BackgroundChemotherapy-induced damage of hematopoietic stem and progenitor cells (HSPC) causes multi-lineage myelosuppression. Trilaciclib is an intravenous CDK4/6 inhibitor in development to proactively preserve HSPC and immune system function during chemotherapy (myelopreservation). Preclinically, trilaciclib transiently maintains HSPC in G1 arrest and protects them from chemotherapy damage, leading to faster hematopoietic recovery and enhanced antitumor immunity.Patients and methodsThis was a phase Ib (open-label, dose-finding) and phase II (randomized, double-blind placebo-controlled) study of the safety, efficacy and PK of trilaciclib in combination with etoposide/carboplatin (E/P) therapy for treatment-naive extensive-stage small-cell lung cancer patients. Patients received trilaciclib or placebo before E/P on days 1–3 of each cycle. Select end points were prespecified to assess the effect of trilaciclib on myelosuppression and antitumor efficacy.ResultsA total of 122 patients were enrolled, with 19 patients in part 1 and 75 patients in part 2 receiving study drug. Improvements were seen with trilaciclib in neutrophil, RBC (red blood cell) and lymphocyte measures. Safety on trilaciclib+E/P was improved with fewer ≥G3 adverse events (AEs) in trilaciclib (50%) versus placebo (83.8%), primarily due to less hematological toxicity. No trilaciclib-related ≥G3 AEs occurred. Antitumor efficacy assessment for trilaciclib versus placebo, respectively, showed: ORR (66.7% versus 56.8%, P = 0.3831); median PFS [6.2 versus 5.0 m; hazard ratio (HR) 0.71; P = 0.1695]; and OS (10.9 versus 10.6 m; HR 0.87; P = 0.6107).ConclusionTrilaciclib demonstrated an improvement in the patient’s tolerability of chemotherapy as shown by myelopreservation across multiple hematopoietic lineages resulting in fewer supportive care interventions and dose reductions, improved safety profile, and no detriment to antitumor efficacy. These data demonstrate strong proof-of-concept for trilaciclib’s myelopreservation benefits.Clinical Trail numberNCT02499770.

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The phenotypic heterogeneity that characterizes human cancers reflects the enormous genetic complexity of the oncogenic process. This complexity can also be seen in mouse models where it is frequently observed that in addition to the initiating genetic alteration, the resulting tumor harbors additional, somatically acquired mutations that affect the tumor phenotype. To investigate the role of genetic interactions in the development of tumors, we have made use of the Eμ-myc model of pre-B and B cell lymphoma. Since various studies point to a functional interaction between Myc and the Rb/E2F pathway, we have investigated the role of E2F activities in the process of Myc-induced lymphomagenesis. Whereas the absence of E2F1 and E2F3 function has no impact on Myc-mediated tumor development, the absence of E2F2 substantially accelerates the time of tumor onset. Conversely, tumor development is delayed by the absence of E2F4. The enhanced early onset of tumors seen in the absence of E2F2 coincides with an expansion of immature B lineage cells that are likely to be the target for Myc oncogenesis. In contrast, the absence of E2F4 mutes the response of the lineage to Myc and there is no expansion of immature B lineage cells. We also find that distinct types of tumors emerge from the Eμ-myc mice, distinguished by different patterns of gene expression, and that the relative proportions of these tumor types are affected by the absence of either E2F2 or E2F4. From these results, we conclude that there are several populations of tumors that arise from the Eμ-myc model, reflecting distinct populations of cells that are susceptible to Myc-mediated oncogenesis and that the proportion of these cell populations is affected by the presence or absence of E2F activities.

8505 Background: Multi-lineage myelosuppression is an acute toxicity of cytotoxic chemotherapy leading to hematologic adverse events and dose reductions and delays. Current therapies are lineage specific and administered after chemotherapy damage.Trilaciclib (T), a highly selective, reversible CDK4/6 inhibitor, is designed to preserve hematopoietic stem and progenitor cells and immune system function during chemotherapy (myelopreservation). We have shown that T mitigates myelosuppression in patients with newly diagnosed extensive-stage small cell lung cancer (ES-SCLC) receiving 1st-line chemotherapy. Methods: In this blinded, placebo-controlled, multicenter Phase 2 study, patients with previously treated ES-SCLC were randomized to T (240 mg/m2) + 0.75 mg/m2 topotecan, T (240 mg/m2) + 1.5 mg/m2 topotecan, or placebo (P) + 1.5 mg/m2 topotecan IV on days 1-5 of 21-day cycles. Patients had access to standard supportive care, except in cycle 1 where prophylactic growth factors were not allowed. Eligible patients had adequate organ function, measurable disease, ECOG PS 0-2, and disease progression during or after prior 1st/2nd-line chemotherapy. Objectives included safety, tolerability, measures of myelosuppression and tumor efficacy. Results: 91 patients were randomized: 30 patients received T + 0.75 mg/m2 topotecan, 32 patients received T + 1.5 mg/m2 topotecan and 28 patients received P + 1.5 mg/m2 topotecan. In patients receiving 1.5 mg/m2 topotecan, T treatment reduced occurrence [40.6% (T) vs 75.6% (P), p = 0.016], and duration in cycle 1 [2 days (T) vs 8 days (P), p = < 0.0001] of severe neutropenia. T-treated patients had fewer RBC transfusions on/after 5 weeks on study, GCSF administrations, and all-cause dose reductions. Chemotherapy efficacy was comparable in both arms (P and T) treated with 1.5 mg/m2 topotecan (median PFS (T) 4.2 months vs (P) 4.2 months, HR = 0.83). OS data is immature. Conclusions: T combined with topotecan mitigated chemotherapy-induced myelosuppression and improved tolerability of topotecan vs P. Results suggest the addition of T to cytotoxic chemotherapy for the treatment of ES-SCLC is clinically beneficial. Clinical trial information: NCT02514447.