Decisions on Non-oncology Breakthrough Therapy Designation Requests in 2017-2019.

BACKGROUND: The US Food and Drug Administration's Breakthrough Therapy Designation (BTD) program is intended to facilitate and expedite development of investigational drugs to address unmet medical needs. The objective of this study is to provide an update on FDA's process for review of BTD requests. METHODS: We reviewed Center for Drug Evaluation and Research (CDER) decisions to grant or deny breakthrough therapy designation requests for non-oncology drugs or biological products ("drugs") from January 1, 2017, through December 31, 2019. Data collection included characteristics of the corresponding drug and condition, reasons for granting or denying breakthrough therapy status, reasons for rescinding or withdrawing breakthrough therapy status after a request was granted (if applicable), and subsequent marketing approval status through 2022. RESULTS: Among 240 requests, 93 (39%) requests were granted and 147 (61%) requests were denied. Granting of requests was more common for conditions where no therapy was available or for orphan diseases. Common reasons for denial included data-related issues, insufficient treatment effect, inadequate study design, endpoint attributes, safety issues, and reliance on post hoc analyses. Among 28 drugs receiving marketing approval as of the end of 2022 for the indication for which BTD was previously granted, 21 (75%) involved a first-in-class mechanism of action. CONCLUSIONS: This analysis describes CDER's decision-making process related to review of requests for breakthrough therapy designations and enhances public awareness regarding efforts to expedite drug development.

Demographic Diversity of Clinical Trials for Therapeutic Drug Products: A Systematic Review of Recently Published Articles, 2017-2022.

The US Food and Drug Administration (FDA) encourages the use of enrollment practices that will lead to clinical trials that reflect the population most likely to use the therapeutic product (drug or biologic), if approved. In doing so, the benefit-risk profile of the product may be assessed more completely and offer patients and their health care providers a better understanding of the drug profile and greater confidence in clinical trial results. The objective of this systematic review was to assess recent literature on the demographic diversity of clinical trial participants, describe the methods used in defining clinical trial diversity, and address knowledge gaps to enhance clinical trial diversity. Our literature search initially yielded 246 articles. After applying our eligibility criteria, we conducted a full-text review and analyzed the contents of the 28 remaining articles in our systematic review. Eleven (39%) of the 28 articles used a reference standard to compare the participation of populations in clinical trials to assess diversity. The majority of the 28 articles reported on adult participants; only 5 included pediatric populations. Most articles found that women and minority populations were underrepresented in clinical trials. Some articles proposed solutions to improve clinical trial diversity; however, several did not comment on clinical trial diversity. Despite a growing emphasis on demographic diversity in research, certain populations continue to be underrepresented in clinical trials. There is a need to standardize the definition of diversity in clinical trials. Future research into effective enrollment approaches and appropriate reference standards could improve demographic diversity.

The human papillomavirus type 8 E2 tethering protein targets the ribosomal DNA loci of host mitotic chromosomes.

For many papillomaviruses, the viral protein E2 tethers the viral genome to the host mitotic chromosomes to ensure persistent, long-term maintenance of the genome during cell division. Our previous studies of E2 proteins from different genera of papillomaviruses have shown that they bind to different regions of the host chromosomes during mitosis. For example, bovine papillomavirus type 1 (BPV-1) E2 binds to all chromosomes as small speckles in complex with the cellular protein Brd4. In contrast, the human papillomavirus type 8 (HPV-8) E2 protein binds as large speckles at the pericentromeric regions of chromosomes. Here we show that these speckles do not contain Brd4, and unlike that of BPV-1, the N-terminal Brd4-interacting domain of HPV-8 E2 is not required for chromosome binding. In contrast to BPV-1 E2, the HPV-8 E2 protein targets the short arms of acrocentric mitotic chromosomes. Furthermore, the E2 protein interacts with the repeated ribosomal DNA genes found in this location and colocalizes with UBF, the RNA polymerase I transcription factor. Therefore, HPV-8 E2 genome tethering occurs by a Brd4-independent mechanism through a novel interaction with specific regions of mitotic chromosomes. Thus, a wide range of viruses have adopted the strategy of linking their genomes to host chromosomes, but individual viruses use different chromosomal targets. Characterization of these targets will enable the development of antiviral therapies to eliminate the viral genomes from infected cells.

Two complexes of spindle checkpoint proteins containing Cdc20 and Mad2 assemble during mitosis independently of the kinetochore in Saccharomyces cerevisiae.

Favored models of spindle checkpoint signaling propose that two inhibitory complexes (Mad2-Cdc20 and Mad2-Mad3-Bub3-Cdc20) must be assembled at kinetochores in order to inhibit mitosis. We have directly tested this model in the budding yeast Saccharomyces cerevisiae. The proteins Mad2, Mad3, Bub3, Cdc20, and Cdc27 in yeast were quantified, and there are sufficient amounts to form stoichiometric inhibitors of Cdc20 and the anaphase-promoting complex. Mad2 is present in two separate complexes in cells arrested in mitosis with nocodazole. There is a small amount of Mad2-Mad3-Bub3-Cdc20 and a much larger amount of a complex that contains Mad2-Cdc20. We use conditional mutants to show that both Mad2 and Mad3 are essential for establishment and maintenance of the spindle checkpoint. Both spindle checkpoint complexes containing Mad2 form in mitosis, not in response to checkpoint activation. The kinetochore is not required to form either complex. We propose that the conversion of Mad1-Mad2 to Cdc20-Mad2, a key step in generating inhibitory checkpoint complexes, is limited to mitosis by the availability of Cdc20 and is kinetochore independent.

Differential kinetochore requirements for establishment and maintenance of the spindle checkpoint are dependent on the mechanism of checkpoint activation in Saccharomyces cerevisiae.

The spindle checkpoint in the yeast Saccharomyces cerevisiae is an intracellular signal transduction pathway comprised of two branches that inhibit two different mitotic transitions in cells treated with benzimidazole drugs such as nocodazole. The kinetochore is an integral component of the MAD2 branch of the spindle checkpoint pathway. Current models propose that the kinetochore is required for both the establishment and maintenance of the spindle checkpoint but a role for the kinetochore in the maintenance of spindle checkpoint in yeast has never been directly tested. We used a temperature sensitive ndc10-1 mutant to inactivate kinetochores before and after arresting cells in mitosis to determine the role of kinetochores in the establishment and maintenance of the spindle checkpoint. We show that both establishment and maintenance requires kinetochore function in response to spindle damage induced by benzimidazole drugs. Excess expression of the Mps1 protein kinase causes wild type cells and ndc10-1 cells to arrest in mitosis. Unlike the spindle checkpoint arrest activated by benzimidazoles, this arrest can be maintained independently of kinetochores. The arrest induced by excess Mps1p is independent of BUB2. Therefore, mitotic arrest induced by excess Mps1p expression is due to the action of the MAD2 branch of the spindle checkpoint pathway and excess Mps1p acts downstream of the kinetochore.