In this JCO Article Insights episode, Dr. Ece Cal interviews Dr. Martin Wermke, author of the JCO article, "Phase I Dose-Escalation Results for the Delta-Like Ligand 3/CD3 IgG-Like T-Cell Engager Obrixtamig (BI 764532) in Patients With Delta-Like Ligand 3+ Small Cell Lung Cancer or Neuroendocrine Carcinomas."

TRANSCRIPT

The disclosures for guests on this podcast can be found in the transcript.

Dr. Ece Cali: Welcome to this episode of JCO Article Insights. This is Dr. Ece Cali, JCO editorial fellow, and today I am joined by Dr. Martin Wermke, Professor for Experimental Cancer Therapy at Dresden University of Technology, to discuss the manuscript “Phase 1 Dose-Escalation Results for the Delta-Like Ligand 3/CD3 IgG-like T-Cell Engager Obrixtamig in Patients with DLL3+ Small Cell Lung Cancer or Neuroendocrine Carcinomas.”

Obrixtamig is a bispecific T-cell engager that binds to DLL3 on tumor cells and CD3 on T-cells. This manuscript presents the phase 1A dose escalation results of Obrixtamig in patients with DLL3+ small cell lung cancer and neuroendocrine carcinomas. In this study, 168 patients were treated with Obrixtamig across four different dosing regimens. 49% of the patients had small cell lung cancer, 42% had extrapulmonary neuroendocrine carcinoma, and 8% had large cell neuroendocrine carcinoma of the lung. Patients received a median of two prior lines of therapy. 33% of the patients had brain metastases at baseline. Of note, this trial did not mandate baseline brain imaging. Maximum tolerated dose was not reached. 88% of the patients experienced a treatment-related adverse event, however, only 3.6% of the patients had to discontinue treatment due to treatment-related AEs, and dose reduction due to treatment-related AEs was documented in 2.4% of the patient population. Similar to the other DLL3-targeted bi-therapies, the most common adverse events included CRS in 57%, dysgeusia in 23%, and pyrexia in 21% of the patients. CRS events were mostly mild. They occurred more frequently in the first two to three doses. 9% of the patients experienced ICANS, of which 3% were graded as Grade 3 or higher.

And let's review the efficacy results. Responses were only seen in patients who received 90 microgram per kg or more once weekly or once every three weeks dosing. The objective response rate in patients who received an effective dose was 28%. If we review by tumor type, 21% of the small cell lung cancer patients, 27% of the extrapulmonary neuroendocrine carcinoma patients, and 70% of the large cell neuroendocrine carcinoma patients had objective response. Median duration of response was 8.5 months, though this data is immature due to short follow-up.

Dr. Wermke, DLL3-targeted bispecific T-cell engagers are reshaping the treatment landscape of small cell lung cancer. This trial investigates Obrixtamig in other high-grade neuroendocrine tumors as well. Can you put this trial into context for us and explain why it may represent an important step forward?

Dr. Martin Wermke: Yeah, thank you for providing me with the opportunity to discuss our data today. I think the data with Obrixtamig in small cell lung cancer are largely similar to what has been observed with other bispecific T-cell engagers such as tarlatamab with respect to the response rate and duration. It has, however, been to be mentioned that BI 1438001 had a bit more liberal inclusion criteria than other trials around. You already mentioned the fact that we allowed the inclusion of patients without mandatory brain imaging, which led to some patients having their brain mets been diagnosed during the treatment with obrixtamig and then adding to the progressive disease patients. That is something which was not the case with the tarlatamab trials where you really had to have a brain imaging before, and in the Phase 1 trial you were even required to treat the brain mets before you included the patient. So it is a bit different, more poorest patient population.

I think the trial adds on existing data by being the first trial to also include non-SCLC neuroendocrine carcinoma of other origin, for example from the gastrointestinal tract, and also by including large cell neuroendocrine carcinoma of the lung, which is a really hard to treat pulmonary neoplasm which currently lacks any standardized treatment. So that is really a step forward which we will build on in the future.

Dr. Ece Cali: And one thing I would note in this trial, only patients with tumor expressing DLL3 were enrolled. Can you tell us a little bit more about this target, DLL3 in the context of neuroendocrine tumors, and does DLL3 expression predict clinical outcomes after treatment with DLL3 BiTEs, or do we actually need other predictive biomarkers for these novel agents?

Dr. Martin Wermke: Yeah, thank you. That's a pretty interesting question. First of all, DLL3 is an atypical notch ligand, which is expressed by the majority of neuroendocrine carcinomas, virtually absent on healthy adult tissues. Therefore, turning it really into a bona fide target for T-cell engaging therapies, pretty low risk for on-target off-tumor side effects. We found that in all the patients we screened, we had an expression rate of about 94% in small cell lung cancer, 80% of large cell neuroendocrine carcinoma of the lung were positive, and also about 80% of the extrapulmonary neuroendocrine carcinoma. So it's really a high prevalence. So the fact that we only included DLL3+ tumors still means we included most of the patients that presented with these diseases.

I think at the moment there are no data suggesting a clear-cut association between DLL3 expression levels and outcome on DLL3 CD3 T-cell engagers. There's also not a lot published. If you want to find this out for tarlatamab, you have to look into their patent to really see the data, but it's not clear-cut and I'm sure we need other markers to complement that. And I think what probably plays a major role is intrinsic T-cell fitness. So the question how really diseased your T-cells are, how old you are, because age also correlates with the fitness of the immune system, and other patient characteristics such as tumor burden, we've seen all across the board that the higher the tumor burden, the lower the rate of prolonged response is in such trials. And I also think we need to focus on other components of the tumor microenvironment. So see how high the T-cell infiltration with obrixtamig is and how abundant suppressive elements like regulatory T-cells or myeloid-derived suppressive cells are. That is work which is currently being done. Data are emerging, but I don't think that at the moment we have any clear biomarker helping us to select who should not receive DLL3 T-cell engagers.

Dr. Ece Cali: Those are great points and there is a lot we need to learn about how to use these novel agents in the future