Expedited Approval of Vitrakvi® Marks Many Firsts in Cancer Therapy
By Rajaneesh K. Gopinath, Ph.D.
Bayer and Loxo Oncology’s revolutionary drug becomes the first ever treatment with a tumor-agnostic indication at the time of initial approval.
Personalized medicine is getting closer to reality with the development of new drugs aimed at targeted therapies. Tumor-agnostics are one such and are defined as treatments prescribed based on a common biomarker rather than the organ where the tumor originated. Last year, for the first time Merck and Co’s Keytruda® (Pembrolizumab) was approved as a tumor-agnostic but the drug was previously used for treating several specific tumor types. Vitrakvi® (larotrectinib) on the other hand has become the first treatment with this indication at the time of initial FDA approval.
Accelerated approval of Vitrakvi®
Vitrakvi’s application was granted both a priority review and breakthrough therapy designation by the FDA. On November 26th, the inhibitor was approved for the treatment of solid tumors that originate from neurotrophic tyrosine receptor kinase (NTRK) gene fusions. This is also the first-in-class oral TRK inhibitor approved for treating the condition. Adults or pediatric patients could intake Vitrakvi® as capsules or liquid formulation respectively. However, they should not harbor a known acquired resistant mutation to NTRK inhibitors.
FDA Commissioner Scott Gottlieb expressed his views over the approval. “Today’s approval marks another step in an important shift toward treating cancers based on their tumor genetics rather than their site of origin in the body,” he said in a statement. “This new site-agnostic oncology therapy isn’t specific to a cancer arising in a particular body organ, such as breast or colon cancer. Its approval reflects advances in the use of biomarkers to guide drug development and the more targeted delivery of medicine.
Clinical Trials and Adverse Reactions
The NTRK genes could fuse to other genes and result in constitutive overexpression of chimeric TRK fusion proteins that has been found to aid the proliferation and survival of many solid tumors. Vitrakvi® was found to be an effective selective inhibitor of these proteins. The FDA approval is based on three clinical trials, the phase I adult trial, phase II NAVIGATE trial and phase I/II pediatric SCOUT trial. The drug demonstrated an overall response rate (ORR) of 75% (N=55) (95% CI, 61%, 85%), across various tumor types, including soft tissue sarcoma, salivary gland, thyroid, lung, melanoma, colon, appendix, breast and pancreas among others. It also registered a 22 percent complete response (CR) rate.
The drug has precautions of neurotoxicity, hepatotoxicity and embryo-fetal toxicity. Some common adverse reactions include the increase in liver enzymes like alanine aminotransferase (ALT) and aspartate transaminase (AST), anemia, fatigue, nausea, dizziness, cough, vomiting, constipation, and diarrhea.
Potential Competition and Challenges
As with the case of most ground-breaking drugs, Vitrakvi® is expensive. At the moment though, only around 2,000 and 3,000 people per year are estimated to develop NTRK gene fusions in the United States. Besides, Roche’s Entrectinib that targets both NTRK gene fusions and ROS1 fusions may soon enter the market despite showing an ORR of only 57%. However, the global collaboration that Loxo Oncology had entered with Bayer last year includes not just the marketing of Vitrakvi® but also another selective TRK inhibitor. LOXO-195 is currently under trials to counter acquired resistance that may emerge following the treatment with Vitrakvi® or other multikinase inhibitors. Therefore, market analysts predict sales of the drug could skyrocket in the years to come.
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