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Why oncology needs dosing redesign.
Optimizing drug dosing in oncology has long been a challenge. The current drug development paradigm is oriented toward identifying a maximum tolerated dose (MTD) in early-stage trials, and evaluating the MTD for drug activity and efficacy in Phase II and III trials. In recent years, the limitations of this approach have become clearer.
First, the existing oncology drug development methodology does not adequately evaluate inter-patient variability in treatment response and toxicity. As a result, the dose-exposure-response relationship is rarely well defined for oncology drugs, despite their narrow therapeutic indices. Secondly, the current approach also leaves room for clinically meaningful pharmacodynamic endpoints—such as target inhibition—to be overlooked, despite their potential importance for new classes of medicine. Neglecting the impact of biological modulation may result in poor outcomes for patients.
Most importantly, the classical drug development paradigm does not adequately characterize long-term toxicity. This oversight is problematic, as patients on new biological therapies are expected to undergo treatment for much longer periods of time. Patients may use targeted drugs for months or years, which increases the importance of evaluating long-term tolerability.
In the wake of evidence that many approved oncology drugs are inadequately characterized with approved doses that may be too high, the FDA’s Oncology Center of Excellence has launched an initiative to reform the dose optimization and dose selection paradigm in oncology drug development. Known as Project Optimus, this initiative recommends a core change in how doses are selected during oncology clinical trials and post-approval studies.
As the design of drug trials is guided by the results of prior research phases, the FDA is recommending a concerted effort to rethink dosing beginning with first-in-human studies. At present, Phase I oncology studies are almost entirely designed to identify and achieve the maximum tolerated dose (MTD), which is unique to oncology drug development. Non-oncology trial designs have a long history of employing dose-ranging approaches that balance efficacy outcomes with toxicity profiles.
In Phase I oncology trials, the objective is to determine the highest tolerable dose, based on the assumption that higher doses will provide greater efficacy (i.e., disease-free survival). In these trials, increasing doses of a drug are sequentially evaluated in small cohorts of patients until a pre-specified rate of dose-limiting toxicity (DLT) is reached. The dose immediately below that which elicited DLT is considered the maximum-tolerated dose (MTD); in most cases, the MTD is then used for Phase II and subsequent Phase III trials, which are used to evaluate drug activity and efficacy. Currently, it is rare for Phase II or III studies of oncology drugs to evaluate more than one dose, although this approach is common in other therapeutic areas.
Trial design flexibility has lagged behind innovation in oncology research. The flourishing of gene therapy, biologics, and anti-body drug conjugates (ADCs) has reinvented how we approach oncology treatment. The promise of more targeted treatment approaches with lower toxicity is a near reality, and will in turn require a much more thoughtful and patient-specific dosing strategy. A true targeted approach requires a molecularly targeted therapy with a tailored dosing regimen that maximizes the benefit/risk ratio for patients receiving the drug.
Clearly, a migration away from MTD-focused study design is long overdue, and the FDA’s guidance has already begun to influence oncology drug development processes. The first impact of Project Optimus concerns imminent drug candidates for regulatory approval. The volume of post-marketing requirements and commitments will increase, placing a greater burden on pharmaceutical companies that have not conducted earlier phase dose optimization. Anecdotally, the pursuit of post-marketing research to further prove and maintain labeling already exceeds two-thirds of all approved drugs. This practice can be expected to grow and become more comprehensive in nature.
In parallel, drugs at various stages of Phase II or III research may require additional testing. Drug candidates in Phase III may be subject to more stringent post-marketing requirements and/or commitments. Phase II drug candidates may require further dose-response analysis to validate the current dose against one or more doses. It remains to be seen how much latitude the agency will grant during this transition period. At the very least, we know the FDA’s go-forward expectation is that the industry will begin conducting randomized dose-ranging studies prior to Phase III.
Finally, Project Optimus is expected to make a substantial imprint on all new Phase I study designs, as these serve as the foundation of oncology dose strategies. The FDA’s ultimate goal is to affect a paradigm shift in Phase I study design and the subsequent interplay between Phase I and II research. All appropriate Phase I trials should determine a range of doses to be studied in Phase II. This pivotal change in strategy will have a cascading effect throughout the drug development process and onward, impacting real-world outcomes.
For patients to fully benefit from the great strides in new oncology treatments, we must architect drug development strategies that include dose optimization but do not unnecessarily delay market entry for critical new drugs. The process of determining the optimal dose will depend on the drug, the target population, and existing clinical data for the drug in question, as well as approved drugs that exhibit a similar mechanism of action.
At the 2013 Conference on Clinical Cancer Research, a panel of experts from the pharmaceutical industry, the FDA, and the American Society of Clinical Oncology co-authored a brief on how to both optimize dose selection and provide a better understanding of the relationship between drug exposure and clinical outcomes. The authors proposed to include adequate PK sampling and pharmacodynamic endpoint measurements in Phase I-III. The authors also suggest incorporating adaptive clinical trial designs in Phase II to characterize the relationship between exposure and clinical outcomes, describe the variability in PK/PD, and optimize the dose. Finally, the authors recommend collecting patient-reported outcomes in Phase II and III and using that data, along with PK/PD endpoints, to guide dose optimization.
The authors also discussed how integrating these data elements could improve clinical outcomes. Performing dose comparison studies in Phase II could help companies identify drugs for which they should define dose-escalation or dose-reduction strategies in Phase III trials. Adaptive clinical trial protocols that include criteria for increasing or decreasing the dose under certain conditions, such as when a patient is experiencing severe side effects, may support drug labels that specify appropriate dose-modification strategies.
Currently, the label for most oncology drugs provides only a starting dose that may need to be modified for each patient based on clinical observation. The provision of a more comprehensive dosing dataset—one that includes a drug’s threshold concentration and a peak exposure associated with excess toxicity—would better enable therapeutic drug monitoring in clinical practice. As targeted therapies are often intended to be taken chronically, their tolerability or efficacy may diminish over time, making therapeutic drug monitoring an immensely valuable tool for ensuring patients in chronic treatment maintain an optimal exposure.
Many pharmaceutical and biopharma organizations are not yet prepared for the impact of Project Optimus. Some are still under the mistaken impression that this transition will incur greater development costs and deliver marginal revenue opportunities. In fact, if companies do not evolve their development strategy, the costs could be substantial. Ignoring the FDA’s guidance will lead to drug approval rejections and even more burdensome post-approval confirmatory commitments.
Beyond a philosophical shift in study design, Project Optimus will require fresh thinking with respect to integrated data, technological infrastructure, and even manufacturing and supply chain optimization. Pivoting to the future under Project Optimus will require companies to overcome three main challenges:
To accelerate speed to market and maximize their chances of a successful clinical trial, pharmaceutical and biopharma companies will need to embrace the Project Optimus paradigm of comprehensive dose characterization. They will require the ability to perform patient-specific and population-level drug response simulations in real time, within clinical trials. Companies must be able to characterize each drug’s pharmacokinetics and pharmacodynamics, and to predict dose-specific adverse events and clinical response. Implementing new dose selection and optimization strategies for each phase of a clinical trial will help pharma companies determine dosing that maximizes efficacy, safety, and tolerability—and ultimately, the usability of their products.
Sirj Goswami, PhD, is the CEO and co-founder of InsightRX, and Jason Rizzo, MBA, is the vice president of Global Biopharma Strategy.