including three exhibiting TGI greater than 80%. PD study confirmed that BCL-xL protein levels were high, and bound with pro-apoptotic proteins PUMA (major binding partner) and BIM in the xenograft tumors of these models. Generally, in comparison with hematologic cancer cells which exhibit dominant BCL-2 complexes (i.e., Toledo), the levels of BCL-xL complexes were consistently higher than those of BCL-2 complexes in the gastric cancer PDXs, implicating a crucial role of BCL-xL in the solid tumors. After treatment with APG-1252, BCL-xL:PUMA, were disrupted and, interestingly, such a decrease in BCL-xL complex signal correlated with TGI. Additionally, the baseline levels of BCL-xL complexes also correlated with TGI. Furthermore, a consequent increase in MCL-1 complexes after APG-1252 treatment indicated that such a compensatory mechanism among anti-apoptotic proteins may confer the drug resistance. Finally, in mouse tumor models derived from HER2+ gastric cancer cell line NCI-N87 or patient-derived xenografts (PDXs), combined treatment with AGP-1252 and HER2 inhibitor lapatinib synergistically inhibited tumor growth, suggesting that lapatinib may be able to increase mitochondrial priming, thus sensitizing cancer cells to APG-1252. Conclusion: Our results demonstrate the on-target antitumor activity of APG-1252, the potential of BCL-xLhigh as a predictive biomarker, and the resistance mechanism conferred by MCL-1. Furthermore, the data provide a scientific rationale for the combined therapy with BCL-xL and HER2 inhibitors to achieve better clinical outcomes in a subset of HER2+ gastric cancers. Citation Format: Jing Deng, Xiaojing Huang, Guoqin Zhai, Kaixiang Zhang, Jiaxing Gu, Tingting Mao, Yan Yin, Ran Tao, Douglas D. Fang, Dajun Yang, Yifan Zhai. Co-targeting BCL-xL and HER2 high expression to overcome apoptosis blockade in gastric cancer [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 74.

Abstract P1-18-09: Tucatinib, a HER2-selective tyrosine kinase inhibitor, increases the anti-tumor activity of trastuzumab antibody-drug conjugates in preclinical models of HER2+ breast cancer

Abstract Background: Tucatinib is an orally administered, reversible HER2-targeted small molecule tyrosine kinase inhibitor that potently and selectively inhibits HER2 relative to the closely related kinase EGFR. In a phase Ib clinical trial in HER2+ metastatic breast cancer, tucatinib in combination with the HER2-targeted antibody-drug conjugate (ADC) ado-trastuzumab emtansine (T-DM1) was well tolerated and demonstrated activity in pretreated patients with HER2-positive metastatic breast cancer (Borges VF et al., 2018). Here, we present preclinical data demonstrating tucatinib potentiates the activity of T-DM1 in HER2+ breast cancer models in vitro, and in vivo. In addition, tucatinib also enhanced the activity of a camptothecin-based HER2 ADC comprising trastuzumab conjugated with 8 exatecan moieties (T-Ex). Methods: In vitro assays were conducted to evaluate the potency of tucatinib, T-DM1 and T-Ex as single agents, and in combination, using a panel of breast cancer cell lines expressing various levels of HER2. The combinatorial effects of tucatinib with T-DM1 or T-Ex was assessed by isobologram analysis to determine additivity, synergy or antagonistic properties of the drug combinations. The activity of tucatinib either alone (50 mg/kg BID) or in combination with T-DM1 (10 mg/kg single dose IV) was evaluated in vivo using the HER2+ breast cancer cell line BT-474, and in 3 patient-derived xenograft (PDX) models of HER2+ breast cancer. Results: Tucatinib demonstrated potent anti-tumor activity in HER2 overexpressing cell lines in vitro with a similar selectivity profile as T-DM1 or T-Ex. When co-administered in vitro and subjected to isobologram analysis, tucatinib and T-DM1 or T-Ex combinations produced additive or synergistic effects. Moreover, tucatinib potently inhibited a subset of cell lines that showed reduced sensitivity to either T-DM1 or T-Ex. In BT-474 cells, the co-administration of tucatinib with T-DM1 in vitro was synergistic and resulted in an increased intracellular concentration of the TDM-1 catabolite Lys-MCC-DM1. The combination of tucatinib with T-DM1 was also more effective than either single agent alone in BT-474 xenografts in vivo and increased the number of complete tumor regressions. In 2 of 3 PDX models tested, the combination of tucatinib with T-DM1 was significantly more active than T-DM1 or tucatinib alone and produced a higher proportion of partial or complete tumor regressions compared with the single agent treatments. Conclusions: These data demonstrate tucatinib results in selective and potent anti-tumor activity in HER2+ tumor derived cell lines, including cell lines that show reduced sensitivity to T-DM1 or T-Ex in vitro. The results also demonstrate that tucatinib is either additive or synergistic when combined with T-DM1 or T-Ex in vitro. In addition, tucatinib in combination with T-DM1 showed enhanced anti-tumor activity in vivo in models of HER2+ breast cancer when compared to T-DM1 as a single agent. These results, taken together with the early clinical data demonstrating preliminary safety and activity of tucatinib with T-DM1, support continued assessment of tucatinib in combination with T-DM1, as well as other HER2 targeted ADCs, in HER2+ metastatic breast cancer patients. Borges VF, Ferrario C, Aucoin N, Falkson C, Khan Q, Krop I, Welch S, Conlin A, Chaves J, Bedard PL, Chamberlain M, Gray T, Vo A, Hamilton E. JAMA Oncol. 2018;4(9):1214-1220. Citation Format: Anita Kulukian, Janelle Taylor, Devra Olson, Margo Zaval, Robert Thurman, Shawna Hengel, Lauren Farr, Tim S Lewis, Scott R Peterson. Tucatinib, a HER2-selective tyrosine kinase inhibitor, increases the anti-tumor activity of trastuzumab antibody-drug conjugates in preclinical models of HER2+ breast cancer [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P1-18-09.

596P - Combined inhibition of MEK and PI3KCA pathway induces synergic antitumor activity in HER2 amplified human colorectal cancer models

596P - Combined inhibition of MEK and PI3KCA pathway induces synergic antitumor activity in HER2 amplified human colorectal cancer models

PO-519 Combined inhibition of MEK and PI3KCA pathway induces synergic antitumor activity in HER2 amplified colorectal cancer models

IntroductionCetuximab and panitumumab, antibodies directed against the epidermal growth factor receptor (EGFR), are an effective clinical therapy for patients with metastatic colorectal cancer (mCRC), particularly for those with KRAS, NRAS, BRAF and PI3KCA wild-type cancer. However, only a fraction of patients receives clinical benefit from therapy with anti-EGFR antibodies. The HER2 gene amplification has been implicated as one of the mechanisms for primary and acquired resistance to anti-EGFR therapies in mCRC. However, little is known about the role of HER2 in cancer resistance to anti-EGFR antibodies.Material and methodsWe transfected stably colon cancer cells, sensitive to anti-EGFR antibodies (LIM1215 and SW48), with HER2 plasmid. We characterised the transfected cells in terms of molecular profile and sensitivity to several drugs through cell proliferation assays and western blot analysis. Furthermore, HER2 amplified cells were engrafted into nude mice and treated to find the best therapeutic treatment.Results and discussionsWe observed a strong upregulation on the HER family receptors EGFR, HER3, and HER4 in cells with HER2 amplification, but also an over-expression of intracellular transducers such as AKT, MAPK, and MEK proteins compared to parental cells. Furthermore, we treated LIM1215-HER2 and SW48-HER2 cells with several combinations of antibodies and small molecules directed to HER receptor family, such as anti-EGFR receptor antibodies of first, second and third generation (cetuximab, SYM004 and MM151); trastuzumab, pertuzumab and lapatinib directed against HER2 receptor; and duligotuzumab as anti-HER3 receptor. We observed a strongest growth inhibition effect after treatment with trastuzumab in combination with lapatinib compared to other treatments. Moreover, we incubated the HER2 amplified cells with drugs directed to the downstream pathway, such as refametinib and pictilisib which are the MEK and PI3KCA inhibitors, respectively. Interestingly, cells with HER2 amplification are highly sensitive to refametinib and pictilisib and further, we observed higher antitumor activity when both drugs were administrated in combination compared to their single treatment and to therapy-based on anti-HER family antibodies. The antitumor activity has been confirmed by the in vivo xenografts CRC models.ConclusionThese results suggest that the treatment with refamentinib and pictilisib could be a strategy for patients with HER2 amplification that do not receive clinical benefit from standard anti-EGFR therapies.

Abstract 4154: Neuropilin-1 expressing macrophages promote neuropilin-1 expression on lymphocytes by direct interaction and exert antitumor activity in HER2 positive breast cancer

Abstract Tumor-infiltrating immune cells (TIIs) in HER2+ breast cancer (BC) play an important role in treatment with anti-HER2 therapy. However, the precise mechanisms of how TIIs exert anti-tumor activity remain unclear. Neuropilin-1 (NRP-1) on macrophages regulates immune functions in various cancers and thus we explored the role of NRP-1 expressing macrophages in anti-tumor activity in HER2+ BC. We show that NRP-1 on macrophages regulated the migration of and chemokine secretion from macrophages in vitro. Furthermore, in vivo studies using a humanized mouse model showed that NRP-1 knockdown of macrophages in adoptively transferring peripheral blood mononuclear cells (PBMCs) suppressed anti-tumor activity and infiltration of CD45+ immune cells into tumors. Interestingly, NRP-1 expressing TIIs were mainly CD4+ T cells, despite little expression of NRP-1 on CD4+ T cells in PBMCs. We found that NRP-1 expression on CD4+ T cells was induced by NRP-1 transfer from macrophages to T cells. In HER2+ BC patients, NRP-1 expressing TIIs correlated with better clinical outcomes. These results demonstrate that NRP-1 expressing macrophages are key subsets of immune cells in trastuzumab-mediated anti-tumor activity and may predict better outcomes for HER2+ BC patients. In conclusion, NRP-1 expression is required for differentiation and activation of macrophages. NRP-1 expressing macrophages promote NRP-1 expression on CD4+ T cells by direct interaction and contribute to anti-tumor immune responses in HER2+ BC. Citation Format: Kosuke Kawaguchi, Eiji SUzuki, Masashi Inoue, Isao Kii, Tatsuki R. Karaoke, Masahiro Hiram, Keiko Iwaisako, Pu Fengling, Mariko Niche, Ayane Yamaguchi, Hironori Haga, Masatoshi Hagiwara, Masakazu Toi. Neuropilin-1 expressing macrophages promote neuropilin-1 expression on lymphocytes by direct interaction and exert antitumor activity in HER2 positive breast cancer. [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 4154.

Pathologic complete response (pCR) rates after neoadjuvant trastuzumab emtansine (T-DM1 [K]) + pertuzumab (P) vs docetaxel + carboplatin + trastuzumab + P (TCHP) treatment in patients with HER2-positive (HER2+) early breast cancer (EBC) (KRISTINE).

500Background: K and P bind different HER2 domains and have marked antitumor activity in HER2+ breast cancer. KRISTINE (NCT02131064) is an open-label phase 3 study comparing neoadjuvant K + P (KP) vs TCHP in patients with HER2+ EBC. This provides the first phase 3 data for a complete neoadjuvant regimen omitting standard chemotherapy. Methods: The primary endpoint was pCR rate (ypT0/is, ypN0). Treatment-naive women with stage II-IIIC centrally assessed HER2+ EBC were randomized to 6 cycles of KP or TCHP and were then evaluated for pCR. The Cochran Mantel-Haenszel χ2-test stratified by hormone receptor status and clinical stage was used to compare pCR rates. The study had 90% power to detect a 15 percentage point increase in pCR from 60% (TCHP) to 75% (KP). Secondary endpoints included breast conserving surgery (BCS) rate, safety, and patient-reported outcomes. Results: Baseline demographic and disease characteristics were comparable between the TCHP (n = 221) and KP (n = 223) arms. pCR rates were 55.7% (9...

Abstract B107: Targeting PI3K and mTOR with GDC-0980, a dual inhibitor, is efficacious in trastuzumab refractory and HER2+/PIK3CA-mutated breast cancer models

Abstract Background: The PI3K-AKT-mTOR signaling plays an important role in breast cancer (BC). Its interaction with HER2 signaling becomes more complex and inter-dependent with acquired anti-HER2 therapy resistance. Targeting mTOR combined with endocrine therapy has shown clinical utility, however, a negative feedback-loop exists downstream of PI3K-AKT-mTOR. Furthermore, BOLERO 1 study clearly showed that PFS was not significantly different between groups (combination of everolimus with trastuzumab (T) plus paclitaxel versus placebo with T plus paclitaxel, 14.95 versus 14.49 months) in the full analysis population. Dual blockade of PI3K/mTOR is therefore an attractive drug for HER2+ BC, especially in T-resistant and PIK3CAmutated conditions. Methodology: Here we have studied the in vitro and in vivo effects of GDC-0980 in HER2+/T-sensitive (BT474), HER2+/T-resistant (BT474HerR), HER2+/PIK3CA (HCC1954, MDA-MB453) and HER2+/PTEN (HCC1569) mutated models. We assessed in vitro anti-proliferative, pro-apoptotic and activation status of the PI3K-AKT-mTOR signaling pathway following GDC-0980 treatment in HER2+ BC cell lines. We next evaluated the impact of GDC-0980 on tumor growth and angiogenesis using xenograft models. Results: 1) GDC-0980 inhibited downstream activation of the PI3K-mTOR signaling pathway effectors, p-AKT (Ser473, The308), p-P70S6K, p-S6RP and p-4EBP1, 2) the anti-proliferative activity of GDC-0980 was observed by 3D-ON-TOP clonogenic assay, 3) consistent with anti-proliferative effects of GDC-0980, the proportion of cells in the G1 phase of the cell cycle increased in all three cell lines with a concomitant decrease in the S phase of their treatment with GDC-0980, 4) the initiation of apoptotic activity (annexin V) of GDC-0980 was significantly superior to that of an allosteric inhibitor of mTOR, RAD001. GDC-0980 also induced apoptotic markers like cleaved CASPASE3, cleaved PARP1, BIM in BT474, BT474HerR & HCC1954 BC cells and 5) in the HER2+/T-sensitive, HER2+/T-resistant and HER2+/PIK3CA mutated BC xenograft models, GDC-0980 inhibited PI3K signaling and had potent anti-tumor activity. Along with its anti-tumor effect, GDC-0980 effectively decreased tumor angiogenesis (tumor micro-vessel density via CD31 staining). These inhibitions were more pronounced when GDC-0980 was combined with T. Conclusions: GDC-0980 inhibits the PI3K-AKT-mTORC1/C2 signaling pathway and results in anti-proliferative and anti-tumor activity in HER2+ breast cancer cells with both wild type and mutated PIK3CA. Citation Format: Pradip De, Yuliang Sun, Jennifer H. Carlson, Xiaoqian Lin, Friedman Lori, Nandini Dey, Brian Leyland-Jones. Targeting PI3K and mTOR with GDC-0980, a dual inhibitor, is efficacious in trastuzumab refractory and HER2+/PIK3CA-mutated breast cancer models. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr B107.

Abstract 5360: The preclinical profile of the duocarmycin-based HER2-targeting ADC SYD985 predicts for clinical benefit in low HER2-expressing breast cancers

Abstract SYD985 is a HER2-targeting ADC based on trastuzumab and vc-seco-DUBA, Synthon's proprietary cleavable linker-duocarmycin payload. Vc-seco-DUBA was coupled to cysteines after partial reduction on the interchain disulfides of trastuzumab. SYD985 was obtained after purification by Hydrophobic Interaction Chromatography to yield a well-defined ADC consisting of predominantly DAR 2 and DAR 4 species. To evaluate the therapeutic potential of this new ADC, and to prepare clinical development, mechanistic in vitro studies and in vivo PDX studies were conducted to compare SYD985 head-to-head to T-DM1 (Kadcyla®), another trastuzumab-based ADC with a toxin of the maytansinoid class in combination with a non-cleavable linker. SYD985 and T-DM1 had similar binding-affinities to HER2 and showed similar internalization. In vitro cytotoxicity assays showed similar potencies and efficacies in HER2 3+ cell lines, but in cell lines with low HER2 expression, SYD985 was 3 to 50-fold more potent than T-DM1. In contrast to T-DM1, SYD985 efficiently induced bystander killing in vitro of HER2 negative (HER2 0) cells when mixed with HER2 3+, 2+, or 1+ cells. SYD985 efficiently killed HER2 0 cells, even in the presence of only 20% of HER2 3+ cells. At pH conditions relevant for tumors, cathepsin B cleavage studies showed efficient release of the active toxin from SYD985 but not from T-DM1. These in vitro data suggest that SYD985 might be a more potent ADC in HER2 expressing tumors in vivo, allowing the treatment of tumor tissues with low or heterogeneous membrane expression of HER2. In line with this, in vivo anti-tumor studies in breast cancer PDX models showed that SYD985 is very active in HER2 3+, 2+, and 1+ models whereas T-DM1 only showed significant anti-tumor activity in HER2 3+ breast cancer PDX models. We conclude that the properties of SYD985 may enable expansion of the target population to patients who have low HER2 expressing breast cancer, a patient population with unmet high medical need. Early phase clinical evaluation with SYD985 is ongoing. Citation Format: Willem Dokter, Miranda van der Lee, Patrick Groothuis, Ruud Ubink, Monique van der Vleuten, Tanja van Achterberg, Eline Loosveld, Desirée Damming, Myrthe Rouwette, David Egging, Diels van den Dobbelsteen, Patrick Beusker, peter goedings, Gijs Verheijden, Jacques Lemmens, Marco Timmers. The preclinical profile of the duocarmycin-based HER2-targeting ADC SYD985 predicts for clinical benefit in low HER2-expressing breast cancers. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5360. doi:10.1158/1538-7445.AM2015-5360

Abstract A15: Dual inhibition of the PI3K-mTOR signaling in combination with HER2 inhibitor is necessary for maximal antitumor activity in HER2+ breast cancer cells

Abstract Background: Despite huge success in the treatment of HER2 amplified/overexpressed breast cancers, resistance is challenging problem even to combinations of HER2 targeting inhibitors. Multiple mechanisms of resistance have been studied and the PI3K-mTOR pathway inhibition is critical for the efficacy of HER2 inhibitors. Activating mutations in PIK3CA can overlap with HER2 overexpression and have been shown to confer resistance to HER2 inhibitors including trastuzumab (T) in preclinical studies. Methods: HER2+/T-sensitive/PIK3CA wild type (BT474) and HER2+/PIK3CA mutated (HCC1954) cells were used for this study. The impact of PIK3CA mutation on the effect of HER2 and dual PI3K/mTOR inhibitors was assayed by immunoblot, proliferation and apoptosis assays. PI3K signaling was examined by immunoblot for phosphoproteins in the HER2-PI3K-mTOR signaling cascade. The combination of dual PI3K/mTOR inhibitor (GDC-0980) with HER2 antibodies (T or T-DM1) was studied in HER2 amplified models with wild type or mutant PIK3CA. Results: Our data showed that 1) PIK3CA mutation in HER2+ cells was responsible for resistance to the HER2-specific antibody trastuzumab, 2) T-resistance conferred by this activating PIK3CA mutation was overcome by blockade of the PI3K-mTOR pathway with GDC-0980, 3) T-DM1 and GDC-0980 combination treatment greatly induced apoptosis of both BT474 and HCC1954 cells as indicated by Annexin V staining, 4) in mice bearing HER2+/T-sensitive/PIK3CA wild type xenografts (BT474), T or T-DM1 blocked tumor growth. The addition of a dual PI3K/mTOR inhibitor more significantly blocked tumor growth when compared to control group, 5) in a HER2+/PIK3CA mutant xenograft (HCC1954), dual PI3K/mTOR inhibition with GDC-0980 in combination with T or T-DM1 was required for blocked of tumor growth and tumor regression, and 6) immununo-staining of tumors from GDC-0980 treated mice showed growth inhibition (Ki67), and a decreased in associated angiogenesis (CD31). Conclusion: These results suggest that the combination of GDC-0980 may be a potential strategy for the treatment of trastzumab-resistant breast cancer mediated by activating mutation of PIK3CA and this combination also provides benefit to HER2+/PIK3CA wild type tumors. Citation Format: Pradip De, Yuliang Sun, Jennifer Carlson, Lori Friedman, Nandini Dey, Brian Leyland-Jones. Dual inhibition of the PI3K-mTOR signaling in combination with HER2 inhibitor is necessary for maximal antitumor activity in HER2+ breast cancer cells. [abstract]. In: Proceedings of the AACR Special Conference: Targeting the PI3K-mTOR Network in Cancer; Sep 14-17, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(7 Suppl):Abstract nr A15.

Abstract P5-19-23: A phase I clinical trial of ganetespib (heat shock protein 90 inhibitor) in combination with paclitaxel and trastuzumab in human epidermal growth factor receptor-2 positive (HER2+) metastatic breast cancer

Abstract Introduction: Targeted therapies in HER2+ metastatic breast cancer (MBC) have significantly improved survival, however efficacy is limited by development of therapeutic resistance. HSP90 is a molecular chaperone involved in the stability and function of multiple signaling onco-proteins. HER2 is an acutely sensitive HSP90 client and HSP90 inhibition can overcome trastuzumab resistance. Ganetespib is a novel, synthetic HSP90 inhibitor with increased potency and tolerability compared with earlier agents. Our group has conducted a single agent ganetespib trial in unselected patients which showed anti-tumor activity in HER2+ and triple negative breast cancer. In addition, preclinical data suggests HSP90 inhibition is synergistic with taxanes with potential for significant clinical activity. Ganetespib has been combined with docetaxel in non-small cell lung cancer, it has not previously been combined with paclitaxel and trastuzumab. This study will define the maximum tolerated dose (MTD) and recommended phase II dose (RP2D) of ganetespib when given with paclitaxel and trastuzumab for patients with HER2+ MBC. Methods: In this 3+3 phase I dose escalation study, patients with trastuzumab resistant HER2+ MBC receive trastuzumab (4mg/kg loading dose, then 2mg/kg) and paclitaxel weekly (80mg/m2) with ganetespib day 1, 8 ,15 of 28 day cycle. Patients are required to have prior pertuzumab and T-DM1 (prior pertuzumab and T-DM1 are not mandated if heavily pretreated prior to their respective FDA approvals). Hormone receptor positive patients are required to have at least one prior line of endocrine therapy. The single agent dose limiting toxicity (DLT) of ganetespib is diarrhea and therefore patients receive prophylactic anti-motility agents. The anticipated MTD of ganetespib in this combination has been informed by experience with docetaxel and based on this only three dose levels of ganetespib are being explored 100mg/m2, 150mg/m2 and a third intermediate cohort of 125mg/m2, if needed. Secondary endpoints include evaluation of effects of ganetespib on the pharmacokinetics of paclitaxel and preliminary assessment of efficacy of the combination (scans at 8 weeks and every 12 weeks thereafter, RECIST 1.1). Results: The first dosing cohort has fully enrolled and there were no significant toxicities or DLTs reported. Median age was 48 years (range 39-49), median prior lines of chemotherapy were 4 (range 3-7) and included prior pertuzumab and T-DM1 in all 3 patients. 5 adverse events have been defined as possibly/probably related to ganetespib – grade 2 anemia and leukopenia, grade 1 diarrhea (2 patients), fatigue, and rash. Enrollment to the second and potentially final cohort is underway. Conclusion: This study will define the RP2D of ganetespib in combination with paclitaxel and trastuzumab. Final safety, pharmacokinetic and preliminary response data for all patients will be presented. This combination, with a novel anti-HER2 agent, has encouraging potential for activity in HER2+ breast cancer which is refractory to other HER2 targeting agents. Citation Format: Komal Jhaveri, Karen Cadoo, Sarat Chandarlapaty, Eleonora Teplinsky, James Speyer, Gabriella D' Andrea, Sujata Patil, Sofia Haque, Kent Friedman, Scott Heese, Deirdre Neville, Francisco Esteva, Clifford Hudis, Shanu Modi. A phase I clinical trial of ganetespib (heat shock protein 90 inhibitor) in combination with paclitaxel and trastuzumab in human epidermal growth factor receptor-2 positive (HER2+) metastatic breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-19-23.

The Preclinical Profile of the Duocarmycin-Based HER2-Targeting ADC SYD985 Predicts for Clinical Benefit in Low HER2-Expressing Breast Cancers.

SYD985 is a HER2-targeting antibody-drug conjugate (ADC) based on trastuzumab and vc-seco-DUBA, a cleavable linker-duocarmycin payload. To evaluate the therapeutic potential of this new ADC, mechanistic in vitro studies and in vivo patient-derived xenograft (PDX) studies were conducted to compare SYD985 head-to-head with T-DM1 (Kadcyla), another trastuzumab-based ADC. SYD985 and T-DM1 had similar binding affinities to HER2 and showed similar internalization. In vitro cytotoxicity assays showed similar potencies and efficacies in HER2 3+ cell lines, but in cell lines with low HER2 expression, SYD985 was 3- to 50-fold more potent than T-DM1. In contrast with T-DM1, SYD985 efficiently induced bystander killing in vitro in HER2-negative (HER2 0) cells mixed with HER2 3+, 2+, or 1+ cell lines. At pH conditions relevant for tumors, cathepsin-B cleavage studies showed efficient release of the active toxin by SYD985 but not by T-DM1. These in vitro data suggest that SYD985 might be a more potent ADC in HER2-expressing tumors in vivo, especially in low HER2-expressing and/or in heterogeneous tumors. In line with this, in vivo antitumor studies in breast cancer PDX models showed that SYD985 is very active in HER2 3+, 2+, and 1+ models, whereas T-DM1 only showed significant antitumor activity in HER2 3+ breast cancer PDX models. These properties of SYD985 may enable expansion of the target population to patients who have low HER2-expressing breast cancer, a patient population with still unmet high medical need.

Abstract 4222: Targeting PI3K and mTOR with BEZ235, a dual inhibitor, is efficacious in trastuzumab refractory and HER2+/PIK3CA-mutated breast cancer models

Abstract Background: PI3K pathway activation is a common event in HER2+ breast cancer (BC) either through inactivation of the tumor suppressor gene, PTEN, or activation of PIK3CA. This PIK3CA mutation leads to an oncogenic activity of the PI3K pathway and contributes to therapeutic resistance to trastuzumab (T). The PI3K pathway inhibitor is therefore an attractive drug for HER2+ BC, especially in T-resistant and PIK3CA mutated conditions. Methodology: Here we have studied the in vitro and in vivo effects of BEZ235 in HER2+/T-sensitive (BT474), HER2+/T-resistant (BT474HerR) and HER2+/PIK3CA (HCC1954) mutated models. We assessed in vitro anti-proliferative and activation status of the PI3K-AKT-mTOR signaling pathway following BEZ235 treatment in HER2+ BC cell lines. We next evaluated the impact of BEZ235 on tumor growth and angiogenesis using xenograft models. Results: 1) BEZ235 inhibited downstream activation of the PI3K signaling pathway effectors, p-AKT (Ser473, The308), p-P70S6K, p-S6RP and p-4EBP1, 2) the anti-proliferative activity of BEZ235 was observed by 3D-ON-TOP clonogenic assay, 3) consistent with anti-proliferative effects of BEZ235, the proportion of cells in the G1 phase of the cell cycle increased in all three cell lines with a concomitant decrease in the S phase of their treatment with BEZ235, 4) the initiation of apoptotic activity (annexin V) of BEZ235 was significantly superior to that of RAD001, an allosteric inhibitor of mTOR, and 5) in the HER2+/T-sensitive, HER2+/T-resistant and HER2+/PIK3CA mutated BC xenograft models, BEZ235 inhibited PI3K signaling and had potent anti-tumor activity. Along with its anti-tumor effect, BEZ235 effectively decreased tumor angiogenesis (tumor micro-vessel density via CD31 staining). These inhibitions were more pronounced when BEZ235 was combined with T. Conclusions: BEZ235 inhibits the PI3K-AKT-mTOR signaling pathway and results in anti-proliferative and anti-tumor activity in HER2+ breast cancer cells with both wild type and mutated PIK3CA. Citation Format: Casey Williams, Yuliang Sun, Jennifer Carlson, Brian Leyland-Jones, Nandini Dey, Pradip De. Targeting PI3K and mTOR with BEZ235, a dual inhibitor, is efficacious in trastuzumab refractory and HER2+/PIK3CA-mutated breast cancer models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4222. doi:10.1158/1538-7445.AM2014-4222

Direct inhibition of PI3K in combination with dual HER2 inhibitors is required for optimal antitumor activity in HER2+ breast cancer cells.

IntroductionDespite multiple advances in the treatment of HER2+ breast cancers, resistance develops even to combinations of HER2 targeting agents. Inhibition of PI3K pathway signaling is critical for the efficacy of HER2 inhibitors. Activating mutations in PIK3CA can overlap with HER2 amplification and have been shown to confer resistance to HER2 inhibitors in preclinical studies.MethodsLapatinib-resistant cells were profiled for mutations in the PI3K pathway with the SNaPshot assay. Hotspot PIK3CA mutations were retrovirally transduced into HER2-amplified cells. The impact of PIK3CA mutations on the effect of HER2 and PI3K inhibitors was assayed by immunoblot, proliferation and apoptosis assays. Uncoupling of PI3K signaling from HER2 was investigated by ELISA for phosphoproteins in the HER2-PI3K signaling cascade. The combination of HER2 inhibitors with PI3K inhibition was studied in HER2-amplified xenograft models with wild-type or mutant PIK3CA.ResultsHere we describe the acquisition of a hotspot PIK3CA mutation in cells selected for resistance to the HER2 tyrosine kinase inhibitor lapatinib. We also show that the gain of function conferred by these PIK3CA mutations partially uncouples PI3K signaling from the HER2 receptor upstream. Drug resistance conferred by this uncoupling was overcome by blockade of PI3K with the pan-p110 inhibitor BKM120. In mice bearing HER2-amplified wild-type PIK3CA xenografts, dual HER2 targeting with trastuzumab and lapatinib resulted in tumor regression. The addition of a PI3K inhibitor further improved tumor regression and decreased tumor relapse after discontinuation of treatment. In a PIK3CA-mutant HER2+ xenograft, PI3K inhibition with BKM120 in combination with lapatinib and trastuzumab was required to achieve tumor regression.ConclusionThese results suggest that the combination of PI3K inhibition with dual HER2 blockade is necessary to circumvent the resistance to HER2 inhibitors conferred by PIK3CA mutation and also provides benefit to HER2+ tumors with wild-type PIK3CA tumors.

OT1-02-02: HALT MBC: HER2 Suppression with the Addition of Lapatinib to Trastuzumab in HER2−Positive Metastatic Breast Cancer (LPT112515).

Abstract Background Lapatinib in combination with trastuzumab enhanced anti-tumor activity in HER2−positive breast cancer (BC) preclinical models. In patients (pts) with trastuzumab-treated, HER2−positive metastatic (M) BC, treatment with the combination was associated with longer progression-free (PFS) and overall survival (OS) compared with lapatinib alone. In pts with stage II/III BC, preoperative treatment with the combination plus paclitaxel resulted in significantly higher pathological complete response rates compared with paclitaxel combined with either agent alone. This evidence supports the concept of dual HER2 blockade as a treatment strategy for HER2−positive BC. This present study is designed to evaluate whether the addition of lapatinib improves PFS among women with HER2−positive MBC receiving trastuzumab as maintenance therapy. Trial Design In this open-label, Phase III study, pts are stratified by line of treatment (first/second) and hormone receptor status (positive/negative) then randomized 1:1 to receive maintenance treatment with either lapatinib (1000mg once daily, continuously) in combination with trastuzumab (6mg/kg once every 3 weeks [Q3W]) or trastuzumab (6mg/kg Q3W) alone. Pts will receive study treatment until disease progression, death, discontinuation due to adverse events or other reasons. Eligibility Criteria Pts with HER2−positive MBC who have completed 12–24 weeks of first- or second-line treatment with trastuzumab plus chemotherapy and have objective response or stable disease. Pts with stable brain metastasis are eligible if entering the study on second-line treatment. Specific Aims The primary objective is to compare PFS of lapatinib in combination with trastuzumab to trastuzumab as continued HER2 suppression therapy. Secondary objectives are to evaluate OS, clinical benefit rate, safety and tolerability. Statistical Methods Efficacy endpoints will be analyzed in the intent to treat population. A total of 193 PFS events from 280 randomized pts will be required to detect a 50% increase in median PFS in pts who receive lapatinib plus trastuzumab compared with trastuzumab (median PFS time is 27 versus 18 weeks, respectively); hazard ratio of 0.67 with an 80% power and a 1-sided type I error of 0.025. Present and Target Accrual Sixteen of the target 280 pts have been randomized. The trial is currently open for accrual in the United States and Canada. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr OT1-02-02.

A phase Ib/II trial of trastuzumab-DM1 (T-DM1) with pertuzumab (P) for women with HER2-positive, locally advanced or metastatic breast cancer (BC) who were previously treated with trastuzumab (T).

1012 Background: The HER2-targeted antibody-drug conjugate T-DM1 has shown encouraging efficacy and safety in patients (pts) with heavily pretreated HER2-positive (HER2+) BC. P is the first HER2-directed dimerization inhibitor for treatment of HER2+ BC. T-DM1 and P bind different subdomains of HER2. Combination of P with T or T-DM1 has shown synergistic antitumor activity in HER2+ xenograft models. Methods: This international, 3+3 design, single-arm, phase 1b/2 study investigated P (840 mg cycle 1,420 mg cycle 2 and beyond) with T- DM1 (3.0 mg/kg in cohort 1 and, in the absence of dose limiting toxicity [DLT], 3.6 mg/kg in cohort 2), in pts with HER2+ locally advanced or metastatic BC. This was followed by a 60 pt expansion into phase 2 at the established dose. Primary objectives included safety and preliminary responses per RECIST. Results: As of October 1, 2009, 37 pts had enrolled; 23 safety evaluable pts (9 in phase 1b and 14 in phase 2) received ≥1 cycle of T-DM1 and P (median of 2 cycles each, range...

Sunitinib (SU) in Combination with Trastuzumab (T) for the Treatment of Advanced Breast Cancer (ABC): Activity and Safety Results from a Phase II Study.

Abstract Background: SU is an oral, multitargeted tyrosine kinase inhibitor of VEGFRs, PDGFRs, KIT, RET, FLT3, and CSF-1R, with single-agent activity in patients (pts) with heavily pretreated ABC (locally recurrent or metastatic breast cancer). T is approved for 2nd-line monotherapy and in combination with taxane-based therapies for 1st-line ABC. The combination of SU + T in HER2+ ABC pts was investigated.Materials and methods: Eligible pts with HER2+ ABC received a starting dose of oral SU 37.5 mg/d (continuous daily dosing [CDD]) and either T administered wkly (iv loading 4 mg/kg then wkly 2 mg/kg) or q3w (loading 8 mg/kg then q3w 6 mg/kg). Due to changing standard of care, the trial was amended to include pts having prior chemotherapy in the 1st-line setting. Previous treatment (tx) with T (± lapatinib) was permitted. The primary endpoint was objective response rate (ORR). Secondary endpoints included safety, progression-free survival (PFS), pharmacokinetics (PK) and quality of life (QoL).Results: As of April 2009, 60 pts were enrolled (6 on the original protocol and 54 under the amendment). Of 54 pts enrolled post-amendment, 6 pts continue on study and 48 have discontinued, 12 due to AEs. Most (n=31; 57%) pts received SU + T as 1st-line tx and 11/31 pts were completely tx-naïve. Pts received a median of 5 cycles (range: 1–16) of SU and 4 cycles (range: 1–15) of T. SU was dose reduced from 37.5 mg/d to 25 mg/d in 39% of pts. All pts were evaluable for safety and 52 pts were evaluable for efficacy. ORR was 34.6% and clinical benefit rate was 48% (2 CR; 16 PR; 7 SD ≥24 wks). Of the 18 responders, 5 pts were completely tx-naïve and 9 pts were 1st-line. Median PFS was 25.3 wks (95% CI, 19.3, 29.1). Most AEs were G1/2. G3 non-hematologic AEs in ≥10% pts were asthenia (17%) and hypertension (11%) and 3 G4 events occurred (LVEF decline, pulmonary embolism, and pancreatitis). Hematologic AEs (G3/4 in ≥10% pts) were neutropenia (22%) and thrombocytopenia (17%). One G5 event (cardiogenic shock) was reported. LVEF decline/LV dysfunction occurred in 21 pts (6 pts had ≥G3 AEs); 18/21 pts (86%) had received prior anthracycline and 12 pts (57%) prior T. There was no significant on-tx change from baseline in the QoL domain. Mean (SD) steady state level for SU was 46.1 (25.9) ng/mL in agreement with prior observations.Conclusions: The combination of SU (37.5 mg/d; CDD schedule) + T (wkly or q3w) showed acceptable tolerability and antitumor activity in HER2+ ABC pts without adversely affecting overall QoL. Citation Information: Cancer Res 2009;69(24 Suppl):Abstract nr 201.

Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells

The melanoma differentiation-associated gene-7 (mda-7) is a member of the interleukin-10 cytokine family and a novel tumor suppressor gene. Adenoviral-mediated mda-7 (Ad-mda7) gene transfer has tumor-specific growth inhibitory and proapoptotic effects in a broad spectrum of cancer cells. In breast cancer cells, adenoviral-induced mda-7 expression triggers antiproliferative effects by downregulation of survival signals, such as Bcl-2 and Akt. The anti-human epidermal growth factor receptor-2 (Her-2) monoclonal antibody, Trastuzumab (Herceptin), increases the sensitivity of Her-2/neu-overexpressing breast cancer cells to chemotherapeutic agents and radiotherapy. In this study, we evaluate the effects of treatment with Ad-mda7 and Herceptin combination therapy in a panel of Her-2/neu-overexpressing cell lines, and in established tumors in nude mice. Compared to individual treatments, the combination of Ad-mda7 and Herceptin elicits supra-additive antitumor activity in Her-2/neu-overexpressing tumor cell lines: increased cell death, cell cycle block and apoptosis. The Ad-mda7 and Herceptin interaction was shown to be synergistic by isobologram analysis. Ad-mda7 does not alter cell surface Her-2/neu levels, but the combination of Ad-mda7+Herceptin results in increased expression of cell surface E-cadherin with concomitant translocation of beta-catenin from the nucleus to the cell membrane. In vivo, the combination of Ad-mda7 and Herceptin showed significantly increased antitumor activity (P<0.003) against Her-2/neu-overexpressing tumors. These data suggest that the combination of Ad-mda7 with Herceptin may be a novel therapy for breast cancer patients whose tumors overexpress Her-2/neu. The observed synergistic effect may improve treatment options for otherwise poorly responsive, Her-2-positive, breast cancer patients.

Overview of treatment results with trastuzumab (Herceptin) in metastatic breast cancer

HER2/ neu amplification/overexpression confers more aggressive and malignant characteristics on breast cancer cells. Patients with HER2/ neu-amplified breast cancer have a worse prognosis than those with normal HER2/ neu expression. Over the past decade, the intracellular signaling pathways associated with this growth factor receptor have been elucidated. Multiple therapeutic strategies that target the HER2/ neu oncoprotein are under development. Trastuzumab (Herceptin; Genentech, Inc, South San Francisco, CA), a humanized monoclonal antibody that binds to the extracellular domain of the HER2/ neu receptor, has undergone phase I, II, and III clinical trials. These studies have shown that, as a single agent, trastuzumab has substantial and reproducible antitumor activity in HER2/ neu-amplified metastatic breast cancer. In addition, when added to chemotherapy, trastuzumab improves antitumor efficacy as measured by time to progression, response rate, and survival. Additional chemotherapy/ trastuzumab combinations are under active evaluation, and new schedules of administration are being tested. Thus, trastuzumab is the first successful example of molecularly targeted therapy in the management of metastatic breast cancer.