On May 23, 2024 Sensei Biotherapeutics, Inc. (Nasdaq: SNSE), a clinical stage immuno-oncology company focused on the discovery and development of next-generation therapeutics for cancer patients, reported encouraging clinical data from the dose escalation portion of its Phase 1/2 trial of SNS-101, a conditionally active, human monoclonal antibody targeting the immune checkpoint VISTA (V-domain Ig suppressor of T cell activation) (Press release, Sensei Biotherapeutics, MAY 23, 2024, View Source [SID1234643617]).

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"I am pleased that SNS-101 has been well-tolerated in the study, reaching its highest planned dose level with no dose limiting toxicities and demonstrating its potential to successfully overcome the prior challenges of VISTA-targeted programs," said Dr. Shiraj Sen, Medical Oncologist and Director of Clinical Research at NEXT Oncology, Dallas, and a principal investigator for the SNS-101 study. "The data show encouraging signs of clinical activity in a heterogeneous population of patients with advanced solid tumors, where you typically wouldn’t expect to see clinical responses, especially in microsatellite stable colorectal and endometrial tumors. There is a continued unmet need for patient populations that have become resistant or don’t respond to current immunotherapy treatment options. I look forward to continuing to evaluate its progress."

Dose escalation portion of the Phase 1/2 clinical trial

The dose escalation portion of the Phase 1/2 clinical trial is designed to evaluate the safety, tolerability, pharmacokinetics, pharmacodynamics, and efficacy of SNS-101. This study assesses SNS-101 both as monotherapy and in combination with Regeneron’s PD-1 inhibitor Libtayo (cemiplimab, 350 mg), in patients with advanced solid tumors with primary (unfavorable candidates for immunotherapy) or acquired PD-1 therapy resistance (progressed on prior anti-PD-1 therapy).

A total of 34 patients received SNS-101 once every 3 weeks, with 16 patients in the monotherapy arm and 18 patients in the combination arm. The majority of patients (85%) had a tumor type that is typically unresponsive to PD-1 monotherapy ("cold" tumors).

As of the April 30, 2024 data cutoff, SNS-101 demonstrated preliminary evidence of promising clinical activity in multiple tumor types, including:

One microsatellite stable (MSS) endometrial cancer patient that received SNS-101 plus cemiplimab had a confirmed partial response (59% decrease) and remains on study at 30+ weeks. MSS endometrial cancer has been previously shown to have a low response rate to monotherapy immunotherapy treatments.
One MSS colorectal cancer (CRC) patient that received SNS-101 plus cemiplimab remained on study for 18 weeks and had tumor regression of 27%. MSS CRC has been previously shown to be unresponsive to PD-1 treatments.
One pembrolizumab-resistant renal cell carcinoma patient that received SNS-101 plus cemiplimab remained on study for 12 weeks and had tumor regression of 18%.
One pembrolizumab-resistant human papillomavirus (HPV)+ head and neck cancer patient that received SNS-101 as monotherapy remained on study for 12 weeks and had tumor regression of 17%.
These clinical data are consistent with preclinical studies suggesting therapeutically relevant clinical doses of SNS-101 at 3mg/kg or higher. Additionally, preliminary flow-based pharmacodynamic analysis showed dose-dependent changes in specific T-cell populations suggesting SNS-101 may be having a pharmacological effect on T-cell subsets.

SNS-101 demonstrated a potentially best-in-class pharmacokinetic (PK) profile with linear elimination kinetics and dose-proportional increases in exposure, supporting once every three week dosing. The data are consistent with lack of target-mediated drug disposition (TMDD), which has been observed in non-conditionally active anti-VISTA antibodies.

SNS-101 was well tolerated alone and in combination with cemiplimab, with no dose-limiting toxicities observed. The majority of AEs were Grade 1 or 2 in severity. Two patients experienced Grade 1 cytokine release syndrome (CRS), one in monotherapy and one in combination, both at the highest dose of SNS-101. Both cases were mild and manageable, demonstrating that SNS-101 has the potential to overcome a key hurdle that hindered first-generation VISTA-targeting approaches. Four patients in the combination cohort experienced immune-mediated events. There were also no significant changes to key inflammatory cytokine levels, including interferon gamma, interleukin-6, interleukin-10, interleukin-8, TNF-alpha, and CCL5-RANTES, across cohorts.

"The dose escalation portion of the Phase 1/2 trial of SNS-101 answers the critical question of whether a pH-selective approach can overcome the previous hurdles associated with targeting VISTA, which included severe safety and PK issues. We believe the topline data presented today marks an important milestone and validates the mechanism of action by demonstrating the potentially best-in-class PK and a well-tolerated safety profile of SNS-101 at therapeutically relevant dose levels," said Ron Weitzman, Chief Medical Officer of Sensei Bio. "We saw promising clinical activity primarily in tumor types that don’t typically respond to PD-1 monotherapy and look forward to progressing through the expansion phase of the study."

Ongoing dose expansion portion of the Phase 1/2 clinical trial

Patient enrollment is advancing in the dose expansion portion of the Phase 1/2 study. The Company expects to report initial data from the dose expansion cohorts and to hold an end-of-Phase 1 meeting with the FDA by the end of 2024.

ASCO presentation

The data will be presented in a poster presentation entitled "Initial results from a first-in-human phase 1 study of SNS-101 (pH-selective anti-VISTA antibody) alone or in combination with cemiplimab in patients with advanced solid tumors," on June 1, 2024, at the 2024 American Society of Clinical Oncology (ASCO) (Free ASCO Whitepaper) Annual Meeting being held in Chicago, IL. The poster will be available on the Sensei website at the start of the poster presentation.

Investor webcast

Sensei will host a webcast on Monday, June 3, 2024, at 8:00 a.m. ET (7:00 a.m. CT) to discuss the data. Participating alongside Company management will be Dr. Shiraj Sen, M.D., Ph.D., Medical Oncologist and Director of Clinical Research at NEXT Oncology-Dallas. Dr. Sen is an investigator on the ongoing Phase 1/2 clinical trial for SNS-101, and lead author of the SNS-101 poster. The live event can be accessed here: View Source and can be accessed on the Investor page of Sensei’s website at View Source A replay of the webcast will be available after the completion of the event.