A Phase Ib Expansion Cohort Evaluating Aurora A Kinase Inhibitor Alisertib and Dual TORC1/2 Inhibitor Sapanisertib in Patients with Advanced Solid Tumors

BACKGROUND

This study further evaluated the safety and efficacy of the combination of alisertib and sapanisertib in an expansion cohort of patients, including a subset of patients with refractory pancreatic adenocarcinoma, with further evaluation of the pharmacodynamic characteristics of combination therapy.

METHODS

Twenty patients with refractory solid tumors and 11 patients with pancreatic adenocarcinoma were treated at the recommended phase 2 dose of alisertib and sapanisertib. Adverse events and disease response were assessed. Patients in the expansion cohort were treated with a 7-day lead-in of either alisertib or sapanisertib prior to combination therapy, with tumor tissue biopsy and serial functional imaging performed for correlative analysis.

RESULTS

Toxicity across treatment groups was overall similar to prior studies. One partial response to treatment was observed in a patient with ER positive breast cancer, and a patient with pancreatic cancer experienced prolonged stable disease. In an additional cohort of pancreatic cancer patients, treatment response was modest. Correlative analysis revealed variability in markers of apoptosis and immune cell infiltrate according to lead-in therapy and response.

CONCLUSIONS

Dual targeting of Aurora A kinase and mTOR resulted in marginal clinical benefit in a population of patients with refractory solid tumors, including pancreatic adenocarcinoma, though individual patients experienced significant response to therapy. Correlatives indicate apoptotic response and tumor immune cell infiltrate may affect clinical outcomes.

Overcoming doxorubicin resistance in triple-negative breast cancer using the class I-targeting HDAC inhibitor bocodepsin/OKI-179 to promote apoptosis

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with a poor prognosis. Doxorubicin is part of standard curative therapy for TNBC, but chemotherapy resistance remains an important clinical challenge. Bocodepsin (OKI-179) is a small molecule class I histone deacetylase (HDAC) inhibitor that promotes apoptosis in TNBC preclinical models. The purpose of this study was to investigate the combination of bocodepsin and doxorubicin in preclinical TNBC models and evaluate the impact on terminal cell fate, including apoptosis and senescence.

METHODS

TNBC cell lines were treated with doxorubicin and CellTiter-Glo was used to assess proliferation and determine doxorubicin sensitivity. Select cell lines were treated with OKI-005 (in vitro version of bocodepsin) and doxorubicin and assessed for proliferation, apoptosis as measured by Annexin V/PI, and cell cycle by flow cytometry. Immunoblotting was used to assess changes in mediators of apoptosis, cell cycle arrest, and senescence. Senescence was measured by the senescence-associated β-galactosidase assay. An MDA-MB-231 xenograft in vivo model was treated with bocodepsin, doxorubicin, or the combination and assessed for inhibition of tumor growth. shRNA knockdown of p53 was performed in the CAL-51 cell line and proliferation, apoptosis and senescence were assessed in response to combination treatment.

RESULTS

OKI-005 and doxorubicin resulted in synergistic antiproliferative activity in TNBC cells lines regardless of p53 mutation status. The combination led to increased apoptosis and decreased senescence. In vivo, the combination resulted in increased tumor growth inhibition compared to either single agent. shRNA knock-down of p53 led to increased doxorubicin-induced senescence that was decreased with the addition of OKI-005 in vitro.

CONCLUSION

The addition of bocodepsin to doxorubicin resulted in synergistic antiproliferative activity in vitro, improved tumor growth inhibition in vivo, and promotion of apoptosis which makes this a promising combination to overcome doxorubicin resistance in TNBC. Bocodepsin is currently in clinical development and has a favorable toxicity profile compared to other HDAC inhibitors supporting the feasibility of evaluating this combination in patients with TNBC.

Phase 1/2 study of monalizumab plus durvalumab in patients with advanced solid tumors

BACKGROUND

The combination of monalizumab (anti-NKG2A/CD94) and durvalumab (anti-programmed death ligand-1) may promote antitumor immunity by targeting innate and adaptive immunity. This phase 1/2 study of monalizumab and durvalumab evaluated safety, antitumor activity, and pharmacodynamics in patients with advanced solid tumors.

MAIN BODY

Immunotherapy-naïve patients aged ≥18 years with advanced disease, Eastern Cooperative Oncology Group performance status of 0-1, and 1-3 prior lines of systemic therapy in the recurrent/metastatic setting were enrolled. In part 1 (dose escalation), patients received durvalumab 1500 mg every 4 weeks (Q4W) with increasing doses of monalizumab Q2W/Q4W (n=15). Dose expansion in part 1 included patients with cervical cancer (n=15; durvalumab 1500 mg Q4W and monalizumab 750 mg Q2W) or metastatic microsatellite stable (MSS)-colorectal cancer (CRC) (n=15; durvalumab 1500 mg Q4W and monalizumab 750 mg Q4W). In part 2 (dose expansion), patients with MSS-CRC (n=40), non-small cell lung cancer (NSCLC; n=20), MSS-endometrial cancer (n=40), or ovarian cancer (n=40) received durvalumab 1500 mg Q4W and monalizumab 750 mg Q2W. The primary endpoint was safety. Secondary endpoints included antitumor activity per Response Evaluation Criteria In Solid Tumors version 1.1 (RECIST v1.1). Exploratory analyses included assessment of T-cell and natural killer (NK) cell activation and proliferation in peripheral blood and the tumor microenvironment (TME). The study enrolled 185 patients (part 1, 45; part 2, 140). No dose-limiting toxicities were observed and the maximum tolerated dose was not reached. In part 2, the most common treatment-related adverse events were fatigue (12.1%), asthenia (9.3%), diarrhea (9.3%), pruritus (7.9%), and pyrexia (7.1%). In the expansion cohorts, response rates were 0% (cervical), 7.7% (MSS-CRC), 10% (NSCLC), 5.4% (ovarian), and 0% (MSS-endometrial). Sustained NK cell activation, CD8+ T-cell proliferation, increased serum levels of CXCL10 (C-X-C motif chemokine ligand 10) and CXCL11, and increased tumor infiltration of CD8+ and granzyme B+ cells were observed.

CONCLUSIONS

Although efficacy was modest, monalizumab plus durvalumab was well tolerated and encouraging immune activation was observed in the peripheral blood and TME.

TRIAL REGISTRATION NUMBER

NCT02671435.

Major cardiovascular adverse events in older adults with early-stage triple-negative breast cancer treated with adjuvant taxane + anthracycline versus taxane-based chemotherapy regimens: A SEER-medicare study

BACKGROUND

Triple-negative breast cancer (TNBC) is more aggressive as compared to other subtypes of breast cancer with characteristic metastatic patterns and a poor prognosis. The standard of care for early-stage TNBC is historically anthracycline and taxane-based chemotherapy (ATAX). Despite the effectiveness of this regimen, anthracyclines carry a small but important risk of cardiotoxicity, which is specifically a concern in the older population. This study evaluates major adverse cardiovascular events (MACE) in older women with TNBC treated with ATAX compared to taxane-based chemotherapy (TAX).

METHODS

Using the Surveillance, Epidemiology, and End Results (SEER)-Medicare database, we identified women aged 66 and older with TNBC diagnosed between 2010 and 2015 (N = 2215). We compared patient and clinical characteristics according to adjuvant chemotherapy regimen (chemotherapy versus no chemotherapy and ATAX versus TAX). Logistic regression was performed to estimate the odds ratios (OR) and 95% confidence intervals (CIs), Kaplan-Meier survival curves were generated to estimate three-year overall survival (OS) and cancer specific survival (CSS). Cox proportional hazards models were used to analyze OS and CSS while controlling for patient and tumor characteristics. MACE was defined as acute myocardial infarction, heart failure, potentially fatal arrhythmia, and cerebral vascular incidence. Few patients experienced a cardiac death and therefore this was excluded in the analysis.

RESULTS

Of the 2215 patients in our cohort, most patients (n = 1334; 60.26%) received TAX compared to ATAX (n = 881; 39.78%). Patients who received ATAX were not statistically significantly more likely than those who received TAX to experience acute myocardial infarction, cerebral vascular accident (CVA), or potentially fatal arrhythmia when controlling for traditional risk factors. Among patients who experienced MACE, there was no difference in OS or CSS in patients who received TAX vs ATAX. Patients who received ATAX were less likely to develop heart failure than those who received TAX (OR 0.63, 95% CI [0.45-0.88], p < 0.01). Patients who developed MACE and who were > 76 years old had worse OS compared to those who experienced MACE and were age 66-75 years old (HR 1.67, 95% CI [1.07-2.62], p = 0.02).

CONCLUSION

Among older women with TNBC, receipt of adjuvant chemotherapy with ATAX was not associated with increased risk of major adverse cardiac events. For those who experienced a cardiac event, there was no difference in survival amongst those who received TAX vs ATAX. Other factors including additional chemotherapy toxicities should be investigated as a potential etiology for the inferior OS previously observed with ATAX vs TAX in older women with node negative or 1-3 positive lymph nodes.

First-in-Human Dose-Escalation Study of the Novel Oral Depsipeptide Class I-Targeting HDAC Inhibitor Bocodepsin (OKI-179) in Patients with Advanced Solid Tumors

(1) Background: Histone deacetylases (HDACs) play a critical role in epigenetic signaling in cancer; however, available HDAC inhibitors have limited therapeutic windows and suboptimal pharmacokinetics (PK). This first-in-human phase I dose escalation study evaluated the safety, PK, pharmacodynamics (PDx), and efficacy of the oral Class I-targeting HDAC inhibitor bocodepsin (OKI-179). (2) Patients and Methods: Patients (n = 34) with advanced solid tumors were treated with OKI-179 orally once daily in three schedules: 4 days on 3 days off (4:3), 5 days on 2 days off (5:2), or continuous in 21-day cycles until disease progression or unacceptable toxicity. Single-patient escalation cohorts followed a standard 3 + 3 design. (3) Results: The mean duration of treatment was 81.2 (range 11-447) days. The most frequent adverse events in all patients were nausea (70.6%), fatigue (47.1%), and thrombocytopenia (41.2%). The maximum tolerated dose (MTD) of OKI-179 was 450 mg with 4:3 and 200 mg with continuous dosing. Dose-limiting toxicities included decreased platelet count and nausea. Prolonged disease control was observed, including two patients with platinum-resistant ovarian cancer. Systemic exposure to the active metabolite exceeded the preclinical efficacy threshold at doses lower than the MTD and was temporally associated with increased histone acetylation in circulating T cells. (4) Conclusions: OKI-179 has a manageable safety profile at the recommended phase 2 dose (RP2D) of 300 mg daily on a 4:3 schedule with prophylactic oral antiemetics. OKI-179 is currently being investigated with the MEK inhibitor binimetinib in patients with NRAS-mutated melanoma in the phase 2 Nautilus trial.

Safety and Efficacy of Tucatinib, Letrozole, and Palbociclib in Patients with Previously Treated HR+/HER2+ Breast Cancer

PURPOSE

To overcome resistance to antihormonal and HER2-targeted agents mediated by cyclin D1-CDK4/6 complex, we proposed an oral combination of the HER2 inhibitor tucatinib, aromatase inhibitor letrozole, and CDK4/6 inhibitor palbociclib (TLP combination) for treatment of HR+/HER2+ metastatic breast cancer (MBC).

PATIENTS AND METHODS

Phase Ib/II TLP trial (NCT03054363) enrolled patients with HR+/HER2+ MBC treated with ≥2 HER2-targeted agents. The phase Ib primary endpoint was safety of the regimen evaluated by NCI CTCAE version 4.3. The phase II primary endpoint was efficacy by median progression-free survival (mPFS).

RESULTS

Forty-two women ages 22 to 81 years were enrolled. Patients received a median of two lines of therapy in the metastatic setting, 71.4% had visceral disease, 35.7% had CNS disease. The most common treatment-emergent adverse events (AE) of grade ≥3 were neutropenia (64.3%), leukopenia (23.8%), diarrhea (19.0%), and fatigue (14.3%). Tucatinib increased AUC10-19 hours of palbociclib 1.7-fold, requiring palbociclib dose reduction from 125 to 75 mg daily. In 40 response-evaluable patients, mPFS was 8.4 months, with similar mPFS in non-CNS and CNS cohorts (10.0 months vs. 8.2 months; P = 0.9). Overall response rate was 44.5%, median duration of response was 13.9 months, and clinical benefit rate was 70.4%; 60% of patients were on treatment for ≥6 months, 25% for ≥1 year, and 10% for ≥2 years. In the CNS cohort, 26.6% of patients remained on study for ≥1 year.

CONCLUSIONS

TLP combination was safe and tolerable. AEs were expected and manageable with supportive therapy and dose reductions. TLP showed excellent efficacy for an all-oral chemotherapy-free regimen warranting further testing. See related commentary by Huppert and Rugo, p. 4993.

The emergence of targeted therapy for HER2-low triple-negative breast cancer: a review of fam-trastuzumab deruxtecan

INTRODUCTION

Metastatic triple-negative breast cancer (TNBC) is an aggressive sub-type of breast cancer. Despite recent advances, metastatic TNBC remains difficult to treat with limited targeted treatment options. Fam-trastuzumab deruxtecan (T-DXd), is a novel antibody-drug conjugate (ADC) targeting human epidermal growth factor receptor 2 (HER2) and is composed of a unique linker bound to the topoisomerase I inhibitor DXd. T-DXd has significant anti-tumor activity in patients with HER2-low TNBC.

AREAS COVERED

This review reports on the mechanism, pre-clinical/clinical studies, efficacy, and tolerability of T-DXd. A literature search was conducted via PubMed using keywords such as 'fam-trastuzumab deruxtecan,' 'Enhertu,' and 'HER2-low cancers.'

EXPERT OPINION

The Phase III Destiny-Breast04 Trial showed benefit in progression-free and overall survival in patients with HER2-low metastatic breast cancers treated with T-DXd compared to treatment of physician's choice chemotherapy. T-DXd is the first pharmaceutical to effectively target a HER2-low population with clinically meaningful efficacy in patients with HER2-low TNBC. Compared to chemotherapy, T-DXd has a similar safety profile, with the additional need for close monitoring for interstitial lung disease. Given the clinical activity of T-DXd in TNBC, it is likely there will be continued efforts to refine HER2-low diagnostics and to develop additional ADCs with other protein targets.

Phase II trial of fulvestrant plus enzalutamide in ER+/HER2- advanced breast cancer

This clinical trial combined fulvestrant with the anti-androgen enzalutamide in women with metastatic ER+/HER2- breast cancer (BC). Eligible patients were women with ECOG 0-2, ER+/HER2- measurable or evaluable metastatic BC. Prior fulvestrant was allowed. Fulvestrant was administered at 500 mg IM on days 1, 15, 29, and every 4 weeks thereafter. Enzalutamide was given at 160 mg po daily. Fresh tumor biopsies were required at study entry and after 4 weeks of treatment. The primary efficacy endpoint of the trial was the clinical benefit rate at 24 weeks (CBR24). The median age was 61 years (46-87); PS 1 (0-1); median of 4 prior non-hormonal and 3 prior hormonal therapies for metastatic disease. Twelve had prior fulvestrant, and 91% had visceral disease. CBR24 was 25% (7/28 evaluable). Median progression-free survival (PFS) was 8 weeks (95% CI: 2-52). Adverse events were as expected for hormonal therapy. Significant (p < 0.1) univariate relationships existed between PFS and ER%, AR%, and PIK3CA and/or PTEN mutations. Baseline levels of phospho-proteins in the mTOR pathway were more highly expressed in biopsies of patients with shorter PFS. Fulvestrant plus enzalutamide had manageable side effects. The primary endpoint of CBR24 was 25% in heavily pretreated metastatic ER+/HER2- BC. Short PFS was associated with activation of the mTOR pathway, and PIK3CA and/or PTEN mutations were associated with an increased hazard of progression. Thus, a combination of fulvestrant or other SERD plus AKT/PI3K/mTOR inhibitor with or without AR inhibition warrants investigation in second-line endocrine therapy of metastatic ER+ BC.

Abstract OT3-09-01: Clinical Trial of Alpelisib and Tucatinib in Patients with PIK3CA-Mutant HER2-Positive Metastatic Breast Cancer

Phosphatidylinositol 3-kinase (PI3K) pathway plays a key role in resistance to the drugs targeting human epidermal growth factor receptor 2 (HER2). Activating mutations in the gene encoding alpha catalytic subunit of PI3K (PIK3CA) are present in approximately 30% of HER2+ tumors. PIK3CA mutations are linked to drug resistance and decreased survival in patients with HER2+ breast cancer. To overcome this resistance mechanism, we designed a phase IB/II clinical trial to evaluate the combination of HER2 small molecule inhibitor tucatinib with PI3K inhibitor alpelisib in patients with HER2+ metastatic breast cancer (NCT05230810). This multicenter clinical trial is conducted through the Academic Breast Cancer Consortium (ABRCC), with the University of Colorado Cancer Center as the lead site. Target enrollment: 40 patients. This is a run-in phase IB/roll-over phase II study. Phase IB will follow Time-to-Event Bayesian Optimal Interval design and enroll from 9 to 19 patients to find the maximum tolerated doses (MTDs) of tucatinib and alpelisib. From 21 to 31 patients will be enrolled in phase II part, for a total of 40 patients in the final efficacy analysis. Main inclusion criteria: 1. Women and men ≥ 18 years old 2. Eastern Cooperative Oncology Group (ECOG) performance status 0-1 3. Presence of activating PIK3CA mutation in the tumor 4. Patients with HR-/HER2+ or HR+/HER2+ breast cancer may enroll; ovarian suppression is mandatory for premenopausal patients with HR+/HER2+ disease 5. HR+/HER2+ patients should be agreeable to concomitant treatment with fulvestrant 6. Prior treatment with at least two FDA-approved HER2-targeted agents 7. Measurable or evaluable disease. Bone only disease is allowed. 8. Subjects with untreated central nervous system (CNS) metastases not needing immediate local therapy, and subjects with previously treated stable or progressive brain metastases may enroll, provided that there is no indication for immediate re-treatment. For patients with treated CNS metastases: time from treatment of CNS disease until the first dose of study drugs should be as follows: WBRT ≥ 21 days, surgical resection ≥ 14 days, SRS ≥ 7 days. 9. Adequate organ and marrow function Main exclusion criteria: 1. Contraindications to undergo contrast brain MRI 2. Leptomeningeal disease 3. Poorly controlled seizures 4. Diabetes mellitus type I, or uncontrolled diabetes mellitus type II 5. Acute pancreatitis within 1 year of screening, or history of chronic pancreatitis 6. History of severe cutaneous hypersensitivity reactions 7. Toxicities of prior cancer therapies that have not resolved to grade 1 or less, except peripheral neuropathy, which must have resolved to grade 2 or less, and alopecia 8. Previous treatment with EGFR or HER2 tyrosine kinase inhibitors, or PI3K/mTOR/AKT inhibitors. 9. Systemic anti-cancer therapy, palliative radiation to extracranial sites, or surgery within 2 weeks of the first dose of study drugs 10. Active bacterial, fungal, or viral infections, hepatitis B, C, or HIV 11. Clinically significant cardio-vascular disease Primary objectives: • Phase IB: safety and tolerability of combination therapy • Phase II: efficacy by progression free survival Exploratory assessment of biomarkers will be performed in the liquid biopsy samples. Study contact: Elena Shagisultanova, MD, PhD, elena.shagisultanova@cuanschutz.edu

Citation Format: Elena Shagisultanova, Kari B. Wisinski, Chelsea D. Gawryletz, Farrah M. Datko, Diana Medgyesy, Jennifer R. Diamond, Virginia F. Borges, Peter Kabos. Clinical Trial of Alpelisib and Tucatinib in Patients with PIK3CA-Mutant HER2-Positive Metastatic Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr OT3-09-01.

Clinical outcomes of adjuvant taxane plus anthracycline versus taxane-based chemotherapy regimens in older adults with node-positive, triple-negative breast cancer: A SEER-Medicare study

BACKGROUND

Triple-negative breast cancer (TNBC) is a subtype of breast cancer associated with an aggressive clinical course. Adjuvant chemotherapy reduces the risk of recurrence and improves survival in patients with node-positive TNBC. The benefit of anthracycline plus taxane (ATAX) regimens compared with non-anthracycline-containing, taxane-based regimens (TAX) in older women with node-positive TNBC is not well characterised.

METHODS

Using the Surveillance, Epidemiology, and End Results-Medicare database, we identified 1106 women with node-positive TNBC diagnosed at age 66 years and older between 2010 and 2015. We compared patient clinical characteristics according to adjuvant chemotherapy regimen (chemotherapy versus no chemotherapy and ATAX versus TAX). Logistic regression was performed to estimate the odds ratios (OR) and 95% confidence intervals (CIs). Kaplan-Meier survival curves were generated to estimate 3-year overall survival (OS) and cancer-specific survival (CSS). Cox proportional hazard models were used to analyse OS and CSS while controlling for patient and tumour characteristics.

RESULTS

Of the 1106 patients in our cohort, 767 (69.3%) received adjuvant chemotherapy with ATAX (364/767, 47.5%), TAX (297/767, 39%) or other regimens (106/767, 13.8%). Independent predictors of which patients were more likely to receive ATAX versus TAX included more extensive nodal involvement (≥4), age, marital/partner status and non-cardiac comorbidities. There was a statistically significant improvement in 3-year CSS (81.8% versus 71.4%) and OS (70.7% versus 51.3%) with the use of any chemotherapy in our cohort (P < 0.01). Three-year CSS and OS for patients who received ATAX versus TAX were similar at 82.8% versus 83.7% (P = 0.80) and 74.2% versus 72.7% (P = 0.79), respectively. There was a trend towards improved CSS and OS in patients with four or more positive lymph nodes who received ATAX versus TAX (hazard ratio 0.66, 95% CI: 0.36-1.23, P = 0.19 and hazard ratio 0.68, 95% CI: 0.41-1.14, P = 0.14, respectively).

CONCLUSION

Among older women with node-positive TNBC, a majority of patients received adjuvant chemotherapy, which was associated with an improvement in CSS and OS. When compared with TAX chemotherapy, there was a trend towards better outcomes with ATAX for patients with ≥4 nodes.

ATM kinase inhibitor AZD0156 in combination with irinotecan and 5-fluorouracil in preclinical models of colorectal cancer

Background

AZD0156 is an oral inhibitor of ATM, a serine threonine kinase that plays a key role in DNA damage response (DDR) associated with double-strand breaks. Topoisomerase-I inhibitor irinotecan is used clinically to treat colorectal cancer (CRC), often in combination with 5-fluorouracil (5FU). AZD0156 in combination with irinotecan and 5FU was evaluated in preclinical models of CRC to determine whether low doses of AZD0156 enhance the cytotoxicity of irinotecan in chemotherapy regimens used in the clinic.

Methods

Anti-proliferative effects of single-agent AZD0156, the active metabolite of irinotecan (SN38), and combination therapy were evaluated in 12 CRC cell lines. Additional assessment with clonogenic assay, cell cycle analysis, and immunoblotting were performed in 4 selected cell lines. Four colorectal cancer patient derived xenograft (PDX) models were treated with AZD0156, irinotecan, or 5FU alone and in combination for assessment of tumor growth inhibition (TGI). Immunofluorescence was performed on tumor tissues. The DDR mutation profile was compared across in vitro and in vivo models.

Results

Enhanced effects on cellular proliferation and regrowth were observed with the combination of AZD0156 and SN38 in select models. In cell cycle analysis of these models, increased G2/M arrest was observed with combination treatment over either single agent. Immunoblotting results suggest an increase in DDR associated with irinotecan therapy, with a reduced effect noted when combined with AZD0156, which is more pronounced in some models. Increased TGI was observed with the combination of AZD0156 and irinotecan as compared to single-agent therapy in some PDX models. The DDR mutation profile was variable across models.

Conclusions

AZD0156 and irinotecan provide a rational and active combination in preclinical colorectal cancer models. Variability across in vivo and in vitro results may be related to the variable DDR mutation profiles of the models evaluated. Further understanding of the implications of individual DDR mutation profiles may help better identify patients more likely to benefit from treatment with the combination of AZD0156 and irinotecan in the clinical setting.

BMS-986158, a Small Molecule Inhibitor of the Bromodomain and Extraterminal Domain Proteins, in Patients with Selected Advanced Solid Tumors: Results from a Phase 1/2a Trial

This phase 1/2a, open-label study (NCT02419417) evaluated the safety, tolerability, pharmacokinetics (PK), and pharmacodynamics of BMS-986158, a selective bromodomain and extraterminal domain (BET) inhibitor. Dose escalation was performed with 3 BMS-986158 dosing schedules: A (5 days on, 2 days off; range, 0.75–4.5 mg), B (14 days on, 7 days off; 2.0–3.0 mg), and C (7 days on, 14 days off; 2.0–4.5 mg). Eighty-three patients were enrolled and received ≥1 BMS-986158 dose. Diarrhea (43%) and thrombocytopenia (39%) were the most common treatment-related adverse events (TRAEs). A lower incidence of TRAEs was found with schedules A (72%) and C (72%) vs. B (100%). Stable disease was achieved in 12 (26.1%), 3 (37.5%), and 9 (31.0%) patients on schedules A, B, and C, respectively. Two patients on schedule A with a 4.5-mg starting dose (ovarian cancer, n = 1; nuclear protein in testis [NUT] carcinoma, n = 1) experienced a partial response. BMS-986158 demonstrated rapid-to-moderate absorption (median time to maximum observed plasma concentration, 1–4 h). As expected with an epigenetic modifier, expression changes in select BET-regulated genes occurred with BMS-986158 treatment. Schedule A dosing (5 days on, 2 days off) yielded tolerable safety, preliminary antitumor activity, and a dose-proportional PK profile.

A dose regimen-finding study to evaluate the safety, tolerability, pharmacokinetics, and activity of oratecan in subjects with advanced malignancies

PURPOSE

Irinotecan is a commonly used chemotherapeutic in solid tumor malignancies. Oratecan is an investigational product comprised of encequidar methanesulfonate, a novel minimally absorbed P-glycoprotein pump inhibitor, and irinotecan. This study sought to determine the maximum tolerated dose (MTD) of oratecan in patients with advanced malignancies.

METHODS

Using a "3 + 3″ dose-escalation design, patients were treated with oratecan on day 1 every 21 days. The irinotecan dose was escalated from 20 to 320 mg/m². The encequidar methanesulfonate dose was fixed at 15 mg (12.9 mg free base). PK sampling for irinotecan, encequidar and its major metabolites was performed following a single dose of oratecan during cycle 1. Patients were treated until disease progression or unacceptable toxicity.

RESULTS

Thirty-five patients were treated. The MTD was determined to be 280 mg/m² every 21 days. Irinotecan and SN-38 plasma concentration-time profile showed that irinotecan exposure increased with dose and followed biexponential decay. Nine of 17 patients at oratecan dose levels 200 mg/m² and above had SN-38 exposures comparable to those with intravenous irinotecan at standard dosing. None of the 35 patients achieved a radiologic response, ten patients had SD for > 8 weeks; the median progression-free survival for all treated patients was 9 weeks (95% CI 8.6-13.9).

CONCLUSIONS

The MTD of oratecan was encequidar methanesulfonate 15 mg plus irinotecan 280 mg/m². Exposure for irinotecan and SN-38 increased with increased dose. Potential antitumor activity was observed at the 280 and 320 mg/m² dose levels. The safety profile of oratecan was comparable to that of intravenous irinotecan.

Abstract 1063: Combination strategies to overcome doxorubicin induced senescence in triple-negative breast cancer

Background: Triple-negative breast cancer (TNBC) is a subtype of breast cancer that lacks the expression of the estrogen receptor, progesterone receptor, and human epidermal growth factor-2 over-expression. Compared to other subtypes of breast cancer, TNBC is associated with a higher risk for metastatic recurrence. While immunotherapy, PARP inhibitors, and sacituzumab govitecan have shown benefit in a subset of TNBC patients, chemotherapy with doxorubicin remains a mainstay of treatment. Senescence is a cellular phenomenon where cells are committed to an arrested state, however, senescent cells are able to secrete pro-tumorigenic factors which can help to promote tumor progression and invasion. It has been suggested that senescence is a potential mechanism of resistance in doxorubicin (dox) treated cells. Transitioning senescence mediated resistance to apoptosis is crucial to the treatment of TNBC. The objective of this study was to evaluate the combination BCL-2 and HDAC inhibitors with dox to overcome resistance and induce apoptosis.

Experimental Procedures: TNBC cell lines resistant and sensitive to doxorubicin were identified using a CellTiter-Glo Viability Assay and resistant cell lines were selected for further analysis. To assess proliferation, dox resistant TNBC cell lines were plated in 96-well plates. Cells were exposed to vehicle control, dox, BCL-2 inhibitor, HDAC inhibitor or the combination of dox and BCL-2 inhibitor or HDAC inhibitor for 72 hours. Cellular proliferation was assessed using the BioSpa live cell analysis system. Apoptosis at 24 hours was analyzed by flow cytometry using Annexin V on cells treated in combination and as single agents. Immunoblotting was performed to evaluate the downstream effects of apoptosis and senescence of drugs as single agents and in combination.

Results: The addition of a BCL-2 inhibitor and HDAC inhibitor to doxorubicin resulted in decreased proliferation in resistant TNBC cell lines compared to single agents and vehicle control by live cell microscopy. Furthermore, the combination of dox and a BCL-2 inhibitor resulted in increased apoptosis when compared to single agents and control using Annexin V staining. The cyclin dependent kinase inhibitors p21 and p16 were over-expressed in cells exposed to combination treatment. Apoptotic proteins BAD, PUMA, cleaved PARP and the anti-apoptotic protein BCL-2 were upregulated in cells treated with a BCL-2 inhibitor with or without dox. The pro-mitotic protein cyclin-B1 was downregulated in resistant cells treated with single agent BCL-2 inhibitor and in combination with dox. Additional mechanistic studies are ongoing.

Conclusion: The combination of doxorubicin with BCL-2 and HDAC inhibitors resulted in decreased cellular proliferation and increased apoptosis. Potential senolytic drugs used with dox represent an exciting potential to overcome dox resistance and warrant further investigation.

Citation Format: Anna R. Schreiber, Stephen Smoots, Betelehem W. Yacob, Adrian TA Dominguez, Cecilia Levandowski, Jennifer R. Diamond, Todd M. Pitts. Combination strategies to overcome doxorubicin induced senescence in triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1063.

Abstract 136: Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer which lacks HER2 overexpression, as well estrogen and progesterone receptor expression. TNBC constitutes 10-15% of all breast cancers but has a worse prognosis due to limited treatment options and high rates of metastatic recurrence. Doxorubicin (dox) remains one of the most active chemotherapy agents for the treatment of TNBC, although de novo and acquired resistance to chemotherapy remains a major challenge. The purpose of this work was to characterize dox resistant cell phenotypes and investigate treatment-induced senescence in p53-mutated (Mut) and wildtype (WT) TNBC cell lines.

Methods: A panel of 12 TNBC cell lines (p53 WT and p53 Mut) were exposed to dox (0-5 uM) for 72 hours and cellular proliferation was determined using the Cell Titer Glo assay. A subset of sensitive and resistant cell lines were treated with dox (0.1, 0.25 uM) or vehicle control and apoptosis was determined by flow cytometry (Annexin-V) at 24 and 48 hrs. Cells were treated with dox or control for 24 hrs and western blotting was performed for mediators of apoptosis. Senescence was analyzed by ß-galactosidase staining following treatment with dox for 3-14 days. shRNA knockdown (KD) of p53 was performed in the CAL-51 (p53 WT cell line) and cells were subject to investigations above.

Results: Doxorubicin treatment resulted in decreased cellular proliferation and increased apoptosis as assessed by Annexin-V expression in a subset of p53 WT and p53 Mut cell lines. Treatment with dox resulted in an increase in the pro-apoptotic proteins BID and p21, as well as a decrease in VAMP in sensitive cell lines. In a subset of cell lines resistant to dox treatment, we observed an increase in cells demonstrating phenotypic features of senescence and ß -galactosidase staining. We observed a decrease in p16 with dox treatment in the CAL-51 (p53 WT cell line) compared to an increase following treatment in p53 Mut cell lines. KD of p53 resulted in an increase in senescent cells following treatment with low dose dox.

Conclusions: Treatment with doxorubicin resulted in different terminal cell phenotypes in TNBC cell lines with apoptosis observed in p53 WT and Mut cell lines. Senescence was observed in resistant cells and KD of p53 increased dox-induced senescence, confirming a role for p53 in mediating terminal cell fate. Efforts are ongoing to understand the role of mutant p53 in mediating terminal cell fate in response to dox and rational combinations to overcome dox-induced senescence may be clinically active in metastatic TNBC.

Citation Format: Stephen G. Smoots, Anna R. Schreiber, Betelehem Yacob, Adrian Dominguez, Cecilia Levandowski, Todd M. Pitts, Jennifer R. Diamond. Doxorubicin-induced senescence as a mechanism of resistance in TNBC cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 136.

Abstract CT249: First-in-human study of TAK-500, a novel STING agonist immune stimulating antibody conjugate (ISAC), alone and in combination with pembrolizumab in patients with select advanced solid tumors

Background: Although immune checkpoint inhibitors (CPIs) have revolutionized cancer treatment, resistance remains a challenge. Reduced interferon (IFN) signaling, immune escape and immunosuppressive tumor phenotypes have been proposed as resistance mechanisms, suggesting innate immune cell stimulation in the tumor microenvironment as a potential strategy to overcome resistance. Stimulator of Interferon Genes (STING) is a cytosolic protein critical for induction of type 1 IFN-dependent innate immunity. Cysteine-cysteine chemokine receptor type 2 (CCR2) is expressed by tumor-infiltrating myeloid cells, including tumor associated macrophages (TAM), and promotes immune escape by limiting CD8+ T-cell infiltration. TAK-500 is an ISAC that consists of three parts: a STING agonist payload based on TAK-676 (currently under phase 1 clinical evaluation [NCT04420884, NCT04879849]), the IgG1 anti-CCR2 antibody (previously evaluated in early phase studies), and a self-immolating maleimide-containing protease-cleavable peptide linker. By targeting STING to CCR2 expressing myeloid cells, TAK-500 has three possible mechanisms of action: activation of IFN response, reprogramming of suppressive intratumoral CCR2+ cells to an inflammatory phenotype, and blockade of suppressive TAM recruitment. TAK-500 thus has the potential to overcome resistance to CPIs in both CPI refractory and immunologically excluded or deserted tumors.

Methods: This phase 1a/1b open-label study (NCT05070247) will evaluate the safety, tolerability, antitumor activity, pharmacokinetics and pharmacodynamics of TAK-500 in patients aged ≥18 years with gastroesophageal adenocarcinoma, pancreatic adenocarcinoma, hepatocellular carcinoma, non-squamous non-small cell lung cancer, squamous cell carcinoma of the head and neck, mesothelioma or triple-negative breast cancer. Patients must have had progressive disease or intolerance to all standard therapy. In the initial dose escalation phase, patients will receive single-agent intravenous (IV) TAK-500 administered once every 3 weeks (Q3W) in 21-day cycles to determine the pharmacologically active dose (PAD) range. An additional escalation cohort will receive TAK-500 in combination with IV pembrolizumab 200 mg Q3W in 21-day cycles, with the initial TAK-500 dose level beginning 1-2 dose levels below the predicted single agent PAD range. Dose escalation in both single agent and combination cohorts will be guided by the Bayesian Optimal Interval design. A subsequent dose expansion phase will evaluate TAK-500 in combination with pembrolizumab. Planned enrollment for both escalation and expansion cohorts is ~106 patients.

Citation Format: Jennifer R. Diamond, Jason T. Henry, Gerald S. Falchook, Anthony J. Olszanski, Harshabad Singh, E. Jane Leonard, Richard C. Gregory, Vicky A. Appleman, John P. Gibbs, Carole E. Harbison, Cong Li, Jessica M. Sapiro, Tomoki Yoneyama, Alexander Parent, Vincent Chung. First-in-human study of TAK-500, a novel STING agonist immune stimulating antibody conjugate (ISAC), alone and in combination with pembrolizumab in patients with select advanced solid tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT249.

Abstract CT120: Phase II study of radiotherapy in combination with chemotherapy and immunotherapy in patients with PD-L1-positive metastatic triple-negative breast cancer

Background: Metastatic triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype lacking hormone receptor expression and HER2 over-expression. Metastatic TNBC has been difficult to treat due to a general lack of targeted therapies, however, immunotherapy has shown substantial activity in a subset of patients. In metastatic TNBC patients with PD-L1-positive (combined positive score (CPS) ≥ 10) disease, KEYNOTE-355 demonstrated that addition of pembrolizumab (PD-1 inhibitor) to chemotherapy (nab-paclitaxel, paclitaxel, or carboplatin/gemcitabine) prolonged median progression free survival (PFS) compared to chemotherapy alone (9.7 months vs 5.6 months). Median 1-year PFS was also increased from 12.0% to 39.1% in these patients treated with pembrolizumab. These data led to the FDA approval of pembrolizumab with chemotherapy in PD-L1-positive metastatic TNBC patients. Despite these encouraging results, the majority of patients do not have long-term disease control. Radiotherapy (RT) in combination with immunotherapy and chemotherapy represents a promising avenue to prolong long-term response. RT can stimulate cellular damage and cause the release of tumor antigens, promoting a local T cell response. In addition, localized RT can result in the shrinkage of distant sites of metastasis via the abscopal effect when used with immunotherapy. The purpose of this study is to investigate the benefit of combining RT with pembrolizumab and chemotherapy in patients with metastatic PD-L1-positive TNBC.

Methods: This two-stage, single-arm phase II study will assess the efficacy of RT in combination with nab-paclitaxel/paclitaxel plus pembrolizumab in PD-L1-positive unresectable or metastatic TNBC patients aged ≥18 years. To be included, patients must have only received &lt; 1 prior line of systemic therapy in the metastatic setting or adjuvant/neoadjuvant setting if metastatic recurrence was within 12 months of treatment. The primary endpoint of the study is the 1-year PFS rate and a total of 29 subjects will be enrolled. Patients will be treated first with RT followed by the initiation of systemic therapy within seven days. Ablative RT will be directed at 1-4 sites of metastatic disease in 3 fractions of 8 Gy each. Nab-paclitaxel or paclitaxel will be given weekly day 1, day 8 every 3 weeks and pembrolizumab will be given every 3 weeks. Imaging will be repeated every 9 weeks to assess response based on RECIST 1.1. Systemic treatment will be continued until disease progression or intolerable toxicity. Treatment beyond progression will be allowed in certain patients who had initial response followed by progression. In these patients, repeat RT to new sites of disease can be administered with continuation of pembrolizumab to investigate the potential of re-sensitizing patients to immunotherapy. Blood will be collected before and after treatment for immune profiling. The sample size was determined using a null hypothesis for the 1-year PFS rate of 39% and an alternate hypothesis of 60%. The sample size of 29 yields a power of 80% to detect this difference with an alpha of 0.1 (1-sided). An interim analysis will be performed after enrollment of seventeen subjects in stage one.

Citation Format: Anna R. Schreiber, Jodi Kagihara, Andrew Nicklawsky, Dexiang Gao, Anosheh Afghahi, Anthony Elias, Peter Kabos, Elena Shagisultanova, Todd Pitts, Julie Lang, Sana Karam, Virginia Borges, Christine Fisher, Jennifer R. Diamond. Phase II study of radiotherapy in combination with chemotherapy and immunotherapy in patients with PD-L1-positive metastatic triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT120.

First-in-human dose escalation study of cyclin-dependent kinase-9 inhibitor VIP152 in patients with advanced malignancies shows early signs of clinical efficacy

PURPOSE

To report on the first-in-human phase I study of VIP152 (NCT02635672), a potent and highly selective CDK9 inhibitor.

PATIENTS AND METHODS

Adults with solid tumors or aggressive non-Hodgkin lymphoma (NHL) who were refractory to or had exhausted all available therapies received VIP152 monotherapy as a 30-minute intravenous, once weekly infusion, as escalating doses (5, 10, 15, 22.5, or 30 mg in 21-day cycles) until the maximum tolerated dose (MTD) was determined.

RESULTS

Thirty-seven patients received {greater than or equal to} 1 VIP152 dose, with 30 mg identified as the MTD based on dose-limiting toxicity of grade 3/4 neutropenia. The most common adverse events were nausea and vomiting (75.7% and 56.8%, respectively), all of grade 1/2 severity. Of the most common events, Grade 3/4 events occurring in > 1 patient were neutropenia (22%), anemia (11%), abdominal pain (8%), increased alkaline phosphatase (8%), and hyponatremia (8%). Day 1 exposure for the MTD exceeded the predicted minimum therapeutic exposure and reproducibly achieved maximal pathway modulation; no accumulation occurred after multiple doses. Seven of 30 patients with solid tumors had stable disease (including 9.5 and 16.8 months in individual patients with pancreatic cancer and salivary gland cancer, respectively), and 2 of 7 patients with high-grade B-cell lymphoma with MYC and BCL2/BCL6 translocations (HGL) achieved durable complete metabolic remission (ongoing at study discontinuation, after 3.7 and 2.3 years of treatment).

CONCLUSION

VIP152 monotherapy, administered intravenously once weekly, demonstrated a favorable safety profile and evidence of clinical benefit in patients with advanced HGL and solid tumors.

Preclinical development of the class I selective histone deacetylase inhibitor OKI-179 for the treatment of solid tumors

Histone deacetylases (HDACs) play critical roles in epigenomic regulation and histone acetylation is dysregulated in many human cancers. While HDAC inhibitors are active in T-cell lymphomas, poor isoform selectivity, narrow therapeutic indices and a deficiency of reliable biomarkers may contribute to the lack of efficacy in solid tumors. In this article, we report the discovery and preclinical development of the novel, orally bioavailable, class I-selective HDAC inhibitor, OKI-179. OKI-179 and its cell active predecessor OKI-005 are thioester prodrugs of the active metabolite OKI-006, a unique congener of the natural product HDAC inhibitor largazole. OKI-006, OKI-005 and subsequently OKI-179, were developed through a lead candidate optimization program designed to enhance physiochemical properties without eroding potency and selectivity relative to largazole. OKI-005 displays anti-proliferative activity in vitro with induction of apoptosis and increased histone acetylation, consistent with target engagement. OKI-179 demonstrated anti-tumor activity in preclinical cancer models with a favorable pharmacokinetic profile and on-target pharmacodynamic effects. Based on its potency, desirable class I HDAC inhibition profile, oral bioavailability, and efficacy against a broad range of solid tumors, OKI-179 is currently being evaluated in a first-in-human phase I clinical trial with plans for continued clinical development in solid tumor and hematologic malignancies.

Evaluating anthracycline + taxane versus taxane-based chemotherapy in older women with node-negative triple-negative breast cancer: a SEER-Medicare study

Purpose

Adjuvant chemotherapy reduces recurrence in early-stage triple-negative breast cancer (TNBC). However, data are lacking evaluating anthracycline + taxane (ATAX) versus taxane-based (TAX) chemotherapy in older women with node-negative TNBC, as they are often excluded from trials. The purpose of this study was to evaluate the effect of adjuvant ATAX versus TAX on cancer-specific (CSS) and overall survival (OS) in older patients with node-negative TNBC.

Patients and methods

Using the SEER-Medicare database, we selected patients aged ≥ 66 years diagnosed with Stage T1-4N0M0 TNBC between 2010 and 2015 (N = 3348). Kaplan–Meier survival curves and adjusted Cox proportional hazards models were used to estimate 3-year OS and CSS. Multivariant Cox regression analysis was used to identify independent factors associated with use of ATAX compared to TAX.

Results

Approximately half (N = 1679) of patients identified received chemotherapy and of these, 58.6% (N = 984) received TAX, 25.0% (N = 420) received ATAX, and 16.4% (N = 275) received another regimen. Three-year CSS and OS was improved with any adjuvant chemotherapy from 88.9 to 92.2% (p = 0.0018) for CSS and 77.2% to 88.6% for OS (p < 0.0001). In contrast, treatment with ATAX compared to TAX was associated with inferior 3-year CSS and OS. Three-year CSS was 93.7% with TAX compared to 89.8% (p = 0.048) for ATAX and OS was 91.0% for TAX and 86.4% for ATAX (p = 0.032).

Conclusion

While adjuvant chemotherapy was associated with improved clinical outcomes, the administration of ATAX compared to TAX was associated with inferior 3-year OS and CSS in older women with node-negative TNBC. The use of adjuvant ATAX should be considered carefully in this patient population.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10549-021-06424-z.

Tackling metastatic triple-negative breast cancer with sacituzumab govitecan

Introduction Metastatic triple-negative breast cancer (TNBC) is an aggressive cancer with poor survival that is difficult to treat due to a lack of targeted options. Conventional therapies targeting hormone receptors (HR) and human epidermal growth factor 2 (HER2) are ineffective and often chemotherapy is standard-of-care. Sacituzumab govitecan is an antibody drug conjugate (ADC) comprised of an active metabolite of irinotecan, SN-38, bound to a humanized monoclonal antibody targeting trophoblastic cell-surface antigen 2 (Trop-2). Trop-2 is highly expressed on the surface of TNBC cells, making it an attractive target. Areas covered We explore the mechanism, pharmacology, efficacy, safety, and tolerability of sacituzumab govitecan. A literature search was conducted via PubMed using keywords such as 'sacituzumab govitecan,' and 'metastatic TNBC.' Expert opinion Sacituzumab govitecan has promising survival benefits in patients with previously treated mTNBC based on data from the ASCENT trial. Common adverse effects were neutropenia, diarrhea, and nausea, however these effects were manageable with supportive care. Sacituzumab govitecan has shown promise in cancers outside of TNBC, such as urothelial and lung and is being evaluated in HR-positive breast cancers. It is likely we will see this therapy used in combination with other novel targeted agents as current clinical trials mature.

A Phase I Study of an MPS1 Inhibitor (BAY 1217389) in Combination with Paclitaxel Using a Novel Randomized Continual Reassessment Method for Dose Escalation

PURPOSE

Monopolar spindle 1 (MPS1) kinase inhibitor, BAY 1217389 (BAY) synergizes with paclitaxel. This phase I study assessed the combination of BAY with paclitaxel using a novel randomized continuous reassessment method (rCRM) to improve dose determination.

PATIENTS AND METHODS

Patients with solid tumors were randomized to receive oral BAY (twice daily 2-days-on/5-days-off) with weekly paclitaxel (90 mg/m²) or paclitaxel monotherapy in cycle 1. Dose escalation was guided by CRM modeling. Primary objectives were to assess safety, establish the MTD of BAY, and to evaluate the pharmacokinetic profiles for both compounds. Simulations were performed to determine the contribution of the rCRM for dose determination.

RESULTS

In total, 75 patients were enrolled. The main dose-limiting toxicities were hematologic toxicities (55.6%). The MTD of BAY was established at 64 mg twice daily with paclitaxel. Inclusion of a control arm enabled the definitive attribution of grade ≥3 neutropenia to higher BAY exposure [AUC_0-12 (P< 0.001)]. After determining the MTD, we included 19 patients with breast cancer at this dose for dose expansion. Other common toxicities were nausea (45.3%), fatigue (41.3%), and diarrhea (40.0%). Overall confirmed responses were seen in 31.6% of evaluable patients. Simulations showed that rCRM outperforms traditional designs in determining the true MTD.

CONCLUSIONS

The combination of BAY with paclitaxel was associated with considerable toxicity without a therapeutic window. However, the use of the rCRM design enabled us to determine the exposure-toxicity relation for BAY. Therefore, we propose that the rCRM could improve dose determination in phase I trials that combine agents with overlapping toxicities.

Moving Towards Targeted Therapies for Triple-Negative Breast Cancer

PURPOSE OF REVIEW

In this review, we discuss targets of interest in Triple-negative breast cancer (TNBC), approved targeted agents and the results of the clinical trials that led to their approval. Additionally, we review ongoing clinical trials evaluating the use of novel targeted agents in the treatment of TNBC.

RECENT FINDINGS

TNBC accounts for 15-20% of all breast cancer cases and is associated with worse clinical outcomes. Patients have a higher risk of metastatic recurrence and inferior overall survival compared to other breast cancer subtypes. Cytotoxic chemotherapy has historically been the mainstay of treatment for TNBC. In recent years, we have seen a surge in clinical trials investigating the use of targeted agents in TNBC and now have approval for targeted therapies in select patients. Inhibitors of PARP (olaparib and talazoparib), PD-L1 (atezolizumab) and an antibody drug conjugate targeting Trop-2 (sacituzumab govitecan-hziy) are now approved for the use in select groups of patients with TNBC.

SUMMARY

Various novel targeted agents as monotherapy, dual targeted combinations, and chemotherapy combinations are currently under investigation. The results are promising and may significantly improve patient outcomes in TNBC.

Sapanisertib Plus Exemestane or Fulvestrant in Women with Hormone Receptor-Positive/HER2-Negative Advanced or Metastatic Breast Cancer

PURPOSE

This open-label, multicenter, phase IB/II study evaluated sapanisertib, a dual inhibitor of mTOR kinase complexes 1/2, plus exemestane or fulvestrant in postmenopausal women with hormone receptor-positive (HR⁺)/HER2-negative (HER2^-) advanced/metastatic breast cancer.

PATIENTS AND METHODS

Eligible patients had previously progressed on everolimus with exemestane/fulvestrant and received ≤3 (phase IB) or ≤1 (phase II) prior chemotherapy regimens. Patients received sapanisertib 3 to 5 mg every day (phase IB), or 4 mg every day (phase II) with exemestane 25 mg every day or fulvestrant 500 mg monthly in 28-day cycles. Phase II enrolled parallel cohorts based on prior response to everolimus. The primary objective of phase II was to evaluate antitumor activity by clinical benefit rate at 16 weeks (CBR-16).

RESULTS

Overall, 118 patients enrolled in phase IB (n = 24) and II (n = 94). Five patients in phase IB experienced dose-limiting toxicities, at sapanisertib doses of 5 mg every day (n = 4) and 4 mg every day (n = 1); sapanisertib 4 mg every day was the MTD in combination with exemestane or fulvestrant. In phase II, in everolimus-sensitive versus everolimus-resistant cohorts, CBR-16 was 45% versus 23%, and overall response rate was 8% versus 2%, respectively. The most common adverse events were nausea (52%), fatigue (47%), diarrhea (37%), and hyperglycemia (33%); rash occurred in 17% of patients. Molecular analysis suggested positive association between AKT1 mutation status and best treatment response (complete + partial response; P = 0.0262).

CONCLUSIONS

Sapanisertib plus exemestane or fulvestrant was well tolerated and exhibited clinical benefit in postmenopausal women with pretreated everolimus-sensitive or everolimus-resistant breast cancer.

Testing Cancer Immunotherapy in a Human Immune System Mouse Model: Correlating Treatment Responses to Human Chimerism, Therapeutic Variables and Immune Cell Phenotypes

Over the past decade, immunotherapies have revolutionized the treatment of cancer. Although the success of immunotherapy is remarkable, it is still limited to a subset of patients. More than 1500 clinical trials are currently ongoing with a goal of improving the efficacy of immunotherapy through co-administration of other agents. Preclinical, small-animal models are strongly desired to increase the pace of scientific discovery, while reducing the cost of combination drug testing in humans. Human immune system (HIS) mice are highly immune-deficient mouse recipients rtpeconstituted with human hematopoietic stem cells. These HIS-mice are capable of growing human tumor cell lines and patient-derived tumor xenografts. This model allows rapid testing of multiple, immune-related therapeutics for tumors originating from unique clinical samples. Using a cord blood-derived HIS-BALB/c-Rag2nullIl2rγnullSIRPαNOD (BRGS) mouse model, we summarize our experiments testing immune checkpoint blockade combinations in these mice bearing a variety of human tumors, including breast, colorectal, pancreatic, lung, adrenocortical, melanoma and hematological malignancies. We present in-depth characterization of the kinetics and subsets of the HIS in lymph and non-lymph organs and relate these to protocol development and immune-related treatment responses. Furthermore, we compare the phenotype of the HIS in lymph tissues and tumors. We show that the immunotype and amount of tumor infiltrating leukocytes are widely-variable and that this phenotype is tumor-dependent in the HIS-BRGS model. We further present flow cytometric analyses of immune cell subsets, activation state, cytokine production and inhibitory receptor expression in peripheral lymph organs and tumors. We show that responding tumors bear human infiltrating T cells with a more inflammatory signature compared to non-responding tumors, similar to reports of "responding" patients in human immunotherapy clinical trials. Collectively these data support the use of HIS mice as a preclinical model to test combination immunotherapies for human cancers, if careful attention is taken to both protocol details and data analysis.

WEE1 Inhibition in Combination With Targeted Agents and Standard Chemotherapy in Preclinical Models of Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal cancer with high incidences of p53 mutations. AZD1775 (adavosertib, previously MK-1775) is a small molecule WEE1 inhibitor that abrogates the G2M checkpoint and can potentially synergize with DNA damaging therapies commonly used in PDAC treatment. The purpose of this study was to identify combination partners for AZD1775, including standard chemotherapy or targeted agents, in PDAC preclinical models. Low powered preliminary screens demonstrated that two of the four PDX models responded better to the combinations of AZD1775 with irinotecan or capecitabine than to either single agent. Following the screens, two full powered PDAC PDX models of differing p53 status were tested with the combinations of AZD1775 and irinotecan or capecitabine. The combinations of AZD1775 and SN38 or 5-FU were also tested on PDAC cell lines. Cellular proliferation was measured using an IncuCyte Live Cell Imager and apoptosis was measured using a Caspase-Glo 3/7 assay. Flow cytometry was conducted to measure alterations in cell cycle distribution. Western blot analysis was used to determine the effects of the drug combinations on downstream effectors. In PDX models with mutated p53 status, there was significant tumor growth inhibition from the combination of AZD1775 with irinotecan or capecitabine (P ≤ 0.03), while PDX models with wild type p53 did not show anti-tumor synergy from the same combinations (P ≥ 0.08). The combination of AZD1775 with SN38 or 5-FU significantly decreased proliferation in all PDAC cell lines, and enhanced apoptosis in multiple cell lines. Cell cycle distribution was disrupted from the combination of AZD1775 with SN38 or 5-FU which was recorded as G2M arrest and decreased G1 phase. AZD1775 inhibited phospho-CDC2 and increased the expression of γH2AX that was either maintained or enhanced after combination with SN38 or 5-FU. The combination of AZD1775 with irinotecan/SN38 or capecitabine/5-FU showed anti-tumor effects in vivo and in vitro in PDAC models. These results support further investigation for these combination strategies to enhance outcomes for PDAC patients.

Clinical Outcomes for Patients With Metastatic Breast Cancer Treated With Immunotherapy Agents in Phase I Clinical Trials

BACKGROUND

Immuno-oncology (IO) agents have demonstrated efficacy across many tumor types and have led to change in standard of care. In breast cancer, atezolizumab and pembrolizumab were recently FDA-approved in combination with chemotherapy specifically for patients with PD-L1-positive metastatic triple-negative breast cancer (TNBC). However, the single agent PD-1/PD-L1 inhibitors demonstrate only modest single agent efficacy in breast cancer. The purpose of this study was to investigate the efficacy of novel IO agents in patients with metastatic breast cancer (MBC), beyond TNBC, treated in phase I clinical trials at the University of Colorado.

METHODS

We performed a retrospective analysis using a database of patients with MBC who received treatment with IO agents in phase I/Ib clinical trials at the University of Colorado Hospital from January 1, 2012 to July 1, 2018. Patient demographics, treatments and clinical outcomes were obtained.

RESULTS

We identified 43 patients treated with an IO agent either as a single agent or in combination. The average age was 53 years; 55.8% had hormone receptor-positive/HER2-negative breast cancer, 39.5% TNBC and 4.7% HER2-positive. Patients received an average of 2 prior lines of chemotherapy (range 0-7) in the metastatic setting. Most patients (72.1%) received IO alone and 27.9% received IO plus chemotherapy. Median progression-free survival (PFS) was 2.3 months and median overall survival (OS) was 12.1 months. Patients remaining on study ≥ 6 months (20.9%) were more likely to be treated with chemotherapy plus IO compared to patients with a PFS < 6 months (77.8% v. 14.7%). No differences in number of metastatic sites, prior lines of chemotherapy, breast cancer subtype, absolute lymphocyte count, or LDH were identified between patients with a PFS ≥ 6 months vs. < 6 months.

CONCLUSIONS

Our phase I experience demonstrates benefit from IO therapy that was not limited to patients with TNBC and confirms improved efficacy from IO agents in combination with chemotherapy. A subset of patients with MBC treated in phase I clinical trials with an IO agent derived prolonged clinical benefit. Predictors of response to immunotherapy in breast cancer remain uncharacterized and further research is needed to identify these factors.

A phase I pharmacokinetic and safety study of Paclitaxel Injection Concentrate for Nano-dispersion (PICN) alone and in combination with carboplatin in patients with advanced solid malignancies and biliary tract cancers

PURPOSE

Paclitaxel injection concentrate for nano-dispersion (PICN) is a Cremophor-free, nanotechnology-driven paclitaxel formulation. This phase I study examined the safety, tolerability, pharmacokinetics and maximum tolerated dose (MTD) of PICN alone and in combination with carboplatin. Its early efficacy in unresectable biliary tract cancers (BTCs) was also evaluated.

METHODS

This multi-center study comprised two parts. Part A contained a dose-escalation cohort following "3 + 3" design using PICN monotherapy in advanced solid tumors (Part A1); Part A2 dose-expansion cohort was then conducted in advanced BTCs due to observed efficacy in Part A1. Part B1 and B2 evaluated escalating dose of PICN with carboplatin in advanced solid tumors. PICN was administered as a 30 min-infusion every 3 weeks without pre-medications for hypersensitivity reactions.

RESULTS

Thirty-six patients received PICN monotherapy in Part A and 21 received PICN plus carboplatin in Part B. The MTD of PICN was determined to be 295 mg/m² both as a monotherapy and in combination with carboplatin at AUC 5. Dose-proportional exposure in paclitaxel C_max and AUC was observed overdose range from 175 to 325 mg/m² for PICN monotherapy and its combination with carboplatin. Carboplatin did not alter PICN exposure. Clinically significant toxicities mainly include neutropenia and peripheral neuropathy. PICN monotherapy yielded a response rate of 20% in unresectable BTCs.

CONCLUSION

This study demonstrated the safety and stable pharmacokinetics of PICN as a monotherapy and in combination with carboplatin. Single-agent PICN showed promising antitumor activity in advanced BTCs, warranting further studies to investigate its role in gastrointestinal cancers.

Real-world evidence from a University Hospital system regarding the uptake of adjuvant pertuzumab and/or neratinib before and after their FDA approval

Purpose

Adjuvant pertuzumab and neratinib are independently FDA-approved for treatment of early-stage HER2-positive breast cancer in combination with or following trastuzumab for one year, respectively. Both agents reduce the risk of recurrence; however, the absolute benefit is modest for many patients with added risk of adverse effects. The purpose of this study was to evaluate the clinical use of adjuvant pertuzumab and neratinib in patients with early-stage HER2-positive breast cancer.

Methods

Patients diagnosed with stage I–III HER2-positive breast cancer treated with trastuzumab at four University of Colorado Health hospitals between July 2016 and April 2019 were identified. Patient demographics, cancer stage, treatment, and administration of pertuzumab and/or neratinib were obtained.

Results

We identified a total of 350 patients who received adjuvant trastuzumab for stage I–III HER2-positive breast cancer; 253 (73.1%) had tumors that were ≥ T2 or node-positive disease. The rate of adjuvant pertuzumab use increased following FDA approval; pertuzumab was administered to the majority of patients with node-positive HER2-positive breast cancer. The use of adjuvant pertuzumab was associated with younger age, premenopausal status, and node-positive disease. Rates of administration of adjuvant neratinib were lower, with only 15.2% of patients receiving this therapy within 3 months of completing adjuvant trastuzumab.

Conclusion

In our cohort of patients treated within a diverse healthcare network, the majority of patients with node-positive HER2-positive breast cancer received adjuvant pertuzumab following FDA approval. The use of adjuvant neratinib was less common, potentially as a result of adverse effects, prolongation of therapy, previous administration of adjuvant pertuzumab, and modest benefit.

Abstract PS12-14: Phase II trial of fulvestrant plus enzalutamide in ER+/Her2- advanced breast cancer

Up to 91% of ER+ breast cancers express androgen receptor (AR), but its function is uncertain. Although AR expression is associated with more indolent tumors, high AR expression relative to ER is associated with endocrine resistance, and in the absence of estradiol or if ER function is blocked, preclinical studies suggest that AR can take over to signal cell survival and proliferation. Following extensive preclinical studies and a brief phase I to demonstrate a lack of significant PK interaction, this phase II trial of fulvestrant plus enzalutamide in ER+/Her2- metastatic breast cancer was conducted. Methods: Eligible patients were women with ECOG 0-2, ER+/Her2- measurable or evaluable metastatic breast cancer without CNS disease. Prior fulvestrant was allowed, if clinically indicated as per treating physician. Fulvestrant was administered in standard dosing at 500 mg IM days 1, 15, 29 and every 4 weeks thereafter. Enzalutamide was given at 160 mg po daily on a continual basis. Fresh tumor biopsies were required at study entry and at about 4 weeks on therapy. The primary efficacy endpoint of the trial was clinical benefit rate at 24 weeks (CBR24). Assuming the undesirable rate of 10% and desirable rate of 30%, a sample size of 24 provided 89% power to detect this 25% rate difference using an exact binomial test with a one-sided alpha of 0.085. Due to the exploratory nature of biomarker analysis, the type I error rate was not adjusted for exploring multiple biomarkers. Results: A total of 38 patients were consented, of whom 32 were eligible. Median age was 61 years (46-87); PS 1 (0-1); a median of 2 prior chemotherapy and 2 prior hormonal therapies for metastatic disease. Twelve patients had prior fulvestrant, and 90% had visceral disease. TEAEs &gt;20% included fatigue, nausea/vomiting, constipation, headache, anorexia, although most were low grade. There were no G4 or G5 toxicities. Median PFS was 2.0 months (0.5-12). CBR24 was 25% (7/28 evaluable).Conclusions: In a heavily pretreated population of women with metastatic ER+/Her2- BC, the combination of fulvestrant plus enzalutamide had manageable side effects, and modest activity. About 25% reached the primary endpoint of clinical benefit of more than 6 months on therapy. Extensive molecular studies of paired fresh biopsies from pretreatment and at 4 weeks are underway. These analyses and correlations with clinical outcome will be described.

Citation Format: Anthony D Elias, Nicole Spoelsta, Gregory A Vidal, Sharon Sams, Peter Kabos, Jennifer R Diamond, Elena Shagisultanova, Anosheh Afghahi, Jose Mayordomo, Tessa McSpadden, Gloria Crawford, Lisa Carter, Kathryn Zolman, Stephanie Armstead, Alyse Winchester, Virginia Borges, Julia Wulfkuhle, Emanuel Petricoin, Dexiang Gao, Jennifer Richer. Phase II trial of fulvestrant plus enzalutamide in ER+/Her2- advanced breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS12-14.

Abstract PS10-03: Interim safety and efficacy analysis of phase IB / II clinical trial of tucatinib, palbociclib and letrozole in patients with hormone receptor and HER2-positive metastatic breast cancer

Background: In hormone receptor-positive / HER2-positive (HR+/HER2+) breast cancer, the HER2 and estrogen receptor (ER) signals merge on the cyclin D1-CDK4/6-RB1 pathway. Thus, a combined pharmacological intervention with individual drugs targeting HER2, ER and CDK4/6 is warranted. Here, we present the safety and efficacy results of the combination of tucatinib with letrozole and palbociclib in patients (pts) with HR+/HER2+ metastatic breast cancer (MBC) (NCT03054363).

Methods: Pts with HR+/HER2+ MBC previously treated with at least 2 HER2-targeted agents were enrolled in this phase IB/II clinical trial. Pts with untreated asymptomatic or stable treated brain metastasis (BM) were included. Pts with treated progressing BM were enrolled after local treatment and classified as treated stable. Treatment consisted of tucatinib 300mg PO BID and letrozole 2.5mg PO daily continuously, and palbociclib 125mg PO daily 21 days on, 7 days off. Due to drug-drug interaction issues found in the middle of the trial and not related to this study, the dose of sensitive CYP3A4 substrate palbociclib was reduced to 75mg for all study participants, as it became evident that tucatinib is a strong CYP3A4 inhibitor. The primary end-points were assessment of safety using CTCAE v.4.03 criteria, and progression free survival (PFS). Secondary end-points included pharmacokinetic evaluation (PKs) and objective response rate by RECIST 1.1. BM response was evaluated using RANO-BM criteria. All pts who received at least one cycle of therapy were assessed for safety.

Results: Between 11.21.2017 and 04.20.2020, we enrolled 42 pts of whom 40 were evaluable. Median age was 52.5 years (range, 22 to 82) and the median number of prior lines of therapy for MBC was 2 (range, 0 to 7); 23 pts (58%) had visceral disease and 15 (38%) had BM. All pts had prior therapy with trastuzumab and pertuzumab and 18 pt (45%) had prior T-DM1. As of 06.15.2020 data cut off, 14 patients were on active therapy while 26 were off study (22 due to progressive disease [PD], 1 due to toxicity and 3 for other reasons). Median follow up time was 6 months. The combination was well tolerated with manageable and expected adverse events (AEs). The most common grade ≥3 AEs were neutropenia (25 pts, 60%), leukopenia (10 pts, 24%), diarrhea (8 pts, 19%), fatigue (6 pts, 14%), and infections (6 pts, 14%). One pt came off study due to asymptomatic grade 4 elevated LFTs that resolved without sequelae. There were no deaths due to AEs. Among 26 pts with measurable disease at the time of data cut-off, 8 pts (31%) had partial response, 16 pts (62%) had stable disease (SD) (7 pts [27%] had SD for ≥ 6 months and 6 pts [23%] have not yet reached 6 months of follow up) and 2 pts (8%) had PD. Among 14 patients with BM and evaluable disease by RANO-BM, 1 pt had complete response in the brain, 6 pts had SD in the brain for ≥6 months, and 7 pts had SD for 2-6 months (4 pts on active therapy have not yet reached 6 months of follow up). Median PFS is 8.7 months (10.1 months for pts without BM and 6.0 months for those with BM). Updated analysis including PKs, tumor response, and PFS will be presented.

Conclusion: The combination of tucatinib with letrozole and palbociclib showed a tolerable and manageable safety profile and evidence of considerable anti-tumor activity that warrant further clinical investigation in pts with HR+/HER2+ MBC.

Citation Format: Elena Shagisultanova, William Gradishar, Ursa Brown-Glaberman, Pavani Chalasani, Andrew J. Brenner, Alison Stopeck, Jose Mayordomo, Jennifer R. Diamond, Peter Kabos, Virginia F. Borges. Interim safety and efficacy analysis of phase IB / II clinical trial of tucatinib, palbociclib and letrozole in patients with hormone receptor and HER2-positive metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS10-03.

New Persistent Opioid and Benzodiazepine Use After Curative-Intent Treatment in Patients With Breast Cancer

BACKGROUND

Opioid and benzodiazepine use and abuse is a national healthcare crisis to which patients with cancer are particularly vulnerable. Long-term use and risk factors for opioid and benzodiazepine use in patients with breast cancer is poorly characterized.

METHODS

We conducted a retrospective population-based study of patients with breast cancer diagnosed between 2008 and 2015 undergoing curative-intent treatment identified through the SEER-Medicare linked database. Primary outcomes were new persistent opioid use and new persistent benzodiazepine use. Factors associated with new opioid and benzodiazepine use were investigated by univariate and multivariable logistic regression.

RESULTS

Among opioid-naïve patients, new opioid use was observed in 22,418 (67.4%). Of this group, 611 (2.7%) developed persistent opioid use at 3 months and 157 (0.7%) at 6 months after treatment. Risk factors for persistent use at 3 and 6 months included stage III disease (odds ratio [OR], 2.16; 95% CI, 1.49-3.12, and OR, 3.48; 95% CI, 1.58-7.67), surgery plus chemotherapy (OR, 1.44; 95% CI, 1.10-1.88, and OR, 2.28; 95% CI, 1.40-3.71), surgery plus chemoradiation therapy (OR, 1.47; 95% CI, 1.10-1.96, and OR, 2.34; 95% CI, 1.38-3.96), and initial tramadol use (OR, 2.66; 95% CI, 2.05-3.46, and OR, 3.12; 95% CI, 1.93-5.04). Among benzodiazepine-naïve patients, new benzodiazepine use was observed in 955 (10.3%), and 111 (11.6%) developed new persistent use at 3 months. Tamoxifen use was statistically significantly associated with new persistent benzodiazepine use at 3 months.

CONCLUSIONS

A large percentage of patients receiving curative-intent treatment of breast cancer were prescribed new opioids; however, only a small number developed new persistent opioid use. In contrast, a smaller proportion of patients received a new benzodiazepine prescription; however, new persistent use after completion of treatment was more likely and particularly related to concurrent treatment with tamoxifen.

Paraneoplastic Encephalitis Associated with Locally Advanced Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer

Paraneoplastic neurologic diseases (PND) are rare but can occur in patients with common malignancies including breast cancer. In patients with hormone receptor (HR)-negative human epidermal growth factor receptor 2 (HER2)-positive breast cancer, PND have been reported in association with anti-Yo antibodies and with clinical presentation of paraneoplastic cerebellar degeneration. We describe the case of a woman with progressively altered mental status and seizures, ultimately requiring admission. Based on her clinical presentation, imaging findings, and evidence of neural-directed antibodies in her serum and cerebrospinal fluid, she was diagnosed with paraneoplastic limbic encephalitis (LE) due to an underlying HR-negative, HER2-positive breast cancer. She showed a transient response to immunosuppression but had more significant improvement after surgical resection and initiation of chemotherapy along with HER2-directed therapy. To the best of our knowledge, this is the first documented case of paraneoplastic LE in a patient with HR-negative, HER2-positive breast cancer likely caused by the production of an unclassified anti-neuronal antibody.

Clinical outcomes of breast cancer patients treated in phase I clinical trials at University of Colorado Cancer Center

Patients with metastatic breast cancer (MBC) refractory to standard of care therapies have a poor prognosis. The purpose of this study was to assess patient characteristics and clinical outcomes for patients with MBC treated on phase I clinical trials. We performed a retrospective review of all patients with MBC who were enrolled in phase I clinical trials at the University of Colorado Cancer Center from January 2012 to June 2018. A total of 208 patients were identified. Patients had a mean age of 57 years and received on average 2.1 (range 0-10) prior lines of chemotherapy. The majority of patients had hormone receptor-positive/HER2-negative breast cancer (58.6%) and 30.3% had triple-negative breast cancer. The median progression free survival (PFS) was 2.8 months (95% CI, 2.3-3.9) and median overall survival (OS) was 11.5 months (95% CI, 9.6-13.2). Independent factors associated with longer PFS in multivariable analysis were treatment in a breast cancer-selective trial or cohort (p = 0.016), age >50 years (p = 0.002), and ≤2 prior lines of chemotherapy in the metastatic setting (p = 0.025). Phase I clinical trials remain a valuable option for select patients with MBC and enrollment should be encouraged when available.

RX-5902, a novel β-catenin modulator, potentiates the efficacy of immune checkpoint inhibitors in preclinical models of triple-negative breast Cancer

BACKGROUND

Triple-negative breast cancer (TNBC) is an aggressive breast cancer subtype with limited systemic treatment options. RX-5902 is a novel anti-cancer agent that inhibits phosphorylated-p68 and thus attenuates nuclear β-catenin signaling. The purpose of this study was to evaluate the ability of β-catenin signaling blockade to enhance the efficacy of anti-CTLA-4 and anti-PD-1 immune checkpoint blockade in immunocompetent, preclinical models of TNBC.

METHODS

Treatment with RX-5902, anti-PD-1, anti-CTLA-4 or the combination was investigated in BALB/c mice injected with the 4 T1 TNBC cell line. Humanized BALB/c-Rag2nullIl2rγnullSIRPαNOD (hu-CB-BRGS) mice transplanted with a human immune system were implanted with MDA-MB-231 cells. Mice were randomized into treatment groups according to human hematopoietic chimerism and treated with RX-5902, anti-PD-1 or the combination. At sacrifice, bone marrow, lymph nodes, spleen and tumors were harvested for flow cytometry analysis of human immune cells.

RESULTS

The addition of RX-5902 to CTLA-4 or PD-1 inhibitors resulted in decreased tumor growth in the 4 T1 and human immune system and MDA-MB-231 xenograft models. Immunologic analyses demonstrated a significant increase in the number of activated T cells in tumor infiltrating lymphocytes (TILs) with RX-5902 treatment compared to vehicle (p < 0.05). In the RX-5902/nivolumab combination group, there was a significant increase in the percentage of CD4+ T cells in TILs and increased systemic granzyme B production (p < 0.01).

CONCLUSIONS

Conclusions: RX-5902 enhanced the efficacy of nivolumab in a humanized, preclinical model of TNBC. Several changes in immunologic profiles were noted in mice treated with RX-5902 and the combination, including an increase in activated TILs and a decrease in human myeloid populations, that are often associated with immunosuppression in a tumor microenvironment. RX-5902 also was shown to potentiate the effects of checkpoint inhibitors of CTLA4 and the PD-1 inhibitor in the 4 T-1 murine TNBC model. These findings indicate that RX-5902 may have important immunomodulatory, as well as anti-tumor activity, in TNBC when combined with a checkpoint inhibitor.

Survival and clinical outcomes of patients with ovarian cancer who were treated on phase 1 clinical trials

BACKGROUND

Patients with ovarian cancer who are enrolled on phase 1 trials typically have platinum-resistant and heavily pretreated disease, with a poor prognosis. In the current study, the authors assessed prognostic factors and survival in women with recurrent ovarian cancer who were treated on phase 1 clinical trials.

METHODS

The authors performed a retrospective analysis of patients treated from 2008 through 2018 at the University of Colorado Cancer Center. Patient characteristics and treatment and toxicity-related survival data were assessed. Descriptive statistics and Cox proportional hazards models were used to identify risk factors associated with survival time.

RESULTS

A total of 132 patients were treated on phase 1 clinical trials. Patients had a median age of 59 years (range, 33-88 years) with a median of 5.5 previous chemotherapy lines (range, 1-13 lines). Of the 132 patients, 53 (40%) were treated on multiple phase 1 trials with a median of 1 (range, 0-5) prior phase 1 trial. The overall response rate was 14.7%. The median overall survival was 11.3 months (95% CI, 9.1-13.4 months). Two patients died on trial due to progression of disease whereas no patients died of treatment-related toxicity. Independent risk factors found to be predictive of shorter survival were an elevated cancer antigen 125 (CA 125) level (hazard ratio [HR], 2.8; 95% CI, 1.6-5.2) and albumin <3.5 g/dL (HR, 2.5; 95% CI, 1.65-3.79). A body mass index >25 kg/m² was predictive of longer survival (HR, 0.65; 95% CI, 0.44-0.96).

CONCLUSIONS

In the current single-institution series, patients with heavily pretreated ovarian cancer who were treated on phase 1 clinical trials experienced a median overall survival of 11.3 months. When available, phase 1 clinical trials represent a reasonable treatment option for patients with heavily pretreated ovarian cancer with a preserved performance status.

Sacituzumab govitecan in previously treated hormone receptor-positive/HER2-negative metastatic breast cancer: final results from a phase I/II, single-arm, basket trial

BACKGROUND

Trophoblast cell-surface antigen-2 (Trop-2) is expressed in epithelial cancers, including hormone receptor-positive (HR+) metastatic breast cancer (mBC). Sacituzumab govitecan (SG; Trodelvy®) is an antibody-drug conjugate composed of a humanized anti-Trop-2 monoclonal antibody coupled to SN-38 at a high drug-to-antibody ratio via a unique hydrolyzable linker that delivers SN-38 intracellularly and in the tumor microenvironment. SG was granted accelerated FDA approval for metastatic triple-negative BC treatment in April 2020.

PATIENTS AND METHODS

We analyzed a prespecified subpopulation of patients with HR+/human epidermal growth factor receptor 2-negative (HER2-) HR+/HER2- mBC from the phase I/II, single-arm trial (NCT01631552), who received intravenous SG (10 mg/kg) and whose disease progressed on endocrine-based therapy and at least one prior chemotherapy for mBC. End points included objective response rate (ORR; RECIST version 1.1) assessed locally, duration of response (DOR), clinical benefit rate, progression-free survival (PFS), overall survival (OS), and safety.

RESULTS

Fifty-four women were enrolled between 13 February 2015 and 1 June 2017. Median (range) age was 54 (33-79) years and all received at least two prior lines of therapy for mBC. At data cut-off (1 March 2019), 12 patients were still alive. Key grade ≥3 treatment-related toxicities included neutropenia (50.0%), anemia (11.1%), and diarrhea (7.4%). Two patients discontinued treatment due to treatment-related adverse events. No treatment-related deaths occurred. At a median follow-up of 11.5 months, the ORR was 31.5% [95% confidence interval (CI), 19.5%-45.6%; 17 partial responses]; median DOR was 8.7 months (95% CI 3.7-12.7), median PFS was 5.5 months (95% CI 3.6-7.6), and median OS was 12 months (95% CI 9.0-18.2).

CONCLUSIONS

SG shows encouraging activity in patients with pretreated HR+/HER2- mBC and a predictable, manageable safety profile. Further evaluation in a randomized phase III trial (TROPiCS-02) is ongoing (NCT03901339).

TRIAL REGISTRATION

ClinicalTrials.gov NCT01631552; https://clinicaltrials.gov/ct2/show/NCT01631552.

Preclinical and Dose-Finding Phase I Trial Results of Combined Treatment with a TORC1/2 Inhibitor (TAK-228) and Aurora A Kinase Inhibitor (Alisertib) in Solid Tumors

PURPOSE

The purpose of this study was to evaluate the rational combination of TORC1/2 inhibitor TAK-228 and Aurora A kinase inhibitor alisertib in preclinical models of triple-negative breast cancer (TNBC) and to conduct a phase I dose escalation trial in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

TNBC cell lines and patient-derived xenograft (PDX) models were treated with alisertib, TAK-228, or the combination and evaluated for changes in proliferation, cell cycle, mTOR pathway modulation, and terminal cellular fate, including apoptosis and senescence. A phase I clinical trial was conducted in patients with advanced solid tumors treated with escalating doses of alisertib and TAK-228 using a 3+3 design to determine the maximum tolerated dose (MTD).

RESULTS

The combination of TAK-228 and alisertib resulted in decreased proliferation and cell-cycle arrest in TNBC cell lines. Treatment of TNBC PDX models resulted in significant tumor growth inhibition and increased apoptosis with the combination. In the phase I dose escalation study, 18 patients with refractory solid tumors were enrolled. The MTD was alisertib 30 mg b.i.d. days 1 to 7 of a 21-day cycle and TAK-228 2 mg daily, continuous dosing. The most common treatment-related adverse events were neutropenia, fatigue, nausea, rash, mucositis, and alopecia.

CONCLUSIONS

The addition of TAK-228 to alisertib potentiates the antitumor activity of alisertib in vivo, resulting in increased cell death and apoptosis. The combination is tolerable in patients with advanced solid tumors and should be evaluated further in expansion cohorts with additional pharmacodynamic assessment.

Abstract 6387: Therapeutic targeting of lipid oxidation and apoptosis in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is currently the fourth leading cause of cancer deaths with more than 56,000 new cases estimated to be diagnosed in 2019. Current treatment options for PDAC include radiation and chemotherapeutic regimens, however these targeted therapies are ineffective for patients with advanced disease progression. Additionally, the dense stromal nature of PDAC tumors create challenges to target the cancer cells resulting in incomplete cell killing and eventual drug resistance. Recent evidence has shown that CPT1A, an enzyme that regulates the entry of lipids into mitochondria for β-oxidation, is strongly expressed in several cancers. CPT1A is located on the mitochondrial membrane and potentially interacts with BCL-2, an anti-apoptotic protein that promotes tumor maintenance and metastasis. Metabolic stress can activate the anti-apoptotic effects of BCL-2, reprograming metabolism to use fat oxidation for cancer survival. Therefore, a co-inhibition using the selective BCL-2 inhibitor, venetoclax, with agents that inhibit CPT1A and β-oxidation, could be a novel strategy for PDAC. There are few studies considering CPT1A as a therapeutic target for PDAC. Current available drugs to target these pathways include the anti-anginal ranolazine, and CPT1A inhibitors etomoxir and perhexiline. Previous studies have shown that expression of BCL-2 by tumor cells is necessary for BCL-2 inhibitors to be effective. We initially wanted to determine the expression of BCL-2 and CPT1A in PDAC cells utilizing western blot and rtPCR, and to confirm their proximity using a proximity ligation assay (PLA). PDAC cells were then plated in 96 well plates and Cell Titer-Glo assays were performed to determine effective concentrations of single agent venetoclax, etomoxir, and perhexiline. The effects of these drugs in combination were then evaluated using a clonogenic assay, which was analyzed using the ImageJ colony area plugin. PDAC cells were then exposed to the combinations and western blots were performed to evaluate changes downstream effectors. We have confirmed the expression of BCL-2 and CPT1A on the mitochondrial membrane using Westerns, rtPCR, and a PLA on several PDAC lines. Though single agent drugs had little effect on cell viability, the combination of venetoclax with CPT1A and β-oxidation inhibitors decreased colony formation in some PDAC cell lines. Western blot analysis revealed the drug combinations affected the phosphorylation of AKT and 4E-BP1 and expression of the pro-apoptotic protein BID. These data suggest that co-targeting BCL-2 and CPT1A have potential for anti-tumor effects in PDAC. Additional research into the role of CPT1A in PDAC biology will elucidate the optimal dosing concentrations and mechanisms for further studies.

Citation Format: Sarah J. Hartman, Nathalie Nadales, Stacey M. Bagby, Betelehem W. Yacob, Brian L. Gittleman, Adriana Estrada-Bernal, Anh T. Le, Christopher H. Lieu, S. Lindsey Davis, Alexis D. Leal, Jennifer R. Diamond, Wells A. Messersmith, Isabel R. Schlaepfer, Todd M. Pitts. Therapeutic targeting of lipid oxidation and apoptosis in pancreatic ductal adenocarcinoma [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 6387.

Abstract 3021: Integrated pharmacokinetic (PK)/pharmacodynamic (PD) modeling leveraging PK, biomarker, and safety data to support dose and schedule selection for the BET inhibitor BMS-986158

Background: BMS-986158 is a potent, selective, and orally bioavailable small-molecule inhibitor of the bromodomain and extraterminal (BET) family of transcription modulators being evaluated in patients with various tumors in a phase 1 clinical study (NCT02419417). An integrated PK/PD analysis leveraging PK, biomarker, and safety data from the phase 1 study was performed to support dose and schedule (Sch) selection further clinical studies with BMS-986158.

Methods: Five doses (0.75-4.5 mg) and 3 dosing regimens (Sch A: 5 days on, 2 days off over 21 days; Sch B: 14 days on, 7 days off; Sch C: 7 days on, 14 days off) were evaluated. Reversible thrombocytopenia (TTP) was the primary safety signal observed, and peripheral gene expression modulation was a PD biomarker indicative of drug target engagement. BMS-986158 serum PK was characterized with a 2-compartment population PK (PPK) model. A semimechanistic PK/PD model describing the platelet-reducing effect with BMS-986158 was developed to characterize platelet profiles for individual patients and to simulate and project the incidence of TTP at different doses and dosing regimens. The association of BMS-986158 exposure with expression modulation of select peripheral BET target genes, including HEXM1 and CCR2, was also examined.

Results: BMS-986158 exhibited linear PK with rapid oral absorption (Tmax ≈ 2-4 h) and a terminal half-life of ≈ 60 h over the dose range of 0.75-4.5 mg. PPK modeling and simulation suggested that at the same dose level, Sch A led to comparable Cmax, with a higher Ctrough and Cavg at steady state compared with Sch B and C across the dosing interval. The semimechanistic PK/PD model predicted a higher incidence rate of TTP with Sch A than Sch C at the same dose level, and the predictions agreed with observed primary safety data from the phase 1 study. The model predicted grade 4 TTP incidence rates of 24% (95% CI, 21%-26%) and 43% (95% CI, 38%-45%) at 4.5 and 6 mg, respectively, with Sch A. This suggests that 4.5 mg would be the maximum tolerated dose, given that a 6 mg dose was predicted to exceed the target dose-limiting toxicity (DLT) rate of grade 4 TTP at 27%. The exploratory analysis of BMS-986158 exposure and expression of selected peripheral genes associated with the BET pathway suggested a direct association between BMS-986158 exposure and the magnitude of peripheral gene expression modulation.

Conclusions: An integrated PK/PD analysis of BMS-986158 incorporating incidence of reversible TTP and modulation of peripheral BET target genes identified a maximum dose of 4.5 mg at Sch A for further clinical development. With the assumption that sustained gene expression modulation is desirable for BMS-986158 efficacy, Sch A, which provides sustained drug exposure, is recommended to enable continuous BET target gene expression modulation.

Citation Format: Xi (Cindy) Chen, Lora Hamuro, Shodeinde Coker, John Hilton, Jennifer R. Diamond, Capucine Baldini, Mark Voskoboynik, Mihaela Cristea, William Edenfield, Kezi Unsal-Kacmaz, Donald Jackson, Abraham Apfel, Ke Xu, Li Zhu, Amit Roy, Akintunde Bello, Ronald Fleming, Paul Statkevich. Integrated pharmacokinetic (PK)/pharmacodynamic (PD) modeling leveraging PK, biomarker, and safety data to support dose and schedule selection for the BET inhibitor BMS-986158 [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 3021.

Phase Ib clinical trial of the anti-frizzled antibody vantictumab (OMP-18R5) plus paclitaxel in patients with locally advanced or metastatic HER2-negative breast cancer

PURPOSE

Vantictumab is a monoclonal antibody that binds to frizzled (FZD) receptors and inhibits canonical WNT signaling. This phase Ib dose escalation study enrolled patients with locally recurrent or metastatic HER2-negative breast cancer who were treated with weekly paclitaxel in combination with escalating doses of vantictumab.

METHODS

Patients were enrolled in dose escalation cohorts treated with weekly paclitaxel 90 mg/m² on days 1, 8 and 15 in combination with vantictumab 3.5-14 mg/kg days 1 and 15 or 3-8 mg/kg day 1 of every 28-day cycle. Primary endpoints were safety, dose-limiting toxicities (DLTs). Secondary endpoints included pharmacokinetics, efficacy and an exploratory biomarker analysis.

RESULTS

Forty-eight female patients with a mean age of 54 were enrolled. The majority (66.6%) received prior chemotherapy for recurrent or metastatic disease; 45.8% were hormone receptor (HR)-positive, HER2-negative and 54.2% triple-negative. The most frequent adverse events related to any study treatment were nausea (54.2%), alopecia (52.1%), fatigue (47.9%), and peripheral neuropathy (43.8%). No DLTs occurred; however, 6 patients experienced fractures outside of the DLT window. The overall response rate was 31.3% and the clinical benefit rate was 68.8%. A 6-gene WNT pathway signature showed significant association with progression-free survival (PFS) and overall survival (OS) for the biomarker high versus biomarker low groups (PFS: p = 0.029 and OS: p = 0.00045, respectively).

CONCLUSIONS

The combination of vantictumab and weekly paclitaxel was generally well tolerated with promising efficacy; however, the incidence of fractures limits future clinical development of this particular WNT inhibitor in metastatic breast cancer.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov registration: NCT01973309.

Wee1 Inhibition Enhances the Anti-Tumor Effects of Capecitabine in Preclinical Models of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. Adavosertib (AZD1775) is a potent, small-molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. The purpose of this study was to investigate the combination of AZD1775 and capecitabine/5FU in preclinical TNBC models. TNBC cell lines were treated with AZD1775 and 5FU and cellular proliferation was assessed in real-time using IncuCyte^® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of downstream effectors. TNBC patient-derived xenograft (PDX) models were treated with AZD1775, capecitabine, or the combination and assessed for tumor growth inhibition. From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p < 0.05 combo vs. adavosertib or capecitabine, TNBC013, p < 0.01 combo vs. adavosertib or capecitabine.) An enhanced anti-proliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single-agent treatment. Treatment with adavosertib as a single agent resulted in a decrease in p-CDC2 in a dose-dependent manner that was also observed in the combination treatment. An increase in γH2AX in two of the four cell lines tested was also observed. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. The combination of adavosertib and capecitabine/5FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Abstract A76: Efficacy of immunotherapy agents in patients with metastatic breast cancer treated in phase I clinical trials

Background: Immuno-oncology (IO) agents have demonstrated exceptional clinical benefit in patients with many tumor types, including melanoma and lung cancer. The PD-L1 inhibitor, atezolizumab, was recently FDA approved in combination with nab-paclitaxel for patients with PD-L1 positive triple-negative breast cancer (TNBC); however, single-agent PD-1/PD-L1 inhibitors demonstrate modest efficacy in breast cancer. The purpose of this study was to investigate the efficacy of IO agents in patients with metastatic breast cancer treated in phase I clinical trials.

Methods: We performed a retrospective analysis using a database of patients with metastatic breast cancer who received treatment with IO agents in phase I/Ib clinical trials at the University of Colorado Anschutz Medical Campus from January 1, 2012 to July 1, 2018. Abstracted data included patient demographics, baseline characteristics, and clinical outcomes.

Results: 208 patients with metastatic breast cancer were treated in phase I/Ib clinical trials; 43 were treated with an IO agent. The average age was 53 years old and 55.8% had hormone receptor-positive/HER2-negative breast cancer, 39.5% TNBC, and 4.6% HER2-positive disease. On average, patients received two prior lines of chemotherapy (range 0-7) in the metastatic setting. 31/43 patients (72.1%) received single agent or combination IO, and 12/43 (27.9%) received IO + chemotherapy. Median progression-free survival (PFS) was 2.3 months and median overall survival (OS) was 12.1 months in all patients. 9/43 (21%) of patients remained on study &gt; 6 months and had a median PFS of 8.6 months. Patients remaining on study &gt; 6 months were more likely to be treated with IO + chemotherapy compared to patients with a PFS &lt; 6 months (77.8% v. 14.7%, p=0.0007). There was no difference in sites of metastasis, prior lines of chemotherapy, breast cancer subtype, absolute lymphocyte count, or LDH between patients with a PFS &gt; 6 months compared to &lt; 6 months.

Conclusions: A subset of patients with metastatic breast cancer treated in phase I clinical trials at our center with an IO agent had derived prolonged clinical benefit. The benefit was not limited to patients with TNBC and was associated with receipt of chemotherapy in combination with IO. Predictors of response to immunotherapy in breast cancer beyond PD-L1 expression remain uncharacterized, and further research is needed to identify these factors.

Citation Format: Jodi A. Kagihara, Jennifer A. Weiss, Andrew Nicklawsky, Dexiang Gao, Virginia F. Borges, Peter Kabos, Antonio Jimeno, Jennifer R. Diamond. Efficacy of immunotherapy agents in patients with metastatic breast cancer treated in phase I clinical trials [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A76.

Nab-paclitaxel and atezolizumab for the treatment of PD-L1-positive, metastatic triple-negative breast cancer: review and future directions

Introduction

Breast cancer is the most common malignancy in women in the United States and triple-negative breast cancer (TNBC) accounts for 15-20%. The standard of care for metastatic TNBC has been limited to cytotoxic chemotherapy with modest efficacy. TNBC is associated with high levels of tumor-infiltrating lymphocytes and PD-L1 expression, supporting the investigation of immune checkpoint inhibitors in this breast cancer subtype.

Areas Covered

This review summarizes the clinical data supporting the use of atezolizumab and nab-paclitaxel in the treatment of metastatic PD-L1-positive TNBC. It examines the pharmacology and toxicity profile of the combination in patients with metastatic TNBC.

Expert Opinion

The addition of atezolizumab to nab-paclitaxel prolonged progression-free survival in both the intention-to-treat and PD-L1-positive subgroups in the first line setting in patients with metastatic TNBC. The IMpassion 130 trial led to FDA-approval of this combination in patients with PD-L1-positive, metastatic TNBC and represents the first approval of immunotherapy for TNBC. This work supports ongoing investigations of other immunotherapy combinations in TNBC, predictive biomarker development and immunotherapy in patients with early stage TNBC. Immunotherapy combinations in TNBC have the potential to lead to improved survival in this group of patients with high risk disease.

Abstract P1-19-25: Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative breast cancer

Background: Triple-negative breast cancer (TNBC) is an aggressive subtype defined by lack of hormone receptor expression and non-amplified HER2. TNBC accounts for approximately 15% of breast cancer cases, however, is associated with an increased risk of cancer recurrence, brain metastasis, and death due to metastatic breast cancer. Mutations in p53 are common in TNBC, occurring in approximately 85% of tumors. While a number of promising targeted therapies are on the horizon in TNBC including immunotherapy, there remains an unmet need for active targeted therapies where chemotherapy remains the standard treatment for metastatic disease and results in a median survival of 12-18 months. Adavosertib (AZD1775) is a potent, small molecule, ATP-competitive inhibitor of the Wee1 kinase that potentiates the activity of many DNA-damaging chemotherapeutics and is currently in clinical development for multiple indications. AZD1775 potentiates the activity of DNA-damaging and antimetabolite chemotherapeutics in preclinical models without TP53-deficiency, possibly due to baseline replicative stress or compromised DNA repair proficiency. A previous unbiased screen of CTEP compounds in TNBC PDX models demonstrated that the combination of adavosertib and capecitabine/5FU had greater anti-proliferative effects than either of the single agents. The purpose of this study was to further investigate the combination of adavosertib and capecitabine/5FU in preclinical TNBC models. Methods: HCC1937, CAL51, MDA-MB-231 and MDA-MB-468 cells were plated in 96-well plates and exposed to increasing concentrations of adavosertib, 5FU, or the combination. Cellular proliferation was assessed in real-time using IncuCyte® Live Cell Analysis. Apoptosis was assessed via the Caspase-Glo 3/7 assay system. Western blotting was used to assess changes in expression of CDC2, phospho-CDC2, H2AX, and Bcl-xL. TNBC PDX models CU_TNBC_012 and CU_TNBC_013 were treated with vehicle, adavosertib, capecitabine, or the combination and assessed for tumor growth inhibition. Results: From the initial PDX screen, two of the four TNBC PDX models demonstrated a better response in the combination treatment than either of the single agents. As confirmation, two PDX models were expanded for statistical comparison. Both PDX models demonstrated a significant growth inhibition in the combination versus either of the single agents. (TNBC012, p&lt;0.05 combo vs adavosertib or capecitabine, TNBC013, p&lt;0.01 combo vs adavosertib or capecitabine ). An enhanced antiproliferative effect was observed in the adavosertib/5FU combination treatment as measured by live cell analysis. An increase in apoptosis was observed in two of the four cell lines in the combination when compared to single agent treatment. Treatment with single agent adavosertib resulted in an increase in p-cdc2 in a dose dependent manner that was also observed in the combination treatment. Similar results were observed with γH2AX in two of the four cell lines tested. No significant changes were observed in Bcl-xL following treatment in any of the cell lines. Conclusions: The combination of adavosertib and capecitabine/5-FU demonstrated enhanced combination effects both in vitro and in vivo in preclinical models of TNBC. These results support the clinical investigation of this combination in patients with TNBC, including those with brain metastasis given the CNS penetration of both agents.

Citation Format: Todd M Pitts, Dennis M Simmons, Kyrie Dailey, Stacey M Bagby, Sarah J Hartman, Betelehem W Yacob, Brian Gittleman, John J Tentler, Diana Cittely, D. Ryan Ormond, Wells A Messersmith, S Gail Eckhardt, Jennifer R Diamond. Wee1 inhibition enhances the anti-tumor effects of capecitabine in preclinical models of triple negative 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 P1-19-25.

First-in-Class Phosphorylated-p68 Inhibitor RX-5902 Inhibits β-Catenin Signaling and Demonstrates Antitumor Activity in Triple-Negative Breast Cancer

RX-5902 is a first-in-class anticancer agent targeting phosphorylated-p68 and attenuating nuclear shuttling of β-catenin. The purpose of this study was to evaluate the efficacy of RX-5902 in preclinical models of triple-negative breast cancer (TNBC) and to explore effects on β-catenin expression. A panel of 18 TNBC cell lines was exposed to RX-5902, and changes in proliferation, apoptosis, cellular ploidy, and effector protein expression were assessed. Gene expression profiling was used in sensitive and resistant cell lines with pathway analysis to explore pathways associated with sensitivity to RX-5902. The activity of RX-5902 was confirmed in vivo in cell line and patient-derived tumor xenograft (PDX) models. RX-5902 demonstrated potent antiproliferative activity in vitro against TNBC cell lines with an average IC₅₀ of 56 nmol/L in sensitive cell lines. RX-5902 treatment resulted in the induction of apoptosis, G₂-M cell-cycle arrest, and aneuploidy in a subset of cell lines. RX-5902 was active in vivo against TNBC PDX models, and treatment resulted in a decrease in nuclear β-catenin. RX-5902 exhibited dose-proportional pharmacokinetics and plasma and tumor tissue in nude mice. Pathway analysis demonstrated an increase in the epithelial-to-mesenchymal transformation (EMT), TGFβ, and Wnt/β-catenin pathways associated with sensitivity to RX-5902. RX-5902 is active against in vitro and in vivo preclinical models of TNBC. Target engagement was confirmed with decreases in nuclear β-catenin and MCL-1 observed, confirming the proposed mechanism of action. This study supports the continued investigation of RX-5902 in TNBC and combinations with immunotherapy.