Rina-S Phase 1/2 Signal Is Strong But Evidence Tier Leaves Approval Path Unproven

Genmab's Rina-S Shows Durable Responses in Platinum-Resistant Ovarian Cancer

Genmab A/S announced positive results from Part C of the Phase 1/2 RAINFOL™-01 trial evaluating rinatabart sesutecan (Rina-S) in 109 patients with platinum-resistant ovarian cancer (PROC). Treatment with Rina-S 120 mg/m² every three weeks achieved a confirmed objective response rate (ORR) of 45.9% (95% CI: 36.3–55.7), including five complete responses (CRs). The median duration of response (mDOR) was 12.1 months (95% CI: 6.5–15.4), with 51% of responders maintaining response at one year. The study also reported a median progression-free survival (mPFS) of 9.5 months (95% CI: 7.6–11.3). Antitumor activity was observed regardless of folate receptor alpha (FRα) expression levels.

• Significant Efficacy in Heavily Pretreated Patients: The Phase 1/2 RAINFOL-01 trial demonstrated a confirmed objective response rate (ORR) of 45.9% (95% CI: 36.3–55.7), including five complete responses, and a median duration of response (mDOR) of 12.1 months (95% CI: 6.5–15.4) in 109 patients with platinum-resistant ovarian cancer. Notably, 51% of responders maintained their response at one year, and antitumor activity was observed irrespective of folate receptor alpha (FRα) expression levels or prior mirvetuximab treatment.
• Durable Progression-Free Survival and Broad Applicability: Rinatabart sesutecan (Rina-S) achieved a median progression-free survival (mPFS) of 9.5 months (95% CI: 7.6–11.3), providing the first reported PFS data for the program. This efficacy was observed in a heavily pretreated population, with over half having received three or four prior lines of therapy, including prior bevacizumab, taxane, and PARP inhibitors, underscoring its potential for broad applicability in this challenging disease setting.
• Manageable Safety Profile and Advancing Clinical Program: The safety profile of Rina-S was manageable, with common treatment-emergent adverse events including fatigue, low-grade gastrointestinal events, and hematologic events. Serious adverse events occurred in approximately one-third of participants, with a low discontinuation rate of 5.5%. No new safety signals were observed for ocular toxicity, peripheral neuropathy, ILD, or stomatitis. These results support the ongoing Phase 3 clinical development program for Rina-S across multiple gynecologic cancers and other solid tumors.

Addressing the Unmet Need in Platinum-Resistant Ovarian Cancer

Platinum-resistant recurrent ovarian cancer carries a poor prognosis, with few treatment options demonstrating meaningful efficacy. The resistance phenotype arises through multiple overlapping mechanisms, making it particularly difficult to address with any single therapeutic strategy.

• Limited efficacy of standard single-agent chemotherapy: Single-agent chemotherapy (pegylated liposomal doxorubicin, weekly paclitaxel, or topotecan) remains the standard of care in platinum-resistant ovarian cancer, yet outcomes remain poor. In the AURELIA trial, median progression-free survival (PFS) with chemotherapy alone was 3.4 months, with an objective response rate (ORR) of only 11.8%.

• Complex, multifactorial resistance mechanisms: Resistance to platinum compounds involves alterations in drug influx and efflux pathways, DNA repair dysregulation, epigenetic modulation, and tumor microenvironment remodeling — including tumor cell heterogeneity and dynamic microenvironmental changes. This biological complexity limits the effectiveness of targeted interventions aimed at any single resistance pathway.

• Efflux-mediated drug resistance: P-glycoprotein (P-gp)-mediated drug efflux is a dominant driver of resistance to multiple chemotherapeutic agents. While co-administration of pump inhibitors has been explored, this two-drug strategy has not yet advanced to established therapy.

• Manageable but clinically significant ADC toxicity: Antibody-drug conjugates (ADCs) such as mirvetuximab soravtansine represent an emerging option, but class-associated toxicities — including ocular toxicity (keratopathy, blurred vision), peripheral neuropathy, and pulmonary toxicity — require active management through prophylactic corticosteroid eye drops, dose interruptions, and dose modifications, adding complexity to treatment delivery.

• Acquired resistance to emerging targeted therapies: Beyond chemotherapy, ADC therapy itself faces the challenge of acquired resistance, compounded by tumor antigen heterogeneity, which can limit the durability of responses to agents targeting folate receptor-alpha (FRα) or other tumor-associated antigens.

RAINFOL-01: Efficacy and Safety Profile of Rinatabart Sesutecan

Several recent clinical investigations have advanced the treatment landscape for platinum-resistant ovarian cancer (PROC), spanning novel antibody-drug conjugates (ADCs), oncolytic viral vectors, and combination immunotherapy strategies.

The OCTAVE phase 1 trial evaluated enadenotucirev, a tumor-selective adenoviral vector, with or without paclitaxel in heavily pretreated patients with platinum-resistant epithelial ovarian cancer. Among the 20 patients who received intravenous enadenotucirev plus paclitaxel, the 4-month progression-free survival (PFS) rate was 64%, with a median PFS of 6.2 months. The objective response rate was 10%, 35% of patients achieved stable disease, and 65% had a reduction in target lesion burden at one or more time points. Five of six patients with matched pre- and post-treatment biopsies demonstrated increased CD8+ T-cell infiltration (mean 3.1-fold) following treatment. Grade ≥3 treatment-emergent adverse events (TEAEs) occurred in 63% of the overall enrolled population, with neutropenia being the most frequent (21%). Six patients discontinued treatment due to TEAEs.

In the ADC space, ZW191 — a FRα-targeted topoisomerase I inhibitor ADC — has been characterized in nonclinical studies with initial clinical data reported. ZW191 demonstrated activity in tumors with both high and low levels of FRα expression across patient-derived xenograft models of ovarian cancer, endometrial cancer, NSCLC, and TNBC, markedly improving on mirvetuximab soravtansine (MIRV), the FDA-approved FRα-targeted ADC. ZW191's novel FRα-targeting antibody showed superior internalization, payload delivery, and penetration through 3D tumor spheroids compared with multiple other clinical-stage ADC antibodies. In vivo, ZW191 demonstrated efficacy in combination with olaparib, bevacizumab, and paclitaxel. Its tolerability profile in GLP non-human primate toxicity studies was attributed to its payload's moderate potency, a feature associated with higher achievable dosing in humans based on a clinical landscape analysis.

The double-blind, randomized phase III AGO-OVAR 2.29/ENGOT-ov34 trial assessed atezolizumab combined with bevacizumab and investigator-selected non-platinum chemotherapy (weekly paclitaxel or pegylated liposomal doxorubicin) in patients with recurrent ovarian cancer ineligible for platinum re-treatment. Among 574 randomized patients, the hazard ratio for overall survival (OS) was 0.83 (95% CI, 0.68 to 1.01; P = .06), with a median OS of 14.2 months in the atezolizumab arm versus 13.0 months with placebo. The hazard ratio for PFS was 0.87 (95% CI, 0.73 to 1.04; P = .12), with median PFS of 6.4 versus 6.7 months, respectively. Neither OS nor PFS improvements reached statistical significance. OS hazard ratios were similar regardless of PD-L1 status. Grade ≥3 adverse events occurred in 72% of atezolizumab-treated patients and 69% of placebo patients.

Rinatabart Sesutecan: A Broadening Horizon for Platinum-Resistant Ovarian Cancer

The recent positive Phase 1/2 results for rinatabart sesutecan (Rina-S) in platinum-resistant ovarian cancer (PROC) mark a potentially significant advance in a disease area with substantial unmet need. Patients with PROC face limited treatment options and poor prognoses, making novel, effective therapies highly sought after. Rina-S, an antibody-drug conjugate (ADC) targeting folate receptor alpha (FRα), has demonstrated an impressive objective response rate of 45.9% and a median progression-free survival of 9.5 months. These figures are particularly compelling given the advanced nature of the disease and the patient population.

A key differentiator for Rina-S is its observed antitumor activity irrespective of FRα expression levels. This stands in contrast to some prior FRα-targeted therapies, where efficacy was often correlated with higher receptor expression, thereby limiting the eligible patient pool. This broader applicability could significantly expand the addressable market for Rina-S, offering a therapeutic option to a wider range of PROC patients. The median duration of response of 12.1 months further suggests a durable clinical benefit, which is crucial for patients battling recurrent disease.

However, as with all early-phase data, these promising results come with considerations. The full safety and tolerability profile of Rina-S, particularly at the 120 mg/m² dose, will need to be thoroughly characterized in larger, pivotal studies. Antibody-drug conjugates, especially those utilizing topoisomerase I inhibitor payloads, can present unique toxicity profiles that require careful management. Furthermore, while the efficacy is strong, the competitive landscape for ovarian cancer treatments, including other FRα-targeting ADCs, is dynamic. Future development will need to clearly establish Rina-S's long-term comparative benefits in terms of overall survival and quality of life to secure its position as a standard of care. The next steps will undoubtedly involve advancing Rina-S into confirmatory Phase 3 trials, where its full potential can be rigorously assessed.