This is a clinical research study taking place in Germany. Patients with colorectal cancer at a stage of the disease where metastases occur may take part in the study. A maximum of 90 people will participate in the study.

There is already a standard therapy for treatment of colorectal cancer. This therapy contains a combination of the medicines leucovorin, fluorouracil, oxaliplatin/irinotecan and bevacizumab/cetuximab/panitumumab.

The sponsoring company is developing the new therapy called arfolitixorin. In this study, patients with colorectal cancer will be given arfolitixorin instead of the standard treatment leucovorin. Different patients will receive treatment with different strengths (doses) of arfolitixorin. Treatment with fluorouracil, oxaliplatin/irinotecan and bevacizumab/cetuximab/panitumumab will also be administrated.

The researchers want to find out if arfolitixorin could have an advantage over the standard therapy with leucovorin. They also want to investigate which dose of arfolitixorin is the maximum tolerated dose and if arfolitixorin is safe to use.

The product being tested, arfolitixorin, like leucovorin, belongs to a group of substances called folates which are naturally occurring forms of a type of B vitamin. Folates are administered in combination with one or more chemotherapeutic agents to enhance their effect on cancer cells.

The main mechanism of action of arfolitixorin is the same as that of leucovorin when used together with fluorouracil. However, leucovorin must first be converted into the active form in the body, whereas arfolitixorin already is in the active form. Leucovorin does not work equally well in all patients. By bypassing the metabolic activation of arfolitixorin, it is assumed that arfolitixorin works in a larger number of patients and has a stronger and longer efficacy in cancer treatment together with fluorouracil.

However, the efficacy of arfolitixorin has not yet been proven, and the substance has not been approved for the treatment of colorectal cancer. To date, arfolitixorin has been tested by around 420 volunteers and patients with colorectal cancer in different clinical studies. These studies have shown that arfolitixorin is safe and potentially can be of clinical benefit in patients with colorectal cancer when used in combination with fluorouracil, oxaliplatin and bevacizumab.

In the largest clinical study completed so far, arfolitixorin was shown to be equally effective compared to standard therapy with leucovorin, but not more effective. Additional results from this study suggested that the dose of arfolitixorin given did not deliver a sufficiently high amount of active substance into the tumor. Therefore, higher doses of arfolitixorin will be tested in this study to possibly achieve a better clinical effect. Further analyses also indicated that high accuracy regarding the timing and duration of the administration of the different treatments is important to achieve better efficacy of arfolitixorin.

Based on the available data, and the risk and benefit assessments performed, the Sponsor deems that it is relevant to further investigate the safety and tolerability, as well as the efficacy of arfolitixorin when given in combination with fluorouracil, oxaliplatin/irinotecan and bevacizumab/cetuximab/panitumumab. The proposed study design is believed to address all the main previous findings with the purpose to increase the efficacy while maintaining an acceptable safety profile.

The study is divided into two parts. In the first part, up to five different doses of arfolitixorin will be investigated to find the maximum tolerated dose of arfolitixorin as well as the optimal duration time of administration.

The second part of the study will be based on the results from the first part. Two doses of arfolitixorin will be tested for safety, tolerability and anti-tumor effect. In the second part, participants will be randomly assigned to one of two dose groups or a control group (receiving the Standard of Care) using a computer program. This so-called randomization procedure is comparable to tossing a coin.

All patients that participate in the study will receive treatment every 2 weeks. The treatment will be given as an infusion into a vein. The number of treatment administrations that will be given is not predetermined but depends on the progression of the patient's disease.The treatment will continue every 2 weeks as long as the patient benefits from the treatment.

During the study period, the patient's disease and potential response to treatment, including shrinkage of the tumor and/or improvement of symptoms, will be monitored by imaging examinations, using so-called computer tomography (CT) or magnetic resonance imaging (MRI). The patient's state of health will also be monitored by physical examinations, and laboratory tests of urine and blood, as well as assessment of any side effects.

This is a Phase 1b/2 study to determine the safety and preliminary efficacy of arfolitixorin (replacing LV) as part of eligible 5-FU based backbone treatment regimens in patients with mCRC eligible for first-line therapy.

The study will include a Phase 1b dose-finding part followed by a randomized Phase 2 dose optimization part including an SoC arm.

Eligible patients will undergo baseline assessments (within 28 days prior to treatment initiation) and repeat imaging using computed tomography (CT) or magnetic resonance imaging (MRI) after 6 and 12 weeks, and every 12 weeks thereafter as long as on study treatment.

In Phase1b, patients will receive treatment with ARFOX + bevacizumab. In Phase 2, patients will receive treatment with arfolitixorin (replacing LV) as part of eligible 5-FU based backbone treatment (i.e., ARFOX + bevacizumab/cetuximab/panitumumab or ARFIRI + bevacizumab/cetuximab/panitumumab) or SoC (including LV) as part of eligible 5-FU based backbone treatment (i.e., FOLFOX + bevacizumab/cetuximab/panitumumab or FOLFIRI + bevacizumab/cetuximab/panitumumab).

All patients will receive treatment every 14 days (+7 days) until progressive disease (PD), or clear clinical deterioration according to the Investigator's judgment, and as long as the patient is tolerating the treatment and agrees to continue.

After completion of study treatment, patients will complete an EOT visit within 30 days of discontinuation, and all patients should be followed in line with the site's SoC scheme.

Subsequent study follow-up contacts/visits will be performed every 90 days (±15 days) after the EOT visit treatment, until 60% of the OS events have been collected or 24 months after last patient in (LPI), whichever comes first. The follow-up contacts may be conducted via telephone, via clinic visits, via local practitioner, via review of medical records or other means found suitable.

At the follow-up visits, information on any subsequent cancer treatments will be collected, recording and assessment of serious adverse events (SAEs) considered to be related to the study treatment will be performed, and survival status will be noted. All AEs collected during the reporting period still ongoing at the EOT visit will be followed until resolution or stabilization, or until deemed not necessary by the Investigator. All SAEs collected during the reporting period still ongoing at the EOT visit will be followed up until the patient has recovered, stabilized, or recovered with sequelae.

During the Phase 1b part of the study, a dose escalation design will be utilized to identify the MTD and the duration of administration of arfolitixorin to be used in combination with 5-FU, oxaliplatin and bevacizumab. A Safety Review Committee (SRC) will review AEs, SAEs, dose-limiting toxicities (DLTs) as defined in the Clinical Study Protocol, and PK data and make recommendations regarding which dose level and cohort size to be tested for the next cohort, as well as the MTD. The SRC may also make recommendations of the duration of the infusion if there are safety findings that potentially correlate to a non-acceptable maximum plasma (peak) drug concentration (Cmax).

The dose escalation schema will be based on a Bayesian optimal interval (BOIN) design where the decision of dose escalation or de-escalation involves a simple comparison of the observed DLT rate at the current dose with the prespecified dose escalation and de-escalation boundaries.

The Phase 2 part of the study will be a randomized study where patients will be allocated to 1 of 2 dose levels of arfolitixorin, or to treatment with SoC. The higher dose level of arfolitixorin will be the MTD as determined in Phase 1b, and the lower dose will be a dose level below the MTD in Phase 1b, as determined by the SRC. The SRC will also review safety and efficacy data on a regular basis during Phase 2.

Inclusion Criteria:

• Signed ICF and ability to comply with protocol requirements.
• Phase 1b: Histologically confirmed RAS mutant, MSS/pMMR, colorectal adenocarcinoma with metastatic disease, eligible for first-line therapy with 5-FU, oxaliplatin, and bevacizumab regimen.

Phase 2:

Histologically confirmed, colorectal adenocarcinoma with metastatic disease, eligible for first-line therapy with 5-FU based backbones, i.e.:

1. Patients with mutated RAS who are candidates for therapy with FOLFOX or FOLFIRI plus bevacizumab.

2. Patients with WT RAS or WT BRAF and left-sided tumors who are candidates for therapy with FOLFOX or FOLFIRI plus cetuximab or panitumumab.

   • Tumor specimen (formalin-fixed, paraffin-embedded [FFPE]) available.
   • Acceptable hematologic laboratory values defined as:

a) Hemoglobin ≥90 g/L. b) Absolute neutrophil count (ANC) ≥1.5 × 109/L. c) Platelets ≥100 × 109/L.

• Adequate organ function as defined by the following laboratory values:

  1. Total serum bilirubin ≤1.5 × upper limit of normal (ULN).
  2. ALT and AST ≤3 × ULN (≤5 × ULN in case of hepatic metastases).
  3. Creatinine ≤1.5 × ULN, or creatinine clearance ≥50 mL/min (as measured according to Cockcroft-Gault equation).

• Age ≥18 years at the time of signing the ICF.

• Radiographically measurable disease per RECIST (version 1.1) within 28 days of treatment allocation.

• Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1.

• Life expectancy of >12 weeks.

• Female patients must be surgically sterile, postmenopausal, or have negative results for a pregnancy test at screening, on a serum or urine sample obtained within 72 hours prior to initiation of study treatment.

• Female patients of childbearing potential must agree to use highly effective contraceptive measures while on study treatment and for at least 15 months (or longer if according to local labels) after study treatment discontinuation. Highly effective methods are those that achieve a failure rate of less than 1% per year when used consistently and correctly (as per the Clinical Trial Coordination Group [CTCG] Recommendations related to contraception and pregnancy testing in clinical trials, Version 1.2, 07 Mar 2024).

• Female patients should agree to refrain from egg cell donation while on study treatment and for at least 15 months after the last dose of study treatment.

• Male patients with female partners of childbearing potential must agree to use adequate contraceptive measures while on study treatment and for at least 12 months (or longer if according to local labels) after study treatment discontinuation.

• Male patients should agree to refrain from sperm donation while on study treatment and for at least 12 months after the last dose of study treatment.

Exclusion Criteria:

• Indication for any mCRC surgery or anti-cancer treatment other than study treatment, including but not limited to resection as confirmed by a MTB.

• Concomitant malignancies or previous malignancies with less than a 2-year disease free interval at the time of signing consent. Patients with adequately treated basal or squamous cell carcinoma of the skin, or adequately treated carcinoma in situ (e.g., cervix) may enroll irrespective of the time of diagnosis. Patients with controlled, advanced prostate cancer are permitted. Ongoing adjuvant antihormonal therapy after breast or prostate cancer is permitted.

• Prior 5-FU, oxaliplatin, irinotecan, bevacizumab, cetuximab, or panitumumab administration for mCRC.

• More than 6 cycles (3 months) of oxaliplatin exposure during adjuvant treatment.

• Known history of central nervous system (CNS) metastases or carcinomatous meningitis.

• Receipt of any investigational product within 14 days or 5 half-lives prior to study treatment initiation, whichever is shortest. Note that participation in any other clinical study is not allowed as long as the patient is on study treatment.

• Prior exposure to arfolitixorin.

• Major surgery, or significant traumatic injury within 8 weeks of study treatment initiation.

• Hypersensitivity to arfolitixorin, 5-FU, oxaliplatin or other platinum agent, irinotecan, bevacizumab, cetuximab or panitumumab, or to their excipients.

• Dihydropyrimidine dehydrogenase (DPD) enzyme deficiency test with a Clinical Pharmacogenetics Implementation Consortium (CPIC) activity score <1.

• Current evidence of any condition that could lead to higher risk or otherwise make participating in this study not in the best interest of the patient, including, but not limited to:

  1. Myocardial infarction or unstable angina within the past 6 months.
  2. Other structural heart disease (e.g., myocarditis, ventricular hypertrophy).
  3. New York Heart Association (NYHA) functional classification Class II or greater.
  4. QT prolongation syndrome >450 ms.
  5. Slow or irregular ventricular rates; other serious arrhythmias requiring medication for treatment.
  6. Left ventricular ejection fraction (LVEF) <55%.
  7. Active infection requiring i.v. antibiotics.
  8. Ongoing drug or alcohol abuse.
  9. Inadequately controlled hypertension (defined as systolic blood pressure >150 mmHg and/or diastolic blood pressure >100 mmHg). Initiation of antihypertensives is permitted provided adequate control is documented over at least 1 week before starting treatment.

• Sensory peripheral neuropathy Grade ≥2.

• Pregnancy or lactation.

• Any medical condition, or ongoing treatment with contraindicated drugs, which in the opinion of the Investigator, places the patient at an unacceptably high risk for toxicities, or any psychological, familial, sociological or geographical condition that potentially hampers compliance with the study protocol and follow-up schedule.

• BRAF-mutant or deficient in mismatch repair (dMMR)/microsatellite instability-high (MSI-H) mCRC.

• Eligibility for treatment with FOLFIRINOX regimens.