The enormous diversity of uncultured microorganisms in soil and other environments provides a potentially rich source of novel natural products, which is critically important for drug discovery efforts. Our investigators reported previously on the creation and screening of an Escherichia coli library containing soil DNA cloned and expressed in a bacterial artificial chromosome (BAC) vector. In that initial study, our group identified novel enzyme activities and a family of antibacterial small molecules encoded by soil DNA cloned and expressed in E. coli. To continue our pilot study of the utility and feasibility of this approach to natural product drug discovery, we have expanded our technology to include Streptomyces lividans and Pseudomonas putida as additional hosts with different expression capabilities, and herein we describe the tools we developed for transferring environmental libraries into all three expression hosts and screening for novel activities. These tools include derivatives of S. lividans that contain complete and unmarked deletions of the act and red endogenous pigment gene clusters, a derivative of P. putida that can accept environmental DNA vectors and integrate the heterologous DNA into the chromosome, and new BAC shuttle vectors for transferring large fragments of environmental DNA from E. coli to both S. lividans and P. putida by high-throughput conjugation. Finally, we used these tools to confirm that the three hosts have different expression capabilities for some known gene clusters.Natural products have been a rich source of pharmaceutical molecules, accounting for greater than 30% of all human therapeutics and more than 60% of antiinfective and anticancer drugs. Despite the advances in high-throughput screening technology and attempts to isolate and culture microorganisms from exotic environments, the discovery of novel natural products remains difficult. However, it has become clear that the vast majority of microorganisms in the environment are still unknown and that most of them are unculturable under standard laboratory conditions (15,38). Since the number of such "unculturable" microbial species in the soil represents at least 98% of the total population, these species constitute a potentially large untapped pool of novel natural products. To access their genetic information, the DNA of these microorganisms can be isolated directly from environmental samples, cloned into suitable vectors, and expressed in surrogate hosts that can be grown in the laboratory and manipulated genetically (9,17,18,26,29,36).Previously, our investigators and others reported on methods to isolate and clone environmental DNA and screen for novel bioactivities (9,17,18,26,29) using Escherichia coli strains and vectors. Although interesting and novel activities have been expressed and identified in this host, the potential advantage of expanding the range of bacterial hosts to capture additional expression capability is clear. We chose to extend our expression host range to include Streptomyces lividans an...

Here we describe the rep gene, isolated from an environmental DNA library, which when transformed into Streptomyces species resulted in increased production of secondary metabolites and accelerated sporulation. We show that Streptomyces lividans strains bearing rep are particularly useful as expression hosts for heterologous antibiotic production.Natural products from environmental microorganisms account for over 30% of all human therapeutics and over 60% of anti-infective and anticancer drugs. These include polyketides, produced by microbes such as Streptomyces, Saccharopolyspora, and Aspergillus species. Although the majority of microorganisms in the environment are still unknown, most are unculturable under standard laboratory conditions. If these uncultured species could be accessed, they could potentially provide a large, untapped pool of novel natural products. In a recent approach, microbial DNA was extracted directly from environmental samples, cloned into suitable vectors, and expressed in surrogate laboratory host strains (2,7,8,10).Because of their ease of use and ability to express polyketides, Streptomyces species are logical surrogate hosts for soil DNA libraries. Streptomyces lividans is usually preferred for genetic manipulation because it lacks methylation-dependent restriction, allowing efficient transfer of DNA from Escherichia coli cloning strains. However, S. lividans does not produce antibiotics as abundantly as does Streptomyces coelicolor, and its morphological development is delayed (6). It has been shown that overexpression of clpX (3) and mutations in the rpsL gene (11) and in glucose-6-phosphate dehydrogenase genes (1) result in increased endogenous actinorhodin synthesis in S. lividans, although it is not currently known whether these results extend to heterologous antibiotics. Therefore, a need remains for an expression host that combines the absence of methylation-dependent restriction systems with a high level of heterologous secondary metabolite production and that can be used conveniently for assaying soil DNA libraries for antiinfective and other activities. We show here that the rep gene, isolated from a soil environmental DNA library, confers to S. lividans both accelerated sporulation and overproduction of endogenous and heterologous secondary metabolites. Thus, S. lividans bearing this gene constitutes an improved expression host for heterologous DNA libraries.Phenotypes conferred by cosmid 2A7. Cosmid 2A7, previously isolated as part of a soil DNA library (2), contains approximately 40.4 kb of soil DNA cloned into the E. coli-Streptomyces shuttle vector pOSI700. When grown in glucosecontaining medium (e.g., SMM or R5 [5]), S. lividans TK24 bearing this cosmid sporulated early (after 3 days in SMM versus 8 days for the control strain) and produced an enhanced level of actinorhodin, an endogenous pigment. To ascertain that this phenotype was encoded on the cosmid, 2A7 was retransformed into S. lividans TK24. Transformants again displayed both early sporulation and early, inc...

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Estrogen receptor (ER) blockade is a well-established therapeutic approach in ER+ breast cancer. A novel oral selective estrogen receptor degrader (SERD), LSZ102, is in development. LSZ102 induces proteasome-mediated degradation of both wild type and mutant ERα in MCF-7 cells. LSZ102 also inhibits transcription of ERα target genes and results in a decrease in cell proliferation in a dose dependent manner. Expression of ERα Y537S results in a shift in inhibition of cell proliferation upon incubation with either LSZ102 or fulvestrant; however, the shift with LSZ102 was less severe. Similarly, LSZ102 induced a more pronounced level of ERα degradation than fulvestrant in the Y537S mutant MCF7 cells. Overall, LSZ102 is effective in the wild type and Y537S ERα mutant setting in vitro. In vivo, LSZ102 treatment of ER+ breast cancer xenografts resulted in inhibition of ERα regulated transcripts and a decrease in ERα protein levels. In the MCF7 xenograft model, expression of ERα Y537S resulted in reduced activity by fulvestrant, but not by LSZ102. In vivo, LSZ102 exhibited single agent and combination efficacy upon co-administration with the CDK4/6 inhibitor ribociclib and the alpha-specific PI3K inhibitor alpelisib. LSZ102 is currently in a Phase I clinical trial in patients with ER+ breast cancer in which it is tested as a single agent, and in combination with either ribociclib or alpelisib. Citation Format: L. Alex Gaither, Choi Lai Tiong Yip, Chunrong Wang, Weiyi Toy, Qing Sheng, Jinyun Chen, Yuji Mishina, Rita Das, Stefan Peukert, Alice Loo, Sarat Chandarlapaty, Adam Crystal, Tinya J. Abrams. Preclinical anticancer activity of LSZ102, a novel oral selective estrogen receptor degrader targeting wild-type and mutant ER [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 922.