PD 0332991, a selective cyclin D kinase 4/6 inhibitor, preferentially inhibits proliferation of luminal estrogen receptor-positive human breast cancer cell lines in vitro

Abstract Introduction Alterations in cell cycle regulators have been implicated in human malignancies including breast cancer. PD 0332991 is an orally active, highly selective inhibitor of the cyclin D kinases (CDK)4 and CDK6 with ability to block retinoblastoma (Rb) phosphorylation in the low nanomolar range. To identify predictors of response, we determined the in vitro sensitivity to PD 0332991 across a panel of molecularly characterized human breast cancer cell lines. Methods Forty-seven human breast cancer and immortalized cell lines representing the known molecular subgroups of breast cancer were treated with PD 0332991 to determine IC50 values. These data were analyzed against baseline gene expression data to identify genes associated with PD 0332991 response. Results Cell lines representing luminal estrogen receptor-positive (ER+) subtype (including those that are HER2 amplified) were most sensitive to growth inhibition by PD 0332991 while nonluminal/basal subtypes were most resistant. Analysis of variance identified 450 differentially expressed genes between sensitive and resistant cells. pRb and cyclin D1 were elevated and CDKN2A (p16) was decreased in the most sensitive lines. Cell cycle analysis showed G0/G1 arrest in sensitive cell lines and Western blot analysis demonstrated that Rb phosphorylation is blocked in sensitive lines but not resistant lines. PD 0332991 was synergistic with tamoxifen and trastuzumab in ER+ and HER2-amplified cell lines, respectively. PD 0332991 enhanced sensitivity to tamoxifen in cell lines with conditioned resistance to ER blockade. Conclusions These studies suggest a role for CDK4/6 inhibition in some breast cancers and identify criteria for patient selection in clinical studies of PD 0332991

A phase I/II study of sitravatinib (MGCD-516) plus nivolumab in patients (pts) with metastatic clear-cell renal cell carcinoma (ccRCC) that progressed on prior VEGF-targeted therapy.

TPS708 Background: Sitravatinib is a potent oral tyrosine kinase inhibitor that targets multiple receptor tyrosine kinase pathways including the vascular endothelial growth factor (VEGF), c-MET, and the Tyro3, Axl, and MER family. These pathways can allow tumor cells to escape immune surveillance despite immune checkpoint therapy. We therefore hypothesized that combining sitravatinib with the anti-PD1 antibody nivolumab will enhance antitumor immune responses in pts with ccRCC. The present study is designed to determine the optimal dose for this combination using efficacy and toxicity as co-primary outcomes. Methods: This phase I/II trial uses the sequentially adaptive late-onset EffTox design (Jin et al. J Am Stat Assoc 2014), which accounts for potential late-onset toxicities induced by immunotherapy, and allows dose-finding based on both the efficacy and toxicity of each successive dose. Eligible pts have metastatic ccRCC that progressed on prior VEGF-targeted therapy. Each pt receives initially a pre-specified daily oral dose, among 4 dose levels (60mg, 80 mg, 120 mg, 150 mg), of sitravatinib monotherapy for 2 weeks to allow the drug to reach a pharmacokinetic steady state. Nivolumab is then added at the dose of 240 mg intravenously every 2 weeks. A maximum of 60 pts will be treated in up to 20 cohorts of 3 pts each. Tumor biopsies and peripheral blood are collected to assess changes in tumor microenvironment and immune markers at 4 different time points: 1) at baseline, up to 14 days prior to initiation of sitravatinib, 2) following 2 weeks of sitravatinib monotherapy, 3) after 2 infusions of nivolumab in combination with sitravatinib, and 4) at disease progression. The primary endpoint is optimal dose of sitravatinib based on toxicity (by week 12) and disease control rate (at week 6). Secondary endpoints include objective response rate, progression-free survival, and overall survival. At deadline for abstract submission, 4 pts have been treated on this study. Clinical trial information: NCT03015740. </jats:p

Targeting CDK4/6 and the Cell Cycle in Combination with Bortezomib in the 5T33MM Myeloma Model.

Abstract Multiple myeloma (MM) is ultimately fatal in part because no effective cell cycle-based therapy has been available to control tumor cell proliferation. Loss of cell cycle control in MM cells stems from coordinated deregulation of Cdk4-cyclin D1 or Cdk6 (Cdk4)-cyclin D2. PD 0332991 is the first orally bioactive small molecule that potently and specifically inhibits Cdk4 and Cdk6. It represents a promising cell cycle-based therapy for myeloma owing to its ability to potently inhibit Cdk4/6 and induce G1 cell cycle arrest in primary human myeloma cells in BM stromal cell co-cultures and to control tumor progression in a xenograft model. However, the efficacy of PD 0332991 in the presence of an intact immune system is unknown. To optimize therapeutic targeting of Cdk4/6 with PD 0332991, we investigated the effectiveness of PD 0332991 in inhibiting Cdk4/6 and controlling myeloma tumor progression in the immunocompetent, bone migrating 5T33MM model. By quantitative real-time PCR analysis, we found that these myeloma cells express a normal plasma cell transcription program such as upregulated Blimp-1 and loss of Bcl-6 expression. However, they proliferate aggressively due to Cdk4 overexpression and impaired p27Kip1 expression, thereby mimicking relapse disease in human myeloma. PD 0332991 potently inhibits Cdk4/6 phosphorylation of Rb in primary 5T33MM cells and induces G1 cell cycle arrest, both in vivo and ex vivo. Accordingly, treatment with PD 0332991 significantly prolongs the survival of tumor-induced 5T33MM mice; a mean of 35 days in the PD 0332991-treated group (N=9) versus 25 days in the vehicle-treated group (N=9, p&amp;lt; 0.003). These findings demonstrate for the first time that PD 0332991 targets Cdk4/6 and controls tumor expansion in the presence of an intact immune system. To further optimize Cdk4/6 targeting in MM, we combined PD 0332991 with bortezomib, a cytotoxic drug widely used in MM treatment. Pretreatment of 5T33MMvt cells with PD 0332991 for 48 hours markedly augmented bortezomib killing, to the same level of twice the dose of bortezomib when it was used alone. These studies of PD 0332991 in the immunocompetent 5T33MM model demonstrate that, as a consequence of Cdk4/6 inhibition and induction of G1 arrest, PD 0332991 sensitizes MM cells to killing by a cytotoxic agent. Targeting Cdk4/6 in combination therapy, therefore, represents a novel and promising strategy for myeloma treatment.</jats:p

Using the Rasch Model to Validate and Enhance the Interpretation of the Functional Assessment of Cancer Therapy–Kidney Symptom Index—Disease-Related Symptoms Scale

AbstractObjectivesThe Functional Assessment of Cancer Therapy–Kidney Symptom Index—Disease-Related Symptoms (FKSI-DRS) was developed to assess patients' kidney-cancer-related symptoms. The Rasch rating scale, a one-parameter logistic item response model, may enhance FKSI-DRS interpretation and validate its measurement properties.MethodsWe applied the Rasch model to FKSI-DRS data from a randomized phase 3 trial in which first-line sunitinib therapy showed superiority to interferon-alfa in patients with metastatic renal cell carcinoma. Of 750 enrolled patients, 668 patients completed the questionnaire on cycle 1, day 28 and were evaluated in the current study. The nine FKSI-DRS items were analyzed to enhance interpretation of the summary score by using an item characteristic curve that related score to probability of reporting specific symptoms.ResultsThe Rasch model fitted the FKSI-DRS well: 8 of 9 items had acceptable infit and outfit statistics (<1.5, >0.5); item difficulty spanned a wide range (−3.23 to 1.64 logits); and the five response categories performed adequately. The item characteristic curve offered enhanced interpretation of FKSI-DRS: For example, an FKSI-DRS score of 27 (mean baseline score for total sample) indicated a 47% chance of reporting “no” to “lack of energy,” although a two-point difference between sunitinib and interferon-alfa, averaged across all assessments (29 vs. 27), corresponded to sunitinib achieving a 28% increase (13% absolute difference) in the probability of reporting “no” to “lack of energy” (60% vs. 47%).ConclusionsData suggest that the FKSI-DRS is an adequate measure of symptom status in patients with metastatic renal cell carcinoma. The Rasch model supports its validation and enhances its interpretation

Induction of sequential G1 arrest and synchronous S phase entry by reversible CDK4/CDK6 inhibition sensitizes myeloma cells for cytotoxic killing through loss of IRF-4.

Abstract Abstract 299 Dysregulation of the cell cycle is a hallmark of cancer. However, targeting the cell cycle in cancer therapy has only been modestly successful since broad-spectrum cyclindependent kinase (CDK) inhibitors lack specificity and are highly toxic. The critical importance of controlling CDK4/CDK6 in cancer treatment is further exemplified by recent evidence of prominent CDK4/CDK6 dysregulation in human cancers, including breast cancer, metastatic lung adenocarcinoma, glioblastoma, mantle cell lymphoma and multiple myeloma (MM). To advance mechanism-based targeting of the cell cycle in cancer, we have developed a novel strategy that both inhibits cell cycle progression and enhances cytotoxic killing in tumor cells using PD 0332991(PD), the only known CDK4/CDK6-specific inhibitor that is also reversible, potent and orally bioavailable. We demonstrated by BrdU pulse-labeling that inhibition of CDK4/CDK6 with PD in primary bone marrow (BM) myeloma cells and human myeloma cell lines (HMCL) (IC50 60nM) leads to a complete early G1 arrest in the absence of apoptosis and upon release of the G1 block, synchronous cell cycle progression to S phase. Furthermore, prolonged early G1 arrest enhances cytotoxic killing of MM cells by diverse clinically relevant drugs at low dose, including bortezomib, carfilzomib (PR-171) and dexamethasone, and this is dramatically augmented during synchronous S phase entry. The enhancement of cytotoxic killing in either G1 arrest or synchronous S phase entry is sustained in the presence of BM stromal cells. This killing is caspase-dependent and triggered by the loss of mitochondrial outer membrane potential and activation of the intrinsic apoptosis pathway. Time course studies of cell cycle-specific gene expression by expression profiling, quantitative real time RT-PCR and immunoblotting further revealed that the expression of IRF-4, essential for normal plasma cell differentiation and myeloma cell survival, is strictly cell cycle-dependent: elevated in G1 and markedly declined in S phase. The IRF-4 protein is also markedly reduced (50%) by bortezomib treatment, resulting in a combined 5-fold reduction in S phase. This suggests that differential enhancement of cytotoxic killing in G1 arrest and S phase is mediated by cell cycle-dependent IRF-4 expression. Indeed, shRNA interference confirms that by antagonizing mitochondrial depolarization, IRF-4 is required to protect myeloma cells from cell cycle-dependent enhancement of bortezomib killing. By timely administration and discontinuation of PD treatment, we have further demonstrated in a human MM 1.S. xenograft myeloma model that it is feasible to induce sequential G1 arrest and synchronous S phase in vivo. This leads to synergistic tumor suppression through amplification of bortezomib killing of myeloma cells, but not normal BM cells. As PD is orally bio-available, specific and low in toxicity, our novel strategy has been implemented in the first phase I/II multi-center clinical trial targeting CDK4/CDK6 with PD in combination with bortezomib and dexamethasone in MM. Preliminary bone marrow immunohistochemistry demonstrates PD preferentially and completely inhibits CDK4/CDK6-specific phosphorylaton of Rb and DNA replication in tumor cells, but not other bone marrow cells in all patients. One patient achieved VGPR (12.5%) while 1 patient each achieved MR and SD respectively for an ORR 25% (Niesvizky et al, submitted). Collectively, our preclinical and clinical data indicate, for the fist time, that selective targeting of CDK4/CDK6 in combination therapy is a promising mechanism-based therapy for MM and potentially other cancers. Disclosures: Off Label Use: PD 0332991 is going to be used as a CDK4/6-specific inhibitor.. Chen:Pfizer, Inc.: Employment, Equity Ownership. Wilner:Pfizer, Inc.: Employment, Equity Ownership. Niesvizky:Millenium: Research Funding, Speakers Bureau; Celgene: Research Funding, Speakers Bureau; Seattle Genetics, Inc: Research Funding; Proteolix: Research Funding, data monitoring committee. Chen-Kiang:Pfizer Inc.: Research Funding. </jats:sec