Inclusion Criteria:
* Histologically or cytologically confirmed, unresectable, locally advanced, or metastatic solid tumor intolerant, refractory to or progressing after standard systemic therapies.
* Must be able to provide archival tumor tissue (formalin-fixed, paraffin-embedded tissue block (FFPE) block or approximately 10-15 freshly cut unstained FFPE slides)
* Must have an Eastern Cooperative Oncology Group (ECOG) Performance Status of ≤ 1.0
* Must have adequate organ function as indicated by the following laboratory values ≤ 7 days before the first dose of study drug(s):
a. Must not have required blood transfusion or growth factor support ≤ 14 days before sample collection at screening for the following:
* Absolute neutrophil count (ANC) ≥ 1.5 × 109/L.
* Platelets ≥ 100 × 109/L.
* Hemoglobin ≥ 90 g/L. b. Estimated glomerular filtration rate (GFR) ≥ 50 mL/min, as determined by the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) c. Serum total bilirubin ≤ 1.5 × Upper Limit of Normal (ULN) (total bilirubin must be ≤ 3 × ULN with direct bilirubin ≤ 1.5 × ULN for patients with Gilbert's syndrome).
d. Aspartate aminotransferase (AST) and alanine aminotransferase (ALT) ≤ 2.5 × ULN or \< 5 × ULN if hepatic metastases are present.
e. Albumin ≥ 2.0 g/dL. f. In Phase 1b Part D, for patients receiving combination therapy with bevacizumab, additional inclusion criteria are listed below:
* Urine dipstick for proteinuria \< 2+ (within 7 days prior to initiation of study treatment). Patients discovered to have ³ 2+ proteinuria on dipstick urinalysis at baseline should undergo a 24-hour urine collection and must demonstrate \< 1 g of protein in 24 hours.
* Coagulation parameters: international normalized ratio (INR) of ≤ 1.5 (or an in-range INR of ≤ 3, if a patient is on a stable dose of therapeutic warfarin) and a partial thromboplastin time (PTT) \< 1.2 × ULN.
* Female of childbearing potential must be willing to use a highly effective method of birth control and refrain from egg donation for the duration of the study and for ≥ 7 months after the last dose of BON-C1393, for ≥ 6 months after the last dose of bevacizumab or capecitabine, whichever comes later. They must also have a negative urine or serum pregnancy test result ≤ 3 days before first dose of study drug/treatment.
* Nonsterile male must be willing to use condom and refrain from sperm donation for the duration of the study and for ≥ 4 months after the last dose of BON-C1393, for ≥ 3 months after the last dose of capecitabine, whichever comes later.
Exclusion Criteria:
* Prior treatment with any B7-H3 or ITGB-6 -targeted ADCs or ADCs containing topoisomerase 1 inhibitor (TOP) inhibitor as payload.
* History of severe allergic reactions, severe reaction to infusion, or hypersensitivity to the active ingredient and excipients of the study drug(s) or protein-based therapeutics.
* Unable to comply with the requirements of the protocol, unless the written approval of the medical monitor has been obtained before informed consent.
* Active hepatitis C.
* Active leptomeningeal disease or uncontrolled, untreated brain metastasis.
* Any major surgical procedure ≤ 28 days (or ≤ 14 days for low-invasive cases \[eg, colostomy\]) before the first dose of study drug. Must have recovered adequately from the surgery and/or complications from the surgical procedures before the first dose of study drug/treatment.
Any of following treatments before the first dose of study drug:
1. Prior systemic anticancer therapy (including targeted therapy and immunomodulators \[eg, interleukin (IL), interferon, thymosin, etc\]) ≤ 14 days, ≤ 28 days for immuno-oncological antibody, ≤14 days or 5 half-lives (whichever is shorter) for chemotherapy, ADCs, or investigational therapy.
2. Radiation therapy (curative) and palliative radiation therapy to the chest ≤ 4 weeks; ≤ 2 weeks for palliative radiation therapy to other areas (ie, limited field and 10 or fewer days or fractions) including whole-brain radiotherapy.
3. Chinese patent medicine with anticancer activity approved by the China NMPA (regardless of the type of cancer) ≤ 14 days (Appendix 4).
4. Herbal remedies with immune-stimulating properties (eg, mistletoe extract) or that are known to potentially interfere with liver or other major organ functions (eg, hypericin) ≤ 14 days or 5 half-lives, whichever is shorter or known.
* Ongoing treatment with a strong CYP3A inhibitor, or strong CYP3A inducer, or strong CYP1A2 inhibitor, or strong CYP1A2 inducer
