Michael P. DiGiovanna

Purpose: The 21-gene recurrence score (RS) assay is used to help formulate adjuvant chemotherapy recommendations for patients with estrogen receptor–positive, early-stage breast cancer. Most frequently, medical oncologists order RS after surgery. Results take an additional 2 weeks to return, which can delay decision making. We conducted a prospective quality-improvement project to assess the impact of early guideline-directed RS ordering by surgeons before the first visit with a medical oncologist on adjuvant therapy decision making. Materials and Methods: Surgical oncologists ordered RS testing following National Comprehensive Cancer Network guidelines at time of diagnosis or at time of surgery between July 1, 2015 and December 31, 2015. We measured the testing rate of patients eligible for RS, time to chemotherapy decisions, rates of chemotherapy use, accrual to RS-based clinical trials, cost, and physician acceptance of the policy and compared the results to patients who met eligibility criteria for early guideline-directed testing during the 6 months before the project. Results: Ninety patients met eligibility criteria during the testing period. RS was ordered for 91% of patients in the early testing group compared with 76% of historical controls ( P < .001). Median time to chemotherapy decision was significantly shorter in the early testing group (20 days; 95% CI, 17 to 23 days) compared with historical controls (32 days; 95% CI, 29 to 35 days; P < .001). There were no significant differences in time to chemotherapy initiation, chemotherapy use, RS-based trial enrollment, or calculated costs between the groups. Conclusion: Early guideline-directed RS testing in selected patients is an effective way to shorten time to treatment decisions.

Purpose Interactions between HER2, estrogen receptor (ER), and insulin-like growth factor I receptor (IGF1R) are implicated in resistance to monotherapies targeting these receptors. We have previously shown in pre-clinical studies synergistic anti-tumor effects for co-targeting each pairwise combination of HER2, IGF1R, and ER. Strikingly, synergy for HER2/IGF1R targeting occurred not only in a HER2+ model, but also in a HER2-normal model. The purpose of the current study was therefore to determine the generalizability of synergistic anti-tumor effects of co-targeting HER2/IGF1R, the anti-tumor activity of triple-targeting HER2/IGF1R/ER in hormone-dependent cell lines, and the effect of using the multi-targeting drugs neratinib (pan-HER) and BMS-754807 (dual IGF1R/insulin receptor). Methods Proliferation and apoptosis assays were performed in a large panel of cell lines representing varying receptor expression levels. Mechanistic effects were studied using phospho-protein immunoblotting. Analyses of drug interaction effects were performed using linear mixed-effects regression models. Results Enhanced anti-proliferative effects of HER/IGF-insulin co-targeting were seen in most, though not all, cell lines, including HER2-normal lines. For ER+ lines, triple targeting with inclusion of anti-estrogen generally resulted in the greatest anti-tumor effects. Double or triple targeting generally resulted in marked increases in apoptosis in the sensitive lines. Mechanistic studies demonstrated that the synergy between drugs was correlated with maximal inhibition of Akt and ERK pathway signaling. Conclusions Dual HER/IGF-insulin targeting, and triple targeting with inclusion of anti-estrogen drugs, shows striking anti-tumor activity across breast cancer types, and drugs with broader receptor specificity may be more effective than single receptor selective drugs, particularly for ER− cells.

The insulin-like growth factor I receptor (IGF1R) has been linked to resistance to HER2-directed therapy with trastuzumab (Herceptin). We examined the anti-tumor activity of figitumumab (CP-751,871), a human monoclonal antibody that blocks IGF1R ligand binding, alone and in combination with the therapeutic anti-HER2 antibody trastuzumab and the pan-HER family tyrosine kinase inhibitor neratinib, using in vitro and in vivo breast cancer model systems. In vitro assays of proliferation, apoptosis, and signaling, and in vivo anti-tumor experiments were conducted in HER2-overexpressing (BT474) and HER2-normal (MCF7) models. We find single-agent activity of the HER2-targeting drugs but not figitumumab in the BT474 model, while the reverse is true in the MCF7 model. However, in both models, combining figitumumab with HER2-targeting drugs shows synergistic anti-proliferative and apoptosis-inducing effects, and optimum inhibition of downstream signaling. In murine xenograft models, synergistic anti-tumor effects were observed in the HER2-normal MCF7 model for the combination of figitumumab with trastuzumab, and, in the HER2-overexpressing BT474 model, enhanced anti-tumor effects were observed for the combination of figitumumab with either trastuzumab or neratinib. Analysis of tumor extracts from the in vivo experiments showed evidence of the most optimal inhibition of downstream signaling for the drug combinations over the single-agent therapies. These results suggest promise for such combinations in treating patients with breast cancer, and that, unlike the case for single-agent therapy, the therapeutic effects of such combinations may be independent of expression levels of the individual receptors or the single-agent activity profile.

Estrogen receptor (ER) and human epidermal growth factor receptor (HER) family receptors interact in breast cancer; co-targeting these receptors is of interest. We previously reported on a synergistic growth inhibition for the combination of trastuzumab plus tamoxifen in HER2+/ER+ BT474 cells, but no induction of apoptosis. Herein we describe the effects of co-targeting in models of differing HER2 overexpression status (MCF7 HER2-normal/ER+, BT474 HER2-overexpressing/ER+). Assays of proliferation were carried-out using WST-1, cell cycle using flow cytometry, and apoptosis by determination of sub-G1 population and by annexin-V. Combining a dual HER2/EGFR kinase inhibitor with anti-estrogens induces apoptosis of BT474 cells. Furthermore, in MCF7 cells, despite HER2-normal status and lack of response to single-agent HER2 inhibitors, addition of HER2 inhibitors or dual HER2/EGFR inhibitor to anti-estrogens augments the antiproliferative effect of anti-estrogens, and converts the drug effect from cytostatic to apoptosis-inducing. ER-HER co-targeting enhanced the antitumor effects and can bring about effects of targeting HER2 in models of HER2-normal breast cancer.

Constitutive activation of the PI3K/Akt/mTOR pathway has been suggested as a mechanism of resistance to trastuzumab therapy. This phase II trial was designed to evaluate the safety and clinical activity of daily oral sirolimus, a mammalian target of rapamycin (mTOR) inhibitor, in combination with trastuzumab in HER2-positive metastatic breast cancer following disease progression on prior trastuzumab therapy. Sirolimus 6 mg oral daily dose was administered with a standard dose and schedule of trastuzumab weekly or every 3 weeks. Pharmacodynamic studies included Western blot analysis of S6K1, phosphoS6K1, and mTOR in peripheral mononuclear cells, circulating tumor cells (CTC), and endothelial cells (CEC). Eleven patients were evaluable for safety; and nine were evaluable for response assessment. Subsequent enrollment was stopped due to slow accrual. Study treatment-related grade 3 toxicity included pneumonitis, myelosuppression (leukopenia/anemia), and dermatologic reactions (mucositis, nail changes and rash), with no grade 4 events. One patient received eight cycles (58 weeks) and achieved a partial response. Five patients treated for a total of 101 weeks (median 12 weeks, range 8–47 weeks) achieved stable disease as best response. Overall response rate was 1/9 (11 %) and clinical benefit rate was 4/9 (44 %). There was no statistically significant correlation between response and post-treatment change in levels of the mTOR pathway biomarkers, CTCs, HER2 CTCs, or CECs. Sirolimus 6 mg administered daily with trastuzumab appears to be well tolerated in patients with metastatic HER2-positive breast cancer following disease progression on prior trastuzumab therapy, with evidence of disease activity. mTOR inhibition may overcome resistance to trastuzumab in some HER2-positive tumors.

Introduction: HER2 and estrogen receptor (ER) are important in breast cancer and are therapeutic targets of trastuzumab (Herceptin) and tamoxifen, respectively. Retinoids inhibit breast cancer growth, and modulate signaling by HER2 and ER. We hypothesized that treatment with retinoids and simultaneous targeting of HER2 and/or ER may have enhanced anti-tumor effects. Methods: The effects of retinoids combined with trastuzumab or tamoxifen were examined in two human breast cancer cell lines in culture, BT474 and SKBR3. Assays of proliferation, apoptosis, differentiation, cell cycle distribution, and receptor signaling were performed. Results: In HER2-overexpressing/ER-positive BT474 cells, combining all-trans retinoic acid (atRA) with tamoxifen or trastuzumab synergistically inhibited cell growth, and altered cell differentiation and cell cycle. Only atRA/trastuzumab-containing combinations induced apoptosis. BT474 and HER2-overexpressing/ER-negative SKBR3 cells were treated with a panel of retinoids (atRA, 9-cis-retinoic acid, 13-cis-retinoic acid, or N-(4-hydroxyphenyl) retinamide (fenretinide) (4-HPR)) combined with trastuzumab. In BT474 cells, none of the single agents except 4-HPR induced apoptosis, but again combinations of each retinoid with trastuzumab did induce apoptosis. In contrast, the single retinoid agents did cause apoptosis in SKBR3 cells; this was only modestly enhanced by addition of trastuzumab. The retinoid drug combinations altered signaling by HER2 and ER. Retinoids were inactive in trastuzumab-resistant BT474 cells. Conclusions: Combining retinoids with trastuzumab maximally inhibits cell growth and induces apoptosis in trastuzumab-sensitive cells. Treatment with such combinations may have benefit for breast cancer patients.

The insulin-like growth factor I receptor (IGF1R) interacts with estrogen receptor-α (ERα) and HER2. We examined the effect of combinations of IGF1R antagonists (α-IR3, AG1024) and anti-estrogens (4-hydroxy tamoxifen, fulvestrant) in two human ER+ breast cancer cell lines: BT474 (HER2 overexpressing, IGF1R low) and MCF7 (HER2 non-overexpressing, IGF1R high). In BT474 cells, growth was inhibited by anti-estrogens, but not by IGF1R antagonists; however, adding IGF1R inhibitors to anti-estrogens enhanced growth inhibition. In MCF7 cells, growth was inhibited by IGF1R and ER antagonists and more so by their combination. In both cell lines, no single agents could induce apoptosis, but combining IGF1R inhibitors with anti-estrogens induced dramatic levels of apoptosis. IGF1R antagonists enhanced the ability of the anti-estrogens to inhibit ER transcriptional activity in BT474 cells, but not in MCF7 cells. The drug combination synergistically inhibited ER and IGF1R activity. Such combinations may be useful therapy for breast cancer.

Purpose: ErbB-2 (human epidermal growth factor receptor 2) overexpression may be predictive of relative resistance and/or sensitivity to specific chemotherapeutic agents. Results from a previous study from the Cancer and Leukemia Group B (CALGB 8541) demonstrated an interaction between ErbB-2 and increasing dose of adjuvant cyclophosphamide, doxorubicin, and fluorouracil (CAF) chemotherapy. Other studies have suggested that evaluation of the phosphorylated/activated form of ErbB-2 might be more precise in defining the impact of ErbB-2 in breast cancer. We have evaluated tumor tissue sections from CALGB 8541 patients to determine whether the interaction of ErbB-2 with CAF dose is dependent on ErbB-2 activation state, and whether phosphorylated ErbB-2 is an adverse prognostic factor in patients treated with CAF. Patients and Methods: Patients were randomly assigned to one of three dosing regimens of CAF. Paraffin samples from 992 of 1,572 patients who participated in CALGB 8541 were available. Of the 570 tumors with any staining for ErbB-2, 488 had tissue available for assay for phosphorylated ErbB-2, which was performed by immunohistochemistry. Results: Of 910 total assessable cases, 112 of 488 ErbB-2-positive cases (23%) stained positively for phosphorylated ErbB-2. The previously described interaction of dosing regimen of CAF with ErbB-2 was not dependent on phosphorylation status of ErbB-2. Conclusion: Monitoring phosphorylation of ErbB-2 with an antiphospho-ErbB-2 antibody did not add further precision to identifying those patients most likely to benefit from increased dose of anthracycline-based adjuvant chemotherapy. Favorable outcomes are observed in ErbB-2-overexpressing patients treated with high-dose CAF regardless of ErbB-2 phosphorylation state.