Key Inclusion Criteria:

          -  Patient has a histologically documented solid tumor that is metastatic or locally
             advanced, for which SoC therapy does not exist, has failed in the patient, or is not
             tolerated by the patient, or for which the patient has been assessed by the
             Investigator as not being a suitable candidate or otherwise ineligible for the SoC
             therapy.

          -  For Part A2 and Part B:

               -  Patient must have a history of primary anti-PD-(L)1 antibody nonresponse
                  presenting (based upon the Investigator's assessment) either as progressive
                  disease or stable disease (e.g., not improving, but also not worsening,
                  clinically or radiographically) after at least 3 cycles of treatment with an
                  anti-PD-(L)1 antibody therapy (alone or in combination with chemotherapy)
                  approved for that tumor type.

               -  Patient must have received their most recent dose of anti-PD-(L)1 antibody
                  therapy within 6 months of enrollment.

               -  For NSCLC patients who have genomic tumor aberrations for which a targeted
                  therapy is available (e.g., anaplastic lymphoma kinase, EGFR), these patients
                  must have progressed on an approved therapy for these aberrations or did not
                  tolerate an approved therapy for these aberrations, or were not considered
                  suitable candidates/ were otherwise ineligible for an approved therapy for these
                  aberrations.

          -  Measurable disease per Response Evaluation Criteria in Solid Tumors (RECIST) v1.1 as
             assessed at Screening.

          -  Patient must have an Eastern Cooperative Oncology Group performance status (PS) 0-1.

          -  Patient must have a predicted life expectancy of ≥ 3 months.

          -  Women of child-bearing potential (WOCBP) must have a negative urine pregnancy test
             within 72 hours prior to first administration of SRK-181 and a negative urine
             pregnancy test on the first day of dosing.

          -  WOCBP and males with female partners of child-bearing potential must agree to use
             adequate birth control throughout their participation and for 90 days following the
             last dose of SRK-181.

        Key Exclusion Criteria:

          -  For Part A1 only:

               -  Patient has had anti-PD-(L)1 antibody therapy ≤ 28 days prior to enrollment.

               -  Patient is receiving concurrent anticancer treatment, including anti-PD-(L)1
                  antibody therapy, either approved or investigational, within 28 days prior to
                  administration of SRK-181.

          -  For Part A2 and Part B only:

               -  Patient is receiving concurrent anticancer treatment, with the exception of an
                  anti-PD-(L)1 antibody therapy for Part A2 or Part B, either approved or
                  investigational, within 28 days prior to administration of SRK-181.

               -  Patient has received biologic therapy (except for anti-PD-(L)1 antibody therapy
                  for Part A2 or Part B), <28 days prior to administration of SRK-181.

               -  Patient has received systemic cytotoxic chemotherapy (except for in combination
                  with anti-PD-(L)1 antibody therapy) <28 days prior to administration of SRK-181.

               -  Patient has received targeted small molecule therapy within 5 half-lives of the
                  compound prior to administration of SRK-181.

               -  Patient has a history of intolerance or treatment discontinuation due to severe
                  irAE or other adverse reaction from prior anti-PD-(L)1 antibody therapy.

          -  Patient has a hypersensitivity to anti-PD-(L)1 antibody therapy.

          -  Patient has the documented presence of neutralizing ADA to anti-PD-(L)1 antibody
             therapy.

          -  Patient has a diagnosis of immunodeficiency, either primary or acquired.

          -  Patient is symptomatic or has uncontrolled brain metastases, leptomeningeal disease,
             or spinal cord compression not definitively treated with surgery or radiation.

          -  Patient has current second malignancy at other sites (exceptions: adequately treated
             in situ carcinoma [e.g., cervical], non-MEL skin cancer, bilateral synchronous
             discordant breast cancer, or indolent prostate cancer under observation). A past
             history of other malignancies is allowed as long as patient has been free of
             recurrence for ≥ 2 years, or if the patient has been treated with curative intent
             within the past 2 years and, in the opinion of the Investigator, is unlikely to have a
             recurrence.

          -  Women who are pregnant or breastfeeding.