A 74-year-old man presents with fatigue, shortness of breath on exertion, and back and rib pain, which is made worse with movement. Investigations reveal he is anemic, calcium, urea, and creatinine are elevated. X-rays reveal multiple lytic lesions in the long bones and ribs, and protein electrophoresis is positive for an immunoglobulin G (IgG) paraprotein. Which of the following is the most likely mechanism for the renal injury?