Four independent studies show rovalpituzumab tesirine ineffective against small cell lung cancer

An accompanying editorial written by Dr. Dipesh Uprety, Dr. Jordi Remon, and JTO Editor Dr. Alex A. Adjei, discusses the recent history of the therapy's clinical trials and suggests some possible reasons why the drug has not been effective.

According to the editorial, SCLC remains a difficult disease to treat, especially at the time of relapse. Currently, topotecan is among the most effective, but it is not the most desirable and favored drug in the second-line setting because of its toxicity profile. Still, it has been difficult for new agents to "beat" this drug in the second-line setting. Several phase III clinical trials have failed to reveal improved survival over topotecan.

In 2017, clinicians were cautiously optimistic when Dr. Charles Rudin and colleagues published one of the first studies on rovalpituzumab tesirine in Lancet Oncology.

"The first in-human phase 1 clinical trial with Rova-T elicited significant enthusiasm because of the efficacy results -- 11 Of 60 assessable patients with pretreated SCLC who received an active dose of Rova-T achieved a confirmed response for an objective response rate (ORR) of 18%, tumors with high DLL3 expression (50% expression on tumor cells), the ORR was 38%. In a post hoc analysis, the ORR did not differ between those treated in the second- or third-line setting," according to the editorial.

But the four studies published in this month's JTO demonstrates that rovalpituzumab tesirine could not displace topotecan as an effective therapy for SCLC.

In one study published in the JTO -- "Efficacy and Safety of Rovalpituzumab Tesirine Compared With Topotecan as Second-Line Therapy in DLL3-High SCLC: Results From the Phase 3 TAHOE Study," lead author Dr. Fiona Blackhall, The University of Manchester, Manchester, United Kingdom, concluded that "compared with topotecan, which is the current standard second-line chemotherapy, Rova-T exhibited an inferior overall survival and higher rates of serosal effusions, photosensitivity reaction, and peripheral edema in patients with SCLC."

A second study published in JTO, "A Phase 1-2 Study of Rovalpituzumab Tesirine in Combination With Nivolumab Plus or Minus Ipilimumab in Patients With Previously Treated Extensive-Stage SCLC," the researchers, led by Dr. Jyoti Malhotra, Rutgers Cancer Institute of New Jersey, New Brunswick, N.J., found that "Despite encouraging antitumor activity in previously treated ES SCLC, combination therapy with Rova-T and nivolumab plus or minus ipilimumab was not well tolerated at the dose levels and administration schedules evaluated."

The third study, "A Phase 1 Study Evaluating Rovalpituzumab Tesirine in Frontline Treatment of Patients with Extensive-Stage SCLC," led by Dr. Christine Hamm, Johns Hopkins Medical Center, Baltimore, Md., the researchers found that there was no clear efficacy benefit of adding Rova-T to chemotherapy and etoposide.

Finally, the fourth study "Rovalpituzumab Tesirine as a Maintenance Therapy After First-Line Platinum-Based Chemotherapy in Patients With Extensive-Stage-SCLC: Results From the Phase 3 MERU Study," by Dr. Melissa Johnson, from Sarah Cannon Research Institute in Nashville, Tenn., found that "Because of the lack of survival benefit in the Rova-T arm, the study did not meet its primary end point and was terminated early."

The editorial's authors suggest three reasons why the therapy has not progressed passed stage I:

First, the Rova-T development strategy is a perfect example of the dangers of moving directly from promising small phase I studies to large registrational phase III studies without confirming the safety and efficacy data in phase II studies.

Second, Rova-T may not be an ideal antibody-drug conjugate. The safety and efficacy of antibody-drug conjugates depend on a number of factors, including the drug-antibody ratio, which is the average number of cytotoxic molecules attached to each antibody, the cytotoxic "payload," in which there is invariably some diffusion of cytotoxin into the bloodstream and normal tissues and the linker, which links the payload to the antibody, must be stable to avoid significant release of the drug into the circulation.

Third, the failure of all the Rova-T trials begs the question of whether DLL3 is a valid target in SCLC.

The authors suggest that future studies should, therefore, focus on better understanding of disease biology and targeting treatment based on the new emerging molecular subtypes.