A Multicenter Study With an Open-label Phase Ib Part Followed by a Randomized, Placebo-controlled, Double-blind, Phase II Part to Evaluate Efficacy, Safety, Tolerability, and Pharmacokinetics of the DNA-PK Inhibitor M3814 in Combination With Capecitabine and Radiotherapy in Participants With Locally Advanced Rectal Cancer

The main purpose of the study is to define maximum tolerated dose (MTD), recommended Phase II dose (RP2D) of M3814 in combination with capecitabine and radiotherapy (RT) in Phase Ib and to evaluate the efficacy of M3814 in terms of Pathological Clinical Response (pCR)/Clinical Complete Response (cCR) when administered in combination with capecitabine and RT versus placebo, capecitabine, and RT in Phase II.