NeoPalAna: Neoadjuvant Palbociclib, a Cyclin-Dependent Kinase 4/6 Inhibitor, and Anastrozole for Clinical Stage 2 or 3 Estrogen Receptor-Positive Breast Cancer

Molecular changes in premenopausal oestrogen receptor-positive primary breast cancer in Vietnamese women after oophorectomy

For premenopausal women with primary ER + breast cancer, oophorectomy (OvX) is an evidence-based cost-effective option and is standard treatment in many countries. However, there is virtually no data describing the effects of OvX on breast tumour biology. We therefore, characterised the endocrine and genome-wide transcriptional impact of OvX in 56 premenopausal women with ER + breast cancer for 2 weeks prior to mastectomy. Plasma estradiol concentrations decreased from 406 ± 41 to 20.7 ± 2.6 pmol/l (mean ± sem) 24 h after OvX, and to 8.1 ± 0.8 pmol/l 2 weeks later at mastectomy. Ki67 decreased in 33/36 (91.7%) tumours. The expression of 655 genes changed significantly (FDR < 1%) with an absolute mean fold-change (FC) ≥ 1.25 (257 up, 398 down). Archetypal oestrogen-regulated genes (TFF1, GREB1, PGR and PDZK1) showed large decreases in expression (FC = 0.20–0.69; p < 1e-6-1e-7). Proliferation-associated genes (e.g. TOP2A, AURKA and UBE2C) were also strongly downregulated (FC = 0.38–0.56; p < 1e-7) along with putative progesterone-regulated genes (e.g. FKBP4, MYB; FC = 0.64–0.68; p < 1e-4-1e-7). The gene expression changes did not differ according to HER2 status and correlated strongly with the changes reported previously after aromatase inhibitor (AI) treatment in postmenopausal women (rho = 0.55, p < 1e-04). However, after OvX the mean FC was significantly higher compared to AI (p < 1e-04). In conclusion, changes in tumoural gene expression after OvX were largely similar, but of a greater magnitude to those observed after AI in postmenopausal patients; however, OvX appeared to have a greater effect on progesterone-regulated genes than AI.

Surgical removal of the ovaries alters the expression of hundreds of genes in the tumour cells of premenopausal women with breast cancer. Ben Haynes from Royal Marsden Hospital in London, UK and colleagues characterised molecular changes in 56 premenopausal women from Vietnam with oestrogen receptor-positive breast cancer who underwent oophorectomies, a standard treatment for this patient population. They showed that blood levels of the hormone estradiol dropped precipitously following ovary-removal surgery. Levels of a protein that was indicative of tumour growth also went down, as did genes involved in regulating hormone signalling and cell proliferation. The results are consistent with those seen in postmenopausal women following treatment with an oestrogen-blocking drug, but oophorectomy had a more dramatic effect. The data could aid the search for predictive biomarkers of who stands to benefit most from ovary removal.

Serum thymidine kinase 1 activity as a pharmacodynamic marker of cyclin-dependent kinase 4/6 inhibition in patients with early-stage breast cancer receiving neoadjuvant palbociclib

BACKGROUND

Thymidine kinase 1 (TK1) is a cell cycle-regulated enzyme with peak expression in the S phase during DNA synthesis, and it is an attractive biomarker of cell proliferation. Serum TK1 activity has demonstrated prognostic value in patients with early-stage breast cancer. Because cyclin-dependent kinase 4/6 (CDK4/6) inhibitors prevent G₁/S transition, we hypothesized that serum TK1 could be a biomarker for CDK4/6 inhibitors. We examined the drug-induced change in serum TK1 as well as its correlation with change in tumor Ki-67 levels in patients enrolled in the NeoPalAna trial (ClinicalTrials.gov identifier NCT01723774).

METHODS

Patients with clinical stage II/III estrogen receptor-positive (ER+)/HER2-negative breast cancer enrolled in the NeoPalAna trial received an initial 4 weeks of anastrozole, followed by palbociclib on cycle 1, day 1 (C1D1) for four 28-day cycles, unless C1D15 tumor Ki-67 was > 10%, in which case patients went off study owing to inadequate response. Surgery occurred following 3-5 weeks of washout from the last dose of palbociclib, except in eight patients who received palbociclib (cycle 5) continuously until surgery. Serum TK1 activity was determined at baseline, C1D1, C1D15, and time of surgery, and we found that it was correlated with tumor Ki-67 and TK1 messenger RNA (mRNA) levels.

RESULTS

Despite a significant drop in tumor Ki-67 with anastrozole monotherapy, there was no statistically significant change in TK1 activity. However, a striking reduction in TK1 activity was observed 2 weeks after initiation of palbociclib (C1D15), which then rose significantly with palbociclib washout. At C1D15, TK1 activity was below the detection limit (<20 DiviTum units per liter Du/L) in 92% of patients, indicating a profound effect of palbociclib. There was high concordance, at 89.8% (95% CI: 79.2% - 96.2%), between changes in serum TK1 and tumor Ki-67 in the same direction from C1D1 to C1D15 and from C1D15 to surgery time points. The sensitivity and specificity for the tumor Ki-67-based response by palbociclib-induced decrease in serum TK1 were 94.1% (95% CI 86.2% - 100%) and 84% (95% CI 69.6% -98.4%), respectively. The κ-statistic was 0.76 (p < 0.001) between TK1 and Ki-67, indicating substantial agreement.

CONCLUSIONS

Serum TK1 activity is a promising pharmacodynamic marker of palbociclib in ER+ breast cancer, and its value in predicting response to CDK4/6 inhibitors warrants further investigation.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01723774. Registered on 6 November 2012.

Neoadjuvant Endocrine Therapy: Who Benefits Most?

Neoadjuvant endocrine therapy (NET) can be effective at downstaging patients with estrogen receptor-positive tumors and identifying those tumors that are endocrine sensitive and resistant. The optimal prognostic markers for stratification are under investigation. Use of NET will allow the identification of patients with estrogen receptor-positive tumors who might benefit from additional treatment and allow better understanding of endocrine resistance.

Preoperative Endocrine Therapy

Purpose of Review

Pre-operative endocrine therapy can be used to down-stage large or locally advanced breast cancers in ER+ disease. In the last four decades, it has evolved from a treatment perceived as an alternative to surgery for those too unfit to undergo surgery or chemotherapy, to the present day where it is a valuable and valid option in the treatment of postmenopausal women with ER-rich (Allred score 7–8, or > 50% staining for ER) breast cancer.

Recent Findings

Emerging data from the metastatic setting is translating into neoadjuvant trials, utilising dual endocrine targeting or combinations of endocrine agents and other targeted drugs, including those acting against components of the PI3K pathway and the cell cycle. The routine use of peri-operative endocrine therapy in all ER+ tumours may help to yield important long-term prognostic information, and guide adjuvant endocrine therapy.

Summary

Pre-operative endocrine therapy is an exciting and evolving area with emerging new approaches. In this review, established evidence and emerging data on its applications are discussed.

Mechanisms of Resistance to CDK4/6 Inhibitors in Breast Cancer and Potential Biomarkers of Response

Randomized clinical trials demonstrated that CDK4/6 inhibitors are highly effective in patients with hormone receptor-positive (HR+), HER2-negative (HER2-) metastatic breast cancer in combination with endocrine therapy. The use of CDK4/6 inhibitors in clinics is becoming common for patients with HR+/HER2- metastatic breast cancer and will certainly increase in the near future. However, patients might show de novo or acquired resistance to these drugs. Molecular alterations have been suggested as determinants for de novo resistance to CDK4/6 inhibitors, but have never been validated in a clinical setting. In addition, molecular mechanisms of acquired resistance to palbociclib have been analyzed only in preclinical studies. Here we review the current knowledge on the available preclinical data about the mechanisms of de novo and acquired resistance to CDK4/6 inhibitors in breast cancer, and clinical data about potential biomarkers of response.

CDK4/6 blockade in breast cancer: current experience and future perspectives

INTRODUCTION

Dysregulated cellular proliferation, one of the hallmarks of cancer, is mediated by aberrant activation of the cell cycle machinery through the biological effects of cyclin-dependent kinases (CDKs). The clinical development of non-selective CDK inhibitors failed due to combined lack of efficacy and excessive toxicity reported by clinical trials across different cancer types. The clinical development of second generation, CDK4/6-selective inhibitors, namely palbociclib, abemaciclib and ribociclib, led to practice-changing results in the setting of breast cancer. Areas covered: This review illustrates how CDK4/6-selective inhibitors got approval for the treatment of patients with either newly diagnosed or pretreated advanced hormone receptor positive, HER2-negative breast cancer. Furthermore, data about potential predictive biomarkers, as well as preclinical and preliminary clinical evidence for potential antitumor activity of CDK4/6 inhibition in other breast cancer subtypes is provided. Expert opinion: Future clinical development of CDK4/6 inhibitors in breast cancer will focus on the following aspects: i) optimization of treatment sequencing for patients with advanced disease, ii) early-stage disease, iii) other subtypes of breast cancer in rationally chosen therapeutic combinations and iv) the identification of predictive biomarkers.

Extending indication of cyclin-dependent kinase 4/6 inhibitors in the adjuvant and neoadjuvant setting

PURPOSE OF REVIEW

A burst of recent activity has surrounded the study of cyclin-dependent kinase 4/6 (CDK 4/6) inhibitors for the treatment of metastatic breast cancer. The success of these drugs in the metastatic setting has pushed the evaluation of these agents in early-stage disease. The use of CDK 4/6 inhibitors as neoadjuvant and adjuvant therapy is a hot topic and several studies are underway.

RECENT FINDINGS

Ongoing studies are exploring the addition of CDK 4/6 inhibitors to endocrine therapy in early breast cancer.

SUMMARY

Identification of the optimal treatment combinations is the goal of current research. Finding biomarkers for patients' selection will be the goal of future research.

CDK4/6 inhibition triggers anti-tumour immunity

Cyclin-dependent kinases 4 and 6 (CDK4/6) are fundamental drivers of the cell cycle and are required for the initiation and progression of various malignancies^1,2. Pharmacologic inhibitors of CDK4/6 have shown significant activity against several solid tumors^3,4. Their primary mechanism of action is thought to be the inhibition of phosphorylation of the retinoblastoma (RB) tumor suppressor, inducing G1 cell cycle arrest in tumor cells⁵. Here, we use murine models of breast carcinoma and other solid tumors to show that selective CDK4/6 inhibitors not only induce tumor cell cycle arrest, but also promote anti-tumor immunity. We confirm this phenomenon through transcriptomic analysis of serial biopsies from a clinical trial of CDK4/6 inhibitor treatment for breast cancer. The enhanced anti-tumor immune response has two underpinnings. First, CDK4/6 inhibitors activate tumor cell expression of endogenous retroviral elements, thus increasing intracellular levels of double-stranded RNA. This in turn stimulates production of type III interferons and hence enhances tumor antigen presentation. Second, CDK4/6 inhibitors markedly suppress the proliferation of regulatory T cells (Tregs). Mechanistically, the effects of CDK4/6 inhibitors on both tumor cells and Tregs are associated with reduced activity of the E2F target, DNA methyltransferase 1. Ultimately, these events promote cytotoxic T cell-mediated clearance of tumor cells, which is further enhanced by the addition of immune checkpoint blockade. Our findings indicate that CDK4/6 inhibitors increase tumor immunogenicity and provide rationale for new combination regimens comprising CDK4/6 inhibitors and immunotherapies as anti-cancer treatment.

Loss of MutL Disrupts CHK2-Dependent Cell-Cycle Control through CDK4/6 to Promote Intrinsic Endocrine Therapy Resistance in Primary Breast Cancer

Significant endocrine therapy-resistant tumor proliferation is present in ≥20% of estrogen receptor-positive (ER⁺) primary breast cancers and is associated with disease recurrence and death. Here, we uncover a link between intrinsic endocrine therapy resistance and dysregulation of the MutL mismatch repair (MMR) complex (MLH1/3, PMS1/2), and demonstrate a direct role for MutL complex loss in resistance to all classes of endocrine therapy. We find that MutL deficiency in ER⁺ breast cancer abrogates CHK2-mediated inhibition of CDK4, a prerequisite for endocrine therapy responsiveness. Consequently, CDK4/6 inhibitors (CDK4/6i) remain effective in MutL-defective ER⁺ breast cancer cells. These observations are supported by data from a clinical trial where a CDK4/6i was found to strongly inhibit aromatase inhibitor-resistant proliferation of MutL-defective tumors. These data suggest that diagnostic markers of MutL deficiency could be used to direct adjuvant CDK4/6i to a population of patients with breast cancer who exhibit marked resistance to the current standard of care.Significance: MutL deficiency in a subset of ER⁺ primary tumors explains why CDK4/6 inhibition is effective against some de novo endocrine therapy-resistant tumors. Therefore, markers of MutL dysregulation could guide CDK4/6 inhibitor use in the adjuvant setting, where the risk benefit ratio for untargeted therapeutic intervention is narrow. Cancer Discov; 7(10); 1168-83. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1047.

Synergistic effect of eribulin and CDK inhibition for the treatment of triple negative breast cancer

Activation of CDK2 in triple negative breast cancer (TNBC) can contribute to non-canonical phosphorylation of a TGFβ signaling component, Smad3, promoting cell proliferation and migration. Inhibition of CDK2 was shown to decrease breast cancer oncogenesis. Eribulin chemotherapy was used effectively in the treatment of TNBC. To this end, we tested therapeutic efficacy of a novel CDK2/9 inhibitor, CYC065, eribulin, and the combination of CYC065 and eribulin in 3 different TNBC cell lines, and an in vivo xenograft model. Specifically, we characterized cell proliferation, apoptosis, migration, cell cycle associated protein expression, treatment-related transcription factor activity, and tumor growth in TNBC. Treatment with CYC065 and eribulin in combination had a superior effect on decreasing cell proliferation, inducing apoptosis, and inhibiting migration in TNBC cell lines in vitro. Combination therapy inhibited non-canonical Smad3 phosphorylation at the T179 site in the protein linker region, and resulted in increased p15 and decreased c-myc expression. In a transcription factor array, combination treatment significantly increased activity of AP1 and decreased activity of factors including NFκB, SP1, E2F, and SMAD3. In an in vivo xenograft model of TNBC, individual and combination treatments resulted in a decrease in both tumor volume and mitotic indices. Taken together, these studies highlight the potential of this novel drug combination, CYC065 and eribulin, to suppress the growth of TNBC cells in vitro and in vivo, warranting further clinical investigation.

De-escalating and escalating treatments for early-stage breast cancer: the St. Gallen International Expert Consensus Conference on the Primary Therapy of Early Breast Cancer 2017

The 15th St. Gallen International Breast Cancer Conference 2017 in Vienna, Austria reviewed substantial new evidence on loco-regional and systemic therapies for early breast cancer. Treatments were assessed in light of their intensity, duration and side-effects, seeking where appropriate to escalate or de-escalate therapies based on likely benefits as predicted by tumor stage and tumor biology. The Panel favored several interventions that may reduce surgical morbidity, including acceptance of 2 mm margins for DCIS, the resection of residual cancer (but not baseline extent of cancer) in women undergoing neoadjuvant therapy, acceptance of sentinel node biopsy following neoadjuvant treatment of many patients, and the preference for neoadjuvant therapy in HER2 positive and triple-negative, stage II and III breast cancer. The Panel favored escalating radiation therapy with regional nodal irradiation in high-risk patients, while encouraging omission of boost in low-risk patients. The Panel endorsed gene expression signatures that permit avoidance of chemotherapy in many patients with ER positive breast cancer. For women with higher risk tumors, the Panel escalated recommendations for adjuvant endocrine treatment to include ovarian suppression in premenopausal women, and extended therapy for postmenopausal women. However, low-risk patients can avoid these treatments. Finally, the Panel recommended bisphosphonate use in postmenopausal women to prevent breast cancer recurrence. The Panel recognized that recommendations are not intended for all patients, but rather to address the clinical needs of the majority of common presentations. Individualization of adjuvant therapy means adjusting to the tumor characteristics, patient comorbidities and preferences, and managing constraints of treatment cost and access that may affect care in both the developed and developing world.

Cyclin-dependent kinase 4/6 inhibitors in breast cancer: palbociclib, ribociclib, and abemaciclib

PURPOSE

The cyclin D-cyclin dependent kinase (CDK) 4/6-inhibitor of CDK4 (INK4)-retinoblastoma (Rb) pathway plays a crucial role in cell cycle progression and its dysregulation is an important contributor to endocrine therapy resistance. CDK4/6 inhibitors trigger cell cycle arrest in Rb protein (pRb)-competent cells. Recent years have seen the development of selective CDK4/6 inhibitors, which have delivered promising results of efficacy and manageable safety profiles. The main objective of this review is to discuss preclinical and clinical data to date, and ongoing clinical trials with palbociclib, ribociclib, and abemaciclib in breast cancer.

METHODS

A literature search of above topics was carried out using PubMed and data reported at international oncology meetings and clinicaltrials.gov were included.

RESULTS

The highly selective oral CDK4/6 inhibitors have been tested in combination with endocrine therapy in Phase III studies in metastatic breast cancer. Results led to the US Food and Drug Administration approval of palbociclib (PD0332991) and ribociclib (LEE011), and abemaciclib (LY2835219) is in development. Studies of these agents, in combination with endocrine therapy, are also underway in ER-positive early breast cancer in the neoadjuvant and adjuvant settings. Moreover, they are also being investigated with other agents in the advanced setting and in triple negative breast cancer.

CONCLUSIONS

After having demonstrated impressive activity in ER-positive, HER2-negative metastatic breast cancer, currently CDK4/6 inhibitors are in further development. It is obvious that this class of agents with their efficacy, low and easily manageable toxicity, and oral dosage is a very important treatment option for breast cancer patients.

Lessons in precision oncology from neoadjuvant endocrine therapy trials in ER+ breast cancer

For post-menopausal women with clinical stage II/III estrogen receptor positive (ER+) breast cancer neoadjuvant endocrine therapy (NET) is an under-utilized and low-toxicity alternative to chemotherapy for increasing breast conservation rates. Individual responses to endocrine therapy can also be used to tailor systemic treatment. The Preoperative Endocrine Prognostic Index (PEPI) was developed to identify patients at low risk of relapse after NET so that adjuvant chemotherapy can safely be avoided. In a recent validation study, patients with pathological stage 1 or 2A breast cancers with a Ki67 value of 2.7% or less in the surgical specimen (PEPI = 0) after 16-18 weeks of aromatase inhibitor therapy had a 97% disease free survival after 5.5 years of median follow up. Two approaches are currently underway to extend the PEPI model. The first is to determine whether fulvestrant increases the PEPI-0 rate versus anastrozole, as this would increase the number of patients who could be safely managed without adjuvant chemotherapy. The second is to develop new approaches for tumors that exhibit endocrine therapy resistance identified during NET. Preliminary studies demonstrate that tumors that exhibit AI resistant proliferation in the neoadjuvant setting is often sensitive to palbociclib, a CDK4/6 inhibitor. Serial Ki67 monitoring before surgery is therefore logical approach to tailored use of adjuvant CDK4/6i adjuvant treatment. Finally serial sampling of the tumor inherent in the PEPI approach facilitates the identification of new therapeutic targets, mechanisms of resistance and monitoring of tumor evolution in response to AI therapy.