Triple-negative breast cancer (TNBC) represents a more aggressive and difficult subtype of breast cancer where responses to chemotherapy occur, but toxicity is significant and resistance often follows. Immunotherapy has shown promising results in various types of cancer, including breast cancer. Here, we investigated a new combination strategy where histone deacetylase inhibitors (HDACi) are applied with immune checkpoint inhibitors to improve immunotherapy responses in TNBC.Testing different epigenetic modifiers, we focused on the mechanisms underlying HDACi as priming modulators of immunotherapy. Tumor cells were co-cultured with human peripheral blood mononuclear cells (PBMCs) and flow cytometric immunophenotyping was performed to define the role of epigenetic priming in promoting tumor antigen presentation and immune cell activation. We found that HDACi up-regulate PD-L1 mRNA and protein expression in a time-dependent manner in TNBC cells, but not in hormone responsive cells. Focusing on TNBC, HDACi up-regulated PD-L1 and HLA-DR on tumor cells when co-cultured with PBMCs and down-regulated CD4+ Foxp3+ Treg in vitro. HDACi significantly enhanced the in vivo response to PD-1/CTLA-4 blockade in the triple-negative 4T1 breast cancer mouse model, the only currently available experimental system with functional resemblance to human TNBC. This resulted in a significant decrease in tumor growth and increased survival, associated with increased T cell tumor infiltration and a reduction in CD4+ Foxp3+ T cells in the tumor microenvironment. Overall, our results suggest a novel role for HDAC inhibition in combination with immune checkpoint inhibitors and identify a promising therapeutic strategy, supporting its further clinical evaluation for TNBC treatment.

Responses to immunotherapy are uncommon in estrogen receptor (ER)-positive breast cancer and to date, lack predictive markers. This randomized phase II study defines safety and response rate of epigenetic priming in ER-positive breast cancer patients treated with checkpoint inhibitors as primary endpoints. Secondary and exploratory endpoints included PD-L1 modulation and T-cell immune-signatures. 34 patients received vorinostat, tamoxifen and pembrolizumab with no excessive toxicity after progression on a median of five prior metastatic regimens. Objective response was 4% and clinical benefit rate (CR + PR + SD > 6 m) was 19%. T-cell exhaustion (CD8 + PD-1 + /CTLA-4 +) and treatment-induced depletion of regulatory T-cells (CD4 + Foxp3 + /CTLA-4 +) was seen in tumor or blood in 5/5 patients with clinical benefit, but only in one non-responder. Tumor lymphocyte infiltration was 0.17%. Only two non-responders had PD-L1 expression >1%. This data defines a novel immune signature in PD-L1-negative ER-positive breast cancer patients who are more likely to benefit from immune-checkpoint and histone deacetylase inhibition (NCT02395627).

Purpose This phase I trial evaluated epigenetic modulation of vascular endothelial growth factor (VEGF) and hypoxia-inducible factor by using a histone deacetylase abexinostat in combination with pazopanib to enhance response and reverse resistance. Patients and Methods Pazopanib was administered once a day on days 1 to 28 and abexinostat was administered orally twice a day on days 1 to 5, 8 to 12, and 15 to 19 (schedule A) or on days 1 to 4, 8 to 11, and 15 to 18 (schedule B). Dose escalation (3 + 3 design) in all solid tumors was followed by dose expansion in renal cell carcinoma (RCC). Results Fifty-one patients with RCC (N = 22) were enrolled, including 30 (59%) with one or more lines of prior VEGF-targeting therapy. Five dose-limiting toxicities, including fatigue (n = 2), thrombocytopenia (n = 2), and elevated AST/ALT (n = 1), were observed with schedule A; one dose-limiting toxicity was observed (elevated AST/ALT) was observed with schedule B. Grade ≥ 3 related adverse events included fatigue (16%), thrombocytopenia (16%), and neutropenia (10%). The recommended phase II dose was established as abexinostat 45 mg/m twice a day administered per schedule B plus pazopanib 800 mg/d. Objective response rate was 21% overall and 27% in the RCC subset. Median duration of response was 9.1 months (1.2 to > 49 months). Eight patients (16%) had durable control of disease for > 12 months. Durable tumor regressions were observed in seven (70%) of 10 patients with pazopanib-refractory disease, including one patients with RCC with ongoing response > 3.5 years. Peripheral blood histone acetylation and HDAC2 gene expression were associated with durable response to treatment. Conclusion Abexinostat is well tolerated in combination with pazopanib, allowing prolonged exposure and promising durable responses in pazopanib- and other VEGF inhibitor-refractory tumors, which supports epigenetically mediated reversal of treatment resistance.

The PARP inhibitor (PARPi) talazoparib may potentiate activity of chemotherapy and toxicity in cells vulnerable to DNA damage. This phase I study evaluated the safety, tolerability, pharmacokinetics, and efficacy of talazoparib and carboplatin. Pharmacokinetic modeling explored associations between DNA vulnerability and hematologic toxicity. Twenty-four patients (eight males; 16 females) with solid tumors were enrolled in four cohorts at 0.75 and 1 mg daily talazoparib and weekly carboplatin (AUC 1 and 1.5, every 2 weeks or every 3 weeks), including 14 patients (58%) with prior platinum treatment. Dose-limiting toxicities included grade 3 fatigue and grade 4 thrombocytopenia; the MTD was not reached. Grade 3/4 toxicities included fatigue (13%), neutropenia (63%), thrombocytopenia (29%), and anemia (38%). After cycle 2's dose, delays/reductions were required in all patients. One complete and two partial responses occurred in germline BRCA1/2 (gBRCA1/2) patients. Four patients showed stable disease beyond 4 months, three of which had known mutations in DNA repair pathways. Pharmacokinetic toxicity modeling suggests that after three cycles of carboplatin AUC 1.5 every 3 weeks and talazoparib 1 mg daily, neutrophil counts decreased 78% [confidence interval (CI), 87-68] from baseline in gBRCA carriers and 63% (CI, 72-55) in noncarriers ( < 0.001). Pharmacokinetic toxicity modeling suggests an intermittent, pulse dosing schedule of PARP inhibition, differentiated by gBRCA mutation status, may improve the benefit/risk ratio of combination therapy. Carboplatin and talazoparib showed efficacy in DNA damage mutation carriers, but hematologic toxicity was more pronounced in gBRCA carriers. Carboplatin is best combined with intermittent talazoparib dosing differentiated by germline and somatic DNA damage mutation carriers. .

Purpose: The histone deacetylase (HDAC) inhibitor panobinostat potentiates anthracycline and cytarabine cytotoxicity in acute myeloid leukemia (AML) cells. We hypothesized that panobinostat prior to and during induction chemotherapy would be tolerable and augment response in patients showing increased histone acetylation.Patients and Methods: Patients received panobinostat 20-60 mg oral daily on days 1, 3, 5, and 8 with daunorubicin 60 mg/m 2 /day intravenously on days 3 to 5 and cytarabine 100 mg/m 2 /day intravenously by continuous infusion on days 3 to 9 ("7þ3"). Peripheral blood mononuclear cells (PBMCs) were isolated for HDAC expression and histone acetylation changes.Results: Twenty-five patients ages 60-85 years (median age, 69) were treated. Fifteen patients had de novo AML, six AML with myelodysplasia-related changes, two AML with prior myeloproliferative neoplasm, one therapy-related myeloid neoplasm, and one myelodysplastic syndrome with excess blasts-2. No dose-limiting toxicities occurred in dose escalation cohorts. In dose expansion, six patients received panobinostat at 60 mg and nine patients at 50 mg due to recurrent grade 1 bradycardia at the 60-mg dose. The complete response (CR)/incomplete count recovery (Cri) rate was 32%. Median overall survival was 10 months: 23 months with CR/CRi versus 7.8 months without CR/CRi (log-rank P ¼ 0.02). Median relapse-free survival was 8.2 months. Increased histone acetylation 4 and 24 hours after panobinostat was significantly associated with CR/CRi.Conclusions: Panobinostat with "7þ3" for older patients with AML was well tolerated. Panobinostat 50 mg on days 1, 3, 5, and 8 starting 2 days prior to "7þ3" is recommended for future studies. Panobinostat-induced increases in histone acetylation in PBMCs predicted CR/CRi.

3001 Background: FOR46, a fully human antibody (ab) conjugated to monomethyl auristatin E (MMAE), targets a tumor selective epitope of CD46, which is highly expressed in mCRPC and treatment-emergent small cell neuroendocrine cancer (t-SCNC). CD46 is enriched in tumor cells upon treatment with androgen signaling inhibitors (ASI). Following dose escalation (Phase 1a), dose expansion was undertaken in 2 cohorts (Phase 1b): 1) Pts with de novo or t-SCNC and 2) pts with mCRPC without a t-SCNC component. Pts with adenocarcinoma enrolled in dose escalation and expansion are included in this analysis. Methods: Eligible pts had mCRPC, with progression on at least 1 ASI, with no prior chemotherapy for CRPC. Phase 1a pts received FOR46 0.1-3.0 mg/kg IV Q3 weeks (wks). The primary objectives in phase 1a were to assess adverse effects (AEs) and select the phase 1b dose; and in phase 1b to assess efficacy. For phase 1b, tumor biopsy in the CRPC setting for assignment to the 2 cohorts was required. CD46 expression was not required for inclusion in the expansion cohort, but was evaluated using a non-epitope specific CD46 polyclonal ab. Histology and CD46 expression were centrally reviewed. Results: Thirty-three pts were enrolled in phase 1a and 10 in phase 1b (including 6 treated in ph1a at the expansion dose or higher). Overall, 36 pts were treated at doses > 1.2 mg/kg. Following excess toxicity in pts with body mass indices > 30 (3 of 3 with Gr 4 neutropenia and 1 of 3 with Gr 3 fatigue at 2.4 mg/kg), further dosing was calculated using adjusted body weight (AJBW) rather than actual weight, allowing escalation to 3.0 mg/kg. The 2.7 mg/kg dose by AJBW was determined to be the MTD and phase 1b dose. The most common AEs at the 2.7 mg/kg dose were neutropenia (77% Gr 3 or 4), infusion reactions (37%, all < Gr 2), fatigue (31%, all < Gr 2) and peripheral neuropathy (24%, all < Gr 2)). Fourteen of 31 evaluable pts (45.2%) at > 1.2 mg/kg achieved a PSA50 response with 10 (32.3%) confirmed. Five pts were not evaluable for PSA response; 3 had no post-baseline PSA and 2 had baseline PSA < 1 ng/mL. The median duration of confirmed PSA50 response is >16 wks (range 6-48+ wks, with 4 ongoing at 12, 24, 25 and 48 wks). 18 pts had measurable lesions; 8 of 18 (44.4%) had tumor regression, with 4 (22.2%) confirmed partial responses (PR). The median duration of response is > 14 wks (range 9 -31+ weeks with 2 ongoing at 13 and 31 wks). Eight pts were evaluable for CD46 expression with a median H-score of 245 (range 0-300). Two pts with PRs had H-scores of 15 and 300; 4 with confirmed PSA50 had H-scores of 10, 15, 40 and 300. Conclusions: FOR46, a novel ADC targeting CD46, demonstrates clinical activity in mCRPC pts, with an acceptable safety profile, similar to other MMAE-containing ADCs. FOR46 merits further investigation in pts with mCRPC, alone and in combination with agents that enhance CD46 expression. Clinical trial information: NCT03575819.

Broad use of germline testing has identified an increasing number of women at risk for breast cancer with a need for effective chemoprevention. We report a novel method to selectively deliver various anti-estrogens at high drug levels to the breast tissue by implanting a device comprised of silastic tubing. Optimized tubing properties allow elution of otherwise poorly bioavailable anti-estrogens, such as fulvestrant, into mammary tissue in vitro and in vivo with levels sufficient to inhibit estrogen receptor activation and tumor cell proliferation. Implantable silastic tubing delivers fulvestrant selectively to mouse mammary fat tissue for one year with anti-tumor effects similar to those achieved with systemic fulvestrant exposure. Furthermore, local delivery of fulvestrant significantly decreases cell proliferation, as assessed by Ki67 expression, most effectively in tumor sections adjacent to tubing. This approach may thereby introduce a potential paradigm shift and offer a promising alternative to systemic therapy for prevention and early interception of breast cancer.

BackgroundPoly(ADP-ribose) polymerase inhibitors (PARPi), coupled to a DNA damaging agent is a promising approach to treating triple negative breast cancer (TNBC). However, not all patients respond; we hypothesize that non-response in some patients may be due to insufficient drug penetration. As a first step to testing this hypothesis, we quantified and visualized veliparib and carboplatin penetration in mouse xenograft TNBCs and patient blood samples.MethodsMDA-MB-231, HCC70 or MDA-MB-436 human TNBC cells were implanted in 41 beige SCID mice. Low dose (20 mg/kg) or high dose (60 mg/kg) veliparib was given three times daily for three days, with carboplatin (60 mg/kg) administered twice. In addition, blood samples were analyzed from 19 patients from a phase 1 study of carboplatin + PARPi talazoparib. Veliparib and carboplatin was quantified using liquid chromatography–mass spectrometry (LC-MS). Veliparib tissue penetration was visualized using matrix-assisted laser desorption/ionization mass spectrometric imaging (MALDI-MSI) and platinum adducts (covalent nuclear DNA-binding) were quantified using inductively coupled plasma–mass spectrometry (ICP-MS). Pharmacokinetic modeling and Pearson’s correlation were used to explore associations between concentrations in plasma, tumor cells and peripheral blood mononuclear cells (PBMCs).ResultsVeliparib penetration in xenograft tumors was highly heterogeneous between and within tumors. Only 35% (CI 95% 26–44%), 74% (40–97%) and 46% (9–37%) of veliparib observed in plasma penetrated into MDA-MB-231, HCC70 and MDA-MB-436 cell-based xenografts, respectively. Within tumors, penetration heterogeneity was larger with the 60 mg/kg compared to the 20 mg/kg dose (RSD 155% versus 255%, P = 0.001). These tumor concentrations were predicted similar to clinical dosing levels, but predicted tumor concentrations were below half maximal concentration values as threshold of response. Xenograft veliparib concentrations correlated positively with platinum adduct formation (R 2 = 0.657), but no PARPi–platinum interaction was observed in patients’ PBMCs. Platinum adduct formation was significantly higher in five gBRCA carriers (ratio of platinum in DNA in PBMCs/plasma 0.64% (IQR 0.60–1.16%) compared to nine non-carriers (ratio 0.29% (IQR 0.21–0.66%, P < 0.0001).ConclusionsPARPi/platinum tumor penetration can be measured by MALDI-MSI and ICP-MS in PBMCs and fresh frozen, OCT embedded core needle biopsies. Large variability in platinum adduct formation and spatial heterogeneity in veliparib distribution may lead to insufficient drug exposure in select cell populations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13058-017-0896-4) contains supplementary material, which is available to authorized users.