Protocol changed to Phase 2

This is a phase 1b, open-label, dose-escalation study o STI-3258 administered intravenously in subjects with relapsed or refractory solid tumors.

This is a Phase 1b, open-label, dose-escalation study o STI-3258 administered intravenously in subjects with relapsed or refractory solid tumors including ovarian, breast, lung, esophageal, gastric, hepatocellular and urothelial cancers.

The study will determine any dose limiting toxicity (DLT), maximum tolerated dose (MTD) and recommended Phase 2 dose (RP2D), assessing safety and preliminary efficacy using ascending dose cohorts and a conventional 3+3 study design.

Inclusion Criteria:

• Histologically or cytologically confirmed advanced cancer that is relapsing or refractory to at least one prior treatment and not a candidate for other treatments or is intolerant to established treatments.
• At least one measurable disease per Response Evaluation Criteria in Solid Tumors v. 1.1 (RECIST 1.1).
• Eastern Cooperative Oncology Group Performance Status ≤ 2.
• Must have a life expectancy of ≥ 6 months.
• Must have adequate bone marrow, hepatic and renal function as assessed by specific laboratory tests.
• Must be recovered ≤ Grade 1 from acute toxicities from previous therapies, excluding alopecia and vitiligo.
• Has not had prior treatment within 2 weeks of screening with high dose corticosteroids.
• Be willing and able to comply with the study schedule and all study requirements.
• Willing to follow all contraception guidelines.

Exclusion Criteria:

• Previous treatment with any systemic therapy or investigational drug within 2 weeks of the first dose of study drug.
• Currently participating in any other interventional clinical study.
• Has a diagnosis of other malignancies if the malignancy has required therapy within the last 3 years or is not in complete remission.
• Has presence of bulky disease defined as any mass > 7 cm in greatest dimension will trigger a discussion with the medical monitor.
• Has left ventricular ejection fraction (LVEF) < 40%.
• New York Heart Association (NYHA) Class ≥ 3.
• Has prolonged QTcF interval on an electrocardiogram.
• Has spinal cord compression or clinically active brain metastases.
• Has a history of Sacituzumab govitecan treatment.
• History of anaphylactic reaction to irinotecan or ≥ Grade 3 toxicity to prior irinotecan treatment.
• Has active or prior COVID-19 infection, with symptoms presenting within 4 weeks of the first dose of study drug.
• Has an active bacterial, viral, or fungal infection.
• Is currently pregnant or breast feeding or planning on either during the study.
• Has chronic or moderate chronic obstructive pulmonary disease or other chronic respiratory conditions unless receiving treatment and stable for 3 months prior to screening.
• Has known HIV or acquired immunodeficiency syndrome-related illness, acute or history of chronic hepatitis B or C.
• Has any significant medical condition, abnormality, or psychiatric illness that would prevent study participation.