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Castration-resistant prostate cancers (CRPCs) lose sensitivity to androgen-deprivation therapies but frequently remain dependent on oncogenic transcription driven by the androgen receptor (AR) and its splice variants. To discover modulators of AR-variant activity, we used a lysate-based small-molecule microarray assay and identified KI-ARv-03 as an AR-variant complex binder that reduces AR-driven transcription and proliferation in prostate cancer cells. We deduced KI-ARv-03 to be a potent, selective inhibitor of CDK9, an important cofactor for AR, MYC, and other oncogenic transcription factors. Further optimization resulted in KB-0742, an orally bioavailable, selective CDK9 inhibitor with potent anti-tumor activity in CRPC models. In 22Rv1 cells, KB-0742 rapidly downregulates nascent transcription, preferentially depleting short half-life transcripts and AR-driven oncogenic programs. In vivo, oral administration of KB-0742 significantly reduced tumor growth in CRPC, supporting CDK9 inhibition as a promising therapeutic strategy to target AR dependence in CRPC., Competing Interests: Declaration of Interests A.N.K. is a founder and member of the scientific advisory board of Kronos Bio, Inc. D.B.F., N.B.S., S.K.D., A.R., M.S.P., and A.N.K. are inventors on patent applications related to KI-ARv-03., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Emerging literature suggests that metabolic pathways play an important role in the maintenance and progression of human cancers. In particular, recent studies have implicated lipid biosynthesis and desaturation as a requirement for tumor cell survival. In the studies reported here, we aimed to understand whether tumor cells require the activity of either human isoform of stearoyl-CoA-desaturase (SCD1 or SCD5) for survival. Inhibition of SCD1 by siRNA or a small molecule antagonist results in strong induction of apoptosis and growth inhibition, when tumor cells are cultured in reduced (2%) serum conditions, but has little impact on cells cultured in 10% serum. Depletion of SCD5 had minimal effects on cell growth or apoptosis. Consistent with the observed dependence on SCD1, but not SCD5, levels of SCD1 protein increased in response to decreasing serum levels. Both induction of SCD1 protein and sensitivity to growth inhibition by SCD1 inhibition could be reversed by supplementing growth media with unsaturated fatty acids, the product of the enzymatic reaction catalyzed by SCD1. Transcription profiling of cells treated with an SCD inhibitor revealed strong induction of markers of endoplasmic reticulum stress. Underscoring its importance in cancer, SCD1 protein was found to be highly expressed in a large percentage of human cancer specimens. SCD inhibition resulted in tumor growth delay in a human gastric cancer xenograft model. Altogether, these results suggest that desaturated fatty acids are required for tumor cell survival and that SCD may represent a viable target for the development of novel agents for cancer therapy., (Mol Cancer Res; 9(11); 1551-61. ©2011 AACR.)

Mutations that inactivate the retinoblastoma (Rb) pathway are common in human tumors. Such mutations promote tumor growth by deregulating the G1 cell cycle checkpoint. However, uncontrolled cell cycle progression can also produce new liabilities for cell survival. To uncover such liabilities in Rb mutant cells, we performed a clonal screen in the Drosophila eye to identify second-site mutations that eliminate Rbf(-) cells, but allow Rbf(+) cells to survive. Here we report the identification of a mutation in a novel highly conserved peptidyl prolyl isomerase (PPIase) that selectively eliminates Rbf(-) cells from the Drosophila eye.

The insulin-like growth factor I receptor (IGF-IR) is a transmembrane tyrosine kinase that is essential to growth and development and also thought to provide a survival signal for the maintenance of the transformed phenotype. There has been increasing interest in further understanding the role of IGF-I signaling in cancer and in developing receptor antagonists for therapeutic application. We describe herein a novel animal model that involves transgenic expression of a fusion receptor that is constitutively activated by homodimerization. Transgenic mice that expressed the activated receptor showed aberrant development of the mammary glands and developed salivary and mammary adenocarcinomas as early as 8 weeks of age. Xenograft tumors and a cell line were derived from the transgenic animals and are sensitive to inhibition by a novel small-molecule inhibitor of the IGF-IR kinase. This new model should provide new opportunities for further understanding how aberrant IGF-IR signaling leads to tumorigenesis and for optimizing novel antagonists of the receptor kinase.

Purpose: To report the long-term survival and late toxicity data of Stage III follicular lymphoma patients treated with primary radiotherapy., Methods and Materials: Sixty-six patients with Stage III follicular small cleaved (FSC) or follicular mixed (FM) non-Hodgkin's lymphoma were treated with total lymphoid irradiation (61 patients) or whole body irradiation (5 patients) as their primary treatment modality from 1963 to 1982 at Stanford University. Adjuvant chemotherapy was given to 13 patients., Results: Median follow-up was 9.5 years with a range of 0.5-24.3 years. Median overall survival, cause-specific survival, freedom from relapse, and event-free survival were 9.5, 18.9, 7.1, and 5.1 years, respectively. Few initial relapses or lymphoma-related deaths were seen beyond the first decade of follow-up. Patient age and number of disease sites were the two strongest predictors of overall survival. The cohort of patients with limited Stage III disease demonstrated an 88% freedom from relapse and a 100% cause-specific survival with up to 23.5 years follow-up., Conclusion: The long-term survival data for Stage III FSC or FM non-Hodgkin's lymphoma treated with primary radiotherapy are at least comparable and possibly better than results achieved with other therapeutic approaches. Patients with limited Stage III disease do particularly well. Whether these results are superior to an initial approach of deferred therapy until clinically indicated is currently unknown.

Currently, the contribution of cellular apoptotic sensitivity to tumor response after radiation therapy remains controversial. To address this issue, the survival of Rat-1 fibroblasts containing a 4-hydroxytamoxifen-regulated c-Myc allele, c-MycER (T. D. Littlewood et al., Nucleic Acids Res., 23: 1686-1690, 1995), after single and fractionated doses of radiation was investigated. This model system allows pharmacological regulation of apoptosis sensitivity in the same cells in vitro and as xenograft tumors derived from these cells in vivo (G. I. Evan et al., Cell, 69: 119-128, 1992; R. M. Alarcon et al., Cancer Res., 56: 4315-4319, 1996). Activating c-MycER in vitro resulted in marked sensitization of Rat-1 fibroblasts to the effects of both single-dose and fractionated irradiation as measured by the induction of apoptosis and clonogenic survival. Overexpression of the antiapoptosis protein Bcl-2 suppressed the induction of apoptosis and increased clonogenic survival in cells with activated c-Myc after single-dose and fractionated radiation. Systemic time-release implant delivery of 4-hydroxytamoxifen to severe combined immunodeficient mice bearing Rat-1-MycER tumors over the course of either single-dose (10 Gy) or fractionated (five fractions of 2 Gy) radiotherapy resulted in prolonged tumor growth delay relative to identical tumors from mice that received placebo implants. Furthermore, tumors derived from Rat-1-MycER cells that overexpressed Bcl-2 exhibited shorter tumor growth delays relative to similarly treated Rat-1-MycER tumors. The length of tumor growth delay after single-dose or fractionated radiotherapy strongly correlated with the extent of radiation-induced apoptosis in the xenograft tumors as measured by terminal deoxynucleotidyl transferase-mediated nick end labeling. These in vivo results provide direct evidence that increasing the sensitivity of tumor cells to die by apoptosis increases the efficacy of fractionated radiotherapy by reducing tumor cell clonogenic survival.

Deregulated c-Myc expression leads to a cellular state where proliferation and apoptosis are equally favored depending on the cellular microenvironment. Since the apoptotic sensitivity of many cells is influenced by the status of the p53 tumor suppressor gene, we investigated whether the induction of apoptosis by DNA damage or non-genotoxic stress are also influenced by the p53 status of cells with altered c-Myc activity. Rat-1 fibroblasts expressing a conditional c-Myc allele (c-MycER), were transfected to express an antisense RNA complimentary to p53 mRNA. Expression of antisense p53 RNA decreased p53 protein levels and delayed p53 accumulation following c-Myc activation. Under hypoxic or low serum conditions, cells expressing antisense p53 were substantially more resistant to c-Myc-induced apoptosis than were control cells. c-Myc activation also sensitized Rat-1 cells to radiation-induced apoptosis. Rat-1 cells expressing antisense p53 RNA were more resistant to apoptosis induced by the combined effects of c-Myc activation and gamma irradiation. In a similar manner, apoptosis induced by c-Myc in serum starved, hypoxic or gamma irradiated fibroblasts was also inhibited by Bcl-2. These data indicate that p53 is involved in c-Myc-mediated apoptosis under a variety of stresses which may influence tumor growth, evolution and response to therapy.

We have developed an animal tumor model system to study the effects of c-Myc activation on apoptosis induction in vivo. Tumors were generated in SCID mice from Rat-1 fibroblasts that constitutively express an inactive c-Myc-estrogen receptor fusion protein (T.D. Littlewood et al, Nucleic Acids Res., 23: 1686 -1690, 1995), which is activated in vivo by the administration of 4-hydroxytamoxifen in time release pellets. We demonstrate that activation of c-Myc results in a substantial increase in the number of apoptotic tumor cells and that this apoptosis is predominant in regions of tumor hypoxia. c-Myc-induced apoptosis of hypoxic cells is inhibited in tumors that overexpress the human Bcl-2 protein. Bcl-2, however, does not prevent p53 protein accumulation or the down-regulation of the cyclin-cdk inhibitor p27 protein following c-Myc activation by 4-hydroxytamoxifen. This result suggests that Bcl-2 does not affect c-Myc function directly but acts downstream of c-Myc to inhibit apoptosis. We propose that the ability of activated c-Myc to enhance cellular proliferation might contribute to the genesis of early neoplasms that are held in check by the alternate ability of c-Myc to induce apoptosis of cells that have outgrown their supply of oxygen or other factors associated with hypoxic regions of solid tumors. Secondary genetic lesions downstream of c-Myc that suppress the apoptotic potential of tumor cells, such as Bcl-2 overexpression, might play an important role in the malignant progression of these tumors because they would disrupt the balance between apoptosis and proliferation initiated by c-Myc deregulation.