Cyclin-dependent Kinases 4 And 6 Research Articles

Next generation selective estrogen receptor degraders in postmenopausal women with advanced-stage hormone receptors-positive, HER2-negative breast cancer

Breast cancer is the most prevalent malignancy in women, and is characterized by its heterogeneity; exhibiting various subgroups identifiable through molecular biomarkers that also serve as predictive indicators. More than two thirds of breast tumors are classified as luminal with positive hormone receptors (HR), indicating that cancer cells proliferation is promoted by hormones. Endocrine therapies play a vital role in the effective treatment of breast cancer by manipulating the signaling of estrogen receptors (ER), leading to a reduction in cell proliferation and growth rate. Selective estrogen receptor modulators (SERMs), such as tamoxifen and toremifene, function by blocking estrogen’s effects. Aromatase inhibitors (AI), including anastrozole, letrozole and exemestane, suppress estrogen production. On the other hand, selective estrogen receptor degraders (SERDs), like fulvestrant, act by blocking and damaging estrogen receptors. Tamoxifen and AI are widely used both in early- and advanced-stage disease, while fulvestrant is used as a single agent or in combination with other agents like the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors (palbociclib, abemaciclib, ribociclib) or alpelisib for advanced-stage disease. Currently, SERDs are recognized as an effective therapeutic approach for the treatment of ER-positive breast cancer, showing proficiency in reducing and blocking ER signaling. This review aims to outline the ongoing development of novel oral SERDs from a practical therapeutic perspective, enhancing our understanding of the mechanisms of action underlying these compounds.

Real-world effectiveness of CDK4/6 inhibitors on patients with HR+/HER2– advanced breast cancer in South Korea, focusing on underrepresented patients

Objective We assessed the real-world effectiveness of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors as first-line treatments in postmenopausal patients with HR+/HER2− advanced breast cancer, focusing on younger (<45 years) and older (>78 years) populations not considered in clinical trials. Methods We analyzed nationwide claims data from the Health Insurance Review and Assessment Service between November 2016 and February 2021. In this retrospective cohort study, patients using CDK4/6 inhibitors and aromatase inhibitors were selected and grouped by age as follows: 45–78 years (trial-enrolled), <45 years (younger), and >78 years (older). We estimated the median real-world progression-free survival (rwPFS) and overall survival (OS) using the Kaplan-Meier method. We conducted Cox regression analysis using a sub-distribution hazard model to evaluate risk factors (age, history of prior systemic treatment, presence of metastasis, comorbidity index, and type of provider) and estimated hazard ratios (HR). Results Among the 2,830 patients who received CDK4/6 inhibitors as first-line therapy, we identified 358 (12.65%) younger and 148 (5.23%) older underrepresented patients. The younger patient group (50.84%) had the highest rate of prior systemic therapy, followed by the trial-enrolled (25.39%) and older patient groups (8.11%). The median rwPFS was shorter in the older group (19.30 months) than those in the younger and the trial-enrolled age groups (30.33 and 34.53 months, respectively; p = .002). The HR of older age for death was 1.59 (95% confidence interval (CI) = 1.24–2.03). For rwPFS, the HR of prior systemic therapy was 1.19 (95% CI = 1.04–1.37). Conclusions The younger age group, which was underrepresented in the trial, did not show a significant difference in risk compared with the enrolled age group. However, the older age group, which was also underrepresented in the trial, faces a risk of mortality but not progression. Patients who fall outside the specified age groups for the clinical trial can still expect the same level of effectiveness in terms of progression.

Abstract PO2-04-09: Combination of the PLK1 Inhibitor Onvansertib and the PI3Kα Inhibitor Alpelisib Overcomes Palbociclib Resistance in PIK3CA-mutated HR+ Breast Cancer

Abstract In the 1st line setting of hormone receptor-positive HER2 negative (HR+/HER2-) metastatic breast cancer, cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors (palbociclib, abemaciclib and ribociclib) are typically used in combination with endocrine therapy. Though initially effective, acquired resistance to either CDK4/6 inhibitors or endocrine therapy eventually leads to disease relapse in most patients. Activating mutations in PIK3CA, the gene encoding alpha catalytic subunit of phosphatidylinositol-4,5-bisphosphat 3-kinase (PI3K) are found in approximately 40% of HR+ breast cancer patients and have been implicated in mediating resistance to CDK4/6 inhibitors. The PI3Kα inhibitor alpelisib is currently approved for PI3KCA-mutant HR+ breast cancer after progression on CDK4/6 inhibitors. However, drug-associated resistance mechanisms may limit its clinical benefit. Synergistic combination therapies have the potential to improve efficacy and overcome resistance mechanisms. Polo-like kinase 1 (PLK1) is a serine-threonine-protein kinase, key cell cycle regulator that controls G2/M entry and mitotic progression, and that has been shown to mediate resistance to palbociclib in HR+ breast cancer. Onvansertib is an oral and highly specific PLK1 inhibitor currently on clinical development in solid tumors and hematological malignancies. Here we evaluated the potential of onvansertib to increase the activity of alpelisib in PIK3CA-mutant HR+ breast cancer preclinical models. The combination of onvansertib and alpelisib synergistically inhibited cell viability and/or colony formation in three PI3KCA-mutant HR+ breast cancer cell lines, MCF-7 (PIK3CA E545K), EFM-19 (PIK3CA H1047L), and T-47D (PIK3CA 1047R). A significant increase in apoptosis was observed in cells treated with the combination compared to either agent alone. We next tested the combination of onvansertib and alpelisib in patient-derived xenograft (PDX) models. For this purpose, palbociclib-resistant PIK3CA-mutant HR+ breast cancer PDXs were established from primary breast tumor (PDX HBCx-86, PIK3CA E545K) or from metastatic bone biopsies of patients who had progressed on endocrine therapy plus palbociclib (HBCx-180, PIK3CA H1047R) or on PI3Kα inhibitor (HBCx-134palboR31, PIK3CA H1047R). PDX tumors were grafted subcutaneously in nude mice and mice were treated with vehicle, onvansertib (45 mg/kg, oral, 5 days a week), alpelisib (25mg/kg, oral, 5 days a week) or the combination. The combination was well tolerated and showed superior anti-tumor activity than the single agents in the 3 PDX models. In the HBCx-86 PDX, although none of the single agents showed activity, the combination induced potent tumor growth inhibition. In the metastasis-derived PDX HBCx-134palboR31, the combination treatment induced pronounced tumor regression in 62% of mice (5/8), with complete response in 25% (2/8), while mice treated with the single agents showed tumor progression. Finally, in the HBCx-180 PDX, established from a patient with primary resistance to palbociclib, the efficacy of the combination was greater and more durable, with significant survival advantage, compared to the monotherapies. Collectively, our preclinical findings suggest that co-targeting PLK1 and PI3Kα with onvansertib and alpelisib respectively, may constitute a promising therapeutic combination strategy for patients with PIK3CA-mutant HR+ breast cancer failing to respond to first-line standard of care therapies. Citation Format: Sreeja Sreekumar, Pierre Painsec, Davis Klein, Dalia Gonzalez, Laura Sourd, Elodie Montaudon, Tod Smeal, Elisabetta Marangoni, Maya Ridinger. Combination of the PLK1 Inhibitor Onvansertib and the PI3Kα Inhibitor Alpelisib Overcomes Palbociclib Resistance in PIK3CA-mutated HR+ Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-04-09.

Abstract PO5-24-01: Narazaciclib’s differential targets and kinase inhibitory activity contribute to the enhanced inhibition of tumor growth in preclinical models

Abstract Despite improvement of outcomes for HR+, HER2- metastatic breast cancer by cyclin dependent kinase 4 and 6 (CDK4/6) inhibitors, safety concerns and disease progression raise a critical need to identify novel approaches. Narazaciclib (ON123300), a novel CDK4/6i, designed to enhance efficacy and safety by its multi-targeted kinase inhibitor activity. Narazaciclib is in Ph I trials; NCT04739293 and CXHL1900340; studying different administration regimens and in endometrial cancer in combination with letrozole (NCT05705505). Our study explored the activity of narazaciclib and its metabolite ON1232580 in comparisons to the FDA approved CDK4/6i and identify additional targets engaged by narazaciclib. To identify direct and secondary targets engaged by narazaciclib and palbociclib, proteome wide Cellular Thermal Shift Assay (CETSA) and Integrative Inferred Kinase Activity (INKA) analysis were performed. Both CETSA and INKA analysis identified additional targets engaged by narazaciclib compared to palbociclib in both MDA-MB-231 lysates and intact cells such as BUB1, CHEK1, AURKA, GSK3α and GSK3β. In TNBC patients with BUB1 overexpression, bioinformatics analysis indicates a low survival correlation. Molecular docking data showed a higher affinity of narazaciclib with BUB1 compared to palbociclib and abemaciclib. The differential activity of narazaciclib was explored by using cohorts of human and mouse breast cancer cell lines and cell based assays. Comparison of narazaciclib’s in vitro IC50 profile to other CDK4/6i was studied against a panel of 370 kinases (HotSpot) and Kd values were determined by KINOMEscan. Intracellular IC50 kinase values were determined by NanoBret technology. Narazaciclib and abemaciclib were found to be the most promiscuous in vitro kinase inhibitors and ribociclib the most specific. Abemaciclib and narazaciclib had similar profiles against the CDK family members. Kd values of CDK4/cyclinD1 binding show similar trends; abemaciclib (0.08 nM), narazaciclib (0.18 nM), palbociclib (0.75 nM) and ribociclib (1.3 nM). Although narazaciclib displayed nM IC50 values in the in vitro assays against many CDKs, narazaciclib was very specific in cellular kinase assays with highest activity against CDK4/6, CSF1R and NUAK1. A stronger inhibition of cell proliferation, as well as induction of apoptosis and senescence were detected in narazaciclib and its metabolite ON1232580 treated PYMT cells, a murine mammary carcinoma model which recapitulates luminal BC subtype, compared to the other CDK4/6i. Both narazaciclib and ON1232580 enhanced CCL5 and CXCL10 mRNA levels, while a higher reduction of PD-L1 and pRb protein levels and a promoting effect on the H2D1 and B2M mRNA levels was shown in narazaciclib and its metabolite treated PYMT cells. Narazaciclib showed significant synergy with anti-PD1 in the EMT-6 syngeneic breast cancer model. A differential effect of narazaciclib on the expression levels of 62 cytokines was detected compared to abemaciclib and palbociclib. Lastly, inhibition of autophagy sensitizes cancer cells to both ON123300 and ON1232580, and induces irreversible cell proliferation inhibition, providing a novel therapeutic approach. Our findings identify important differences generated from assay models studying kinase inhibition, binding and pathway engagement. Understanding the role of the differential targets engaged by narazaciclib, the potential enhanced antitumor immunity and the sensitization by autophagy inhibitors to cell death, will guide future clinical studies. Citation Format: Petros Kechagioglou, Debomita Chakraborty, Camille Dupont, Hajime Yurugi, Ute Distler, Stefan Tenzer, Alexey Chernobrovkin, Kristina Riegel, Julianne Mooz, Mahil Lamber, Volker Dötsch, Stephen Cosenza, Steven Fruchtman, Krishnaraj Rajalingam. Narazaciclib’s differential targets and kinase inhibitory activity contribute to the enhanced inhibition of tumor growth in preclinical models [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-24-01.

Abstract PO3-04-10: Real-world progression-free survival and overall survival of palbociclib plus endocrine therapy in Japanese patients with HR+/HER2- ABC in the first- or second-line setting: A multicenter observational study

Abstract Introduction Palbociclib (PAL), a selective, oral inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), plus (+) endocrine therapy (ET) is standard therapy for the treatment of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) and was launched in December 2017 in Japan. Efficacy and safety of PAL + ET was shown by randomized clinical studies, PALOMA-2 and PALOMA-3. Further, recent large real-world studies, P-REALITY/P-REALITY X, confirmed effectiveness of PAL+ aromatase inhibitor (AI) for HR+/HER2- ABC in routine United States clinical practice. However, there is limited real-world evidence (RWE) for PAL in Japan. To strengthen the RWE of PAL+ET for HR+/HER2- ABC treatment under different clinical practice and healthcare system, we examine the real-world effectiveness of PAL + ET as 1st line (1L) and 2nd line (2L) treatment for HR+/HER2- ABC in Japan. Methods In this multicenter, observational study, patients with HR+/HER2- ABC, who initiated PAL + ET from 15 December 2017 to 31 December 2020 were enrolled. To reduce selection bias, all patients who started PAL during the above period were listed and their eligibility confirmed. Eligible patients had 1) diagnosis of HR+/HER2- ABC; 2) received PAL + ET as 1L or 2L treatment; 3) at least 6 months of follow up from start of PAL or died within that period. The 1L treatment was defined as the first systemic therapy received for ABC regardless of recurrence timing if receiving adjuvant treatment. The subsequent treatment after 1L treatment was defined as a 2L treatment. The primary endpoint was real-world progression-free survival (rwPFS) defined as the time from PAL+ET start to physician-documented disease progression or death due to any cause, whichever occurs first. Secondary endpoints included overall survival (OS), and chemotherapy-free survival (CFS). Results were stratified by treatment line (ie. 1L or 2L). rwPFS, OS, and CFS were analyzed with the Kaplan-Meier method (NCT05399329). Results In this study, 677 patients were enrolled. Among them, 419 (62%) patients and 258 (38%) patients received PAL + ET as 1L and 2L, respectively. The median age was 59.0 (range 29-87)　and 470 patients (69.8%) were postmenopausal. 49.0% patients had visceral involvement and 63.8% had a disease-free interval &amp;gt;24 months, defined as date of breast cancer surgery to the diagnosis date of recurrence, and 26.9% had de novo metastatic disease. The starting dose of PAL was 125 mg (89%), 100mg (9%), and 75mg (2%); dose reductions during the treatment period were required for 72% of patients. The most common ET combined with PAL was fulvestrant (FUL; 56.3% in 1L, 76.7% in 2L) followed by letrozole (LET; 37.9% in 1L, 16.3% in 2L). After a median follow-up of 36.2 months, the median rwPFS (95% CI) was 24.5 months (19.9-29.4) for 1L treatment and 14.5 months (10.2-18.3) for 2L treatment. Among the 604 patients initiating at 125 mg/day, the median rwPFS was 25.6 months (21.3-30.4) for 1L treatment and 14.3 months (9.7-18.3) for 2L treatment. Although median OS was not reached (NR) in 1L, median OS of 2L was 44.1 months (39.2 -NR). The 48-months OS rates for 1L and 2L treatment were 62.0% (55.4-67.9) and 48.4 % (40.4-55.9), respectively. The median CFS was 36.7 months (31.8-43.9) for 1L treatment and 23.8 months (20.5-27.3) for 2L treatment. Conclusions Our real-world data are consistent with findings form the PALOMA-2 and PALOMA-3 studies and those from RWE in routine United States clinical practice. FUL was the most commonly endocrine partner with PAL regardless of treatment lines. These observations add to the body of evidence supporting PAL effectiveness in clinical practice for Japanese ABC patients. Citation Format: Norikazu Masuda, Masaya Hattori, Tersuhiro Yoshinami, Takuho Okamura, Ken-ichi Watanabe, Takahiro Nakayama, Hiroko Masuda, Michiko Tsuneizumi, Daisuke Takabatake, Michiko Harao, Hiroshi Yoshino, Natsuko Mori, Hiroyuki Yasojima, Chiya Oshiro, Madoka Iwase, Miki Yamaguchi, Takafumi Sangai, Shinsuke Sasada, Takanori Ishida, Manabu Futamura, Nobuyoshi Kosaka, Yoshiyuki Shibasaki, Shigenori Nagai. Real-world progression-free survival and overall survival of palbociclib plus endocrine therapy in Japanese patients with HR+/HER2- ABC in the first- or second-line setting: A multicenter observational study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-04-10.

Economic assessment of abemaciclib for the adjuvant treatment of luminal HER2- breast cancer from the perspective of the Spanish health system.

Abemaciclib is an oral inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6). Data from the clinical trial monarchE (2023) showed improved survival from invasive disease. The aim of the present article was to conduct an economic assessment of adjuvant treatment with abemaciclib in women with luminal, HER2- and node-positive breast cancer. A Markov model was constructed with four mutually exclusive health states (disease-free, local recurrence, distal recurrence and death). Analyses were based on the clinical trial monarchE which compared an intervention group (abemaciclib + hormone therapy [HT]) with HT alone. The effectiveness measure used was quality-adjusted life years (QALY), with unit costs and utilities being obtained from existing literature. The incremental cost-utility ratio (ICUR) was used to compare the two treatment strategies. Total costs were €98,765 and €17,935 for the abemaciclib plus HT group and the HT alone group, respectively. The health outcome was 10.076QALY for the intervention group and 9.495QALY for the control group, with the ICUR being€139,173/QALY. Despite the significant gains of abemaciclib as adjuvant treatment in terms of progression-free survival, this treatment is not cost-effective for the Spanish National Health System at published prices. It may be cost-effective with an appropriate discount on the official price.

Differential synergistic effects of palbociclib and doxorubicin on doxorubicin-resistant cancer cells with diverse tumor origins

Palbociclib is a dual inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6). Palbociclib has frequently been studied in breast cancer cells and has also been linked to function of P-glycoprotein (P-gp), main protein responsible for cancer drug resistance. However, the effect of Palbociclib on cancer drug resistance and specifically doxorubicin-resistant cells overexpressing P-gp have limitedly been studied in the literature. Here, we aimed to decipher the possible synergistic effects of Palbociclib and Doxorubicin combination treatment in doxorubicin-resistant not only breast cancer, which has restrictedly been studied previously, but leukemia and cervical cancer cell lines in the presence of sensitive counterparts to totally explore the mechanistic properties of the Palbociclib in cancer drug resistance. Our results underlined that Palbociclib differentially displayed synergistic effect with doxorubicin in a cell type-specific manner and increased the efficacy of Doxorubicin in Doxorubicin-resistant cells. As a monotherapy, palbociclib has been shown to decrease the expression of MDR-1 in doxorubicin-resistant cells, and when used in combination with doxorubicin, it has been shown to increase the accumulation of doxorubicin in the cell and consequently induce apoptosis. This is the first report that proposes the Palbociclib as a candidate for combination therapy to limit the Doxorubicin resistance in different cancer origins in clinics.

Calcification-associated molecular traits and therapeutic strategies in hormone receptor-positive HER2-negative breast cancer.

Mammographic calcifications are a common feature of breast cancer, but their molecular characteristics and treatment implications in hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer remain unclear. We retrospectively collected mammography records of an HR+/HER2- breast cancer cohort (n = 316) with matched clinicopathological, genomic, transcriptomic, and metabolomic data. On the basis of mammographic images, we grouped tumors by calcification status into calcification-negative tumors, tumors with probably benign calcifications, tumors with calcification of low-moderate suspicion for maligancy and tumors with calcification of high suspicion for maligancy. We then explored the molecular characteristics associated with each calcification status across multiple dimensions. Among the different statuses, tumors with probably benign calcifications exhibited elevated hormone receptor immunohistochemical staining scores, estrogen receptor (ER) pathway activation, lipid metabolism, and sensitivity to endocrine therapy. Tumors with calcifications of high suspicion for malignancy had relatively larger tumor sizes, elevated lymph node metastasis incidence, Ki-67 staining scores, genomic instability, cell cycle pathway activation, and may benefit from cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors. Our research established links between tumor calcifications and molecular features, thus proposing potential precision treatment strategies for HR+/HER2- breast cancer.

Abstract 5871: Unveiling mechanisms of CDK4/6 inhibitor resistance in ER+ breast cancer models with acquired resistance

Abstract Introduction: Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, including palbociclib, ribociclib, and abemaciclib, have revolutionized the treatment of estrogen receptor-positive (ER+) breast cancer. However, the development of resistance to these inhibitors poses a formidable challenge in the clinical management of ER+ breast cancer. This study aims to explore the common resistance mechanisms in three CDK4/6 inhibitor-resistant models induced by chronic exposure to these agents. Methods: We developed models of resistance to palbociclib, ribociclib, and abemaciclib by repeatedly exposing murine xenografts to these CDK4/6 inhibitors. Resistance was confirmed through cell viability assays and in vivo tumorigenesis studies. The tumors were sequenced using NGS analyses, and genes of interest were validated through Western blotting and qPCR. Results: In all resistant models, we identified a common resistant mechanism via NGS analyses, which was characterized by the overexpression of the FAT1, CCNE1, and AR genes. The upregulation of these genes at mRNA and protein levels was confirmed by qPCR analyses and western blotting, respectively. Our data indicate that upregulation of FAT1, CCNE1, and AR genes may play a critical role in mediating resistance to CDK4/6 inhibitors, namely palbociclib, ribociclib, and abemaciclib. Conclusion: Our investigation uncovered a shared mechanism, characterized by the overexpression of FAT1, CCNE1, and AR genes, that underlay CDK4/6 inhibitors-induced drug resistance in ER+ breast cancer. These findings shed light on the shared pathways that drive CDK4/6 inhibitor resistance and provide insights into potential therapeutic targets for overcoming this resistance in breast cancer patients. Understanding these mechanisms is crucial for the development of more effective treatment strategies for CDK4/6 inhibitor-resistant cancers. Citation Format: Bin Li, Gaoxiang Liu, Ting Ni, Wenting Shi, Qingyang Gu. Unveiling mechanisms of CDK4/6 inhibitor resistance in ER+ breast cancer models with acquired resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5871.

A Signal-finding Study of Abemaciclib in Heavily Pretreated Patients with Metastatic Castration-Resistant Prostate Cancer: Results from CYCLONE 1.

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors radically changed the treatment paradigm for breast cancer. Similar to estrogen receptor in breast cancer, androgen receptor signaling activates cyclin D-CDK4/6, driving proliferation and resistance to hormonal manipulation in prostate cancer. This study was designed to detect signals of clinical activity for abemaciclib in treatment-refractory metastatic castration-resistant prostate cancer (mCRPC). Eligible patients had progressive mCRPC, measurable disease, and previously received ≥1 novel hormonal agent(s) and 2 lines of taxane chemotherapy. Abemaciclib 200 mg BID was administered on a continuous dosing schedule. Primary endpoint was objective response rate (ORR) without concurrent bone progression. This study was designed to detect a minimum ORR of 12.5%. At trial entry, forty (90.9%) of 44 patients had objective radiographic disease progression, four (9.1%) had prostate-specific antigen (PSA)-only progression, and 20 (46.5%) had visceral metastases (of these, 60% had liver metastases). Efficacy analyses are as follows: ORR without concurrent bone progression: 6.8%; disease control rate: 45.5%; median time to PSA progression: 6.5 months (95% CI: 3.2, NA); median radiographic PFS; 2.7 months (95% CI: 1.9, 3.7); and median OS: 8.4 months (95% CI: 5.6, 12.7). Most frequent grade ≥3 TEAEs were neutropenia (25.0%), anemia, and fatigue (11.4% each). No grade 4 or 5 AEs were related to abemaciclib. Abemaciclib monotherapy was well tolerated and showed clinical activity in this heavily pretreated population, nearly half with visceral metastases. This study is considered preliminary proof-of-concept and designates CDK4/6 as a valid therapeutic target in prostate cancer.

Ribociclib leverages phosphodiesterase 4 inhibition in the treatment of neutrophilic inflammation and acute respiratory distress syndrome

IntroductionOverwhelming neutrophil activation and oxidative stress significantly contribute to acute respiratory distress syndrome (ARDS) pathogenesis. However, the potential of repurposing ribociclib, a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor used clinically in cancer treatment, for treating neutrophilic ARDS remains uncertain. This study illustrated the ability and underlying mechanism of ribociclib for treating ARDS and neutrophilic inflammation. MethodsPrimary human neutrophils were used to determine the therapeutic effects of ribociclib on respiratory bursts, chemotactic responses, and inflammatory signaling. In vitro and silico analyses were performed to determine the underlying molecular mechanisms. The potential of ribociclib repurposing was evaluated using an in vivo ARDS model in lipopolysaccharide (LPS)-primed mice. ResultsWe found that treatment using ribociclib markedly limited overabundant oxidative stress (reactive oxygen species [ROS]) production and chemotactic responses (integrin levels and adhesion) in activated human neutrophils. Ribociclib was also shown to act as a selective inhibitor of phosphodiesterase 4 (PDE4), thereby promoting the cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway, leading to the inhibition of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) phosphorylation, and calcium influx. Notably, prophylactic administration and post-treatment with ribociclib ameliorated neutrophil infiltration, lung inflammation, accumulation of oxidative stress, pulmonary destruction, and mortality in mice with LPS-induced ARDS. ConclusionWe demonstrated for the first time that ribociclib serves as a novel PDE4 inhibitor for treating neutrophilic inflammation and ARDS. The repurposing ribociclib and targeting neutrophilic PDE4 offer a potential off-label alternative for treating lung lesions and other inflammatory conditions.

Recent progress of CDK4/6 inhibitors' current practice in breast cancer.

Dysregulated cellular proliferation represents a hallmark feature across all cancers. Aberrant activation of the cyclin-dependent kinase 4 and 6 (CDK4/6) pathway, independent of mitogenic signaling, engenders uncontrolled breast cancer cell proliferation. Consequently, the advent of CDK4/6 inhibition has constituted a pivotal milestone in the realm of targeted breast cancer therapy. The combination of CDK4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) has emerged as the foremost therapeutic modality for patients afflicted with hormone receptor-positive (HR + )/HER2-negative (HER2-) advanced breast cancer. At present, the Food and Drug Administration (FDA) has sanctioned various CDK4/6i for employment as the primary treatment regimen in HR + /HER2- breast cancer. This therapeutic approach has demonstrated a substantial extension of progression-free survival (PFS), often amounting to several months, when administered alongside endocrine therapy. Within this comprehensive review, we systematically evaluate the utilization strategies of CDK4/6i across various subpopulations of breast cancer and explore potential therapeutic avenues following disease progression during application of CDK4/6i therapy.

Targeted Liposomes Sensitize Plastic Melanoma to Ferroptosis via Senescence Induction and Coenzyme Depletion.

Ferroptotic cancer therapy has been extensively investigated since the genesis of the ferroptosis concept. However, the therapeutic efficacy of ferroptosis induction in heterogeneous and plastic melanoma has been compromised, because the melanocytic and transitory cell subpopulation is resistant to iron-dependent oxidative stress. Here, we report a phenotype-altering liposomal nanomedicine to enable the ferroptosis-resistant subtypes of melanoma cells vulnerable to lipid peroxidation via senescence induction. The strategy involves the ratiometric coencapsulation of a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor (palbociclib) and a ferroptosis inducer (auranofin) within cRGD peptide-modified targeted liposomes. The two drugs showed a synergistic anticancer effect in the model B16F10 melanoma cells, as evidenced by the combination index analysis (<1). The liposomes could efficiently deliver both drugs into B16F10 cells in a targeted manner. Afterward, the liposomes potently induced the intracellular redox imbalance and lipid peroxidation. Palbociclib significantly provoked cell cycle arrest at the G0/G1 phase, which sensitized auranofin-caused ferroptosis through senescence induction. Meanwhile, palbociclib depleted intracellular glutathione (GSH) and reduced nicotinamide adenine dinucleotide phosphate (NADPH), further boosting ferroptosis. The proof-of-concept was also demonstrated in the B16F10 tumor-bearing mice model. The current work offers a promising ferroptosis-targeting strategy for effectively treating heterogeneous melanoma by manipulating the cellular plasticity.

Sacituzumab Govitecan (Trodelvy)

&#x0D; CADTH recommends that Trodelvy should be reimbursed by public drug plans for the treatment of adult patients with unresectable locally advanced or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative (IHC 0, IHC 1+, or IHC 2+/ISH–) breast cancer who have received endocrine-based therapy and at least 2 additional systemic therapies in the metastatic setting, if certain conditions are met.&#x0D; Trodelvy should only be covered to treat adult patients with unresectable locally advanced or metastatic HR-positive, HER2-negative breast cancer who have been previously treated with at least 1 taxane, at least 1 prior anticancer hormonal treatment, and at least 1 cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor in any setting, have experienced treatment failure after 2 to 4 prior systemic chemotherapy regimens for metastatic disease, and have good performance status.&#x0D; Trodelvy should only be reimbursed if it is prescribed by clinicians with expertise and experience in treating breast cancer in approved centres, and if the price of Trodelvy is reduced.&#x0D;

Palbociclib-associated nephrotoxicity in a patient with breast cancer

A patient with advanced breast cancer developed acute kidney injury and generalized renal tubular dysfunction manifested as Fanconi syndrome and distal renal tubular acidosis after treatment with palbociclib, a cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitor. A kidney biopsy showed acute tubular injury characterized by dilated tubular lumens, flattened epithelium, and loss of brush borders, with no significant interstitial fibrosis. This case illustrates the importance of close and long-term follow-up of kidney function and electrolyte levels after the initiation of a CDK4/6 inhibitor.

CDK4/6 inhibitors in lung cancer: current practice and future directions.

Lung cancer is the leading cause of cancer-related deaths worldwide, and ∼85% of lung cancers are classified as nonsmall cell lung cancer (NSCLC). These malignancies can proliferate indefinitely, in part due to dysregulation of the cell cycle and the resulting abnormal cell growth. The specific activation of cyclin-dependent kinases 4 and 6 (CDK4/6) is closely linked to tumour proliferation. Approximately 80% of human tumours exhibit abnormalities in the cyclin D-CDK4/6-INK4-RB pathway. Specifically, CDK4/6 inhibitors either as monotherapy or combination therapy have been investigated in pre-clinical and clinical studies for the treatment of NSCLC, and promising results have been achieved. This review article focuses on research regarding the use of CDK4/6 inhibitors in NSCLC, including the characteristics and mechanisms of action of approved drugs and progress of pre-clinical and clinical research.

Use of Pharmacokinetic and Pharmacodynamic Data to Develop the CDK4/6 Inhibitor Ribociclib for Patients with Advanced Breast Cancer.

Ribociclib is an orally bioavailable, selective cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor. CDK4/6inhibition by ribociclib leads to retinoblastoma tumor suppressor protein (Rb) reactivation, thereby restoring Rb-mediated cell cycle arrest. Ribociclib is approved for the treatment of patients with hormone receptor-positive/human epidermal growth factor receptor-2-negative (HR+/HER2-) advanced breast cancer (ABC), at the dose of 600mg once daily (QD) during cycles of 21days on/7days off, with optional dose reduction to 400 mgand 200mg. Ribociclib is rapidly absorbed with a median time to reach maximum plasma concentration of 2.4h, mean half-life of 32.0h and oral bioavailability of 65.8% at 600mg. It is eliminated mainly by hepatic metabolism (~84% of total elimination), mostly by cytochrome P450 (CYP) 3A4. Age, body weight, race, baseline Eastern Cooperative Oncology Group status, food, mild hepatic impairment, mild-to-moderate renal impairment, proton pump inhibitors, and combination partners (non-steroidal aromatase inhibitors or fulvestrant) have no clinically relevant impact on ribociclib exposure. Ribociclib inhibits CYP3A at 600mg leading to increased exposure of CYP3A substrates. Strong CYP3A inhibitors or inducers increase or decrease, respectively, ribociclib exposure. Exposure-safety and exposure-efficacy analyses support the clinical benefit of the 600mg QD starting dose, with potential individualized dose reductions to 400 mgand 200mg for effective management of the adverse events neutropenia and QTcF interval prolongation, while maintaining efficacy, in patients with HR+/HER2- ABC. Overall, these clinical pharmacology data informed ribociclib dose justification and clinical development, as well as its prescribing information for clinical use in advanced breast cancer patients.

A network meta-analysis of efficacy and safety for first-line and second/further-line therapies in postmenopausal women with hormone receptor-positive, HER2-negative, advanced breast cancer

BackgroundHormone receptor-positive/human epidermal growth factor receptor 2-negative (HR + /HER2 −) advanced breast cancer is a prevalent subtype among postmenopausal women. Despite the growing number of randomized clinical trials (RCTs) exploring this topic, the efficacy and safety of first-line and second/further-line treatments remain uncertain. Accordingly, our aim was to conduct a comprehensive evaluation of the efficacy and safety of these therapies through network meta-analysis.MethodsRCTs were identified by searching Pubmed, Embase, and major cancer conferences. The efficacy of interventions was assessed using the hazard ratios (HRs) of progression-free survival (PFS) and overall survival (OS), while safety was indicated by the incidence of any grade adverse events (AEs), grade 3–5 AEs, AEs leading to treatment discontinuation, and AEs leading to death. Both time-variant HRs fractional polynomial models and time-invariant HRs Cox-proportional hazards models were considered for handling time-to-event data. Safety indicators were analyzed using Bayesian network meta-analysis. Additionally, subgroup analyses were conducted based on patient characteristics.ResultsA total of 41 RCTs (first-line 17, second/further-lines 27) were included in the analysis. For first-line treatment, the addition of Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors to endocrine therapy significantly improved therapeutic efficacy in terms of both PFS and OS, demonstrating the best performance across all mechanisms. Specifically, the combination of Abemaciclib and Letrozole demonstrated the most favorable performance in terms of PFS, while Ribociclib plus Fulvestrant yielded the best outcomes in OS. Incorporating the immune checkpoint inhibitor Avelumab into the regimen with CDK4/6 inhibitors and selective estrogen receptor degraders significantly enhanced both PFS and OS in second-line or later treatments. Regarding safety, endocrine monotherapy performed well. Regarding safety, endocrine monotherapy performed well. There is mounting evidence suggesting that most CDK4/6 inhibitors may demonstrate poorer performance with respect to hematologic AEs. However, additional evidence is required to further substantiate these findings.ConclusionsCDK4/6 inhibitors, combined with endocrine therapy, are pivotal in first-line treatment due to their superior efficacy and manageable AEs. For second/further-line treatment, adding immune checkpoint inhibitors to CDK4/6 inhibitors plus endocrine therapy may produce promising results. However, to reduce the results’ uncertainty, further trials comparing these novel treatments are warranted.Trial registrationRegistration number: PROSPERO (CRD42022377431).

Enhancing immunogenic responses through CDK4/6 and HIF2α inhibition in Merkel cell carcinoma

Approximately 50% of Merkel cell carcinoma (MCC) patients facing this highly aggressive skin cancer initially respond positively to PD-1-based immunotherapy. Nevertheless, the recurrence of MCC post-immunotherapy emphasizes the pressing need for more effective treatments. Recent research has highlighted Cyclin-dependent kinases 4 and 6 (CDK4/6) as pivotal cell cycle regulators gaining prominence in cancer studies. This study reveals that the CDK4/6 inhibitor, palbociclib can enhance PD-L1 gene transcription and surface expression in MCC cells by activating HIF2α. Inhibiting HIF2α with TC-S7009 effectively counteracts palbociclib-induced PD-L1 transcription and significantly intensifies cell death in MCC. Simultaneously, co-targeting CDK4/6 and HIF2α boosts ROS levels while suppressing SLC7A11, a key regulator of cellular redox balance, promoting ferroptosis- a form of immunogenic cell death linked to iron. Considering the rising importance of immunogenic cell death in immunotherapy, this strategy holds promise for improving future MCC treatments, markedly increasing immunogenic cell death across various MCC cell lines, thus advancing cancer immunotherapy.

ERK hyperactivation serves as a unified mechanism of escape in intrinsic and acquired CDK4/6 inhibitor resistance in acral lentiginous melanoma.

Patients with metastatic acral lentiginous melanoma (ALM) suffer worse outcomes relative to patients with other forms of cutaneous melanoma (CM), and do not benefit as well to approved melanoma therapies. Identification of cyclin-dependent kinase 4 and 6 (CDK4/6) pathway gene alterations in >60% of ALMs has led to clinical trials of the CDK4/6 inhibitor (CDK4i/6i) palbociclib for ALM; however, median progression free survival with CDK4i/6i treatment was only 2.2 months, suggesting existence of resistance mechanisms. Therapy resistance in ALM remains poorly understood; here we report hyperactivation of MAPK signaling and elevated cyclin D1 expression serve as a mechanism of intrinsic early/adaptive CDK4i/6i resistance. ALM cells that have acquired CDK4i/6i resistance following chronic treatment exposure also exhibit hyperactivation of the MAPK pathway. MEK and/or ERK inhibition increases CDK4i/6i efficacy against therapy naïve and CDK4i/6i-resistant AM cells in xenograft and patient-derived xenograft (PDX) models and promotes a defective DNA repair, cell cycle arrested and apoptotic program. Notably, gene alterations poorly correlate with protein expression of cell cycle proteins in ALM or efficacy of CDK4i/6i, urging additional strategies when stratifying patients for CDK4i/6i trial inclusion. Concurrent targeting of the MAPK pathway and CDK4/6 represents a new approach for patients with metastatic ALM to improve outcomes.