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From Payload to Preservation – Monomethyl Auristatin E (MMAE) in Enfortumab Vedotin as the next Radiosensitizer for Bladder Preservation?

The evolution of bladder preservation strategies has historically paralleled advances in systemic therapy for muscle-invasive bladder cancer (MIBC). Radiosensitizing agents incorporated into trimodality therapy have generally been drawn from systemic regimens that demonstrated efficacy in the perioperative setting. Cisplatin became the dominant radiosensitizer, not only because of its activity in metastatic disease, but because randomized trials established a survival benefit with neoadjuvant cisplatin-based chemotherapy. A similar transition may now be occurring with enfortumab vedotin. The rapid emergence of enfortumab vedotin–based therapy in earlier disease states, particularly after the presentation of data from the randomized phase 3 EV-303 and EV-304 trials, has redefined expectations for systemic therapy in MIBC and has created a compelling rationale to evaluate enfortumab vedotin in combination with radiation as part of contemporary bladder preservation approaches.

The biologic rationale for combining enfortumab vedotin with radiation is grounded in the cytotoxic properties of its payload. Monomethyl auristatin E (MMAE), the microtubule inhibitor delivered by enfortumab vedotin, shares mechanistic features with taxanes, a class of agents with a long and well-established history as radiosensitizers. Microtubule inhibition promotes the accumulation of tumor cells in the G2/M phase of the cell cycle, the phase most sensitive to ionizing radiation, and interferes with mitotic spindle formation and DNA damage repair. These effects enhance radiation-induced cytotoxicity and provide a biologic foundation for concurrent administration. The radiosensitizing potential of microtubule inhibition is therefore not theoretical; it is supported by decades of clinical experience across multiple tumor types, including urothelial bladder cancer.

Prospective cooperative group trials established the feasibility of taxane-based chemoradiation in bladder preservation therapy well before the modern immunotherapy era. The multicenter phase I/II NRG Oncology RTOG 0524 study evaluated weekly paclitaxel administered concurrently with daily radiation in patients with MIBC who were not candidates for cystectomy. This regimen demonstrated durable disease control with acceptable toxicity and confirmed that paclitaxel could function as an effective radiosensitizer in the bladder preservation setting.1.2 These historical data established microtubule inhibition as a validated radiosensitization strategy and provide a direct conceptual bridge to the current use of antibody–drug conjugates delivering potent microtubule inhibitors.

The key distinction between traditional taxanes and enfortumab vedotin is not the mechanism of cytotoxicity but the precision of drug delivery. By selectively delivering a microtubule inhibitor to tumor cells expressing Nectin-4, enfortumab vedotin may preserve the radiosensitizing advantages of taxanes while limiting systemic toxicity. This targeted delivery raises the possibility of improving the therapeutic ratio during concurrent radiation therapy, particularly in patients who are medically frail. The relatively mild degree of myelosuppression observed with enfortumab vedotin, compared with cisplatin, may further facilitate safe integration with radiation.

Enfortumab vedotin plus pembrolizumab will soon become the dominant perioperative systemic therapy regimen, driven by the transformative results of the EV-303 and EV-304 trials. The randomized, phase 3 EV-303 (KEYNOTE-905) study evaluated perioperative enfortumab vedotin plus pembrolizumab in patients with MIBC who were ineligible for or declined cisplatin-based chemotherapy. This trial demonstrated statistically significant improvements in event-free survival and overall survival compared with surgery alone. Importantly, the regimen produced a substantial pathologic complete response rate of 57.1%, compared with an 8.6% rate for patients in the control arm that did not receive any systemic therapy.3 These findings established enfortumab vedotin plus pembrolizumab for this unmet need population that previously lacked acceptable perioperative treatment strategies, and it led to recent regulatory approval in the United States.4

The subsequent phase 3 EV-304 (KEYNOTE-B15) trial extended these findings to cisplatin-eligible patients and directly compared perioperative enfortumab vedotin plus pembrolizumab with standard neoadjuvant gemcitabine and cisplatin. This study demonstrated the superiority of the enfortumab-based regimen across multiple clinically meaningful endpoints, including event-free survival, overall survival, and pathologic complete response. The combination achieved a pathologic complete response rate of 55.8%, substantially higher than the 32.5% complete response rate observed with chemotherapy.5 Collectively, the results of EV-303 and EV-304 represent the most consequential advances in the management of MIBC in decades, creating a new standard of care for all undergoing treatment of MIBC with radical cystectomy.

The implications of these findings extend directly to bladder preservation strategies. Historically, systemic therapy advances in the perioperative setting have driven the selection of radiosensitizing agents used in trimodality therapy. As cisplatin became the standard neoadjuvant therapy, it also became the default concurrent radiosensitizer. The emergence of enfortumab vedotin–based therapy as the new systemic backbone, therefore, creates a clear and logical rationale to evaluate this agent in combination with radiation therapy.

From a clinical perspective, the combination of enfortumab vedotin and radiation is particularly attractive for patients who are not candidates for cystectomy or who seek organ preservation. Radiation therapy remains the cornerstone of bladder preservation, but outcomes depend heavily on the effectiveness of concurrent systemic therapy. Multiple early-phase studies are actively evaluating enfortumab vedotin in combination with radiation, with additional cooperative group trials in planning stages.

Some actively accruing clinical trials evaluating enfortumab vedotin with radiation are listed below:

  • STAR-EV: Enfortumab Vedotin and Stereotactic Radiation for Localized, Cisplatin-Ineligible Muscle-Invasive Bladder Cancer (NCT06394570)
  • EV-PRIME: Enfortumab Vedotin and Pembrolizumab Combined With Radiotherapy as Bladder-Sparing Trimodality Therapy in Muscle-Invasive Bladder Cancer (NCT06470282)
  • CONSOLIDATE: Enfortumab Vedotin With Concurrent Radiation for Locally Advanced Bladder Cancer (NCT06434350)
  • PEVRAD: Enfortumab Vedotin and Pembrolizumab with Radiation for Muscle-Invasive Bladder Cancer (NCT05879653)

Written by: Evan Yu, MD, Section Head of Cancer Medicine in the Clinical Research Division at Fred Hutchinson Cancer Center. He also serves as the Medical Director of Clinical Research Support at the Fred Hutchinson Cancer Research Consortium and is a Professor of Medicine in the Division of Oncology and Department of Medicine at the University of Washington School of Medicine in Seattle, WA

References:

  1. Michaelson MD, et al. A Phase 1/2 Trial of a Combination of Paclitaxel and Trastuzumab With Daily Irradiation or Paclitaxel Alone With Daily Irradiation After Transurethral Surgery for Noncystectomy Candidates With Muscle-Invasive Bladder Cancer (Trial NRG Oncology RTOG 0524). Int J Radiat Oncol Biol Phys. 2017; 97:995-1001.
  2. Dahl DM, et al. Long-term outcomes of chemoradiation for muscle-invasive bladder cancer in noncystectomy candidates. Final results of NRG Oncology RTOG 0524—a phase 1/2 trial of paclitaxel + trastuzumab with daily radiation or paclitaxel alone with daily irradiation. Eur Urol Oncol. 2024; 7:83-90.
  3. Powles T, et al. Enfortumab Vedotin and Pembrolizumab in Untreated Advanced Urothelial Cancer. N Engl J Med. 2024; 390:875-88.
  4. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-pembrolizumab-enfortumab-vedotin-ejfv-muscle-invasive-bladder-cancer
  5. Galsky MD, et al. Neoadjuvant and adjuvant enfortumab vedotin (EV) plus pembrolizumab (pembro) for participants with muscle-invasive bladder cancer (MIBC) who are eligible for cisplatin: Randomized, open-label, phase 3 KEYNOTE-B15 study. J Clin Oncol 44, Number 7_suppl. LBA630 (2026).