Transient CDK4/6 inhibition protects hematopoietic stem cells from chemotherapy-induced exhaustion

Co-delivery of protopanaxatriol/icariin into niche cells restores bone marrow niches to rejuvenate HSCs for chemotherapy-induced myelosuppression

BACKGROUND

Up to 80 % of chemotherapeutic drugs induce myelosuppression in patients. Chemotherapy not only impairs of hematopoietic stem cells (HSCs) but also damages bone marrow niches (vascular and endosteal). Current treatments for myelosuppression overlook these chemotherapy-induced damages to bone marrow niches and the critical role of niche restoration on hematopoietic regeneration. Ginsenoside protopanaxatriol (PPT) protects vascular endothelium from injury, while icariin (ICA) promotes osteogenic differentiation. The combination of PPT and ICA aims to restore damaged vascular and endosteal niches, thus rejuvenating HSCs for treating myelosuppression.

PURPOSE

This study aims to develop effective, bone marrow niche-directed PPT/ICA therapies for treating chemotherapy-induced myelosuppression.

METHODS

3D cell spheroids were used to investigate the effects of PPT/ICA on cell-cell interactions in vascular niches, osteogenesis, and extracellular matrix (ECM) secretion in endosteal niches. In vitro mimic niche models were designed to access the drug combination's efficacy in rejuvenating and mobilizing in HSCs within bone marrow niches. The delivery capability of PPT/ICA to key niche cell types (mesenchymal stromal cells (MSCs), endothelial cells (ECs), and osteoblasts (OBs)) via nanocarriers has been determined. DSS6 peptide-modified nanoparticles (DSS6-NPs) were prepared for specific co-delivery of PPT/ICA into key niche cell populations in vivo.

RESULTS

PPT can prevent vascular niche injury by restoring vascular EC cell-cell adhesion and the intercellular interactions between ECs and MSCs in 5-fluorouracil (5-FU)-damaged cell spheroids. ICA repaired 5-FU-damaged endosteal niches by promoting osteogenesis and ECM secretion. The combination of PPT and ICA restores key HSC niche factor gene expressions, normalizing HSC differentiation and mobilization. The in vitro cellular uptake efficiency of nanocarriers in a mimic niche is positively correlated with their in vivo delivery into bone marrow niche cells. DSS6-NPs greatly enhance the delivery of PPT/ICA into MSCs and OBs within bone marrow niches. Co-loading of PPT/ICA into DSS6-NPs effectively repairs damaged bone marrow niches and promotes HSC rejuvenation in vivo.

CONCLUSION

The combination of PPT and ICA effectively prevents injury to the vascular and endosteal niches, thereby promoting hematopoietic regeneration in the bone marrow. This study provides novel niche-directed PPT/ICA therapies for managing chemotherapy-induced myelosuppression.

Trilaciclib dosage in Chinese patients with extensive-stage small cell lung cancer: a pooled pharmacometrics analysis

This study aimed to analyze potential ethnic disparities in the dose-exposure-response relationships of trilaciclib, a first-in-class intravenous cyclin-dependent kinase 4/6 inhibitor for treating chemotherapy-induced myelosuppression in patients with extensive-stage small cell lung cancer (ES-SCLC). This investigation focused on characterizing these relationships in both Chinese and non-Chinese patients to further refine the dosing regimen for trilaciclib in Chinese patients with ES-SCLC. Population pharmacokinetic (PopPK) and exposure-response (E-R) analyses were conducted using pooled data from four randomized phase 2/3 trials involving Chinese and non-Chinese patients with ES-SCLC. PopPK analysis revealed that trilaciclib clearance in Chinese patients was approximately 17% higher than that in non-Chinese patients with ES-SCLC. Sex and body surface area influenced trilaciclib pharmacokinetics in both populations but did not exert a significant clinical impact. E-R analysis demonstrated that trilaciclib exposure increased with a dosage escalation from 200 to 280 mg/m2, without notable changes in myeloprotective or antitumor efficacy. However, the incidence of infusion site reactions, headaches, and phlebitis/thrombophlebitis rose with increasing trilaciclib exposure in both Chinese and non-Chinese patients with ES-SCLC. These findings suggest no substantial ethnic disparities in the dose-exposure-response relationship between Chinese and non-Chinese patients. They support the adoption of a 240-mg/m2 intravenous 3-day or 5-day dosing regimen for trilaciclib in Chinese patients with ES-SCLC.

A live single-cell reporter system reveals drug-induced plasticity of a cancer stem cell-like population in cholangiocarcinoma

Cancer stem cells (CSC) play an important role in carcinogenesis and are acknowledged to be responsible for chemoresistance in cholangiocarcinoma (CCA). Studying CCA CSC has been challenging, due to lack of consensus CSC markers, and to their plastic nature. Since dual expression of the core pluripotent factors SOX2/OCT4 has been shown to correlate with poor outcome in CCA patients, we selected the SOX2/OCT4 activating short half-life GFP-based live reporter (SORE6-dsCopGFP) to study CSC dynamics at the single-cell level. Transduction of five human CCA cell lines resulted in the expression of 1.8-13.1% GFP-positive (SORE6POS) cells. By live imaging, we found that SORE6POS CCA cells possess self-renewal capacity and that they can be induced to differentiate. Significantly, the SORE6POS cells were highly tumorigenic, both in vitro and in vivo, thus implicating the characteristics of primary CSCs. When we then analyzed for selected CSC-related markers, we found that the majority of both CD133+/CD44+, and CD133+/LGR5+ CCA cells were SORE6POS cells. Exposing transduced cells to standard CCA chemotherapy revealed higher growth rate inhibition at 50% (GR50s) for SORE6POS cells compared to GFP-negative (SORE6NEG) ones indicating that these CSC-like cells were more resistant to the treatment. Moreover, the chemotherapy induced SORE6POS from SORE6NEG cells, while retaining the existing SORE6POS population. Finally, treatment of transduced cells with CDK4/6 inhibitors in vitro for 3 days resulted in a lowered CSC number in the culture. Thus, applying a live reporter system allowed us to elucidate the stem cell diversity and drug-induced plasticity of CCA CSCs. These findings have clear implications for future management of such patients.

Trilaciclib use in extensive-stage small cell lung cancer (ES-SCLC): are clinical benefits seen in the real-world setting?

BACKGROUND

Trilaciclib, in comparison to placebo plus carboplatin, etoposide, ± atezolizumab (PEA), has shown significant reductions in incidence of severe neutropenia (SN) among patients with extensive-stage small cell lung cancer (ES-SCLC). Despite these findings, real-world utility remains limited.

METHODS

A single-center quasi-experimental study compared trilaciclib + PEA (PEAT) versus PEA in ES-SCLC patients. The study period ranged from April 1, 2021 to July 31, 2022, for the PEAT recipients and February 1, 2020, to February 28, 2021, for PEA recipients. The primary endpoint evaluated was incidence of SN after cycle 1 and during the treatment period. Secondary endpoints included measures related to myelopreservation and patient outcomes.

RESULTS

Among 34 PEAT and 44 PEA patients, baseline characteristics were similar, except for a higher median age (69 vs 64 years) and more males (64.7% vs 38.6%) in the PEAT cohort. The PEAT cohort exhibited a lower SN rate (3%) versus the PEA cohort (18%), with statistical significance demonstrated on multivariate analysis (p = 0.015). Additionally, the PEAT cohort also demonstrated significant reductions in red blood cell transfusion requirements (3% vs 23%; p = 0.02), grade 3-4 anemia (6% vs 25%; p = 0.03), and grade 3-4 thrombocytopenia (0% vs 11%, p = 0.045).

CONCLUSION

Trilaciclib, in combination with PEA, demonstrated an improvement in the safety profile without compromising survival outcomes in ES-SCLC patients. These findings underscore the potential benefits of incorporating trilaciclib in real-world clinical settings for enhanced patient care.

miR-29 is an important driver of aging-related phenotypes

Aging is a consequence of complex molecular changes, but whether a single microRNA (miRNA) can drive aging remains unclear. A miRNA known to be upregulated during both normal and premature aging is miR-29. We find miR-29 to also be among the top miRNAs predicted to drive aging-related gene expression changes. We show that partial loss of miR-29 extends the lifespan of Zmpste24-/- mice, an established model of progeria, indicating that miR-29 is functionally important in this accelerated aging model. To examine whether miR-29 alone is sufficient to promote aging-related phenotypes, we generated mice in which miR-29 can be conditionally overexpressed (miR-29TG). miR-29 overexpression is sufficient to drive many aging-related phenotypes and led to early lethality. Transcriptomic analysis of both young miR-29TG and old WT mice reveals shared downregulation of genes associated with extracellular matrix organization and fatty acid metabolism, and shared upregulation of genes in pathways linked to inflammation. These results highlight the functional importance of miR-29 in controlling a gene expression program that drives aging-related phenotypes.

Small cell lung cancer: emerging subtypes, signaling pathways, and therapeutic vulnerabilities

Small cell lung cancer (SCLC) is a recalcitrant cancer characterized by early metastasis, rapid tumor growth and poor prognosis. In recent decades, the epidemiology, initiation and mutation characteristics of SCLC, as well as abnormal signaling pathways contributing to its progression, have been widely studied. Despite extensive investigation, fewer drugs have been approved for SCLC. Recent advancements in multi-omics studies have revealed diverse classifications of SCLC that are featured by distinct characteristics and therapeutic vulnerabilities. With the accumulation of SCLC samples, different subtypes of SCLC and specific treatments for these subtypes were further explored. The identification of different molecular subtypes has opened up novel avenues for the treatment of SCLC; however, the inconsistent and uncertain classification of SCLC has hindered the translation from basic research to clinical applications. Therefore, a comprehensives review is essential to conclude these emerging subtypes and related drugs targeting specific therapeutic vulnerabilities within abnormal signaling pathways. In this current review, we summarized the epidemiology, risk factors, mutation characteristics of and classification, related molecular pathways and treatments for SCLC. We hope that this review will facilitate the translation of molecular subtyping of SCLC from theory to clinical application.

Effect of Hepatic Impairment on Trilaciclib Pharmacokinetics

Trilaciclib is a first-in-class, intravenous cyclin-dependent kinase 4 and 6 inhibitor approved for reducing the incidence of chemotherapy-induced myelosuppression in adult patients with extensive-stage small cell lung cancer receiving a platinum/etoposide-containing or topotecan-containing regimen. No dose adjustment is recommended for participants with mild hepatic impairment (HI) based on previous population pharmacokinetic (PK) analysis. This open-label, parallel-group study examined the impact of moderate and severe HI on the PK of trilaciclib. The study employed a reduced study design. Participants with moderate (Child-Pugh B, n = 8) and severe (Child-Pugh C, n = 5) HI and matched healthy controls (n = 11) received a single intravenous dose of trilaciclib 100 mg/m2. The unbound fraction of trilaciclib was comparable between the HI groups and the matched healthy control group. The unbound trilaciclib extent of exposure (i.e., area under the concentration-time curve) in participants with moderate and severe HI was ∼40% and ∼60% higher, respectively, compared with healthy matched controls based on Child-Pugh classification. Ad hoc analysis using National Cancer Institute classification showed similar results. The US Food and Drug Administration-approved trilaciclib dose of 240 mg/m2 should be reduced by ∼30%, to 170 mg/m2, for patients with moderate or severe HI.

Strategy of combining CDK4/6 inhibitors with other therapies and mechanisms of resistance

Cell cycle-dependent protein kinase 4/6 (CDK4/6) is a crucial kinase that regulates the cell cycle, essential for cell division and proliferation. Hence, combining CDK4/6 inhibitors with other anti-tumor drugs is a pivotal clinical strategy. This strategy can efficiently inhibit the growth and division of tumor cells, reduce the side effects, and improve the quality of life of patients by reducing the dosage of combined anticancer drugs. Furthermore, the combination therapy strategy of CDK4/6 inhibitors could ameliorate the drug resistance of combined drugs and overcome the CDK4/6 resistance caused by CDK4/6 inhibitors. Various tumor treatment strategies combined with CDK4/6 inhibitors have entered the clinical trial stage, demonstrating their substantial clinical potential. This study reviews the research progress of CDK4/6 inhibitors from 2018 to 2022, the related resistance mechanism of CDK4/6 inhibitors, and the strategy of combination medication.

Kinase-inactivated CDK6 preserves the long-term functionality of adult hematopoietic stem cells

ABSTRACT

Hematopoietic stem cells (HSCs) are characterized by the ability to self-renew and to replenish the hematopoietic system. The cell-cycle kinase cyclin-dependent kinase 6 (CDK6) regulates transcription, whereby it has both kinase-dependent and kinase-independent functions. Herein, we describe the complex role of CDK6, balancing quiescence, proliferation, self-renewal, and differentiation in activated HSCs. Mouse HSCs expressing kinase-inactivated CDK6 show enhanced long-term repopulation and homing, whereas HSCs lacking CDK6 have impaired functionality. The transcriptomes of basal and serially transplanted HSCs expressing kinase-inactivated CDK6 exhibit an expression pattern dominated by HSC quiescence and self-renewal, supporting a concept, in which myc-associated zinc finger protein (MAZ) and nuclear transcription factor Y subunit alpha (NFY-A) are critical CDK6 interactors. Pharmacologic kinase inhibition with a clinically used CDK4/6 inhibitor in murine and human HSCs validated our findings and resulted in increased repopulation capability and enhanced stemness. Our findings highlight a kinase-independent role of CDK6 in long-term HSC functionality. CDK6 kinase inhibition represents a possible strategy to improve HSC fitness.

CDK4/6 inhibitor abemaciclib combined with low-dose radiotherapy enhances the anti-tumor immune response to PD-1 blockade by inflaming the tumor microenvironment in Rb-deficient small cell lung cancer

Background

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors have shown significant activity against several solid tumors by reducing the phosphorylation of the canonical CDK4/6 substrate retinoblastoma (Rb) protein, while the anti-tumor effect of CDK4/6 inhibitors on Rb-deficient tumors is not clear. Most small cell lung cancers (SCLCs) are Rb-deficient and show very modest response to immune checkpoint blockade (ICB) despite recent advances in the use of immunotherapy. Here, we aimed to investigate the direct effect of CDK4/6 inhibition on SCLC cells and determine its efficacy in combination therapy for SCLC.

Methods

The immediate impact of CDK4/6 inhibitor abemaciclib on cell cycle, cell viability and apoptosis in four SCLC cell lines was initially checked. To explore the effect of abemaciclib on double-strand DNA (ds-DNA) damage induction and the combination impact of abemaciclib coupled with radiotherapy (RT), western blot, immunofluorescence (IF) and quantitative real-time polymerase chain reaction (qRT-PCR) were performed. An Rb-deficient immunocompetent murine SCLC model was established to evaluate efficacy of abemaciclib in combination therapy. Histological staining, flow cytometry analysis and RNA sequencing were performed to analyze alteration of infiltrating immune cells in tumor microenvironment (TME).

Results

Here, we demonstrated that abemaciclib induced increased ds-DNA damage in Rb-deficient SCLC cells. Combination of abemaciclib and RT induced more cytosolic ds-DNA, and activated the STING pathway synergistically. We further showed that combining low doses of abemaciclib with low-dose RT (LDRT) plus anti-programmed cell death protein-1 (anti-PD-1) antibody substantially potentiated CD8+ T cell infiltration and significantly inhibited tumor growth and prolonged survival in an Rb-deficient immunocompetent murine SCLC model.

Conclusions

Our results define previously uncertain DNA damage-inducing properties of CDK4/6 inhibitor abemaciclib in Rb-deficient SCLCs, and demonstrate that low doses of abemaciclib combined with LDRT inflame the TME and enhance the efficacy of anti-PD-1 immunotherapy in SCLC model, which represents a potential novel therapeutic strategy for SCLC.

The impact of myelosuppression on quality of life of patients treated with chemotherapy

Side effects from chemotherapy-induced myelosuppression can negatively affect patients' quality of life (QoL). Neutropenia increases infection risk, and anemia frequently results in debilitating fatigue. Additionally, the bleeding risk associated with thrombocytopenia can lead to fear and anxiety. However, traditional interventions for myelosuppression fall short of the ideal. Granulocyte colony-stimulating factors reduce the risk of severe neutropenia but commonly lead to bone pain. Erythropoiesis-stimulating agents are not always effective and may cause thromboembolic events, while transfusions to correct anemia/thrombocytopenia are associated with transfusion reactions and volume overload. Trilaciclib, which is approved for reducing myelosuppression in patients with extensive-stage small cell lung cancer, together with several investigational agents in development for managing myelosuppression have the potential to improve QoL for patients on chemotherapy.

Preclinical evaluation of CDK4 phosphorylation predicts high sensitivity of pleural mesotheliomas to CDK4/6 inhibition

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited therapeutic options. We evaluated the impact of CDK4/6 inhibition by palbociclib in 28 MPM cell lines including 19 patient-derived ones, using various approaches including RNA-sequencing. Palbociclib strongly and durably inhibited the proliferation of 23 cell lines, indicating a unique sensitivity of MPM to CDK4/6 inhibition. When observed, insensitivity to palbociclib was mostly explained by the lack of active T172-phosphorylated CDK4. This was associated with high p16INK4A (CDKN2A) levels that accompany RB1 defects or inactivation, or (unexpectedly) CCNE1 overexpression in the presence of wild-type RB1. Prolonged palbociclib treatment irreversibly inhibited proliferation despite re-induction of cell cycle genes upon drug washout. A senescence-associated secretory phenotype including various potentially immunogenic components was irreversibly induced. Phosphorylated CDK4 was detected in 80% of 47 MPMs indicating their sensitivity to CDK4/6 inhibitors. Its absence in some highly proliferative MPMs was linked to very high p16 (CDKN2A) expression, which was also observed in public datasets in tumours from short-survival patients. Our study supports the evaluation of CDK4/6 inhibitors for MPM treatment, in monotherapy or combination therapy.

The AsiDNA™ decoy mimicking DSBs protects the normal tissue from radiation toxicity through a DNA-PK/p53/p21-dependent G1/S arrest

AsiDNA™, a cholesterol-coupled oligonucleotide mimicking double-stranded DNA breaks, was developed to sensitize tumour cells to radio- and chemotherapy. This drug acts as a decoy hijacking the DNA damage response. Previous studies have demonstrated that standalone AsiDNA™ administration is well tolerated with no additional adverse effects when combined with chemo- and/or radiotherapy. The lack of normal tissue complication encouraged further examination into the role of AsiDNA™ in normal cells. This research demonstrates the radioprotective properties of AsiDNA™. In vitro, AsiDNA™ induces a DNA-PK/p53/p21-dependent G1/S arrest in normal epithelial cells and fibroblasts that is absent in p53 deficient and proficient tumour cells. This cell cycle arrest improved survival after irradiation only in p53 proficient normal cells. Combined administration of AsiDNA™ with conventional radiotherapy in mouse models of late and early radiation toxicity resulted in decreased onset of lung fibrosis and increased intestinal crypt survival. Similar results were observed following FLASH radiotherapy in standalone or combined with AsiDNA™. Mechanisms comparable to those identified in vitro were detected both in vivo, in the intestine and ex vivo, in precision cut lung slices. Collectively, the results suggest that AsiDNA™ can partially protect healthy tissues from radiation toxicity by triggering a G1/S arrest in normal cells.

Myeloprotection with trilaciclib in Chinese patients with extensive-stage small cell lung cancer receiving chemotherapy: Results from a randomized, double-blind, placebo-controlled phase III study (TRACES)

INTRODUCTION

Trilaciclib is a transient cyclin-dependent kinase 4/6 inhibitor that decreases the incidence of chemotherapy-induced myelosuppression in extensive-stage small cell lung cancer (ES-SCLC). TRACES study was designed to assess the safety, efficacy and pharmacokinetics (PK) of trilaciclib before chemotherapy in Chinese patients with ES-SCLC.

METHODS

The study included an open-label safety run-in part (Part 1) and double-blinded, placebo-controlled part (Part 2) where patients received trilaciclib or placebo before chemotherapy. Treatment-naïve or previously treated ES-SCLC patients received intravenous trilaciclib (240 mg/m2) or placebo before etoposide/carboplatin or topotecan, respectively. Primary endpoints were PK, safety and duration of severe neutropenia (DSN) in Cycle 1 in Part 1 and Part 2. Exploratory endpoints included the effect of trilaciclib on other myeloprotection endpoints, safety and antitumor efficacy.

RESULTS

Overall, 95 Chinese patients were enrolled, of which 12 and 83 patients were in Part 1 and Part 2, respectively. In Part 1, trilaciclib was well tolerated. Non-compartmental analysis results revealed no substantial differences in the main exposure parameters. In Part 2, 41 patients received trilaciclib, and 42 received placebo. Patients in trilaciclib arm vs placebo arm had a clinically and statistically significant decrease in DSN (mean [SD]) in Cycle 1 (0 [1.7] vs 2 [3.0] days; P = 0.0003), with improvements in additional neutrophil, red blood cell, and platelet measures. After a median follow-up of 14.1 months, the median overall survival was 12.0 months in trilaciclib arm and 8.8 months in placebo arm (HR, 0.69; 95 % CI: 0.40-1.22). Median progression-free survival was 4.8 months and 4.3 months, respectively (HR, 0.86; 95 % CI: 0.53-1.39). Trilaciclib had a well-tolerated safety profile.

CONCLUSIONS

Trilaciclib in the Chinese population demonstrated a similar PK and safety profile as seen in other global trials. There was significant reduction of DSN in Cycle 1, thereby substantiating the myeloprotective effects of trilaciclib in Chinese ES-SCLC patients.

Indole-3-carboxaldehyde ameliorates ionizing radiation-induced hematopoietic injury by enhancing hematopoietic stem and progenitor cell quiescence

Indole-3-carboxaldehyde (I3A), one of tryptophan metabolites derived from gut microbiota, extends the lifespan of mice after high-dose ionizing radiation exposure. Persistent myelosuppression is the most common and fatal complication for victims of nuclear accidents and patients undergoing radiotherapy, with few therapeutic options available. However, whether and how I3A protects ionizing radiation-induced hematopoietic toxicity remain unknown. In this study, we demonstrated that I3A treatment effectively ameliorated radiation-induced hematopoietic injury through accelerating peripheral blood cells recovery, promoting bone marrow cellularity restoration and enhancing functional HSPC regeneration. Additionally, I3A also suppressed intracellular reactive oxygen species production and inhibited apoptosis in irradiated HSPCs. Mechanistically, I3A treatment significantly increased HSPC quiescence, thus conferring HSPCs with resistance against radiation injury. Finally, I3A treatment could improve survival of lethally irradiated mice. Taken together, our data suggest that I3A acts as a gut microbiota-derived paracrine factor that regulates HSPC regeneration and may serve as a promising therapeutic agent for ionizing radiation-induced myelosuppression.

CDK4 phosphorylation status and rational use for combining CDK4/6 and BRAF/MEK inhibition in advanced thyroid carcinomas

Background

CDK4/6 inhibitors (CDK4/6i) have been established as standard treatment against advanced Estrogen Receptor-positive breast cancers. These drugs are being tested against several cancers, including in combinations with other therapies. We identified the T172-phosphorylation of CDK4 as the step determining its activity, retinoblastoma protein (RB) inactivation, cell cycle commitment and sensitivity to CDK4/6i. Poorly differentiated (PDTC) and anaplastic (ATC) thyroid carcinomas, the latter considered one of the most lethal human malignancies, represent major clinical challenges. Several molecular evidence suggest that CDK4/6i could be considered for treating these advanced thyroid cancers.

Methods

We analyzed by two-dimensional gel electrophoresis the CDK4 modification profile and the presence of T172-phosphorylated CDK4 in a collection of 98 fresh-frozen tissues and in 21 cell lines. A sub-cohort of samples was characterized by RNA sequencing and immunohistochemistry. Sensitivity to CDK4/6i (palbociclib and abemaciclib) was assessed by BrdU incorporation/viability assays. Treatment of cell lines with CDK4/6i and combination with BRAF/MEK inhibitors (dabrafenib/trametinib) was comprehensively evaluated by western blot, characterization of immunoprecipitated CDK4 and CDK2 complexes and clonogenic assays.

Results

CDK4 phosphorylation was detected in all well-differentiated thyroid carcinomas (n=29), 19/20 PDTC, 16/23 ATC and 18/21 thyroid cancer cell lines, including 11 ATC-derived ones. Tumors and cell lines without phosphorylated CDK4 presented very high p16CDKN2A levels, which were associated with proliferative activity. Absence of CDK4 phosphorylation in cell lines was associated with CDK4/6i insensitivity. RB1 defects (the primary cause of intrinsic CDK4/6i resistance) were not found in 5/7 tumors without detectable phosphorylated CDK4. A previously developed 11-gene expression signature identified the likely unresponsive tumors, lacking CDK4 phosphorylation. In cell lines, palbociclib synergized with dabrafenib/trametinib by completely and permanently arresting proliferation. These combinations prevented resistance mechanisms induced by palbociclib, most notably Cyclin E1-CDK2 activation and a paradoxical stabilization of phosphorylated CDK4 complexes.

Conclusion

Our study supports further clinical evaluation of CDK4/6i and their combination with anti-BRAF/MEK therapies as a novel effective treatment against advanced thyroid tumors. Moreover, the complementary use of our 11 genes predictor with p16/KI67 evaluation could represent a prompt tool for recognizing the intrinsically CDK4/6i insensitive patients, who are potentially better candidates to immediate chemotherapy.

Real-World Outcomes of Trilaciclib Among Patients with Extensive-Stage Small Cell Lung Cancer Receiving Chemotherapy

INTRODUCTION

Trilaciclib was recently approved in the USA for reducing chemotherapy-induced myelosuppression (CIM) among adults with extensive-stage small cell lung cancer (ES-SCLC) when administered prior to chemotherapy. There is limited understanding of real-world outcomes of trilaciclib.

METHODS

A comprehensive literature review was conducted using a keyword search in the MEDLINE, Embase, and conference abstracts. Additional studies were identified through communications with the authors of relevant studies. Published and unpublished real-world studies of trilaciclib- and comparable non-trilaciclib-treated patients with ES-SCLC were included. Evidence on myelosuppressive hematologic adverse events (HAEs), cytopenia-related healthcare utilization, and other reported outcomes (e.g., hospitalizations, dose reduction, and treatment delay) were synthesized. If feasible, outcomes were compared qualitatively between the trilaciclib and historical reference groups, and between first-line trilaciclib initiators and the overall trilaciclib population. Weighted averages were estimated for selected outcomes using sample size as the weight.

RESULTS

The literature search identified five unique studies based on eight records-two included trilaciclib only, two non-trilaciclib only, and one both. In trilaciclib cohorts, the weighted average prevalence of grade ≥ 3 myelosuppressive HAEs in ≥ 1 lineage, ≥ 2 lineages, and all three lineages was 40.5%, 14.5%, and 7.5%, respectively. All rates were numerically lower compared to the historical non-trilaciclib cohorts (58.8%, 28.0%, 13.0% respectively). Cytopenia-related healthcare utilization was also lower in the trilaciclib cohorts. In general, first-line trilaciclib initiators had numerically lower myelosuppressive HAEs and cytopenia-related healthcare utilization than the overall trilaciclib patients.

CONCLUSIONS

The existing evidence suggests that trilaciclib may reduce single and multilineage grade ≥ 3 myelosuppressive HAEs and cytopenia-related healthcare utilization among patients with ES-SCLC in the real world. It is a promising new treatment for CIM prevention in ES-SCLC and may bring greater benefits to first-line trilaciclib initiators. Future studies are recommended to further evaluate the real-world effectiveness of trilaciclib.

FRMD8 targets both CDK4 activation and RB degradation to suppress colon cancer growth

Cyclin-dependent kinase 4 (CDK4) and retinoblastoma protein (RB) are both important cell-cycle regulators that function in different scenarios. Here, we report that FERM domain-containing 8 (FRMD8) inhibits CDK4 activation and stabilizes RB, thereby causing cell-cycle arrest and inhibiting colorectal cancer (CRC) cell growth. FRMD8 interacts separately with CDK7 and CDK4, and it disrupts the interaction of CDK7 with CDK4, subsequently inhibiting CDK4 activation. FRMD8 competes with MDM2 to bind RB and attenuates MDM2-mediated RB degradation. Frmd8 deficiency in mice accelerates azoxymethane/dextran-sodium-sulfate-induced colorectal adenoma formation. The FRMD8 promoter is hypermethylated, and low expression of FRMD8 predicts poor prognosis in CRC patients. Further, we identify an LKCHE-containing FRMD8 peptide that blocks MDM2 binding to RB and stabilizes RB. Combined application of the CDK4 inhibitor and FRMD8 peptide leads to marked suppression of CRC cell growth. Therefore, using an LKCHE-containing peptide to interfere with the MDM2-RB interaction may have therapeutic value in CDK4/6 inhibitor-resistant patients.

Investigating potential immune mechanisms of trilaciclib administered prior to chemotherapy in patients with metastatic triple-negative breast cancer

PURPOSE

In a phase II trial in patients with metastatic triple-negative breast cancer (mTNBC; NCT02978716), administering trilaciclib prior to gemcitabine plus carboplatin (GCb) enhanced T-cell activation and improved overall survival versus GCb alone. The survival benefit was more pronounced in patients with higher immune-related gene expression. We assessed immune cell subsets and used molecular profiling to further elucidate effects on antitumor immunity.

METHODS

Patients with mTNBC and ≤ 2 prior chemotherapy regimens for locally recurrent TNBC or mTNBC were randomized 1:1:1 to GCb on days 1 and 8, trilaciclib prior to GCb on days 1 and 8, or trilaciclib alone on days 1 and 8, and prior to GCb on days 2 and 9. Gene expression, immune cell populations, and Tumor Inflammation Signature (TIS) scores were assessed in baseline tumor samples, with flow cytometric analysis and intracellular and surface cytokine staining used to assess immune cell populations and function.

RESULTS

After two cycles, the trilaciclib plus GCb group (n = 68) had fewer total T cells and significantly fewer CD8+ T cells and myeloid-derived suppressor cells compared with baseline, with enhanced T-cell effector function versus GCb alone. No significant differences were observed in patients who received GCb alone (n = 34). Of 58 patients in the trilaciclib plus GCb group with antitumor response data, 27 had an objective response. RNA sequencing revealed a trend toward higher baseline TIS scores among responders versus non‑responders.

CONCLUSION

The results suggest that administering trilaciclib prior to GCb may modulate the composition and response of immune cell subsets to TNBC.

Update on Classic and Novel Approaches in Metastatic Triple-Negative Breast Cancer Treatment: A Comprehensive Review

Triple-negative breast cancer (TNBC) accounts for almost 15% of all diagnosed breast cancers and often presents high rates of relapses and metastases, with generally poor prognosis despite multiple lines of treatment. Immunotherapy has radically changed the approach of clinicians towards TNBC in the last two to three years, even if targeted and specific therapeutic options are still missing; this unmet need is further justified by the extreme molecular and clinical heterogeneity of this subtype of breast cancer and by the weak response to both single-agent and combined therapies. In March 2023, the National Comprehensive Cancer Network (NCCN), the main association of cancer centers in the United States, released the last clinical practice guidelines, with an update on classic and novel approaches in the field of breast cancer. The purpose of this comprehensive review is to summarize the latest findings in the setting of metastatic TNBC treatment, focusing on each category of drugs approved by the Food and Drug Administration (FDA) and included in the NCCN guidelines. We also introduce part of the latest published studies, which have reported new and promising molecules able to specifically target some of the biomarkers involved in TNBC pathogenesis. We searched the PubMed and Scopus databases for free full texts reported in the literature of the last 5 years, using the words "triple-negative breast cancer" or "TNBC" or "basal-like". The articles were analyzed by the authors independently and double-blindly, and a total of 114 articles were included in the review.

The efficacy and safety of Trilaciclib in preventing chemotherapy-induced myelosuppression: a systematic review and meta-analysis of randomized controlled trials

Background: This study aims to assess the clinical efficacy and safety of Trilaciclib in preventing chemotherapy-induced myelosuppression in adult patients through meta-analysis. Methods: The PubMed, Embase, Cochrane Library, Clinical Trials, EU Clinical Trials Register, and International Clinical Trials Registry Platform were searched up to 25 October 2022. Only randomized controlled trials (RCTs) comparing the clinical outcomes of Trilaciclib and Trilaciclib plus chemotherapy for treating malignant cancers in adult patients were included. The primary outcome included the incidence of SN, FN, the DSN, and administration of ESAs, G-CSFs, and RBC or platelet transfusions, while the secondary outcomes included the risk of adverse events (AEs) and severe adverse events (SAEs). Results: In total, four randomized controlled trials (RCTs) involving 345 patients with SCLC or breast cancer were included in this meta-analysis. Results showed that administration of Trilaciclib significantly reduced the occurrence of SN (19.3% vs. 42.2%, OR = 0.31), FN (3.22% vs. 6.72%, OR = 0.47), anemia (20.5% vs. 38.2%, OR = 0.38) and shortened the DSN during treatment. The proportion of patients receiving therapeutic use of ESAs (4.03% vs. 11.8%, OR = 0.31), G-CSF (37.0% vs. 53.5%, OR = 0.52), RBC transfusions (19.8% vs. 29.9%, OR = 0.56) was also statistically lower in the experimental group than in the control group. Meanwhile, the ORR, overall survival, and progress-free survival of the two groups were identical, and no negative impact of Trilaciclib on the clinical outcomes of chemotherapy treatments was found. Other chemotherapy-induced adverse events (AEs) and severe adverse events (SAEs) like diarrhea, fatigue, nausea, and vomiting were identical regardless of Trilaciclib usage. Conclusion: Trilaciclib demonstrated its efficacy in reducing the occurrence of chemotherapy-induced myelosuppression and utilization of supportive care interventions without undermining the clinical benefits of chemotherapy regimens during treatment with an acceptable safety profile.

Selective protection of normal cells from chemotherapy, while killing drug-resistant cancer cells

Cancer therapy is limited by toxicity in normal cells and drug-resistance in cancer cells. Paradoxically, cancer resistance to certain therapies can be exploited for protection of normal cells, simultaneously enabling the selective killing of resistant cancer cells by using antagonistic drug combinations, which include cytotoxic and protective drugs. Depending on the mechanisms of drug-resistance in cancer cells, the protection of normal cells can be achieved with inhibitors of CDK4/6, caspases, Mdm2, mTOR, and mitogenic kinases. When normal cells are protected, the selectivity and potency of multi-drug combinations can be further enhanced by adding synergistic drugs, in theory, eliminating the deadliest cancer clones with minimal side effects. I also discuss how the recent success of Trilaciclib may foster similar approaches into clinical practice, how to mitigate systemic side effects of chemotherapy in patients with brain tumors and how to ensure that protective drugs would only protect normal cells (not cancer cells) in a particular patient.

Population pharmacokinetics and exposure-response of trilaciclib in extensive-stage small cell lung cancer and triple-negative breast cancer

AIMS

Trilaciclib is a first-in-class, intravenous cyclin-dependent kinase 4/6 inhibitor that provides multilineage protection from chemotherapy-induced myelosuppression. This analysis aimed to characterize the population pharmacokinetics (PK) of trilaciclib, identify potential covariates influencing trilaciclib PK, and evaluate exposure-response relationships in extensive-stage small cell lung cancer (ES-SCLC) and triple-negative breast cancer (TNBC) trials.

METHODS

Population PK analysis was performed using data from healthy volunteers (n = 72), patients with ES-SCLC (n = 111) and patients with TNBC (n = 14). Exposure-response analyses were conducted to investigate the impact of trilaciclib exposure (AUC) on myeloprotective efficacy, antitumour efficacy and safety. Logistic regression and Cox regression models were used for binary and time-to-event endpoints, respectively.

RESULTS

Trilaciclib PK was described by a three-compartment model. Sex, body surface area, baseline albumin concentration and age were identified as significant covariates on trilaciclib PK but did not have clinically relevant impact on exposure. Based on exposure-response analyses, lower and higher exposures of trilaciclib at clinical doses (200-280 mg/m² ) were associated with similar myeloprotective effects. Trilaciclib exposure did not impact the antitumour effects of chemotherapy. Higher exposure to trilaciclib was associated with higher probabilities of headache, phlebitis/thrombophlebitis and injection site reactions.

CONCLUSION

No dose adjustments are required based on the covariates tested. Trilaciclib resulted in optimal myeloprotective effects with no impact on antitumour effects of chemotherapy. However, higher exposure increased the probabilities of adverse events. The data further support selection of the recommended phase 2 dose (trilaciclib 240 mg/m² ).

Prostaglandin E2 prevents radiotherapy-induced alopecia by attenuating transit amplifying cell apoptosis through promoting G1 arrest

BACKGROUND

Growing hair follicles (HFs) harbor actively dividing transit amplifying cells (TACs), rendering them highly sensitive to radiotherapy (RT). Clinically, there is still a lack of treatment options for radiotherapy-induced alopecia (RIA).

OBJECTIVE

Our present study aimed to investigated the effect and mechanism of local prostaglandin E2 (PGE2) treatment in RIA prevention.

METHODS

We compared the response of growing HFs to radiation with and without local PGE2 pretreatment in a mouse model in vivo. The effect of PGE2 on the cell cycle was determined in cultured HF cells from fluorescent ubiquitination-based cell cycle indicator mice. We also compared the protective effects of PGE2 and a cyclin-dependent kinases 4/6 (CDK4/6) inhibitor against RIA.

RESULTS

The local cutaneous PGE2 injection reduced RIA by enhancing HF self-repair. Mechanistically, PGE2 did not activate HF stem cells, but it preserved more TACs for regenerative attempts. Pretreatment of PGE2 lessened radiosensitivity of TACs by transiently arresting them in the G1 phase, thereby reducing TAC apoptosis and mitigating HF dystrophy. The preservation of more TACs accelerated HF self-repair and bypassed RT-induced premature termination of anagen. Promoting G1 arrest by systemic administration of palbociclib isethionate (PD0332991), a CDK4/6 inhibitor, offered a similar protective effect against RT.

CONCLUSIONS

Locally administered PGE2 protects HF TACs from RT by transiently inducing G1 arrest, and the regeneration of HF structures lost from RT is accelerated to resume anagen growth, thus bypassing the long downtime of hair loss. PGE2 has the potential to be repurposed as a local preventive treatment for RIA.

Chemotherapy-induced thrombocytopenia: literature review

Chemotherapy-induced thrombocytopenia (CIT) is a common condition that frequently results in reduced chemotherapy dosages, postponed treatment, bleeding, and unfavorable oncological outcomes. At present, there is no clear suggestions for preventing or treating CIT. Thrombopoietin (TPO) replacement therapy has been invented and used to treat CIT to promote the production of megakaryocytes and stimulate the formation of platelets. However, this treatment is limited to the risk of immunogenicity and cancer progression. Therefore, an unmet need exists for exploring alternatives to TPO to address the clinical issue of CIT. Application of appropriate therapeutic drugs may be due to understanding the potential mechanisms of CIT. Studies have shown that chemotherapy significantly affects various cells in bone marrow (BM) microenvironment, reduces their ability to support normal hematopoiesis, and may lead to BM damage, including CIT in cancer patients. This review focuses on the epidemiology and treatment of cancer patients with CIT. We also introduce some recent progress to understand the cellular and molecular mechanisms of chemotherapy inhibiting normal hematopoiesis and causing thrombocytopenia.

CDK inhibitors from past to present: A new wave of cancer therapy

Deregulation of the cell cycle machinery, which has been linked to dysregulation of cyclin-dependent kinases (CDKs), is a defining characteristic of cancer, eventually promoting abnormal proliferation that feeds tumorigenesis and disease development. In this regard, several CDK inhibitors (CDKIs) have been developed during the last few decades (1st, 2nd, and 3rd generation CDKIs) to inhibit cancer cell proliferation. 1st and 2nd generation CDKIs have not received much clinical attention for the treatment of cancer patients because of their limited specificity and high toxicity. However, the recent development of combination strategies allowed us to reduce the toxicity and side effects of these CDKIs, paving the way for their potential application in clinical settings. The 3rd generation CDKIs have yielded the most promising results at the preclinical and clinical levels, propelling them into the advanced stages of clinical trials against multiple malignancies, especially breast cancer, and revolutionizing traditional treatment strategies. In this review, we discuss the most-investigated candidates from the 1st, 2nd, and 3rd generations of CDKIs, their basic mechanisms of action, the reasons for their failure in the past, and their current clinical development for the treatment of different malignancies. Additionally, we briefly highlighted the most recent clinical trial results and advances in the development of 3rd generation FDA-approved selective CDK4/6 inhibitors that combat the most prevalent cancer. Overall, this review will provide a thorough knowledge of CDKIs from the past to the present, allowing researchers to rethink and develop innovative cancer therapeutic regimens.

Trilaciclib prior to gemcitabine plus carboplatin for metastatic triple-negative breast cancer: phase III PRESERVE 2

Triple-negative breast cancer (TNBC) is an aggressive malignancy for which cytotoxic chemotherapy remains the backbone of treatment. Trilaciclib is an intravenous cyclin-dependent kinase 4/6 inhibitor that induces transient cell cycle arrest of hematopoietic stem and progenitor cells and immune cells during chemotherapy exposure, protecting them from chemotherapy-induced damage and enhancing immune activity. Administration of trilaciclib prior to gemcitabine plus carboplatin (GCb) significantly improved overall survival (OS) compared with GCb alone in an open-label phase II trial in patients with metastatic TNBC, potentially through protection and direct activation of immune function. The randomized, double-blind, placebo-controlled, phase III PRESERVE 2 trial will evaluate the efficacy and safety of trilaciclib administered prior to GCb in patients with locally advanced unresectable or metastatic TNBC. Clinical Trial Registration: NCT04799249 (ClinicalTrials.gov).

Rationale for combination of paclitaxel and CDK4/6 inhibitor in ovarian cancer therapy - non-mitotic mechanisms of paclitaxel

Taxanes and CDK4/6 inhibitors (CDK4/6i) are two families of successful anti-mitotic drugs used in the treatment of solid tumors. Paclitaxel, representing taxane compounds, has been used either alone or in combination with other agents (commonly carboplatin/cisplatin) in the treatment of many solid tumors including ovarian, breast, lung, prostate cancers, and Kaposi's sarcoma. Paclitaxel has been routinely prescribed in cancer treatment since the 1990s, and its prominent role is unlikely to be replaced in the foreseeable future. Paclitaxel and other taxanes work by binding to and stabilizing microtubules, causing mitotic arrest, aberrant mitosis, and cell death. CDK4/6i (palbociclib, ribociclib, abemaciclib) are relatively new cell cycle inhibitors that have been found to be effective in breast cancer treatment, and are currently being developed in other solid tumors. CDK4/6i blocks cell cycle progression at the G1 phase, resulting in cell death by mechanisms not yet fully elucidated. At first glance, paclitaxel and CDK4/6i are unlikely synergistic agents as both are cell cycle inhibitors that work at different phases of the cell cycle, and few clinical trials have yet considered adding CDK4/6i to existing paclitaxel chemotherapy. However, recent findings suggest the importance of a non-mitotic mechanism of paclitaxel in cancer cell death and pre-clinical data support rationale for a strategic paclitaxel and CDK4/6i combination. In mouse tumor model studies, drug sequencing resulted in differential efficacy, indicating complex biological interactions of the two drugs. This article reviews the rationales of combining paclitaxel with CDK4/6i as a potential therapeutic option in recurrent ovarian cancer.

CDK4: a master regulator of the cell cycle and its role in cancer

The cell cycle is regulated in part by cyclins and their associated serine/threonine cyclin-dependent kinases, or CDKs. CDK4, in conjunction with the D-type cyclins, mediates progression through the G₁ phase when the cell prepares to initiate DNA synthesis. Although Cdk4-null mutant mice are viable and cell proliferation is not significantly affected in vitro due to compensatory roles played by other CDKs, this gene plays a key role in mammalian development and cancer. This review discusses the role that CDK4 plays in cell cycle control, normal development and tumorigenesis as well as the current status and utility of approved small molecule CDK4/6 inhibitors that are currently being used as cancer therapeutics.

Pharmacokinetic Drug-Drug Interaction Studies Between Trilaciclib and Midazolam, Metformin, Rifampin, Itraconazole, and Topotecan in Healthy Volunteers and Patients with Extensive-Stage Small-Cell Lung Cancer

Background and Objective

Trilaciclib is a cyclin-dependent kinase 4/6 inhibitor indicated to decrease the incidence of chemotherapy-induced myelosuppression in patients with extensive-stage small-cell lung cancer. Trilaciclib is a substrate and time-dependent inhibitor of cytochrome P450 3A4 and an inhibitor of multidrug and toxin extrusion 1, multidrug and toxin extrusion 2-K, organic cation transporter 1, and organic cation transporter 2. Here, we investigate the pharmacokinetic drug–drug interaction potential of trilaciclib.

Methods

Two phase I studies were conducted as prospective, open-label, fixed-sequence drug–drug interaction studies in healthy subjects (n = 57, n = 20) to investigate potential interactions between intravenously administered trilaciclib (200 or 240 mg/m²) and orally administered midazolam (5 mg), metformin (1000 mg), itraconazole (200 mg), and rifampin (600 mg). A population pharmacokinetic model was fit to phase Ib/IIa data in patients with extensive-stage small-cell lung cancer (n = 114) to assess the impact of trilaciclib dose and exposure (area under the plasma concentration–time curve) on topotecan clearance.

Results

Coadministration with trilaciclib had minimal effects on the exposure (area under the plasma concentration–time curve from time 0 to infinity) of midazolam (geometric least-square mean ratio [GMR] vs midazolam alone 1.065; 90% confidence interval [CI] 0.984–1.154) but statistically significantly increased plasma exposure (GMR 1.654; 90% CI 1.472–1.858) and decreased renal clearance (GMR 0.633; 90% CI 0.572–0.701) of metformin. Coadministration of trilaciclib with rifampin or itraconazole decreased trilaciclib area under the plasma concentration–time curve from time 0 to infinity by 17.3% (GMR 0.827; 90% CI 0.785–0.871) and 14.0% (GMR 0.860; 0.820–0.902), respectively, vs trilaciclib alone. Population pharmacokinetic modeling showed no significant effect of trilaciclib on topotecan clearance.

Conclusions

Overall, the drug–drug interaction and safety profiles of trilaciclib in these studies support its continued use in patients with extensive-stage small-cell lung cancer.

Clinical Trial Registration

Study 106: EudraCT number: 2019-002303-18; Study 114: not applicable; Study 03: Clinicaltrials.org: NCT02514447; August 2015.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40261-022-01179-x.

Combination Approaches to Target PD-1 Signaling in Cancer

Cancer remains the second leading cause of death in the US, accounting for 25% of all deaths nationwide. Immunotherapy techniques bolster the immune cells' ability to target malignant cancer cells and have brought immense improvements in the field of cancer treatments. One important inhibitory protein in T cells, programmed cell death protein 1 (PD-1), has become an invaluable target for cancer immunotherapy. While anti-PD-1 antibody therapy is extremely successful in some patients, in others it fails or even causes further complications, including cancer hyper-progression and immune-related adverse events. Along with countless translational studies of the PD-1 signaling pathway, there are currently close to 5,000 clinical trials for antibodies against PD-1 and its ligand, PD-L1, around 80% of which investigate combinations with other therapies. Nevertheless, more work is needed to better understand the PD-1 signaling pathway and to facilitate new and improved evidence-based combination strategies. In this work, we consolidate recent discoveries of PD-1 signaling mediators and their therapeutic potential in combination with anti-PD-1/PD-L1 agents. We focus on the phosphatases SHP2 and PTPN2; the kinases ITK, VRK2, GSK-3, and CDK4/6; and the signaling adaptor protein PAG. We discuss their biology both in cancer cells and T cells, with a focus on their role in relation to PD-1 to determine their potential in therapeutic combinations. The literature discussed here was obtained from a search of the published literature and ClinicalTrials.gov with the following key terms: checkpoint inhibition, cancer immunotherapy, PD-1, PD-L1, SHP2, PTPN2, ITK, VRK2, CDK4/6, GSK-3, and PAG. Together, we find that all of these proteins are logical and promising targets for combination therapy, and that with a deeper mechanistic understanding they have potential to improve the response rate and decrease adverse events when thoughtfully used in combination with checkpoint inhibitors.

Targeting CDK4 and CDK6 in cancer

Cyclin-dependent kinase 4 (CDK4) and CDK6 are critical mediators of cellular transition into S phase and are important for the initiation, growth and survival of many cancer types. Pharmacological inhibitors of CDK4/6 have rapidly become a new standard of care for patients with advanced hormone receptor-positive breast cancer. As expected, CDK4/6 inhibitors arrest sensitive tumour cells in the G1 phase of the cell cycle. However, the effects of CDK4/6 inhibition are far more wide-reaching. New insights into their mechanisms of action have triggered identification of new therapeutic opportunities, including the development of novel combination regimens, expanded application to a broader range of cancers and use as supportive care to ameliorate the toxic effects of other therapies. Exploring these new opportunities in the clinic is an urgent priority, which in many cases has not been adequately addressed. Here, we provide a framework for conceptualizing the activity of CDK4/6 inhibitors in cancer and explain how this framework might shape the future clinical development of these agents. We also discuss the biological underpinnings of CDK4/6 inhibitor resistance, an increasingly common challenge in clinical oncology.

CDK4/6 Inhibitors in Combination Therapies: Better in Company Than Alone: A Mini Review

The cyclin D-CDK4/6 complexes play a pivotal role in controlling the cell cycle. Deregulation in cyclin D-CDK4/6 pathway has been described in many types of cancer and it invariably leads to uncontrolled cell proliferation. Many efforts have been made to develop a target therapy able to inhibit CDK4/6 activity. To date, three selective CDK4/6 small inhibitors have been introduced in the clinic for the treatment of hormone positive advanced breast cancer patients, following the impressive results obtained in phase III clinical trials. However, since their approval, clinical evidences have demonstrated that about 30% of breast cancer is intrinsically resistant to CDK4/6 inhibitors and that prolonged treatment eventually leads to acquired resistance in many patients. So, on one hand, clinical and preclinical studies fully support to go beyond breast cancer and expand the use of CDK4/6 inhibitors in other tumor types; on the other hand, the question of primary and secondary resistance has to be taken into account, since it is now very clear that neoplastic cells rapidly develop adaptive strategies under treatment, eventually resulting in disease progression. Resistance mechanisms so far discovered involve both cell-cycle and non-cell-cycle related escape strategies. Full understanding is yet to be achieved but many different pathways that, if targeted, may lead to reversion of the resistant phenotype, have been already elucidated. Here, we aim to summarize the knowledge in this field, focusing on predictive biomarkers, to recognize intrinsically resistant tumors, and therapeutic strategies, to overcome acquired resistance.

Low Intensity Ultrasound as an Antidote to Taxane/Paclitaxel-induced Cytotoxicity

The taxane family of compounds, including Taxol/paclitaxel and Taxotere/docetaxel, are surprisingly successful drugs used in combination or alone for the treatment of most major solid tumors, especially metastatic cancer. The drugs are commonly used in regimen with other agents (often platinum drugs) as frontline treatment, or used as a single agent in a dose dense regimen for recurrent cancer. The major side effects of taxanes are peripheral neuropathy, alopecia, and neutropenia, which are grave burden for patients and limit the full potential of the taxane drugs. Especially in the current treatment protocol for peripheral neuropathy, taxane dosage is reduced once the symptoms present, resulting in the loss of full or optimal cancer killing activity.

Substantial efforts have been made to address the problem of cytotoxic side effects of taxanes, though strategies remain very limited. Following administration of the taxane compound by infusion, taxane binds to cellular microtubules and is sequestered within the cells for several days. Taxane stabilizes and interferes with microtubule function, leading to ultimate death of cancer cells, but also damages hair follicles, peripheral neurons, and hemopoietic stem cells. Currently, cryo-treatment is practiced to limit exposure and side effects of the drug during infusion, though the effectiveness is uncertain or limited.

A recent laboratory finding may provide a new strategy to counter taxane cytotoxicity, that a brief exposure to low density ultrasound waves was sufficient to eliminate paclitaxel cytotoxicity cells in culture by transiently breaking microtubule filaments, which were then relocated to lysosomes for disposal. Thus, ultrasonic force to break rigid microtubules is an effective solution to counter taxane cytotoxicity. The discovery and concept of low intensity ultrasound as an antidote may have the potential to provide a practical strategy to counter paclitaxel-induced peripheral neuropathy and alopecia that resulted from chemotherapy.

Taxanes are a class of important drugs used in chemotherapy to treat several major cancers. This article reviews a new laboratory discovery that ultrasound can be used as an antidote for the peripheral cytotoxicity of taxane drugs and discusses the potential development and application of low intensity ultrasound to prevent side effects in chemotherapeutic treatment of cancer patients.

Cytokinetic-driven myeloprotection after cytotoxic chemotherapy: from an old idea to a new clinical approach

Chemotherapy is the backbone of the treatment of several solid tumours and lymphomas. Myelotoxicity is often a dose-limiting toxicity and myeloprotection has always been investigated. In fact, over the years, several approaches have been studied in order to reduce the incidence of haematological toxicities and allow patients to receive effective, full-dose, chemotherapy. After the use of stimulating factors, such as granulocyte colony-stimulating factors and erythropoiesis-stimulating agents, in the very last years, a new approach has emerged. Trilaciclib, a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor, has been studied and it has been demonstrated in several clinical trials to reduce the incidence of myelotoxicity in small-cell lung cancer patients treated with chemotherapy or chemo-immunotherapy. Its potential role has not been fully studied yet, but it represents a highly effective tool to reduce myelotoxicity, widen the applicability of full-dose chemotherapy, even in frailer patients, and finally to increase the efficacy of chemotherapy in those tumours where relative dose intensity is a standard to achieve to get the best clinical results.

Targeting CDK4/6 for Anticancer Therapy

Cyclin-dependent kinase 4/6 (CDK4/6) are key regulators of the cell cycle and are deemed as critical therapeutic targets of multiple cancers. Various approaches have been applied to silence CDK4/6 at different levels, i.e., CRISPR to knock out at the DNA level, siRNA to inhibit translation, and drugs that target the protein of interest. Here we summarize the current status in this field, highlighting the mechanisms of small molecular inhibitors treatment and drug resistance. We describe approaches to combat drug resistance, including combination therapy and PROTACs drugs that degrade the kinases. Finally, critical issues and perspectives in the field are outlined.

CDK4/6 inhibitors induce replication stress to cause long-term cell cycle withdrawal

CDK4/6 inhibitors arrest the cell cycle in G1-phase. They are approved to treat breast cancer and are also undergoing clinical trials against a range of other tumour types. To facilitate these efforts, it is important to understand why a cytostatic arrest in G1 causes long-lasting effects on tumour growth. Here, we demonstrate that a prolonged G1 arrest following CDK4/6 inhibition downregulates replisome components and impairs origin licencing. Upon release from that arrest, many cells fail to complete DNA replication and exit the cell cycle in a p53-dependent manner. If cells fail to withdraw from the cell cycle following DNA replication problems, they enter mitosis and missegregate chromosomes causing excessive DNA damage, which further limits their proliferative potential. These effects are observed in a range of tumour types, including breast cancer, implying that genotoxic stress is a common outcome of CDK4/6 inhibition. This unanticipated ability of CDK4/6 inhibitors to induce DNA damage now provides a rationale to better predict responsive tumour types and effective combination therapies, as demonstrated by the fact that CDK4/6 inhibition induces sensitivity to chemotherapeutics that also cause replication stress.

Cyclin-dependent Kinases 4/6 Inhibitors in Neuroendocrine Neoplasms: from Bench to Bedside

PURPOSE OF REVIEW

Cyclin-dependent kinases (CDKs) are key regulators that play an important role in cell division. Palbociclib, ribociclib and abemaciclib showed significant antitumor activity in several malignancies and, recently, also a myeloprotective effect for trilaciclib when added to chemotherapy. The purpose of this review is to highlight the current evidence for CDK4/6 inhibitors in neuroendocrine neoplasms (NENs).

RECENT FINDINGS

Preclinical results showed a promising antitumor activity of CDK4/6 inhibitors in neuroendocrine tumors (NETs), but so far, the very few small clinical trials did not show a strong impact on progression free survival (PFS) and objective response in NETs. Meanwhile, the CDK4/6 inhibitor trilaciclib revealed significant effects in reducing chemotherapy-induced myelosuppression in small cell lung cancer (SCLC). Up to date, CDK4/6 inhibitors are still considered investigational in NETs as antitumor agents, whereas trilaciclib can be used in the routine clinical practice in extensive stage SCLC patients for reducing myelotoxicity of standard chemotherapy.

Trilaciclib Prior to Chemotherapy in Patients with Metastatic Triple-Negative Breast Cancer: Final Efficacy and Subgroup Analysis from a Randomized Phase II Study

PURPOSE

We report final antitumor efficacy results from a phase II study of trilaciclib, an intravenous cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, administered prior to gemcitabine plus carboplatin (GCb) in patients with metastatic triple-negative breast cancer (NCT02978716).

PATIENTS AND METHODS

Patients were randomized (1:1:1) to group 1 [GCb (days 1, 8); n = 34], group 2 [trilaciclib prior to GCb (days 1, 8); n = 33], or group 3 [trilaciclib (days 1, 8) and trilaciclib prior to GCb (days 2, 9); n = 35]. Subgroup analyses were performed according to CDK4/6 dependence, level of programmed death-ligand 1 (PD-L1) expression, and RNA-based immune signatures using proportional hazards regression. T-cell receptor (TCR) β CDR3 regions were amplified and sequenced to identify, quantify, and compare the abundance of each unique TCRβ CDR3 at baseline and on treatment.

RESULTS

Median overall survival (OS) was 12.6 months in group 1, not reached in group 2 (HR = 0.31; P = 0.0016), 17.8 months in group 3 (HR = 0.40; P = 0.0004), and 19.8 months in groups 2 and 3 combined (HR = 0.37; P < 0.0001). Efficacy outcomes were comparable regardless of cancer CDK4/6 dependence status and immune signatures. Administering trilaciclib prior to GCb prolonged OS irrespective of PD-L1 status but had greater benefit in the PD-L1-positive population. T-cell activation was enhanced in patients receiving trilaciclib.

CONCLUSIONS

Administering trilaciclib prior to GCb enhanced antitumor efficacy, with significant improvements in OS. Efficacy outcomes in immunologic subgroups and enhancements in T-cell activation suggest these improvements may be mediated via immunologic mechanisms.

Budget impact analysis of trilaciclib for decreasing the incidence of chemotherapy-induced myelosuppression in patients with extensive-stage small cell lung cancer in the United States

BACKGROUND: Chemotherapy-induced myelosuppression, which commonly manifests as neutropenia, anemia, and/or thrombocytopenia, is a frequent and severe complication of standard treatment regimens for patients with extensive-stage small cell lung cancer (ES-SCLC). Trilaciclib is a first-in-class myeloprotective therapy indicated to decrease the incidence of chemotherapy-induced myelosuppression when administered prior to a platinum-/etoposide-containing regimen or topotecan-containing regimen for ES-SCLC. OBJECTIVE: To estimate the budget impact of administering trilaciclib prior to chemotherapy to manage chemotherapy-induced myelosuppression in adults with ES-SCLC from a US payer perspective. METHODS: A budget impact model was developed to assess the impact of introducing trilaciclib to a hypothetical 1 million-member health insurance plan. The model compared 2 market scenarios: a current scenario of standard treatments for ES-SCLC without trilaciclib, and an alternative scenario of standard treatment plus trilaciclib. Population, clinical, and cost inputs were derived from published literature and trilaciclib clinical trial data. Model outcomes included the number of myelosuppressive adverse events (AEs), costs of treatment, costs of AE management, total cost, and per-member per-month (PMPM) costs. The budget impact of trilaciclib was calculated as the difference in cost (2021 US dollars) between the 2 scenarios over a 1- to 5-year time horizon. Scenario and deterministic sensitivity analyses were conducted to assess uncertainty around key model inputs. RESULTS: An estimated total of 301 patients were eligible for treatment with trilaciclib over a 5-year period. The use of trilaciclib was estimated to reduce the number of myelosuppressive AEs over a 5-year period (events avoided included 108 for neutropenia, 7 for febrile neutropenia, 23 for anemia, and 46 for thrombocytopenia) compared with the scenario without trilaciclib. The adoption of trilaciclib was associated with a cost saving of $801,254 ($0.013 PMPM) over 5 years. The acquisition cost for trilaciclib ($3,704,199) was offset by the reduction in AE management cost ($4,282,748) and reduction in prophylactic granulocyte colony-stimulating factor use ($222,704). The cost savings associated with trilaciclib began in year 1 (total $34,388; $0.003 PMPM) and accrued over time. CONCLUSIONS: The acquisition cost of trilaciclib is projected to be offset by a reduction in the costs of managing AEs related to myelosuppression when added to standard chemotherapy regimens for ES-SCLC. The net budget impact of trilaciclib is estimated to be a cost saving. DISCLOSURES: This research was funded by G1 Therapeutics, Inc., and implemented by ZS Associates, an independent consultancy that collated the model inputs and performed the budget impact analysis. The study sponsor was involved in the study design; collection, analysis, and interpretation of data; writing of the report; and the decision to submit the report for publication. The journal open access fee was funded by G1 Therapeutics, Inc. Moran, Chioda, and Huang are employed by G1 Therapeutics, Inc. Chioda and Huang report stocks and stock options for G1 Therapeutics, Inc. Goyal and Deniz are employed by ZS Associates. Goyal reports consulting fees from G1 Therapeutics, Inc. Abraham reports consulting fees from Coherus, G1 Therapeutics, Inc. (unrelated to this study and manuscript), Mylan/Viatris, and Sandoz and participation on a data safety monitoring board or advisory board for G1 Therapeutics, Inc. MacDonald reports consulting fees from Coherus, G1 Therapeutics, Inc. (unrelated to this study and manuscript), Mylan/Viatris, and Sandoz. Deniz reports no disclosures. A synopsis of the current study was presented in poster format at the Virtual AMCP Annual Meeting, April 12-16, 2021.

CDK4 and CDK6 kinases: From basic science to cancer therapy

Cyclin-dependent kinases 4 and 6 (CDK4 and CDK6) and their activating partners, D-type cyclins, link the extracellular environment with the core cell cycle machinery. Constitutive activation of cyclin D–CDK4/6 represents the driving force of tumorigenesis in several cancer types. Small-molecule inhibitors of CDK4/6 have been used with great success in the treatment of hormone receptor–positive breast cancers and are in clinical trials for many other tumor types. Unexpectedly, recent work indicates that inhibition of CDK4/6 affects a wide range of cellular functions such as tumor cell metabolism and antitumor immunity. We discuss how recent advances in understanding CDK4/6 biology are opening new avenues for the future use of cyclin D–CDK4/6 inhibitors in cancer treatment.

Exosomal miR-122-5p is Related to the Degree of Myelosuppression Caused by Chemotherapy in Patients with Colorectal Cancer

Purpose

As rapidly dividing cells are usually the target of anticancer chemotherapy, it is inevitable that rapidly dividing normal cells become damaged, with myelosuppressive effects being a serious side effect of this therapy. Many recent studies have found that exosomal microRNAs (miRNAs) are related to the occurrence of some diseases.

Patients and Methods

Small RNA sequencing was used to investigate differential exosomal miRNAs with the same expression trend between groups after chemotherapy: MildA (before chemotherapy in patients with mild myelosuppression) and MildB (after chemotherapy in patients with mild myelosuppression); SevereA (before chemotherapy in patients with severe myelosuppression) and SevereB (after chemotherapy in patients with severe myelosuppression). A Venn diagram was generated to screen exosomal miRNAs related to chemotherapy. Small RNA sequencing was also used to investigate differentially expressed exosomal miRNAs among these groups, and exosomal miRNAs related to myelosuppression after chemotherapy was explored using a Venn diagram. RT-qPCR was applied to further verify the sequencing results. We performed target gene prediction and functional analysis for candidate exosomal miRNAs.

Results

Compared with that in the MildA or SevereA group, an increase in exosomal miR-122-5p was found in the MildB or SevereB group, and the expression level was lower in the SevereB group than in the MildB group. However, we found no notable difference in its expression level between the MildA and SevereA groups. Similar results were not obtained for the remaining miRNAs. RT-qPCR confirmed the screening results. Further analyses indicated that exosomal miR-122-5p targets CDK4 to inhibit the cell cycle.

Conclusion

The expression level of exosomal miR-122-5p in the serum of patients with colorectal cancer correlates with the severity of myelosuppression caused by chemotherapy, and miR-122-5p targets CDK4 to inhibit cell cycle progression.

Cell size is a determinant of stem cell potential during aging

Stem cells are remarkably small. Whether small size is important for stem cell function is unknown. We find that hematopoietic stem cells (HSCs) enlarge under conditions known to decrease stem cell function. This decreased fitness of large HSCs is due to reduced proliferation and was accompanied by altered metabolism. Preventing HSC enlargement or reducing large HSCs in size averts the loss of stem cell potential under conditions causing stem cell exhaustion. Last, we show that murine and human HSCs enlarge during aging. Preventing this age-dependent enlargement improves HSC function. We conclude that small cell size is important for stem cell function in vivo and propose that stem cell enlargement contributes to their functional decline during aging.

Cell-based therapeutics for the treatment of hematologic diseases inside the bone marrow

Cell-based therapies could overcome the limitations of traditional drugs for the treatment of refractory diseases. Cell exchange between the bone marrow and blood is bidirectional. Several kinds of cells in the blood have the capability to enter the bone marrow by interacting with sinusoidal cells under specific physiological or pathological conditions. These cells are the potential living therapeutics or delivery vehicles to treat or prevent bone marrow-related hematologic diseases. In this review, we summarized the in vivo molecular mechanisms and kinetics of these cells in entering the bone marrow. The advances in the fabrication of living cell drugs and the strategies to design cell-based carriers into the bone marrow were discussed. The latest studies on how to use blood cells as living drugs or as drug carriers to improve therapeutic outcomes of hematologic diseases inside the bone marrow were highlighted.

Trilaciclib and the economic value of multilineage myeloprotection from chemotherapy-induced myelosuppression among patients with extensive-stage small cell lung cancer treated with first-line chemotherapy

AIMS

Proliferating hematopoietic stem and progenitor cells (HSPCs) are susceptible to chemotherapy-induced damage, resulting in myelosuppressive adverse events (AEs) such as neutropenia, anemia, and thrombocytopenia that are associated with high health care costs and decreased quality of life (QoL). In this study, a trial-based cost-effectiveness analysis was performed to help assess the economic impact of administering trilaciclib, a myeloprotective therapy that protects multilineage HSPCs from chemotherapy-induced damage, prior to standard first-line chemotherapy, using data from a pivotal Phase II study of trilaciclib in the setting of extensive-stage small cell lung cancer (ES-SCLC, NCT03041311).

METHOD

The aim of this study was to assess the cost-effectiveness of administering trilaciclib prior to chemotherapy versus chemotherapy alone among patients with ES-SCLC from a United States payer perspective. Data on the rate and frequency of myelosuppressive AEs and health utility were derived from the pivotal study of trilaciclib. Costs of managing myelosuppressive AEs and costs of chemotherapy treatment were sourced from published literature. Outcomes included the number of myelosuppressive AEs, costs (in 2021 US dollars), quality-adjusted life-years (QALYs), incremental cost, incremental QALY, and an incremental cost-effectiveness ratio.

RESULTS

Administering trilaciclib prior to chemotherapy was associated with a reduction in neutropenia (82%), febrile neutropenia (75%), anemia (43%), and thrombocytopenia (96%) compared with chemotherapy alone. Additionally, trilaciclib prior to chemotherapy was cost-saving compared with chemotherapy alone ($99,919 vs $118,759, respectively) and associated with QALY improvement (0.150 vs 0.145, respectively). Probabilistic sensitivity analyses showed 58% of iterations projecting cost savings and QALY improvement with trilaciclib.

CONCLUSIONS

The findings suggest that the use of trilaciclib prior to first-line chemotherapy in patients with ES-SCLC can be cost-beneficial owing to fewer myelosuppressive AEs and lower costs, together with a favorable QoL profile.

Therapy-Induced Senescence: Opportunities to Improve Anticancer Therapy

Cellular senescence is an essential tumor suppressive mechanism that prevents the propagation of oncogenically activated, genetically unstable, and/or damaged cells. Induction of tumor cell senescence is also one of the underlying mechanisms by which cancer therapies exert antitumor activity. However, an increasing body of evidence from preclinical studies demonstrates that radiation and chemotherapy cause accumulation of senescent cells (SnCs) both in tumor and normal tissue. SnCs in tumors can, paradoxically, promote tumor relapse, metastasis, and resistance to therapy, in part, through expression of the senescence-associated secretory phenotype. In addition, SnCs in normal tissue can contribute to certain radiation- and chemotherapy-induced side effects. Because of its multiple roles, cellular senescence could serve as an important target in the fight against cancer. This commentary provides a summary of the discussion at the National Cancer Institute Workshop on Radiation, Senescence, and Cancer (August 10-11, 2020, National Cancer Institute, Bethesda, MD) regarding the current status of senescence research, heterogeneity of therapy-induced senescence, current status of senotherapeutics and molecular biomarkers, a concept of "one-two punch" cancer therapy (consisting of therapeutics to induce tumor cell senescence followed by selective clearance of SnCs), and its integration with personalized adaptive tumor therapy. It also identifies key knowledge gaps and outlines future directions in this emerging field to improve treatment outcomes for cancer patients.

Palbociclib in breast cancer neoadjuvant setting

Cyclin-dependent kinase 4/6 inhibitors represent a major advance in breast cancer treatment, emerging as the standard of care of the initial treatment of hormone receptor-positive and HER2-negative metastatic breast cancer. Their activity in this subset of patients leads to interest in their use in the adjuvant and neoadjuvant settings. This case report presents a real-life case of cyclin-dependent kinase 4/6 inhibitors use in a patient initially considered to have stage IV luminal HER2-negative breast cancer with liver metastasis. The discrepancy of treatment response between the breast tumor and liver node led to a repetition of the liver biopsy, which revealed metastasis of a neuroendocrine tumor of unknown primary. The breast tumor showed a partial response, and the initial therapeutic strategy was then redefined for curative intent. While cyclin-dependent kinase 4/6 inhibitors are not yet approved for clinical practice in the neo / adjuvant treatment of hormone receptor-positive breast cancer, this case report portrays a successful example of its application in a neoadjuvant setting.

Myeloprotective Effects of Trilaciclib Among Patients with Small Cell Lung Cancer at Increased Risk of Chemotherapy-Induced Myelosuppression: Pooled Results from Three Phase 2, Randomized, Double-Blind, Placebo-Controlled Studies

Purpose

Trilaciclib is an intravenous cyclin-dependent kinase 4/6 inhibitor indicated to decrease the incidence of chemotherapy-induced myelosuppression (CIM) by protecting hematopoietic stem and progenitor cells and immune system function from chemotherapy-induced damage (myeloprotection). Here, we investigated the myeloprotective effects of trilaciclib among patients at increased risk of CIM.

Patients and Methods

Data were pooled from three randomized, double-blind, placebo-controlled, phase 2 clinical studies of trilaciclib administered prior to chemotherapy in patients with extensive-stage small cell lung cancer (ES-SCLC). Myeloprotective outcomes were evaluated in patient subgroups based on age (<65 or ≥65 years), risk of chemotherapy-induced febrile neutropenia (FN), and risk of anemia or red blood cell (RBC) transfusions. For the FN and anemia analyses, risk factors were identified from published literature and used to classify patients into FN and anemia risk categories. Subgroup analysis based on age was also performed on patient reported outcome (PRO) measures.

Results

In total, 123 patients received trilaciclib and 119 patients received placebo. Myeloprotective benefits of trilaciclib were observed regardless of age, with greater effects observed among patients aged ≥65 years. Across FN risk factors and categories, trilaciclib had beneficial effects on neutrophil-related endpoints vs placebo, with greater effects observed in patients at higher risk of FN. Effects on RBC-related endpoints favored trilaciclib vs placebo, regardless of anemia risk factors and categories. Improvements in PROs with trilaciclib were observed irrespective of age group, but with greater improvements and less deterioration from baseline observed in older patients.

Conclusion

By both decreasing the incidence of CIM and improving quality of life, trilaciclib has the potential to allow patients receiving chemotherapy for ES-SCLC, including patients who are older or more vulnerable to CIM, to receive chemotherapy on schedule and at standard-of-care doses, and to improve the experience for patients receiving chemotherapy to treat ES-SCLC.

Clinical Trial Numbers

NCT02499770; NCT03041311; NCT02514447.

Trilaciclib prior to chemotherapy reduces the usage of supportive care interventions for chemotherapy-induced myelosuppression in patients with small cell lung cancer: Pooled analysis of three randomized phase 2 trials

Background

Supportive care interventions used to manage chemotherapy‐induced myelosuppression (CIM), including granulocyte colony‐stimulating factors (G‐CSFs), erythropoiesis‐stimulating agents (ESAs), and red blood cell (RBC) transfusions, are burdensome to patients and associated with greater costs to health care systems. We evaluated the utilization of supportive care interventions and their relationship with the myeloprotective agent, trilaciclib.

Methods

Data were pooled from three independent randomized phase 2 clinical trials of trilaciclib or placebo administered prior to chemotherapy in patients with extensive‐stage small cell lung cancer (ES‐SCLC). The impact of supportive care on the duration of severe neutropenia (DSN), occurrence of severe neutropenia (SN), and occurrence of RBC transfusions on/after week 5 was analyzed across cycles 1–4. Concordance and association between grade 3/4 anemia, RBC transfusions on/after week 5, and ESA administration was also evaluated.

Results

The use of G‐CSFs, ESAs, or RBC transfusions on/after week 5 was significantly lower among patients receiving trilaciclib versus placebo (28.5% vs. 56.3%, p < 0.0001; 3.3% vs. 11.8%, p = 0.0254; and 14.6% vs. 26.1%, p = 0.0252, respectively). Compared with placebo, trilaciclib significantly reduced DSN and SN, irrespective of G‐CSF administration. RBC transfusions and ESAs were most often administered in patients with grade 3/4 anemia; however, patients typically received RBC transfusions over ESA administration.

Conclusions

By improving CIM and reducing the need for associated supportive care, trilaciclib has the potential to reduce the burden of myelosuppression on patients receiving myelosuppressive chemotherapy for the treatment of ES‐SCLC.

Trial registration

ClinicalTrials.gov (NCT02499770; NCT03041311; NCT02514447).