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.