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CytomX Therapeutics Announces First Patient Dosed in Combination Arm of Phase 1 Study of CX-801 plus KEYTRUDA® (pembrolizumab) in Patients with Metastatic Melanoma

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CytomX Therapeutics (NASDAQ: CTMX) has announced the dosing of the first patient with CX-801 in combination with KEYTRUDA® in an ongoing Phase 1 study for metastatic melanoma patients. CX-801 is a masked interferon alpha-2b PROBODY® cytokine designed to target tumors while reducing systemic toxicities. The combination trial follows successful clearance of three CX-801 monotherapy dose escalation cohorts. The study aims to address the high unmet need in PD-1 refractory melanoma patients. While interferon alpha-2b has proven anti-cancer activity, its use has been limited due to poor tolerability. Initial Phase 1a translational and biomarker data are expected in the second half of 2025.
CytomX Therapeutics (NASDAQ: CTMX) ha annunciato la somministrazione della prima dose di CX-801 in combinazione con KEYTRUDA® in uno studio di Fase 1 in corso per pazienti con melanoma metastatico. CX-801 è una citochina PROBODY® interferone alfa-2b mascherata, progettata per colpire i tumori riducendo al contempo le tossicità sistemiche. Lo studio combinato segue il successo nel completamento di tre coorti di dose escalation con monoterapia CX-801. L'obiettivo dello studio è rispondere all'alta necessità insoddisfatta nei pazienti con melanoma refrattario a PD-1. Sebbene l'interferone alfa-2b abbia dimostrato attività anticancro, il suo utilizzo è stato limitato a causa della scarsa tollerabilità. I primi dati traslazionali e sui biomarcatori della Fase 1a sono attesi nella seconda metà del 2025.
CytomX Therapeutics (NASDAQ: CTMX) ha anunciado la dosificación del primer paciente con CX-801 en combinación con KEYTRUDA® en un estudio de Fase 1 en curso para pacientes con melanoma metastásico. CX-801 es una citoquina PROBODY® interferón alfa-2b enmascarada diseñada para atacar tumores mientras reduce las toxicidades sistémicas. El ensayo combinado sigue al exitoso cierre de tres cohortes de escalada de dosis con monoterapia CX-801. El estudio tiene como objetivo abordar la alta necesidad insatisfecha en pacientes con melanoma refractario a PD-1. Aunque el interferón alfa-2b ha demostrado actividad anticancerígena, su uso ha sido limitado debido a su baja tolerabilidad. Se esperan los datos iniciales translacionales y de biomarcadores de la Fase 1a en la segunda mitad de 2025.
CytomX Therapeutics (NASDAQ: CTMX)는 전이성 흑색종 환자를 대상으로 진행 중인 1상 연구에서 CX-801과 KEYTRUDA® 병용 투여를 받은 첫 환자 투여를 발표했습니다. CX-801은 종양을 표적으로 하면서 전신 독성을 줄이도록 설계된 마스크드 인터페론 알파-2b PROBODY® 사이토카인입니다. 이 병용 임상시험은 CX-801 단독요법의 3개 용량 증량 코호트가 성공적으로 완료된 후 진행됩니다. 이 연구는 PD-1 저항성 흑색종 환자들의 높은 미충족 수요를 해결하는 것을 목표로 합니다. 인터페론 알파-2b는 항암 효과가 입증되었지만, 내약성이 낮아 사용이 제한되어 왔습니다. 1a상 초기 전임상 및 바이오마커 데이터는 2025년 하반기에 발표될 예정입니다.
CytomX Therapeutics (NASDAQ : CTMX) a annoncé l'administration de la première dose de CX-801 en combinaison avec KEYTRUDA® dans une étude de Phase 1 en cours chez des patients atteints de mélanome métastatique. CX-801 est une cytokine PROBODY® interféron alpha-2b masquée, conçue pour cibler les tumeurs tout en réduisant les toxicités systémiques. L'essai en combinaison fait suite à la réussite des trois cohortes d'escalade de dose en monothérapie CX-801. L'étude vise à répondre au besoin important non satisfait chez les patients atteints de mélanome réfractaire au PD-1. Bien que l'interféron alpha-2b ait démontré une activité anticancéreuse, son utilisation a été limitée en raison d'une faible tolérance. Les premières données translationnelles et sur les biomarqueurs de la Phase 1a sont attendues dans la seconde moitié de 2025.
CytomX Therapeutics (NASDAQ: CTMX) hat die Behandlung des ersten Patienten mit CX-801 in Kombination mit KEYTRUDA® in einer laufenden Phase-1-Studie bei Patienten mit metastasiertem Melanom bekannt gegeben. CX-801 ist ein maskiertes Interferon Alpha-2b PROBODY®-Zytokin, das darauf ausgelegt ist, Tumore gezielt anzugreifen und gleichzeitig systemische Toxizitäten zu reduzieren. Die Kombinationsstudie folgt auf den erfolgreichen Abschluss von drei Dosissteigerungs-Kohorten mit CX-801-Monotherapie. Die Studie zielt darauf ab, den hohen ungedeckten Bedarf bei PD-1-refraktärem Melanom zu adressieren. Obwohl Interferon Alpha-2b eine nachgewiesene antitumorale Wirkung hat, ist seine Anwendung aufgrund schlechter Verträglichkeit eingeschränkt. Erste translationale und Biomarker-Daten aus Phase 1a werden für die zweite Hälfte des Jahres 2025 erwartet.
Positive
  • Successful completion of first three CX-801 monotherapy dose escalation cohorts
  • Strategic partnership with Merck for combination therapy with KEYTRUDA®
  • Potential to address high unmet need in PD-1 refractory melanoma market
  • Initial data expected in H2 2025
Negative
  • Early-stage Phase 1 trial with no efficacy data yet
  • Historical challenges with interferon alpha-2b toxicity profile

Insights

CytomX's progression to testing CX-801+KEYTRUDA combination marks positive advancement addressing unmet needs in melanoma treatment.

CytomX has reached an important clinical development milestone with their first patient dosed in the combination arm studying CX-801 with KEYTRUDA in metastatic melanoma. This progression follows successful clearance of three monotherapy dose escalation cohorts, suggesting acceptable early safety signals for CX-801.

Their innovative approach with CX-801 (a masked interferon alpha-2b PROBODY® cytokine) is scientifically notable. Interferon alpha-2b has established anti-cancer properties but has historically faced significant clinical limitations due to systemic toxicities. The company's conditional activation technology aims to solve this longstanding challenge by localizing interferon activity to the tumor microenvironment while minimizing systemic exposure.

This targeted approach could potentially unlock the therapeutic benefit of interferon when combined with checkpoint inhibition. Specifically, the trial focuses on PD-1 refractory melanoma, an important patient population with limited treatment options after progression on initial immunotherapy.

The company's platform technology for conditional activation represents a differentiated approach in the competitive immuno-oncology landscape. If successful, this combination could provide a new option for patients who currently have few alternatives after failing standard checkpoint inhibitor therapy.

We should expect initial translational and biomarker data from this Phase 1a study in H2 2025, which will provide the first signal of whether this approach can generate meaningful clinical activity while maintaining an acceptable safety profile. This combination approach could potentially address the challenge of primary or acquired resistance to PD-1 inhibition that affects many melanoma patients.

SOUTH SAN FRANCISCO, Calif., May 19, 2025 (GLOBE NEWSWIRE) -- CytomX Therapeutics, Inc. (Nasdaq: CTMX), a leader in the field of masked, conditionally activated biologics, today announced that the first patient has been dosed with CX-801 in combination with KEYTRUDA® (pembrolizumab), Merck’s anti-PD-1 therapy, in the ongoing Phase 1 dose escalation study (NCT06462794) evaluating safety and initial clinical activity in patients with metastatic melanoma.

CX-801 is a dually masked interferon (IFN) alpha-2b PROBODY® cytokine. CX-801 has been intentionally designed by CytomX to harness the power of Interferon alpha-2b’s immune stimulating properties in combination with checkpoint inhibition. Interferon alpha-2b has well known single agent anti-cancer activity in multiple tumor types, including in melanoma. However, its use has been limited due to its poor tolerability arising from systemic toxicities. CX-801 is designed to localize the potency of IFN alpha-2b to tumors and reduce systemic toxicities, enabling combination strategies.

CytomX is conducting a focused Phase 1 dose escalation study of CX-801 in metastatic melanoma. The combination arm of the study evaluating CX-801 in combination with KEYTRUDA® has been initiated following successful the clearance of the first three CX-801 monotherapy dose escalation cohorts.

“We are excited to begin evaluating this combination therapy that has the potential to provide significant clinical benefit to patients with PD-1 refractory melanoma, which remains an area of high unmet need,” said Dr. Wayne Chu, M.D., chief medical officer of CytomX Therapeutics. “Utilizing CytomX’s proprietary conditional activation platform to maintain potency and widen interferon’s therapeutic index, CX-801 is well suited to combine with KEYTRUDA® and could become an important component of combination immuno-oncology therapy. We look forward to initial Phase 1a translational and biomarker data in advanced melanoma in the second half of 2025.”

KEYTRUDA® is a registered trademark of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA

About CytomX Therapeutics

CytomX is a clinical-stage, oncology-focused biopharmaceutical company focused on developing novel conditionally activated, masked biologics designed to be localized to the tumor microenvironment. By pioneering a novel pipeline of localized biologics, powered by its PROBODY® therapeutic platform, CytomX’s vision is to create safer, more effective therapies for the treatment of cancer. CytomX’s robust and differentiated pipeline comprises therapeutic candidates across multiple treatment modalities including antibody-drug conjugates (ADCs), T-cell engagers, and immune modulators such as cytokines. CytomX’s clinical-stage pipeline includes CX-2051 and CX-801. CX-2051 is a masked, conditionally activated ADC directed toward epithelial cell adhesion molecule (EpCAM), armed with a topoisomerase-1 inhibitor payload. CX-2051 has potential applicability across multiple EpCAM-expressing epithelial cancers, including CRC, and was discovered in collaboration with ImmunoGen. CX-801 is a masked interferon alpha-2b PROBODY® cytokine with broad potential applicability in traditionally immuno-oncology sensitive as well as insensitive (cold) tumors. CytomX has established strategic collaborations with multiple leaders in oncology, including Amgen, Astellas, Bristol Myers Squibb, Regeneron and Moderna. For more information about CytomX and how it is working to make conditionally activated treatments the new standard-of-care in the fight against cancer, visit www.cytomx.com and follow us on LinkedIn and X (formerly Twitter).

CytomX Therapeutics Forward-Looking Statements

This press release includes forward-looking statements. Such forward-looking statements involve known and unknown risks, uncertainties and other important factors that are difficult to predict, may be beyond our control, and may cause the actual results, performance, or achievements to be materially different from any future results, performance or achievements expressed or implied in such statements, including those related to CX-801. Accordingly, you should not rely on any of these forward-looking statements, including those relating to the potential benefits, safety and efficacy or progress of CytomX’s or any of its collaborative partners’ product candidates, including CX-801 and CX-2051, the potential benefits or applications of CytomX’s PROBODY® therapeutic platform, CytomX’s or its collaborative partners’ ability to develop and advance product candidates into and successfully complete clinical trials, including the ongoing and planned clinical trials of CX-801 and CX-2051 and the timing of initial and ongoing data availability for our clinical trials, including CX-801 and CX-2051, and other development milestones. Risks and uncertainties that contribute to the uncertain nature of the forward-looking statements include: the unproven nature of CytomX’s novel PROBODY® therapeutic technology; uncertainties around the Company’s ability to raise sufficient funds to carry out its planned research and development; CytomX’s clinical trial product candidates are in the initial stages of clinical development and its other product candidates are currently in preclinical development, and the process by which preclinical and clinical development could potentially lead to an approved product is long and subject to significant risks and uncertainties, including the possibility that the results of preclinical research and early clinical trials, including initial CX-801 results, may not be predictive of future results; the possibility that CytomX’s clinical trials will not be successful; the possibility that current preclinical research may not result in additional product candidates; CytomX’s dependence on the success of CX-2051 and CX-801; CytomX’s reliance on third parties for the manufacture of the Company’s product candidates; possible regulatory developments in the United States and foreign countries, including China and the European Union; and the risk that we may incur higher costs than expected for research and development or unexpected costs and expenses or may not obtain expected savings from our announced restructuring. Additional applicable risks and uncertainties include those relating to our preclinical research and development, clinical development, and other risks identified under the heading "Risk Factors" included in CytomX’s Quarterly Report on Form 10-Q filed with the SEC on May 12, 2025. The forward-looking statements contained in this press release are based on information currently available to CytomX and speak only as of the date on which they are made. CytomX does not undertake and specifically disclaims any obligation to update any forward-looking statements, whether as a result of any new information, future events, changed circumstances or otherwise.

PROBODY is a U.S. registered trademark of CytomX Therapeutics, Inc. All other trademarks are the properties of their respective owners.

Company Contact:
Chris Ogden
SVP, Chief Financial Officer
cogden@cytomx.com

Investor Contact:
Precision AQ (formerly Stern Investor Relations)
Stephanie Ascher
stephanie.ascher@precisionaq.com

Media Contact:
Redhouse Communications
Teri Dahlman
teri@redhousecomms.com


FAQ

What is CytomX's CX-801 and how does it work in melanoma treatment?

CX-801 is a dually masked interferon alpha-2b PROBODY® cytokine designed to target tumors while reducing systemic toxicities. It's being developed to harness interferon's immune-stimulating properties in combination with checkpoint inhibition for melanoma treatment.

When will CTMX release initial data for the CX-801 and KEYTRUDA combination trial?

CytomX expects to release initial Phase 1a translational and biomarker data for the combination therapy in advanced melanoma in the second half of 2025.

Why is CytomX combining CX-801 with KEYTRUDA for melanoma treatment?

The combination aims to address the high unmet need in PD-1 refractory melanoma patients by combining KEYTRUDA's checkpoint inhibition with CX-801's tumor-targeted interferon activity while minimizing systemic toxicities.

What progress has CTMX made in the CX-801 clinical trials?

CytomX has successfully completed three CX-801 monotherapy dose escalation cohorts and has now begun dosing the first patient in the combination arm with KEYTRUDA®.
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