Early-phase development of cancer prevention agents: challenges and opportunities

Translation of a Tissue-Selective Rexinoid, UAB30, to the Clinic for Breast Cancer Prevention

This review focuses on our efforts to translate a low-toxicity retinoid X receptor-selective agonist, UAB30, to the clinic for the prevention of breast cancers. The review is divided into several sections. First, the current status of breast cancer prevention is discussed. Next, preclinical studies are presented that support translation of rexinoids to the clinic for cancer prevention. While current FDAapproved retinoids and rexinoids demonstrate profound effects in treating cancers, they lack sufficient safety for long term use in the high risk population that is otherwise disease free. The review stresses the need to identify cancer preventive drugs that are effective and safe in order to gain wide use in the clinic. Due to the heterogeneity of the disease, UAB30 is evaluated for the prevention of ER-positive and ER-negative mammary cancers. Since selective estrogen receptor modulators and aromatase inhibitors are used clinically to prevent and treat ER-positive breast cancers, preclinical studies also must demonstrate efficacy of UAB30 in combination with existing drugs under use in the clinic. To support an Investigational New Drug Application to the FDA, data on pharmacology and toxicity as well as mutagenicity is gathered prior to human trials. The review concludes with a discussion of the outcomes of human Phase 0/1 clinical trials that determine the safety and pharmacology of UAB30. These studies are essential before this agent is evaluated for efficacy in phase 2 trials. Success in phase 2 evaluation is critical before long-term and costly phase 3 trials are undertaken. The lack of surrogate biomarkers as endpoints for phase 2 evaluation of rexinoid preventive agents is discussed.

Cancer Prevention: Obstacles, Challenges and the Road Ahead

Approaches to reduce the global burden of cancer include two major strategies: screening and early detection and active preventive intervention. The latter is the topic of this Commentary and spans a broad range of activities. The genetic heterogeneity and complexity of advanced cancers strongly support the rationale for early interruption of the carcinogenic process and an enhanced focus on prevention as a priority strategy to reduce the burden of cancer; however, the focus of cancer prevention management should be on individuals at high risk and on primary localized disease in which screening and detection should also play a vital role. The timing and dose of (chemo-)preventive intervention also affects response. The intervention may be ineffective if the target population is very high risk or already presenting with preneoplastic lesions with cellular changes that cannot be reversed. The field needs to move beyond general concepts of carcinogenesis to targeted organ site prevention approaches in patients at high risk, as is currently being done for breast and colorectal cancers. Establishing the benefit of new cancer preventive interventions will take years and possibly decades, depending on the outcome being evaluated. We also propose that comparative effectiveness research designs and the value of information obtained from large-scale prevention studies are necessary in order for preventive interventions to become a routine part of cancer management.

Antioxidants meet molecular targets for cancer prevention and therapeutics

A fine balance between oxidants and antioxidants is required for the normal functioning of living systems. A deregulation of this balance has been implicated in many adverse effects and diseases, including cancer. Extensive research has been done in the area of cancer prevention and therapeutics by a wide range of antioxidants, especially naturally occurring and diet-based agents. However, additional efforts are still needed toward clinical development of the most promising antioxidant agents. For this purpose, it is important to focus our efforts toward (i) defining/validating new targets; (ii) identifying novel agents followed by assessments of their efficacy, safety/toxicity, metabolism, and bioavailability in appropriate model systems; and (iii) conducting clinical trials in an appropriate population. Although research with specific antioxidants is important, an emerging critical issue that is up for a debate is whether the "whole foods" concept is better for cancer prevention than a single agent. Recent work has suggested that the dietary phytochemicals can enhance the bioavailability of different nutrients and can target multiple molecular pathways to yield a better response. Another critical issue that is often ignored during target-based agent development is a lack of focus on the appropriate population for a specific target. It is possible that a specific target may not be appropriate for certain people. Further, we need to design quick "phase 0" clinical trials to eliminate the agents with little clinical potential. Thus, multidisciplinary efforts of researchers from diverse scientific disciplines are needed in order to take the most promising antioxidant agents from the bench to the bedside.